THE
ARTISTIC ANATOMY OF ANIMALS

[v]

PREFACE

A few lines will suffice to explain why we have compiled
the present volume, to what wants it responds, and what
its sphere of usefulness may possibly embrace.

In our teaching of plastic anatomy, especially at the École
des Beaux-Arts—where, for the past nine years, we have
had the very great honour of supplementing the teaching
of our distinguished master, Mathias Duval, after having
been prosector for his course of lectures since 1881—it is
our practice to give, as a complement to the study of human
anatomy, a certain number of lessons on the anatomy of
those animals which artists might be called on to represent.

Now, we were given to understand that the subject
treated in our lectures interested our hearers, so much so
that we were not surprised to learn that a certain number
repeatedly expressed a desire to see these lectures united
in book form.

To us this idea was not new; for many years the work in
question had been in course of preparation, and we had
collected materials for it, with the object of filling up a
void of which the existence was to be regretted. But our
many engagements prevented us from executing our project
as early as we would have wished. It is this work
which we publish to-day.

[vi]

Fig. I.—Reproduction of a Sketch by Barye (Collections of the Anatomical Museum of the École des
Beaux-Arts—Huguier Museum).

Putting aside for a moment the wish expressed by our
hearers, we feel ourselves in duty bound to inquire whether
the utility of this publication is self-evident. Let it be
clearly understood that we wish to express here our opinion[vii]
on this subject, while putting aside every personal sentiment
of an author.

No one now disputes the value of anatomical studies
made in view of carrying out the artistic representation of
man. Nevertheless—for we must provide against all contingencies—the
conviction on this subject may be more or
less absolute; and yet it must possess this character in an
intense degree in order that these studies may be profitable,
and permit the attainment of the goal which is
proposed in undertaking them. It is in this way that we
ever strive to train the students whose studies we direct;
not only to admit the value of these studies, but to be
materially and deeply convinced of the fact without any
restriction. Such is the sentiment which we endeavour to
create and vigorously encourage. And we may be permitted
to add that we have often been successful in this
direction.

Therefore it is that, at the beginning of our lectures, and
in anticipation of possible objections, we are accustomed
to take up the question of the utility of plastic anatomy.
And in so doing, it is in order to combat at the outset the
idea—as mischievous as it is false—which is sometimes
imprudently enunciated, that the possession of scientific
knowledge is likely to tarnish the purity and freshness of
the impressions received by the artist, and to place shackles
on the emotional sincerity of their representation.

[viii]

Fig. II.—Reproduction of a Sketch of Barye (Collections of the Anatomical Museum of the École des
Beaux-Arts—Huguier Museum).

It is chiefly by employment of examples that we approach
the subject. These strike the imagination of the
student more forcibly, and the presentation of models of
a certain choice, although rough in execution, is, in our
opinion, preferable to considerations of an order possibly
more exalted, but of a character less clearly practical. Let
us, then, ask the question: Those artists whose eminence
nobody would dare to question, did they study anatomy?
If the answer be in the affirmative, we surely cannot permit
ourselves to believe that we can dispense with a similar[ix]
course. And, as proof of the studies of this class which
the masters have made, we may cite Raphael, Michelangelo,
and, above all, Leonardo da Vinci; and, of the
moderns, Géricault. And we may more clearly define
these proofs by an examination of the reproductions of
their anatomical works, chosen from certain of their special
writings.[1]

Accordingly, there is no scope for serious discussion, and
it only remains for us to enunciate the opinion that it is
necessary that we should imitate those masters, and, with
a sense of respectful discipline, follow their example.

Here, with regard to the anatomy of animals, we pursue
the same method, and the example chosen shall be that of
Barye. His talent is too far above all criticism to allow
that this example should be refused. The admiration
which the works of this great artist elicit is too wide-spread
for us to remain uninfluenced by the lessons furnished by
his studies. It is sufficient to see the sketches relating
to these studies, and his admirable casts from nature
which form part of the anatomical museum of the École
des Beaux-Arts, to be convinced that the artistic temperament,
of which Barye was one of the most brilliant
examples, has nothing to lose by its association with researches
the precision of which might seem likely to check
its complete expansion.

[x]

Fig. III.—Reproduction of a Sketch of Barye (Collections of the Anatomical Museum of the
École des Beaux-Arts—Huguier Museum).

In those sketches we find proofs of observation so scrupulous
that we cannot restrain our admiration for the man[xi]
whose ardent imagination was voluntarily subjected to the
toil of study so profound.

If the example of Barye, with whom we associate the
names of other great modern painters of animals, can determine
the conviction which we seek to produce, we shall be
sincerely glad. To contribute to the propagation of useful
ideas, and to see them accepted, gives a feeling of satisfaction
far too legitimate for us to hesitate to say what we
should feel if our hope be realized in this instance.

ÉDOUARD CUYER.

[xii]

Fig. IV.—Reproduction of a Sketch of Barye (Collections of Anatomical Museum of the
School of Fine Arts—Huguier Museum).

[xiii]

Detailed
Table of
Contents.

CONTENTS

[xv]

LIST OF ILLUSTRATIONS

[1]

THE ARTISTIC ANATOMY OF ANIMALS

INTRODUCTION

GENERALITIES OF COMPARATIVE ANATOMY

Of the animals by which we are surrounded, there are some
which, occupying a place in our lives by reason of their
natural endowments, are frequently represented in the works
of artists—either as accompanying man in his work or in
his amusements, or as intended to occupy the whole interest
of the composition.

The necessity of knowing, from an artistic point of view,
the structure of the human body makes clear the importance
we attach, from the same point of view, to the study of the
anatomy of animals—that is, the study of comparative
anatomy. The name employed to designate this branch of
anatomy shows that the object of this science is the study
of the relative position and form which each region presents
in all organized beings, taking for comparison the corresponding
regions in man. The head in animals compared with
the human head; the trunk and limbs compared to the
trunk and limbs of the human being—this is the analysis we
undertake, and the plan of the subject we are about to
commence.

Our intention being, as we have just said, the comparison
of the structure of animals with that of man, should we
describe the anatomy of the human being in the pages[2]
which follow? We do not think so. Plastic human
anatomy having been previously studied in special works,[2]
we take it for granted that these have been studied before
undertaking the subject of comparative anatomy. We
will therefore not occupy time with the elementary facts
relative to the skeleton and the superficial layer of muscles.
We will not dilate on the division of the bones into long,
short, large, single, paired, etc. All these preliminary
elements we shall suppose to have been already studied.

This being granted, it is, nevertheless, necessary to take
a rapid bird’s-eye view of organized beings, and to recall the
terms used in their classification.

Animals are primarily classed in great divisions, based
on the general characters which differentiate them most.
These divisions, or branches, allow of their being so grouped
that in each of them we find united the individuals whose
general structure is uniform; and under the name of vertebrates
are included man and the animals with which our
studies will be occupied. The vertebrates, as the name
indicates, are recognised by the presence of an interior
skeleton formed by a central axis, the vertebral column,
round which the other parts of the skeleton are arranged.

The vertebrate branch is divided into classes: fishes,
amphibians or batrachians, reptiles, birds, and mammals.

The mammals—from the Latin mamma, a breast—are
characterized by the presence of breasts designed for the
alimentation of their young. Their bodies are covered with
hair, hence the name pilifères proposed by Blainville; and,
notwithstanding that in some individuals the hairs are few,
the character is sufficient to distinguish them from all other
vertebrates.

We find united in this class animals which, at first, seem
out of place, such as the whale and the bat; and, from their
external appearance alone, the former would appear to[3]
belong to the fishes, and the latter to birds. Yet, on studying
their structure, we find that, not only do these animals
merit a place in the class which they occupy, because they
possess the distinctive characters of mammals; but, still
further, their internal structure is analogous to that of man
and of the other individuals of this class.

Notwithstanding this similarity of structure, the whale
is not without some points of difference from its neighbours
the horse and the dog; therefore, in order to place each of
these animals in a position suitable to it, mammals are
divided into secondary groups called orders. The first of
these orders includes, under the name primates, man and
apes. The latter contain animals which approach birds in
certain characters of their organism, forming a link between
the latter and mammals.

We find, in studying the regions of the body in some of the
vertebrates, that, while they present differences from the
corresponding regions of the human body, they also offer
most striking analogies. We can, for example, recognise
the upper limb of man in the anterior one of quadrupeds,
in the wing of the bat, in the paddle of the seal, etc. It is,
so to speak, those variations of a great plan which give
such a charm to the study of comparative anatomy.

The division of classes into orders, which we have just
mentioned, being still too general, it was found necessary to
establish subdivisions—more and more specialized—to
which the names families, genera, species, and varieties were
given.

[4]

CHAPTER I

OSTEOLOGY AND ARTHROLOGY

THE TRUNK

The Vertebral Column

We commence the study of the skeleton with a description
of the trunk.

Fig. 1.—A Human Skeleton in the Attitude of a Quadruped. To
give a general Idea of the position of the Bones in other
Vertebrates.

The trunk being, in quadrupeds, horizontal in direction
(Fig. 1), the two regions of which it consists occupy, for this
reason, the following positions: the thorax occupies the
anterior part, the abdomen is placed behind it; the vertebral
column is horizontal, and is situated at the superior aspect
of the trunk; it projects beyond the latter: anteriorly, to
articulate with the skull; and, posteriorly, to form the
skeleton of the tail, or caudal appendix.

The number of the vertebræ is not the same in all mammalia.
Of the several regions of the vertebral column, the
cervical shows the greatest uniformity in the number of the
vertebræ of which it consists, with but two exceptions
(eight or nine in the three-toed sloth, and six in the manatee);
we always find seven cervical vertebræ, whatever the length
of the neck of the animal. There are no more than seven
vertebræ in the long neck of the giraffe, but they are very
long ones; and not less than seven in the very short neck
of the dolphin, in which they are reduced to mere plates of
bone not thicker than sheets of cardboard. If the cervical
region presents uniformity in the number of its bones, it is
not so with the other regions of the column.

[5]The following table shows their classification in some
animals:

Vertebræ.

It is worthy of notice that in birds the number of the
cervical vertebræ is not constant, as in mammals; they are[6]
more numerous than the dorsal. These latter are almost
always joined to one another by a fusion of their spinous
processes; the two or three last vertebræ are similarly
united to the iliac bones, between which they are fixed. The
dorsal vertebræ thus form one piece, which gives solidity to
the trunk, and provides a base of support to the wings,
for the movements of flying. There are, so to speak, no
lumbar vertebræ, the bones of that region, which cannot be
differentiated from the sacrum, having coalesced with the
bones of the pelvis.

Vertebræ.

In reptiles, the relation between the number of the cervical
vertebræ and that of the dorsal is very variable; some
serpents are devoid of cervical vertebræ, having only dorsal
ones—that is, vertebræ carrying well-developed ribs.

Vertebræ.

Fig. 2.—Size of the Atlas compared with the Transverse Dimensions
of the Corresponding Parts of the Skull in Man.

1, Atlas; 2, mastoid process; 3, external occipital protuberance;
4, inferior maxilla.

Regarding the direction of the vertebral column in animals,
in which the trunk is not vertical, it is evident that the
spinous processes point upward, and that in comparing them
with those of man they must be arranged so that the superior
surface of the human vertebra will correspond to the anterior[7]
surface of that of the quadruped. Of the cervical vertebræ,
the atlas and axis call for special notice. Apropos of the
atlas, we find that it, in the human being, is narrower than
the corresponding parts of the skull, and is therefore hidden
under the base of the cranium (Fig. 2); in quadrupeds its
width is equal to that of the skull, and sometimes exceeds,
because of the great development of its wing-shaped transverse
processes, that of the neighbouring parts of the head
(Fig. 3). On this account those transverse processes often
project under the skin of the lateral surfaces of the upper
part of the neck.

Fig. 3.—Size of the Atlas compared with the Transverse Dimensions
of the corresponding Regions of the Skull in a Dog.

1, Atlas; 2, zygomatic arch; 3, external occipital protuberance; 4,
inferior maxilla.

The axis is furnished on its anterior surface with the odontoid
process, which articulates with the anterior (or inferior)
arch of the atlas, according to the direction of the neck.
The spinous process, flattened from without inwards, is
more or less pointed; it is elongated from before backwards,
so as partly to overlap the atlas and the third cervical
vertebra.

We find that this process overlaps less and less the neighbouring
vertebræ when we examine in succession the bear,
the cat, the dog, the ox, and the horse. With regard to the
other vertebræ of this region, they diminish in width from[8]
the second to the seventh; and, in some animals, the anterior
surface of the body presents a tubercle which articulates
with a cavity hollowed in the posterior surface of that
of the vertebra before it; this feature dwindles away in the
dorsal and lumbar regions.

The spinous process, slightly developed in the third
cervical vertebra, gradually increases in size to the seventh,
the spinous process of which, long and pointed, well deserves
the name of the prominent which is bestowed on it; but it
should not be forgotten that the spinous process of the axis
is equally developed.

On the inferior surface of the body of each of the vertebræ
is found a prominent crest, especially well marked at the
posterior part; this crest is but slightly developed in the
bear and in the cat tribe, and is not found in swine.

The transverse processes of the cervical vertebræ, from
their relation to the trachea, are known as the tracheal
processes.

The most marked characteristic of the dorsal vertebræ is
furnished by the spinous processes. They are long and
narrow. As a rule, the spinous processes of the foremost[9]
dorsal vertebræ are the most developed and are directed
obliquely upwards and backwards. As we approach the
last vertebræ of this region, the processes become shorter
and tend to become vertical, and the last ones are even, in
some cases, directed upwards and forwards; this disposition
is well marked in the dog and the cat. In the cetaceans, on
the contrary, the length of the spinous processes increases
from the first to the last.

In the horse the spinous processes of the first dorsal
vertebræ produce the prominence at the anterior limit of the
trunk, where the mane ends, which is known as the withers.

Fig. 4.—Lumbar Vertebræ of a Quadruped (the Horse): Superior
Surface.

1, Spinous process; 2, anterior articular process and transverse process
of the first lumbar vertebra of the left side; 3, costiform process.

The lumbar vertebræ are thicker than the preceding;
they are known by their short and latterly-flattened spinous
processes, and still more readily by their transverse processes,
which, as they are evidently atrophied ribs, it is more
accurate to denominate costiform processes (Fig. 4). These
are long, flattened from above downwards, and directed
outwards and forwards.

The true transverse processes are represented by tubercles[10]
situated on the superior borders of the articular processes
of each of the vertebræ of the lumbar region. Apropos of
these different osseous processes, we are reminded that they
are also present in the human skeleton.

In the horse the costiform processes of the fifth and sixth
lumbar vertebræ articulate, and are sometimes ankylosed,
one with the other; the terminal ones articulate with the base
of the sacrum. Sometimes the processes of the fourth and
fifth are thus related; this is the case in the figure (4) given;
here the costiform processes of the fourth and fifth vertebræ
articulate, and the two terminal ones have coalesced.

In the ox, the same processes are more developed than in
the horse; their summits elevating the skin, produce,
especially in animals which have not much flesh, prominences
which limit the flanks in the superior aspect. The costiform
processes of the last lumbar vertebræ are separate from each
other; those of the latter are not in contact with the sacrum.

The Sacrum.[3]—This bone, single and median, is
formed by the mutual coalescence of several vertebræ, which
vary in number according to the species observed.

Vertebræ Constituting the Sacrum.—Bears, 5; dogs, 3;
cats, 3; rabbits, 4; swine, 4; horses, 5; camels, 4;
oxen, 5; sheep, 4.

The sacrum is situated between the two iliac bones; with
which it articulates, and contributes to the formation of the
pelvis. It is obliquely placed, from before backwards, and
from below upwards; immediately behind the lumbar
section of the vertebral column; and is continued by the
coccygeal vertebræ, which form the skeleton of the tail.

It is triangular in outline, and is generally more narrow in
proportion than in the human being. All things considered,
it is more large and massive, and of greater density, in species
which sometimes assume the upright posture, rather than in[11]
those which cannot assume that attitude; for example, the
sacrum of the ape, of the bear, of the dog, and of the opossum
are proportionately larger than those of the horse.[4]

Its superior surface presents a crest, formed by the fusion
of the spinous processes of the vertebræ which form it. In
certain species these processes are attached only by their
bases, and are separated from each other superiorly. In
the pig they are wholly wanting.

The Coccygeal Vertebræ.—These vertebræ, few in
number (and sometimes ankylosed) in the human being,
form in the latter a small series, the coccyx; which is inclined
forwards, that is to say, towards the interior of the
pelvis. In quadrupeds, on the contrary, their number is
large; they are not ankylosed, and they form the skeleton
of the caudal appendix.

The first coccygeal vertebræ—that is, those which are next
the sacrum—present characters which are common to those
of other regions: they have a body, a foramen, and processes.
As we trace them backwards, these characters become
gradually effaced; and they become little more than
small osseous cylinders simply expanded at their extremities.

Direction and Form of the Spinal Column

The curves of the vertebral column are, in quadrupeds,
slightly different from those which characterize the human
spine. First, instead of their being, as in the latter, curves
in the antero-posterior aspect, because of the general attitude
of the body, they are turned in the supero-inferior direction.

The cervical region is not a single curve, as in the human
being. It presents two: one superior, with its convexity
looking upwards; the other inferior, the convexity of which
is turned downwards. This arrangement reminds one of
that of a console.

[12]The dorsal and lumbar regions are placed in a single curved
line, more or less concave downwards; so that in the lumbar
region there is no curve analogous to that which exists in
man; a form which, in the latter, is due to the biped attitude—that
is to say, the vertical position of the trunk.
Briefly, there is in quadrupeds one dorso-lumbar curve; and
not both a dorsal and a lumbar, with convexities in opposite
directions.

At the extremity of the dorso-lumbar region is the
sacrum and the caudal appendix, which describe a curve
of which the concavity is directed downwards and forwards.

It is necessary to point out that it is not the curves of the
three anterior portions of the spinal column which determine
the form of the superior border of the neck and
shoulders, and of the same part of the trunk. For the first
portion, there is a ligament which surmounts the cervical
region, and substitutes its modelling influence for that of the
vertebræ. It is the superior cervical ligament, which arises
from the spinous process of the first cervical vertebræ, and is
inserted into the external occipital protuberance on the
upper part of the posterior surface of the skull. The summits
of the spinous processes of the vertebræ alone give form to
the superior median border of the trunk. In this connection
we here repeat that it is not the general curvature of the
vertebral column which produces the withers, but the great
length of the spinous process of the first vertebræ of the
dorsal region.

The Thorax

The dorsal vertebræ form the posterior limit in man, and
superior in quadrupeds, of the region of the trunk known
as the thorax. A single bone, the sternum, is situated at
the aspect opposite; the ribs bound the thorax on its sides.

In its general outlines the thorax in quadrupeds resembles
that of man—that is to say, that, as in the latter, the anterior
portion—superior in the human being—is narrower than the
part opposite. But the progressive widening takes place in
a more regular and continuous fashion, so that it presents[13]
a more definitely conical outline. This purely conical form
is nevertheless found in the human species, but only during
infancy; the inferior portion of the thoracic cage being then
widely expanded, because of the development of the abdominal
viscera, which at that period are relatively large.

Fig. 5.—A Transverse Section of the Thorax of a Man placed
Vertically—that is to say, in the Direction which it would
assume in a Man placed in the Attitude of a Quadruped (a
Diagrammatic Figure).

1, Dorsal vertebra; 2, sternal region; 3, costal region of one side;
3′, costal region of the other side.

But the proportionate measurements of the thorax are
different. Indeed, we may recall that in man the thorax is
flattened from before backwards, so that the distance
between the sternum and the vertebral column is shorter
than the distance from the rib of one side to the corresponding
one of the opposite side (Fig. 5). In animals, on the
contrary, it is flattened laterally. Its vertical diameter—measured
from the sternum to the vertebral column—is
greater than the transverse measurement (Fig. 6).

Fig. 6.—A Vertical Section of the Thorax of a Quadruped
(Diagrammatic).

1, Fifth dorsal vertebra; 2, sternal region; 3, costal region of one side;
3′, costal region of the opposite side.

From this results a peculiar arrangement of the muscles
that we are able to bring directly into prominence, which
presents points of interest from the point of view of the contraction
of the subcutaneous layer. Indeed, in man the
region occupied by the pectorals is very broad; it is a wide
surface turned directly forward. In quadrupeds, this region
of the pectorals is narrowed. It is not spread out, as in the
preceding instances; and the appearance it presents is
explained by the fact that the thorax is compressed laterally.
If we examine the thorax on one of its lateral surfaces, the
muscles, on the contrary, are more extended. We see the
contour of the vertebral column, and the median part of the
abdomen; and, especially in the horse, between the great[14]
dorsal and the great oblique of the abdomen, we find a large
space, in which the ribs, with the intercostals which join them,
are uncovered; the muscles in question separate the one
from the other, under the influence, it would seem, of the
great dimensions of the lateral wall of the thorax.

The Sternum.—The sternum is, in quadrupeds, directed
obliquely downwards and backwards; its form varies in
different species. In the carnivora, it consists of eight bones,
irregularly cylindrical in form, being slightly flattened from
within outwards, and thickened at their extremities. They
remain separate, and this contributes elasticity and flexibility
to the thorax. The first nine costal cartilages articulate
directly with the sternum. The first of these cartilages
articulates with a nodule situated a little above the middle
of the first bone of the sternum.

In the horse the sternum is flattened laterally in its
anterior portion, and from above downwards in its posterior[15]
half. The six bones which form the sternum are connected
by cartilage. The keel-shaped piece, situated in front of the
sternum, is also cartilaginous. This process, but slightly
marked posteriorly, becomes more and more prominent in
front, and terminates at its anterior extremity by a prolongation,
slightly curved backwards, which projects for some
centimetres beyond the cavity in which the first costal
cartilage is received. This process is known as the tracheal
process, or rostral cartilage. The posterior extremity of the
sternum, flattened from above downwards, ends in a cartilaginous
plate; concave superiorly, and convex inferiorly:
this is the abdominal prolongation, or xiphoid appendix.

In the ox, the sternum is formed of two distinct bones,
which are united by an articulation. One, the anterior, is
short, and forms the first portion of the sternum; it is
slightly flattened from side to side, and vertical in direction.
The other, the posterior, is longer, and is formed by the
fusion of several small bones; it is placed horizontally, and
is flattened from above downwards. At the level of articulation
of these two portions, and because of their different
directions, the bone is bent. This bend occurs at the point
of articulation of the second costal cartilage. On the
superior border of the anterior segment the cartilage of
the first rib is articulated. The xiphoid appendix, which
is cartilaginous, is attached to the extremity of a long
process of the last bone of the sternum.

The shape of the anterior extremity of the sternum is
influenced by the presence or absence of clavicles. We have
seen that in some quadrupeds the clavicles are wanting. In
the first case, this extremity is large, and approaches in shape
to the corresponding part of the human sternum, which is so
clearly designed to give a point of support to the anterior
bone of the shoulder. In the second, on the contrary, this
extremity is narrow.

The sternum in birds is very different from that in mammalia,
which we have been studying. It varies greatly in
extent and shape, under the influence of certain conditions.
To understand the cause of these variations it is necessary
to remember that in man (as, indeed, in other animals; but[16]
the example of man, for that which follows, will be more
striking, on account of the mobility of his upper limbs) the
sternum gives origin to the pectoral muscles, and that these
muscles are inserted into other parts of the thoracic limbs,
designed by their contraction to draw the arms downwards,
forwards, and inwards—that is, when these are in a state of
abduction and in a horizontal direction, they draw them
towards the anterior surface of the thorax and downwards.
Now, this movement is similar to that made by birds
during flight. It is necessary to add that, in the latter
case, the more the displacement of the upper limbs has
of force and extent, the more the pectoral muscles are
developed.

For these reasons, birds, in which, during flight, the movements
of the thoracic limbs—the wings—are necessarily
energetic, present a great development of the pectoral
muscles; having consequently, because an extent of surface
for the origin of the muscles commensurate with their development
is necessary, a very large and peculiarly shaped
sternum (Figs. 18, 6; and 21, 6). Indeed, not only is the
sternum large, but, further, in order to form a deeper surface,
proportionately adapted to the muscles which arise from and
cover it, its anterior surface presents, in the median line, a
prominent crest known as the keel. This prominence forms
two lateral fossæ. We cite as examples, the sternum of the
eagle, the vulture, the falcon, and the hawk.

Fig. 7.—Sternum of a Bird (the Cock): Left Side, External Surface.

1, Keel; 2, internal slot; 3, external slot; 4, internal process; 5, external
process; 6, inferior ribs; 7, costal process; 8, surface for articulation
with the coracoid bone.

All birds are not, however, equally adapted to flight, for
in the domestic cock, which flies but a short distance, and
badly, the sternum is less developed (Fig. 7); it is also
diminished by slots, which diminish its surface. These slots,
two on each side, are called from their position the internal
and external slots. They are bounded by narrow, elongated,
bony processes, an internal and an external; the expanded
lower extremity of the latter overlaps the last inferior ribs
(see p. 19). The part of the external border which surmounts
this external process is hollowed out into grooves, which
receive the inferior ribs, and terminates superiorly in an
osseous projection known as the costal prominence.

In the ostrich, the cassowary, and the apteryx, which run,[17]
but do not fly, the sternum has the form of a plate of bone
slightly convex, but without a keel.

The shape of the sternum, correlated to the faculty of
flight (or of swimming; apropos of which we may cite the
penguin, of which the rudimentary wings resemble fins,
and perform their functions only), or the absence of this
faculty, has furnished the division of birds into two groups.
In one are included, under the name Carinates (carina, keel),
those in which the sternum is provided with a keel; in the
other division are those in which the sternum is not furnished
with one. These latter, on account of their unique mode of
progression, are more nearly allied to the mammals.

The keel is developed in flying mammals (bats).

Ribs and Costal Cartilages.—There are on each side
of the thorax as many ribs as there are dorsal vertebræ.
In animals, as in man, the ribs which articulate with the
sternum by their cartilages are called true, or sternal ribs;
those whose cartilages do not articulate with the sternum[18]
are called false, or asternal. The longer ribs are those
situated in the middle region of the thorax.

The ribs are directed obliquely downwards and backwards,
and this obliquity is more marked in the posterior ones than
in the anterior. They are, however, less oblique than in
the human being; what proves this is that the first rib in man
is oblique, while in quadrupeds it is vertical.

The curvature of the ribs is less pronounced in quadrupeds
than in the human being, but this is not equal in all animals.
The ribs of the bear are more curved than those of the dog;
the latter has ribs more curved than those of the horse.

Each rib, at its vertebral extremity, presents, from within
outwards, a wedge-shaped head for articulation with two
dorsal vertebræ, a neck, and a tuberosity. External to the
tubercle are found some rough impressions, for muscular
attachments, which correspond to the angle of the human
rib.

In the following table, we give the number and classification
of the ribs of some animals:

Number of the Ribs on Each Side of the Thorax.

The costal cartilages, by which the first ribs are united to
the sternum (sternal ribs), whilst the latter are united one
to the other without being directly connected with the
sternum (asternal ribs), are, as a rule, in quadrupeds, directed
obliquely downwards, forwards, and inwards; each forms,
with the rib to which it belongs, an obtuse angle more or less
open anteriorly. Their length is proportionate to that of
the ribs. The cartilages, which are continued from the
asternal ribs, unite and form the borders, directed obliquely
downwards and forwards, of the fossa which is found at the[19]
inferior and posterior part of the thorax, and which forms
the lateral limits of the epigastric region. In the dog and cat
the ribs are thick and almost cylindrical; the costal cartilages
are thicker at the margin of the sternum than at their
costal extremity. In the ox, the ribs are flattened laterally
and are very broad, the more so as we examine a portion
further from the vertebral column. From the second to the
twelfth they are quadrangular in the superior fourth, and
thicker than in the rest of their extent. The first costal
cartilage is vertical; the following ones are progressively
more oblique in a direction downwards and forwards. The
four or five cartilages which succeed the first unite with slight
obliquity to the sternum; their union with that bone gives
the impression of a very strong, well-knit apparatus. The
costal cartilages which unite with the sternum are flattened
laterally in the portions next the ribs, and flattened from
front to back in the rest of their extent.

In the horse the ribs increase in length from the first to the
ninth; they are flattened from without inwards, and increase
in width from the first to the sixth or seventh, and the following
ones become narrower. The costal cartilages, from
the second to the eighth, are, as in the ox, at first flattened
laterally, near the ribs; while near the sternum they are
flattened from front to back.

In birds, the ribs are each furnished with a flat process
(Fig. 18, 10), which springs from the posterior border, is
directed backwards, and overlaps the external surface of
the succeeding rib. These processes are not found, as a rule,
on the first or last ribs.

As for the costal cartilages, they are, as a rule, ossified,
and receive the name of inferior ribs (Fig. 18, 11), united to
the preceding (superior ribs; Fig. 18, 9) by articulation;
by the other extremity they are joined to the sternum; the
first superior ribs generally want them. Sometimes the last
inferior rib becomes connected with the one that precedes it,
not articulating with the sternum; and thus recalls the
relations of the asternal ribs which we have noticed in our
study of the mammals.

In the bat, as in birds, the costal cartilages are ossified.

[20]

THE ANTERIOR LIMBS[5]

The anterior limbs, homologous to the upper limbs in
man, are formed, as in the latter, of four segments: the
shoulder, the arm, the forearm, and the hand. These limbs,
considered in the vertebral series, present themselves under
very different aspects, which are determined by the functions
they are called upon to perform.

Fig. 8.—Anterior Limb of the Bat: Left Side, Anterior Surface.

1, Clavicle; 2, scapula; 3, humerus; 4, radius; 5, cubitus; 6, carpus;
7, thumb; 8, metacarpus; 9, phalanges.

They constitute the forepaw in terrestrial mammals; in
aerial vertebrates they form wings; in aqueous mammals
they act as paddles. In whatever series we study them,
we can readily find the relationship of the different parts;
it is very easy to recognise the same bones in the upper limbs
of the human being, the wings of the bat (Fig. 8) and of
birds (Fig. 21), and in the anterior paddles of the seal (Fig. 9)
and of the dolphin.

Fig. 9.—Anterior Limb of the Seal: Left Side, External Surface.

1, Scapula; 2, humerus; 3, radius; 4, ulna; 5, carpus;
6, metacarpus; 7, phalanges of the fingers.

In quadrupeds, the shoulder and arm are hidden, the
latter more or less completely, in the muscular mass which
binds it to the lateral wall of the trunk; so that the anterior
limbs only present; free from the trunk: the elbow, forearm,
and hand.

The Shoulder

In some vertebrates, the shoulder is formed of two bones—the
scapula and clavicle; in others of only one bone—the
scapula; the clavicle in this case does not exist.

[21]The Scapula or Omoplate.—The scapula is situated
on the lateral surface of the thorax, and is directed obliquely,
from above downwards and from behind forwards.

We must first recall, so as to be able to make a comparison,
that in man this bone is placed at the posterior surface of the
thoracic cage; so that if we look at the human thorax
on one of its lateral aspects we see chiefly the external
border of the scapula; it is the external surface (homologous
to the posterior surface of the human scapula) which
we see in its full extent when we look on the same surface
of the thorax in quadrupeds.

Fig. 10.—Situation and Direction
of the Scapula in the
Human Being, the Trunk being
Horizontal, as in Quadrupeds.
Vertical and Transverse Section
of the Thorax (Diagrammatic
Figure).

1, Contour of the thorax; 2, 2, the
scapula.

Fig. 11.—Position and Direction
of the Scapula in Quadrupeds.
Vertical and Transverse Section
of the Thorax (Diagrammatic
Figure).

1, Contour of the thorax; 2, 2, the
scapula.

To sum up, if we fancy the human being in the position
of the quadruped, the scapula will have its surfaces almost
parallel to the ground (Fig. 10); while in quadrupeds, the
surfaces are situated in a plane which is almost perpendicular
to the ground (Fig. 11). This position of the scapula in an
almost vertical plane is designed to give the necessary point
of support to the osseous columns that form the skeleton
of the other portions of the anterior limbs.

Fig. 12.—Left Scapula of
the Human Being, Posterior
Surface, placed
in the Position which
it would Occupy in the
Skeleton of a Quadruped.

1, Cervical border; 2, spinal border—the
scapula here represented, being from
a hoofed animal, has a cartilage of extension
attached to its spinal border; 3,
axillary border; 4, supraspinous fossa;
5, subspinous fossa; 6, spine of the
scapula; 7, glenoid cavity; 8, coracoid
process. The scapula of the horse has no
acromion process, but it is easy, if we
compare the human scapula, to judge of
the position which this process would
occupy if it were present.

Because of this position of the scapula (Figs. 12 and 13),
the spinal border is superior, the cervical, anterior, and the
axillary, posterior. In direct contrast to what obtains in the
human scapula, the spinal border is the shortest of the[22]
three; except in the bat, and the majority of the
cetaceans.

Fig. 13.—Left Scapula of a Horse:
External Surface.

1, Cervical border; 2,
spinal border; 3, axillary
border; 4, supraspinous fossa;
5, subspinous fossa; 6,
scapular spine; 7, glenoid
cavity; 8, coracoid process;
9, acromion process.

In certain animals (in the ungulates [hoofed[6]]—pigs, oxen,
sheep, horses) the superior, or spinal, border of the scapula is
surmounted by a cartilage called the cartilage of prolongation.

Fig. 14.—Vertical and Transverse
Section, at the Site of the
Shoulders, of the Thorax of the
Horse (Diagrammatic Figure).

1, Outline of the thorax at the level
of the third dorsal vertebra; 2, 2,
scapula; 3, spinal border of the
scapula; 4, cartilage of prolongation;
5, contour of the skin.

This is the cause why the border to which it is fixed is so
slightly noticeable under the skin in these animals; indeed,
in the upper part, the bone and cartilage are not distinguishable
in the contour of the corresponding region of the back;
being applied to the lateral surfaces of the spinous processes,
the prominence formed by the extremities of which is directly
continuous with the plane of the scapula (Fig. 16).

Fig. 15.—Vertical and Transverse
Section, at the Plane
of the Shoulders, of the
Thorax of a Dog (Diagrammatic
Figure).

1, Outline of the thorax at the
level of the third dorsal vertebra;
2, 2, scapula; 3, spinal border of
the scapula; 4, contour of the skin.

[23]In quadrupeds whose scapula, on the contrary, is wanting
in the cartilage of prolongation (in the clawed,[7] such as the
cat and dog), the superior border of the scapula is visible,
especially when the animal is resting on its fore-limbs, particularly
when it crouches; at such a time the skin is markedly
raised by that border; and the spinous processes of
the vertebræ, beyond which it projects, occupy the bottom
of a fossa (Fig. 15). The internal surface of the scapula
is turned towards the ribs; it is known, as in man (in whom
this surface is anterior), as the subscapular fossa.

Fig. 16.—Left Clavicle of the Cat:
Superior Surface (Natural Size).

1, Internal extremity; 2, external extremity.

Fig. 17.—Clavicle of the
Dog (Natural Size).

Its external surface is divided into two parts by the spine
of the scapula; which, in some animals, terminates inferiorly
in a flat and clearly distinct process, the homologue of the[24]
acromion process of the human scapula. The two regions
separated by the spine are known as the supraspinous fossa
and the infraspinous fossa. The supraspinous fossa is anterior
to the spine, and the infraspinous is posterior to it. The
surfaces of the scapula are, in quadrupeds, flatter than
in the human being, and in particular the subscapular fossa,
which is also less concave. Some authors attribute this to
the lesser curvature of the ribs in quadrupeds. A few words
will suffice to prove that there must be another reason.
The scapula is not in immediate contact with the ribs; the
subscapular fossa is not moulded on them. Besides, the
form of the scapula is, as in other parts of the skeleton,
dependent on the disposition of muscles, and the development
of these latter is correlated to the extent and energy
of the movements which the individual is able or required[25]
to execute. But the movements which those muscles
produce (more especially the rotation of the humerus) are,
in quadrupeds, less extensive than in the human being;
and, consequently, the muscles which produce them are,
proportionally, less strongly developed. The inferior angle
(superior and external in man), situated at the junction of
the cervical and axillary borders, presents the glenoid
cavity, which, looking downwards, receives the articular
surface of the superior extremity of the bone of the arm—that
is to say, the head of the humerus. Above this
cavity, on the lower part of the cervical border, is situated
a tubercle which reminds us of the coracoid process of
the human scapula. The region occupied by the glenoid
cavity is separated from the body of the bone by a constriction—the
neck of the scapula.

Fig. 18.—Skeleton of the Shoulder of a Bird (Vulture): Antero-External
View of the Left Side.

1, Left clavicle; 2, inferior portion of the right clavicle, forming by its
ankylosis with that of the other side the fourchette; 3, coracoid bone;
4, scapula; 5, articular surface for humerus; 6, superior half of the
sternum; 7, keel of sternum; 8, spinous process of the dorsal vertebræ;
9, superior ribs; 10, process of one of these ribs; 11, inferior ribs.

In birds the scapula is elongated in a direction parallel to
the vertebral column, and very narrow in the opposite
(Fig. 18): it is also flat, and has no spine. Its coracoid
process is represented by a peculiar bone—the coracoidean
or coracoid bone—which we shall describe later on when
we come to the study of the clavicle and of the anterior
region of the shoulder (see p. 26).

The Clavicle.—The clavicle is found only in the human
being, and in animals whose anterior limbs, possessing
great freedom of movement in all directions, require
that the scapula should possess a point of support which,
while affording this, can be displaced with it, or draw it
in certain directions. Now, this point of support is
furnished by the clavicle.

In animals possessed of hoofs (ungulates), such as the
sheep, ox, and horse, the clavicle does not exist. Indeed,
in them the freedom of movement of the anterior limbs is
limited; they move by projection in the forward and
backward directions only; they merely fulfil the functions
of giving support to and carrying about the body. The
clavicle is rudimentary in the cat and the dog; in the cat
it is a small, elongated bone (Fig. 16), 2 centimetres in
length, thin and curved, connected with the sternum and
the scapula by ligamentous bundles. In the dog it is[26]
represented by a small osseous plate only (Fig. 17),
which is not connected with any of the neighbouring
bones.

It is on the deep surface of a muscle which passes from
the head and neck to the humerus (mastoido-humeral, a
muscle common to the arm, neck, and head) in which this
rudimentary bone is found to be developed.

The clavicle exists in perfect state in mammals which
use their limbs for digging, grasping, or flying; the insectivora
(hedgehog, mole) and some rodents (squirrel, woodchuck)
are provided with it.

The cheiroptera (bats) possess an extremely well-developed
clavicle, on account of the varied movements which their
thoracic limbs execute.

This formation of the shoulder which favours flight in
the bat is even more remarkable in birds. In these latter
(Fig. 18) the clavicles, fused together by their lower extremities,
form one bone, having the shape of the letter V or U,
which is known as the fourchette; this bone, acting as a
true spring, keeps the shoulders apart, and prevents their
approximation during the energetic movements which flight
necessitates.

In birds whose power of flight is strong, the two limbs
of this bone are widely separated and thick, and the fourchette
is U-shaped. Those whose flight is awkward and
but slightly energetic have the limbs of the fourchette
slender; they unite at a more acute angle, and the bone is
V shaped.

Furthermore, a bone named the coracoid joins the scapula
to the sternum; this bone, often fused with the scapula,
where it contributes to the formation of the glenoid cavity,
represents in birds the coracoid process of the human[27]
scapula. If we fancy this process directed inwards, and
sufficiently lengthened to join the sternum, we shall have
an idea of the disposition of the bone we are now discussing,
and the reasons for which the name has been chosen by
which it is designated. The coracoid bone, like the fourchette
which it reinforces, offers to the wings a degree of support
proportionate to the efforts developed by those limbs; for
this reason it is thick and solid in birds of powerful flight.

The superior extremity of each branch of the fourchette,
at the level of its junction with the coracoid and the scapula,
bounds, with these latter, a foramen which gives passage to[28]
the tendon of the elevator muscle of the wing, or small
pectoral. The importance of the fourchette being, as we
have seen, in proportion to the movements of flying, it is
easy to understand that the bone is not found in the ostrich.

The Arm

A single bone, the humerus, forms the skeleton of this
portion of the thoracic limb.

The Humerus.—The bone of the arm is, in quadrupeds,
inclined from above downwards and from before backwards.

It is, with relation to other regions, short in proportion
as the metacarpus is elongated, and as the number of digits
is lessened. In the horse, for example, whose metacarpus
is long, and in which but one digit is apparent, the humerus
is very short. The slight development in length of the
humerus explains its close application to the side of the
animal as far as the elbow.

In animals in which the humerus is longer, the bone is
slightly free, as well as the elbow, at its inferior extremity.
Later on we will return to the consideration of this
peculiarity and of the proportions of the humerus, after
we have studied the other parts of the fore-limbs.

The humerus in quadrupeds is inflected like the letter S;
in man this general form is less accentuated, the humerus
being almost straight. On its body, which appears twisted
on its own axis, we find the musculo-spiral groove,[8] which
crosses the external surface, and is very deep in some animals.
Above this groove, and on the external surface, there exists
a rough surface which is the impression of the deltoid. In[29]
some species this rugosity is very prominent, and is called
the tuberosity of the deltoid; it is prolonged downwards by
a border which forms the anterior crest of the musculo-spiral
groove and limits this latter in front. The external border
of the bone, or posterior crest of the groove, limits it behind.

The superior extremity is enlarged, and remarkable in
three portions which it presents; these are: an articular
surface and two tuberosities.

The articular surface, or head of the humerus, smooth and
round, is in contact with the glenoid cavity of the scapula.
This head in the human skeleton is directed upwards and inwards;
in quadrupeds its direction is upwards and backwards.
The inferior extremity, having in both one and
the other its long axis directed transversely, and the point
of the elbow looking backwards in all, the result is that the
head of the humerus is not situated vertically above the
same regions; in the first, it is almost directly above the
internal part of this extremity; in the latter, it is situated
above its posterior surface, or the point of the elbow in
the complete skeleton. This difference of direction is correlated
with the position of the scapula, the glenoid cavity
of which, as we have already seen, is in man turned outwards,
whereas in quadrupeds it looks downwards. In
the latter case the scapula consequently rests on the head
of the humerus; and this position is most favourable for the
performance of the functions which the anterior limbs have
to fulfil in these latter.

Of the tuberosities of the head of the humerus, one is
situated on the external aspect—it is the great tuberosity, or
trochiter; the other is placed internally—it is the small
tuberosity, or trochin. The great tuberosity is divided into
three parts—summit, convexity, and crest; these different
parts give insertion to the muscles of the shoulder. We
recollect that the facets (anterior, middle, and posterior) of
the great tuberosity of the humerus in man give attachment
to the muscles of the same region. The head of the humerus
in the human body projects above the tuberosities. We
shall see afterwards, when dealing with some special quadrupeds,
that in some of these, on the other hand, the tuberosities[30]
are on a higher level than the articular head of the
bone. Between the two tuberosities is the bicipital groove.

In man, the superior extremity of the humerus, although
covered by the deltoid, reveals its presence by elevating
the corresponding portion of the latter. In quadrupeds, the
anterior part of this extremity, although similarly covered by
muscular bundles, produces a prominence under the skin.
This prominence is situated at the summit of the angle
formed by the opposing directions of the scapula and the
bone of the arm, and constitutes what is known by
the name of the point of the shoulder, or of the point of
the arm.

The inferior extremity, transversely enlarged, presents an
undulating articular surface, which reminds us of the trochlea
and the condyle of the human humerus; on which, however,
the condyle is more sharply defined from the trochlea.

In the human skeleton, the internal lip of the trochlea
descends lower than the external; and also lower than the
condyle. In the bear, the cat, and the dog, it is the same.
In the ox and the sheep, the condyle is lower than the
trochlea, but only very little lower. In the horse the
arrangement is still the same, but a little more accentuated.

On the lateral parts of this extremity we find: internally,
a prominence, the epitrochlea; and, externally, another,
the epicondyle. It is from this latter that the crest arises,
which, passing upwards, forms the posterior limit of the
groove of torsion.

The two prominences, which we have just described from
a general point of view, present special arrangements which
it is necessary to point out. When we examine the form
of the outline of the inferior extremity of the humerus in
man, the bear, the cat, the dog, the ox, and the horse, we
find in following this order that the extremity tends to
become narrow transversely, and that the epicondyle and
the epitrochlea are less and less prominent on the external
and internal aspects respectively. These two processes,
indeed, project backwards; the epitrochlea always remaining
more developed than the epicondyle. Because of this
projection backwards, the cavity situated on the posterior[31]
surface of the inferior extremity, the olecranon fossa, is
very deep, more so than in the humerus of man. Its borders
being thus formed by the two processes, are very prominent.
In front we find the coronoid fossa, which is less deep than
that of which we have just spoken.

Fig. 19.—Inferior Extremity of
the Left Humerus of a Felide
(Lion).

1, Epitrochlea; 2, supra-epitrochlear
foramen.

There exists in some mammals an osseous canal, situated
above the epitrochlea, and known as the supratrochlear
canal (Fig. 19). It is bounded by a plate of bone which
at its middle portion is detached from the shaft of the
humerus, and blends with the latter at both its extremities.
The brachial artery and median nerve pass through the
foramen.

Fig. 20.—Inferior Extremity of
the Left Human Humerus,
showing the Presence of a
Supratrochlear Process.

1, Epitrochlea; 2, supra-epitrochlear
process.

A similar condition is sometimes found, as an abnormality,
in man, which presents itself under the following aspect
(Fig. 20): an osseous prominence more or less long, in the
shape of a crochet-needle—supra-epitrochlear process—situated
5 or 6 centimetres above the epitrochlea; the
summit of this process gives attachment to a fibrous band,
which is inserted by its other end into the epitrochlea and
the internal intermuscular aponeurosis. The fibro-osseous
ring thus formed gives passage to the brachial artery and the[32]
median nerve, or in case of a premature division of this
artery to the ulnar branch of the same.[9]

There is also found in some mammals a perforation of
the thin plate of bone which, in others, separates the olecranon
fossa from the coronoid. This perforation is sometimes
found as an abnormality in the human humerus.

Fig. 21.—Skeleton of a Bird (Vulture): Left Surface.

1, Cranium; 2, face; 3, cervical vertebræ; 4, spinous processes of
the dorsal vertebræ; 5, coccygeal vertebræ; 6, sternum; 7, keel; 8,
superior ribs; 9, inferior ribs; 10, clavicle; 11, coracoid bone (for the
details of the skeleton of the shoulder, see Fig. 18); 12, humerus; 13,
radius; 14, ulna; 15, carpus; 16, hand (for details of the skeleton of
this region, see Fig. 31); 17, ilium; 18, ischium; 19, pubis (for the details
of the pelvis, see Fig. 46); 20, femur; 21, tibia; 22, fibula; 23, osseous
nodule, which some anatomists think represents the calcaneum; it is
the sole vestige of the tarsus; 24, metatarsus; 25, foot; 26, first toe (for
the details of the skeleton of the foot, see Fig. 48).

As does the sternum and the skeleton of the shoulder, the
humerus of birds presents differences correlated to the
functions which the thoracic limbs are destined to fulfil.
Lying on the side of the thorax, directed obliquely downwards
and backwards (Fig. 21), it is proportionately longer
in individuals of powerful flight than in those which fly
less or not at all. In the vulture it projects beyond the
posterior part of the pelvis; in the cock it does not even
reach the anterior border of the same. To these differences
in length are added differences in volume and in the development
of the processes which serve for muscular attachment,
which are more considerable in birds of powerful flight.

The humerus is so placed that the radial border, external
in man and quadrupeds, looks upwards, with the result that
the surface of the bone of the arm, which in these latter is
anterior, in the former looks outwards. The humeral head,
which is turned forwards and a little inwards, is convex
and elongated in the vertical direction. Behind and above
this head is found a crest for the insertion of muscles. It is
the same for the region below, where there is a tuberosity
whose inferior surface presents a pretty large opening
which looks inwards to a fossa from the floor of which a
number of minute openings communicate with the interior
of the bone. This is the pneumatic foramen of the humerus.

It is of interest to remember in connection with this subject
that in birds, in keeping with the conditions of flight, every
system of organs is adapted to diminish the weight of the
body. We particularly draw attention to the osseous
framework, the structure of which is such that the weight[33]
of the animal is greatly lessened. This condition is secured
by the pneumaticity. The bone consists of a cover of
compact tissue, which, instead of enclosing marrow, is
hollowed out by cavities which contain air, and communicate
with special pouches, the air-sacs, which are appendages of
the lungs.[10]

[34]The antibrachial extremity of the humerus is flattened
from without inwards. It terminates in two articular
surfaces, which articulate with the radius and ulna.

The olecranon process of the ulna being slightly developed,
it follows that the olecranon fossa is not large; neither is
the coronoid.

General View of the Form of the Forearm and Hand

We now proceed to the study of the two regions of the
fore-limbs which present the greatest variety in regard to
the number of bones and also in regard to form and proportions.
These two regions are the forearm and the hand.

It is first of all necessary to say that in man, when the
fore-limb hangs beside the body, and the dorsum of the hand
looks backwards, the two bones of the forearm are parallel,
and that this position is known by the name of supination.
It is also necessary to remember that there is another
attitude, in which the radius, crossing the ulna, and carrying
the hand with it, displaces the latter in such a way that the
palmar surface looks backwards. This second position is
known as pronation.

Let us now suppose that a man wishes to walk in the
attitude of a quadruped. It will be necessary, in order that
his upper limbs, being for the moment anterior ones, may act
as members of support, to place the forearm in pronation, in
order that, as is more normal, the hands may rest on the
ground by their palmar surfaces. In this position the radius,
being rotated on its own axis at its upper extremity and
around the ulna in the rest of its extent, shall have its
inferior extremity situated on the inner side of the corresponding
extremity of the latter.

Such is the situation of the bones of the forearm and the
attitude of the hand in quadrupeds. In short, quadrupeds
have their anterior members in the position of pronation.

Fig. 22.—The Human Hand resting for its Whole Extent on its
Palmar Surface: Left Side, External Surface.

The individual whom we have just supposed placed in the
attitude of a quadruped would be able to maintain this
position by pressing on the ground more or less extensive
portions of his hands; the whole palm of the hand may
be applied to the ground (Fig. 22); or the fingers
only—that[35]
is to say, the phalanges (Fig. 23); or the extremities of
the fingers only—that is to say, the third phalanges (Fig. 24).
This last position, which is certainly difficult to maintain,
should here be regarded rather as theoretical.

Fig. 23.—The Human Hand resting
on its Phalanges: Left
Side, External Surface.

We shall meet with each of these modes of support in
certain groups of animals. Thus, the bear, badger, and the
majority of rodents, have the paws applied to the ground
by the whole extent of the palmar surface of the hand, from
the wrist to the tips of the fingers. They are therefore called
plantigrade, from the analogy, in this case, of the palm of
the hand to the plantar surface, or sole of the foot.

Fig. 24.—The Human Hand resting
on the Tips of some of its
Third Phalanges: Left Side,
External View.

In others, such as the lion, tiger, panther, cat, wolf, and
fox, the support is made no longer on the whole extent of
the palmar surface, but on the corresponding surface of the
fingers only—the metacarpus is turned back, and, consequently,
the wrist—that is to say, the carpus—is removed
from the ground. These are the digitigrades.

Lastly, the ruminants (sheep, oxen, deer, etc.), and also the
pig, ass, and horse, rest on the third phalanx only. In
them not only is the metacarpus turned back, but also the
two first phalanges. The wrist is very far removed from
the ground. In these animals, the third phalanx is
enclosed in a case of horn, a nail (the hoof), and because[36]
the support of the limb is on that nail, the name of unguligrades
has been given them. Nevertheless, as the point
of support is on the third phalanx, which is also known by
the name of phalangette, we are of opinion that, in order to
specify definitely, although they walk on their fingers, as
do the digitigrades, the support is provided not by the
whole extent of those appendages, they might receive
the name of phalangettigrades.

It is necessary among the ruminants to make an exception
of the camel and the llama, which are digitigrades.

Just in proportion as the hand is raised from the ground, as
we have just seen in passing from the plantigrades to the
digitigrades and unguligrades, the number of bones of that
region diminishes, the bones of the forearm coalesce, and[37]
the ulna tends to disappear; the hand becomes less and less
suitable for grasping, climbing, or digging, so as to form
an organ exclusively adapted for walking and supporting
the body.

Thus, the bear (plantigrade) has five digits, and the
power of performing the movements of supination and
pronation. Indeed, we know with what facility this animal
is able to move his paws in every direction, and climb a tree
by grasping it with his fore-limbs. It is well known,
however, that no animal except the ape can perform the
movements of rotation of the radius around the ulna
with the same facility as man; and that none possesses the
same degree of suppleness, extent, and variety of movements
of the forearm and hand.

In the digitigrades there is one finger which is but slightly
developed, and which is always removed from the ground—that
is, the thumb: there is also a little less mobility of the
radius around the ulna.

In the ungulates the limbs are simply required to
perform the movements of walking, and form veritable
columns of support, which become the more solid as
they are less divided. The bones of the forearm are fused
together; there is therefore no possibility of rotation
of the radius around the ulna. The metacarpus is
reduced to a single piece, which in the horse constitutes
what is known as the canon. The number of digits
becomes diminished, so that in ruminants there are not
more than two, and in the horse but one. We should,
however, add that, up to the present, we have taken into
account only perfect digits, those that rest on the ground.
We shall see further on that there exist supplementary
digits, but that they are only slightly developed, and are
represented in some cases by mere osseous spurs; it is this
fact that has permitted us to ignore them in the general
study which we have just made.

Because, as we have already said, the unguligrades have
the inferior extremity of the digit encased in a horny sheath,
which forms the hoof of the horse and the corresponding
structures (onglons) in the ox, those animals have been[38]
placed in a special group, which is based on that peculiarity—that
is, the group of ungulate mammals.

The plantigrades and digitigrades, of which the paws
have their surfaces of support strengthened by an epidermic
sole and fatty pads, have the free extremities of the third
phalanges covered on their dorsal surface by nails or claws;
hence they are named unguiculate mammals.

The bat and birds have the bones of the forearm so
arranged that the radius cannot rotate around the ulna. This
is necessary in order that during flight, when the wing is
being lowered, the radius and hand shall not be able to turn;
for, if such rotation took place, each stroke of the wing would
place it in a vertical position, which would occasion a loss of
resistance incompatible with the effect to be obtained.

The Forearm

The skeleton of the forearm in quadrupeds is vertical in
direction; consequently, it forms with the arm an angle
open anteriorly; this is well seen on examining the lateral
surface. If we examine it on its anterior surface, we find
a slight obliquity directed downwards and inwards. In
animals in which the bones of the forearm are separate—that
is to say, susceptible of supination and pronation—we
find a more close resemblance to those of the human
skeleton. The ulna, the superior extremity of which always
projects beyond that of the radius, has a shaft which gradually
narrows from above downwards. Its inferior extremity
is terminated by a round head in those animals in which the
ulna is fully developed; in others, as it is atrophied, it ends
in a thin, long process.

The ulna presents at its superior extremity a posterior
process, the olecranon, which forms the point of the elbow.
We find on the anterior surface of the same, another process,
the coronoid.

Fig. 25.—Superior Extremity of
the Bones of the Human Forearm:
Left Side, Superior Surface.

1, Radius; 2, ulna; 3, olecranon
process; 4, coronoid process.

Fig. 26.—Superior Extremity of
the Bones of the Forearm of
the Dog: Left Limb, Superior
Surface.

1, Radius; 2, ulna; 3, olecranon
process; 4, coronoid process.

It is necessary to dwell on the relations of these parts.
In man the head of the radius is situated at the anterior
part of the external surface of the superior extremity of the
ulna (Fig. 25); indeed, the small sigmoid cavity with
which[39]
the head articulates is situated on the outer side of the
coronoid process, and this apophysis is placed in front.
In the plantigrades and digitigrades the head of the radius
is placed still more forward, so much so that it is situated
almost in front of the superior extremity of the ulna (Fig. 26).
In the unguligrades it is placed directly in front of this
latter (Fig. 27).

Fig. 27.—Superior Extremity of the Bones of the Forearm of
the Horse: Left Limb, Superior Surface.

1, Radius; 2, ulna; 3, olecranon process; 4, coronoid process.

Further, the displacement of the radius is made at the
expense of the superior extremity of the neighbouring bone;
the radius appears to appropriate more and more the parts
which in man belong exclusively to the ulna—for example,
the coronoid process. In the plantigrades and the digitigrades
half of the process still belongs to the ulna and the
remainder to the radius. In the ungulates—the horse, for
example—the coronoid process belongs to the radius; the
ulna, situated behind the latter, is correspondingly diminished
in size.

In brief, when we study this region of the skeleton in
plantigrades, then in digitigrades, and finally in unguligrades,
we find a kind of progressive absorption of one of the two
bones (ulna) by the other (radius), which thus becomes the
more developed.

It is easy to explain this partial disappearance of the
ulna. When the forearm is capable of performing the[40]
movements of pronation and supination, the ulna is completely
developed, for it is in its small sigmoid cavity that
the head of the radius revolves, and it is around its inferior
extremity, the head, that the corresponding extremity of
the radius turns. But when the movements of rotation
of the forearm do not exist, the inferior extremity of the
ulna becomes functionally useless and disappears. As to
its rôle in the movements of the region of the wrist,
that is nil, for we may remember—we will observe it again
when we come to treat of the articulations—that the hand
articulates with the radius alone (radio-carpal articulation);
this is the reason that, when the forearm possesses the
fullest mobility, the hand follows the movements which
that bone makes around the ulna.

It is not so with the articulation at the elbow-joint; there
it is the ulna, which, with the humerus, forms the essential
parts (humero-ulnar articulation); its olecranon process[41]
limits the movement of extension of the forearm. It is for
this reason that, even in those quadrupeds in which the ulna
is atrophied, the olecranon process presents a relatively
considerable degree of development.

We know that on the posterior surface of the inferior
extremity of the bones of the human forearm are grooves
in which pass the tendons of the posterior and external[42]
muscles which, belonging to this region, are directed for
insertion towards the hand.

Fig. 28.—Inferior Extremity of the Bones of the Forearm of a
Man: Left Side, Posterior Surface, Position of Supination.

1, Radius; 2, ulna; A, groove for the long abductor and short extensor
muscles of the thumb; B, groove for the radial muscles; C, groove for the
long extensor of the thumb; D, groove for the special extensor of the index
finger and of the common extensor of the fingers; E, groove for the proper
extensor of the little finger; F, groove for the posterior ulna.

In animals, because of the movement of rotation of the
radius, the surface of this bone, which is anterior, corresponds
to the posterior surface of the same in man. (To
possess a clear conception of this, it is necessary to remember
that, in this latter, the bones of the forearm are always
described as in the position of supination; they are thus
represented in Fig. 28. The direction of the surfaces of
the radius is the reverse of that in animals, since the latter
have the radius always in a state of pronation.)

Fig. 29.—Inferior Extremity of the Bones of the Forearm of the
Dog: Left Side, Anterior Surface, Normal Position—that
is, the Position of Pronation.

1, Radius; 2, ulna; A, groove for the long abductor and for the short
extensor of the thumb; B, groove for the radials; D, groove for the long
extensor of the thumb, the special extensor of the index-finger, and the
common extensor of the fingers; E, groove for the special extensor of the
little finger.

Consequently it is on the anterior surface of the bone that
we find the grooves concerning which it is necessary to give
some details. Regarding them in passing from the radius
towards the ulna, those grooves give passage to the tendons
of the muscles whose names occupy the columns on p. 43.
The letters which are referred to each serve to define their
order, and to facilitate reference to Figs. 28, 29, and 30.

Fig. 30.—Inferior Extremity of the Bone of the Forearm of the
Horse: Left Side, Anterior Surface.

1, Radius; A, groove for the long abductor and the short extensor of
the thumb; B, groove for the radials; D, groove for the common extensor
of the digits; E, groove for the special extensor of the little finger.

We should mention that the groove E is situated, both in
man and in the dog, at the level of the inferior radio-ulnar
articulation; but that in the horse, as the ulna does not
exist at that level, the groove is situated on the external
surface of the inferior extremity of the radius. It is necessary
to add that, in some horses, the ulna is, nevertheless,[43]
represented in this region by a tongue-like process of bone;
and in such cases the groove is situated in front of this
process, at the level of the line of coalescence, which there
represents the articulation.

It is also useful to note, with reference to the groove F,
in which passes, in man, the tendon of the posterior ulnar
muscle, that, when the forearm is in pronation, the radius
alone being displaced, we can only see this groove on the
surface which looks backwards; and that it is then separated
from the groove which contains the tendon of the special
extensor of the little finger by an interval equal to the thickness[44]
of the head of the ulna.[12] When
the forearm is supinated,
the two grooves are found, on the other hand, one
beside the other: and the tendons which they contain are
very naturally in contact.

In birds the forearm is flexed on the arm, and the latter
being directed downwards and backwards, the former is,
consequently, directed upwards and forwards. Further,
because of the position of the humerus, which, as we mentioned
on p. 32, has its inferior extremity so turned that
the surface which is anterior in man becomes external, the
radius, instead of being outside the ulna, is placed above it.
This latter is larger than the radius, but its olecranon process
is very slightly developed.

The Hand

The hand in animals, as in man, is formed of three parts—the
carpus, metacarpus, and fingers. In man, the forearm
and the hand being described in the position of supination;
the bones of the carpus are named in passing from the most
external to the most internal—that is to say, from that
which corresponds to the radial side of the forearm to that
which corresponds to the ulnar side. In animals in which,
as we know, but it is not unprofitable to repeat, the hand
is in pronation, the radial side of the forearm being placed
inside, we enumerate the carpal bones in counting the
most internal as the first; this is the only method which
permits us, in taking our point of departure from the human
skeleton as our standard, to recognise the homologies of the
bones of the carpal region.

These bones, eight in number, are arranged in two transverse
rows, of which one, the first, is superior or anti-brachial;
the other, the second, is inferior or metacarpal.
Each of these rows contains four bones. Considered in
the order we have indicated above—that is to say, proceeding
from the radial to the ulnar side—they are thus named:
scaphoid, semilunar, cuneiform, and pisiform, in the first[45]
row; trapezium, trapezoid, os magnum, and unciform, in
the second. The number of these bones is not the same
in all animals on account of the coalescence or absence of
some. In each row the bones are placed side by side, with
the exception of the pisiform, which being placed on the
palmar surface of the cuneiform, produces a small projection
in man, but a very pronounced one in quadrupeds.

The pisiform is called the hooked bone in some veterinary
anatomies. If we consider the hook which it forms, we
may recognise that the name is appropriate; but from
the point of view of comparison with the human carpus,
the name is unfortunate, for it creates confusion between
the true pisiform (the fourth bone in the upper row), and
the last bone in the lower row, which is the veritable unciform
bone. We do not here seek for similarity of form, but
homology of regions; and it is only by using the same
names to denote the same things that we can succeed in
determining such homology.

Taken as a whole, the bones of the carpus form a mass
which, by its superior border, articulates with the bones
of the forearm, and by its inferior border is in relation with
the metacarpal region. Its dorsal surface (anterior in
quadrupeds) is slightly convex; its palmar surface (posterior
in quadrupeds) is excavated, and forms a groove in
which pass the tendons of the flexors of the fingers. This
last, in man, has the appearance of a gutter, because of the
prominences caused by the projection of the internal and
external bones beyond their fellows.

In quadrupeds the palmar groove is especially determined
by the pisiform bone, of which we have just mentioned the
great development.

The region occupied by the carpus, in the unguligrades,
is known as the knee; it would have been more appropriately
named had it been called the wrist.

The number of the metacarpal bones in mammals never
exceeds five, but it often falls below it; the same is true
for the digits. The first are generally equal in number to
the latter; an exception is met with in ruminants, whose
two metacarpals coalescing soon after birth, form but[46]
one bone; this, the canon bone, articulates with two
digits.

The number of metacarpals and digits diminishes in proportion
as the limbs cease to be organs of prehension, and
become more exclusively organs of support and locomotion.

The number of phalanges is two for the thumb and three
for each of the other digits; except in the cetaceans, in
which they are more numerous.

In the bat, the metacarpals and phalanges are very long,
and form the skeleton of the wing; these phalanges are
not furnished with nails; the thumb, which is very short,
is alone provided with one (Fig. 8).

With regard to the relative dimensions of the bones of
the metacarpus, it is necessary to remember that, in the
human being, the second metacarpal is the longest; then,
in the order of decrease, come the third, fourth, fifth, and
first. In quadrupeds we shall also find differences in
length (see the chapter relating to the anterior limbs in
certain animals), but the order of decrease is not always
that which we have just mentioned.

In man the articular surface, situated at the inferior extremity
of each of the metacarpals, is rounded, and is
called the head. This allows the first phalanx, which is
in relation with that surface, to be displaced in every
direction; indeed, this phalanx can not only be flexed and
extended, but it can also be moved laterally; this latter
movement allows of the fingers being separated and drawn
together.

In quadrupeds which can only perform the movements of
flexion and extension of the digits—for example, the horse—the
inferior extremity of the metacarpal has not a rounded
head of a regular outline; it is marked by a prominent
median crest, directed from before backwards, so that the
articular surfaces, which fit more exactly, form a sort of hinge
which allows of backward and forward movements only, and
permits no lateral displacement. In man, at the level of the
inferior extremity of the first metacarpal, in the vicinity of the
articulation of this bone with the first phalanx of the thumb,
we find two sesamoid bones—small bones developed in[47]
the fibrous tissue which surrounds the articulation. We
also meet with such structures, but more rarely, at the level
of the corresponding articulation of the index and auricular
digits; and, more rarely still, at those of the middle and
ring fingers. In quadrupeds, these bones are normally
developed, and we shall see afterwards that in some
animals, as they reach a considerable size, they are able to
influence the external outlines; we shall see this, for example,
in the horse.

Fig. 31.—Skeleton of the Superior Limb of a Bird (Vulture):
Left Side, External Surface.

1, Humerus; 2, radius; 3, ulna; 4, radial bone of the carpus; 5, ulnar
bone of the carpus; 6, first metacarpal; 7, second metacarpal; 8, third
metacarpal; 9, first digit, the homologue of the thumb; 10, first phalanx
of the second digit; 11, second phalanx of the second digit; 12, third
digit.

The hand, in birds, is directed obliquely downwards and
backwards (Fig. 31). For the better understanding of its
position in relation to the forearm, we should remember
that this latter, as we have described (p. 44), directed
obliquely upwards and forwards, has the radius placed
above the ulna; the hand being oblique in the opposite
direction and placed under the forearm is, by this arrangement,
inclined towards the ulnar border of the latter.

Fig. 32.—Superior Limb of the Human Being, the Different
Segments being placed in the Attitude which the Corresponding
Parts occupy in Birds: Left Side, External Surface.

For the rest, in order to be able to distinguish readily the
corresponding parts in the hand of a bird and that of a man,
we merely have to place the human forearm obliquely, in a
direction upwards and forwards (Fig. 32), the radius being
above; this position we can obtain by semi-pronation;[48]
then, to incline strongly the hand downwards and backwards,
moving the ulnar border of the hand towards
the ulna; the thumb is then anterior, the little finger
posterior, and the palm of the hand is turned towards the
trunk.

The carpus in birds is formed by two bones only, with
which the skeleton of the forearm articulates. That
which is in contact with the radius is called the radial bone
of the carpus; and that with which the ulna articulates
is named the ulnar bone.

The metacarpus is formed of three bones; the first,
which is very short, is fused at its superior extremity with
the adjoining one; this latter and the third, both longer than
the first, but of unequal size, are fused at their extremities.
The metacarpal, which articulates with the radial bone of
the carpus, is larger than the one which is in line with the
ulna. To the metacarpus succeed three digits, of which the
central is the longest, and is formed of two phalanges; the
other two are formed each by a small, stylet-shaped bone.
The middle finger, situated on the prolongation of the
metacarpal, which articulates with the radial bone of the
carpus, has its first phalanx large and flattened transversely;
this phalanx seems to have been formed by the union of
two bones of unequal development; the second phalanx[49]
is styloid in form. As to the other two fingers, they are
placed, one in front and the other behind; the first, which
articulates with the short metacarpal, fused at its upper
end with the principal bone of the metacarpus, in position
represents the thumb. The other, which is the third
finger, articulates with the inferior extremity of the thinnest
bone of the metacarpus; it is sometimes closely united
to the corresponding border of the first phalanx of the large—that
is to say, of the median—digit.

The Anterior Limbs in Certain Animals

Plantigrades: Bear (Fig. 33).—The scapula of the bear
approaches in shape to a trapezium, of which the angles
have been rounded off. The anterior border (cervical) is
strongly convex in the part next the glenoid cavity. The
junction of the superior (spinal) and the cervical border
forms almost a right angle, the summit of which corresponds
to the origin of the spine. At its posterior angle
there is a prominence, directed downwards, the surface of
which is hollowed and is separated from the infraspinous
fossa by a crest, so that at this level a third fossa is added to
the infraspinous one. The neck of the scapula is but slightly
marked. The acromion is prominent, and projects a little
beyond the glenoid cavity.

[50]

Fig. 33.—Skeleton of the Bear: Left Lateral Surface.

1. Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6, first dorsal vertebra; 7, fourteenth and
last dorsal vertebra; 8, lumbar vertebræ; 9, sacrum; 10, coccygeal vertebræ; 11, sternum; 12, ninth and last
sternal rib; 13, costal cartilages; 14, acromion process; 15, third fossa on the external surface of the scapula;
16, great tuberosity of the humerus; 17, musculo-spiral groove; 18, epicondyle; 19, radius; 20, ulna; 21,
olecranon process; 22, carpus; 23, pisiform; 24, metacarpus; 25, phalanges; 26, ilium, external fossa;
27, pubis; 28, tuberosity of the ischium; 29, obturator foramen; 30, great trochanter of the femur; 31,
condyles of the femur; 32, patella, or knee-cap; 33, anterior tuberosity of the tibia; 34, fibula; 35, tarsus;
36, calcaneum, or heel-bone; 37, metatarsus; 38, phalanges.

The clavicle is rudimentary, but, as an example of the
complete development of this bone in plantigrade quadrupeds,
we may cite the marmoset.

The humerus is furnished at its superior extremity with a
large tuberosity, wide, and situated in front of the head of
the bone; the effect of this is that the bicipital groove is
internal. As in man, the great tuberosity does not reach so
high as the humeral head, but it approaches more nearly
to that level. The deltoid impression is very extensive,
and descends pretty far down on the body of the bone. The
epitrochlea is prominent; the epicondyle is surmounted by
a well-marked crest, curved and flexuous in outline.

The articular surface, which is in contact with the
radius, is not a regularly formed condyle; it is a little[51]
flattened on its anterior surface, and presents at this level
a slight depression which corresponds to a small eminence
on the anterior aspect of the superior extremity of the
radius. The surface which articulates with the ulna, viewed
on its anterior aspect, has the shape of a slightly-marked
trochlea; except at the level of the internal lip, which, as
in man, descends lower than the surface for articulation
with the radius (condyle). Behind, the trochlea is more
clearly defined.

The bear possesses a considerable power of rotation of
the radius; the bones of the forearm are joined only at
their extremities, while in the remainder of their extent
they are widely separated. The ulna terminates below in
a head and a styloid process; these articulate with the two
last bones of the first row of the carpus—viz., the cuneiform
and pisiform. The bones of the carpus are seven
in number, the scaphoid and the semilunar being fused
together.

The metacarpals, five in number, differ very little from
one another in regard to length, though they increase in
size from the first to the fifth; this may be demonstrated
by looking at the palmar surface of the hand. It is the
reverse of that which we find in man, for the fifth metacarpal
is the thickest of all, and the first is the most
slender.

At the level of each metacarpo-phalangeal articulation
are two sesamoid bones.

The third digit is the longest. The terminal phalanges
present two very different portions: one, the anterior, is
curved and pointed; it serves to support the nail, whose
shape it assumes; the other, posterior, forms a sort of
sheath into which the base of the nail is received.

The inferior portion of the posterior surface of this latter
part articulates with the second phalanx in the case of
each of the last four digits, but with the first phalanx in
the case of the thumb.

[52]

Fig. 34.—Skeleton of the Dog: Left Lateral Surface.

1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6, thirteenth
and last dorsal vertebra; 7, lumbar vertebræ;
8, sacrum; 9, coccygeal vertebræ; 10, anterior extremity of the sternum; 11, xiphoid appendix; 12, ninth and last sternal
rib; 13, costal cartilages; 14, spinal border of the scapula; 15, supraspinous fossa of the scapula; 16, infraspinous fossa of the
scapula; 17, great tuberosity of the humerus; 18, deltoid impression; 19, musculo-spiral groove; 20, olecranon process; 21,
radius; 22, carpus; 23, pisiform; 24, metacarpus; 25, sesamoid bones; 26, phalanges; 27, ilium, iliac crest; 28, pubis;
29, tuberosity of the ischium; 30, great trochanter of the femur; 31, patella, or knee-cap; 32, anterior tuberosity of the tibia;
33, fibula; 34, tarsus; 35, calcaneum, or heel-bone; 36, metatarsus; 37, sesamoid bones; 38, phalanges.

Digitigrades: Cat, Dog (Fig. 34).—In these animals the
anterior (cervical) border of the scapula is convex; the
posterior (axillary) border is straight or slightly concave.
The supraspinous and infraspinous fossæ are of equal extent
(Figs. 35 and 36). The neck is short. The spine of the
scapula becomes more and more prominent towards its
inferior extremity, where it ends in a twisted and inflexed
portion, which represents the acromion process; this process
terminates at the level of the glenoid cavity. The
coracoid process is represented by a small tubercle, slightly[54]
curved inwards; this tubercle is situated above the glenoid
cavity, at the inferior part of the cervical border.

[53]

Fig. 35.—Scapula of the Dog: Left Side, External Surface.

1, Posterior or axillary border; 2, superior or spinal border; 3, anterior
or cervical border; 4, spine of scapula; 5, coracoid process; AA′, length
of spinal border.

Fig. 36.—Left Scapula of the Cat: External Surface.

1, Posterior or axillary border; 2, superior or spinal border; 3, anterior
or cervical border; 4, spine of the scapula; 5, coracoid process; AA′,
length of the spinal border.

In the dog, the posterior angle, formed by the junction
of the axillary and the superior (spinal) borders, is obtuse;
the spine rises perpendicularly from the surface of the bone.
The width of the scapula, measured at the level of the
spinal border (from A to A′, Fig. 35), equals about half the
length of the spine. We must, however, make an exception
for the turnspit dog, in which the superior border
equals three-fourths of that length. The scapula is, in this
case, of a more compact type; it is broader, but shorter.
In the cat, the anterior outline of the scapula, formed by
the union of the cervical border and the corresponding half
of the spinal, is more convex; the posterior angle is not
obtuse, as in the dog. The spine is bent slightly downwards
and backwards; before terminating in the acromion
process it presents a triangular projection, the apex
of which is directed downwards. The tubercle which represents
the coracoid process is curved inwards more
strongly than that of the dog, thus resembling more
closely the appearance of this process in the human
being.

All proportions considered, the scapula of the cat is
broader than that of the dog; its width, measured along
the length of its spinal border (from A to A′, Fig. 36),
equals three-fourths of the length of the spine.

The clavicle is rudimentary; it is, however, better developed
in the cat than in the dog. The clavicle of the cat
is represented by a small, elongated bone, curved in outline,
the convexity being turned forward; it is united to
the acromion and the sternum by ligamentous fibres; that
of the dog is merely a scale-like osseous plate situated on
the posterior surface of a muscle of this region (see Figs. 16
and 17).

The humerus is long and twisted in the shape of an S. The
inferior articular surface has the form of a simple pulley,
for the condyle is very slightly marked. The internal part
of this articular surface descends lower than the external;
this condition resembles that found in the human being,[55]
where the inner lip of the trochlea is lower than the
condyle.

In the dog, the olecranon fossa communicates with the
coronoid by an opening.

In the cat, there is a supra-epitrochlear canal (see Fig. 19),
but no olecranon perforation.

The bones of the forearm articulate at their extremities.
The body of the radius is united to the body of the ulna by
a short, thick, interosseous ligament; the fibres of this
ligament, though short, do not prevent the production of
some movements at the articulations of the bones.

The radius so crosses the ulna that above, it is in
front and external to the latter, while below, it is internal.
This bone is flattened from front to back, and slightly
convex anteriorly. Its superior extremity is formed,
externally, of a portion which represents the head of the
radius in man; internally, by another portion which
represents half of the coronoid process of the ulna, which,
in the human being, belongs exclusively to the latter (see
p. 39, the encroachment of the radius on the ulna). This
extremity is surrounded with a vertical articular surface
which is placed in contact with a small cavity which is
hollowed out on the ulna (the lesser sigmoid cavity); and
presents at its superior aspect a surface which articulates
with the inferior extremity of the humerus. The shaft of
the bone has on its internal border rugosities analogous to
the imprint of the pronator radii teres of the human skeleton;
these rugosities, indeed, give insertion to a muscle of the
same function, and bearing the same name. The inferior
extremity, broader than the superior, is hollowed on its
external aspect by a small cavity which receives the inferior
extremity of the ulna; its inferior surface (concave)
articulates with the carpus; its anterior surface (the homologue
of the posterior surface of the corresponding extremity
of the human radius) presents grooves which serve for
the passage of the tendons of the muscles which pass
from the forearm to the back of the hand. (For the
names of the muscles whose tendons pass in these grooves,
see Fig. 29.)

[56]The ulna is furnished at its superior extremity with an
olecranon process, which is more prominent than that of
the human ulna; this process is compressed laterally, and
its internal surface is hollowed; there we also find a great
sigmoid cavity, and a coronoid process situated at the
internal part of the anterior surface, a process which, as we
have previously shown, it shares with the radius.

The shaft of the bone, prismatic and triangular, diminishes
in thickness as it approaches the lower extremity, which
articulates with the corresponding extremity of the radius.
In the dog, the ulna terminates inferiorly in a blunt point,
without enlargement, analogous to the head of the human
ulna; in the cat, by a head which is prolonged into a
styloid process, by which it articulates with a portion of
the carpus.

The carpus consists of seven bones—three in the superior
row and four in the inferior. In the superior row the
scaphoid and semilunar bones are fused together. The
pisiform is elongated and expanded at its two extremities;
it forms a prominence which, directed backwards, projects
beyond the level of the other bones of this region.

The metacarpal bones are five in number; they are enumerated
from within outwards; they articulate with the carpus
and with each other. The inferior extremity of each metacarpal
bone presents the form of a condyle in front; and is
divided behind so as to form two lateral condyles, which are
separated by a median crest; on these posterior condyles
are applied two small sesamoid bones. The metacarpal
bone of the thumb is very short; the third and fourth are
the longest. The metacarpus, as a whole, is directed vertically.

Fig. 37.—Skeleton of the Finger of a Felide (Lion): Left Side,
Internal Surface.

1, Metacarpus; 2, sesamoid bones; 3, first phalanx; 4, second phalanx;
5, third phalanx; 6, gutter for the reception of the base of the nail; 7,
prominent osseous crest formed to lodge in the concavity of the nail.

The phalanges are three in number for each finger, except
the thumb, which has but two. The first phalanx, directed
almost horizontally forwards, is the longest; the second is
directed downwards and forwards; the third consists of
two portions: a posterior part, which forms a sort of sheath
into which the base of the nail is received; and an anterior,
conical in form, and curved in crochet shape, which forms a
support for the nail (Fig. 37).

[57]The third and fourth digits are the longest; the second
and fifth are of equal length; the thumb is the shortest;
it does not touch the ground, and does not even reach the
articulation of the metacarpal bone and first phalanx of the
second finger.

In the cat, the metacarpal bone of the thumb, although
shorter than any of the others, is quite as thick. The
third digit is a little longer than either the second or
fourth. In animals of this genus, the claws, in the condition
of repose, are retracted, and removed from the
ground; this prevents their being worn, and thus preserves
their sharpness. At such times the third phalanx
is received into a groove which is found on the external
surface of the second phalanx. In the dog, the claws are
not tractile.

[58]

Fig. 38.—Skeleton of the Pig: Left Lateral Surface.

1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra;
6, first dorsal vertebra; 7, fourteenth and last dorsal
vertebra; 8, lumbar vertebræ; 9, sacrum; 10, coccygeal vertebræ; 11, anterior extremity of the sternum; 12, xiphoid
appendix; 13, seventh and last sternal rib; 14, costal cartilage; 15, cartilage of prolongation of the scapula; 16, great
tuberosity of the humerus; 17, olecranon process; 18, radius; 19, ulna; 20, pisiform; 21, metacarpus; 22, phalanges of
the two great toes; 23, phalanges of the external toe; 24, ilium; 25, pubis; 26, tuberosity of the ischium; 27, great
trochanter; 28, knee-cap; 29, anterior tuberosity of the tibia; 30, fibula; 31, tarsus; 32, calcaneum; 33, metatarsus;
34, phalanges of the two great toes; 35, phalanges of the external toe.

[59]Unguligrades:
Pig (Fig. 38).—The scapula is markedly
narrowed in the region above the glenoid cavity. The
spine is atrophied at both its extremities, so that at its
inferior part we do not find the acromion process. In
its middle portion the spine is prominent, and presents a
triangular process which turns backwards, overlapping a
part of the infraspinous fossa; this latter is much larger
than the supraspinous. The spinal border is surmounted
by the cartilage of prolongation, the superior margin of
which is convex; this cartilage extends posteriorly beyond
the posterior (axillary) border of the bone.

The small tuberosity of the superior extremity of the
humerus is but slightly developed; the great tuberosity, on
the contrary, is very large. The bicipital groove is situated
internal to this. The deltoid impression is scarcely marked.

The forearm is short, directed obliquely downwards and
inwards, thus forming with the hand an angle, of which the
apex is directed inwards. The two bones of the forearm
are strongly bound to one another by an interosseous ligament,
which is formed of very short fibres. The radius
appropriates, at its superior extremity, the coronoid
process of the ulna. The latter is, notwithstanding, well
developed in the rest of its extent; it has a flattened
shaft which almost completely overlaps the posterior
surface of the radius; its inferior extremity reaches to the
carpus.

The carpus is formed of eight bones—four in the superior
row, and four in the inferior. The third bone of the
superior row (cuneiform) is more in contact with the ulna
than with the radius.

There are but four metacarpal bones; there is no metacarpal
of the thumb. The two median metacarpal bones
are the longest; they are those which correspond to the
digits which alone touch the ground. The internal digit
and the external one are thin and short; they are functionless,
as a rule, taking no part in supporting the limbs on
the ground. Notwithstanding this, they are formed, as
the other digits, of a number of phalanges, which give
them the semblance of perfect digits. (We shall soon see
that in certain animals there exist digits which, being incomplete
with regard to the numbers of their constituent
bones, more accurately merit the name of imperfect
digits.)

The third phalanges are each enclosed in a horny hoof,
to which the name of onglon has been given.

We have already drawn attention to the smaller lateral[60]
digits, and noted the general fact that they do not come in
contact with the ground. It is necessary to modify this
statement by adding that under certain conditions they
give a slight amount of support; for example, when the
individual is the subject of excessive obesity, the limbs
yield under the weight, and the nails of the lateral digits
may touch the ground.

A similar fact may be noticed in pigs of ordinary bulk at
the moment when, during walking, each of the fore-limbs
commences to bear the weight—that is to say, when it is
directed obliquely downwards and forwards; then all the
digits are in contact with the ground.

[61]

Fig. 39.—Skeleton of the Ox: Left Lateral Surface.

1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra;
6, first dorsal vertebra; 7, thirteenth and last dorsal
vertebra; 8, lumbar vertebræ; 9, sacrum; 10, coccygeal vertebræ; 11, sternum; 12, xiphoid appendix; 13, eighth and
last sternal rib; 14, costal cartilages; 15, spine of scapula; 16, cartilage of prolongation of the scapula; 17, great tuberosity
of the humerus; 18, musculo-spiral groove; 19, olecranon process; 20, radius; 21, carpus; 22, pisiform; 23, metacarpus;
24, rudimentary metacarpal; 25, sesamoid bones; 26, first phalanges; 27, second phalanges; 28, third phalanges; 29, anterior
iliac spine; 30, pubis; 31, tuberosity of the ischium; 32, great trochanter; 33, supracondyloid fossa of the femur; 34,
patella, or knee-cap; 35, anterior tuberosity of the tibia; 36, fibula; 37, coronoid tarsal bone; 38, tarsus; 39, calcaneum; 40,
metatarsus; 41, rudimentary metatarsus; 42, sesamoid bones; 43, first phalanges; 44, second phalanges; 45, third phalanges.

Unguligrades (Ungulates): Sheep, Ox (Fig. 39).—The
scapula, which is of elongated form, is very narrow in the
vicinity of the glenoid cavity. The spine, which becomes
more and more salient towards its inferior part, terminates
abruptly in a border, which, forming an acute angle with the
crest, produces a projection which represents the acromion
process—a very rudimentary acromion, for it does not reach
the level of the glenoid cavity. The supraspinous fossa is
much smaller than the infraspinous; it hardly equals one-third
the extent of the latter. The anterior border, thin and
convex in its superior portion, is concave in the rest of its
extent; the posterior border is thick and slightly concave;
the spinal border is surmounted by the cartilage of prolongation.
In the ox the spine of the scapula, in its middle
portion, is flexed a little backwards on the infraspinous
fossa.

The great tuberosity of the humerus is highly developed;
its summit, very prominent, is flexed over the bicipital
groove; a prominence of the small tuberosity also bends
over the groove, with the result that at this level the latter
is converted into a sort of canal. At the inferior extremity
the condyle, although not large, is recognisable; for it is
separated from the trochlea by a depression in form of a
groove. In contrast to the condition found in man, the
condyle descends to a level a little below that of the internal
lip of the trochlea. (For the arrangement of the
epicondyle and the epitrochlea, see p. 30.) In
the sheep,[62]
the deltoid impression is but slightly marked; in the ox,
it is more evident.

The forearm is directed obliquely downwards and inwards,
so as to form, with the hand, an angle of which the
apex is internal; this angular outline of the knee (wrist) is
so characteristic of ruminants that the corresponding region
of the horse, when salient inwards, receives the name of
ox-knee. The radius bears the coronoid process, and the
larger part of the articular surface which comes in contact
with the inferior extremity of the humerus; the condyle
and the trochlea articulate with the radius in front; while
behind, the trochlea articulates with that part of the sigmoid
cavity which belongs to the ulna. The posterior
surface of the shaft of the radius is flattened; its anterior
surface is slightly convex. The inferior extremity articulates
with the carpus by a surface which is directed obliquely
downwards and inwards. The shaft of the ulna is very
slender, and fused in its middle third with the body of the
radius; it terminates below, at the level of the external
part of the inferior extremity of the radius, by a slightly
expanded portion which, fused with this latter, forms the
articular surface for the carpal bones.

In the ox the forearm is short; in the sheep it is proportionally
longer.

The bones of the carpus are six in number—four in the
upper row, and two in the lower; they form an irregular
cuboid mass which contributes to the formation of the
region known as the knee in ruminants, as in the horse; we
have already remarked that the name ‘wrist’ would be
more accurate. The anterior surface in its foremost part
is vertical, and is slightly convex from side to side. At its
posterior and external part the pisiform bone forms a prominence.

The metacarpus consists of two bones only—one, well
developed, which is known as the principal metacarpal, or
the canon bone (this is the name given to the region in the
hoofed animals); and a rudimentary one, which is situated
at the superior and external aspect of the preceding metacarpal.
Sometimes there is found a third metacarpal[63]
at the internal aspect; but, when present, it is but very
slightly developed.

The principal metacarpal consists of two metacarpals
fused together; on this account the bone is longitudinally
marked in the median line by a slight depression which
marks the junction of the two bones of which it is
formed. In some ruminants (certain species of chevrotains)
the coalescence does not take place, and the two metacarpals
remain separate.

The anterior surface of the principal metacarpal is convex
transversely; its posterior surface is flattened. The superior
extremity of this bone articulates by two facets with the
two bones of the inferior row of the carpus; on the internal
part of the anterior surface of this extremity is found a
tubercle. The inferior extremity is divided into two parts
by a fissure or notch; each part is articular, and consists
of two separate condyles, which are separated from each
other by an antero-posterior crest; on each side of this
crest, and behind, are found two sesamoid bones. As for
the external rudimentary metacarpal bone, it is nothing
more than a small, short tongue of bone; which, in goats
and sheep, is often absent.

The division of the inferior extremity of the principal
metacarpal into two parts is correlated with the two perfect
digits which give the foot of the ruminant its forked appearance.
Each digit consists of three phalanges, which are
directed obliquely downwards and forwards; further, these
phalanges are inclined a little outwards from the axis of
the limb, so that the two digits diverge from each other as
they descend.

The first phalanx, which is the longest, articulates
superiorly with the principal metacarpal; its inferior
extremity terminates in a trochlea, and the lip of this,
which is situated towards the axis of the limb, descends
lower than that of the opposite side; this arrangement is
correlated with the divergent direction of the digits. The
second phalanx has its superior extremity moulded on the
trochlea which terminates the extremity of the first; its
inferior extremity is articular, and elongated from before[64]
backwards. On the posterior surface of this extremity is
found a sesamoid bone.

With regard to the third phalanx, it presents the form
of a triangular pyramid, and displays a postero-superior
concave surface with which the second phalanx articulates;
an anterior, convex surface, which terminates in a point
on its anterior part; and an internal surface, which is
flattened. The third phalanx of each digit is contained
in a hoof (onglon).

There is also found in ruminants two imperfect rudimentary
digits, which are represented by two small bones
situated behind the articulation of the metacarpal and the
digits which we have just been studying. These rudimentary
digits are each enveloped in a layer of horn; they
constitute the spurs. The two digits of the ruminants
represent the third and fourth fingers of the human hand;
the two lateral digits, greatly atrophied, are the homologues
of the second and fifth fingers; the thumb is not
present.

It is the same as regards the metacarpal bones, which form,
by their union, the principal metacarpal; the external represents
the fourth metacarpal, and the internal the third. It is
to the latter that the tubercle, of which we have already
made mention, belongs; and with the signification of which,
because it gives attachment to a muscle, we shall concern
ourselves in the section on myology (see Radial Muscles).

Fig. 40.—Skeleton of the Horse: Left Lateral Surface.

1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical
vertebra; 6, first dorsal vertebra; 7, eighteenth and last dorsal vertebra; 8, lumbar vertebræ;
9, sacrum; 10, coccygeal vertebræ; 11, sternum; 12, xiphoid appendix;
13, eighteenth and last sternal rib; 14, costal cartilage; 15, scapula; 16, cartilage
of extension; 17, great tuberosity of the humerus; 18, deltoid crest; 19,
olecranon process; 20, radius; 21, carpus; 22, pisiform; 23, principal metacarpal;
24, metacarpal, external rudimentary; 25, large sesamoids; 26, first phalanx;
27, second phalanx; 28, third phalanx; 29, ilium, showing external iliac
fossa; 30, pubis; 31, tuberosity of the ischium; 32, great trochanter; 33,
infratrochanteric crest, or third trochanter; 34, supracondyloid fossa of the
femur; 35, knee-cap; 36, anterior tuberosity of the tibia; 37, the fibula; 38,
tarsus astragalus; 39, calcaneum; 40, principal metatarsal; 41, rudimentary
external metatarsal; 42, large sesamoids; 43, first phalanx; 44, second phalanx; 45, third phalanx.

To face p. 64.

Unguligrades: Horse (Fig. 40).—The scapula is narrow,
compared with that of the animals we have just been considering.
The anterior border is convex in its superior
portion, and concave in its inferior; the posterior border
is slightly hollowed out. The supraspinous fossa is less in
extent than the infraspinous; but the difference is less than
that between the same fossæ in the ox and the sheep; in
the ox, as we have already indicated, the proportion is one-third;
in the horse, one-half. The spine, which disappears
at the extremities, is rough and thick in its middle third,
there forming a kind of tuberosity—tuberosity of the spine.
Above and in front of the glenoid cavity is found a strong
process consisting of a rugous base, and a summit which is[65]
directed inwards. This forms a kind of hook curved
towards the inside; it represents the coracoid process.
The scapula is surmounted by the cartilage of prolongation,
of which the superior border, which is thin and curved,
is parallel to the superior border of the prominence of the
withers; the cartilage forms, consequently, the lateral
surface of this region. The cartilage of prolongation
undergoes ossification in old horses. The humerus is short;
the bicipital groove, situated on the anterior surface of the
superior extremity, separates the greater tuberosity from
the lesser, and is divided into two parts by a median ridge;
it is this portion of the humerus which forms the prominence
known as the point of the shoulder, or point of the arm. The
deltoid impression well deserves the name of tuberosity
which has been given to it, for it is very prominent; the
musculo-spiral groove is very deep.

At the inferior extremity, the trochlea is large; the
portion corresponding to the condyle of the humerus in
man is, in proportion to the latter, of small extent. The
olecranon fossa is deep. The epicondyle and the epitrochlea
are somewhat different from those of the human bone. In
the latter, the epitrochlea is salient towards the inner side,
causing an increased transverse diameter of the inferior
extremity of the humerus. In the horse—it is the same in
ruminants—this tuberosity projects backwards, folds on itself
in forming the internal boundary of the olecranon cavity,
and exceeds in diameter, in the antero-posterior direction,
the prominence of the epicondyle, which presents a nearly
similar arrangement. This latter has, however, a part
which, projecting externally, is situated at the inferior
part of a crest, that forms the posterior boundary of the
musculo-spiral groove. The result is that, contrary to the
condition found in the human being, the epicondyle is more
prominent transversely than the epitrochlea, but this latter
is more salient on the posterior aspect. The epitrochlea
and the epicondyle offer a larger surface for the origin of
muscles of the forearm than the same prominences in the
human bone do for the analogous muscles of the same
region.

[66]Some veterinary anatomists have given to the inferior
and external articular surface of the humerus the name of
trochlea; and to the internal one, that of condyle. On
this account they designate the external prominence as the
epitrochlea, and the internal one as the epicondyle. In
addition to the fact that this point of view is not legitimate,
it produces inevitable confusion when comparing the parts
with those of the human humerus, and this confusion exists,
not alone in describing the bone, but also in the description
of the muscular attachments, and in the comparison of the
muscles of the forearm of quadrupeds with the corresponding
muscles in the human species.

The radius is placed in front of the ulna; its body,
slightly convex forwards, has the anterior surface convex
transversely, and the posterior surface plane in the same
direction. It is to the external part of this latter that the
ulna is applied, which is completely fused with the radius.

The superior extremity of the radius is a little larger than
the inferior. Its superior aspect, concavo-convex, moulded
on the inferior articular surface of the humerus, presents
internally two cavities, which receive the lips of the trochlea,
and, externally, another, smaller, cavity, which receives the
condyle. The radius articulates with the trochlea and the
condyle, having appropriated a portion of the ulna, as is
proved by the presence of the coronoid process, which belongs
to the former. This superior extremity presents, internally,
a tuberosity into which the biceps is inserted; this is the
bicipital tuberosity; and on the other side is another tuberosity,
which is a little more prominent than the preceding.

The inferior extremity, which is flattened from before
backwards, is furrowed on its anterior surface by grooves for
the passage of muscles (the names of the muscles whose
tendons pass in these grooves have already been given on
p. 43). It articulates at the lower end with the superior
row of the carpus, and it terminates laterally in tuberosities:
one, external, on which is found a groove for the tendon of
the lateral extensor of the phalanges, the homologue of the
special extensor of the little finger; the other, internal, is a
little more prominent than the one we have just described.[67]
These tuberosities are visible under the skin which covers
the superior and lateral parts of the region known as the
knee; but which, we again repeat, is no other than the
wrist.

The ulna has a triangular shaft, situated at the posterior
surface of the radius, with which it is fused. It disappears
completely at the level of the inferior third of the forearm.
Occasionally, in some horses, the ulna is abnormally long,
in the form of a slender tongue of bone; and extends to the
neighbourhood of the external tuberosity of the inferior
extremity of the radius (see Fig. 79, p. 196). Its superior
extremity is chiefly represented by the olecranon process,
which is voluminous in bulk, and forms the projection known
as the point of the elbow. This process is flattened laterally;
its internal surface is excavated; the anterior surface, which
is concave, forms a part of the great sigmoid cavity; the
remainder of the cavity is formed by the radius.

In the ass, the ulna is a little longer than in the horse—that
is to say, it descends lower; and the radius is a little
more convex anteriorly.

The carpal bones are seven in number—four in the superior
row, and three in the inferior. The trapezium is wanting in
the latter. Sometimes, however, in certain varieties of horses
the trapezium is developed, but then it is no more than a very
small osseous nodule. The pisiform bone, situated at the
external part of the first row of bone, is prominent posteriorly.
It is of rounder form and flattened from without
inwards. It articulates with the trapezium and the radius.
It presents, on its external surface, a groove for the passage of
the tendon of the posterior ulnar muscle, which is named by
veterinary anatomists the external flexor of the metacarpus.

The carpus, as a whole, is of an irregularly cuboid shape;
its anterior surface, slightly convex from side to side, forms
the skeleton of the region of the knee (wrist). The metacarpus
is formed of three bones: the principal metacarpal
and the two rudimentary ones.

The principal metacarpal, which forms the region of the
canon, is directed vertically; its anterior surface is slightly
convex transversely. This surface is covered by a number[68]
of tendons, which slightly alter its appearance; so that it is
the principal base of this part of the fore-limb. Its posterior
surface is flattened. The superior extremity of this metacarpal
presents plane surfaces, variously inclined, with which the
bones of the inferior row of the carpus articulate. On the
anterior surface, and a little to the inner side, is found a
tuberosity, which is destined for the insertion of the anterior
extensor of the metacarpus, the homologue of the radial
muscles. The inferior extremity is formed by two condyles,
an internal and an external; between which is found a
median crest.

This extremity, the superior extremity of the first phalanx,
which articulates with it, together with two sesamoid bones—the
great sesamoids—which are situated on its posterior
surface, collectively form the region which from its rounded
outlines is called the ball.

With regard to the rudimentary metacarpals, external
and internal, to which some authors give the name of fibulæ,
they are applied to the sides of the posterior surface of the
principal metacarpal. They are elongated bones, of which
the superior extremity, which is a little thickened, is called
the head; the lateral bones of the second row of the
carpus partly rest on the heads of these. They become
more slender as they descend, and terminate opposite
the inferior fourth of the principal metacarpal. Each ends
in a slight swelling, to which the name button has been
given. The internal one is the better developed.

The rudimentary metacarpals are vestiges of atrophied
digits, as will be explained further on.

The single finger of the horse consists of three phalanges.
The first phalanx, which is directed obliquely downwards
and forwards, corresponds to the constricted region situated
below the ‘ball,’ and known as the pastern. It is flattened
from before backwards; its anterior surface is convex transversely,
while the posterior surface is plane. Its superior
extremity is moulded on the inferior extremity of the
principal metacarpal, and its inferior extremity, which is
smaller, presents a trochlea with which the second phalanx
articulates. This is also directed downwards and forwards,[69]
and is shorter. It corresponds to the region which, situated
between the pastern and the hoof, is known as the cornet.

The third phalanx, situated entirely within the hoof,
has the same direction as the first and second. It is
large and broad, and presents three surfaces separated by
well-marked angular borders (see Fig. 96). The anterior
surface is oblique downwards and forwards; it is convex
transversely. The inferior surface is slightly hollowed,
and is in relation with the sole, or plantar surface of the
hoof.

The superior surface, which is articular, is divided by a
median ridge into two lateral cavities, which correspond to
the trochlea on the inferior surface of the lower extremity
of the second phalanx. The inferior border corresponds
in shape with the hoof. The superior border presents
in its median part a projection, the pyramidal eminence,
which prolongs at this level the anterior surface of the bone.
Finally, the posterior border, which is concave, is in contact
with a sesamoid bone, the lesser sesamoid, which increases
the superior articular surface behind, and is also in contact
with the second phalanx.

As we have just seen, the horse possesses but one digit.
In the ancestors of the animal—that is, in the prehistoric
species which are now extinct (orohippus, miohippus, protohippus,
or hipparion)—the number of digits was larger; this
fact conclusively proves that the rudimentary metacarpals of
the existing horse are vestiges of digits which have disappeared
through want of use. In the first of those ancestors—orohippus—there
were four digits; all save the first, the
thumb, being then developed. In the others of the series
there existed but three digits. It must, however, be noted
that in those animals it is always the digit which corresponds
to the middle finger of the pentedactyl hand that is longest.
In other less ancient species the lateral fingers are reduced
to the condition of mere splints of bone. It follows from
what has been said that the digit which persists in the equine
species should be considered as the third finger, and that the
rudimentary metacarpals represent lateral digits considerably
atrophied.

[70]This disappearance of the lateral digits cannot excite
surprise when we consider the functions of the organs.
Becoming useless, they must undergo gradual atrophy from
want of use.

There undoubtedly is, in this former existence of supplementary
digits in the horse, something analogous to what
we still find in the pig; where the two principal digits are
accompanied by two shorter ones, which very probably,
from their infrequent use, are destined to disappear in a
more or less distant future.

Proportions of the Arm, the Forearm, and the
Metacarpus

As a supplement to the study of the anterior limbs which
we have just finished, it appears necessary to give some
indications of the relative proportions of certain of the
segments which form these limbs in the plantigrades, the
digitigrades, and the ungulates.

First, we would remark that, in following this order of
classification, the scapula becomes less and less narrow,
and assumes a form more and more elongated. In order to
convince ourselves of this, it will be sufficient to study the
bone first in man, then in the bear, the cat, dog, ox, and
finally in the horse.

As to the proportions of length, which are those we
should chiefly study, we shall commence with the
comparison of the forearm and arm—that is to say,
the radius and the humerus. The radius is found to
be longer in proportion to the humerus, as the number
of digits is smaller, and the hand loses more and more the
functions of an organ of prehension. In man, the radius is
shorter than the humerus; in the horse, on the contrary, it
is longer.

To give an idea of this proportion, we shall employ what
is known as the antibrachial index. This index gives the
relation which exists between the length of the forearm and
that of the humerus; the length of this latter, whatever
may be the actual measurement, is represented by a fixed[71]
figure, the number 100. A very simple arithmetical operation
gives the proportion—

The index is less than 100 if the forearm is shorter than
the bone of the arm. The index is more than 100 if, on the
contrary, the forearm is longer.

In man, the radius is shorter than the humerus; indeed,
in adult individuals of the white race the average index is 74.

In the bear, the length of the radius approaches closely
to that of the humerus; the index is about 90. In the
skeleton of a bear in the anatomical museum of the École
des Beaux-Arts, the humerus is 33 centimetres in length,
and the radius 30 centimetres.

In the cat, the radius is very little shorter than the
humerus. In the dog they are equal. The antibrachial
index of the latter is, accordingly, 100.

In the horse, the radius is longer than the humerus; the
index is therefore above 100. Thus, in the skeleton of the
horse which we have in the museum of the École des Beaux-Arts, the index is 113—length of humerus, 29 centimetres;
length of radius, 33 centimetres. In other skeletons which
we have measured we found: in one, 108—humerus, 34
centimetres; radius, 37 centimetres; in another, 116—humerus,
25 centimetres; radius, 29 centimetres.

The metacarpal bone undergoes, relatively to the humerus,
a proportional elongation, analogous to that of the forearm.

In man, the length of the metacarpus is contained about
5¹⁄₂ times in that of the humerus; in the bear, it is contained
4 times; in the dog, 2¹⁄₂ times; in the horse, 1¹⁄₃ times only.

It is well known that the proportions vary according to
race, and that what we have here given are but the general
indications.

The Articulations of the Anterior Limbs

The knowledge of human arthrology which we presume
the reader to have previously acquired makes it unnecessary
for us to enter into numerous details regarding the configuration[72]
of the articular osseous surfaces and the disposition of
the fibrous bands that retain them in position. Accordingly,
in the description which follows, and also in that of the articulations
of the posterior limbs, we shall occupy ourselves but
very briefly with the details above referred to, so as to devote
ourselves especially to the indication of the movements—that
is to say, of that which, while easily comprehended
on recollection of former studies, presents the greatest
interest from the artistic standpoint in these studies in
comparative anatomy.

The Scapulo-Humeral Articulation.—The head of the
humerus and the glenoid cavity of the scapula being in
contact, the two bones are bound together by a rather loose
articular capsule, which is strengthened by the muscles of
this region which fulfil the function of active ligaments.

This articulation, so movable in every direction in the
human species, is not so much so in quadrupeds; the arm in
the latter, as also the shoulder, being kept in contact with
the lateral region of the thorax by the numerous muscles
which surround it.

Of the movements performed by the humerus, flexion and
extension are the most extensive; those of abduction and
adduction are much less so.

It is necessary, before proceeding further, to determine
what the two principal movements which we have just
mentioned really are, viz., flexion and extension.

We know that in man the displacements of the humerus
which take place in the antero-posterior direction are known
as movement or projection forwards, and movement or projection
backwards, respectively. We do not say that
the humerus is flexed or extended, because, in reality, on
account of the position which the skeleton of the shoulder
occupies, it is not able to flex or place itself on the line of
prolongation of the scapula with which it articulates.

In quadrupeds it is not so. The humerus and the scapula
are contained in almost the same vertical plane; and the
bone of the arm can take, in relation to the latter, the
positions characteristic of flexion and extension—that is, of
approach to the scapula and removal from it.

[73]What makes the meanings of these terms a little confusing
is that, in human anatomy, some authors consider the
backward movement of the humerus as extension, and the
forward movement as flexion; in order to be able to
compare these movements to those that the femur executes
in relation to the pelvis.

Now, in our opinion, the indication of this correspondence
is not absolutely necessary; since it ceases to be exact if
we wished, from the point of view of the direction given to
other segments of the skeleton, to establish the same relation
between the elbow and the articulation of the knee.

It is therefore indispensable, when discussing quadrupeds,
to discontinue these terms, in order the more readily to
recognise that: in flexion the inferior extremity of the
humerus is directed backwards; in extension, on the contrary,
it is directed forwards. In the first case the humerus
approaches the scapula; in the second, on the contrary, it
moves away from it.

These movements, which take place during walking, are
executed in the following manner: When one of the anterior
limbs is at the end of that stage of progression which is called
support (see p. 289, Displacements of the Limbs)—that is to
say, during the time that the foot remains in contact with the
ground, whilst the trunk is moving forward—the direction of
this limb becomes more and more oblique downwards and
backwards. At a certain moment the limb is raised from
the ground, to be carried forwards, in order to be again
pressed on the ground, and recommence a new resting stage.
In these different phases the humerus is flexed. But at
the moment that the limb, when carried forwards, is about
to resume its contact with the ground it becomes directed
obliquely downwards and forwards; then the humerus is in
the position of extension.

During these movements of the humerus, there exists an
essential factor—that is, the scapular balance. (It is the
same as what occurs in man when he balances his arm in
the antero-posterior plane.) When the humerus is flexed,
the scapula moves in such a way that the superior portion
projects forwards; when it is extended, the scapula, on the[74]
other hand, is inclined more backwards. But it is necessary
to add that, during these displacements, the scapulo-humeral
angle varies; it tends to close during the flexion
of the humerus, and becomes more open during extension.

Fig. 41.—Flexion of the
Humerus: Right Anterior
Limb of the Horse, External
Surface (after a Chromophotographic
Study by Professor
Marey).

The movements and the relations of the humerus and
the scapula are clearly represented in Figs. 41 and 42,
reproduced from the chromophotographic studies of Professor
Marey—studies relative to the analyses of the movements
of the horse.[13] They show clearly the movements of flexion
and extension of the humerus, also the balancing of the
scapula which accompanies the movements.

Fig. 42.—Extension of the
Humerus: Right Anterior
Limb of the Horse, External
Surface (after a Chromophotographic
Study by Professor
Marey).

The Articulation of the Elbow, or the Humero-ulnar
Articulation.—In this articulation, which is constructed in
the form of a true hinge, the movements of flexion and extension
alone are possible. In flexion, the forearm, directed
forwards, is folded on the arm, with which, in certain circumstances,
it comes in contact. For example, in a horse of[75]
mettle which leaps over an elevated obstacle, the animal
forcibly raises his fore-limbs by flexing them. Flexion is
produced to the same extent, and even more so, and for a
longer period, in felides which crouch.

In extension, on the contrary, the forearm is carried backward.
This movement being limited only by the contact of
the tip of the olecranon with the bottom of the olecranon
fossa of the humerus, the forearm is enabled, in this case, to
move until it is in line with the arm. For example, during
walking, when one of the anterior limbs, having reached the
end of its resting stage, is considerably inclined downwards
and backwards.

The apex of the olecranon process—that is to say, the point
of the elbow—forms a marked prominence, more salient in
flexion than in extension, as in the corresponding region of
the human elbow.

The Radio-ulnar Articulation.—It is in the dog and
the cat, in which the two bones of the forearm articulate by
their extremities only, and remain separate in the rest of
their extent, that the articulations call for special notice.

In the upper part, the radius rotates on itself; while
below, it rotates around the ulna. It follows that the forearm,
which in all quadrupeds is in a state of permanent
pronation, can, in carnivora, take the position of supination,
or rather, of demi-supination. In fact, whatever be the
mobility of the two bones of the forearm, the movement is
not able to bring the palmar surface to the front, but only to
direct it towards the median line.

The Articulation of the Wrist.—Here are found, as in
man, three superimposed articulations: the radio-carpal,
intercarpal, and carpo-metacarpal.

If we remember the movements which take place at the
plane of these articulations in man, and take account of the
fact that the mobility of the limbs is reduced just in proportion
as they are simplified in structure so as to become organs of
support only, we can easily comprehend that, in the horse and
the ox, and, in a word, animals that have a canon bone, the
movements of the wrist are little varied in character, while
in carnivoræ, on the other hand, they are relatively more so.

[76]We will remember that in the ox and the horse the region
of the wrist is called the knee.

In flexion, the hand is bent backwards; in extension it
is carried forwards. These two movements take place
especially in the radiocarpal and intercarpal articulations.
In the first of these articulations, it is the superior row of
the carpus which glides backwards and forwards on the
corresponding articular surface of the forearm. In the
second articulation, it is the second row which moves;
gliding on the inferior articular surfaces of the row above
it. This inferior row carries the metacarpus with it; for
the carpo-metacarpal articulation is much less mobile than
either of the other two.

In flexion, the articular surfaces are separated from one
another in front; and the changes of form which result
from this are noticeable on the anterior surface of the
‘knee.’ Moreover, at that moment this region contrasts
markedly in its outlines with the parts above it and below
it—that is to say, with the corresponding surfaces of the
forearm and of the canon bone.

As for the lateral movements, by which the hand is
inclined outwards and inwards in its movements at the
wrist, they exist to an appreciable extent in the cat and the
dog only; in order to understand this, it is enough to compare
the shape of the articular surfaces of this region in
carnivora and the horse, for example. In the latter, those
surfaces are almost plane; in the cat, on the contrary, they
are curved (inferior surface of the forearm, concave; superior
border of the carpus, convex). These latter, then, are, in
form, similar to those which exist at the same level in the
human being; this explains the possibility of analogous
movements of the whole hand—that is to say, of the movements
of abduction and adduction.

The Metacarpo-phalangeal Articulations.—With regard
to the mobility, it is in these articulations, as in those of the
wrist—that is to say, although in all quadrupeds the first
phalanges can be flexed and extended on the metacarpus,
it is only in the cat and dog that lateral movement is possible.
Indeed, in the horse, in which the principal metacarpal terminates[77]
inferiorly in two convex surfaces, which are separated
by a crest; and where the whole articulates with a
cavity on the superior extremity of the first phalanx;
because of the hinging of these surfaces, there can only
be movements of opening and closing of this articulation.
The first phalanx is directed backwards during flexion
and forwards during extension. In the dog and the cat the
digits can be separated from each other, and also drawn
together—that is to say, abducted and adducted; but, as
in man, these movements can be made only when the first
phalanges are in the state of extension. During flexion
they are impossible, because of the tension of the lateral
ligaments, which increases as the flexion is more pronounced.
This can be demonstrated, for example, in the cat, which,
in order to separate the digits, opens the hand widely—that
is to say, forcibly raises the first phalanges.

The Interphalangeal Articulations.—The phalanges
are in contact with one another by surfaces, which,
on one side, are of trochlear form, and, on the other, are
moulded on these trochleæ; accordingly, at the level of
these articulations, the movements of flexion and extension
only can take place.

In the felidæ, the claws which the third phalanges bear
cannot be utilized when the latter are in a state of extension,
at which time, being forcibly raised, they are, in fact,
placed on the outer sides of the phalanges, which are
grooved to receive them. But when the animal wishes
to use them, it flexes those third phalanges, of which
the terminal extremity is then projected forward, and
the claws are ready to fulfil their function. But at
the same time it extends the first phalanges, to produce
a certain tension of the flexors of the digits, and thus
enable the latter to act with greater efficacy, with a
minimum of contraction. We can demonstrate this action
experimentally on ourselves. It is enough to carry the
first phalanges forcibly into a state of extension; the
third phalanges then become flexed, quite spontaneously,
by the tension of the tendons of the flexors which are
inserted into them.

[78]At the same time, if we examine the felidæ which we have
taken as examples, when the first phalanges are in the state
of extension, the digits will be found to be separable, as we
have already indicated in connection with the metacarpo-phalangeal
articulations, with the result that the claws are
then able to lacerate a wider surface.

The extension of the ungual phalanx, which determines
the retraction of the claw and stops its action, is the
mechanical result of an elastic, fibrous apparatus which is
attached to each of the third phalanges, and has its origin
of the second.

THE POSTERIOR LIMBS[14]

The posterior limbs are divided, as are the inferior limbs
of the human being, of which they are the homologues, into
four parts: pelvis, thigh, leg, and foot.

The Pelvis

The pelvis, which incompletely limits the abdominal
cavity, inferiorly in the vertical position of the body and
posteriorly in the normal attitude of quadrupeds, is formed
by the iliac bones and sacrum—the coccyx forming a prolongation
of the latter. We have already described the two
latter (pp. 10 and 11) in connection with the vertebral
column, of which they form the inferior or posterior portion
or segment, according to the attitude of the individual.

The Iliac Bone.—The iliac or coxal bone, is a paired or non-symmetrical
bone, united below to its fellow of the opposite
side, while it is separated from it above by the sacrum.

In all animals, as well as in man, the iliac bone, at the
beginning of life, consists of three parts, which afterwards
unite and fuse together and join at the middle of the bottom
of a deep cavity which is situated on the outer aspect of the
bone—the cotyloid cavity.

Of those three portions when examined in the human iliac
bone, that above the cavity is the ilium; that on the inside
is the pubis; and the last, the lower one, is the ischium. In[79]
quadrupeds, the iliac bone being, in its entirety, directed
much more obliquely downwards and backwards, the relative
position of these constituent parts is a little modified: the
ilium is in front, the pubis is still internal, but in a more
inferior position, and the ischium is behind the cotyloid
cavity. We notice this peculiarity of the development of
the iliac bone because it is customary to continue to apply to
the osseous regions which correspond to these parts the
names by which they were known when independent bones.

Fig. 43.—The Left Iliac
Bone of the Human
Being: External Surface,
placed in the Position
which it would
occupy in the Skeleton
Of a Quadruped.

1, Cotyloid cavity; 2, ilium;
3, iliac crest; 4, anterior iliac
crest; 5, posterior iliac spine;
6, pubis; 7, tuberosity of the
ischium; 8, obturator foramen;
9, ischiadic spine.

The bones which form the skeleton of the pelvis of quadrupeds
are proportionally more elongated and less massive
than those of the human pelvis (Figs. 43 and 44).

Fig. 44.—Left Iliac Bone of A
Quadruped (Horse): External
Surface.

1, Cotyloid cavity; 2, ilium, external
iliac fossa (directed upward in the horse);
3, iliac crest; 4, anterior iliac spine
(directed inwards in the horse, it is the
angle of the haunch); 5, posterior iliac
spine (directed inwards in the horse; it
is the angle of the haunch); 6, pubis;
7, tuberosity of the ischium; 8, obturator
foramen; 9, ischiadic spine, or
subcotyloid foramen.

We find, on the external surface of the iliac bone, the
cotyloid cavity, whose border is interrupted by the cotyloid
notch; a deep notch which looks downwards.

[80]In front of this cavity is the ilium. This portion, narrow
in the part which is next the cavity, is directed forwards and
upwards, expanding more and more as it passes upwards.
It presents an external or superior surface (external in some
animals, superior in others), which recalls the external
iliac fossa; and an internal or inferior surface, at the superior
part of which is found the auricular surface for articulation
with the sacrum.

The anterior border of the ilium is rough; this is the iliac
crest, at the extremities of which we find, below or outside,
a prominence which corresponds to the anterior superior
iliac spine of man; and internally another projection which
corresponds to the posterior iliac spine.

Immediately above the cotyloid cavity is a rough crest,
which is known as the supracotyloid crest, which is, however,
no other than the homologue of the sciatic spine. In
front of this prominence, the border of the ilium, which is
notched, forms the great sciatic notch.

If, still taking the cotyloid cavity as the point of
departure, we proceed inwards—that is, towards the median
line of the body—we find the pubis; if in a posterior
direction, the ischium. These two portions, pubis and
ischium, limit an oval orifice, the subpubic foramen.

In the human skeleton, the pubis of one side is united
to that of the opposite side, to form the pubic symphysis.
In the animals which we are now studying a portion of the
ischium enters into the formation of the symphysis; in
other words, it is formed, not only by the body of the pubis,
but also by the descending branch or ramus of the pubis
and a portion of the ascending branch or ramus of the
ischium, which are fused with those of the opposite side. It
results that, though in the human being the symphysis
is short and the ischio-pubic arch large, in quadrupeds it
is the opposite. In them the arch is a mere slot, and being
formed by the ischium alone, merits the name of the
ischial arch. The ischio-pubic symphysis is very large, and
forms a horizontal surface relatively extensive, a sort of
floor, on which rest certain organs which occupy the
cavity of the pelvis.

Fig. 45.—Pubic Region of the Pelvis of a Marsupial (Phalanger,
Fox).

1, Symphysis pubis; 2, obturator foramen; 3, marsupial bones.

[81]The posterior and external angle of the ischium is rough
and prominent; it is the tuberosity of the ischium. This
forms a projection under the skin; it also does in man when
the trunk is strongly inclined forwards, while the thighs are
maintained in the vertical position. In marsupials—opossum,
kangaroo, and phalanger—the pelvis at its pubic
region is surmounted by two bones, situated one on each side
of the median line, and arranged in the form of a fork of two
prongs (Fig. 45). These, which are called marsupial bones,
support the pouch which, in animals of this genus, lodges
their young, which, at the time of birth, are incapable of
supporting a separate existence, their development being
absolutely incomplete.

In the cetaceans—for example, the dolphin—because of
the absence of posterior limbs, the pelvis is represented
by two separate bones only, which have no connection with
the vertebral column. In birds, the pelvis is remarkable
for its elongated form (see for its form Fig. 21, and for
details Fig. 46). The cotyloid cavity is pierced by an
opening, and presents on its posterior border, which is[82]
here a little prominent, a surface with which the great
trochanter is in contact.

The ilium is very highly developed, and is fused in the
median line with the ilium of the opposite side, the last dorsal
vertebræ, the lumbar vertebræ, and the sacrum. Because
of these relations with the dorsal vertebræ, it is in contact
anteriorly with the last ribs, which consequently emerge
from each side of the iliac region of the pelvis.

The ischium forms a plate of bone which, in part, closes
the external portion of the cavity of the pelvis. Its superior
border is separate for a certain distance from the external
border of the ilium; there is thus left an opening of more
or less considerable size, which represents or takes the place
of the great sciatic notch.

Fig. 46.—Pelvis of a Bird (the Cock): External Surface, Left Side.

1, Ilium; 2, ischium; 3, pubis; 4, inferior extremity of the pubis;
5, sciatic foramen; 6, oval foramen, homologous to the obturator; 7,
coccygeal vertebræ.

The pubis, long and slender, is in connection with the
inferior border of the ischium, of which it follows the general
direction; and circumscribes with this latter, below the
cotyloid cavity, an oval orifice, which is the homologue of
the obturator foramen. Its inferior extremity reaches
beyond the corresponding part of the ischium, bending[83]
towards the middle line, but without joining the pubis of
the opposite side. On this account there is no symphysis
pubis in birds. Nevertheless, an exception must be noted
in the case of the ostrich, the pubic bones of which meet in
the middle line, and are articulated in form of a symphysis.

The Thigh

A single bone, the femur, forms the skeleton of this
portion of the lower limb.

The Femur.—The bone of the thigh is, in man, directed
downwards and inwards; this obliquity, we may remind
the reader, is due to the difference in length of the two
condyles which form its inferior extremity; the internal
is the more prominent, the result of which is that when
the femur is held vertically, the internal condyle descends
lower than the external. Now, as those two articular
expansions rest on the horizontal plane formed by the upper
extremity of the tibia, it follows that the superior part of
the femur inclines towards the side of the shorter condyle—that
is to say, outwards—and that, the leg being
vertical, it and the bone of the thigh unite in forming an
angle, of which the apex is directed towards the inner side
of the knee.

In many mammals the two condyles are equally prominent,
the result of which is that the femur inclines neither
inwards nor outwards, but is contained in a plane parallel
to the axis of the trunk; while the leg is included in the
same plane. Nevertheless, although contained in the
plane which we have just indicated, the femur is obliquely
placed, and directed downwards and forwards; it accordingly
forms, with the pelvis, an angle, of which the opening
is directed to the anterior aspect of the body.

In reptiles and in birds the femur and leg are both placed
in the same plane, but this plane is not parallel to the
axis of the trunk. This is the result, on the one hand, of
the thorax being wide, and, on the other hand, of the femur,
which is directed forwards, being in contact by its anterior
extremity with the lateral aspect of the costal region, it is[84]
thus necessarily placed in a direction forwards and outwards,
and the knee is further removed from the axis of the trunk
than is the articulation which unites the thigh with the
pelvis.

The femur, like the humerus, is almost completely enveloped
by muscular masses, which bind it to the lateral
walls of the abdomen. Its inferior extremity alone is free,
and is always the more so in proportion to its elongation—that
is to say, as it belongs to an animal whose foot is more
divided. The femur in this respect conforms to the law
which we have indicated in connection with the bone of the
arm, in which the development, as to length, is in proportion
to the division of the hand.

If we compare the femur of certain animals with that
of man, we see that the corresponding details of form
are readily recognisable, but they are slightly modified.
Thus, on examining the superior extremity, we find there
a head, a neck, a great trochanter, and a lesser; but the
neck is usually short and thick, and the great trochanter
does not occupy the same level with regard to the articular
head of the bone. In man, the great trochanter does not
rise to the level of the head of the femur; in the dog and
the cat it approaches that level; in the horse and in
ruminants it rises above it.

With regard to the inferior extremity, its surfaces
undergo modifications which are further accentuated as
we pass from the digitigrades to the ungulates, or unguligrades.
We know that in man the femoral trochlea
is continuous behind, without interruption, with the condyles—that
is to say, that each of the condyles is the continuation
of one of the lips of the trochlea. We have just
said that the trochlea is continuous without interruption
with the condyles; this is accurate. Nevertheless, we
must remark that, at the level of the junction of these
surfaces, the bone presents a slight constriction, which is
more marked on the external than on the internal aspect.
This constriction, which is but slightly marked in man, is
accentuated in the dog and the cat; in the ruminants and
the solipeds it is still more pronounced so that we may[85]
say that in these latter the trochlea and the condyles are
almost completely separated.

There is another modification in regard to the prominence
and extent of the two lips of the trochlea. In
man, the external lip of the trochlea reaches higher than the
internal, and it is more prominent in front. In the dog,
these lips are equal with regard to thickness, but the
external still reaches higher than the internal; in the
cat, they are equal in every respect; in ruminants and
solipeds the internal lip is wider, thicker, and rises higher
than the external.

In animals the trochlea is, as a general rule, narrower
than in man, and the condyles are more prominent posteriorly;
so that, when viewed from one of the lateral
aspects, the inferior extremity of the femur is, in them,
better developed in the antero-posterior direction.

In birds, the femur is shorter than the bones of the leg;
its great trochanter is in contact with a prominence which
occupies the posterior part of the border of the cotyloid
cavity. Instead of articulating at the level of the knee,
with the knee-cap and tibia only, as in man, it articulates,
in addition, with the superior extremity of the fibula. A
similar arrangement is found in marsupials and reptiles.

The Knee-cap.—This bone, developed in the thickness of
the tendon of the triceps muscle of the thigh, is in contact,
by its posterior surface, with the femoral trochlea. The
two articular surfaces which are applied to the lips of the
trochlea present, with regard to their extent, an inequality
which is in proportion to the arrangement which we have
above indicated—that is, while in man it is the external
surface which is the larger, in the horse it is the internal.
We shall see what the general form of the knee-cap is
when we come, later on, to study more particularly the
posterior limbs of some animals.

The Leg

The skeleton of the leg consists of two bones: the tibia
and the fibula. The tibia is the more internal and the[86]
larger of the two; the fibula is slender, and situated on the
outer side, and a little posterior to, the preceding. The
fibula is more or less developed according to the species;
in some it is complete, in others it is very much atrophied.

This peculiarity may be compared with that which we
have drawn attention to regarding the development of the
ulna; but here the seriation is less distinct. Not only in
the different species, but even in the individuals of the same
species, the development of the fibula presents little regularity.
In quadrupeds, the bones of the leg are directed
obliquely downwards and backwards, so that they form,
with the femur, which is directed obliquely downwards
and forwards, an angle, the apex of which is placed at the
anterior surface of the knee.

Tibia.—The tibia of quadrupeds is readily comparable
with that of man; as in the case of the latter, its shaft has
three surfaces—an external, which is hollowed out in its
upper portion, and becomes anterior below; an internal,
slightly convex and subcutaneous; the posterior, which
presents, in its superior part, a crest, the oblique line of the
tibia, and some rugosities. The borders separate the
surfaces. The anterior border, or crest of the tibia, is
prominent in its superior part; below it gradually disappears
in passing towards the internal aspect of the
inferior extremity. The external and internal borders
separate the corresponding surfaces from the posterior one.

The superior extremity is thick, and expands in forming
three tuberosities: two lateral and an anterior. The
anterior tuberosity, situated at the superior part of the
crest of the tibia, is very prominent; for this reason the
superior extremity is very much expanded in the antero-posterior
direction—hence it results that this diameter is
equal to the transverse, and sometimes even greater. In
man, it is the latter which is the larger. The anterior
tuberosity is visible under the skin.

The inferior extremity, less thick, is prolonged internally
by a prominence which corresponds to the internal malleolus
of man. In animals whose fibula is but slightly
developed the tibia presents, on the external part of its[87]
inferior extremity, a small prominence, which replaces the
fibular malleolus. The ruminants must, however, be excepted,
in which we find in this region a special bone, which
certain authors look on as the inferior part of the fibula
(see p. 97). The inferior surface of this extremity of the
tibia is articular; and is in contact with one of the tarsal
bones, the astragalus. Because the superior surface of
this latter has the form of a pulley, a pulley much more
marked than that on the human astragalus, the corresponding
surface of the tibia, which has the opposite form,
presents two lateral cavities, separated by a median ridge,
which is directed forwards and slightly outwards; this
ridge projects into the groove of the pulley.

The Fibula.—This bone, situated at the back of the
external surface of the tibia, is, as we have said, more or
less developed. Its superior extremity, or head, articulates
with the external tuberosity of the tibia. Its inferior
extremity, when it exists—it is this which disappears in
animals which have the fibula incompletely developed—forms
a prominence which, placed on the external surface
of the inferior extremity of the tibia, articulates with the
astragalus, and recalls the external malleolus of man.

We have stated above that it is the inferior extremity
of the fibula which disappears when the bone is incompletely
developed; it is necessary to except the bat, in
which the fibula, fairly well developed at its inferior
extremity, by which it articulates with the tibia, thins
off in its superior portion, and does not reach the corresponding
extremity of the latter. Further, as in this
animal the surface of the knee, which corresponds to the
anterior surface of the same region in other animals, is
turned backwards, the result is that the fibula is situated
on the inner side of the tibia, instead of being placed on
the outer.

The Foot

The foot, in animals, as well as in man, is formed of three
portions, which, as we pass from the part which articulates
with the leg towards the terminal extremity, are: the tarsus,[88]
the metatarsus, and the toes. These three portions are the
homologues of the carpus, the metacarpus, and the fingers,
which, as we have already seen in the case of the hand, are
the osseous groups which form its skeleton. The tarsus
is formed of short bones, as the carpus is; these are, in
man, seven in number. The bones are arranged in two
rows: one, the posterior, formed of two bones superimposed—the
astragalus, by which the tarsus articulates with the leg,
and the calcaneum, which forms the prominence of the heel;
and an anterior row formed of five juxtaposed ones—the
cuboid, situated externally, and the scaphoid internally, in
front of which are found the three cuneiforms. To the
tarsus succeeds the metatarsus, whose form reminds us very
much of that of the metacarpals.

With regard to the toes, which we enumerate in proceeding
from the most internal to the most external, they are formed
of phalanges, which are three in number for the four outer
toes; but the number is reduced to two in the case of the
first—that is, the so-called great-toe.

The bones of the tarsus are not seven in all animals; they
are fewer in ruminants and solipeds. We already know
that, in the latter, the metacarpals and the digits are
equally reduced in number; the same is the case for the
metatarsals and the toes. We will analyze these differences
when dealing with the species individually.

Fig. 47.—Posterior Limb of the Horse placed in the Position which
it should occupy if the Animal were a Plantigrade: Left Limb,
External Surface.

1, Tibia; 2, astragalus; 3, calcaneum; 4, metatarsus; 5, first phalanx;
6, second phalanx; 7, third phalanx.

When we studied the anterior limbs, we saw in passing
from the plantigrades to the digitigrades, and finally the
ungulates, or unguligrades, as the hand became hyperextended,
the carpus was raised and more and more removed
from the ground. We shall establish the existence
of the same condition in the posterior limbs; in the
plantigrades the tarsus rests on the ground; in the digitigrades
it is removed from it; while in the unguligrades the
distance which separates it from the point of support is
still more considerable; and it is, indeed, necessary to
imagine that if these latter were plantigrades, would
occupy the position on the ground which is indicated by
Fig. 47.

In veterinary anatomy the tarsus is called the ham; a[89]
name we adopt in conformity with usage, but which we
cannot but regret, as in human anatomy the ham is the
region of the posterior surface of the knee.

The general arrangement of the region of the digits of the
posterior limbs in birds, presents some points of interest.

We shall merely say with regard to the metatarsus, that
it is formed by a single bone, which in the cock is furnished
towards its inferior third with a pointed process, the spur.
At the inferior part, there is, however, found another, which
is but very slightly developed, and with which the first
phalanx of the innermost toe articulates.

The toes are, in the majority of species, four in number:[15]
an internal, which is directed backwards, and corresponds to
the great-toe; the others are directed forwards. This
arrangement is constant in grallatores (wading birds), gallinaceæ[16]
(domestic fowls), and raptores (birds of prey).

In climbing birds (parrots, woodpeckers, and toucans), the[90]
innermost toe is not only directed backward, but the external
toe accompanies it in that direction; consequently, there are
two posterior and two anterior toes. Sometimes they are
all directed forwards; this disposition is found in the
martins. In some birds, the number of toes is reduced to
three: the cassowary shows this reduction; in others, the
number is still further diminished—the ostrich, for example,
has but two.

Fig. 48.—Skeleton of the Foot of a Bird (the Cock): Left Side,
External Surface.

1, Metatarsus; 2, spur; 3, rudimentary metatarsal; 4, first toe;
5, second toe; 6, third toe; 7, fourth toe.

Further, we find that, in general, the number of the
phalanges increases, when we examine the toes in commencing
with the most internal (Fig. 48): this has two;
then the following one three; that which comes next in
order has four; and the most external toe has five. The
phalanges of this last are short; so that, although it is
formed by a larger number of bones, it is not the longest of
the toes.

THE POSTERIOR LIMBS IN SOME ANIMALS.

Plantigrades: Bear (Fig. 33, p. 50).—The external
iliac fossa is very deep. The femur is longer than the
bones of the leg; the great trochanter does not reach the[91]
level of the head of the femur. The fibula is well developed;
it is united to the tibia at its superior and inferior extremities
only.

The foot, which, as in the case of the hand, rests on the
ground by the whole extent of its plantar surface, presents
five toes; the shortest of these is the internal—that is, the
toe which corresponds to the great-toe in man; the third
and fourth are the longest, and they are almost equal; there
is a very slight difference in favour of the fourth, which is
slightly superior in dimensions to the third.

Digitigrades: Cat, Dog (Fig. 34, p. 52).—The external
iliac fossa, which looks outwards, is deep; the iliac
crest is convex anteriorly, the convexity is continued from
one iliac spine to the other.

Fig. 49.—Pelvis of the Dog, seen from Above.

1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA′, bi-iliac diameter;
BB′, bi-ischial diameter.

In the dog, the distance which separates the anterior
iliac spines is less than that which separates the ischia
(Fig. 49). On a skeleton which we measured, the transverse
diameter, the distance from the anterior iliac spine of one
side to that of the opposite side, was 8 centimetres, whilst the
distance which separated the ischia was 105 millimetres;
on another skeleton, the first measurement was 127 metres,
and the second was 146 millimetres. It seems to us unnecessary
to multiply examples.

Fig. 50.—Pelvis of a Felide (Lion), viewed from Above.

1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA′, bi-iliac diameter;
BB′, bi-ischial diameter.

In the cat, the iliac spines are but slightly marked; the[92]
result is that the iliac crest is almost confounded with the
inferior and superior borders of the ilium. The two diameters
referred to above are almost equal (Fig. 50).

We draw particular attention to what we have just
noted in regard to the transverse proportions of the
iliac and ischiatic regions of the dog and the cat. These
relations are evidently of importance with regard to shape,
since the iliac crests and the ischia are noticeable beneath the
skin.

In the dog, the shaft of the femur is slightly convex in
front; but in the cat it is straight. The borders of the shaft
are slightly marked, so that it is almost cylindrical. The linea
aspera, less prominent than in man, gains in width what it
loses in elevation; it constitutes what may almost be called
a rough surface. This surface is narrower in its middle
portion than at its extremities, where it bifurcates to go
upwards to the two trochanters, and downwards to the two
condyles. At the superior extremity, the neck is short, the
great trochanter reaching almost to the level of the head of
the femur; the digital cavity, which is situated on the internal
surface of the great trochanter, is very deep. At its
inferior extremity it projects strongly backward. The
trochlea is narrow; in the cat its two lips are equally prominent,
while in the dog the external is a little more elevated[93]
than the internal, which on its part is a little thicker. The
trochlea is still more independent of the condyles than in the
human femur; it is separated from these latter by a slight
constriction.

The knee-cap is long and narrow.

The tibia of the dog is slightly curved from before backward:
it has the form of an elongated S; this conformation
is in great part due to the very marked projection of the
anterior tuberosity and of the superior portion of the crest,
which, a little below that tuberosity, turns abruptly backwards,
and thus describes a curve the concavity of which
is directed forward. The superior part of the external
surface is very much hollowed out.

The superior extremity is much thicker than the inferior
one. It is not only wide in the transverse direction, but is
more especially extended from before backwards; the prominence
of the anterior tuberosity is the cause of the elongation
of this antero-posterior diameter. On the posterior part of
the external tuberosity is found a surface to which the
superior extremity of the fibula is applied.

The inferior extremity presents an articular surface, which
is formed of two lateral cavities, separated by a crest, which
is directed obliquely forwards and outwards. The internal
part is prominent, and forms the internal malleolus.

With regard to the fibula, it is united to the tibia by its
extremities and by the inferior half of its shaft. This latter
is more expanded below than in its upper part. The
superior extremity is flattened from without inwards. The
inferior extremity projects beyond the articular surface of the
tibia, and forms the external malleolus, which, instead of, as
in man, descending further than the tibial malleolus, stops
at the same level, and even descends a little less than does
the latter.

In the cat, the curve of the tibia is less pronounced; this is
due to the fact that the crest, instead of being concave in its
middle portion, is slightly convex anteriorly. The fibula, less
flattened than that of the dog, is united to the tibia by
its extremities only, and is separate in the rest of its extent.

The bones of the tarsus are seven in number, and arranged[94]
as in man, with this difference (which is easily comprehended),
that their general relations are changed on account of the
vertical direction of the tarsus. For example, the astragalus,
instead of being above the calcaneum, is situated in front of
it; the cuneiform bones, instead of being situated in front
of the scaphoid, are found below it, etc.

These animals have but four well-developed metatarsals;
that which corresponds to the great-toe is represented merely
by a small style-shaped bone, situate at the internal part of
the region.

Nevertheless, we find this toe fully developed in some dogs.
Notwithstanding this, the bones which form it are, however,
but rudimentary, and much smaller than those of the innermost
digit of the fore-limb.

Sometimes it is double; this condition is demonstrable
in individuals belonging to breeds of large size. The median
metatarsals are more fully developed than the other bones
of the same region which are next them. Viewed as a whole,
the metatarsal bones are a little longer than the metacarpals;
the result is that the distance which separates the tarsus
from the ground is a little greater than that which separates
the carpus from the plane on which the anterior limbs rest.
The length of the calcaneum still further exaggerates this
difference, and, as in the animals with which we shall occupy
ourselves later on, the projection which this bone forms is
distinctly higher than that which is produced by the pisiform.

The metatarsus, as a whole, is a little narrower than the
metacarpus; not only on account of the presence of a thumb
in the anterior limb, but, further, because the bones of this
latter region are wider than those of the corresponding part
of the posterior limb.

The phalanges closely resemble those of the anterior
limbs.

Unguligrades: Pig (Fig. 38, p. 58).—The pelvis in
this animal presents a few of the characters which we
shall again meet with in the ruminants and the solipeds;
however, the posterior (or internal) iliac spines are relatively
more widely separated from one another than in the latter.[95]
This arrangement reminds us of that found in the carnivora.

The femur presents nothing very special. The knee-cap
is thick, and ovoid in outline.

The fibula is completely developed, as in the carnivora;
and is connected with the tibia at both its extremities.

The tarsus consists of seven bones. The astragalus and
the calcaneum differ slightly from those of ruminants.

The foot, like the hand, has two median digits which rest
on the ground by their third phalanges; and an internal and
an external digit, which are removed from it. The metatarsals
are a little longer than the metacarpals.

Fig. 51.—Pelvis of the Ox: Superior Surface.

1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA′, bi-iliac diameter;
BB′, bi-ischiadic diameter.

Unguligrades: Sheep, Ox (Fig. 39, p. 61).—The
pelvis of ruminants of this group closely resembles that of
the horse, which we will study later on (see p. 99). That
which we must at once point out is that, with regard to
the ratio formed by a comparison of the bi-iliac and bi-ischiatic
diameters, it may be placed between the ratio
obtained in comparing those diameters in the pelvis of the
carnivora and that of the solipeds. Indeed, in the ruminants,
the distance which separates the ischia exceeds the
width of one iliac only, and does not equal, as in the
felide, the total width of the anterior part of the pelvis[96]
(Fig. 51). In the skeleton of the ox, which forms part of the
anatomical museum of the École des Beaux-Arts, the bi-ischiadic
diameter is 39 centimetres, whilst the width of one
iliac crest is 29 centimetres, so that, in contrast to that which
we find in the dog, the width of the ischiadic region is less
than that formed in front by the addition of the iliac crests.

The great trochanter is large, and extends beyond the level
of the plane in which the head of the femur is found.

In the ox, the linea aspera, instead of being a narrow crest,
is spread out, and forms in reality a surface; the posterior
surface of the femur. At the inferior and external part of this
surface is situated a cavity which surmounts the corresponding
condyle, and is known as the supracondyloid fossa. On the
internal part of the same region there are a series of tubercles,
which, because of their position in relation to the corresponding
condyle, constitute the supracondyloid crest.

The internal lip of the trochlea is much thicker and much
more prominent than the external.

The details which we have just now examined in connection
with the ox are less marked in the sheep.

The trochlea, narrow as a whole, is clearly separate from
the condyles by a very marked constriction.

The patella, which is thickened in the antero-posterior
direction, has the shape of a triangular pyramid with the
base upwards. Its posterior surface, which articulates
with the trochlea, presents an arrangement which is adapted
to the disposition of this latter—that is to say, the surface
which is in contact with the internal lip is larger
than that which articulates with the lip of the opposite
side.

The tibia of the ox is proportionately shorter than that of
the sheep. The shaft of this bone is flattened from before
backwards, in its inferior half. The median crest of the
articular surface of the inferior extremity is the most prominent
part of that region.

Fig. 52.—Tarsus of the Ox: Posterior Left Limb, Antero-external
Surface.

1, Tibia; 2, coronoid bone of the tarsus; 3, superior articular surface
of the astragalus; 4, inferior articular surface of the astragalus; 5,
calcaneum; 6, cuboido-scaphoid bone; 7, great cuneiform bone—the
small cuneiform bone is situated at the back of the latter; 8, principal
metatarsal—the small, or rudimentary, metatarsal bone is very small;
it is situated at the back of the preceding, and is not to be seen in the
sketch. It would be visible if the view were directly lateral, but then
the superior and inferior articular surfaces of the astragalus would be less
apparent.

The fibula is extremely atrophied. The shaft and superior
extremity of this bone are represented merely by a simple
ligamentous cord, which is sometimes ossified. There remains
of the fibula, as a portion well and distinctly developed,[97]
the inferior extremity only. This presents itself under
the form of a small bone situated in the region ordinarily
occupied by the inferior extremity of the outer bone of the
leg—that is to say, the external part of the inferior extremity
of the tibia; this little bone articulates with the
astragalus and the calcaneum. Some authors consider it
to be a tarsal bone, and describe it under the name of the
coronoid bone of the tarsus (Fig. 52, 2). It is not, perhaps,
quite legitimate to describe it as a bone of this region, for[98]
it has not a homologue in the tarsus of other animals. Its
external surface is rough; its superior border is furnished
with a small pointed process occupying a depression which
is provided for it by the tibia. It reaches lower down than
the latter, and forms in this way a sort of external malleolus,
which frames, on the outer aspect, the mortise in which the
astragalus is maintained.

The tarsus, as a whole, has an elongated form; it is formed
of five bones: the astragalus, calcaneum, cuboid and scaphoid,
which coalesce, to form a single bone, and two cuneiform
bones, which correspond to the second and third cuneiform
bones of the human foot. These cuneiforms are called, from
their size, commencing internally, by the names small and
great cuneiform.

The calcaneum is long and narrow; it is longer than that
of the horse; it is on the anterior and external part that
the bone (coronoid tarsal bone) which represents the inferior
extremity of the fibula is situated. It forms the prominence
known as the point of the ham, a prominence which is no
other than the heel, which, in the unguligrades, is, as we
have already said, very far removed from the ground.

The astragalus, which is elongated in the vertical direction,
has three articular surfaces disposed in the form of
trochleæ: a superior trochlea, which is in contact with the
skeleton of the leg, and which is present in all animals; an inferior,
which replaces the articular head found on the anterior
aspect of the astragalus in man; this articulates with the
portion of the scaphoido-cuboid that corresponds to the
scaphoid; and, lastly, a posterior trochlea with which the
calcaneum articulates. Of these three trochleæ, the superior
is the most strongly marked. Between this latter and the
inferior is found, on the anterior surface of the astragalus,
a deep depression, which, during flexion of the foot on the
leg, receives a prominence which the inferior extremity of
the tibia presents in its median portion.

We can easily recognise the trochleæ which we have been
discussing, in the little bones which children use ‘to play
at bones’; these bones are no other than the astragali of
sheep.

[99]We have already mentioned that the scaphoid and the
cuboid are ankylosed; they form by their union an irregular
bone, on which the astragalus and calcaneum are supported.

The cuneiforms articulate with the internal half of the
superior extremity of the principal metatarsal; the external
half of this metatarsal articulates with the portion of
bone which represents the cuboid.

The metatarsus is represented by a principal metatarsal,
formed by the coalescence of two metatarsals; we also find
in this region a very small rudimentary metatarsal.

The metatarsus is a little longer than the metacarpus; its
transverse measurement is a little less; on the other hand,
it is a little thicker in antero-posterior direction; from these
two differences it results that the body of the metatarsus
is quadrilateral, whereas the metacarpus presents only an
anterior and a posterior surface.

The rudimentary metatarsal is a very small roundish
bone, situated at the back of the superior extremity of the
principal metatarsal.

The phalanges closely resemble those of the anterior limbs;
nevertheless, the first and second phalanges differ from the
latter in the fact that they are a little longer and narrower.

At the back of the metatarso-phalangeal articulations, as
in the corresponding region of the anterior limbs, are found
the sesamoid bones. Such also exist at the articulations of
the second and third phalanges.

Unguligrades: Horse (Fig. 40, p. 64).—The pelvis of
the horse presents a general form which sharply differentiates
it from that of the carnivora; in fact, the ilium is twisted in
such a way that the external iliac fossa does not look outwards,
but upwards. It results from this twist that the anterior
iliac spine, which we have seen to be directed downwards in
the carnivora, has become external; and this prominence is
much farther removed from the vertebral column than in
the dog or cat. On the other hand, the posterior iliac spine,
which is directed upwards in the carnivora, has become
internal; it is also placed nearer to the vertebral column,
with the result that the distance which separates this spine[100]
from that of the bone of the opposite side is proportionately
less.

The internal iliac spine, which is conical in shape, and
curved upwards, forms a prominence known as the angle of
the crupper; the external iliac spine, thick and provided
with tuberosities, forms a clearly-defined prominence; this is
the angle of the haunch.

The iliac crest, extending directly from one spine to the
other, is curved, its concavity being turned upwards. The
external iliac fossa, which looks upward, is limited anteriorly
by this crest, and is, like the latter, slightly hollowed. The
portion of the bone which connects the ilium to the region
occupied by the cotyloid cavity is extremely narrow; posteriorly,
the bone enlarges again to form the ischial and
pubic portions.

Fig 53.—Pelvis of the Horse: Superior Surface.

1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA′, bi-iliac diameter;
BB′, bi-ischiatic diameter.

The tuberosity of the ischium, thick and curved upwards,
but less so than in the ox, forms the most prominent part of
the posterior border of the region of the thigh; this projecting
portion, so sharply defined in spare subjects, is known
as the point or angle of the buttock. Contrary to what we have
indicated in the case of the dog, the distance which separates
the ischiatic tuberosities is inconsiderable in proportion to
that which we find between the external iliac spine of one
side and that of the opposite. The bi-ischiatic diameter
does not even equal the width of one iliac bone measured
at the level of its crest (Fig. 53). On the skeleton of the
horse in the École des Beaux-Arts, the distance which separates
the tuberosities of the ischia is 225 millimetres; that
between the two spines of each iliac bone is 25 centimetres.

The anterior region of the crupper is thus much broader
than that occupied by the ischia.

The femur is relatively short. Its shaft is rectilinear, and
does not present the anterior convexity which is found on
the human femur, and which we indicated when discussing
that of the dog. The shaft of the bone, instead of being
prismatic and triangular, presents four surfaces; the
anterior, internal, and external, almost pass into each other,
being separated one from the other merely by rounded
and slightly marked borders; the posterior surface, which[101]
is plane, replaces the linea aspera, which in the horse, instead
of presenting the appearance of a crest, is considerably
widened. The numerous irregularities which this surface
presents give insertion to the muscles which correspond to
those attached to the linea aspera.

Between this posterior surface and the external is found
a rough prominence which curves forward; this was designated
by Cuvier the third trochanter; it replaces the external
branch of the superior line of bifurcation of the linea aspera;
other authors call it the infratrochanteric crest, because it is
situated below the great trochanter. At the inferior part of
the same region is found a deep fossa, the borders of which
are rough; this is the supracondyloid fossa.

Between the posterior surface and the internal are found:
above, the lesser trochanter, which is long and rough;
below, at the level of the supracondyloid fossa, an equally
rough surface known by the name of the supracondyloid
crest.

The superior extremity is flattened from before backwards.
The neck is not well marked. The great trochanter is very
prominent, and projects beyond the level of the head of the
femur. We divide the great trochanter into three parts:
the summit, which is the most elevated portion; the convexity,[102]
which is situated in front; and the crest, formed by
muscular impressions, situated outside and below the convexity.
The digital fossa is situated behind and below the
summit of the great trochanter. With regard to the lesser
trochanter, it is placed so far down that it really forms
part of the shaft of the bone, with which, besides, we have
described it.

On the inferior extremity of the femur are two condyles
and a trochlea; the condyles are clearly separated from this
latter by a marked constriction.

The trochlea is directed with a slight obliquity downwards
and inwards; its internal lip is much thicker and more
prominent than the external; this is, accordingly, a condition
exactly the opposite of that which characterizes the
corresponding region of the human femur.

The knee-cap is lozenge-shaped; its superior angle projects
upward, and produces a prominence at the part which
corresponds to the base of the human patella, the part
which is here the thickest portion of the bone. Its anterior
surface is convex and rough. Its posterior surface presents
two lateral articular facets, separated by a crest; this
surface is in contact with the trochlea of the femur, and,
as it is the internal lip of the latter which is the more
developed, it results therefrom that the internal articular
surface of the knee-cap is larger than the external.

The knee-cap contributes to the formation of the region of
the posterior limb which is called the stifle.

The tibia is large in its upper portion; in its inferior part
it is flattened from before backwards. The posterior surface
of the shaft presents an oblique line, below which are found
vertical rough lines for the insertion of muscles. The external
surface is hollowed out in its upper part. The
anterior tuberosity of the tibia rises just to the level of the
flat articular surface; it is hollowed in its median portion
by a vertical groove of elongated form, which receives the
ligament that binds the knee-cap to the tibia. The external
tuberosity is more prominent than the internal; in it is
found a groove for the passage of the anterior tibial muscle.

The inferior extremity, flattened from before backwards,[103]
presents a surface which is moulded on the trochlea of the
astragalus; the median crest of this surface is thick, and
descends lower posteriorly than the tuberosities which are
situated on the external and internal aspects of this
extremity.

Of the two tuberosities, that which is internal is comparable
to the internal malleolus of man, the one on the outer
side forms a sort of external malleolus; but this latter here
belongs to the tibia, and not to the fibula.

The fibula, in fact, does not reach the inferior extremity
of the tibia; it is a poorly developed bone, elongated and
terminating inferiorly in a point, at the middle of the shaft
of the tibia or at its lower third. Its superior extremity,
which is slightly expanded, articulates with the tuberosity
which occupies the outer aspect of the corresponding extremity
of the tibia.

Fig. 54.—Tarsus of the Horse: Left Posterior Limb, Anterior
Surface.

1, Tibia; 2, internal tuberosity of the inferior extremity of the tibia
(homologue of the internal malleolus of man); 3, external tuberosity
of the inferior extremity of the tibia (homologue of the external malleolus);
4, median crest lodged in the groove of the pulley of the astragalus; 5,
pulley of the astragalus; 6, internal tuberosity of the astragalus; 7,
calcaneum; 8, cuboid; 9, scaphoid; 10, great cuneiform, the small cuneiform
is placed behind this latter; 11, principal metatarsal; 12, external
rudimentary metatarsal. The internal rudimentary metatarsal, being
more slender than the external, does not appear in the figure.

The bones of the tarsus are six in number: the calcaneum
and astragalus form the upper row; the cuboid, scaphoid,
and two cuneiforms form the lower (Fig. 54).

The astragalus has not, as in ruminants, an inferior
trochlea for articulation with the scaphoid; this portion of
the bone presents a surface which is slightly convex. It
articulates with the tibia by a trochlea that occupies not only
the superior surface, but also the anterior. This trochlea,
which is directed slightly obliquely downwards and outwards,
has a very pronounced form; its lips, which are extremely
prominent, determine by their anterior part one of the
features which we recognise on the anterior aspect of the
ham—a feature which is still more accentuated when the
metatarsus (canon) is extended on the leg. On the internal
surface of the astragalus is found a tubercle, which forms a
projection in the corresponding region of the ham.

The calcaneum, which is not quite so long as that of
the ox, forms by its summit a prominence which is called
the point of the ham.

The cuboid is small; the scaphoid is large, and flattened
from above downwards. Of the two cuneiforms, the more
external is the larger; it closely resembles the scaphoid;
it is flattened from above downwards as is the latter; but[104]
it is a little smaller in size. The small cuneiform, which
occupies the inner side of the tarsus, is the smallest bone in
this region; it is sometimes divided into two parts; this
raises the number of the cuneiforms to three, and that of the
bones of the tarsus to seven.

The bones of the metatarsus and the phalanges are equal
in number to the corresponding bones in the anterior limbs;
they are formed on a type analogous to that of these latter.
Accordingly, we shall merely indicate the differences which
characterize them.

The principal metatarsal is longer than the metacarpal of[105]
the same class; its shaft is more cylindrical; its inferior
extremity is somewhat thicker. The external rudimentary
metatarsal is better developed than the internal; in the
metacarpus the reverse is the case.

The phalanges so far resemble those of the anterior limb
that, as differential characters, we need point out only the
following: the first phalanx of the hind-foot is a little
shorter than that of the fore-foot; its inferior extremity
is a little narrower, and its superior extremity a little
thicker. The second phalanx is a little less expanded
laterally.

The difference in appearance which the three phalanges,
anterior and posterior, respectively present are to be borne
in mind; for they are correlated to the general form of the
fore and hind feet. We will establish this point when we
come to study the hoof (see Figs. 101 and 102, p. 257). In
the fore-foot the ungual phalanx has its inferior surface
limited externally by a circular border, while the same bone
of the hind-foot has this surface a little narrower, more concave,
and limited by two curved borders which unite
anteriorly to form an angle—an arrangement which gives to
the general outline of this region the form of the letter V.

Articulation of the Posterior Limbs

The Coxo-femoral Articulation.—The head of the
femur is received in the cotyloid cavity; these are the osseous
surfaces in contact in this articulation. They are maintained
in position by a fibrous capsule and a round ligament.
To this latter is found attached, in the horse, a fasciculus
which, commencing, as does the round ligament, at the depression
on the head of the femur, emerges from the cotyloid
cavity by the notch which is present in its circumference,
and is attached to the anterior border of the pubes, to blend
with the tendon of the rectus muscle of the abdomen. This
is the pubio-femoral ligament.

The movements which this joint permits are the same in
the quadrupeds as in man, but less extensive. They are:
flexion and extension, abduction and adduction, the two[106]
latter being much more limited than the former. There is
also rotation.

By flexion, the inferior extremity of the femur is directed
forwards; the bone of the thigh then takes a more oblique
direction than the normal. This movement takes place, for
example, when the animal carries forward one of its hinder
limbs. Extension, which takes place in an inverse sense, is
produced when the foot is fixed on the ground, while the
body is projected forward. It is also produced in the
action of kicking.

As for the lateral movements—viz., abduction and adduction—they
are less extensive than the preceding movements.
The absence of the pubio-femoral ligament in other
quadrupeds than the horse explains why in them abduction
is less limited than in the latter. Indeed, it is the tension of
this ligament, occasioned by the abduction of the thighs,
which arrests more quickly the movement in question.

Articulation of the Knee.—This articulation, as in man,
is formed by the femur, the patella, and the tibia.

In the horse the ligament of the patella is not single, but
consists of three parts, designated, on account of their
position, by the respective names of external, internal, and
median patellar ligaments. The two former come from the
angles on the corresponding borders of the knee-cap; the
median springs from the anterior surface and inferior angle of
the same bone. They all three pass to their termination on
the anterior tubercle of the tibia. The external ligament
is the strongest, and the internal ligament the least
developed.

In the dog, the cat, the pig, and the sheep, the patellar
ligament consists of a single band. The articulation is
further strengthened on the sides by lateral ligaments—an
internal and an external.

With regard to the principal movements, these are flexion
and extension, to which may be added movements of rotation
of limited extent. In flexion, the leg bends on the thigh;
its inferior extremity is directed upwards and backwards;
the angle which the tibia naturally forms with the femur
becomes less obtuse.

[107]But
it should be understood that one part of this description—that
which has relation to the leg—holds good
only when the femur is in its normal condition, or in flexion.
Indeed, at the close of the movement in which, during a step,
the foot is in contact with the ground—that is, at the termination
of the resting stage—the inferior extremity of the tibia
is directed backwards. But the femur is then in a state of
extension, and in regard to this latter the attitude of the
leg is unchanged.

Fig. 55.—Extension of the Leg: Right Posterior Limb of the
Horse, External Surface. (After a Chronographic Study by
Professor Marey.)

At this moment, notwithstanding the direction, which
recalls that which it has at the time of flexion, the leg is not
bent on the thigh; on the contrary, it is almost in the line
of its continuation (Fig. 55). As we have done in connection
with the articulations of the anterior limbs, we borrow
this figure from the interesting chronophotographic studies
of Professor Marey.[17]

The Tibio-tarsal Articulations and of the Bones of the
Tarsus.—In the region which veterinary anatomists call the
ham, the articulations of the leg and foot alone call for special[108]
study in the case of the horse. The articulations of the
bones of the tarsus, and of these with the metatarsus, do not
offer any interest with regard to mobility, this being almost
wholly absent at that level.

The leg and the astragalus, in a general way, are placed in
contact by such articular surfaces that the resulting joint,
which is a true hinge, permits movements of flexion and extension
only. Indeed, as we have indicated above, the tibia
is furnished, on the inferior surface, with a crest that fits into
the deep groove which is situated on the corresponding
surface of the astragalus.

During flexion, the anterior surface of the foot tends to
approach the anterior surface of the leg, the angle formed
by these two segments becoming more and more narrowed.
The displacement in the opposite direction characterizes
extension.

In other quadrupeds, the articulations which bind together
the bones of the tarsus possess a little more freedom of movement.
The shape of these bones, and particularly the shape
of the surfaces of the astragalus, which are in contact with
them, allow movements in this region, in the case of the dog
and cat, which, without being so extensive as those of the
human foot, in the subastragaloid articulation, nevertheless,
recall the mobility which we find in the human species
at this level—that is to say, rotation, abduction, and
adduction of the foot.

As for the articulations of the metatarsus with the
phalanges, and of the phalanges with one another, they resemble
those of the anterior limb too closely that it should
be necessary to study them here. Such a study would
be, in this case, but a repetition (see p. 76, a description of the
articulations in question).

THE HEAD IN GENERAL, AND IN SOME
ANIMALS IN PARTICULAR.

When we compare, by the examination of one of their
lateral aspects, the skull of man and the same region in other
mammals, it is easy to observe that the relative development
of the cranium and face is entirely different. In the[109]
case of man the cranium is large, and the face relatively
small; in animals the face is proportionally much more
highly developed. The measure of the facial angle permits
us to note these differences, and the figures relative to the
value of this angle are sufficiently demonstrative to induce us
to indicate those which are, in a general way, connected with
some of the forms in individuals which here occupy our
attention. In the first place, we must remember that the
angle in question is more acute, as the cranium is less developed
in proportion to the facial region (Figs. 56 and 57). It
is especially to this character that we wish to draw attention.

Fig. 56.—Human Skull: Measure of the Facial Angle by the
Method of Camper. Angle BAC = 80°.

The internal wall of the cranial cavity is marked by the dotted line.

Fig. 57.—Skull of the Horse: Measure of the Facial Angle by
the Method of Camper.[18] Angle BAC = 13°.

The internal wall of the cranial cavity is shown by the dotted line.

Besides, in animals the cranium is very prominent
superiorly, and the face, more or less elongated, is sharply
projected downwards and forwards; in man the cranial region
occupies not only the superior, but also the posterior part;
the face is short and of a compact form. The human head,
in its general aspect, may be compared to a sphere, while
the skull of the quadrupeds presents the aspect of a quadrangular
pyramid, with the base turned upwards and the
summit at the incisor teeth.

Direction of the Head.—Before entering on the study
of the bones of the head, it is necessary, in our opinion, to
agree as to the position in which we shall suppose it to be
placed.

The question may seem to be one of little importance;
nevertheless, it cannot be regarded as indifferent, since
authors are not all agreed on this subject.

Some suppose it to be placed vertically—that is, with the
incisor teeth turned directly downwards. Others, on the
contrary, suppose it to be placed horizontally, resting on the
whole length of the lower jaw, the face being then turned
upwards. These two extreme methods of arrangement appear[110]
to us to possess inconveniences—at least, for comparison
with the human head.

Indeed, if, when the head is vertical, the same regions of the
face (forehead, nose) are, in the case of animals as well as man,
turned forward, the lower jaw ceases to merit its appellation,
as it is then situated, not below, but behind the upper.[111]
Furthermore, if this position is chosen, for example, for modelling
or drawing, it cannot be obtained without difficulty
when we have to deal with an isolated piece of the skeleton,
on account of the absence of equilibrium, which it is necessary
to obviate. It is true that the question of convenience
should not take precedence of all others, and it suffices for
us in this connection to recall, in regard to the human pelvis,
that, although the older anatomists used to represent it as
resting commodiously on the three angles which terminate
it at its lower part (ischial tuberosities and coccyx), this
attitude being false, it is customary now to incline the
superior aspect forwards, inasmuch as this arrangement
more nearly conforms to reality, in spite of the fact that it
is a little more difficult so to dispose an isolated pelvis.
Further, to return to the head; if its vertical direction can
be demonstrated, for example, in many horses, it is not sufficiently
general to be adopted as the classic position.

In regard to the facility of placing in position, the horizontal
direction is certainly to be preferred; but this is also
far removed from the natural position in the animal while in
the state of repose. On the other hand, the mind is not
satisfied with the idea that certain regions of the face,
such as the nose and the forehead, are then directed upwards.
And yet it is necessary to come to a decision, seeing that
what we are now investigating applies also to the position
to which it is necessary to give the preference in placing the
skeleton of the head when we wish to draw it in profile.
That which we adopt is a compromise, but to us it seems
more rational.

The position of the head of the horse, to be normal,
should be such as to give it an inclination of 45°. In this[112]
case the lower jaw is still posterior; and, for this reason, we
see in adopting this position some inconveniences from a
didactic point of view. Accordingly, we will suppose the
head brought a little nearer to the horizontal, and this, from
the imaginative point of view, has certainly an advantage
which we cannot afford to neglect when addressing artists.

Indeed, let us suppose that to a clay model of a human
head we wish to give the aspect of the head of a quadruped.
We should elevate the occiput; and then, taking hold of the
lower part of the face, we should lengthen it, not in a direction
precisely antero-posterior, but downwards and forwards. It
is obviously this latter procedure which, on the other
hand, is carried out when a person wishes to give to his
own face some resemblance to the muzzle of a quadruped.

It is true that, in the position we have adopted, the face
is directed obliquely downwards and forwards, and that there
may result a certain confusion in describing the position
of its different parts. On this account, with the object
of not making complications, we purpose, for the present,
to substitute, for example, for the term ‘antero-superior’—which
when speaking of the position of the forehead and
nose would be more exact—the term ‘anterior,’ which is
sufficiently comprehensible. The mouth will be, for the
same reason, referred to as being situated at the inferior
part of the face, and not the antero-inferior.

The Skull.—The elevation of the cranial region becomes
especially appreciable when we examine the occipital
bone. Before verifying this fact, it is not superfluous to
recall the general arrangement which this bone presents in
the human skull. A portion of the occipital bone occupies
the base of the skull; but this base in man is horizontal; to
this region succeeds the shell-shaped portion of the occipital
bone, which, passing vertically upwards, forms with the
preceding portion an angle situated at the level of the external
occipital protuberance, and of the curved line which
starts from it on each side. In animals a portion of the
occipital bone is horizontal, it is true; but this bone being
sharply bent at the level of the occipital foramen and condyles,
the result is that the portion which surmounts these latter[114]
looks backwards, and is limited above by the external
occipital protuberance, which forms the culminating
point of the skull; this point is situated between the
ears.

Fig.
58.—Skull of one of the Felidæ (Jaguar): Left Lateral Aspect.

1, Posterior surface of the occipital bone; 2, external occipital
protuberance; 3, condyle of the occipital bone; 4, jugular process;
5, parietal bone; 6, frontal bone; 7, orbital process; 8, orbital cavity;
9, squamous portion of the temporal bone; 10, external auditory canal,
in front of which is situated the zygomatic process; 11, tympanic bulla;
12, superior maxillary bone; 13, intermaxillary or incisor bone; 14,
nasal bone; 15, anterior orifice of the nasal cavity; 16, malar bone;
17, ungual or lachrymal bone; 18, inferior maxillary bone; 19, condyle
of the inferior maxillary bone; 20, coronoid process; 21, incisor teeth;
22, canine teeth; 23, molar teeth.

Fig. 59.—Skull of the Lion: Left Lateral Aspect.

This figure is intended to show that in the lion the contour of the face
between the nasal bones and the cranial region is more flattened than
in other felidæ, such as the tiger, jaguar, panther, and domestic cat.
This difference is shown by comparison of this figure with the preceding
one (Fig. 58). We are indebted to M. Tramond, the well-known
naturalist, for the indication of this differential character which, from
the artistic plastic point of view, is one of real interest.

This protuberance, prolonged on each side by the superior
curved line of the occipital bone, is so much the more
prominent as this bone bends sharply a second time, so
as to form a third portion, which, looking forwards, forms
part of the anterior aspect of the skull, and proceeds to
articulate with the parietals. On this third portion is
found a crest which, proceeding from the occipital protuberance,
is continuous in front with the parietal crests,
to which we will again refer in speaking of the parietal
bones.

On the inferior surface of the human occipital bone are
found, at the level of, and external to, the condyles two bony
elevations which bear the name of jugular eminences. They
are long in quadrupeds, and constitute what are designated
by some authors the styloid processes, but they must
not be confounded with the processes of the same name
which in the case of man form part of the temporal bone.
These processes are very highly developed in the pig, horse,
ox, and sheep.

In the ox, the occipital bone is deprived of the protuberance,
and is not bent on itself in the anterior portion,
neither does it form the most salient part of the skull; this
latter, which is situated at the level of the horns, belongs
to the frontal bone. In the pig, also, the occipital bone
is not bent upon itself in its anterior portion, but forms
the summit of the head. The occipital protuberance,
hollowed on its posterior surface, rises vertically, and
rests upon the parietal bone, with which it forms an acute
angle.

The parietals, two separate bones in the dog and the
cat, but fused in the median line in the ox, sheep, and horse,
are of special interest in regard to the two crests which, in
the carnivora, and also in the pig and the horse, occupy
their external surface, and, after diverging from one
another, are continued by a crest which crosses the frontal[115]
bone and ends at the external orbital process of the latter
bone.

These crests, known as the parietal or temporal crests,
recall both in position and relations the temporal curved
line of the parietal bone of man. They contribute, as in
the case of the latter, to the formation of the boundaries
of the temporal fossa.

Fig. 60.—Skull of the Dog: Left Lateral Aspect.

1, Posterior surface of the occipital bone; 2, external occipital protuberance;
3, occipital condyle; 4, jugular process; 5, parietal bone;
6, frontal bone; 7, orbital process; 8, orbital cavity; 9, external auditory
canal, in front of which is found the zygomatic process; 10, tympanic
bulla; 11, superior maxillary bone; 12, intermaxillary or incisor bone;
13, nasal bone; 14, anterior opening of the cavity of the nasal fossæ;
15, malar bone; 16, lachrymal bone; 17, inferior maxillary bone; 18, condyle
of the inferior maxillary bone; 19, coronoid process; 20, incisor
teeth; 21, canine teeth; 22, molar teeth.

In the carnivora, these crests are situated, throughout their
whole length, in the median line, the temporal fossæ being,
accordingly, as extended as they possibly can be. In certain
species, the development of these crests is such that they
form by their union a vertical plate, which, in separating the
two temporal fossæ, gives them a greater depth. In the pig,
the parietal crests, analogous in this respect to the temporal
curved lines of the parietal bones of man, are separated by[116]
an interval, proportionately less extended, however, than
that of the human skull. The parietal bone in the ox and the
sheep does not enter into the formation of the anterior surface
of the skull; it is formed by an osseous plate, narrow and
elongated transversely, which, with the occipital bone, constitutes
the base of the region of the nape of the neck. It is
bent upon itself at the level of its lateral portions so as to
occupy the temporal fossa.

The anterior surface of the frontal bone, which is depressed
in the median line in the dog, but plane in the horse, is
limited by two crests, which, situated on the prolongation
of the parietal crests, diverge more and more from one
another in proportion as they occupy a lower position.
This surface terminates externally in two processes, which
are the homologues of the external orbital processes of the
human frontal bone.

The superior border of these orbital processes, situated
on the prolongation of the corresponding parietal crests,
contributes to limit the temporal fossa. Each of these
orbital processes terminates in the following manner: In the
bear, dog, cat, and pig, in which the orbital cavities are incompletely
bounded by bone, this process, slightly developed,
is not in connection, by its inferior extremity, with any other
part of the skeleton of the region. In the ox and the sheep,
it articulates with a process of the malar bone. In the
horse, it articulates with the zygomatic process of the
temporal bone. The inferior margin of this process forms
a part of the boundary of the anterior opening of the orbital
cavity.

The supra-orbital foramen, which does not exist in carnivora,
occupies in the horse the base of the orbital process. In
the ox, it is situated a little nearer the middle line; and its
anterior orifice opens into an osseous gutter which is directed
upwards towards the base of the horn, while inferiorly it
meets the inferior border of the frontal bone; in the sheep this
groove is but slightly developed. In this latter, as in the ox,
it is the frontal bone which forms the most elevated portion
of the skull. In fact, being bent upon itself at a certain level,
its external surface is formed of two planes: one, posterior,[117]
which is inclined downwards and directed backwards; the
other, anterior, is also inclined downwards, but with a forward
obliquity. At the union of these planes the bone forms an
elbow, on either side of which are found the osseous processes
on which the horns are mounted.

Fig. 61.—Skull of the Pig: Left Lateral Aspect.

1, Occipital bone; 2, condyle of the occipital; 3, jugular process;
4, parietal bone; 5, parietal crests; 6, frontal bone; 7, orbital process;
8, orbital cavity; 9, external auditory canal; 10, zygomatic process;
11, superior maxillary bone; 12, intermaxillary or incisor bone; 13,
nasal bone; 14, anterior orifice of the cavity of the nasal fossæ; 15,
malar bone; 16, lachrymal bone; 17, inferior maxillary bone; 18, condyle
of the inferior maxillary bone; 19, incisor teeth; 20, canine teeth;
21, molar teeth.

In the bear, the anterior margin of the frontal bone is
prolonged by two small tongues of bone, which, descending
on the lateral borders of the nasal bones, articulate with the
superior half of the latter.

The temporal bone is, as in man, furnished with a squamous[118]
portion, from which springs the zygomatic process, which
is directed towards the face, to terminate in the following
manner: in the carnivora, the pig, and ruminants, it
articulates with the malar bone by its inferior border;
in the horse, it insinuates itself as a sort of wedge between
the malar bone and the orbital process of the frontal bone,
with which it articulates, as we have already pointed out,
and contributes, by a portion situated in front of this
articulation, to form the boundary of the anterior opening
of the corresponding orbital cavity. As in man, the zygomatic
process arises by two roots: one, transverse, behind
which is situated the glenoid cavity of the temporal bone;
the other, antero-posterior, which proceeds to join above
with the superior curved line of the occipital bone.

Behind the glenoid cavity is found the external auditory
canal, and, further back still, the mastoid process. This
latter, but slightly developed in the carnivora, a little more
so in the ruminants, and still more in the horse, has its
external surface traversed by a crest, the mastoid crest,
which, after becoming blended with the antero-posterior
root of the zygomatic process, proceeds with this latter to
join the superior occipital curved line.

Below the auditory canal is situated a round prominence,
highly developed in carnivora; this is the tympanic bulla,
also called the mastoid protuberance; it is an appendage of
the tympanum.

The Face

The bone of this region, around which all the others come
to be grouped, is, as in man, the superior maxillary. The
relations of this maxillary with the neighbouring bones is
not exactly the same in all animals; for example, in the ox,
sheep, and horse, in which the bones of the nose are wide in
their upper part, and in which the lachrymal bone, which is
very highly developed, encroaches on the face, the superior
maxillary does not meet the frontal bone; it is separated
from it by the above-named bones. It unites with it, on the
other hand, in the dog and the cat. In the bear, it is separated
from the bones of the nose by a small tongue of bone which[119]
springs from the anterior border of the frontal—a process
which we have noticed in connection with this latter.

Fig. 62.—The Skull of the Ox: Left Lateral Aspect.

1, Occipital condyle; 2, jugular process; 3, parietal bone; 4, frontal
bone; 5, osseous process, which serves to support the horn (horn-core);
6, orbital cavity; 7, external auditory canal, in front of which is found
the zygomatic process; 8, temporal fossa; 9, superior maxillary bone;
10, intermaxillary or incisor bone; 11, nasal bone; 12, anterior orifice
of the cavity of the nasal fossæ; 13, malar bone; 14, lachrymal bone;
15, inferior maxillary bone; 16, condyle of the inferior maxillary bone;
17, incisor teeth; 18, molar teeth.

In the pig, ox, sheep, and horse, the external surface is
traversed, to a greater or less extent, by a crest which is
situated on the prolongation of the inferior border of the
malar bone. This crest, which is straight in the horse, but
curved with its convexity upwards in the ox and the sheep,
is known as the maxillary spine or the malar tuberosity: it
gives attachment to the masseter muscle, and, in the horse,
is distinctly visible under the skin. It does not exist in the
carnivora. On the same surface is situated the sub-orbital
foramen.

The inferior border is hollowed out into alveoli, in
which are implanted the superior molar and canine teeth.
This border is prolonged forwards from the alveolus,[120]
which corresponds to the first molar tooth, to terminate,
after a course more or less prolonged, at the alveolus
of the canine. This space, more or less considerably expanded,
which thus separates these teeth is called the interdental
space; but this denomination is not applicable to
ruminants, because these latter possess neither canine nor
incisor teeth in the upper jaw (see p. 125, dentition of the
ox and sheep). The superior maxillary bone of one side and
that of the opposite side do not meet in the median line in the
region which corresponds to the incisor teeth; they are separated
by a bone which, in the human species, is present only
at the commencement of life, and afterwards coalesces with
the maxilla; this is the intermaxillary or incisor bone.
This bone, which is paired, is formed of a central part, which
bears the superior incisor teeth; it is prolonged upwards
and backwards by two processes: one, external, which insinuates
itself between the superior maxillary and the nasal
bone, except in the sheep, in which it remains widely separated
from the latter; the other, internal, which is united to
that which belongs to the bone of the opposite side to form
part of the floor of the cavity of the nasal fossæ; the external
border of this process, which is separated from the body of the
bone by a notch, forms the internal boundary of the corresponding
incisor opening or the incisor slit. Owing to the
absence of superior incisors in ruminants, the intermaxillary
bone presents no alveoli.

The malar bone, and the os unguis or lachrymal, are
more or less developed according to the species considered.
With regard to the malar bone, it is most important to
notice the part which it takes in the formation of the
zygomatic arch, and that its inferior border contributes
to form the crest to which is attached the masseter
muscle.

As for the nasal bones, they present differential characters
which, as they affect the form of the region which they
occupy, are worthy of notice.

Fig. 63.—Skull of the Horse: Left Lateral Aspect.

1, Posterior surface of the occipital bone; 2, external occipital protuberance;
3, occipital condyle; 4, jugular process; 5, parietal bone;
6, frontal bone; 7, orbital cavity; 8, zygomatic process of the temporal
bone; 9, external auditory canal; 10, mastoid process; 11, superior
maxillary bone or maxilla; 12, intermaxillary or incisor bone; 13, nasal
bone; 14, malar bone; 15, lachrymal bone; 16, inferior maxillary
bone or mandible; 17, inferior maxillary fissure; 18, condyle of the inferior
maxillary bone; 19, coronoid process of the inferior maxillary bone;
20, incisor teeth; 21, canine teeth; 22, molar teeth.

Their dimensions in length are proportional to those of
the face. Very small in man, they are more developed
in carnivora. We recognise in the latter the two curves[121]
which characterize them in the human species, and which
we clearly notice when we view them on one of their
lateral aspects: a concavity above, and a convexity below.
These curves are more or less accentuated—very strongly
marked in the bulldog, and scarcely at all in the greyhound.
Moreover, in the carnivora also the nasal bones are wider
below than above, and form, by their junction, a semicircular
notch which limits, in its superior portion, the
anterior opening of the cavity of the nasal fossæ. In the
horse they present an opposite arrangement with regard to
their dimensions in width; broad above, each terminates[122]
below by forming a pointed process which, separated from the
intermaxillary bones, is prolonged in front of the nasal orifice.

The inferior maxillary bone is, as in man, formed of a
body and two branches. But among the many special
characteristics of form and size which sharply differentiate
it from the human bone, one detail must be
indicated; this is the absence of a mental prominence.
Hence it results that the anterior border of the body of the
lower jaw, instead of being directed obliquely downwards
and forwards, is, on the contrary, oblique downwards
and backwards, and that in certain animals this border is
actually found almost exactly on the prolongation of the
inferior border of the body of the bone.

On the external surface of the body are found the three
mental foramina. The superior border is hollowed out by
alveoli.

With regard to the branches (rami), they terminate in two
processes: one, the posterior, is the condyle; the other,
situated more forwards, is the coronoid process, which gives
insertion to the temporal muscle. These two processes are
separated by the sigmoid notch.

Fig. 64.—Skull of the Hare: Left Lateral Aspect.

1, External occipital protuberance; 2, occipital condyle; 3, parietal
bone; 4, frontal bone; 5, orbital process; 6, orbital cavity; 7, zygomatic
process; 8, external auditory canal; 9, superior maxillary bone;
10, intermaxillary or incisor bone; 11, nasal bone; 12, anterior opening
of the nasal fossa; 13, malar bone; 14, inferior maxillary bone; 15,
condyle of the inferior maxillary bone; 16, incisor teeth; 17, molar
teeth.

For reasons which we will explain further on (see p. 127,
movements of the lower jaw), the condyle presents differences
of form. In the carnivora, it is strongly convex from
before backwards, expanded transversely, and firmly mortised
in the glenoid cavity of the temporal bone; in the
ruminants, it is less convex from before backwards, it is
more slightly concave in the transverse direction; in the
rodents—we give as an example the hare (Fig. 64)—the
condyle is still convex from before backwards, but it is
flattened from without inwards.

In the animals in which the muscles of mastication are
very highly developed, and especially in the carnivora, the
osseous regions occupied by these muscles are more extensive
and more deep than in the human species. The length of
the coronoid process, the depth of the temporal fossa, the
extent of the zygomatic arch, the appearance of the external
surface of each of the rami of the lower jaw, deeply hollowed
out for accommodation of the masseter, and to provide extensive[123]
surfaces of insertion for this muscle, are sure proofs
furnished by the skeleton of the occasionally enormous development
of the muscles of mastication.

In the carnivora, a rather strong process, which is directed
backwards, occupies the angle of the inferior maxilla; it is,
accordingly, situated below the region of the condyle.

The teeth which the jaws carry vary in number, and even
in appearance, according to species; it is useful to note their
differences. In order to establish the nature of these latter
more effectively, we will first recall the fact that in man the
teeth, thirty-two in number, are equally distributed between
the jaws, and are divided into incisors, canines, and molars,
of which the arrangement is thus formulated:

[124]We also note that the incisors are edged, the canines are
pointed, and that the molars, cubical in shape, have their
surface of contact provided with tubercles.

The teeth of the cat are thirty in number; they are thus
arranged:

Those of the dog number forty-two:

In these animals, the incisors, such as are not damaged by
use, are furnished, on the free border of their crown, with
three tubercles, of which one, the median, is more developed
than those which are situated laterally. We denote these teeth,
commencing with those nearest the median line, by the names
central incisors or nippers, intermediate and corner incisors.
The canines, or fangs, are long and conical; they are curved
backwards and outwards. The upper canines, which are
larger than those of the lower jaw, are separated from the most
external of the incisors (corner) by an interval in which the
canines of the lower jaw are received. The lower canines, on
the other hand, are in contact with the neighbouring incisors,
and are each separated from the first molar which succeeds
them by a wider interval than that which is situated between
the corresponding teeth in the upper jaw.

The molars differ essentially from the teeth of the same
class in the human species. Their crown terminates in a
cutting border bristling with sharp-pointed projections; this
formation indicates that these teeth are principally designed
for tearing. During the movement of raising the lower jaw,
which is so energetic in the carnivora, they act, indeed, in
the same manner as the two blades of a pair of scissors. The
largest molars are: in the dog, the fourth of the upper jaw,
and the fifth in the opposite one; in the cat, the third both
above and below.

[125]The pig has forty-four teeth disposed in the following
manner:

Of the incisors, the nippers and the intermediate ones of the
upper jaw have their analogues in those of the horse; in the
lower jaw, the corresponding teeth, straight, and directed forward,
rather resemble the same incisors in rodents. The
corner incisor teeth are much smaller, and are separated from
the neighbouring teeth. The canine teeth, also called tusks
or tushes, are greatly developed, especially in the male. The
molars increase in size from the first to the last; they are not
cutting, as in the carnivora, but they are not flattened and
provided with tubercles on their surfaces of contact as in the
herbivora.

In the ox and the sheep the teeth are thirty-two in
number:

As we see from this dental formula, the incisors are found
only in the lower jaw; they are replaced in the upper jaw
by a thick cartilaginous pad on which the inferior incisors
find a surface of resistance.

These have their crowns flattened from above downwards,
and gradually become thinner from the root to the anterior
border, which is edged and slightly convex. These teeth
gradually wear away. In proportion to the progress of this
wear, on account of the fact that it involves the anterior
borders and upper surfaces of the incisor teeth, and that
these teeth are narrower towards the root than at the opposite
extremity, the intervals which separate them tend to
become wider and wider; and when the roots become exposed
by the retraction of the gums, they are then separated
from one another by a considerable interval. The molars
have their grinding surface comparable to that of the horse;
they increase in size from the first to the sixth.

[126]The teeth of the horse are forty in number; they are
thus distributed:

As they become worn, these teeth continue to grow, and as,
on the one hand, this phenomenon takes place throughout
the whole life of the animal, and, on the other hand, the
process of wear brings out and makes visible at the surface
of friction parts formerly deeper and deeper, and of which
the configuration varies at different levels, there result
special features which permit the determination of the age of
the animal by an examination of its jaws. The incisors are
called, commencing with those situated nearest the middle
line, central incisors or nippers, intermediate and corner incisors.
The canines, also designated as the fangs, exist only
in the male. It is exceptional to find them in the mare, and
when they exist in this latter they are less developed than
those of the horse. The molars have cuboid crowns; the
surface of friction is almost square in the case of the upper
molars, and is inclined so as to look inwards; in the case of
the inferior ones, it is a little narrowed, and is inclined so
as to look outwards. In the upper jaw the external surface
of the crown is hollowed by two longitudinal furrows;
in the lower jaw the same surface has only one furrow,
which at times is but slightly marked.

In the hare the teeth are twenty-eight in number:

The four incisors of the upper jaw are divided into two
groups; one of these is formed by the two principal teeth,
the other by two very small incisors which are placed behind
the preceding.

Having studied the jaws and examined the arrangement
of the teeth, we should say a few words on the movements
which the lower jaw is able to execute. In
man, these movements are varied in character: the jaw
is lowered and raised; it can also be projected forwards[127]
and drawn backwards, or carried to the right or left side
by lateral movements. Owing to the different modes of
nutrition of animals, with which the shape of the teeth
is clearly correlated, being more specialized than in the
human species, the lower jaw is moved in a fashion less
varied and in the direction most suitable for the mastication
of the foods which form the aliment of the species considered.
Moreover, this is plainly shown in the skeleton by the shape
of the condyle of the lower jaw (see p. 122, different forms of
this condyle). In the carnivora, whose teeth, as we have
seen, are all cutting ones, the jaw rises and falls; the food
then is, if we consider the two jaws, cut as by the blades
of a pair of scissors. In the ruminants, the incisors exist
only in the lower jaw, but the molars are thick and well
developed; the food is ground by these latter as by millstones,
and the movements which favour this action are,
above all, the lateral. As for the rodents, in which the
incisors are formed for filing down and cutting through hard
resisting bodies, their lower jaw moves in the antero-posterior
direction, in such a way that the inferior incisors alternately
advance and recede beneath those of the upper jaw. The
free cutting border of these teeth effectively fulfils the function
to which they are destined; their constant wear preserves
and revivifies the chisel edge which characterizes
them, without leading to their destruction, for the incisors
in rodents are of continuous growth.

THE SKULL OF BIRDS

The Skull of Birds (Fig. 65).—If, because it is less
important from the artistic point of view, we do not consider
it necessary to describe in detail the skull of birds,
we yet think it useful to indicate, in their general lines, the
peculiarities it presents.

Fig. 65.—Skull of the Cock: Left Lateral Surface.

1, Occipital bone; 2, parietal bone; 3, frontal bone; 4, ethmoid bone;
5, cavity of the tympanum; 6, quadrate bone; 7, superior maxillary
bone; 8, malar bone; 9, nasal bone; 10, 10, intermaxillary bone; 11,
nasal orifice; 12, os unguis or lachrymal bone; 13, inferior maxillary bone.

In this group the skull is generally pear-shaped; to the
cranium, of which the bones are arranged in such a way
as to give it a form more or less spherical, succeeds a face
more or less elongated, according as the bill is more or less
developed.

In general, the bones of the skull coalesce very early, with[128]
the result that it is only in very young individuals that we
can determine their presence.

We find the skull to consist of an occipital bone, two
parietals, a frontal, etc.; we will indicate but one detail in
connection with these bones: it is the presence of a single
condyle for the articulation of the occipital bone with the
atlas. We also note the quadrate bone, which is situated on
the lateral part of the cranium, is movable on this latter,
and acts as an intermediary between it, the bones of the face,
and the lower jaw. The quadrate bone is regarded as a
detached portion of the temporal; on the signification of
this we do not now propose to dwell.

On the anterior portion of the face we find the nasal bones,
which, articulating with the frontal on one side, circumscribe,
on the other, the posterior border of the nares. The nasal
bone of the one side is separated from that of the opposite by
the intermaxillary or premaxillary bone, which forms the
skeleton of the superior mandible.

The superior maxillaries, which are rudimentary, are
situated on the lateral parts, and prolonged backward by an
osseous style which articulates with the quadrate bone;
this styloid bone, the homologue of the malar, is designated
by certain authors as the jugal or quadrato-jugal bone.

It is with the quadrate bone also that the inferior
maxillary articulates.

[129]

CHAPTER II

MYOLOGY

The first point to decide in commencing this study is the
order in which we shall consider the different muscles which
we have to examine. It must not be forgotten that in the
present work we compare the organization of animals with
that of man, which we already know, and that it is on the
construction of this latter that, in these studies, the thought
must at each instant be carried back in order to establish
this comparison. Now, the general tendency which we
notice in our teaching of anatomy, when one regards the
region of the trunk in the human figure (a living model or
a figure in the round), is first to consider the anterior aspect.
It is the latter that, for this reason, we study at the very
beginning; we next deal with the posterior surface of the
trunk, because it is opposite; lastly, the lateral surfaces,
because they unite with the preceding surfaces, the one to
the other.

In studying an animal, it is usually by one of its lateral
aspects that one first observes it; it is, in fact, by these
aspects that it presents its greatest dimensions, and that the
morphological characters as a whole can be more readily
appreciated. Hence, possibly, the order of description
adopted in most texts, or in the figures which accompany
them. The first representation of the human figure as a
whole, in a treatise on anatomy, represents the anterior
aspect; the first view of the horse as a whole, in a treatise
on veterinary anatomy, for example, is, on the other hand,
a lateral view.

[130]We break with this latter custom, and, without taking into
account the tendency above indicated, we will commence
our analysis with the study of the aspect of the trunk,
which corresponds to the anterior aspect of the same region
in man.

The first muscles usually presented for study to artists
being the pectorals, it is their homologues that we will first
describe here. We will afterwards describe the abdominal
region, then the muscles which occupy the dorsal aspect
of the trunk. With regard to the lateral surfaces, they will
be found, by this fact alone, almost completely studied,
since the muscles of the two preceding (back and abdomen),
spreading out, so to speak, over them, contribute to their
formation. Nothing further will remain but to incorporate
with them the muscles of the shoulder; but these will be
studied in connection with the anterior limbs, from which
they cannot be separated.

The neck, in man, may be considered in an isolated fashion,
because, on account of its narrowness in proportion to the
width of the shoulders, it is clearly differentiated from the
trunk; for this reason we combine the study of it with
that of the head. In animals, because of the absence or
slight development of the clavicles, the neck is generally
too much confounded with the region of the shoulders to
make it legitimate to separate it from that region in too
marked a fashion. It will, accordingly, be considered next.

We will then undertake the study of the muscles of the
limbs, and end with the myology of the head.

[131]

THE MUSCLES OF THE TRUNK

We shall divide them into muscles of the thorax, of the
abdomen, and of the back.

Muscles of the Thorax

The Pectoralis Major (Fig. 66, 1, 2; Fig. 67, 3, 4;
Fig. 68, 7; Fig. 69, 10; Fig. 70, 11).—Further designated
by the name of superficial pectoral, this muscle is described
in treatises on veterinary anatomy as formed of two portions:
an anterior one, called the sterno-humeral muscle;
the other, situated below and behind the preceding, bearing
the name of sterno-aponeurotic.

It occupies the region of the breast, and, as a whole, it
takes origin from the median portion of the sternum, from
which it is directed towards the arm and forearm.

The anterior portion (sterno-humeral muscle)—thick,
forming an elevation under the skin, and really constituting
the pectoral region—is directed downwards and outwards
to be inserted into the anterior margin of the humerus—that
is to say, to the ridge which limits in front the spiral
groove of this bone.

The other part (sterno-aponeurotic muscle) is situated
more posteriorly, and corresponds to the region known in
veterinary anatomy as the inter-fore-limb space, which is
limited laterally on each side by the superior portion of
the forearm, of which the point of junction with the trunk
bears the name ars. Arising from the sternum, as we
have above indicated, this portion is directed outwards,
to be joined with the terminal aponeurosis of the sterno-humeral,
and with that which covers the internal surface
of the forearm.

All things considered, the sterno-humeral muscle may be
regarded as the representative of the upper fibres of the
great pectoral of man, of which the attachments, owing to
the more or less complete absence of the clavicle in the
domestic mammals, the fibres must be concentrated on the[132]
sternum; the sterno-aponeurotic portion then representing
the inferior fasciculæ of the same muscle.

Fig. 66.—Myology of the Horse: Anterior Aspect of the Trunk.

1, Pectoralis major (sterno-humeral); 2, pectoralis major (sterno-aponeurotic);
3, mastoido-humeralis; 4, point of the shoulder; 5, sterno-mastoid
or sterno-maxillary: 6, inferior portion of the platysma myoides
of the neck, divided; 7, triceps cubiti; 8, brachialis anticus; 9, radialis
(anterior extensor of the metacarpus); 10, scapular region.

The great pectoral muscle of one side is separated from
that of the opposite side along the median line, and especially
above and in front, by a groove which is more or less
deep, according as the muscles are more or less developed.
At the bottom of this groove, suggestive of that which
exists in the corresponding region in man, is found, as in
this latter, the median portion of the sternum.

The preceding description particularly applies to the
arrangement which the great pectoral presents in the horse;
in other animals it is marked by some distinctive characters.
In the pig, it is inserted into the sternum as far only as the
level of the third costal cartilage; in the ox and sheep, it[133]
extends as far as the sixth; in the dog, it is attached to the
two first sternal pieces only—that is to say, as far as the
third costal cartilage. Moreover, in the latter, as in the
cat, the two portions which we have indicated are less
readily distinguished.

The great pectoral, by its contraction, draws the
fore-limb towards the middle line—that is to say, adducts
it.

The Pectoralis Minor (Fig. 67, 6; Fig. 68, 8; Fig. 69,
11; Fig. 70, 12, 26).—This muscle, also called the deep
pectoral, is, in animals, larger than the superficial pectoral,
therefore certain authors prefer to give to this muscle and
the preceding one the names of deep and superficial pectoral
respectively. This nomenclature is evidently legitimate,
and conforms more to reality, since it does not bring in
the notion of dimensions which here is found in contradiction
to nomenclature; but, in order to establish more
clearly the parallelism with the corresponding muscles in
man, we think it better, nevertheless, to give them the
names by which it has been customary to designate them
in connection with the latter.

We will recall at the outset that the lesser pectoral
muscle in man is completely covered by the great. In
animals this is not the case; the lesser pectoral being
very highly developed, projects beyond the great pectoral
posteriorly, and occupies to a greater or less extent the
inferior surface of the abdomen.

It also consists of two parts: one anterior, which we
designate by the name of sterno-prescapular; the other,
posterior, bearing that of sterno-humeral.[20]

The sterno-prescapular muscle, being covered by the
sterno-humeral, has little interest for us. It arises from[134]
the sternum, and is directed towards the angle formed by
the junction of the scapula and humerus; then it is reflected
upwards and backwards, to terminate on the
anterior margin of the shoulder by insertion into the
aponeurosis, which covers the supraspinatus muscle.

We can, especially in the horse after removal of the skin,
recognise it, at the level of this region, in the interspace
limited by the superficial muscles (Fig. 70, 26).

In the dog and cat this portion of the muscle does
not exist. The other division of the muscle, the sterno-trochinian,
is more interesting. It arises from the abdominal
aponeurosis and the posterior part of the sternum;
hence it passes forward, turns under the superficial pectoral,
and is inserted into the lesser tuberosity (trochin) of the
humerus.

In the pig, dog, and cat, it is inserted into the greater
tuberosity (trochiter) of the bone of the arm.

The superior border of this muscle is in relation with
a superficial vein, which is distinctly visible in the horse—the
subcutaneous thoracic vein, which in this animal is
called the vein of the spur.

The sterno-humeral muscle, in contracting, draws the
shoulder and the whole anterior limb backwards.

Serratus Magnus (Fig. 67, 2;
Fig. 69, 8; Fig. 70, 9).—This
muscle, which is situated on the lateral aspect of
the thorax, is covered to a considerable extent by the
shoulder, the posterior muscular mass of the arm, and by
the great dorsal muscle.

It arises by digitations from the external surface of the
dorsal vertebræ; from the first eight in the horse, ox, and
dog.

[135]

Fig. 67.—Myology of the Horse: Inferior Aspect of the Trunk.

1, Anterior extremity of the sternum; 2, point of the shoulder and
inferior portion of the mastoido-humeral muscle; 3, pectoralis major
(sterno-humeral); 4, pectoralis major (sterno-aponeurotic); 5, point of
the elbow; 6, pectoralis minor (sterno-trochinian); 7, serratus magnus;
8, external oblique; 9, sheath of the rectus abdominis; 10, linea alba;
11, the umbilicus; 12, external oblique divided in order to expose the
rectus abdominis; 13, rectus abdominis.

The muscular bundles, converging as they proceed, towards
the scapula, pass under this bone, to be inserted
into the superior portion of the subscapular fossa, near[136]
the spinal border. The inferior portion of its posterior
digitations is visible in the ox and in the horse; these
digitations are less visible in the pig. They are not seen
at all in the dog (Fig. 68) or cat, for in these animals the
great dorsal muscle covers them completely.

The great serratus muscle, by the position which it
occupies and the arrangement that it presents, forms with
the corresponding muscle of the opposite side a sort of
girth, which supports the thorax, and at the same time
helps to fix the scapula against the latter.

When it contracts, in taking its fixed point at the ribs,
it draws the superior portion of the scapula downwards and
backwards in such a way that this bone has its inferior
angle directed forwards and upwards. If it takes its fixed
point at the shoulder, it then acts on the ribs, raises them,
and so becomes a muscle of inspiration.

Because of the connections of the serratus magnus with the
levator anguli scapulæ, some authors consider it as united
with the latter. But as the latter muscle is visible only
in the region of the neck (see p. 157), and as it is separately
described in man, we prefer to distinguish them from one
another. We shall recall the connections to which we
have just made allusion when describing the cervical
region.

Muscles of the Abdomen

The abdominal wall is, as in man, formed by four large
muscles: the external oblique, the internal oblique, and
the transversalis, which form the lateral walls, and the
rectus abdominis, situated on each side of the middle
line of the abdomen. This latter, because of the general
direction of the trunk in quadrupeds, has its superficial
surface directed downwards.

The arrangement of these muscles closely corresponds to
that which we find in the human species.

The External Oblique Muscle (Fig. 67, 8, 12; Fig. 68, 5;
Fig. 69, 9; Fig. 70, 10).—This muscle arises, by digitations,
from a number of ribs, which varies according to the species,
the number of the ribs being itself variable for each of them,[137]
as we pointed out in connection with the osteology of the
thorax. Indeed, the great oblique arises from the eight or
nine posterior ribs in the dog and the ox, and from the
thirteen or fourteen posterior in the horse. It is attached,
besides, to the dorso-lumbar aponeurosis.

These attachments are arranged in a line directed obliquely
upwards and backwards, and the first digitations—that is
to say, the most anterior ones—dovetail with the posterior
digitations of origin of the great serratus muscle.

The fleshy fibres are directed downwards and backwards,
and terminate in an aponeurosis which covers the inferior
aspect of the abdomen, and proceeds to form the linea alba
by joining with that of the muscle of the opposite side,
and also to be inserted into the crural arch.

This aponeurosis of the external oblique is covered by
an expansion of elastic fibrous tissue, which doubles it externally,
and which is known as the abdominal tunic. This
latter is further developed as the organs of the digestive
apparatus are more voluminous, and their weight, consequently,
more considerable. For this reason, in the
large herbivora, as the ox and the horse, this tunic is extremely
thick, whereas in the pig, cat, and dog it is, on the
contrary, reduced to a simple membrane. Indeed, in these
latter, the abdominal viscera being less developed, the
inferior wall of the abdomen does not require so strong a
fibrous apparatus for supporting them. The great oblique,
when it contracts, compresses the abdominal viscera in all
circumstances under which this compression is necessary;
it also acts as a flexor of the vertebral column.

The Internal Oblique Muscle.—This muscle, which is
covered by the preceding, arises from the anterior superior
iliac spine (external angle in ruminants and solipeds) and
the neighbouring parts. From this origin its muscular
fibres, the general direction of which is opposite to that of
the fibres of the external oblique, diverging, proceed to
terminate in an aponeurosis, which contributes to the
formation of the linea alba, and to be attached superiorly
to the internal surface of the last costal cartilages. It
has the same action as the great oblique. What it presents[138]
of special interest is the detail of form which it determines
in the region of the flank; this detail is the cord of the flank.
It is characterized by an elongated prominence which,
starting from the iliac spine, is directed obliquely downwards
and forwards, to terminate near the cartilaginous
border of the false ribs.

Often very apparent in the ox, and still more so in the
cow, the cord in question contrasts with the depression
which surmounts it; this depression is situated below the
costiform processes of the lumbar vertebræ, and is called
the hollow of the flank. It is so much the more marked
as the mass of the intestinal viscera is of greater weight.

We sometimes meet with a case of the presence of this
hollow in the horse. But when in the latter, the flank
is well formed, the hollow is scarcely visible, and the cord
but slightly prominent. It is only in emaciated subjects
that these details are found clearly marked.

Transversalis Abdominis.—This muscle being deeply
situated does not present any interest for us. We will,
however, point out, in order to complete the series
of muscles which form the abdominal wall, that the
direction of its fibres is transverse, and that they extend
from the internal surface of the cartilages of the false
ribs, and the costiform processes of the lumbar vertebræ
to the linea alba.

The Rectus Abdominis (Fig. 67, 13; Fig. 68, 6).—This
muscle, enclosed, as it is in man, in a fibrous sheath
(Fig. 67, 9) formed by the aponeuroses of the lateral
muscles of the abdomen, is a long and wide fleshy band,
which, as in the human species, reaches from the thorax to
the pubis.

What distinguishes it in quadrupeds is that there are
costal attachments which extend further on the sternal
surface of the thorax, and the number of its aponeurotic
insertions, which, in general, is more considerable. These
are, indeed, six or seven in number in the pig and in
ruminants, and about ten in the horse.

It is true that we may find but three in the cat and
dog; still, we often find as many as six. These intersections[139]
are not marked on their exterior by transverse grooves,
such as we find in the human species in individuals with
delicate skin and whose adipose tissue is not very much
developed.

The rectus abdominis is covered, in its anterior portion,
by the sterno-trochinian muscle (posterior segment of the
small pectoral). In contracting, this muscle brings the
chest nearer the pelvis, and as a result flexes the vertebral
column. It also contributes to the compression of the
abdominal viscera.

Pyramidalis Abdominis.—This unimportant little
muscle, which in man is situated at the lower part of the
abdomen, extends from the pubis to the linea alba. It is
not present in the domestic animals.

We consider it interesting, however, to point out, although
the fact is not a very useful one as regards external form,
that this muscle is distinctly developed in marsupials.

We know that in the opossum, the kangaroo, and the
phalanger fox, the young are brought forth in an entirely
incomplete state of development, and that, during a certain
period, they are obliged to lodge in a pouch which is placed
at the lower part of the abdomen of the mother. Now,
this pouch contains the mammary glands; but the young,
being too feeble to exercise the requisite suction, the
pyramidal muscles come to their assistance. These muscles,
in contracting, approximate to one another two bones which
are placed above the pubis, the (so-called) marsupial bones
(see Fig. 80); by their approximation the bones in question,
which are placed behind and on the outer side of the
mammary glands, compress the latter, and thus is brought
about the result which the little ones, on account of their
feebleness, would, without that intervention, be incapable
of obtaining for themselves.

[140]

Muscles of the Back

Trapezius (Fig. 68, 1, 2; Fig. 69,
1, 2; Fig. 70, 1, 2).—This
muscle, more or less well developed, according to the
species, is divided into two portions, of which the names
indicate the respective situations—a cervical and a
dorsal.

These two parts, considered in the order in which we find
them, take their origin from the superior cervical ligament
and from the spinous processes of the first dorsal vertebræ.
From these different points the fibres are directed towards
the shoulder; the anterior are, consequently, oblique
downwards and backwards, and the posterior are directed
downwards and forwards. They are inserted into the
scapula in the following manner: the fibres of the dorsal
portion are attached to the tuberosity of the spine; those
of the cervical region are also fixed into the same spine,
but into a considerably larger surface.

The cervical portion occupies, in the region of the neck,
an area relatively smaller than the corresponding portion
of the trapezius in man. This diminished degree of development
results from the absence, complete, or nearly
so, of the clavicle in the animals which we are now considering.
We remember, that the trapezius of man is partly
inserted into the clavicle, and the disappearance of this
latter cannot fail to bring modifications in the general disposition
of the corresponding portion of the muscle. There
results a disconnection of this latter, and it becomes
united to other muscular fibres to form a muscle with
which we shall soon have to deal—the mastoido-humeral
(see p. 150).[141]

Fig. 68.—Myology of the Dog: Superficial Layer of Muscles.

1, Trapezius, cervical portion; 2, trapezius, dorsal portion; 3,
superior outline of the scapula; 4, latissimus dorsi;
5, external oblique muscle; 6, rectus abdominis; 7, pectoralis major of the right side; 8, pectoralis minor (sterno-trochinian);
9, 9, mastoido humeral muscle; 10, tendinous intersection, at the level of which is found a rudimentary
clavicle; 11, sterno-mastoid muscle; 12, infrahyoid muscles; 13, omo-tracheal or acromio-tracheal muscle;
14, splenius; 15, levator anguli scapulæ; 16, deltoid muscle, spinal portion; 17, deltoid, acromial portion; 18, superior
extremity of the humerus; 19, supraspinatus; 20, infraspinatus; 21, biceps cubiti; 22, brachialis anticus; 23, triceps
cubiti, long head; 24, triceps cubiti, external head; 25, olecranon process; 26, radialis (anterior extensor of the metacarpus);
27, iliac crest; 28, gluteus maximus; 29, gluteus medius; 30, biceps cruris; 31, semitendinosus; 32, semi-membranosus;
33, gastrocnemius; 34, tensor of the fascia lata; 35, sartorius; 36, fascia lata drawn up by the triceps;
37, the patella or knee-cap; 38, ischio-coccygeal muscle; 39, superior sacro-coccygeal; 40, lateral sacro-coccygeal;
41, inferior sacro-coccygeal.

As specific differences we should add that the trapezius
occupies a more or less extensive portion of the median
and superior regions of the neck; terminating at a considerable
distance from the head in the dog and horse, it,
on the contrary, approaches it in the pig and in ruminants.
The cervical portion, when it contracts, draws the scapula
upwards and forwards, the dorsal portion draws it upwards[142]
and backwards. When the trapezius acts as a whole the
scapula is raised.

The Latissimus Dorsi (Fig. 68, 4; Fig.
69, 5; Fig. 70, 5).—This
muscle arises by an aponeurosis, the so-called dorso-lumbar
aponeurosis, from the spinous processes of the last
dorsal vertebræ (the seven last in the dog, fourteen or
fifteen last in the horse), from the spinous processes of the
lumbar vertebræ, and from the last ribs. Its fleshy fibres
are directed downwards and forwards, being more oblique
in direction posteriorly, and pass on the inner side of the
posterior muscular mass of the arm, to be inserted into
the internal lip of the bicipital groove of the humerus,
or, a little lower down, on the median portion of the
internal surface of the same bone. This latter mode of
insertion is met with in the horse and the ox.

The anterior fibres cover the posterior angle of the scapula
(as in man, where the corresponding angle, but in this case
inferior, is covered by the same muscle), and, a little higher
up, are in their turn concealed by a portion of the dorsal
fibres of the trapezius. It covers, to a greater or less
extent, the great serratus muscle. These relations are
similar to those found in the human species.

We find that the fleshy fibres of the great dorsal are
prolonged more or less backwards if we examine this muscle
in the dog, the ox, the pig, and the horse. Indeed, the fibres
reach to the thirteenth rib in the dog and the cat (that is
to say, the last rib), the eleventh in the ox, tenth in the
pig, and twelfth only in the horse. We say ‘only’ in connection
with this last because it is necessary to remember
that the ribs are eighteen in number on each side of the
thorax of this animal, and that, accordingly, the fleshy
fibres of the great dorsal muscle are, relatively, of small
extent.

When this muscle contracts it flexes the humerus upon
the scapula, and helps to draw the whole of the anterior
limb backwards and upwards.[143]

Fig. 69.—Myology of the Ox: Superficial Layer of Muscles.

1, Trapezius, cervical portion; 2, trapezius, dorsal portion; 3, outline of the scapula; 4, spine of the scapula;
5, latissimus dorsi; 6, small posterior serratus; 7, prominence caused by the costiform processes of the lumbar vertebræ;
8, serratus magnus; 9, external oblique; 10, pectoralis major (sterno-humeral); 11, mastoido-humeralis; 12, atlas;
13, atlas; 14, parotid gland; 15, sterno-mastoid muscle; 16, infrahyoid muscles; 17, omo-trachelian or acromio-trachelian
muscle; 18, deltoid; 19, brachialis anticus; 20, triceps, long head; 21, triceps, external head; 22, olecranon;
23, radialis (anterior extensor of the metacarpus); 24, anterior iliac spine; 25, gluteus maximus; 26, gluteus medius;
27, biceps cruris; 28, semitendinosus; 29, gastrocnemius; 30, tensor of the fascia lata; 31, fascia lata covering the triceps
of the thigh; 32, patella; 33, ischio-coccygeal muscle; 34, superior ischio-coccygeal; 35, lateral ischio-coccygeal;
36, inferior ischio-coccygeal.

There is a muscular fasciculus which, because of its
relations with the muscle we have just been studying, is
known as the supplementary muscle of the latissimus dorsi.[144]
But as, on the other hand, this fasciculus is in relation
with the triceps, we shall in preference consider it in relation
with this latter (see p. 173).

The aponeurosis by which the great dorsal arises from
the vertebral column covers, as in man, the muscles which
occupy the grooves situated on each side of the spinous
processes—the spinal muscles or common muscular mass,
if we regard them as a whole (Fig. 70, 7); the sacro-lumbar
and the long dorsal muscles covering the transverse spinal,
if we consider them as distinct.

It would be superfluous to enter here into a detailed
examination of these muscles.

If they are but little developed the spinous processes
become prominent under the skin; if they are more so they
may by their thickness project beyond the level of these
processes, and these latter thus come to lie in a groove more
or less marked, which, on account of the division which is
determined by its presence, has caused the regions which
it occupies to be designated by the names double back and
double loins.

The muscles are extensors of the vertebral column.

Under the aponeurosis of the great dorsal muscle there is
found in man another muscle, the serratus posticus inferior,
which, on account of being deeply placed and its slight
thickness, offers nothing of interest in connection with
the study of external form. It arises from the spinous
processes of the three last dorsal vertebræ and those of
the three first lumbar; it then passes upwards and outwards,
and divides into four digitations, to be inserted into
the inferior borders of the four last ribs. We repeat that
it is covered by the great dorsal muscle.

In the pig, ox, and horse, which have this latter muscle
less developed in its posterior portion, the same small
serratus muscle, known as the posterior serratus, is visible
in the superficial layer of muscles (Fig. 69, 6; Fig. 70, 6).
The number of its digitations is more or less considerable
according to the species examined.

The Rhomboid Muscle (Fig. 70, 21).—In order to
make intelligible the position of the rhomboid in the superficial[145]
layer in quadrupeds, it appears to us necessary to
recall the anatomical characters of the muscle as found in
man. The rhomboid arises from the inferior portion of the
posterior cervical ligament, from the spinous process of the
seventh cervical vertebræ and the four or five upper dorsal;
thence passing obliquely downwards and outwards, it is inserted
into the spinal border of the scapula, into the portion
of this border which is situated below the spine; it sometimes
extends to the middle of the interval which separates
this latter from the superior internal angle of the same
bone.

The portion of the muscle which arises from the cervical
ligament and the seventh cervical vertebra is often separated
from the lower portion by a cellular interspace. For this
cause some anatomists have described the rhomboid as
consisting of two parts—the superior or small rhomboid
and the inferior or large rhomboid, on account of the position
occupied by each, and of their difference in volume.

This muscle can only be seen in the region of the back, in
the space limited externally by the spinal border of the
scapula, below by the latissimus dorsi, and internally by the
trapezius, which covers it in the rest of its extent. It is
not in this space that it is seen in certain quadrupeds. As
we pointed out in the section on osteology, the spinal border
of the scapula is short, and it seems to be due to this
limitation in length that the trapezius and the latissimus dorsi
muscle are, at this level, in contact the one with the other
in such a way that they fill up the interval in which the
rhomboid is seen in man.

In the horse we can partly see it in the superficial muscular
layer, but in the region of the neck only, at the superior
border of the shoulder. Indeed, as we have already pointed
out, the trapezius does not reach the occipital protuberance;
for this reason a part of the anterior portion of the rhomboid
may be seen—that is, the portion which corresponds to the
superior part of the human muscle.[146]

Fig. 70.—Myology of the Horse: Superficial
Layer of Muscles.

1, Trapezius, cervical
portion; 2, trapezius,
dorsal portion;
3, superior outline
of the scapula;
4, spine of the scapula;
5, latissimus dorsi
muscle; 6, small posterior
serratus; 7,
spinal muscles, or
common muscular
mass; 8, ribs; 9, serratus magnus; 10,
external oblique; 11, pectoralis major
(sterno-humeral); 12, pectoralis minor
(sterno-trochinian); 13, atlas; 14, parotid gland; 15, mastoido-humeralis; 16, point of the arm; 17, sterno-mastoid, or sterno-maxillary;
18, jugular groove; 19, infrahyoid muscles; 20, omo-trachelian muscle; 21, rhomboid; 22, splenius; 23, levator
anguli scapulæ; 24, deltoid; 25, supraspinatus; 26, terminal part of the sterno-prescapular, a portion of the small
pectoral muscle; 27, brachialis anticus; 28, triceps cubiti, middle or long head; 29, triceps cubiti, external head; 30, olecranon;
31, radial extensor (anterior extensor of the metacarpus); 32, anterior iliac spine; 33, anterior portion of the gluteus maximus—the
aponeurosis of the muscle has been divided in order to expose the gluteus medius; 34, posterior portion of the
gluteus maximus; 35, gluteus medius; 36, biceps cruris; 37, semitendinosus; 38, point of the buttock; 39, gastrocnemius;
40, tensor of the fascia lata; 41, triceps cruris; 42, ischio-coccygeal muscle; 43, superior sacro-coccygeal; 44, lateral sacro-coccygeal;
45, inferior sacro-coccygeal.

But whether it be covered by the trapezius, or, as we
find in the cat and dog, by the mastoido-humeral muscle
(see p. 150), which is very broad in this region, we do not
the[147]
less recognise its presence; and in the horse and ox, in particular,
it forms an elongated prominence beginning at the
level of the scapula, and tapering as it ascends, towards
the posterior part of the head.

Its origins are similar to those which we have already
described in the human rhomboid. It arises from the cervical
ligament and the spinous processes of the foremost
dorsal vertebræ; its fibres converge and pass to the scapula,
to be inserted into its superior or spinal border, or into the
internal surface of the cartilage of prolongation.

It assists in keeping the scapula applied to the thoracic
cage, and when it contracts, draws the scapula upwards
and forwards.

Taking its fixed point at the scapula, it acts on the neck
by its anterior fibres, and extends it.

We shall soon have occasion to mention this muscle again,
in connection with the study of the muscles of the neck.

The Cutaneous Muscle of the Trunk (Fig. 71).—Immediately
beneath the skin which covers the neck,
shoulders, and trunk is found a vast cutaneous muscle,
analogous to that which, in the human species, exists only
in the cervical region.

This thin muscle, whose function is to move the skin
which strongly adheres to it, and in this way to remove
from it material causes of irritation (insects, for example),
is of considerable thickness in the region of the trunk;
where it constitutes what certain authors have designated
by the name of panniculus carnosus. In this region it extends
from the posterior border of the shoulder to the thigh, and,
in the vertical direction, from the apices of the spinous
process of the dorso-lumbar vertebræ to the median line of
the abdomen.

Arising above from the supraspinous ligament of the dorso-lumbar
and sacral regions (except in the carnivora; see
below) by an aponeurosis which, posteriorly, covers the
muscles of the hind-limbs, its fibres are directed to the elbow,
on which they are arranged in two layers: a superficial,
which becomes continuous with the panniculus muscle of
the shoulder; and a deep, which passes on the inner[148]
side of the shoulder to be inserted into the internal surface
of the humerus; this latter exists only in the dog and
cat.

The most inferior fibres, behind, at the level of the
knee-cap form a triangular process which in the horse
receives the name of the stifle fold, from the name
veterinarians give to the region of the articulation of the
knee. This fold of skin, which commences on the antero-internal
surface of this region, is directed upwards, and
then forwards, to end by gradually disappearing over the
corresponding part of the abdomen.

Fig. 71.—Myology of the Horse: Panniculus Muscle of the Trunk.

In the same animal the muscular fibres of the panniculus
of the trunk arise along a line which connects the stifle-joint
to the withers, a line which is, consequently, oblique upwards
and forwards. Now, as the fleshy layer is thicker
than the aponeurosis, the result is that the mode of constitution
of this muscle can be recognised under the skin.
Indeed, we can see in some animals, occasionally very distinctly,
a slight elevation starting from the region of the
abdomen in the neighbourhood of the knee, and thence
directed obliquely upwards and forwards. This elevation
is produced by the fleshy portion of the panniculus.

In the carnivora, the panniculus of the trunk is not
attached to the supraspinous ligament; it is blended with
the same muscle of the opposite side, passing over the
spinous region of the vertebral column.

From this arrangement results a great mobility of the
skin which covers the back. Further, it explains why it is[149]
possible to lift up this skin along with the panniculus which
it covers, and to which it adheres, throughout the whole
extent of the dorso-lumbar column. As we pointed out
above, there is also a panniculus muscle of the shoulder
and one of the neck. We will deal with them when treating
of the regions to which those muscles belong.

The Coccygeal Region

As a sequel to the study of the muscles of the region of
the trunk very naturally comes the description of those which,
belonging to the region of the coccyx, are destined for the
movements of the caudal appendix, of which this latter
constitutes the skeleton. The muscles may not seem to
be of much importance with regard to external form, but,
as they form part of the superficial muscular layer, and
as the mass of each is seen in the form of the tail in some
animals (the lion, for example), they merit our attention for
a moment. A few lines will suffice to give an idea of them.
They are: the ischio-coccygeal, superior sacro-coccygeal, lateral
sacro-coccygeal, and inferior sacro-coccygeal.

The Ischio-coccygeal (Fig. 18, 38; Fig. 69,
33; Fig. 70, 42).—This
muscle, triangular in shape, better developed in the
carnivora than in the horse, arises from the spine of the
ischium, or from the supracotyloid crest, which replaces
this latter in the solipeds and the ruminants. Thence its
fleshy mass is directed upwards, expanding as it proceeds to
be inserted into the transverse processes of the first two
coccygeal vertebræ after insinuating itself between two of the
following muscles, the lateral and inferior sacro-coccygeal.

In the dog and cat, the muscle is in great part covered by
the great gluteal. In the ox, by a peculiar arrangement of
the corresponding region of the muscles of the thigh—an
arrangement which we will examine in connection with the
study of the latter—it is more exposed than in the horse,
and gives origin to an outline which corresponds to its general
form in the region situated immediately below the root of
the tail.

It is a depressor of the whole caudal appendix.

[150]The
Superior Sacro-coccygeal (Fig. 68, 39; Fig. 69, 34;
Fig. 70, 43).—The fasciculi which form this muscle
arise from the crest of the sacrum, and proceed thence to
end successively on the coccygeal vertebræ. It is in contact
in the middle line with the corresponding muscle of the
opposite side.

It raises the tail and inclines it laterally; if the muscle
of one side contracts at the same time as that of the other
the tail is elevated directly.

The Lateral Sacro-coccygeal (Fig. 68, 40; Fig. 69, 35;
Fig. 70, 44).—Situated on the lateral part of the caudal
region, this muscle arises, in the dog, from the internal border
of the iliac bone and the external border of the sacrum; in
the horse, it arises from the crest of the sacrum. It is inserted
into the coccygeal vertebræ.

It produces lateral movement of the tail.

The Inferior Sacro-coccygeal (Fig. 68, 41; Fig. 69, 36;
Fig. 70, 43).—This muscle, which is fairly thick, arises from
the inferior surface of the sacrum and the corresponding
surface of the sacro-sciatic ligament; it is inserted into
the coccygeal vertebræ.

It depresses the caudal appendix.

Muscles of the Neck

Mastoido-humeralis (Fig. 66, 3; Fig. 68, 9, 9, 10;
Fig. 69, 12; Fig. 70, 15).—One of the most important
muscles of the region of the neck in man is the sterno-cleido
mastoid. We recollect that, in its inferior part, it is divided
into two bundles, one of which arises from the manubrium
of the sternum, and the other from the inner third of the
clavicle, whence the denominations of the sternal portion
and clavicular portion. The muscle formed by the union
of these two portions is then directed obliquely outwards,
backwards, and upwards, to be inserted into the mastoid
process of the temporal bone and the two external thirds of
the superior curved line of the occipital bone.

Now, the animals which we are here considering have but
a rudimentary clavicle or are entirely without it. From[151]
the absence of this item of the skeleton there necessarily
result modifications in the arrangement of the muscles of
this region, which we must at the very outset explain, before
undertaking the special study of the muscle which is the
subject of the present paragraph.

Let us suppose, for the more definite arrangement of our
ideas, that the clavicle is altogether absent, although we
do find it in a rudimentary state in some animals and
completely developed in others (marmot, bat), and we will
proceed to indicate what this absence determines.

The great pectoral muscle in man arises in part from the
clavicle; this origin not being possible in animals which have
no clavicle, its attachments, as we have already seen, are
concentrated on the sternum. The trapezius in man similarly
arises in part from the clavicle; for the reasons above indicated
its clavicular fasciculi cannot exist in distinct form in
the animals which have no clavicle.

The sterno-cleido mastoid, whose inferior attachments we
mentioned above, cannot have a clavicular portion.

It is the same in the case of the deltoid, which, we know,
arises in part from the anterior bone of the shoulder.

Of the four muscles which have partial clavicular origins
in man, two are known to us in connection with animals—the
great pectoral and the trapezius. What has become
of the other two, the sterno-cleido mastoid and the
deltoid?

It is this which we now proceed to investigate. After a
fashion simple enough, but which it is necessary to describe,
the clavicular fasciculi of the trapezius and the corresponding
fasciculi of the sterno-cleido mastoid are united the one
to the other; the portion of the deltoid which in man
arises from the clavicle, by reason of the absence of this
latter, is also combined with the fleshy mass formed by
the preceding muscles. From this fusion results the
muscle known as the mastoido-humeral. This muscle,
which consists of a long fleshy band situated on the
lateral aspect of the neck, takes its origin, as a general
rule, from the posterior surface of the skull and the upper
part of the neck, from which it passes obliquely downwards[152]
and backwards, covering the scapulo-humeral angle—that is,
the region known as the point of the shoulder or arm—and
is inserted into the anterior border of the humerus, the
border which, limiting anteriorly the musculo-spiral groove,
forms a continuation of the deltoid impression. On account
of the regions with which it is related, Bourgelat named this
muscle the muscle common to the head, neck, and arm.

It is at the level of the scapulo-humeral angle that the
vestiges of the clavicle are found.

This bone is represented in some animals—the pig, ox,
and horse—by a single tendinous intersection, more or less
apparent, which extends transversely from the scapula to
the anterior extremity of the sternum. In the dog and the
cat, we find, besides, on the deep surface of the muscle and
at the level of this tendinous intersection, the rudiment of
the clavicle of which we made mention in the section on
Osteology (see p. 25).

It is beneath the intersection, the existence of which we
have just pointed out, that is found that portion of the
mastoido-humeral muscle which corresponds to the clavicular
fasciculi of the deltoid; that portion which is situated above
the intersection corresponds to the clavicular fibres of the
sterno-cleido-mastoid and of the trapezius.

The mastoido-humeral presents certain varieties in different
animals.

In the dog and the cat, this muscle, which is blended above
with the sterno-mastoid (see p. 153), to be inserted with it
into the mastoid process and the mastoid crest, covers the
neck for a considerable extent from the superior curved line
of the occipital bone to which it is attached, to the trapezius
with which it unites posteriorly, but from which it separates
below. Between these two extreme points of its superior
portion it is attached to the cervical ligament.

In the pig and in ruminants, in which the trapezius
approaches more closely to the head, the mastoido-humeral
occupies, in consequence, a less extent of the cervical region.

In the horse, the mastoido-humeral neither covers the
neck nor joins the trapezius; indeed, we have already
shown that it is separated by a considerable distance from[153]
the head. In the limited interval between these two
muscles a part of the rhomboid and parts of other muscles
are seen with which we shall soon be occupied.

This muscle, as regards the horse, is described by some
anatomists as consisting of two parts: one anterior, or
superficial; the other posterior, or deep. In reality, the
first only corresponds to the mastoido-humeral, which
we are considering; the posterior may be more exactly
regarded as representing a special muscle of quadrupeds,
but which is here a little deformed, the omo-trachelian (see
p. 155).

When the mastoido-humeral contracts, taking its fixed
point above, it acts as an extensor of the humerus, and
carries the entire fore-limb forwards. If it takes its fixed
point below—that is to say, at the humerus—it inclines
the head and neck to its own side. If it contracts at the
same time as the mastoido-humeral of the opposite side,
then the head and the neck are carried into the position of
extension.

The Sterno-mastoid (Fig. 66, 5; Fig. 68, 11; Fig. 69, 15;
Fig. 70, 17).—Having described the clavicular portion of
the sterno-cleido-mastoid in connection with the mastoido-humeral,
because it forms a part of the latter, we have,
in order to complete the homologies of this muscle, to study
now that which corresponds to its sternal portion. This is
the sterno-mastoid muscle. In all the quadrupeds with which
we are here concerned this muscle arises from the anterior
extremity of the sternum; narrow and elongated in form,
it passes towards the head in a direction parallel to the
anterior border of the mastoido-humeral, from which it is
separated by an interspace which, along its whole length,
lodges superficially the jugular vein; hence the name of
jugular groove, which is given to this part of the neck
(Fig. 10, 18).

It is inserted, in the case of the dog and cat, into the
mastoid process, where it is united with the mastoido-humeral;
in the ox it is divided into two portions—one
which goes to the base of the occipital bone, the other
passing in front of the masseter is by the medium of the[154]
aponeurosis of this latter attached to the zygomatic crest.
This latter part is considered by some writers as forming
a portion of the panniculus muscle of the neck.

In the horse it is attached to the angle of the lower jaw
by a tendon, which an aponeurosis that passes under the
parotid gland binds to the mastoido-humeral muscle and
the mastoid process.

By reason of this insertion into the jaw, in the case of
the solipeds, this muscle is further named the sterno-maxillary.

When it contracts, it flexes the head, and inclines it
laterally. This movement is changed to direct flexion when
the two sterno-mastoid muscles contract simultaneously.

In man, the sterno-cleido-mastoid and the trapezius
leave a triangular space between them, which, being limited
inferiorly by the middle third of the clavicle, is known as
the supraclavicular region; this region, being depressed,
especially in its inferior part, has also been given the name
of supraclavicular fossa—popularly called the ‘salt-cellar.’

The muscles which form the floor of this region, passing
from above downwards, are: a very small portion of
the complexus, splenius, levator anguli scapulæ, posterior
scalenus, and anterior scalenus; then, crossing these latter,
and most superficial, is the omo-hyoid muscle.

An analogous region, but of only slight depth, exists in
quadrupeds; its borders are formed by the mastoido-humeral
and trapezius muscles.

It is not limited below by the clavicle—we know, indeed,
that this, or the intersection which represents it, belongs
to the mastoido-humeral muscle—but by the inferior portion
of the spine of the scapula.

It is of greater or less extent according to the species
considered.

In the dog, cat, pig, and ox, it is narrow, for the muscles
which bound it approach one another pretty closely. It has,
as in man, the form of a triangle, with the apex above.
In the horse it is much broader, and, contrary to the
arrangement which it presents in the human species, the
widest part is directed upwards.

[155]The muscles which we find there are, consequently, more
or less numerous. In the dog and cat they are: a portion
of a muscle which we do not normally meet with in man—the
omo-trachelian—then in a decreasing extent: supraspinatus,
levator anguli scapulæ and splenius.

In the pig: the omo-trachelian, supraspinatus, and the
terminal portion of the sterno-prescapular—the anterior
part of the lesser or deep pectoral muscle.

In the ox: the omo-trachelian only.

But in the horse we find the omo-trachelian, the supraspinatus,
and the terminal extremity of the sterno-prescapular;
then in a larger extent of area the levator anguli
scapulæ and the splenius; and, finally, the anterior portion
of the rhomboid.

Among the muscles which we have just enumerated are
some that we have already studied; these are the sterno-prescapular
and the rhomboid. We will examine the supraspinatus
muscle in connection with the region of the shoulder.

As to the scaleni muscles and the complexus, they are
deeply situated, whereas the omo-hyoid is visible in the
anterior region of the neck only.

There remain for us, accordingly, to examine, at the
present juncture, but the omo-trachelian, levator anguli
scapulæ, and splenius muscles.

The Omo-trachelian Muscle (Fig. 68, 13; Fig. 69, 17;
Fig. 70, 20).—Also called the acromio-trachelian, levator
ventri scapulæ,[21] the angulo-ventral muscle, and the
transverso-scapular,[22]
etc., this muscle is described by some hippotomists
as belonging to the mastoido-humeral, of which it then
forms its posterior or deep portion (see p. 153).

The omo-trachelian muscle is found in all mammalia,[156]
man alone excepted. It is, however, sometimes found in
the human being; but it then constitutes an anomaly.

In the dog, pig, and ox, it arises from the inferior part
of the spine of the scapula, in the region of the acromion, and
terminates on the lateral portion of the atlas.

In the cat it is attached besides to the base of the occipital
bone. It is visible in the space limited by the trapezius
and the mastoido-humeral, the direction of which it crosses
obliquely.

In the horse it appears to be blended in clearly defined
fashion with the mastoido-humeral. Attached below, like
this latter, to the anterior border of the humerus, it covers
the scapulo-humeral angle; and is attached by its upper
portion to the transverse processes of the first four cervical
vertebræ.

We remember that the transverse processes are often,
from their relation with the trachea, known as the tracheal
processes. Hence the word ‘trachelian,’ which forms part
of the name of the muscle with which we are now dealing.

By its contraction it helps to draw the anterior limb
forwards.

When this muscle, as an abnormality, exists in man, it
arises from the clavicle or the acromion process, traverses
the supraclavicular fossa, and is inserted into the transverse
processes of the atlas or axis, or of both these
vertebræ, or of the cervical vertebræ below these latter.
It is then known by the names of the elevator of the clavicle
or elevator of the scapula, and, finally, as the cleido-omo-transversalis
(Testut).[23]