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A MANUAL 


OF THE 


ANATOMY OF VERTEBRATED ANIMALS. 


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yah 


A MANUAL 


OF THE 


ANATOMY OF VERTEBRATED 
ANIMALS. 


BY 


THOMAS H. HUXLEY, LLD., F.RBS. 


LONDON: 
J. & A. CHURCHILL, NEW BURLINGTON STREET. 
q 1871. 


LONDON: PRINTED BY WILLIAM CLOWES AND SONS, STAMFORD STREET 
AND CHARING CROSS. 


PREFACE. 


THE present work is intended to provide students of com- 
parative anatomy with a condensed statement of the most 
important facts relating to the structure of vertebrated 
animals, which have hitherto been ascertained. Except in 
a very few cases, I have intentionally abstained from bur- 
dening the text with references ; and, therefore, the reader, 
while he is justly entitled to hold me responsible for any 
errors he may detect, will do well to give me no credit for 
what may seem original, unless his knowledge is sufficient 
to render him a competent judge on that head. 

About two-thirds of the illustrations are original, the 
rest * are copied from figures given by Agassiz, Bischoff, 
Burmeister, Busch, Carus, Dugés, Flower, Gegenbaur, 
Hyrtl, Von Meyer, Miller, Pander and D’Alton, Parker, 
Quatrefages, and Traquair. 

A considerable portion of the book has been in type for 

* Namely, Figures 1, 6, 10, 11, 12, 13, 15, 18, 23, 26, 28, 29, 30, 31, 


36, 39, 41, 42, 46, 50951, 54, 55, 56, 57, 58, 59, 60, 61, 75, 79, 82, 101, 
107, 108, 109, 110. 


vi PREFACE. 


some years; and this circumstance must be my excuse 
for appearing to ignore the views of several valued contem- 
poraries. J refer more especially to those contained in 
recently published works of Professors Flower and Gegen- 


baur. 


London, September, 1871. 


CONTENTS. 


CHAPTER I. 
PAGE 
A General View of the Organization of the Vertebrata—the 
Vertebrate Skeleton . : - = : : : 4 5 1 
CHAPTER II. 
The Muscles and the Viscera—A General View of the Organiza- 
tion of the Vertebrata : 6 é : c - 6 - 46 
CHAPTER III. 
The Provinces of the Vertebrata—The Class Pisces . 5 0 alile, 
CHAPTER IV. 
The Class Amphibia. 5 c : : ‘ : ¢ 4 elige 
CHAPTER V. 
The Classification and the Osteology of the Reptilia . - 5 IIE 
CHAPTER VI. 
The Classification and the Osteology of Birds ; : 4 eee 
CHAPTER VII. 
The Muscles and the Viscera of the Sauropsida . 5 5 » 299 


CHAPTER VIII. 


The Classification and Organization of the Mammalia . 5 . 319 


THE ANATOMY 


OF 


VERTEBRATED ANIMALS. 


CHAPTER I. 


A GENERAL VIEW OF THE ORGANIZATION OF THE VERTE- 
BRATA—THE VERTEBRATE SKELETON. 


The Distinctive Characters of the Vertebrata.—The Verte- 
brata are distinguished from all other animals by the circum- 
stance that a transverse and vertical section of the body 
exhibits two cavities, completely separated from one another 
bya partition. The dorsal cavity contains the cerebro-spinal 
nervous system; the ventral, the alimentary canal, the 
heart, and, usually, a double chain of ganglia, which passes 
under the name of the “sympathetic.” It is probable 
that this sympathetic nervous system represents, wholly 
or partially, the principal nervous system of the Annulosa 
and Mollusca. And, in any case, the central parts of 
the cerebro-spinal nervous system, viz. the brain and the 
spinal cord, would appear to be unrepresented among 
invertebrated animals. For these structures are the results 
of the metamorphosis of a part of the primitive epidermic 
covering of the germ, and only acquire their ultimate 
position, in the interior of the dorsal tube, by the develop- 
ment and union of outgrowths of the blastoderm, which 
are not formed in the Invertebrata.* 


* It is possible that an excep- tain resemblance to a vertebrate 
tion to this rule may be found in notochord; and the walls of the 
the Ascidians. ‘The tails of the pharynx are perforated, much as 
larvee of these animals exhibit an in Amphioxus. 
axial structure, which has a cer- 


2 THE ANATOMY OF VERTEBRATED ANIMALS, 


Again, in the partition between the cerebro-spinal and | 
visceral tubes, certain structures, which are not represented 
in invertebrated animals, are contained. During the em- 
bryonic condition of all vertebrates, the centre of the parti- 
tion is occupied by an elongated, cellular, cylindroidal mass 
—the notochord, or chorda dorsalis. And this structure per- 
sists throughout life in some Vertebrata; but, in most, it is 
more or less completely replaced by a jointed, partly fibrous 
and cartilaginous, and partly bony, vertebral column. 

In all Vertebrata, that part of the wall of the visceral tube 
which lies at the sides of, and immediately behind, the 
mouth, exhibits, at a certain stage of embryonic develop- 
ment, a series of thickenings, parallel with one another 
and transverse to the axis of the body, which may be five 
or more in number, and are termed the visceral arches. 
The intervals between these arches become clefts, which 
place the pharyngeal cavity, temporarily or permanently, 
in communication with the exterior. Nothing correspond- 
ing with these arches and-clefts is known in the IJnverte- 
brata. 

A vertebrated animal may be devoid of articulated limbs, 
and it never possesses more than two pairs. These are 
always provided with an internal skeleton, to which the 
muscles moving the limbs are attached. The limbs of 
invertebrated animals are commonly more numerous, and 
their skeleton is always external. 

When invertebrated animals are provided with masti- 
catory organs, the latter are either hard productions of the 
alimentary mucous membrane, or are modified limbs. Ver- 
tebrated animals also commonly possess hard productions 
of the alimentary mucous membrane in the form of teeth ; 
but their jaws are always parts of the walls of the parietes 
of the head, and have nothing to do with limbs. 

All vertebrated animals have a complete vascular system. 
In the thorax and abdomen, in place of a single peri- 
visceral cavity in communication with the vascular system, 
and serving as a blood-sinus, there are one or more serous 
sacs. These invest the principal viscera, and may or may 


THE DEVELOPMENT OF THE VERTEBRATA. 3 


not communicate with the exterior—recalling, in the latter 
ease, the atrial cavities of Mollusca. 

In all Vertebrata, except Amphioxus, there is a single 
valvular heart, and all possess a hepatic portal system; the 
blood of the alimentary canal never being wholly returned 
directly to the heart by the ordinary veins, but being more 
or less completely collected into a trunk—the portal vein, 
which ramifies through and supplies the liver. 


The Development of the Vertebrata.—The ova of Vertebrata 
have the same primary composition as those of other animals, 
consisting of a germinal vesicle, containing one or many 
germinal spots, and included within a vitellus, upon~ the 
amount of which the very variable size of the vertebrate 
ovum chiefly depends. The vitellus is surrounded by a 
vitelline membrane, and this may receive additional invest- 
ments in the form of layers of albumen, and of an outer, 
coriaceous, or calcified shell. 

The spermatozoa are always actively mobile, and, save in 
some rare and exceptional cases, are developed in distinct 
individuals from those which produce ova. 

Impregnation may take place, either subsequently to the 
extrusion of the egg, when, of course, the whole development 
of the young goes on outside the body of the oviparous 
parent; or it may occur before the extrusion of the egg. 
In the latter case, the development of the egg in the interior 
of the body may go no further than the formation of a patch 
of primary tissue ; as in birds, where the so-called cicatricula, 
or “tread,” which is observable in the new-laid egg, is of this 
nature. Or, the development of the young may be completed 
while the egg remains in the interior of the body of the 
parent, but quite free and unconnected with it; as in those 
vertebrates which are termed ovoviviparous. Or, the young 
may receive nourishment from its viviparous parent, before 
birth, by the close apposition of certain vascular appendages 
of its body to the walls of the cavity in which it undergoes 
its development. 

The vascular appendages in question constitute the chief 


4 THE ANATOMY OF VERTEBRATED ANIMALS. 


part of what is called the placenta, and may be developed from | 
the umbilical vesicle (as in Mustelus among Sharks), or from 
the allantois and chorion (as in most mammals). At birth, 
they may be either simply detached from the substance of 
the parental organism, or a part of the latter may be thrown 
off along with them and replaced by a new growth. In 


Fig. 1.—Diagrammatic section of the pregnant uterus of a deciduate 
placental mammal (Homo): wu, uterus; 7, Fallopian tube; c, neck 
of the uterus ; du, uterine decidua; ds, decidua serotina ; dr, decidua 
reflera ; z,2', villi; ch, chorion; am, amnion; nb, umbilical vesicle ; 
al, allantois. 


the highest vertebrates, the dependence of the young upon 
the parent for nutrition does not cease even at birth; but 
certain cutaneous glands secrete a fluid called milk, upon 
which the young is fed for a longer or shorter time. 


When development takes place outside the body, it may 
be independent of parental aid, as in ordinary fishes; but, 
among some reptiles and in most birds, the parent supplies 


THE DEVELOPMENT OF THE VERTEBRATA, 5 


the amount of heat, in excess of the ordinary temperature 
of the air, which is required, from its own body, by the 
process of incubation. 


The first step in the development of the embryo is the 
division of the vitelline substance into cleavage-masses, of 
which there are at first two, then four, then eight, and so 
on. The germinal vesicle is no longer seen, but each 
cleavage-mass contains a nucleus. The cleavage-masses 
eventually become very small, and are called embryo-cells, 
as the body of the embryo is built up out of them. The 
process of yelk-division may be either complete or partial. 
In the former case, it, from the first, affects the whole 
yelk ; in the latter, it commences in part of the yelk, and 
gradually extends to the rest. The blastoderm, or em- 
bryogenic tissue in which it results, very early exhibits 
two distinguishable strata—an inner, the so-called mucous 
stratum (hypoblast), which gives rise to the epithelium of 
the alimentary tract; and an outer, the serous stratun 
(epiblast), from which the epidermis and the cerebro-spinal 
nervous centres are evolved. Between these appears the 
intermediate stratum (mesoblast), which gives rise to all the 
structures (save the brain and spinal marrow) which, in the 
adult, are included between the epidermis of the integu- 
ment and the epithelium of the alimentary tract and its 
appendages. 

A linear depression, the prinvitive groove (Fig. 2, A, c), 
makes its appearance on the surface of the blastoderm, and 
the substance of the mesoblast along each side of this groove 
grows up, carrying with it the superjacent epiblast. Thus 
are produced the two dorsal lamine, the free edges of which 
arch over towards one another, and eventually unite, so as 
to convert the primitive groove into the cerebro-spinal canal. 
The portion of the epiblast which lines this, cut off from 
the rest, becomes thickened, and takes on the structure of 
the brain, or Hncephalon, in the region of the head; and 
of the spinal cord, or Myelon, in the region of the spine. 
The rest of the epiblast is converted into the epidermis. 


THE ANATOMY OF VERTEBRATED ANIMALS. 


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THE F@TAL APPENDAGES. 7 


The part of the blastoderm which lies external to the dor- 
sal laminz forms the ventral lamine ; and these bend down- 
wards and inwards, at a short distance on either side of the 
dorsal tube, to become the walls of a ventral, or visceral, 
tube. The ventral lamine carry the epiblast on their outer 
surfaces, and the hypoblast on their inner surfaces, and thus, 
in most cases, tend to constrict off the central from the 
peripheral portions of the blastoderm. The latter, extend- 
ing over the yelk, in¢loses it in a kind of bag. This bag is 
the first-formed and the most constant of the temporary, 
or fetal, appendages of the young vertebrate, the wmbilical 
vesicle. 

While these changes are occurring, the mesoblast splits, 
throughout the regions of the thorax and abdomen, from 
its ventral margin, nearly up to the notochord (which has 
been developed, in the meanwhile, by histological differen- 
tiation of the axial indifferent tissue, immediately under 
the floor of the primitive groove), into two lamelle. One of 
these, the visceral lamella, remains closely adherent to the 
hypoblast, forming with it the splanchnopleure, and eventu- 
ally becomes the proper wall of the enteric canal; while 
the other, the parietal lamella, follows the epiblast, forming 
with it the somatopleure, which is converted into the parietes 
of the thorax and abdomen. The point of the middle line 
of the abdomen at which the somatopleures eventually unite, 
is the umbilicus. 

The walls of the cavity formed by the splitting of the 
ventral lamin acquire an epithelial lining, and become the 
great pleuroperitoneal serous membranes. 

The Fetal Appendages of the Vertebrata.—At its outer 
margin, that part of the somatopleure which is to be 
converted into the thoracic and abdominal wall of the 
embryo, grows up anteriorly, posteriorly, and laterally, 
over the body of the embryo. The free margins of 
this fold gradually approach one another, and, ulti- 
mately uniting, the inner layer of the fold becomes 
converted into a sac filled with a clear fluid, the Am- 
nion ; while the outer layer either disappears, or coa- 


8 THE ANATOMY OF VERTEBRATED ANIMALS. 


lesces with the vitelline membrane, to form the Chorion 
(Fig. 3). 


Fig. 3. 


weet 


Fig, 3.—Later stages of the development of the body of a Fowl than ~ 
those represented in Fig. 2.-E, embryo at the third day of incuba~ _ 
tion; g, heart; h, eye; 7, ear; , visceral arches and clefts; /, m, 
anterior and posterior folds of the amnion which have not yet united 
over the body ; 1, 2, 3, first, second, and third cerebral vesicles; la, _ 
vesicle of the third ventricle—F, embryo at the fifth day of incuba- 
tion. The letters as before, except m, 0, rudiments of the anterior _ 
and posterior extremities ; Am, amnion; All (the allantois, hanging 
down from its pedicle); Um, umbilical vesicle.—G, under-view of 
the head of the foregoing, the first visceral arch being cut away. 


Thus the amnion incloses the body of the embryo, but 
not the umbilical sac. At most, as the constricted neck, 


THE VISCERAL ARCHES AND CLEFTS. 9 


which unites the umbilical sac with the cavity of the future 
intestine, becomes narrowed and elongated into the vitelline 
duct, and as the sac itself diminishes in relative size, the 
amnion, increasing in absolute and relative dimensions, and 
becoming distended with fluid, is reflected over it (Fig. 1). 
-_A third fcetal appendage, the Allantois, commences as a 
single, or double, outgrowth from the under-surface of 
the mesoblast, behind the alimentary tract; but soon 
takes the form of a vesicle, and receives the ducts of 
the primordial kidneys, or Wolffian bodies. It is supplied 
with blood by two arteries, called hypogastric, which spring 
from the aorta; and it varies very much in its development. 
It may become so large as to invest all the rest of the 
embryo, in the respiratory, or nutritive, processes of which 
it then takes an important share. 

The splitting of the ventral lamine, and the forma- 
tion of a pleuroperitoneal cavity, appear to take place in 
all Vertebrata. Usually, there is a more or less distinct 
umbilical sac; but in fishes and Amphibia there is no 
‘amnion; and the allantois, if it is developed at all, remains 
very small in these two groups. 

Reptiles, birds, and mammals have all these fetal appen- 
dages. At birth, or when the egg is hatched, the amnion 
bursts and is thrown off, and so much of the allantois as 
lies outside the walls of the body, is similarly exuviated ; 
but that part of it which is situated within the body is very 
generally converted, behind and below, into the urinary 
bladder, and, in front and above, into a ligamentous cord, 
the wrachus, which connects the bladder with the front wall 
of the abdomen. The umbilical vesicle may either be cast 
off, or taken into the interior of the body and gradually 
absorbed. 


The majority of the visceral clefts of fishes and of many 
Amphibia remain open throughout life; and the visceral 
arches of all fishes (except Amphioxus), and of all Anyphibia, 
throw out filamentous or lamellar processes, which receive 
branches from the aortic arches, and, as branchic, subserve 


10 THE ANATOMY OF VERTEBRATED ANIMALS. 


respiration. In other Vertebrata all the visceral clefts | 
become closed and, with the frequent exception of the first, 
obliterated; and no branchiz are developed upon any of | 
the visceral arches. 


Tn all vertebrated animals, a system of relatively, or abso- 
lutely, hard parts affords protection, or support, to the softer 
tissues of the body. These, according as they are situated 
upon the surface of the body, or are deeper-seated, are called 
exoskeleton, or endoskeleton. 

The Vertebrate Endoskeleton.—This consists of connective 
tissue, to which cartilage and bone may be added in various 
proportions; together with the tissue of the notochord and 
its sheath, which cannot be classed under either of these 
heads. The endoskeleton is distinguishable into two inde- 
pendent portions—the one azial, or belonging to the head 
and trunk ; the other, appendicular, to the limbs. 

The awial endoskeleton usually consists of two systems of 
skeletal parts, the spinal system, and the cranial system, the 
distinction between which arises in the following way in the 
higher Vertebrata. 

The primitive groove is, at first, a simple straight depres- 
sion, of equal diameter throughout; but, as its sides rise, and 
the dorsal laminz gradually close over (this process com- 
mencing in the anterior moiety of their length, in the 
future cephalic region), the one part becomes wider than 
the other, and indicates the cephalic region (Fig. 4, A). The 
notochord, which underlies the groove, terminates in a point, 
at a little distance behind the anterior end of the cephalic 
enlargement, and indeed under the median of three dilata- 
tions which it presents. So much of the floor of the enlarge- 
ment as lies in front of the end of the notochord, bends 
down at right angles to the rest; so that the anterior en- 
largement, or anterior cerebral vesicle, as it is now called, lies 
in front of the end of the notochord; the median enlarge- 
ment, or the middle cerebral vesicle, above its extremity ; 
and the hinder enlargement, or the posterior cerebral 
vesicle, behind that extremity (Fig.4,D and E). Theunder- 


THE PROTOVERTEBRE. 11 


surface of the anterior vesicle lies in a kind of pit, in front 
of, and rather below, the apex of the notochord, and the 
pituitary gland is developed in connection with it. From 
the opposite upper surface of the same vesicle the pineal 
gland is evolved, and the part of the anterior cerebral vesicle 
in connection with which these remarkable bodies arise, 
is the future third ventricle. 

Behind, the posterior cerebral vesicle passes into the 
primitively tubular spinal cord (Fig. 4, A). Where it does 
so, the head ends, and the spinal column begins; but no 
line of demarcation is, at first, visible between these two, 
the indifferent tissues which ensheath the notochord pass- 
ing, without interruption, from one region to the other, and 
- retaining the same character throughout. 

The first essential differentiation between the skull and 
the vertebral column is effected by the appearance of the 
protovertebre. At regular intervals, commencing at the 
anterior part of the cervical region, and gradually extending 
backwards, the indifferent tissue on each side of the 
notochord undergoes a histological change, and gives rise 
to more opaque quadrate masses, on opposite sides of the 
notochord (Fig. 2, B, C). Hach pair of these gradually 
unite above and below that structure, and send arched pro- 
longations into the walls of the spinal canal, so as to con- 
stitute a protovertebra. 

No protovertebre appear in the floor of the skull, so 
that, even in this early stage, a clear distinction is drawn 
between the skull and the spinal column. 


The Spinal System—The protovertebre consist at first 
of mere indifferent tissue; and it is by a process of histo- 
logical differentiation within the protovertebral masses, 
that, from its deeper parts, one of ‘the spinal ganglia and 
a cartilaginous vertebral centrwm,—trom its superficial layer, 
a segment of the dorsal muscles, are produced. 

Chondrification extends upwards into the walls of the 
dorsal tube, to produce the newral arch and spine of each 
vertebra; and, outwards, into the wall of the thoracic and 


12 THE ANATOMY OF VERTEBRATED ANIMALS. 


Fig. 4. 


Fig. 4.—Successive stages of the development of the head of a Chick. 
I, II, II, first, second, and third cerebral vesicles ; Ia, vesicle of the 
cerebral hemisphere ; Jb, vesicle of the third ventricle; a, rudiments 
of the eyes and optic nerves; 3, of the ears; g, of the olfactory 


OSSIFICATION OF THE VERTEBRZ. 13 


organs; d, the infundibulum; e, the pineal gland; c, protoverte- 

bre ; i, notochord; 1, 2, 3, 4, 5, visceral arches; V, VII, VIII, the 

trigeminal, portio dura, and ninth and tenth pairs of cranial nerves; , 

the nasal process; /, the maxillary process ; «, the first visceral cleft. 

A, B, upper and under views of the head of a Chick at the end of the 

second day. C, side-view at the thirdday. D, side-view at seventy- 

five hours. E, side-view of the head of a Chick at the fifth day, 

which has been subjected to slight pressure. F, head of a Chick at 

the sixth day, viewed from below. 
abdominal part of the ventral tube, to give rise to the trans- 
verse processes and ribs. In fishes, the latter remain distinct 
and separate from one another, at their distal ends; but, in 
most reptiles, in birds, and in mammals, the ends of some 
of the anterior ribs, on both sides, unite together, and then 
the united parts coalesce in the middle line to form a median 
subthoracic cartilage—the sternum. 

When ossification sets in, the centra of the vertebre are 
usually ossified, in great measure, from ringlike deposits 
which closely invest the notochord; the arches, from two 
lateral deposits, which may extend more or less into the 
centrum. The vertebral and the sternal portions of a rib 
may each have a separate ossific centre, and become distinct 
bones; or the sternal parts may remain always cartilagin- 
ous. The sternum itself is variously ossified. 

Between the completely ossified condition of the verte- 
bral column and its earliest state, there are a multitude of 
gradations, most of which are more or less completely 
realised in the adult condition of certain vertebrated animals. 
The vertebral column may be represented by nothing but 
a notochord with a structureless, or more or less fibrous, 
or cartilaginous sheath, with or without rudiments of carti- 
laginous arches and ribs. Or there may be bony rings, or en- 
sheathing ossifications, in its walls; or it may have ossified 
neural arches and ribs only, without cartilaginous or osseous 
centra. The vertebre may be completely ossified, with very 
deeply biconcave bodies, the notochord remaining persistent 
in the doubly conical intervertebral substance; or, ossifica- 
tion may extend, so as to render the centrum concave on 
one surface and convex on the other, or even convex at each 
end, 


14 THE ANATOMY OF VERTEBRATED ANIMALS. 


Vertebre which have centra concave at each end have 
been conveniently termed amphicelous ; those witha cavity 
in front and a convexity behind, proceelous; where the 
position of the concavity and convexity is reversed, they are 
opisthoceelous. 

In the Mammalia, the centra of the vertebre are usually 
flat at each end, the terminal faces being discoidal epiphyses. 
developed from centres of ossification distinct from that of 
the centrum itself. 

The centra of the vertebree may be united together by 
synovial joints, or by ligamentous fibres—the intervertebral 
ligaments. The arches are connected by ligaments, and 
generally, in addition, by overlapping articular processes 
called zygapophyses, or oblique processes. 

In a great many Vertebrata, the first and second cervical. 
or atlas and amis, vertebre undergo a singular change; the 
central ossification of the body of the atlas not coalescing 
with its lateral and inferior ossifications, but either persist- 
ing as a distinct os odontoidewm, or ankylosing with the 
body of the axis, and becoming the so-called odontoid process 
of this vertebra. 

In Vertebrata with well-developed hind limbs, one or 
more vertebre, situated at the posterior part of the trunk, 
usually become peculiarly modified, and give rise to a 
sacrum, with which the pelvic arch is connected by the 
intermediation of expanded and ankylosed ribs. In front 
of the sacrum the vertebre are artificially classed as cervical, 
dorsal, and lumbar. The first vertebra, the ribs of which 
are connected with the sternum, is dorsal, and all those 
which lie behind it, and have distinct ribs, are dorsal. 
Vertebre without distinct ribs, between the last dorsal and 
the sacrum, are lumbar. Vertebrz, with or without ribs, in 
front of the first dorsal are cervical. 

The vertebre which lie behind the sacrum are caudal or 
coccygeal. Very frequently, downward processes of these 
vertebra inclose the backward continuation of the aorta, 
and may be separately ossified as swbcaudal, or chevron, 
bones. 


A SEGMENT OF THE SKELETON. 15 


A tolerably complete segment of the spinal skeleton may 
be studied in the anterior part of the thorax of a crocodile 
(Fig. 5). It presents a procelous vertebral centrum (C), united 
with which by the newrocentral suture is the newral arch, 
which rises into the neural spine (N.S.). Two processes, the 
prezygapophyses (Z), extend from the front part of the arch, 
and have flat articular surfaces turned dorsally. Two others 
of similar form, but having their articular surfaces turned 
yentrally, proceed from the posterior face of the neural 
arch, and are the postzygapophyses (Z’). By these, which are 


St Str 

Fig. 5A segment of the endoskeleton in the anterior thoracic region 
of the body of a Crocodile.— C, the centrum or body of the vertebra ; 
N.S, the neural spine ; Z, the prezygapophysis ; Z’, the postzygapo- 
physis; 7-t, the transverse process which articulates with the tuber; 
culum of the rib (t) ; Cp.t, that which articulates with the capitulum 
of the rib (Cp); V.r, the ossified vertebral rib; V.7’, the part of 
the vertebral rib which remains cartilaginous ; S¢.7, the sternal rib ; 
St, an artificially separated segment of the sternum; P.u, the uici- 
nate process. 


often called oblique, or articular, processes, the vertebra 
articulates with the corresponding processes of its pre- 
decessor or successor in the series. The transverse pro- 
cesses are two on each side, one superior and one inferior. 
The former (7.t) articulates with the tuberculum of the 
rib, the latter (Cp.t) with its capitulum. They may, there- 
fore, be called capitular and tubercular transverse processes 
respectively. Each rib is divided by an articulation into 


16 THE ANATOMY OF VERTEBRATED ANIMALS. 


a vertebral (V.r) and a sternal (St.r) part. The former re- | 


mains unossified for a considerable distance at its distal 


end (V.7’); the latter is more or less converted into car- | 


tilage bone. The proximal end of the vertebral rib bifur- 
cates into a tuberculum (t) and a capitulwm (Cp). The distal 
end of the sternal rib unites with the more or less ossi- 
fied but unsegmented cartilage, which forms the sternum 
(St). A cartilaginous, or partly ossified, uneinate process (P.u) 
projects from the posterior edge of the vertebral rib, over 
the intercostal space. The student will find it convenient 
to familiarise himself with the conception of such a spinal 
segment as this, as a type, and to consider the modifica- 
tions hereafter described with reference to it. 

In the majority of the Vertebrata, the caudal vertebre 
gradually diminish in size towards the extremity of the 
body, and become reduced, by the non-development of osse- 
ous processes or arches, to mere centra. But, in many fishes, 
which possess well-ossified trunk vertebrz, no distinct 
centra are developed at the extremity of the caudal region, 
and the notochord, invested in a more or less thickened, 
fibrous, or cartilaginous sheath, persists. Notwithstanding 
this embryonic condition of the axis of the tail, the superior 
and inferior arches, and the interspinous bones, may be 
completely formed in cartilage or bone. 

Whatever the condition of the extreme end of the spine 
of a fish, it occasionally retains the same direction as the 
trunk part, but is far more generally bent up, so asto form 
an obtuse angle with the latter. In the former case, the ex- 
tremity of the spine divides the caudal fin-rays into two 
nearly equal moieties, an upper and a lower, and the fish is 
said to be diphycercal (Fig. 6, A). In the latter case, the 
upper division of the caudal fin-rays is much smaller than 
the lower, and the fish is heterocercal (Fig. 6, B, C). 

In most osseous fishes the hypwral bones which support 
the fin-rays of the inferior division become much expanded, 
and either remain separate, or coalesce into a wedge- 
shaped, nearly symmetrical bone, which becomes ankylosed 
with the last ossified vertebral centrum, The inferior fin- 


ct 


THE TAILS OF FISHES. 


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Fig. 6. 


18 THE ANATOMY OF VERTEBRATED ANIMALS, 


rays are now disposed in such a manner as to give the tail | 
an appearance of symmetry with respect to the axis of the 
body, and such fishes have been called homocercal. Of these 
homocercal fish, some (as the Salmon, Fig. 6) have the 
notochord unossified, and protected only by bony plates 
developed at its sides. In others (as the Stickleback, 
Perch, &c.), the sheath of the notochord becomes completely 
ossified and united with the centrum of the last vertebra, 
which then appears to be prolonged into a bony wrostyle. 
The Cranial System—As has been stated, no protover- 
tebre appear on the floor of the skull; nor is there any 


( wired a i ~ 
| 


Fig. 7.—The cartilaginous cranium of a Fowl at the sixth day of in- 
cubation, viewed from below.—P, the pituitary space; tr, the tra- 
becule, uniting in front, in the bifurcated ethmovomerine plate; Qu, 
the quadrate cartilage ; Sc, the semicircular canals ; Co, the cochlea ; 
h, the notochord imbedded in the basilar plate. 


cranium, nor any developmental stage of a cranium, in 
which separate cartilaginous centres are known to occur in 
this region. 

On the contrary, when chondrification takes place, it — 
extends continuously forward, on each side of the notochord, 
and usually invests the anterior termination of that body, 
more or less completely, as a basilar plate. 


THE CRANIAL SKELETON. 19 


The basilar plate does not extend under the floor of the 
pituitary fossa, but the cartilage is continued forwards on 
each side of this, in the form of two bars, the trabecule 
cranii. In front of the fossa, the trabecule reunite and end 
in a broad plate, usually bifurcated in the middle line—the 
ethmovomerine plate. 

On each side of the posterior boundary of the skull, 
the basilar cartilage grows upwards, and meets with its 
fellow in the middle line, thus circumscribing the occipital 
foramen, and furnishing the only cartilaginous part of the 
roof of the skull; for any cartilaginous upgrowths which 
may be developed in the more anterior parts of the skull 
do not ordinarily reach its roof, but leave a wide, merely 
membranous space, or fontanelle, over the greater part of 
the brain. 

Before the skull has attained this condition, the organs 
of the three higher senses have made their appearance in 
pairs at its sides; the olfactory being most anterior, the 
ocular next, the auditory posterior (Fig. 4). 

Each of these organs is, primitively, an involution, or sac, 
of the integument; and each acquires a particular skeleton, 
which, in the case of the nose, is furnished by the ethmo- 
vomerine part of the skull; while, in that of the eyes, it 
appertains to the organ, is fibrous, cartilaginous, or osse- 
ous, and remains distinct from the skull. In the case of the 
ear, it is cartilaginous, and eventually osseous: whether 

-primitively distinct or not, it early forms one masswith the 
skull, immediately in front of the occipital arch, and often 
constitutes a very important part of the walls of the fully- 
formed cranium. 

The ethmovomerine cartilages spread over the nasal 
sacs, roof them in, cover them externally, and send down 
a partition between them. The partition is the proper 
ethmoid, the lamina perpendicularis of human anatomy; the 
posterolateral parts of the ethmovomerine cartilages, on 
each side of the partition, occupy the situation of the pre- 
frontals, or lateral masses of the ethmoid of human anatomy. 
The ingrowths of the lateral walls, by which the nasal 


20 THE ANATOMY OF VERTEBRATED ANIMALS. 


mucous membrane acquires a larger surface, are the tur- 
binals. . 

Riblike cartilaginous rods appear in the first, second. 
and, more or fewer, of the succeeding, visceral arches in all 
but the lowest Vertebrata. The upper ends of the first and 
second of these become connected with the auditory capsule, 
which lies immediately above them. 

The first visceral arch bounds the cavity of the mouth 
behind, and marks the position of the mandible or lower jaw. 
The cartilage which it contains is termed Meckel’s cartilage. 

The cartilagimous rod contained in the second visceral 
arch of each side is the rudiment of the hyoidean apparatus. 


Fig. 8.—Under-view of the head of a Fowl at the seventh day of in- 
cubation.—Ja, the cerebral hemispheres causing the integument to 
bulge; a, the eyes; g, the olfactory sacs; 4, the fronto-nasal process ; 
J, the maxillary process; 1, 2, the first and second visceral arches ; 
x, the remains of the first visceral cleft. 

Like the preceding, it unites with its fellow in the ventral 

median line, where the so-called “body ” of the hyoid arises. 
A ridge, continued forward from the first visceral arch 

to the olfactory sac (Fig. 4, F; Fig. 8,1), bounds the mouth 
on each side, and is called the mazillary process. A carti- 
laginous palato-pterygoid rod, developed in this process, 


THE FORMS OF THE SKULL. 21 


becomes connected with Meckel’s cartilage behind, and with 
the prefrontal cartilage in front. 

The maxillary process is, at first, separated by a notch 
corresponding with each nasal sac, from the boundary of 
the antero-median part of the mouth, which is formed hy 
the free posterior edge of a fronto-nasal process (Fig. 4, F; 
Fig. 8, &). This separates the nasal sacs, and contains the 
cartilaginous, ethmovomerine, anterior termination of the 
skull. The notch is eventually obliterated by the union of 
the fronto-nasal and maxillary processes, externally ; but it 
may remain open internally, and then gives rise to the pos- 
terior nasal aperture, by which the nasal cavity is placed in 
communication with that of the mouth. 


The General Modifications of the Vertebrate Skull. — The 
lowest vertebrated animal, Amphiowus, has no skull. In 
a great many fishes the development of the skull carries 
it no further than to a condition which is substantially 
similar to one of the embryonic stages now described ; that 
is to say, there is a cartilaginous primordial cranium, with 
or without superficial granular ossifications, but devoid of 
any proper cranial bones. The facial apparatus is either 
incompletely developed, as in the Lamprey; or, the upper jaw 
is represented, on each side, by a cartilage answering to the 
palato-pterygoid and part of Meckel’s cartilage, while the 
larger, distal portion of that cartilage becomes articulated 
with the rest, and forms the lower jaw. This condition is 
observable in the Sharks and Rays. In other fishes, and 
in all the higher Vertebrata, the cartilaginous cranium and 
facial arches may persist to a greater or less extent; but 
bones are added to them, which may be almost wholly mem- 
brane bones, as in the Sturgeon; or may be the result of 
the ossification of the cartilaginous cranium itself, from 
definite centres, as well as of the development of superim- 
posed membrane bones. 

The Osseous Brain-case-—When the skull undergoes com- 
plete ossification, osseous matter is thrown down at not 
fewer than three points in the middle of its cartilaginous 


22 THE ANATOMY OF VERTEBRATED ANIMALS. 


floor. The ossific deposit, nearest the occipital foramen, 
becomes the basi-occipital bone; that which takes place‘ in 
the floor of the pituitary fossa becomes the basisphenoid; 
that which appears in the reunited trabecule, in front of the 
fossa, gives rise to the presphenoid. Again, in front of, and 
outside, the cranial cavity, the ethmoid may be represented 
by one or more distinct ossifications. 

An ossific centre may appear in the cartilage on each 
side of the occipital foramen, and give rise to the ex-occipital; 
and above it, to form the swpra-occipital. The four occi- 
pital elements, uniting together more or less closely, com- 
pose the occipital segment of the skull. 

In front of the auditory capsules and of the exit of the 
third division of the fifth nerve, a centre of ossification 
may appear on each side and give rise to the alisphenoid ; 
which, normally, becomes united below with the basi- 
sphenoid. 

In front of, or above, the exits of the optie nerves, the 
orbitosphenoidal ossifications may appear and unite below 
with the presphenoid. 

In front of the occipital sezment, the roof of the skull is 
formed by membrane; and the bones which complete the two 
segments of which the basisphenoid and presphenoid form 
the basal parts, are membrane bones, and are disposed in 
two pairs. The posterior are the parietals, the anterior the 
frontals; and the segments which they complete are re- 
spectively called parietal and frontal. Thus the walls of the 
cranial cavity in the typical ossified skull are divisible into 
three segments—I. Occipital, II. Parietal, III. Frontal— 
the parts of which are arranged with reference to one 
another, the sensory organs and the exits of the first, 
second, fifth, and tenth pairs of cranial nerves (I., I1., V., 
and X.), in the manner shown in the annexed diagram * :— 


* The names of the purely which are preformed in cartilage 
membrane bones in this diagram _ are in smaller type, as BasispHE- 
are in large capitals, as PARI- nom. — 

ETAL; while those of the bones 


23 


THE TYPICAL BONY SKULL. 


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24 THE ANATOMY OF VERTEBRATED ANIMALS, 


The cartilaginous cases of the organs of hearing, or the 
periotic capsules, are, as has been said, incorporated with the — 
skull between the ex-occipitals and the alisphenoids—or, in 
other words, between the occipital and the parietal segments 
of the skull. Each of them may have three principal ossifi- 
cations of itsown. The one in front is the pro-otic ; the one 
behind and below, the opisthotic; and the one which liesabove, 
and externally, the epiotic. The last is in especial relation 
with the posterior vertical semicircular canal; the first with 
the anterior vertical semicircular canal, between which, and 
the exit of the third division of the fifth nerve, it lies. These 
three ossifications may coalesce into one, as when they con- 
stitute the petrosal and mastoid parts of the temporal bone 
of human anatomy; or the epiotic, or the opisthotic, or 
both, may coalesce with the adjacent supra-occipital and 
ex-occipitals, leaving the pro-otic distinct. The pro-otic is, 
in fact, one of the most constant bones of the skull in the 
lower Vertebrata, though it is commonly mistaken, on the 
one hand for the alisphenoid, and on the other for the 
entire petro-mastoid. Sometimes a fourth, pterotic ossifi- 
cation, is added to the three already mentioned. It lies on 
the upper and outer part of the ear-capsule between the 
pro-otic and the epiotic (see the figure of the cartilaginous 
cranium of the Pike, infra). 


In some Vertebrata the base of the skull exhibits a long 
and distinct splint-like membrane bone*—the parasphenoid, 
which underlies it from the basi-occipital to the pre- 


* Bones may be formed in two 
ways. They may be preceded by 
cartilage, and the ossific deposit 
in the place of the future bone 
may at first be deposited in the 
matrix of that cartilage; or the 
ossific deposit may take place, 
from the first, in indifferent, or 
rudimentary connective, tissue. 
In this case the bone is not pre- 
figured by cartilage. In the skulls 
of Elasmobranch fishes, and in 
the sternum and epicoracoid of 


Lizards, the bony matter is simply 
ossified cartilage, or cartilage bone. 
The parietal or frontal bones, on 
the other hand, are always devoid 
of cartilaginous rudiments, or, in 
other words, are membrane bones. 

In the higher Vertebrata the 
cartilage bones rarely, if ever, re- 
main as such; but the primitive 
ossified cartilage becomes, in great 
measure, absorbed and replaced 
by membrane bone, derived from 
the perichondrium, 


THE BONES OF THE FACE. 25 


sphenoidal region. In ordinary fishes and Amphibia, this 
bone appears to replace the basisphenoid and presphenoid 
functionally, while in the higher Vertebrata it becomes 
confounded with the basisphenoid. The Vomer is a similar, 
splint-like, single or double, membrane bone, which, in like 
manner, underlies the ethmoid region of the skull. 

In addition to the bones already mentioned, a prefrontal 
bone may be developed in the prefrontal region of the nasal 

capsule, and bound the exit of the olfactory nerve externally. 

A postfrontal bone may appear behind the orbit above the 
alisphenoid. Sometimes it seems to be a mere dismember- 
ment of that bone; but, in most cases, the bone so named 
is a distinct membrane bone. 

Furthermore, on the outer and upper carers of- the 
auditory capsule a membrane bone, the squamosal, is very 
commonly developed; and another pair of splint-bones, the 
nasals, cover the upper part of the ethmovomerine cham- 
bers, in which the olfactory organs are lodged. 


The Osseous Facial Apparatus.—The bones of the face, 
which constitute the inferior arches of the skull, appear 
within the various processes and visceral arches which 
have been enumerated. Thus, the premawille are two bones 
developed in the oral part of the naso-frontal process, one 
on each side of the middle line, between the external nasal 
apertures, or anterior nares, and the anterior boundary of 
the mouth. 

Ossification occurs in the palato-pterygoid cartilage at 
two chief points, one in front and one behind. The ante- 
rior gives rise to the palatine bone, the posterior to the 
pterygoid. Outside these, several membrane bones may 
make their appearance in the same process. The chief of 
these is the mawilla, which commonly unites, in front, with 
the premaxilla. Behind the maxilla there may be a 
second, the jugal; and occasionally behind this lies a 
third, the quadrato-jugal. 

Between the maxilla, the prefrontal, and the premaxilla, 
another membrane bone, called lachrymal, from its ordinary 


26 THE ANATOMY OF VERTEBRATED ANIMALS. 


relation to the lachrymal canal, is very generally developed; 


and one or more supra-orbital and post-orbital ossifications. 


may be connected with the bony boundaries of the orbit. 


When these and the postfrontal membrane bone are 


simultaneously developed, they form two series of bony 
splints attached to the lateral wall of the skull, one set 
above and one below the orbit, which converge to the lach- 
rymal. The upper series (lachrymal, supra-orbital, post- 
frontal, squamosal), terminates posteriorly over the proxi- 
mal end of the quadrate bone, or mandibular suspensorium. 
The lower series (lachrymal, maxillary, jugal, quadrato- 
jugal) ends over the distal end of that bone, with which the 
quadrato-jugal is connected. The two series are connected 
behind the orbit by the post-orbital (when it exists), but 
more commonly by the union of the jugal with the post- 
frontal and squamosal. The Ichthyosawria, Chelonia, Croco- 
dilia, and some Lacertilia, exhibit this double series of bones 
most completely. 


Each nasal passage, at first very short, passes between 
the premaxilla below, the ethmoid and vomer on the inner 
side, the prefrontal above and externally, and the palatine 
behind, to open into the fore part of the mouth. And, 
before the cleft between the outer posterior angle of the 
naso-frontal process and the maxillary process is closed, 
this passage communicates, laterally, with the exterior, 
and, posteriorly, with the cavity of the orbit. When the 
maxillary and the naso-frontal processes unite, the direct 
external communication ceases; but the orbito-nasal passage, 
or lachrymal canal, as it is called, in consequence of its 
function of conveying away the secretion of the lachrymal 
gland, may persist, and the lachrymal bone may be de- 
veloped in especial relation with it. 

In the higher Vertebrata, the nasal passages no longer com- 
municate with the fore part of the cavity of the mouth; for 
the maxillaries and palatines, regularly, and the pterygoid 
bones, occasionally, send processes downwards and inwards, 
which meet in the middle line, and shut off from the mouth 


THE OSSEOUS MANDIBLE. 27 


a canal which receives the nasal passages in front, while 
it opens, behind, into the pharynx, by what are now the 
posterior nares. 


Two ossifications commonly appear near the proximal end 
of Meckel’s cartilage, and become bones moveably articulated 
together. The proximal of these is the quadrate bone found 
in most vertebrates, the malleus of mammals; the distal is 
the os articulare of the lower jaw in most vertebrates, but 


Fig. 9. 


Fig. 9.—The head of a foetal Lamb dissected so as to show Meckel’s 
cartilage, 17; the malleus, m; the incus,2; the tympanic, Ty; the 
hyoid, H; the squamosal, Sq; pterygoid, Pt; palatine, p/; lachrymal, 
L; premaxilla, pmx; nasalsac, VN; Eustachian tube, Lu. 


does not seem to be represented in mammals. The re- 
mainder of Meckel’s cartilage usually persists for a longer 
or shorter time, but does not ossify. It becomes surrounded 
by bone, arising from one or several centres in the adjacent 
membrane, andthe ramus of the mandible thus formed, articu- 
lates with the squamosal bone in mammals, but in other 
Vertebrata is immoveably united with the os articulare. 
Hence the complete ramus of the mandible articulates 


28 THE ANATOMY OF VERTEBRATED ANIMALS. 


directly with the skull in mammals, but only indirectly, or 
through the intermediation of the quadrate, in other Verte- 
brata. In birds and reptiles, the proximal end of the 
quadrate bone, articulates directly (with a merely apparent 
exception in Ophidia), and independently of the hyoidean 
apparatus, with the periotic capsule. In most, if not all 
fishes, the connection of the mandibular arch with the skull 
is effected indirectly, by its attachment to a single cartilage 
or bone, the hyomandibular, which represents the proximal 
end of the hyoidean arch (see Fig. 24). 

The ossification of the hyoidean apparatus varies im- 
mensely in detail, but usually gives rise to bony lateral 
arches, and a median portion, bearing much the same rela- 
tion to them as the sternum has to the ribs. When the 
lateral arches are complete they are connected directly with 
the periotic capsule. 

The proximal end of the hyoidean arch is often united, 
more or less closely, with the outer extremity of the bone, 
called columella auris, or stapes, the imner end of which, 
in the higher Vertebrata, is attached to the membrane of the 
fenestra ovalis. 

In ordinary fishes, a fold of the integument extends 
backwards from the second visceral arch over the per- 
sistent branchial clefts; within this is developed a series 
of raylike membrane bones, termed opercular and bran- 
chiostegal, which become closely connected with the hyoidean 
arch. A corresponding process of the skin is developed in ~ 
the Batrachian Tadpole, and grows backwards over the 
branchiz. Its posterior edge, at first free, eventually unites 
with the integument of the body, behind the branchial clefts, 
the union being completed much earlier on the right side, 
than on the left. 

In most mammals a similar fold of integument gives 
rise to the pinna, or external ear. 

The branchial skeleton bears the same relation to the 
posterior visceral arches that the hyoidean does to the 
second, When fully developed, it exhibits ossified lateral 
arches, connected by median pieces, and, frequently, pro- 


ASYMMETRICAL CRANIA. 29 


vided with radiating appendages which give support to the 
branchial mucous membrane. It is only found in those 
Vertebrata which breathe by gills—the classes Pisces and 


Fig. 10. 


Fig. 10.—The skull of a Plaice (Platessa vulgaris), viewed from above. 
The dotted line a, 6, is the true morphological median line; Or. Or, 
the position of the two eyes in their orbits; Eth, ethmoid; Prf, 
prefrontal; Fr, left frontal; Fl, right frontal; Pa, parietal; SO, 
supra-occipital ; Ep. O, epiotic. 


Amphibia. In the higher Vertebrata, the posterior of the two 
pairs of cornua with which the hyoidean apparatus is gene- 
rally provided, are the onlyremains of the branchial skeleton. 


30 THE ANATOMY OF VERTEBRATED ANIMALS. 


The skull and face are usually symmetrical in reference 


to a median vertical plane. But, in some Cetacea, the bones 


about the region of the nose are unequally developed, 
and the skull becomes asymmetrical. In the Flatfishes 
(Pleuronectide), the skull becomes so completely distorted 
that the two eyes lie on one side of the body, which is, in 
some cases, the left, and, in others, the right side. In 
certain of these fishes, the rest of the skull and facial bones, 
the spine, and even the limbs, partake in this asymmetry. 
The base of the skull and its occipital region are compara- 
tively little affected; but. in the interorbital region, the 
frontal bones and the subjacent cartilaginous, or mem- 
branous, side-walls of the cranium are thrown over to one 
side ; and, frequently, undergo a flexure, so that they become 
convex towards that side, and concave in the opposite di- 
rection. The prefrontal bone of the side from which the 
skuil is twisted sends back a great process above the eye of 
that side, which unites with the frontal bone, and thus in- 
closes this eye in a complete bony orbit. It is along this 
fronto-prefrontal bridge that the dorsal fin-rays are con- 
tinued forwards, just as if this bridge represented the 
morphological middle of the skull. (Fig. 10.) 

The embryonic Plewronectide have the eyes in their 
normal places, upon opposite sides of the head; and the 
cranial distortion commences only after the fish are hatched. 

The Appendicular Endoskeleton—The limbs of all verte- 
brated animals make their appearance as buds on each side 
of the body. In all but fishes, these buds become divided 
by constrictions into three segments. Of these, the proximal 
is called brachiwm in the fore-limbs, femwr in the hind; 
the middle is antebrachium, or crus; the distal is manus, or 
pes. Each of these divisions has its proper skeleton, com- 
posed of cartilage and bone. The proximal division, 
normally, contains only one bone, os humeri, or humerus, 
in the brachium—and os femoris, or femur, in the thigh ; 


the middle, two bones, side by side, radius and ulna, or — 


tibia and fibula ; the distal, many bones, so disposed as to 
form not more than five longitudinal series, except in the 


4 


THE CARPUS AND THE TARSUS. 31 


Ichthyosawria, where marginal bones are added, and some 
of the digits bifurcate. 

The skeletal elements of the manus and pes are divi- 
sible into a proximal set, constituting the carpus or tarsus ; 
and a distal set, the digits, of which there are normally five, 
articulated with the distal bones of the carpus and tarsus. 
Hach digit has a proximal basi-digital (metacarpal, or meta- 
tarsal) bone, upon which follows a linear series of phalanges. 
Tt is convenient always to count the digits in the same way, 
commencing from the radial or tibial side. Thus, the thumb 
is the first digit of the hand in man; and the great toe the 
first digit of the foot. Adopting this system, the digits 
may be represented by the numbers i, ii, iil, iv, v. 

There is reason to believe that, when least modified, the 
carpus and the tarsus are composed of skeletal elements 
which are alike in number and in arrangement. One of 
these, primitively situated in the centre of the carpus or 
tarsus, is termed the centrale ; on the distal side of this are 
five carpalia, or tarsalia, which articulate with the several 
metacarpal or metatarsal bones ; while, on its proximal side, 

are three bones—one radiale or tibiale, articulating with the 
: radius or tibia; one wlnare or fibulare, with the ulna or fibula; 
and one intermedium, situated between the foregoing. Car- 
: pal and tarsal bones, or cartilages, thus disposed are to be 
met with in some Amphibia and Chelonia (Fig. 11), but, com- 
monly, the typical arrangement is disturbed by the suppres- 
sion of some of these elements, or their coalescence with 
one another. Thus, in the carpus of man, the radiale, in- 
termedium, and ulnare are represented by the scaphoides, 
lunare, and cuneiforme respectively. The pisiforme is a 
sesamoid bone developed in the tendon of the flexor carpi 
ulnaris, which has nothing to do with the primitive carpus. 
The centrale is not represented in a distinct shape, having 
probably coalesced with one of the other elements of the 
carpus. The fourth and fifth carpalia have coalesced, and 
form the single wneiforme, In the tarsus of man the astra- 
galus represents the coalesced tibiale and intermedium; the 
caleaneum, the fibulare, The naviculare is the centrale. Like 


32 THE ANATOMY OF VERTEBRATED ANIMALS. 


the corresponding bones in the carpus, the fourth and fifth 
tarsalia have coalesced to form the cuboides. 


Fig. 11. 


Fig. 11.—The right forefoot of the Chelonian Chelydra, and the right 
hind-foot of the Amphibian Salamandra.—U. ulna; R. radius; F. 
fibula; 7. tibia. 

Proximal carpal bones: r. radiale; 7. intermedium; w. ulnare; the 
centrale is the middle unlettered bone. 

Proximal tarsal bones: ¢. tibiale ; 7. intermedium; f. fibulare; c. cen- 
trale; 1, 2, 3, 4, 5, distal carpalia and tarsalia; 1, 11, I, Iv, V, 
digits. 

The Position of the Limbs.—In their primitive position, 
the limbs are straight, and are directed outwards, at right 
angles to the axis of the body; but, as development pro- 
ceeds, they become bent in such a manner that, in the 
first place, the middle division of each limb is flexed down- 
wards and towards the middle line, upon the proximal divi- 
sion; while the distal division takes an opposite bend upon 
the middle division. Thus the ventral aspects of the ante- 
brachium and crus come to look inwardly, and the dorsal 
aspects outwardly; while the ventral aspects of the manus 
and pes look downwards, and their dorsal aspects look up- 
wards. When the position of the limbs has been no further 


THE POSITION OF THE LIMBS. 33 


altered than this, the radius in the antebrachium, and the 
tibia in the crus, are turned forwards, or towards the head; 
the ulna and the fibula backwards, or towards the caudal ex- 
tremity. On looking at these parts with respect to the axis 
of the limb itself, the radius and the tibia are pre-awial, or 
in front of the axis; while the ulna and fibula are post- 
axial, or behind it. The same axis traverses the centre of 
the middle digit, and there are therefore two pre-axial, or 
radial, or tibial digits; and two post-axial, or ulnar, or 
fibular digits, in each limb. The most anterior of the 
digits (i) is called pollex, in the manus; and hallux, in the 
pes. The second digit (ii) is the index ; the third (111) the 
medius; the fourth (iv) the annularis; and the fifth (v) 
the minimus. 

In many Amphibia and Reptilia, the limbs of the adult do 
not greatly depart from this primitive position; but in, 
birds and in mammals, further changes occur. Thus, in 
all ordimary quadrupeds, the brachium is turned back- 
wards and the thigh forwards, so that both elbow and 
knee lie close to the sides of the body. At the same time, 
the forearm is flexed upon the arm, and the leg upon the 
thigh. In Man a still greater change occurs. In the 
natural erect posture, the axes of both arm and leg are 
parallel with that of the body, instead of being perpendi- 
cular to it. The proper ventral surface of the brachium 
looks forwards, and that of the thigh backwards, while the 
dorsal surface of the latter looks forwards. The dorsal sur- 
face of the antebrachium looks outwards and backwards, 
that of the leg directly forwards. The dorsal surface of the 
manus is external, that of the pes, superior. Thus, speak- 
ing broadly, the back of the arm corresponds with the front 
of the leg, and the outer side of the leg with the inner side 
of the arm, in the erect position. 

In Bats, a line drawn from the acetabulum to the foot is 
also, inthe natural position, nearly parallel with the long 
axis of the body. But, in attaining this position, the leg 
is bent at the knee and turned backwards; the proper 
dorsal surface of the thigh looking upwards and forwards, 
| D 


34 THE ANATOMY OF VERTEBRATED ANIMALS. 


while the corresponding surface of the leg looks backwards 
and upwards, and the ungual phalanges are turned back- 
wards. 

The chief modifications of the manus and pes arise 
from the excess, or defect, in the development of particular 
digits, and from the manner in which the digits are con- 
nected with one another, and with the carpus or tarsus. In 
the Ichthyosauria and Plesiosawria, the Turtles, the Cetacea 
and Sirenia, and, in a less degree, in the Seals, the digits are 
bound together and cased in a common sheath of integu- 
ment, so as to form paddles, in which the several digits have 
little or no motion on one another. 

The fourth digit of the manus in the. Pterosawria, and 
the four ulnar digits in the Bats, are vastly elongated, to 
support the web which enables these animals to fly. In 
existing birds the two ulnar, or post-axial, digits are aborted, 
the metacarpals of the second and third are ankylosed to- 
gether, and the digits themselves are inclosed in a common 
jntegumentary sheath; the third invariably, and the second 
usually, is devoid of a claw. The metacarpal of the pollex 
is ankylosed with the others, but the rest of that digit is 
free, and frequently provided with a claw. 

Among terrestrial mammals, the most striking changes of 
the manus and pes arise from the gradual reduction in the 
number of the perfect digits from the normal number of five 
to four (Sus), three (Rhinoceros), two (most Rwminantia), or 
one (EHquide). 


The Pectoral and Pelvic Arches——The proximal skeletal 
elements of each pair of limbs (hwmeri or femora) are 
supported by a primitively cartilaginous, pectoral, or pelvic 
girdle, which lies external to the costal elements of the 
vertebral skeleton. This girdle may consist of a simple 
cartilaginous are (as in the Sharks and Rays), or it may be 
complicated by subdivisions and additions. 

The pectoral arch may be connected with the skull, or 
with the vertebral column, by muscles, ligaments, or dermal 
ossifications, though, primitively, it. is perfectly free from 


THE PECTORAL ARCH. 35 


and independent of, both; but it is never united with the 
vertebre by the intermediation of ribs. At first, it consists 
of one continuous cartilage, on each side of the body, dis- 
tinguishable only into regions and processes, and affording 
an articular surface to the bones, or cartilages, of the limb. 
But ossification usually sets up in the cartilage, in such a 
‘way, as to give rise to a dorsal bone, called the scapula, or 
‘sshoulderblade, which meets, in the articular, glenoidal 
eavity for the humerus, with a ventral ossification, termed 
the coracoid. 

By differences in the mode of ossification of the various 
parts, and by other changes, that region of the primitively 


Fig. 12. 


Fig, 12.—Side-view of the pectoral arch and sternum of a Lizard 
(Iguana tuberculata).—Sc, scapula; s.sc, supra-scapula; er, cora- 
coid; gi, glenoidal cavity; St, sternum ; z.st, xiphisternum ; m.sc, 
mesoscapula; p.cr, precoracoid ; m.cr, mesocoracoid ; e.cr, epicora- 
coid; cl, clavicle; z.cl, interclavicle. 

cartilaginous pectoral arch, which lies above the glenoidal 

cavity, may be ultimately divided into a scapula and a supra- 

scapula ; while that which lies on the ventral side may pre- 
sent not.only a coracoid, but a precoracoid and an epi- 
coracoid. 

In the great majority of the Vertebrata above fishes, the 


36 THE ANATOMY OF VERTEBRATED ANIMALS. 


coracoids are large, and articulate with the antero-external 
margins of the primitively cartilaginous sternum, or breast- 
bone. But, in most mammals, they do not reach the ster-| 
num, and, becoming ankylosed with the scapula, they 
appear, in adult life, as mere processes of that bone. 
Numerous Vertebrates possess a clavicula, or coliar-bone, 
which is connected with the pre-axial margin of the scapula 
and coracoid, but takes no part in the formation of the 


Fig. 13. 


Fig. 13.—Ventral view of the sternum and pectoral arches of Jguana 
tuberculata. he letters as in Fig. 12, 


glenoid cavity, and is usually, if not always, a membrane 
bone. In many Vertebrata, the inner ends of the clavicles 
are connected with, and supported by, a median membrane 
bone which is closely connected with the ventral face of 
the sternum. This is the interclavicula, frequently called 
episternum. 


THE PELVIC ARCH. BY 


The pelvic, like the pectoral, arch at first consists of a 
simple continuous cartilage on each side, which, in Verte- 
brata higher than fishes, is divided by the acetabulum, or 
articular cavity for the reception of the head of the femur, 
into a dorsal and a ventral moiety. 

Three separate ossifications usually take place in this 
cartilage—one in the dorsal, and two in the ventral, moiety. 
Hence, the pelvic arch eventually consists of a dorsal por- 
tion, called the iliwm, and of two ventral elements, the pubis 
anteriorly, and the ischiwm posteriorly. All these generally 
enter into the composition of the acetabulum. 

The ilium corresponds with the scapula. In the higher 
Vertebrata the outer surface of the latter bone becomes 


Fig. 14.—Side-view of the left Os innominatum of Man: JI, ilium; 
Is, ischium; Pb, pubis; A, acetabulum; Pp, Poupart’s ligament. 


divided by a ridge into two fosse. The ridge, called the 
spine of the scapula, frequently ends in a prominent process 
termed the acromion, and with this, in Mammalia, the cla- 
vicle articulates. In like manner, the outer surface of the 
ilium becomes divided by a ridge which grows out into a 
great crest in Man and other Mammalia, and gives attach- 
ment to muscles and ligaments. 

The ischium corresponds very nearly with the coracoid 


38 THE ANATOMY OF VERTEBRATED ANIMALS. 


in the pectoral arch; the pubis with the precoracoid, and 
more or less of the epicoracoid. 

The pelvis possesses no osseous element corresponding 
with the clavicle, but a strong ligament, the so-called Pou- 
parts ligament, stretches from the ilium to the pubis in 
many Vertebrata, and takes its place. (Fig. 14, Pp.) 

On the other hand, the marsupial bones of certain mam- 
mals, which are ossifications of the tendons of the external 
oblique muscles, seem to be unrepresented in the pec- 
toral arch; while there appears to be nothing clearly corre- — 
sponding with a sternum in the pelvic arch, though the © 
precloacal cartilage, or ossicle, of Lizards has much the same 
relation to the ischia as the sternum has to the coracoids. 

Very generally, though not universally, the ilia are closely | 
articulated with the modified ribs of the sacrum. The pubes 
and ischia of opposite sides usually meet in a median © 
ventral symphysis ; but in all birds, except the Ostrich, this 
union does not take place. 


The Limbs of Fishes——The limbs of Fishes have an endo- 
skeleton which only imperfectly corresponds with that of 
the higher Vertebrates. For while homologues of the car- 
tilaginous, and even of the bony, constituents of the pec- 
toral and pelvic arches of the latter are traceable in Fishes, 
the cartilaginous, or ossified, basal and radial supports of 
the fins themselves cannot be identified, unless in the most — 
general way, with the limb-bones, or cartilages, of the other 
Vertebrata. 

In its least modified form, as in Lepidosiren, the endo- 
skeleton of the fish’s fin is a simple cartilaginous rod, 
divided into many joints; and articulated, by its proximal 
end, with the pectoral arch. The Hlasmobranchii possess 
three basal cartilages which articulate with the pectoral 
arch, and are called, respectively, from before backwards 
—propterygial, mesopterygial, and metapterygial basalia. 
With these are articulated linear series of radial cartilages, 
upon which osseous, or horny, dermal fin-rays are super- 
imposed. (Fig. 15.) 


THE LIMBS OF FISHES. 39 


Among the Ganoid fishes, the fins of Polypterus are, fun- 
damentally, like those of the Hlasmobranchii; but the pro- 
pterygial, mesopterygial, and metapterygial basalia, are 
more or less ossified, and are succeeded by a series of elon- 
gated radialia, which are also, for the most part, ossified. 
Beyond these follow some small additional radialia, which 


Fig. 15. 


Fig.15.—The right pectoral member of the Monkfish (Squatina): h, 
propterygium ; ms, mesopterygium ; mt, metapterygium. 


remain cartilaginous, and are embraced by the bases of the 
fin-rays. In the other Ganoids the propterygial basale dis- 
appears, and some of the radialia, pushing themselves be- 
tween the mesopterygial and metapterygial basalia, articu- 
late directly with the pectoral arch. The mesopterygial 


40 THE ANATOMY OF VERTEBRATED ANIMALS. 


basale is embraced by, and becomes more or less incorpo- 
rated with, the large anterior fin-ray. 

From these Ganoids the passage is easy to the Teleostei, 
in which, also, the mesopterygial basale always becomes 
fused with the anterior fin-ray, whence the latter seems to 
articulate directly with the shoulder-girdle. Four bones, of 
very similar general form, usually articulate with the pec- 
toral arch, beneath and behind the mesopterygial basale 
and its fin-ray. At their distal ends small cartilaginous 
nodules may lie, and these are embraced by the fin-rays. 
Of these four bones, or partially ossified cartilages, the lower- 
most and hindermost answers to the metapterygial basale 
of the Shark; the others seem to be radialia. (See the 
figure of the Pike’s pectoral fin, infra.) 

The ventral fins have basal and radial cartilages and fin- 
rays, more or less resembling those of the fore limbs. 

In most Ganoids and Teleosteans the pectoral and pelvic 
arches are, in part, or completely, ossified; the former fre- 
quently presenting distinct scapular and coracoid bones. 
To these, in all Ganoids and Teleosteans, membrane bones, 
representing a clavicle, with supra-clavicular and post-clavi- 
cular ossifications, are added. 

In all Elasmobranchs and Ganoids, and in a large pro- 
portion of the Teleosteans, the pelvic fins are situated far 
back on the underside of the body, and are said to be 
“ventral” in position; but, in other Teleosteans, the ventral 
fins may move forward, so as to be placed immediately 
behind, or even in front of, the pectoral fins. In the former 
case they are said to be “ thoracic,” in the latter “ jugular.” 

The Vertebrate Hxoskeleton.—The Hxoskeleton never attains, 
in vertebrated animals, the functional importance which it 
so frequently possesses among the Invertebrata, and it varies 
very greatly in the degree of its development. 

The integument consists of two layers—a superficial, non- 
vascular substance, the epidermis, composed of cells, which 
are constantly growing and multiplying in the deeper, 
and being thrown off in the superficial, layers; and a deep 
vascular tissue, the dermis, composed of more or less 


THE EXOSKELETON. 41 


completely-formed connective tissue. An exoskeleton may 
be developed by the hardening of either the epidermis, or 
the dermis. 

The epidermal exoskeleton results from the conversion into 
horny matter of the superficial cells of the epidermis. The 
horny plates thus formed are moulded upon, and follow the 
configuration of, arez, or processes, of the dermis. When the 
latter are overlapping folds, the horny epidermic investment 
is called a scale, sywama. When the dermic process is papilli- 
form, and sunk in a pit of the dermis, the conical cap of modi- 
fied epidermis which coats it, is either a hair or a feather. To 
‘become a hair, the horny cone simply elongates by continual 

addition of new cells to its base; but,in a feather, the horny 
cone, which also elongates by addition to its base, splits up, 
for a greater or less distance along the middle line of its 
under-surface, and then spreads out into a flat vane, sub- 
divided into barbs, barbules, &c., by a further process of 
splitting of the primary horny cone. 

The epidermis remains soft and delicate in Fishes and 
Amphibia. In Reptilia it sometimes takes the form of 
plates, which attain a great size in many Chelonia; some- 
times, that of overlapping scales, as in Ophidia and many 
Lacertilia ; but, sometimes, it remains soft, as in some Che- 
lonia and in the Chameleons. Epidermic plates in the form 
of nails appear upon the terminal phalanges of the limbs. 

All Aves possess feathers. In addition, the beak is partly 
or completely ensheathed in horn, as in some Reptilia. 
Cornified epidermic tubercles, or plates, are developed on 
the tarsi and toes, the terminal phalanges of which (and 
sometimes those of the wing) have nails. Beside these, 
some birds possess spurs, which are ensheathed in horn, on 
the legs or wings. 

In Mammalia the horny exoskeleton may take all the 
forms already mentioned, except that of feathers. Im some 
Cetacea it is almost absent, being reduced to a few hairs, 
present only in the fetal state. The Pangolin (Manis), on 
the other hand, is almost completely covered with scales, 
the Armadillos with plates, and most terrestrial mammals 


42 THE ANATOMY OF VERTEBRATED ANIMALS. 


with a thick coat of hair. The greater part of the mass of 
the horns of Oxen, Sheep, and Antelopes, is due to the epi- 
dermic sheath which covers the bony core. Where the 
horny epidermis becomes very thick, as in the hoof of the 
Horse, and in the horn of the Rhinoceros, numerous long 
papille of the dermis extend into it. These papille, how- 
ever, are comparable to the ridges of the bed of the nail, 
not to the papille of the hairs. 


Fig. 16. 


Fig. 16.—A, outline of a Pike pied to show the fins: P, pectoral; 
V, ventral; A, anal; C, caudal; D, dorsal, fins. Op., operculum ; 
P. Op. ,preoperculum Br. , branchiostegal rays. —B, scales of the der- 
mal exoskeleton of the same fish. 


The dermal exoskeleton arises from the hardening of the 
dermis; in the majority of cases by the deposit of bone- 
earth, in more or less completely-formed connective tissue, 
though the resulting hard tissue has by no means always the 
structure of bone. It may happen that cartilage is de- 
veloped in the dermis; and, either in its primary state, or 
ossified, gives rise to exoskeletal parts. 

No dermal exoskeleton (except that of the fin-rays) is 
found in the lowest fishes, Amphioxus and the Marsipo- 
branchiit. In most Teleostei the integument is raised up 
into overlapping folds; and, in these, calcification takes 


THE EXOSKELETON. 43 


place in lamine, of which the oldest is the most superficial, 
and lies immediately beneath the epidermis. As a general 
rule, the calcified tissue of the “scale” thus formed, does 
not possess the structure of true bone in the Teleostei. But 
in other fishes, the dermal calcification may consist of true 
bone (as in the Sturgeon); or, as in the Sharks and Rays, 
may take on the structure of teeth, and consist mainly of a 
tissue exactly comparable to dentine, capped with enamel, 
and continuous by its base with a mass of true bone, which 
takes the place of the crusta petrosa, or cement of the teeth. 

A form of dermal exoskeleton, which is peculiar to and 
highly characteristic of fishes, is found in the fin-rays. These 
are developed in the integument either of the median line of 
the body, or in that of the limbs. In the former case, they 
usually enter into, or support, folds of the integument which 
are termed dorsal, caudal, or anal fins—according as they 
lie in the dorsal region, or at the extremity of the body, or 
on the ventral aspect, behind the anus. Ordinary fin-rays 
are composed of a hornlike, or more or less calcified, sub- 
stance, and are simple at the base, but become jointed trans- 
versely, and split up longitudinally, towards their extremities 
(Fig.6). ach fin-ray consists of two nearly equal and simi- 
lar parts, which cohere by their applied faces for the greater 
part of their extent; but, at the base of the ray, the halves 
commonly diverge, to embrace, or more or less completely 
coalesce with, cartilaginous or osseous elements of the exo- 
skeleton. In the median fins, these are the interspinous 
cartilages, or bones, which lie between the fin-rays and the 
superior or inferior spines of the vertebra. In the paired 
fins, they are radial or basal, cartilaginous or osseous, 
elements of the endoskeleton. 

The Amphibia in general are devoid of dermal exoskeleton, 
but the Cecilie have scales like those of fishes. Ceratophrys 
has plates of bone developed in the dorsal integument, 
which seem to foreshadow the plates of the carapace of 
the Chelonia; and the extinct Labyrinthodonts possessed a 
very remarkable ventral exoskeleton. 

The Ophidia have no dermal exoskeleton. Many Lizards 


44, THE ANATOMY OF VERTEBRATED ANIMALS. 


have bony dermal plates corresponding in form and size 
with the epidermal scales. All Crocodilia have such bony 
plates in the dorsal region of the body and tail ; and in some, 
such as the Jacares and Caimans, and the extinct Teleo- 
sawria, they are also developed in the ventral region. In 
these animals there is a certain correspondence between the 
segments of the exoskeleton and those of the endoskeleton. 
But the dermal exoskeleton attains its greatest development 
in the Chelonia, and will be particularly described under the 
head of that order. 

In the Mammalia the development of a dermal exoskele- 
ton is exceptional, and occurs only in the loricated Edentata, 
in which the dorsal region of the head and body, and the 
whole of the tail, may be covered with shields of dermal 
bone. 

In connection with the dermis and epidermis, the glan- 
dular and pigmentary organs of the integument may be 
mentioned. Integumentary glands do not appear to exist 
in Fishes, but they attain an immense development in some 
of the Amphibia, asthe Frog. Among Reptilia, Lizards fre- 
quently present such glands in the femoral and cloacal 
regions; and, in Crocodiles, integumentary glands, which 
secrete a musky substance, lie beneath the jaw. In Birds 
they attain a considerable size in the uropygial gland; and, 
in Mammalia, acquire a large development in connection with 
the sacs of the hairs, or as independent organs, in the form 
of sweat-glands, musk-glands, or mammary glands. 

The colour of the integument may arise from pigment- 
granules, deposited either in the epidermis or in the 
dermis; and in the latter case, it is sometimes contained in 
distinct chromatophores, as in the Chameleon. 


45 


CHAPTER II. 


THE MUSCLES AND THE VISCERA—A GENERAL VIEW OF 
THE ORGANIZATION OF THE VERTEBRATA. 


THE muscular system of the Vertebrata consists of muscles 
related partly to the exoskeleton, partly to the endoskeleton, 
and partly to the viscera, and formed both of striated and 
unstriated muscular fibre. The latter is confined to the 
vessels, the viscera, and the integument; the parts of the 
endoskeleton being moved upon one another exclusively by 
striated muscular fibre. The muscles of the endoskeleton 
may be divided, like the endoskeleton itself, into one system 
appertaining to the trunk and head, and another belonging 
to the limbs. 

The Muscular System of the Trunk and Head.—This con- 
sists of two portions, which differ fundamentally in their 
origin, and in their relations to the endoskeleton. The one 
takes its origin in the protovertebre; each protovertebra 
becoming differentiated, as we have seen, into three parts; 
a spinal ganglion and a segment of the vertebral endo- 
skeleton, in the same plane, and a more superficial sheet 
of muscular fibres. These muscular fibres are consequently 
situated above the endoskeleton, or are episkeletal. Other 
muscular fibres are developed below the endoskeleton, and 
may be termed hyposkeletal muscles. The hyposkeletal 
muscles are separated from the episkeletal, not only by the 
endoskeleton of the trunk (or the vertebre and their pro- 
longations, the ribs), but by the ventral branches of the 
spinal nerves. 

As the episkeletal muscles are developed out of the proto- 
vertebre, they necessarily, at first, present as many seg- 


46 THE ANATOMY OF VERTEBRATED ANIMALS. 


ments as there are vertebra, the interspaces between them 
appearing as intermuscular septa. The development of the 
hyposkeletal muscles has not been worked out, but it appears 
to take place much later than that of the episkeletal set. 

In the lowest Vertebrata—as, for example, in ordinary 
fishes—the chief muscular system of the trunk consists of 
the episkeletal muscles, which form thick lateral masses of 
longitudinal fibres, divided by transverse intermuscular 
septa into segments (or Myotomes) corresponding with the 
vertebre. The lateral muscles meet in the middle line 
below, and divide, in front, into a dorso-lateral mass con- 
nected with the skull, and a ventro-lateral attached, in part, 
to the pectoral arch, and, in part, continued forwards to the 
skull, to the hyoidean apparatus, and to the mandible. Pos- 
teriorly, the lateral muscles are continued to the extremity 
of the tail. The hyposkeletal muscular system appears to 
be undeveloped. 

In the higher Vertebrata, both the episkeletal and hypo- 
skeletal muscular systems are represented by considerable 
numbers of more or less distinct muscles. The dorso- 
lateral division of the lateral muscle of the fish is repre- 
sented by the superior caudal muscles, and by the erector 
spine ; which, as it splits up, anteriorly, and becomes 
attached to the vertebre, and to the ribs, and to the skull, 
acquires the names of spinalis, semispinalis, longissimus 
dorsi, sacrolumbalis, inter-transversalis, levatores costarwm, 
complexus, splenius, recti postici, and recti laterales. 

The yentro-lateral division of the fish’s lateral muscle is 
represented, in the middle line of the trunk and head, by a 
series of longitudinal muscles; and, at the sides, by obliquely- 
directed muscles. The former are the recti abdominis, ex- 
tending from the pelvis to the sternum—the sterno-hyoidei, 
between the sternum and the hyoidean apparatus—the 
genio-hyoidei, which pass from the hyoid to the symphysis 
of the mandible. The latter are the obliqui externi of the 
abdomen—the external intercostales of the thorax—the sub- 
clavius stretching from the first rib to the clavicle; the 
scalent from the anterior dorsal ribs to the cervical ribs and 


EPISKELETAL AND HYPOSKELETAL MUSCLES. 47 


transverse processes, and the sterno- and cleido-mastoider 
from the sternum and clavicle to the skull. 

The fibres of all these oblique muscles take a direction, 
from parts which are dorsal and anterior, to others which 
are ventral and posterior. 

The trunk muscles of the lower Amphibia exhibit ar- 
rangements which are transitional between those observed 
in Fishes and that which has been described in Man, and 
which substantially obtains in all abranchiate Vertebrata. 

The muscles of the jaws and of the hyoidean apparatus 
appear to be, in part, episkeletal, and, in part, hyposkeletal. 
The mandible is depressed by a muscle, the digastric, arising 
from the skull, and supplied by a branch of the seventh 
nerve: it is raised by a muscular mass, which is separable 
into masseter, temporal, and pterygoid muscles, according to 
its connection with the maxillo-jugal bones, the sides of the 
skull, or the palato-pterygoid bones, and is supplied by the 
fifth nerve. 

The proper facial muscles belong to the system of cuta- 
neous muscles, and receive branches from the seventh nerve. 

The hyposkeletal system is formed, partly, of longi- 
tudinal muscles which underlie the vertebral column; and 
partly, of more or less oblique, or even transverse fibres, 
which form the innermost muscular walls of the thorax and 
of the abdomen. 

The former are the subcaudal intrinsic flexors of the tail; 
the pyriformis, psoas, and other muscles proceeding from the 
inferior faces of the vertebra to the hind limb; the longus 
colli, or intrinsic flexor of the anterior part of the vertebral 
column; and the recti capitis antici, or flexors of the head 
upon the vertebral column. The latter are the obliquus 
internus of the abdomen, the fibres of which take a direction 
erossing that of the external oblique muscle ; and the trans- 
versalis, which lies innermost of the abdominal muscles, and 
has its fibres transverse. In the thorax, the inéercostales 
interni continue the direction of the internal oblique, and 
the triangularis sterni that of the transversalis, The dia- 
phragm and the levator ani must also be enumerated among 


48 THE ANATOMY OF VERTEBRATED ANIMALS. 


the hyposkeletal muscles. The hyposkeletal muscles of the 
posterior moiety of the body attain a great development in 
those Vertebrata which have no hind limbs, such as Ophidia 
and Cetacea. 

The Muscular System of the Limbs.—The muscles of the 
limbs of Fishes are very simple, consisting, on each face of 
the limb, of bundles of fibres, which proceed (usually in two 
layers) obliquely, from the clavicle and supraclavicle to the 
fin-rays. The pectoral and pelvic arches themselves are 
imbedded in the lateral muscles. 

In the Amphibia and all the higher Vertebrata, the muscles 
of the limbs are divisible into—intrinsie, or those which take 
their origin within the anatomical limits of the limb (in- 
cluding the pectoral or pelvic arch); and ewtrinsic, or those 
which arise outside the limb. 

Supposing the limb to be extended at right angles to the 
spine (its primitive position), it will present a dorsal aspect 
and a ventral aspect, with an anterior, or pre-avial, and a 
posterior, or post-awial, side. 

In the Vertebrata above fishes, the following muscles, which 
occur in Man, are very generally represented : 

Extrinsic muscles attached to the pectoral and pelvic arches, 
on the dorsal aspec —In the fore limb, the cleidomastoideus, 
from the posterolateral region of the skull to the clavicle; 
the trapezius, from the skull and spines of many of the ver- 
tebre to the scapula and clavicle; the rhomboidei, from the 
spines of vertebrae to the vertebral edge of the scapula, 
beneath the foregoing. Sometimes there is a trachelo- 
acromialis, from the transverse processes of the cervical 
vertebre to the scapula. 

On the ventral aspect, the subclavius, which passes from the 
anterior rib to the clavicle, may be regarded as, in part, a 
muscle of the limb; the pectoralis minor, from the ribs to 
the coracoid. 

Between the dorsal and the ventral aspects muscular fibres 
arise from the cervical and dorsal ribs, and pass to the inner 
aspect of the vertebral end of the scapula: anteriorly, these 
are called levator anguliscapule ; posteriorly, serratus magnus. 


THE MUSCLES OF THE LIMBS. 49 


An omohyoid muscle frequently connects the scapula with 
the hyoidean arch. 
_ The posterior limb does not seem to offer any muscles 
‘exactly homologous with the foregoing. So far, however, 
as the recti panic, the obliquus externus, and the fibres 
of the erector spine, are attached to the pelvic girdle, they 
‘correspond i in a general way with the pre-axial, or protractor, 
muscles of the pectoral arch; and the ischio-coccygeal 

muscles, when they are developed, are, in relation to the 
pelvic arch, retractors, though, owing to the relative fixity 
of the pelvis, they act in protracting, or flexing, the caudal 
region. 

The psoas minor, proceeding from the under-surfaces of 
posterior dorsal (or lumbar) vertebre to the ilium, or pubis, 
is a protractor of the pelvis, but, as a hyposkeletal muscle, 
has no homologue in the fore limb. 

Extrinsic muscles attached to the humerus or femur, on the 
dorsal aspect.—In the fore limb there is the post-axial latissi- 
mus dorsi passing from spines of dorsal vertebre to the 
humerus. On the ventral aspect, the pectoralis major extends 
from the sternum and ribs to the humerus. 

In the hind limb, the gluteus maximus, so far as it arises 
from the sacral and coccygeal vertebrez, and is inserted into 
the femur, repeats the relations of the latissimus dorsi. In 
the absence of anything corresponding with the sternum, or 
the ribs, no exact homologue of the pectoralis major can be 
said to exist, though the pectineus comes near it. The psoas 
major, passing from posterior dorsal or lumbar vertebra—the 
pyriformis from sacral vertebre—the femoro-coccygeus (when 
it exists) from caudal vertebree—to the femur, are all hypo- 
skeletal muscles, without homologues in the anterior ex- 
tremity. 

All the other muscles of the limbs are intrinsic, taking 
their origins from the pectoral or pelvic arches, or from 
some of the more proximal segments of the limb-skeleton, 
and having their insertion in the more distal segments. 
They are thus arranged in Man and the higher Mammalia : 
_ Intrinsic muscles proceeding from the pectoral or pelvic 

E 


50 THE ANATOMY OF VERTEBRATED ANIMALS. 


arches to the humerus or femur, on the dorsal aspect.—In the 
fore limh, the deltoides proceeds from the clavicle and sca- 
pulato the humerus. This superficial shoulder-muscle con- 
tinues the direction of the fibres of the trapezius ; and, when 
the clavicle is rudimentary, the adjacent portions of the two 
muscles coalesce into a cephalo-humeralis muscle. Beneath 
the deltoid the supra-spinatus, on the pre-axial side of the 
spine of the scapula; the infra-spinatus, and the teres major 
and minor, on its post-axial side, run from the dorsal aspect 
of the scapula to that of the head of the humerus. 

In the hind limb, the tensor vagine femoris, which passes 
from that part of the ilium which corresponds with the 
spine and acromion of the scapula, to the femur, appears to 
answer better to the deltoid than does the gluteus maximus, 
which, at first sight, would seem to be the homologue of 
that muscle. 

The tliaeus, proceeding from the inner surface of the crest 
of the ilium to the smaller trochanter, answers to the supra- 
spinatus ; the gluteus medius and minimus, which arise from 
the outer surface of the ilium, to the infra-spinatus and teres, | 

In the fore limb, a muscle, the subscapularis, is attached 
to the inner face of the scapula, and is inserted into the 
humerus. No muscle exactly corresponding with this 
appears to exist in the hind limb. 

On the ventral aspect in the fore limb, the coracobrachialis 
passes from the coracoid to the humerus. Inthe hind limb, 
a number of muscles proceed from the corresponding (ischio- 
pubic) part of the pelvic arch to the femur. These are, 
from the outer surface of the pubis, the pectineus, and the 
great adductors of the femur; with the obtwrator externus, 
from the outer side of the ischiopubic fontanelle, or ob- 
turator membrane. The gemelli and the quadratus femoris 
take their origin from the ischium. 

No muscle is attached to the proper inner surface of the 
ilium, so that there is no homologue of the subscapularis in 
the hind limb, On the other hand, a muscle, the obturator 
internus, attached to the inner surface of the ischiopubic 
fontanelle, and winding round to the femur, has no homo- 


THE MUSCLES OF THE LIMBS. 51 


logue in the upper extremity of the higher Vertebrata, unless 
it be the so-called coracobrachialis, which arises from the 
inner surface of the coracoid in many Sauropsida. 

Muscles of the Antebrachiwm and Crus.—On the dorsal aspect 
of the fore limb, as of the hind limb, certain muscles arise 
in part from the arch, and, in part, from the bone of the 
proximal segment of the limb, and go to be inserted into 
the two bones of the second segment. These are, in the 
fore limb, the triceps extensor and the supinator brevis; in 
the hind limb, the quadriceps extensor. 

There is this difference between these two homologous 
groups of muscles—that in the fore limb, the principal 
mass of the muscular fibres goes, as the triceps, to be 
inserted into the post-axial bone (ulna), and the less por- 
tion, as supinator brevis, into the pre-axial bone (radius) ; 
whereas, in the hind limb, it is the other way, almost the 
whole of the muscular fibres passing, as the quadriceps, to 
the pre-axial bone (tibia), the tendon commonly developing 
a sesamoid patella ; while only a few fibres of that division 
of the quadriceps which is called the “ vastus externus” pass 
to the post-axial bone (fibula). 

On the ventral aspect, the fore limb presents three muscles, 
arising either from the pectoral arch, or from the humerus, 
and inserted into the two bones of the forearm. On the 
pre-axial side are two muscles; one dowble-headed, the biceps, 
arising from the scapula and the coracoid, and inserted into 
the radius. A second, the supinator longus, passes from the 
humerus to the radius. On the post-axial side, the bra- 
chialis anticus arises from the humerus, and is inserted into 
the ulna. The hind limb has two muscles, the sartorius, 
arising from the ilium, and the gracilis, from the pubis, 
in place of the biceps brachii, and inserted into the pre-axial 
bone, the tibia, which corresponds with the radius. Two 
other muscles, the semi-membranosus and semi-tendinosus, 
pass from the ischium to the tibia, and replace, without 
exactly representing, the swpinator longus. Corresponding 
with the brachialis anticus is the short head of the biceps 
femoris, arising from the femur, and inserted into the post- 


52 THE ANATOMY OF VERTEBRATED ANIMALS. 


axial bone of the leg, the fibula. The long head of the 
biceps femoris, which proceeds from the ischium, appears to 
have no representative in the fore limb. 

In the fore limb, a muscle, the pronator teres, passes 
obliquely from the post-axial condyle of the humerus to 
the radius. In the hind limb, a corresponding muscle, the 
popliteus, proceeds from the post-axial condyle of the 
femur to the tibia. The pronator quadratus, which passes 
from the ulna to the radius, has its analogue, in some 
Marsupialia and Reptilia, in muscles which extend from 
the fibula to the tibia. 

The Muscles of the Digits—The remaining muscles of 
the two limbs are, primarily, muscles of the digits, and are J 
attached either to the basi-digital (metacarpal or metatarsal) J 
bones, or tothe phalanges, though they may acquire secon- 
dary connections with bones of the tarsus or carpus. The 
plan upon which they are arranged, when they are most com- 
pletely developed, will be best understood by commencing § 
with the study of their insertion in any one of those digits 
which possesses a complete set; such, for example, as the 
fifth digit of the manus, or little finger, in Man and the 
higher Primates. 

On the dorsal aspect this digit presents: first, attached to 
the base of its metacarpal bone, the tendon of a distinct 
muscle, the extensor carpi ulnaris. Secondly, spreading out 
over the phalanges into an aponeurosis, which is principally 
attached to the first and second, is a tendon belonging to 
another muscle, the extensor minimi digiti. Thirdly, enter- 
ing the same expansion is one tendon of the extensor com- 
munis digitorum. 

On the ventral aspect there are: first, attached to the 
base of the metacarpal, the tendon of a distinct muscle, the 
jlewor carpi ulnaris ; secondly, arising from the sides and 
ventral face of the metacarpal, and inserted into either side 
of the base of the proximal phalanx, two muscles, the inter- 
ossei; thirdly, inserted into the sides of the middle phalanx 
by two slips, a tendon of the flewor perforatus ; and fourthly, 
passing between these two slips, and inserted into the base 


; THE MUSCLES OF THE LIMBS. 53 


of the distal phalanx, a tendon of the flexor perforans. Thus 
there are special depressors, or flexors, for each segment of 
the digit. There appear, at first, to be but three elevators, 
or extensors, but, practically, each segment has its elevator. 
‘For the tendons of the extensor communis and extensor 
mimimi digiti are attached to the middle and the proximal 
phalanges; and the distal phalanx is specially elevated by 
the tendons of two little muscles, which, in Man, are 
usually mere subdivisions of the interossei,and pass upwards, 


"Exb2. 


YE. fies. 


Fig. 17.—Part of the middle digit of the manus of an Orang with the 
flexors and extensors of the phalanges:—mcp., metacarpal bone; 
Ph. 1, Ph. 2, Ph. 3, the three phalanges; Ext. 1, the deep long ex- 
tensor tendon from the extensor indicis ; Ext. 2, the superficial long 
extensor tendon from the extensor communis; I.e. the interosseous 
short extensor; Jf. the interosseous short flexor; F.pns. the deep 

_ long flexor (perforans) ; F.pts. the superficial long flexor (perforatus). 


joining the extensor sheath, to be finally inserted into the 
distal phalanx. 

The fifth digit of the pes, or little toe, sometimes pre- 
sents the same disposition of muscles, namely : 

On the dorsal aspect : first, the peroneus tertius for the 
metatarsal bone; secondly, one tendon from the eatensor 
digitorum brevis, but this last is commonly absent in Man; 
thirdly, one tendon from the extensor digitorum longus. 

On the ventral aspect: first, the peroneus brevis, attached 


54 THE ANATOMY OF VERTEBRATED ANIMALS. 


to the base of the metatarsal; secondly, two interosset ; 
thirdly, a perforated flexor; and fourthly, a perforating 
flexor, like those of the manus. The divisions of the inter- 
ossei, which send tendons to the extensor sheath on the 
dorsum of the digits of the foot in Man, are hardly distinct 
from the ventral divisions of those muscles. 

In addition to the muscles which have been mentioned, 
the fifth digit has an abductor and an adductor, which may 
be regarded as subdivisions of the interossez, arising within 
the manus or pes, and inserted into opposite sides of the 
proximal phalanx; and an opponens, a muscle attached to the 
ventral face of the carpus or the tarsus, and inserted into the 
post-axial edge of the shaft of the metacarpal or metatarsal. 

Finally, a lwmbricalis muscle proceeds from the tendon 
of the perforating flexor, on the pre-axial side of the digit, 
to the extensor sheath. 

None of the other digits of the manus, or of the pes, has a 
greater number of muscles than this; in fact, all the others 
have fewer muscles, some of those enumerated being sup- 
pressed. What are often regarded as muscles special to man, 
such as the extensor proprius indicis and extensor minim 
digiti, are only remains of muscles which are more fully 
developed in lower mammals, and send tendons to all four 
of the ulnar digits. 

Only the pollex has an opponens.* Only the pollex and 
hallux have adductors and abductors. Some of the digits 
lack one or more of the ventral, or of the dorsal, muscles. 

The correspondence between the muscles which have been 
mentioned, at their insertion in the digits, is clear enough, 
but some difficulties present themselves when the muscles 
are traced to their origins. 

In Man the flexors and extensors of the digits (except the 
interosset) of the fore limb, arise in part from the humerus, 
and in part from the bones of the forearm, but not within 
the manus. On the contrary. none of the flexors and ex- 
tensors of the digits of the pes arise from the femur, while 
some of them arise within the pes itself. The origins of 


* T have seen an opponens in the hallux of an Orang. 


THE MUSCLES OF THE LIMBS. 55 


‘the muscles seem to be, as it were, higher up in the fore 
‘limb than in the hind limb. Nevertheless, several of the 
muscles correspond very closely. Thus, on the dorsal 
aspect, the extensor ossis metacarpi pollicis passes from the 
post-axial side of the proximal region of the antebrachium 
obliquely to the trapezium and the metacarpal of the pollex, 
just as its homologue, the tibialis anticus, passes from the 
post-axial side of the upper part of the leg to the ento- 
cuneiform and the base of the metatarsal of the hallux; 
the two muscles correspond exactly. But the extensors of 
the phalanges of the pollex, and the deep extensors of the 
other digits of the manus, arise on the same side of the 
antebrachium, below the extensor ossis metacarpi pollicis ; 
while, in the leg, one of the deep extensors of the hallux, 
and all those of the other digits, arise still lower down, viz. 
from the caleaneum. 

Not less remarkable is the contrast between the more 
superficial sets of extensors in the two limbs. In the fore 
limb, proceeding from the pre-axial to the post-axial side, 
the following extensor muscles arise from the external or 
pre-axial condyle of the humerus: the extensor carpi radi- 
alis longus to the base of the second metacarpal ; the extensor 
carpi radialis brevis to the base of the third metacarpal ; the 
extensor communis digitorum to the four ulnar digits; the 
extensor minimi digiti to the fifth digit; the extensor carpi 
ulnaris to the base of the fifth metacarpal. In the hind limb, 
there are no homologues of the first two of these muscles. 
The homologue of the extensor communis is the long extensor, 
which arises, not from the femur, but from the fibula. The 
peroneus tertius,* passing from the dorsal face of the fibula 
to the fifth metatarsal, is the only representative of the 
extensor carpi ulnaris. 

On the ventral aspect of the human fore limb, two deep 


* This muscle, which lies alto- 
gether on the dorsal face of the 
hind limb, and which I have seen 
only in Man, should not be con- 
founded, as it often is, with one 
or more muscles, the peronei 3tit, 
Ati, et Sti digiti, which are very 


often developed in other Mam- 
malia, but arise on the ventral 
tace of the fibula, and send their 
tendons below the external mal- 
leolus to the extensor sheaths of 
the fifth, fourth, and even third 
digits. 


56 THE ANATOMY OF VERTEBRATED ANIMALS. 


flexors arise from the radius, ulna, and interosseous mem- 
brane, and run parallel with one another, though discon- 
nected, to the digits. These are, on the pre-axial side—the 
flewor pollicis longus, to the distal phalanx of the pollex; 
and the flexor digitorum perforans, to the distal phalanges 
of the other digits. 

In the hind limb, two homologous muscles, the flexor hal- 
lucis longus and the flexor digitorum perforans, arise from the 
tibia and fibula and interosseous membrane, and their ten- 
dons are distributed to the distal phalanges of the digits. 
Bvt, before they divide, the tendons become connected to- 
gether in such a way, that many of the digits receive tendi- 
nous fibres from both sources. 

In the fore limb, there are no other deep flexors, but the 
internal, or post-axial, condyle of the humerus gives origin 
to a number of muscles. These, proceeding from the pre- 
axial to the post-axial side, are the fleaor carpi radialis to the 
base of the second metacarpal; the palmaris longus to the 
fascia of the palm, the flexor perforatus digitorum to the 
middle phalanges of the four ulnar digits; the flexor carpi 
ulnaris to the base of the fifth metacarpal. The sesamoid, 
pisiform bone is developed in the tendon of the last muscle. 

The only muscle which exactly corresponds with any of 
these, in the hind limb, is the plantaris ; which, in Man, is 
a slender and insignificant muscle proceeding from the outer 
(post-axial) condyle of the femur to the plantar fascia—and 
answers to the palmaris longus. In many quadrupeds, as 
the Rabbit and Pig, the plantaris is a large muscle, the ten- 
don of which passes over the end of the calcaneal process 
ensheathed in the tendo-achillis, and divides into slips, 
which become the perforated tendons of more or fewer of 
the digits. The flexor carpi radialis is also roughly repre- 
sented by the tibialis posticus—a muscle which passes from 
the tibia and interosseous membrane to the entocuneiform, 
and therefore differs in insertion, as well as in origin, from 
its analogue in the fore limb. The flexor perforatus digi- 
torwm of the foot takes its origin sometimes from the calca- 
neum; sometimes, in part from the calcaneum, and in 


THE ELECTRICAL ORGANS. 57 


part from the perforating flexor; or it may be closely 
connected with the tendons of the plantaris. The peroncus 
brevis represents the flexor carpi ulnaris by its insertion, 
but it arises no higher than the fibula, and has no sesamoid. 

Two most important muscles yet remain to be con- 
sidered in the leg. The one of these is that which is in- 
serted by the tendo-achillis into the caleaneum, and arises 
by four heads, two from the condyles of the femur (called 
gastrocnemius), and two from the tibia and fibula (called 
soleus). The other muscle is the peroneus longus, arising 
from the fibula, passing behind the external malleolus, and 
then crossing the foot to the base of the metatarsal of the 
hallux. 

The latter muscle does not appear to have any represen- 
tative in the fore hmb. The gastrocnemius and soleus may 
possibly represent the crural part of the perforated flexor, 
since in many of the Vertebrata, the tendo-achillis is but 
loosely connected with the calcaneum, and passes over it 
into the plantar fascia and the perforated tendons. A 
peculiar adductor muscle of the hallux in Man and Apes is 
the transversalis pedis, which is inserted into the basal 
phalanx of the hallux, and arises from the distal ends of 
the metatarsals of the other digits. The muscle sometimes 
has an analogue in the manus. 


Electrical Organs.—Certain fishes belonging to the genera 
Torpedo (among the Hlasmobranchii), Gymnotus, Malap- 
terurus, and Mormyrus (among the Teleostei), possess 
organs which convert nervous energy into electricity, just 
as muscles convert the same energy into ordinary motion, 
and therefore may well be mentioned in connection with 
the nervous system. The “electrical organ” is always 
composed of nearly parallel lamelle of connective tissue, 
inclosing small chambers, in which lie what are termed the 
electrical plates. These are cellular structures, in one face 
of which the final ramifications of the nerves, which are 
supplied to the organ by one or many trunks, are dis- 
tributed. The face on which the nerves ramify is in all 


58 THE ANATOMY OF VERTEBRATED ANIMALS. 


the plates the same, being inferior in Torpedo, where the 
lamelle are disposed parallel to the upper and under surfaces 
of the body; posterior in Gymnotus, and anterior in Malap- 
terwrus, the lamelle being disposed perpendicularly to the 
axis in these two fishes. And this surface, when the dis- 
charge takes place, is always negative to the other. 


Fig. 18.—The Torpedo, with its electrical apparatus displayed.—é, 
branchiz ; c, brain; e, electric organ; g, cranium ; m e, spinal cord: 
n, nerves to the pectoral fins; nl, nervi laterales ; np, branches of 
the pneumogastric nerves going to the electric organ; 0, eye. 


In Torpedo the nerves of the electrical organs proceed 
from the fifth pair, and from the “ electric lobe” of the 
medulla oblongata, which appears to be developed at the 
origin of the pneumogastrics. In the other electrical fishes 


THE ENCEPHALON. 59 


the organs are supplied by spinal nerves; and in Malapte- 
rurus, the nerve consists of a single gigantic primitive fibre, 
which subdivides in the electrical organ. 

The ordinary Rays possess organs of much the same 
structure as the electrical apparatus, at the sides of the tail. 


The Nervous System: the Encephalon.—In all vertebrated 
animals except Amphioxus, the brain exhibits that separa- 
tion into a fore-brain, mid-brain, and hind-brain, which results 
from its embryonic division by two constrictions, into the 
three thin-walled vesicles—the anterior, middle, and pos- 


| terior cerebral vesicles—already mentioned. The cavities 


of these vesicles—the primitive ventricles of the brain— 
freely communicate at first, but become gradually dimi- 
nished by the thickening of their sides and floors. The cavity 
of the anterior vesicle is, in the adult human brain, repre- 
sented by the so-called third ventricle; that of the middle 
vesicle, by the wer a tertio ad quartum ventriculum; that of 
the posterior vesicle, by the fourth ventricle. 

The floor and sides of the posterior vesicle, in fact, thicken 
and become the medulla oblongata; together with the pons 
varolii, in those animals which possess the latter structure. 
The posterior part of the roof is not converted into nervous 
matter, but remains thin and attenuated ; the ependyma, or 
lining of the cerebral cavity, and the arachnoid, or serous 
membrane which covers the brain externally, coming nearly 
into contact, and forming, to all appearance, a single thin 
membrane, which tears with great readiness, and lays open 
the cavity of the fourth ventricle. Anteriorly, on the other 
hand, the roof becomes converted into nervous matter, and 
may enlarge into a complex mass, which overhangs the 
posterior division, and is called the cerebellum. The pons 
varolii, when it exists, is the expression of commissural 
fibres, which are developed in the sides and floor of the 
anterior part of the posterior cerebral vesicle, and connect 
one half of the cerebellum with the other. 

Thus the hind-brain differs from the posterior cerebral 
vesicle in being differentiated into the medulla oblongata 


60 THE ANATOMY OF VERTEBRATED ANIMALS. 


(or myelencephalon) behind, and the cerebellum with the pons 
varolii (which together constitute the metencephalon) in front. 


Fig. 19. 


Fig. 19.—Diagrammatic horizontal section of a Vertebrate brain. The 
following letters serve for both this figure and Fig. 20:—Mb, Mid- 
brain. What lies in front of this is the fore-brain, and what lies 
behind, the hind-brain. £.¢. the lamina terminalis ; Olf, the ol- 
factory lobes; Hmp, the hemispheres; 7h. #, the thalamence- 
phalon; Pn, the pineal gland; Py, the pituitary body; FM, the 
foramen of Munro; CS, the corpus striatum; Zh, the optic tha- 
lamus; CQ, the corpora quadrigemina; CC, the crura cerebri; 
Cb, the cerebellum; PV, the pons varolii; MO, the medulla 
oblongata; J, olfactorii; JZ, optici; ZZJ, point of exit from the 
brain of the motores oculorum; JV, of the pathetici; VJ, of the 
abducentes ; V-XJJ, origins of the other cerebral nerves. 1, olfac- 
tory ventricle; 2, lateral ventricle; 3, third ventricle; 4, fourth 
ventricle; +, iter a tertio ad quartum ventriculum. 


The floor of the middle cerebral vesicle thickens, and 
becomes converted into two great bundles of longitudinal 


THE ENCEPHALON. 61 


fibres, the crura cerebri. Its roof, divided into two, or four, 
conyexities by a single longitudinal, ora crucial, depression, 
is converted into the “optic lobes,” corpora bigemina or 
quadrigemina. And these parts, the optic lobes, the crura 
cerebri, and the interposed cavity, which either retains the 
form of a ventricle, or is reduced to a mere canal (the 
iter a tertio ad quartum ventriculum), are the components 
of the mid-brain or mesencephalon. 


Fig. 20.—A longitudinal and vertical section of a Vertebrate brain. 
The letters as before. The lamina terminalis is represented by the 
strong black line between FM and 3. 


The anterior cerebral vesicle undergoes much greater 
changes than either of the foregoing; for, in the first place, 
it throws out from its anterior lateral parietes two hollow 
prolongations, the hemispheres (or prosencephala), and each 
of these again protrudes from its anterior end a smaller 
hollow process, the olfactory lobe (or rhinencephalon). By 
the development of these processes the anterior vesicle 
becomes divided into five parts—one median and posterior, 
and four anterior and paired. The median and posterior, 
which remains as the representative of the greater part ‘of 
the original anterior cerebral vesicle, is the vesicle of the 
third ventricle (or thalamencephalon). Its floor is produced 
into a conical process, the infundibulum, the blind end of 
which is connected with the pituitary body, or hypophysis 
cerebri. Its sides thicken greatly, acquire a ganglionic 


62 THE ANATOMY OF VERTEBRATED ANIMALS. 


structure, and become the optic thalami. Its roof, on the 
other hand, resembles that of the fourth ventricle, in 
remaining very thin, and, indeed, a mere membrane, The 
pineal gland, or epiphysis cerebri, is developed in connection 
with the upper wall of the third ventricle; and, at the sides 
of its roof, are two nervous bands, which run to the pineal 
gland, and are called its peduncles. 

The front wall of the vesicle, in part, becomes the so-called 
lamina terminalis, which is the delicate anterior boundary 
of the third ventricle. In certain directions, however, it 
thickens and gives rise to three sets of fibres, one trans- 
verse and two vertical—the former lying in front of the 
latter. The transverse fibres pass on either side into the 
corpora striata, and constitute the anterior commissure which 
connects those bodies. The vertical fibres are the anterior 
pillars of the fornix, and they pass below into the floor of 
the third ventricle, and into the corpora mammillaria, when. 
those structures are developed. 

The outer and under wall of each cerebral hemisphere 
thickens and becomes the corpus striatum, a ganglionic 
structure which, from its origin, necessarily abuts against 
the outer and anterior part of the optic thalamus. The 
line of demarcation between the two corresponds with the 
lower lip (tenia semicircularis) of the aperture of communi- 
cation (called the foramen of Munro) between the third ven- 
tricle and the cavity of the cerebral hemisphere, which is now 
termed the lateral ventricle. In the higher Vertebrata, the 
upper lip of the foramen of Munro thickens, and becomes 
converted into a bundle of longitudinal fibres, which is con- 
tinuous, anteriorly, with the anterior pillars of the fornix 
before mentioned. Posteriorly, these longitudinal fibres are 
continued backwards and downwards along the inner wall 
of the cerebral hemisphere, following the junction of the 
corpora striata and optic thalami, and pass into a thicken- 
ing of the wall of the hemisphere, which projects into the 
lateral ventricle, and is called the hippocampus major, Thus 
a longitudinal commissural band of nervous fibres, extend- 
ing from the floor of the third ventricle to that of the lateral 


: THE MODIFICATION OF THE BRAIN. 63 
yentricle, and arching over the foramen of Munro, is pro- 
‘duced. The fibres of opposite sides unite over the roof of 
the third ventricle, and constitute what is called the body 
of the fornix. Behind this union the bands receive the 
name of the posterior pillars of the fornix. 

The optic thalami may be connected by a grey soft com- 
missure; anda posterior commissure, consisting of transverse 
nerve-fibres, is generally developed between the posterior 
ends of the two thalami. 

In the Mammalia, a structure, which is absent in other 
Vertebrata, makes its appearance; and, in the higher members 
of that class, this corpus callosum is the greatest and most im- 
portant mass of commissural fibres. It is a series of trans- 
verse fibres, which extends from the roof of one lateral ventri- 
cle to that of the other, across the interval which separates 
the inner wall of one hemisphere from that of the other. 

When the corpus callosum is largely developed, its an- 
terior part crosses the interspace between the hemispheres 
considerably above the level of the fornix; so that between 
the fornix and it, a certain portion of the inner wall of each 
hemisphere, with the intervening space, is intercepted. The 
portion of the two inner walls and their interspace, thus 
isolated from the rest, constitutes the septwm lucidum, with 
its contained fifth ventricle. 

The Modifications of the Brain.—The chief modifications 
in the general form of the brain arise from the development 
of the hemispheres relatively to the other-parts. In the 
lower vertebrates the hemispheres remain small, or of so 
moderate a size as not to hide, by overlapping, the other 
divisions of the brain. But, in: the higher Mammalia, 
they extend forwards over the olfactory lobes, and back- 
wards over the optic lobes and cerebellum, so as com- 
pletely to cover these parts; and, in addition, they are 
enlarged downwards towards the base of the brain. The 
cerebral hemisphere is thus, as it were, bent round its 
corpus striatum, and it becomes distinguished into regions, or 
lobes, which are not separated by any very sharp lines of 
demarcation, These regions are named the frontal, parietal, 


64 THE ANATOMY OF VERTEBRATED ANIMALS. 


occipital, and temporal lobes—while, on the outer side of the 
corpus striatum, a central lobe (the insula of Reil) les in 
the midst of these. The lateral ventricles are prolonged 
into the frontal, occipital, and temporal lobes, and acquire 
what are termed their anterior, posterior, and descending, 
cornua. 

Furthermore, while, in the lower vertebrates, the surface 
of the cerebral hemispheres is smooth; in the higher, it be- 
comes complicated by ridges and furrows, the gyri and sulci, 
which follow particular patterns. The superficial vascular 
layer of connective tissue which covers the brain, and is 
called pia mater, dips into these sulci: but the arachnoid, 
or delicate serous membrane, which, on the one hand, covers 
the brain, and, on the other, lines the cranium, passes from 
convolution to convolution without entering the sulci.. The 
dense periosteal membrane which lines the interior of the 
skull, and is itself lined by the parietal layer of the arach- 
noid, goes by the name of the dura mater. : 

The general nature of the modifications observable in the 
brain as we pass from the lower to the higher mammalia 
is very well shown by the accompanying figures of the brain 
of a Rabbit, a Pig, and a Chimpanzee (Figs. 21 & 22). 

In the Rabbit, the cerebral hemispheres leave the cere- 
bellum completely exposed when the brain is viewed from 
above. There is but a mere rudiment of the Sylvian fissure 
at Sy, and the three principal lobes, frontal (A), occipital (B), 
and temporal (C), are only indicated. The olfactory nerves 
are enormous, and pass by a broad smooth tract, which 
occupies a great space in the lateral aspect of the brain, 
into the natiform protuberance of the temporal lobe (C). 

In the Pig, the olfactory nerves and tract are hardly less 
conspicuous ; but the natiform protuberance is more sharply 
notched off, and begins to resemble the unciform gyrus in 
the higher Mammalia, of which it is the homologue. The 
temporal gyri (C'), though still very small, begin to enlarge 
downwards and forwards over this. The upper part of the 
cerebral hemisphere is much enlarged, not only in the 
frontal, but also in the occipital region, and to a great extent 


Fig. 21.—Lateral views of the brains of a Rabbit, a Pig, and a Chim- 
panzee, drawn of nearly the same absolute size. The Rabbit’s brain 
is at the top; the Pig’s, in the middle, the Chimpanzee’s, lowest. 


FP 


66 THE ANATOMY OF VERTEBRATED ANIMALS. 


Cl, the olfactory lobe; A., the frontal lobe; B., the occipital lobe ; 
C., the temporal lobe ; Sy., the Sylvian fissure ; In., the insula; S. Or., 
supraorbital; S.f., W.F., I.F., superior, middle, and inferior frontal 
gyri; A.P, antero-parietal; P.P., postero-parietal gyri; R, sulcus 
of Rolando; P. PJ, postero-parietal lobule; O.P/., external perpen- 
dicular or occipito-temporal sulcus; An, angular gyrus; 2, 3, 4, an- 
nectent gyri; A.7., M.T., P.7T. the three temporal, and S.Oc., 
M. Oc., I, Oc. the three occipital gyri. 
hides the cerebellum when the brain is viewed from above. 
What in the Rabbit was a mere angulation at Sy, in the 
Pig has become a long sulcus—the Sylvian fissure, the 
lips of which are formed by a gyrus, the Sylvian, or angular, 
gyrus. Two other sets of gyri, more or less parallel with 
this, are visible upon the outer surface of the hemisphere; 
and at the entrance of the Sylvian fissure, at Jn, there is an | 
elevation which answers to the insula, or central lobe. 
In the Chimpanzee, the olfactory nerves, or rather lobes, } 
are, relatively, very small, and the tracts which connect them 
with the uncinate gyri (substantie perforate) are completely 
hidden by the temporal gyri (C'). The Sylvian fissure is 
very long and deep, and begins to hide the insula, on which 
a few fan-shaped gyri are developed. The frontal lobes are 
very large, and overlap the olfactory nerves for a long } 
distance; while the occipital lobes completely cover and 
extend beyond the cerebellum, so as to hide it completely 
from an eye placed above. The gyri and sulci have now } 
attamed an arrangement which is characteristic of all the 
highest Mammalia. The fisswre of Rolando (R) divides the 
antero-parietal gyrus (A.P) from the postero-parietal (P.P). } 
These two gyri, with the postero-parietal lobule (P.PI.), and 
part of the angular gyrus (A), constitute the Parietal lobe. 
The frontal lobe, which les anterior to this, the occipital lobe, 
which lies behind it, and the temporal lobe, which lies below 
it, each present three tiers of gyri, which, in the case of the 
frontal and occipital lobes, are called superior, middle, and 
inferior—in that of the temporal lobe, anterior, middle, 
and posterior. The inferior surface of the frontal lohe, 
which lies on the roof of the orbit (8. Or.), presents many 
small sulci and gyri. 
On the inner face of the cerebral hemisphere (Fig. 22) | 


ig. 22.—Inner views of the cerebral hemispheres of the Rabbit, 
Pig, and Chimpanzee, drawn as before, and placed in the same order 
Ol. olfactory lobe: C.c. corpus cailosum; A.c. anterior commissure ; 
H. hippocampal sulcus ; Un. uncinate ; MW. marginal; C. callosal gyri ; 


Tp. internal perpendicular; Ca. calcarine; Coll. collateral sulci: 
F. fornix. 


68 THE ANATOMY OF VERTEBRATED ANIMALS, 


the’ only suleus presented by the Rabbit’s brain is that 
deep and broad depression (H), which runs parallel with the 
posterior pillar of the fornix, and gives rise, in the interior 
of the descending cornu of the lateral ventricle, to the} 
projection which is termed the hippocampus major. In} 
the Pig, this hippocampal sulcus (H) is much narrower and } 
less conspicuous; and a marginal (M) and a callosal (C) 
gyrus are separated by a well-marked calloso - marginal } 
sulcus. As in the Rabbit, the uncinate gyrus forms the in- } 
ferior boundary of the hemisphere. In the Chimpanzee, the 
marginal and callosal gyri are still better marked. There } 
is a deep internal perpendicular, or occipito-parietal, sulcus } 
(Ip). The calearine sulcus (Ca) causes a projection into J 
the floor of the posterior cornu, which is the hippocampus } 
minor ; while the collateral sulcus (Coll) gives rise to the emi- | 
nence of that name in both the posterior and descending } 
cornua. The hippocampal sulcus (H) is relatively insigni- | 
ficant, and the lower edge of the temporal lobe is formed by } 
the posterior temporal gyrus. 

In the Rabbit, the corpus callosum is relatively small, } 
much inclined upwards and backwards; and its anterior | 
extremity is but slightly bent downwards, so that the so- } 
called genw and rostrwm are inconspicuous. The Pig’s } 
corpus callosum is larger, more horizontal, and possesses } 
more of a rostrum: in the Chimpanzee, it is still larger, } 
somewhat deflexed, and very thick posteriorly; and has a 
large rostrum. In proportion to the hemispheres, the } 
anterior commissure is largest in the Rabbit and smallest } 
in the Chimpunzee. The Rabbit and the Pig have a single } 
corpus mammillare, the Chimpanzee has two. The cere- 
bellum of the Rabbit is very large in proportion to the 
hemispheres, and is left completely uncovered by them in } 
the dorsal view. Its median division, or vermis, is straight, 
symmetrical, and large in proportion to the lateral lobes. } 
The flocculi, or accessory lobules developed from the latter, } 
are large, and project far beyond the margins of the lateral 
lobes. The ventral face of the metencephalon presents 
on each side, behind the posterior margin of the pons: 


THE MYELON. 69 


yarolii, flattened rectangular are, the so-called corpora 
trapezoidea. 

In the Pig, the cerebellum is relatively smaller, and is 
partially covered by the hemispheres; the lateral lobes are 
larger in proportion to the vermis and the flocculi, and 
extend over the latter. The corpora trapezoidea are smaller. 
In the Chimpanzee, the relatively still smaller cerebellum is 
completely covered; the vermis is very small in relation to 
the lateral lobes, which cover and hide the insignificant 
flocculi. There are no corpora trapezoidea. 

Tn all the characters now mentioned the brain of Man 
differs far less from that of the Chimpanzee than that of 
the latter does from the Pig’s brain. 


The Myelon—The spinal canal, and the cord which it 
contains, are lined by continuations of the three mem- 
branes which protect the encephalon. The cord is sub- 
cylindrical, and contains a median longitudinal canal, the 
eanalis centralis, the remains of the primitive groove. It is 
divided by anterior and posterior median fissures into two 
lateral halves, which are, usually, connected only by the 
comparatively narrow isthmus, which immediately sur- 
rounds the canalis centralis. The cord may, in the adult, 
extend through the whole spinal canal, or it may come to 
an end at any point between the caudal extremity and the 
anterior thoracic region. 

The distribution of the two essential constituents of 
nervous tissue, ganglionic corpuscles and nerve-fibres, is 
very definite in the spinal cord, ganglionic corpuscles being 
confined to the so-called “ grey matter” which constitutes 
the isthmus, and spreads out into two masses, each of which 
ends in an anterior (or ventral) and a posterior (or dorsal) 
horn. Nerve-fibres also abound in the grey matter; but 
the so-called “ white matter,” which constitutes the external 
substance of the cord, contains only the fibrous nervous 
matter, and has no ganglionic corpuscles. 

The spinal nerves arise in opposite pairs from the two 
halves of the cord, and usually correspond in number with 


0 THE ANATOMY OF VERTEBRATED ANIMALS. 


Fig. 23.—A diagrammatic view of the Chiet Trunks of the Cerebro- 
spinal and Sympathetic Nervous Systems of Rana esculenta seen 
from below (twice the size of nature). I. The olfactory nerves. 
N. The olfactory sac. II. The optic nerve. O. The eye. JL, op. 
The optic lobes. Ta. Optic tracts passing from the optic lobes to 


THE CEREBRAL NERVES. 71 


the chiasma, behind which lies the pituitary body. III. Oculomo- 
iorius. {V. Patheticus. V. The trigeminal, with which the abducens 
(VI.), facialis (VII.), and the upper end of the sympathetic (VS.), 
are closely connected. Branches of this nervous plexus are J’.a, 
the nasal and ophthalmic branches of the fifth and the abducens 
V, b, c, d, the palatine, maxillary, and mandibular branches of the 
fifth. V7, e, the tympanic branch into which the proper facial nerve 
( VII.) enters, and, with a branch of the vagus, forms the so-called 
facial nerve ot the Frog, F. VIII. The auditory nerve. X., with 
its branches Xi, X2, X38, X4, represents the glossopharyngeal und 
the vagus. ‘The medulla oblongata (Myelencephalon) ends, and the 
medulla spinalis (Myelon) begins, about the region marked by the 
letter 17. MM 1-10, the spinal nerves. JM 2, the brachial nerves, 
M 7, 8, 9, the ischiatic plexus, trom which proceed the crural 
N.c.) and ischiatic (N.i.) nerves. S. The trunk ot the sympa- 
thetic. S.M. “he communicating branches with the spinal ganglia. 
S 1-10. The sympathetic ganglia. 


the vertebre through, or between, which they pass out 
(Fig. 23). Hach nerve has two roots, one from the dorsal, and 
one from the ventral, region of its half of the cord. The 
former root has a ganglionic enlargement, and only con- 
tains sensory fibres; the latter has no ganglion, and ex- 
clusively contains motor fibres.* After leaving the vertebral 
canal, each spinal nerve usually divides into a dorsal and a 
ventral branch; but, in the Ganoid fishes, each of these 
branches is a distinct nerve, arising by its own proper roots. 


The Cerebral Nerves.—The greatest number of pairs of 
nerves ever given off from the vertebrate brain is twelve, in- 
eluding the so-called olfactory nerves, and the optic nerves, 
which, as has been seen, are more properly diverticula of 
the brain, than nerves in the proper sense of the word. 

The olfactory “nerves” (olfactorii) constitute the first 
pair of cerebral nerves. They always retain their primary 
connection with the cerebral hemispheres, and frequently 
contain, throughout life, a cavity, the olfactory ventricle, 
which communicates with the lateral ventricle. 

The optic “nerves” (optici) are the second pau of cere- 
bral nerves. In the Lampreys and Hags (Marsipobranchiz) 
these nerves retain their embryonic origin from the thala- 


* Amphioxus appears to be an exception to this, as to most other, 
rules of Vertebrate anatomy. 


72 THE ANATOMY OF VERTEBRATED ANIMALS. 


mencephalon, and each goes to the eye of its own side. 
In other Vertebrata, the nerves cross one another at the 
base of the brain (Teleostei), or are fused together into a 
chiasma (Ganoidei, Elasmobranchii, and all the higher Verte- 
brata). Inthe higher Vertebrata, again, the fibres of the optic 
nerves become connected chiefly with the mesencephalon. 

All the other cerebral nerves differ from these in arising, 
not as diverticula of any of the cerebral vesicles, but by 
histological differentiation of the primitive brain-case, or 
lamine dorsales of the skull. 

The third (motores oculorwn) and fourth (pathetici) pairs 
of nerves are distributed to the muscles of the eye; the 
third to the majority of these muscles, the fourth to the 
superior oblique muscles.. The third pair of nerves issues 
from the crura cerebri, or inferior division of the meten- 
cephalon, upon the base of the brain; the fourth pair, from 
the forepart of the upper division of the metencephalon, 
immediately behind the optic lobes, upon the superior 
surface of the brain. This region is known as the Valve of 
Vieussens in the Mammalia, 

All the other cerebral nerves originate in the posterior 
division of the hind-brain—the myelencepkalon. The great 
jifth pair (trigemini) passes out from the sides of the meten- 
cephalon, and supplies sensory nerves to the integument of 
the head, and motor nerves to most of the muscles of the 
jaws, by its three divisions—the ophthalmic, the superior 
mawillary, and the inferior mawillary, nerves. 

Of these divisions the two latter are, very generally, 
closely connected together, while the ophthalmic division 
remains distinct. The ophthalmic division passes to the 
cleft between the trabecula and the maxillary process (which 
nearly corresponds with the orbit, and might be termed the 
orbito-nasal cleft), and is distributed to the inner and the 
outer side of that cleft. Hence its main branches are nasal 
and lachrymal. The two maxillary nerves, on the other 
hand, are distributed to the inner and outer sides, or ante- 
rior and posterior boundaries, of the buccal cleft. Hence 
the superior maxillary belongs to the posterior, or -outer, 


- 


THE CEREBRAL NERVES. 73 


ide of the maxillary process, while the inferior maxillary 
appertains to the anterior region of the first visceral arch. 
e superior maxillary commonly unites with the outer, 
or lachrymal, division of the ophthalmic; the inferior maxil- 
lary with the anterior division of the facial. 

In the higher Vertebrata, the trigeminal nerve usually 
has two very distinct roots, a dorsal sensory, provided with 
a ganglion (the Casserian ganglion), and a ventral motor, 
on-ganglionated. The fibres of the latter pass almost ex- 
clusively into the inferior maxillary division. In addition, 
the ophthalmic division may have a ganglion (ciliary); the 
superior maxillary another (sphenopalatine or Meckelian), 
and the inferior maxillary a third (otic). 

The sixth pair (abducentes) issues from the inferior sur- 
ace of the brain, at the junction of the myelencephalon 
ith the metencephalon. It supplies the external straight 
muscles of the eye; with the muscles of the nictitating 
membrane, and the retractor bulbi, or musculus choanoides, 
when such muscles exist. 

The seventh pair (faciales) supplies the superficial facial 
muscles, and ultimately divides into two branches, one of 
which is in relation with the mandibular, and the other with 
the hyoidean arch. 

The five nerves which have just been mentioned are often 
intimately connected together. Thus, in the Lepidosiren, 
he three motor nerves of the eyeball are completely fused 
ith the ophthalmic division of the fifth.* In the Myxinoid 
shes there are no motor nerves of the eyeball; but, in the 
Lamprey, the rectus externus and inferior, and the obliquus 
inferior, are supplied by the ophthalmic, while the oculo- 
motor and the pathetic unite into a common trunk, which 
gives branches to the rectus swperior and internus, and 
obliquus superior. The oculomotor, the pathetic, and the 


* Tam greatly disposed to think 
that the motor nerves of the eye 
more nearly retain their primary 
relations in Lep/dosiren than in 
any other vertebrated animal ; 
and that they are really the motor 


portions of the nerves of the or- 
bito-nasal cleft, the third and 
fourth appertaining to the inner 
division of the ophthalmic, the 
sixth to its outer division. 


74. THE ANATOMY OF VERTEBRATED ANIMALS. 


abducens, are more or less confounded with the ophthalmic 
in the Amphibia; but in Teleostei, Ganoidei, Elasmobranchii, 

and in all the higher Vertebrata, the nerves of the muscles’ 
of the eye are distinct from the fifth pair, except where the 

oculomotor unites with the ophthalmic into the ciliary 

ganglion. 

The facial and the trigeminal nerves have common roots 
in fishes. In Amphibia, though the roots are distinct, the 
facial may be completely united with the ganglion of the 
trigeminal, as in the Frog. In all abranchiate Vertebrata 
the two nerves are quite distinct. 

Whether the nerves are distinct or not, a palatine, or 
vidian, nerve (which, in the higher Vertebrata, is especially 
connected with the facial) runs through, or beneath, the 
base of the skull, parallel with its long axis; and, after 
uniting with the superior maxillary, and usually contri- 

' buting to form the sphenopalatine, or Meckelian, ganglion, is 
distributed to the mucous membrane of the roof of the 
mouth; and the mandibular division of the seventh, or 
chorda tympani, unites with the inferior maxillary division 
of the fifth nerve. 

The eighth pair (auditorii) is formed by the nerves of the 
organ of hearing. 

The ninth pair (glossopharyngei) is especially distributed 
to the pharyngeal and lingual regions of the alimentary 
canal, and, primarily, supplies the boundaries of the second 
visceral cleft. 

The tenth pair (pnewmogastrici or vagi) consists of very 
remarkable nerves, which pass to the gullet and stomach, 
the respiratory and vocal organs, to some parts of the 
integument of the body, and to the heart. In the Ichthyop- 
sida they give off, in addition, long lateral nerves to the 
integuments of the sides of the body. In the higher Verte- 
brata, these lateral nerves are represented only by small 
branches distributed chiefly to the occipital region. The 
ninth and tenth pairs are both motor and sensory in func- 
tion, and are often so intimately connected as to form almost 
one nerve. 


THE EXITS OF THE CEREBRAL NERVES. 75 


The eleventh pair (accessorii) are cerebral only by courtesy, 
as these nerves take their origin from the spinal cord, by 
roots which issue between the proper anterior and posterior 
roots of the spinal nerves, and, joining together, form, on 
each side, a nerve which passes out with the pneumogastric, 
partly joining it, and partly going to muscles which arise 
from the head and anterior vertebre, and are inserted into 
the pectoral arch. 

The spinal accessory exists in no Ichthyopsid vertebrate, 
but is found in all Sawropsida, with the exception of the 
Ophidia, and in the Mammalia. 

The twelfth and last pair (hypoglossi) are the motor nerves 
of the tongue, and of some retractor muscles of the hyoidean 
apparatus. 

In the Ichthyopsida the first cervical nerve supplies the 
distributional area of the hypoglossal; but in all the abran- 
chiate Vertebrata there is a hypoglossal, which traverses a 
foramen in the ex-occipital, though it often remains closely 
connected with the first cervical, and may rather be re- 
garded as a subdivision of that nerve, than as a proper 
cerebral nerve. 

Thus the nerves arising from the hind-brain, in all the 
higher Vertebrata, fall into three groups: Ist, a sensori- 
motor, pre-auditory, set (3rd, 4th, 5th, 6th, 7th); 2nd, the 
purely sensory auditory nerve (8th) ; 3rd, the sensori-motor, 

post-auditory, set (9th, 10th, 12th). 
~The apertures by which several of these nerves leave the 
skull, retain a very constant relation to certain elements 
of the cranium on each side. Thus: 
a. The filaments of the olfactory nerve always leave 
the cranium between the lamina perpendicularis, or body 
of the ethmoid, and its lateral or prefrontal portion. 

b. The optic nerve constantly passes out behind the 
centre of the orbitosphenoid and in front of that of the 
alisphenoid. 

ce. The third division of the trigeminal, or fifth nerve, 
always leaves the skull behind the centre of the alisphenoid 
and in front of the pro-otic. 


76 THE ANATOMY OF VERTEBRATED ANIMALS. 


i 


d. The glossopharyngeal and pneumogastric always make 
their exit behind the centre of the opisthotic, and in front 
of the centre of the ex-occipital. 

The apertures for the exit of the cranial nerves denoted 
in the paragraphs, a. b. c. d., when surrounded by bone, and 
well defined, are called respectively : a, the olfactory foramen ; 
b, the optie foramen; c, the foramen ovale; d, the foramen 
lacerum posterius. The adjacent bones may take equal shares 
in bounding these foramina, or the foramina may be alto- 
gether in one bone; but their positions, as here defined, 
never change. 

Another point to be especially considered respecting the 
general disposition of the cranial nerves, is the relation 
which some of them bear to the visceral arches and clefts, 
and which has already been incidentally mentioned. Thus, 
the seventh nerve is distributed to the posterior part of the 
first visceral arch, and to the anterior part of the second 
visceral arch, its two branches inclosing the first visceral 
cleft. In like manner, the ninth (glossopharyngeal) nerve 
is distributed to the hinder part of the second arch and to 
the front part of the third, its branches inclosing the 
second visceral cleft. The first. branch of the pneumo- 
gastric has similar relations to the third and fourth arches 
and to the third cleft; and in branchiate Vertebrata, the 
other anterior branches of the pneumogastric are similarly 
distributed to the successive branchial arches, the two divi- 
sions of each branch inclosing a branchial cleft. 

The second and the third divisions of the trigeminal are 
distributed, in an analogous manner, to the anterior region 
of the first visceral arch, and to the posterior or outer 
region of the maxillo-palatine process—the gape of the 
mouth representing a visceral cleft between the two. The 
inner and outer portions of the first division of the tri- 
geminal are similarly related to the inner, or anterior, 
region of the maxillo-palatine process, and the outer side 
of the trabecula cranii—the orbito-nasal fissure representing 
the cleft between the two. 

Considerations of this kind suggest that the trabecule 


THE SYMPATHETIC NERVES. Ta 


and the maxillo-palatine processes may represent pre-oral 
visceral arches, which are bent forward; and, in the case of 
the trabecule, coalesce with one another. Such an hypothesis 
would enable us to understand the signification of the naso- 
palatine canal of the Myxinoid fishes, which would be simply 
the interspace, or passage, between the trabeculz (which 
must have originally existed if ever they were distinct 
visceral arches) not yet filled up; and the anomalous process 
of the roof of the oral cavity, which extends towards the 
pituitary body in the embryos of the Vertebrata in general, 
might be regarded as the remains of this passage. 

On this hypothesis, six pair of inferior arches belong to 
the skull—namely, the trabecular and maxillo-palatine, in 
front of the mouth; the mandibular, the hyoidean, and two 
others (first and second branchial), behind it. For, as there 

: are three cranial nerves embracing the first three visceral 
clefts which lie behind the mouth, there must be four 
post-oral, cranial, visceral arches. 
Supposing that the occipital segment in the brain-case 
answers to the hindermost, or second branchial, cranial, 
visceral arch, the invariable attachment of the proximal 
ends of the mandibular and hyoidean arches to the auditory 
capsule leads me to assign the parietal and the frontal 
segments to the maxillo-palatine and trabecular visceral 
arches. And thus the ossifications of the auditory capsule, 
alone, are left as possible representatives of the neural 
arches of the three anterior post-oral visceral arches. 

But these speculations upon the primitive composition of 
the skull, however interesting, must not, as yet, be placed 
upon the same footing as the doctrine of its segmentation, 
which is simply a generalisation of anatomical facts. 


The Sympathetic—A Sympathetic Nervous System has 
been observed in all the Vertebrata except Amphioxus and 
the Marsipobranchii. It consists, essentially, of two longi- 
tudinal cords, placed one upon each side of the inferior 
face of the cranio-spinal axis. Hach cord receives commu- 
nicating fibres from the spinal nerves of its own side, and, 


78 THE ANATOMY OF VERTEBRATED ANIMALS. 


when complete, from all the cranial nerves except those of 
the special senses of hearing, sight, and smell—the Vidian 
nerves constituting the anterior terminations of the sympa- 
thetic cords. At the points of communication ganglia are 
developed, and the nerves which emerge from these ganglia 
are distributed to the muscles of the heart and vessels, and 
to those of the viscera. These peripheral nerves of the 
sympathetic system frequently present small ganglionic 
enlargements. 

In the Marsipobranchii, the place of the sympathetic 
appears to be taken, to a great extent, by the pneumogastric ; 
and, in Myzxine, the two pneumogastrics unite upon the in- 
testine, and follow it, as a single trunk, to the anus. 


The Sensory Organs.—The organs of the three higher 
senses—Smell, Sight, and Hearing—are situated, as has 
been already described, in pairs, upon each side of the skull, 
in all vertebrate animals except the lowest fishes; and, in 
their earliest condition, they are alike involutions of the 
integument. 

The Olfactory Apparatus acquires no higher complication 
than this, being either a single sac (Amphiowus (?) Marsipo- 
branchii), or, more commonly, two, the surfaces of which 
are increased by plaiting, or by the development of turbinal 
cartilages, or bones, from the lateral portions of the eth- 
moid. Upon these, nervous filaments arising from the olfac- 
tory lobe of the brain are distributed. The cavities of the 
olfactory sacs may be placed in communication with that 
of the mouth by the nasal passages; or, as in the great 
majority of fishes, they may have only an external aperture, 
or apertures. 

In Reptiles, Birds, and Mammals, a peculiar nasal gland 
is frequently connected with, and pours its secretion into, 
each olfactory chamber. 

The foramina incisiva, left between the premaxillaries and 
the palatine plates of the maxillaries in Mammalia, are 
sometimes closed by the mucous membranes of the nasal and 
oral cavities, and sometimes not. In the latter case they 


THE EYE. 79 


are the canals of Stenson, and place these two cavities in 
communication. Glandular diverticula of the mucous mem- 
brane, supplied with nervous filaments from both the 
olfactory and the fifth pair, may open into these canals. 
They are called, after their discoverer, the “ organs of 
Jacobson.” 


The Hye is formed by the coalescence of two sets of 
structures, one furnished by involution of the tegument, 
the other by an outgrowth of the brain. 

The opening of the integumentary depression which is 
primarily formed on each side of the head in the ocular 
region becomes closed, and a shut sac is the result. The 
outer wall of this sac becomes the transparent cornea of 
the eye; the epidermis of its floor thickens, and is meta- 
morphosed into the crystalline lens; the cavity fills with 
the aqueous humour. A vascular and muscular ingrowth 
taking place round the circumference of the sac, and, 
dividing its cavity ito two segments, gives rise to the iris. 
The integument around the cornea, growing out into a fold 
above and below, results in the formation of the eyelids, and 
‘the segregation of the integument which they inclose, as 
the soft and vascular conjunctiva. The pouch of the con- 
junctiva very generally communicates, by the lachrymal 
duct, with the cavity of the nose. It may be raised, on its 
inner side, into a broad fold, the nictitating membrane, moved 
by aproper muscle or muscles. Special glands—the lachry- 
mal externally, and the Harderian on the inner side of the 
eyeball—may be developed in connection with, and pour 
their secretion on to, the conjunctival mucous membrane. 

The posterior chamber of the eye has a totally distinct 
origin. Very early, that part of the anterior cerebral vesicle 
which eventually becomes the vesicle of the third ventricle, 
throws out a diverticulum, broad at its outer, and narrow 
at its inner end, which applies itself to the base of the in- 
tegumentary sac. The posterior, or outer, wall of the diver- 
ticulum then becomes, as it were, thrust in, and forced 
towards the opposite wall, by an ingrowth of the adjacent 


80 THE ANATOMY OF VERTEBRATED ANIMALS. 


connective tissue ; so that the primitive cavity of the diver- 
ticulum, which, of course, communicates freely with that of 
the anterior cerebral vesicle, is obliterated. The broad end of 
the diverticulum acquiring a spheroidal shape, while its 
pedicle narrows and elongates, the latter becomes the optic 
nerve, while the former, surrounding itself with a strong 
fibrous sclerotic coat, remains as the posterior chamber of 
the eye. The double envelope, resulting from the folding 
of the wall of the cerebral optic vesicle upon itself, gives 
rise to the retina and the choroid coat: the plug, or in- 
growth of connective tissue, gelatinises and passes into the 
vitreous humour, the cleft by which it entered becoming obli- 
terated. 

Even in the higher Vertebrata the optic nerve is, at first, 
connected exclusively with the vesicle of the third ventricle, 
and makes no decussation with its fellow. But by degrees 
the roots of origin of each nerve extend over to the opposite 
side of the brain, and round the thalamus, to the mesen- 
cephalon on that side, and the trunks of the two nerves 
become intermixed below the third ventricle, in a close and 
complicated manner, to form a chiasma. 

In Amphioxus and Myxine, the eyes are very imperfectly 
developed, appearing to consist of little more than a rudi- 
mentary lens imbedded in the pigment, which encloses the 
termination of the optic nerve; and in Myaine, this rudi- 
mentary eye is hidden by muscles and integument. It ap- 
pears doubtful whether in these fishes, and in the Lampreys, 
the eye is developed in the same way as in other Vertebrata. 

In all other Vertebrata, the eyes have the typical structure, 
though sometimes, as in the Blind-fish (Amblyopsis) and the 
Mole, they have no functional importance. In the Ichthy- 
opsida and Sawropsida, but not in Mammalia, the sclerotic 
is often partially ossified, the ossification usually forming a 
ring around its anterior moiety. It becomes enormously 
thickened in the Cetacea. 

Except in Amphioxus and the Myxinoid fishes, the eye- 
ball is moved by six muscles; of these, four, proceeding 
from the interior of the orbit to the periphery of the eye- 


THE EAR. 81 


ball, and surrounding the optic nerve, are termed superior, 
inferior, internal, and external recti. The other two are 
onnected with the upper and the lower margins of the 
rbit respectively, and pass thence to the outer side of the 
bulb. These are the superior and the inferior obliqui. In 
many Reptiles and Mammals a continuous funnel-shaped 
heet of muscle, the musculus choanoides, lies within the four 
ecti, and is attached to the circumference of the posterior 
oiety of the ball of the eye. It would appear, from the 
distribution of the nerves, which has already been described, 
that the musculus choanoides, the external rectus, and the 
nictitating muscle, constitute a group of eye-muscles mor- 
phologically distinct from the other three recti, the obliqui, 
and the levator palpebre superioris. In many Reptiles, and 
in the higher Vertebrata, the eyelids are closed by circular 
muscular fibres, constituting an orbicularis palpebrarum, 
and are separated by straight fibres proceeding from the 
back of the orbit, usually to the upper eyelid only, as the 
levator palpebree superioris; but sometimes to both lids, 
when the luwer muscle is a depressor palpebre inferioris. 

The Harderian and lachrymal glands are not found in 
fishes; but the former is met with in the Batrachia, and 
both are of common occurrence in the Sawropsida and 
Mammalia. 

In Lacertilia, Crocodilia, Aves, and many Fishes, a pecu- 
liar vascular membrane, covered with pigment, like the 
choroid, projects from near the entrance of the optic nerve, 
on the outer side of the globe of the eye, into the vitreous 
humour, and usually becomes connected with the capsule 
‘of the lens. This is the pecten, or marsupiwn. 


The Ear.—The first rudiment of the internal ear is an 
involution of the integument into a small sac, which is 
situated on each side of the posterior cerebral vesicle, just 
above the end of the second visceral cleft. The mouth of 
the involution soon closes, and a shut sac results. The sac 
enlarges, and, by a remarkable series of changes, its upper 
part becomes (ordinarily) converted into three semicircular 
G 


82 THE ANATOMY OF VERTEBRATED ANIMALS. 


canals—the anterior and posterior vertical, and the external 
or horizontal canals of the membranous labyrinth. The body 
of the sac remains, for the most part, as the vestibule; but a 
cecal process, which eventually becomes shut off from the 
vestibule, is given off downwards and inwards, towards the 
base of the skull, and is the rudiment of the scala media of 
the cochlea, This may be called the membranous cochlea. 

In the anomalous vertebrate, Amphiowus, no ear has yet 
been discovered. The Hag (Myaine) has only one, and in 
the Lampreys (Petromyzon) there are only two, semicircular 
canals; but, in fishes in-general, all three are developed, 
and it is a question whether the cochlea is not also repre- 
sented. 

In fishes, the periotic cartilage and its ossifications in- 
close this membranous labyrinth, externally, and present 
no merely membranous gaps, or fenestre, towards the first 
visceral cleft, or the space which represents it. 

But in higher Vertebrata (Amphibia, Sauwropsida, Mam- 
malia), in which the membranous labyrinth is always in- 
closed within a complete bony periotic capsule, the outer 
wall of this capsule invariably remains unossified over one 
or two small oval arew, which consequently appear like 
windows with membranous panes, and are termed the 
fenestra ovalis and the fenestra rotunda. 

The fenestra ovalis is situated in that part of the periotic 
mass which bounds the chamber containing the membranous 
vestibule externally ; and it is always found that when both 
the pro-otic and the opisthotic bones exist, they contribute 
nearly equal shares to the formation of its boundaries. In 
fact, the fenestra ovalis is situated in the line of junction of 
these two bones. The fenestra rotunda, on the other hand, is 
below the fenestra ovalis, and lies altogether in the opisthotic. 
It forms part of the outer wall of the cavity in which the 
membranous cochlea is lodged. 

In the Sauwropsida and Mammalia, this membranous 
cochlea, become flattened and bandlike, and its communi- 
cation with the vestibule obliterated, is lodged in a conical 
cavity, in such a manner as to divide that cavity into two 


THE EAR. 83 


portions, called scale, which only communicate at their 
japices. The base of the one scala, called scala vestibuli, 
opens into the cavity which contains the membranous vesti- 
ule: that of the other, scala tympani, abuts against, and is 
jas it were stopped by, the membrane of the fenestra rotunda. 
|The cavity of the membranous cochlea stretched between, 
and helping to divide, these two scale, is called the scala 
|} media. 

In Reptiles, Birds, and Ornithodelphous Mammals, the 
cochlea is only slightly bent or twisted upon itself. But, in 
jthe higher Mammalia, it becomes coiled in a flat or conical 
spiral of one-and-a-half (Cetacea, Hrinaceus) to five (Celo- 
genys Paca) turns. 

The membranous labyrinth is filled with a clear fluid, the 
ndolymph, and usually contains otolithes of various kinds. 
Between the membranous labyrinth and the walls of the 
cavity of the periotic mass in which it is contained, lies 
another clear fluid, the perilymph, which extends thence into 
the scale vestibuli and tympani. 

In all animals which possess a fenestra ovalis, its mem- 
brane gives attachment to a disc, whence an ossified rod, 
or arch, proceeds. Where the former structure obtains, as 
in Birds, most Reptiles, and some Amphibia, the bone is com- 
monly called columella awris; when the latter, as in most 
Mammals, stapes. But there is really no difference of im- 
ortance between stapes and columella, and it is advisable to 
use the former name for the bone under all its forms. 

In the majority of Vertebrata of higher organization 
an fishes, the first visceral cleft does not become wholly 
obliterated, but its upper part remains as a transversely 
elongated cavity, by means of which the pharynx would be 
laced in communication with the exterior, were it not that 
he opposite sides of the canal grow togethef into a mem- 
branous partition—the membrana tympani. So much of the 
canal as lies external to thisis the external auditory meatus ; 
while what lies internal to it, is the tympanum, or drum of 
the ear, and the Eustachian tube, which places the tympa- 
num in communication withthe pharynx. While the outer 


84. THE ANATOMY OF VERTEBRATED ANIMALS. 


wall of the tympanum is the tympanic membrane, its imner 
wall is the periotic mass with its fenestre ; and, in all 
Vertebrata below Mammals, the outer end of the stapes is 
either free, or, more commonly, is fixed to the tympanic 
membrane, and thus the latter and the membrane of the 
fenestra ovalis become mechanically connected. In all these 
animals the mandible is connected with the skull by the 
intermediation of an os quadratum. 
But, in the Mammalia, the mandible is articulated directly 
with the squamosal, and the quadratwm is converted into 
one of the so-called ossicula auditis, and named the malleus. 
The malleus becomes attached to the membrana tympani, 
by a special process; while its other extremity, which was 
continuous with Meckel’s cartilage in the embryo, is con- 
verted into the processus gracilis, or Folianus, and lies be- 
tween the tympanic, the squamosal, and the periotic bones. 
In the singular lizard Sphenodon (A, Fig. 24), the anterior 
cornu of the hyoid is continuous with the distal end of the 
stapes, and the latter sends a cartilaginous process upwards, 
which passes into the wall of the periotic capsule, just be- 
hind the proximal end of the os quadratum. Thus the stapes 
stands out at right angles to the hyoid cornu, and the latter 
becomes divisible into a supra-stapedial part, and a part 
which lies below the stapes, and answers to the styloid 
process, or stylohyal, of the Mammalia. The supra-stape- 
dial part is represented by cartilage, or ligament, in other 
Sauropsida, but seems not to ossify. In the Mammalia 
(B, Fig. 24) the supra-stapedial part ossifies, becomes the! 
incus, and its proximal end is usually articulated by : 
synovial joint with the malleus (= quadratum). A distine 
ossification, the os orbiculare, usually arises at that pa: 
of the hyoidean cartilage in which the stapes and the incu, 
unite. That part of the hyoidean cartilage which is converted 
into the styloid process is generally connected with the orbicu- 
lare by muscular fibres, which constitute the stapedius muscle. 
On the other hand, the posterior, or short process of the incus, 
is connected by ligament with that part of the periotic mass_ 
into which the styloid process is directly continued, and it} 


THE SKELETON OF THE VISCERAL ARCHES. 85 


‘is hard to say whether the styloid part of the hyoid is con- 
tinued into the incus by these ligaments or by the stapedius. 
But, however this may be, the malleus and the incus are the 
proximal ends of the mandibular and hyoidean arches 
respectively. 

Tn osseous fishes (C, Fig. 24), which have no fenestra ovalis 
or stapes, the supra-stapedial part of the hyoid becomes a 
large bone—the hyomandibular. On the other hand, the 
proximal extremity of the quadrate cartilage atrophies, loses 


Fig. 24. 


Pe 
Mi fil 


Fig. 24.—Diagram of the skeleton of the first and second visceral 
arches in a Lizard (A), a Mammal (B), and an Osseous Fish (C). 
The skeleton of the first visceral arch is shaded, that of the second is 
left nearly unshaded. J. First visceral arch. Meck. Meckel’s car- 
tilage. Art. Articulare. Qu. Quadratum. Mpt. Metapterygoid; 
M. Malleus; p.g., Processus gracilis. JJ. Second visceral arch. 
Hy. yoidean cornu. St. H, Stylohyal. S. Stapedius. Stp. Stapes. 
S. Stp. Supra-stapedial. HM. Hyomandibular. The arrow indicates 
the first visceral cleft. Pc. The periotic capsule. Pig. The pterygoid. 


its direct connection with the periotic capsule, and becomes 
distinctly ossified, as the metapterygoid. In the Sharks, 
even the ascending, metapterygoid, part of the quadrate, 
is lost. 

The quadrate and supra-stapedial portions of the first 
and second visceral arches coalesce in the Chimera, Dipnot, 
and many Amphibia, into a single cartilaginous plate. 


In the Mammalia, and to some extent in Aves, osseous 
matter is deposited in the fibrous tissue which surrounds 
the sides and base of the tympanic membrane, and gives 
rise to a special tympanic bone. In most Mammalia, ossifi- 


86 THE ANATOMY OF VERTEBRATED ANIMALS. 


cation extends into the sides and floor of the tympanum 
and external meatus; and a process of integument, chiefly _ 
derived from the second visceral arch, is converted into a 
concha, or external ear. 


The Organ of Taste is the mucous membrane which covers 
the tongue, especially its posterior region, and probably also 
a part of that lining the fauces. When the sense is well 
developed, the mucous membrane is raised into numerous 
papillz of various forms, and is well supplied with filaments 
from the glossopharyngeal nerve. 

The sense of Touch is diffused over the integument and 
over the mucous membrane of the buccal cavity, which is, 
strictly speaking, a part of the integument. 

As special organs of touch in the higher Vertebrata, the 
nervous papille, containing “tactile corpuscles,” and the 
long facial hairs, the papille of which are well supplied with — 
nerves, termed vibrisse, may be mentioned. 

In most, if not all Fishes, the integument of the body 
and of the head contains a series of sacs, or canals, usually 
disposed symmetrically on each side of the middle line, and 
filled with a clear gelatinous substance. The walls of the 
sacs, or canals, are abundantly supplied with nerves, and 
the terminations of the latter enter rounded papille, which 
project into the gelatinous contents. These sensory organs — 
are known as the “ organs of the lateral line,” or ‘ mucous 
canals ;” and they were formerly supposed to be the secre- 
tory glands of the slimy matter which coats the bodies of 
fishes, and which is really modified epidermis. 


The Alimentary Canal.—This part of vertebrate organi- — 
zation always exhibits a differentiation into mouth, pharynx, 
cesophagus, stomach, and intestine; and the last has always — 
a median, or nearly median, aperture on the ventral surface : 
of the body. It may open by itself; or into a cloaca, or 
chamber common to it, the urinary, and the genital organs. 

The intestine is generally distinguishable into small and 
large; and, at the junction of the two, one or two ceca are 
frequently developed from the former. 


| 
| 
| 


+ 


THE LIVER AND THE TEETH. 87 


The stomach and intestine are invested by a peritoneal 
membrane, and connected, by mesogastric and mesenteric folds 
of that membrane, with the median dorsal wall of the abdo- 
minal cavity. Glands appertaining to the lymphatic system 
frequently abound in the mesenteric folds, and a highly 
vascular gland of this system, the spleen, is always (except 
in Amphiowus, Myxine, and the Leptocephalide) developed 
in close proximity to the stomach. A pancreatic gland very 
generally pours its secretion into the anterior end of the 
intestine. Salivary glands very commonly open into the 
mouth; and, in the higher Vertebrata, anal glands are not 
unusually developed in connection with the termination of 
the rectum. 

The structures connected with the alimentary canal of 
vertebrate animals, which are most characteristic and pecu- 
liar, are the liver and the teeth. 


The Liver.—In invertebrate animals this organ is always 


ultimately resolvable into cecal tubes, the ends of the 


hepatic ducts, which are lined with an epithelium, and not 
reticulated; and it has no receptacle for the bile. In most 
Vertebrata the ends of the hepatic ducts have not been 


- satisfactorily traced, nor is it certain that the immense pro- 


portional mass of hepatic corpuscles is contained in tubes 
continuous with them: if such be the case, the tubes must be 
reticulated. The ducts of the vertebrate liver very frequently 
pour the bile, directly or indirectly, into a receptacle, the gall- 
bladder. Amphiowus stands alone among vertebrated animals, 
in having a cecal diverticulum of the intestine for a liver. 


The Teeth.—Teeth, in Mollusca and Annulosa, are always 
“ecderonic,” cuticular, or epithelial structures. In Verte- 
brata true teeth are invariably “ enderonic,” or developed, 
not from the epithelium of the mucous membrane of the 
alimentary canal, but from a layer between this and the 
vascular deep substance of the enderon, which answers to 
the dermis in the integument. The horny “teeth” of the 
Lampreys, and of Ornithorhynchus, appear to be ecderonic 


$8 THE ANATOMY OF VERTEBRATED ANIMALS. 


structures, homologous with the “baleen” of the Cetacea, 


with the palatal plates of the Sirenia, or the beaks of Birds | 


and Reptiles, and not with true teeth. 


The dense calcified tissue called dentine, characterised — 


by the close-set parallel tubuli which radiate through it, 
branching as they go, constitutes the chief mass of true 
teeth; but the dentine may be coated with ordinary bony 


tissue, which then receives the name of cementum, and its — 


crown may be capped with imperforate, prismatically fibrous, 
enamel. 


The teeth are moulded upon papille of the mucous mem- — 


brane, which may be exposed, but are more usually sunk in 
a fold or pit, the roof of which may close in so as to form a 
dental sac. And there may be one set of teeth, or several ; 
the sacs of the new teeth, in the latter case, being developed 
either as diverticula of the old ones, or independently of 
them. 

In the majority of the Mammalia the teeth are limited in 
number, as well as definite in their forms and their mode of 
succession. There are two sets of teeth, forming a first, deci- 
duous, or milk dentition, and a second, or permanent dentition. 
The deciduous dentition, when most completely developed, 
consists of incisor, canine,and molar teeth. The incisors are 
distinguished from the rest by the lodgment of the upper set 
in the premaxille, and the correspondence of the lower set 
with the upper. Their number and form vary. The dis- 
tinction between canines and molars is one of form and 
position in regard to the remaining teeth; the most anterior 
of the teeth behind the premaxillo-maxillary suture, if it is 


sharp and projecting, receiving the name of canine. There — 


are never more than four canines. The other teeth are molars, 


and ordinarily do not exceed four upon each side, above and — 


below. What is called a dental formula is a convenient 
combination of letters and figures for making the number 
and disposition of the teeth obvious. Thus, let di, de, dm 
represent, respectively, the deciduous, or milk set of incisors, 
canines, and molars. Then, by placing after each of these 
symbols figures arranged so as to show the number of the 


tieaie. (> 


DENTAL FORMUL. 89 


teeth of the kind symbolised, on each side of each jaw, we 

shall have the dental formula of a given animal. The 

dental formula of a child over two years of age is thus— 
. 99 

di. = de. == dm. = = 20: which means that the 

child should have two incisors, one canine, and two molars 

on each side of each jaw. 

The neck of the sac of each deciduous tooth gives off a 
diverticulum, in which one of the permanent teeth is de- 
veloped; as it grows, it causes the absorption of the fang 
of the corresponding deciduous tooth, which thus becomes 
shed, and is replaced from below by the permanent tooth. 
The same letters, but without the prefix d, are used for the 
permanent incisors and canines; but the permanent teeth, 
which replace the deciduous molars, are called premolars, 
and have the symbol pm. Furthermore, three or, it may be, 
four permanent grinding teeth, on each side of each jaw, are 


_ developed altogether behind the milk molars, and thus come 


into place without replacing any other tooth from below. 
These are called molars, and have the symbol m. Thus the 
formula of the permanent dentition in Man is written: 

i en: 5) A 
= c. a pm. = m. = = 32; there being two incisors, 
one canine, two premolars, and three molars on each side 
above and below. It is a rule of very general applica- 
tion among the Mammalia, that the most anterior molar 
comes into place and use before the deciduous molars are 
shed. Hence, when the hindermost premolar, which imme- 
diately precedes the first molar, comes into use by the 
shedding of the last milk molar, the crown of the first molar 
is already a little ground down; and this excess of wear of 
the first molar over the adjacent premolar long remains 
obvious. The fact that, in the permanent dentition, the last 
premolar is less worn than the first molar which imme- 
diately follows it, is often a valuable aid in distinguishing 
the premolar from the molar series. 

No vertebrate animal has teeth in any part of the ali- 
mentary canal save the mouth and pharynx—except a 


90 THE ANATOMY OF VERTEBRATED ANIMALS. 


snake (Rachiodon), which has a series of what must be termed 
teeth, formed by the projection of the inferior spinous pro- 
cesses of numerous anterior vertebre into the cesophagus. 
And, in the highest Vertebrata, teeth are confined to the 
premaxille, maxille, and mandible. 


The Circulatory Organs.—The heart of the vertebrate em- 
bryo is at first a simple tube, the anterior end of which 
passes into a cardiac aortic trunk, while the posterior end 
is continuous with the great veins which bring back blood 
from the umbilical vesicle—the omphalomeseraic veins. 

The cardiac aorta immediately diyides into two branches, 
each of which ascends, in the first visceral arch, in the 
form of a forwardly convex aortic arch, to the under side 
of the rudimentary spinal column, and then runs, parallel 
with its fellow, to the hinder part of the body, as a pri- 
mitive subvertebral aorta. The two primitive aorte very 
soon coalesce throughout the greater part of their length 
into one trunk, the definitive subvertebral aorta; but the 
aortic arches, separated by the alimentary tract, remain 
distinct. Additional arterial trunks, to the number of four 
in the higher Vertebrata, and more in the lower, are succes- 
sively developed, behind the first, in the other visceral arches, 
and further connect the cardiac and subvertebral aorte. 

In the permanently branchiate Vertebrata, the majority of 
these aortic arches persist, giving off vessels to the branchial 
tufts, and becoming converted into afferent and efferent 
trunks, which carry the blood to and take it from these 
tufts. (Fig. 25, A, B, C, D, E.) 

In the higher Amphibia, which, though branchiate in the 
young state, become entirely air-breathers in the adult con- 
dition, such as the Batrachia (Fig. 25, F) and Cecilia, the 
permeable aortic arches are reduced to two (the middle pair 
of the three which supply the external gills, and the fourth 
pair of embryonic aortic arches) by the obliteration of the 
cavities of the dorsal ends of the others. Of the posterior 
arches, the remains of the fifth and sixth become the trunks 
which give off the pulmonary arteries, and, in the Batrachia, 


eS 


MODIFICATIONS OF THE AORTIC ARCHES. 91 


Fig. 25. 
Mn. Hy. Br! Br? Br? Brf Br: Br:© Br:7 
janie Sas te 


« (eeeleeel. 


De SL Vas AV VI «Villy A 


alee" 


ea) 


OL 


1 
1 
' 
\ 


1 
' 
Bo Ee EE St Va WIS IE ea 


Fig. 25.—A diagram intended to show the manner in which the aortic 
arches become modified in the series of the Vertebrata. 

A. A hypothetically perfect series of aortic arches, corresponding with 
the nine postoral visceral arches; of which evidence is to be found in 
some Sharks and Marsipobranchii. A.C. Cardiac aorta ; A.D. Dorsal 


92 THE ANATOMY OF VERTEBRATED ANIMALS. 


or subvertebral aorta, 1.—1x. the aortic arches, corresponding with 
Mn., the mandibular; Hy., the hyoidean, and Br.i— Br.7, the seven 
branchial visceral arches. 1. 11. 111. Iv. Vv. vi. vil., the seven branchial 
clefts. he first visceral cleft is left unnumbered, and one must be 
added to the number of each branchial cleft to give its number in 
the series of visceral clefts. 

B. Hypothetical diagram of the aortic arches in the Shark Heptanchus, 
which has seven branchial clefts. Sp. The remains of the first 
visceral cleft as the spiracle. Branchize are developed on all the 
arches, 

C. Lepidosiren.—The first arch has disappeared as such, and the first 
visceral cleft is obliterated. Internal branchize are developed in 
connection with the second, fifth, sixth, and seventh aortic arches; 
external branchize in connection with the fourth, fifth, and sixth. 
PA.the pulmonary artery. The posterior two visceral cletts are 
obliterated. 

D. A Teleostean Fish.—The first aortic arch and first visceral cleft 
are obliterated, as before. Thesecond aortic arch bears the pseudo- 
branchia (Ps.B.), whence issues the ophthalmic artery, to terminate 
in the choroid gland (Ch.) The next four arches bear gills. ‘he 
seventh and eighth arches have been observed in the embryo, but 
not the ninth, and the included clefts are absent in the adult. 

E. The Axolotl (Siredon), a perennibranchiate amphibian. The third, 
fourth, fifth, and sixth aortic arches, and the anterior four branchial 
clefts, persist. The first visceral cleft is obliterated, 

F. The Frog.—The three anterior aortic arches are obliterated in the 
adult, The place of the third, which is connected with the anterior 
external gill in the Tadpole, is occupied by the common carotid and 
the rete mirabile (carotid gland, Ca.G.) which terminatesit. The 
fourth pair of aortic arches persist. ‘The fifth and sixth pair lose 
their connections with the subvertebral aortic trunk, and become 
the roots of the cutaneous and pulmonary arteries. ‘lhe first 
visceral cleft becomes the tympanum, but all the others are oblite- 
rated in the adult. 


cutaneous branches. The anterior, or third, primitive aortic 
arch becomes the common carotid trunk, and ends in the 
carotid gland, whence the internal and external carotids 
arise. In those Vertebrata which never possess gills, the 
arches become reduced either to two pair, as'in some Lacer- 
tilia; or to one pair, as in other Reptilia; or to a single 
arch, as in Aves and Mammalia. The aortic arches thus 
retained are, in the Lizards in question, the third and the 
fourth pairs in order from before backwards; but the 
fourth pair only, in other Reptiles; in Birds, the right arch 
only of the fourth pair; and in Mammals, the left arch only 
of the fourth pair. The fifth pair of arches give off the 
pulmonary arteries, the so-called ‘‘ ductus arteriosus” repre- 


THE DEVELOPMENT OF THF VASCULAR SYSTEM. 93 


senting the remains of the primitive connection of these 
arches with the fourth pair and the subvertebral aorta. 
The dorsal ends of the first, second,and third arches become 
obliterated; but their cardiac ends, and the branches which 
they give off, become the arteries of the head and upper 
extremities. 


The embryonic aorta gives off omphalomeseraic branches 
(Fig. 26, 0) tothe umbilical vesicle; and ends, at first, in the 
hypogastric arteries (which are distributed to the allantois 
in the abranchiate Vertebrata), and a median caudal con- 
tinuation. The blood from the umbilical vesicle is brought 
back, as before mentioned, by the omphalomeseraic veins 
(Fig. 26, o'), which unite in a dilatation close to the head; the 
dilatation (sinus venosus) receives, on each side, a short 
transverse venous trunk, the ductus Cuvieri (Fig. 26, DC.), 
which is itself formed, upon each side, by the junction of 
the anterior and posterior cardinal veins, which run back- 
wards and forwards, parallel with the spine, and bring back 
the blood of the head and of the trunk. 

The blood of the allantois is returned by the wmbilical 
vein, or veins (Fig. 26, w’), which are formed in the anterior 
wall of the abdomen, and open into the venous sinus before 
mentioned. The blood of the posterior extremities and 
kidneys is, after a while, brought to the same point by a 
special median vein, the vena cava inferior (Fig. 26, cv.). 

The development of the liver effects the first great change 
in the arrangements now described. It, as it were, in- 
terrupts the course of the omphalomeseraic vein, which is 
not only the vein of the umbilical sac but also that of the 
intestine, and converts it into a meshwork of canals, which 
communicate, on one side, with the cardiac part of the vein, 
and, on the other side, with its intestinal part. The latter 
is thus converted into the vena’ porte (Fig. 26, vp.), dis- 
tributing the blood of the stomach and intestines to the 
liver; while the former becomes the hepatic vein (vh), carrying 
the hepatic blood to the inferior cava, and thence to the 
heart. 


94 THE ANATOMY OF VERTEBRATED ANIMALS. 


The umbilical vein further gives a branch to the liver; 
while, on the other hand, it communicates directly with the — 
venous sinus (now almost merged in the vena cava inferior) — 
by a trunk called ductus venosus (Fig. 26, Dv.), 


0” 


Fig. 26.—Diagram of the arrangement of the principal vessels in a 
human foetus. A. the heart; 7.A. the aortic trunk or cardiac 
aorta; c. the common carotid ; c! the external carotid; c"' the internal 
carotid ; s. subclavian; v, vertebral artery; 1, 2, 3, 4, 5, the aortic 
arches—the,persistent /eft aortic arch is hidden; A.' subvertebral 
aorta; o,omphalomeseraic artery, going to the umbilical vesicle v, with 
its vitelline duct dv.; 0, omphalomeseraic vein; zp, the vena porte ; 
L. the liver; uu, the hypogastric or umbilical arteries, with their — 
placental ramifications, w'x'; u' the umbilical vein; Dv, the ductus 
venosus; vi, the hepatic vein; cv,the vena cava inferior; vil, the 
iliac veins; az, a vena azygos; vc',a vena cardinalis posterior ; 
DC. a ductus Cuvieri; the anterior cardinal vein is seen com- 
mencing in the head and running down to the ductus Cuvieri on the 
under side of the numbers 1, 2, 3, 4,5; P, the lungs, 


ee ee ee wee 


When the umbilical vesicle and allantois cease to have any 
further import, as at birth, or before, the omphalomeseraic 


THE MODIFICATIONS OF THE VASCULAR SYSTEM. 95 


arteries have become intestinal arteries, and the omphalo- 
meseraic vein, the vena porte. The hypogastric arteries are 
obliterated, except so much of them as is converted into the 
common iliac arteries. The umbilical vein, or veins, also 
disappear, or are represented by mere ligaments, 

Of the three veins which openinto the venous sac—viz., the 
inferior cava, and the right and left ductus Cuvieri,—all may 
persist, the latter receiving the title of right and left superior 
cave. Or, as very often happens in the higher Vertebrata, 
the left ductus Cuvieri becomes more or less obliterated ; the 
yeins which properly open into it acquiring a connection 
with the right ductus, which then remains as the sole 
superior cava. The posterior cardinal veins give off anas- 
tomosing branches, which are converted into the vene 
azygos ; the anterior cardinal-veins become metamorphosed 
into the external jugular veins and vene innominate, 

In Fishes, the sinus venosus and the cardinal veins persist 
throughout life; but the anterior cardinal veins, which 
bring back the blood from the head and from the anterior 
extremities, are called vene jugulares. 

The caudal veins are either directly continued into the 
cardinal veins, as in Marsipobranchii and Elasmobranchit, or 
branch out into the kidneys, as in many Teleostei. In either 
case the efferent renal veins open into the cardinal veins. 

The portal veins, conveying the blood of the chylopoietic 
viscera, and sometimes that of other organs and of the abdo- 
minal walls, may be one or many. In Amphiowus and Myzxine 
the vein is rhythmically contractile, and forms a portal 
heart. 

In most Amphibia and Reptilia the sinus venosus persists, 
and is rhythmically contractile, valves being placed at its 
opening into the right auricle. 

The anterior cardinal veins are represented by jugular 
veins, the posterior cardinal by vertebral veins ; these, and 
the veins of the anterior extremities, when they are 
present, pour their blood into-the ductus Cuviert, which are 
now termed anterior vene cave, 

The vena cava inferior takes its origin chiefly by the 


96 THE ANATOMY OF VERTEBRATED ANIMALS. 


coalescence of the efferent veins of the kidneys and re- 
productive organs, and does not always receive the whole — 
of the hepatic veims—more or fewer of the latter opening © 
independently into the sinus venosus. : 

The blood which leaves the kidneys by its efferent veins 
is supplied, not only by the renal arteries, but by the veins 
of the caudal region, and of the hinder extremities, which 
branch out like a vena porte in the substance of the 
kidneys. This renal portal system is less developed in 
Reptilia than in Amphibia. All the blood of the posterior 
extremities and caudal region does not traverse the kidneys, 
however, more or less of it being led away by great branches 
of the iliac veins, which run along the anterior wall of the 
abdominal cavity, either as two trunks, or united into one. 
These vence abdominales anteriores are eventually distri- 
buted to the liver, along with the branches of the proper 
vene porte. 

In Birds, the sinus venosus is not distinct from the right 
auricle, and there are two anterior vene cave. The vena 
cava inferior arises, as in Mammals, by the union of the 
two common iliac veins. It receives both the right and 
the left hepatic veins, and, in addition, the anterior abdo- 
minal vein no longer enters the portal system, but passes 
up the anterior wall of the abdomen and through the 
hepatic fissure to join the inferior cava. 

The caudal and pelvic veins unite into three principal 
trunks, of which one is median and two are lateral. The 
median enters into the portal system. The lateral branches 
pass along and through the kidney, receiving veins from 
it, but giving none to it; and eventually, after receiving the — 
ischiatic veins, unite with the crural veins to form the com- 
mon iliacs. Thus there is no renal portal system in birds. 

In Mammalia, the sinus venosus is not distinct from the 
right auricle. The anterior cave are frequently reduced to 
one, the right. The vena cava inferior commences in the 
caudal region, and receives all the blood of the posterior 
moiety of the body, except so much as is carried away by 
the azygous veins. The anterior abdominal veins are repre- 


THE MODIFICATIONS OF THE HEART. 97 


sented only during fetal life, by the umbilical vein or 
yeins. The efferent veins of the kidneys open directly 
into the trunk of the inferior vena cava, and the portal 
yein is composed exclusively of radicles proceeding from 
the chylopoietic viscera. 

Many of the veins of Amphiowus, the meee vein of 
Myzine, dilatations of the caudal vein in the Hel, the ven 
cave and the iliac and axillary veins of many Amphibia, 
the veins of the wing of Bats, possess a rhythmical con- 
tractility, which, in combination with the disposition of their 
valves, assists the circulation of the blood. 

In Vertebrata of all classes, and in very diverse parts of 
the body, both veins and arteries occasionally break up into 
numerous branches of nearly equal size, which may or may 
not unite again into larger trunks. These are called retia 
mirabilia. 


Modifications of the Heart—Great changes go on in 


the structure of the heart, pari passu with the modifica- 


tions of the rest of the circulatory system, in the develop- 
ment of the highest Vertebrata. The primitively simple tube 
becomes bent upon itself, and divided from before back- 


wards into an aortic, or ventricular, and a venous, or auri- 


cular, portion. A median septum then grows inward, divid- 
ing the auricular and ventricular chambers into two, so that 
a right auricle and right ventricle become separated from 
a left auricle and left ventricle. A similar longitudinal 


division is effected in the cardiac aorta. The septa are so 
- disposed in the auriculo-ventricular chamber that the right 


auricle communicates with the venous sac and the trunks 


of the visceral and body veins, while only the veins from 
the lungs enter into the left auricle. And the cardiac 
aorta is so divided that the left ventricle communicates 
with the chief aortic trunk, the right with the pulmonary 
artery. Valves are developed at the auriculo-ventricular 
apertures and at the origins of the aortic and pulmonary 
trunks, and thus the course of the circulation is determined. 
The septum between the auricles remains incomplete for a 
H 


98 THE ANATOMY OF VERTEBRATED ANIMALS. 


much longer period than that between the ventricles—and 


the aperture by which the auricles communicate is called | 


the foramen ovale. 


In the adult state of Aves and Mammalia, the foramen | 


ovale is closed; there is no direct communication between 
the arterial and venous cavities or trunks; there is only one 
aortic arch; and the pulmonary artery alone arises from the 
right ventricle. In the Crocodilia, the auricles and ven- 
tricles of opposite sides are completely separate; but there 
are two aortic arches, and one of these, the left, arises from 
the right ventricle along with the pulmonary artery. In all 
Reptilia, except Crocodiles, there is but one ventricular 
cavity, though it may be divided more or less distinctly into 
a cavum venosum and a cavum arteriosum. The auricles are 
completely separated (except in some Chelonia), and the 
blood of the left auricle flows directly into the cavwm arterio- 
sum, while that of the right passes immediately into the 
cavum venosum. The aortic arches and the pulmonary artery 
all arise from the cavum venosum (or a special subdivision 
of that cavity called the cavum pulmonale) ; the ostium of the 


pulmonary artery being farthest from, and that of the right — 


aortic arch nearest to. the cavum arterioswn. 
In all Amphibia, the spongy interior of the ventricle is 


undivided, and the heart is trilocular, though the auricular — 


septum is sometimes small and incomplete. In all Pisces, 
except Lepidosiren, there is no auricular septum. In 4Am- 
phioxus the heart remains in its primitive state of a simple, 
contractile, undivided tube. 

In the Ganoidei, the Elasmobranchii, and the Amphibia, 
the walls of the enlarged commencement of the cardiac 
aorta, called the bulbus aorte, contain striped muscular 
fibre, and are rhythmically contractile. 

The Ganoidei and Elasmobranchii possess, not merely the 
ordinary semilunar valves, at the junction between the 
ventricle and the cardiac aorta, but a variable number of 
additional valves, set, in transverse rows, upon the inner 
wall of the aortic bulb. 

The change of position which the heart and the great 


THE BLOOD-CORPUSCLES. 99 


-yessels of the highest Vertebrata undergo during embryonic 


life is exceedingly remarkable, and is repeated as we ascend 


‘in the series of adult vertebrates. 


At first, the heart of a mammal lies under the middle of the 
head, immediately behind the first visceral arches, in which 
the first pair of aortic arches ascend. As the other pairs of 
aortic arches are developed the heart moves backward ; but 
the fourth pair of aortic arches, by the modification of one 
of which the persistent aorta is formed, lies, at first, no 
farther back than the occipital region of the skull, to which, 


as we have seen above, the fourth pair of visceral arches 


belongs. As the two pairs of cornua of the hyoid belong 
to the second and the third visceral arches, the larynx is 
probably developed within the region of the fourth and 
fifth visceral arches; hence, the branches of the pneumo- 
gastric, with which it is supplied, must, originally, pass 
directly to their destination. But, as development pro- 
ceeds, the aortic arches and the heart become altogether 
detached from the visceral arches and move back, until, at 
length, they are lodged deep in the thorax. Hence the 
elongation of the carotid arteries; hence also, as the larynx 
remains relatively stationary, the singular course, in the 


adult, of that branch of the pneumogastric, the recurrent 


laryngeal, which primitively passed to the laryngeal region 
behind the fourth aortic arch, and consequently becomes 
drawn out into a long loop—the middle of it being, as it 
were, pulled back, by the retrogression of the aortic arch 
into the thorax. 


The Blood Corpuscles——Corpuscles are contained in the 
blood of all Vertebrata. In Amphiowus they are all of one 
kind, colourless and nucleated. The genus Leptocephalus, 
among the Teleoste/, is said to possess the same pecu- 
liarity ; but in all other known Vertebrata, the blood con- 
tains corpuscles of two kinds. 

In Ichthyopsida and Sawropsida, both kinds are nu- 
cleated; but one set are colourless, and exhibit ameboid 
movements, while the others are red, and do not display 


100 THE ANATOMY OF VERTEBRATED ANIMALS. 


contractility. Except in the Marsipobranchii, which have 


round blood-corpuscles, the red corpuscles are oval. They | 
attain a larger size in the perennibranchiate Amphibia 


than in any other Vertebrates. 

In Mammalia, the blood-corpuscles are also of two kinds, 
colourless and red, the colourless possessing, and the red 
being devoid of, nuclei. It is but very rarely that a nu- 
cleated corpuscle, with a red colour especially developed 
about the nucleus, is seen in Mammalian blood; but such 
cases do occur; and, from this and other circumstances, it 
is probable that the Mammalian red corpuscle is a free- 
coloured nucleus. 

.The colourless corpuscles of Mammalia are spheroidal, 
and exhibit ameboid movements; the red corpuscles are 
flattened, usually circular, but sometimes oval (Camelide) 
dises, devoid of contractility. 


The Lymphatic System.—This system of vessels consists, 
chiefly, of one or two principal trunks, the thoracic duct, or 
ducts, which underlie the vertebral column, and communi- 
cate, anteriorly, with the superior ven cave, or with the 
veins which open into them. 

From these trunks, branches are given off, which ramify 
through all parts of the body, except the bulb of the eye, 
the cartilages, and the bones. In the higher Vertebrata, 
the larger branches are like small veins, provided with 
definite coats, and with valves opening towards the larger 
trunks, while their terminal ramifications form a capillary 


network; but, in the lower Vertebrates, the lymphatic — 


channels assume the form of large and irregular sinuses, 
which not unfrequently completely. surround the great 
vessels of the blood system. 

The lymphatics open into other parts of the venous 
system besides the affluents of the superior cave. In Fishes 
there are, usually, two caudal lymphatic sinuses which open 
into the commencement of the caudal vein. In the Frog, 
four such sinuses communicate with the veins, two in the 
coccygeal, and two in the scapular, region. The walls of 


THE RESPIRATORY ORGANS. 101 


these sinuses are muscular, and contract rhythmically, so 
that they receive the name of Lymphatic hearts. The pos- 
‘terior pair of these hearts, or non-pulsating sinuses cor- 
responding with them, are met with in Reptilia and Aves. 

Accumulations of indifferent tissue in the walls of some 
of the lymphatic sinuses are to be met with in Fishes; 
but it is only in the Crocodilia, among Reptilia, that an 
accumulation of such tissue, traversed by lymphatic canals 
and bloodvessels, is apparent, as a Lymphatic gland, in the 
mesentery. Birds possess a few glands in the cervical 
region ; and, in Mammalia, they are found, not only in the 
mesentery, but in many parts of the body. 

The Spleen is substantially a lymphatic gland. The 
Thymus—a glandular mass with an internal cavity, but 
devoid of any duct—which is found in all Vertebrata except 
Amphiowus, appears to belong to the same category. It is 
developed in the neighbourhood of the primitive aortic 
arches, and is double in most of the lower Vertebrata, but 
single in Mammalia. 

_ The nature of two other “ductless glands,” the Thyroid 
gland and the Suprarenal capsules, which occur very widely 
among the Vertebrata, is by no means well understood. 

The thyroid gland is a single or multiple organ, formed 
of closed follicles, and is situated near the root of the aorta, 
or the great lingual, or cervical, vessels which issue from it. 

The suprarenal capsules are follicular organs, often 
abundantly supplied with nerves, which appear to occur in 
Fishes, and are very constant in the higher Vertebrata, at 
the anterior ends of the true kidneys. 


The Lymph Corpuscles, which float in the plasma of the 
lymphatic fluid, always resemble the colourless corpuscles 
of the blood. 


The Respiratory Organs.—V ertebrated animals may possess 
either branchie for breathing the air contained in water, or 
lungs for atmospheric respiration ; or they may possess both 
kinds of respiratory organs in combination. 


102 THE ANATOMY OF VERTEBRATED ANIMALS. 


Except in Amphiowus, the branchie are always lamellar, 
or filamentous, appendages of more or fewer of the visceral | 
arches ; being sometimes developed only on the proper bran- 
chial arches, sometimes extending to the hyoidean arch, or | 
(as would appear to be the case with the spiracular branchiz 
of some fishes) even to the mandibular arch. The branchie 
are always supplied with blood by the divisions of the 
cardiac aorta; and the different trunks which carry the 
aérated blood away, unite to form the subvertebral aorta, 
so that all vertebrated animals with exclusively branchial 
respiration have the heart filled with venous blood. 

In the early life of many branchiated Vertebrata, the 
branchize project freely from the visceral arches to which 
they are attached, on the exterior of the body; and in some 
Amphibia, such as the Axolotl (Siredon), they retain their 
form of eaternal plumelike appendages of the neck through- 
out life. But in the adult life of most Fishes, and in the 
more advanced condition of the Tadpoles of the higher 
Amphibia, the branchie are internal, being composed of 
shorter processes, or ridges, which do not project beyond 
the outer edges of the branchial clefts; and, generally, — 
become covered by an operculum developed from the second 
visceral arch. 

The lungs of vertebrated animals are sacs, capable of 
being filled with air, and developed from the ventral wall of 
the pharynx, with which they remain connected by a shorter 
or longer tube, the trachea, the division of this for each 
lung being a bronchus. Venous blood is conveyed to them 
directly from the heart by the pulmonary arteries, and 
some * or all of the blood which they receive goes back, no 
less directly, to the same organ by the pulmonary veins. 

The vascular distribution thus described constitutes an 
essential part of the definition of a lung, as many fishes 
possess hollow sacs filled with air; and these sacs are de- 
veloped, occasionally, from the ventral, though more com- 
monly from the dorsal, wall of the pharynx, esophagus, or 


* Generally all, but in some of the blood supplied to the lungs 
Amphibia, such as Proteus, part enters the general circulation. 


THE ORGANS OF VOICE. 103 


stomach. But such air-sacs—even when they remain per- 
manently connected with the exterior by an open passage or 
pneumatic duct—are air-bladders, and not lungs, because they 
receive their blood from the adjacent arteries of the body, 
and not direct from the heart, while their efferent vessels 
are connected only with the veins of the general circulation. 

The wall of each pulmonic air-sac is at first quite simple, 
but it soon becomes cellular by the sacculation of its 
parietes. In the lower pulmonated Vertebrata, the sacculation 
is more marked near the entrance of the bronchus; and when 
the lung-sac is long, as in many Amphibia and in Snakes, 
the walls of the posterior end may retain the smooth con- 
dition of the embryonic lung. In Chelonia and Crocodilia, 
the lung is completely cellular throughout, but the bronchi 
do not give off branches in the lungs. In Birds, branches 
are given off at right angles; and, from these, secondary 
branches, which lie parallel with one another, and eventually 
anastomose. In Mammalia, the bronchi divide dichoto- 
mously into finer and finer bronchial tubes, which end in 
sacculated air-cells. 

Blind air-sacs are given off from the surfaces of the lungs 
in the Chameleonide, and the principal bronchial tubes 
terminate in large air-sacs in Aves. 

The Larynx and the Syrine—The trachea is commonly 
kept open by complete, or incomplete, rings of cartilage, 
and the uppermost of these undergo special modifications, 
which convert them into a Larynx, an organ which, under 
certain circumstances, becomes an instrument of voice. 

When completely developed, the larynx presents a ring- 
like cartilage called cricoid, which lies at the summit of the 
trachea. With the anterior and dorsal edge of this, two 
arytenoid cartilages are moveably articulated, and a thyroid 
cartilage of a V-shape, open behind, is articulated move- 
ably with its sides. Folds of the mucous membrane, con- 
taining elastic tissue, termed the vocal cords, stretch from the 
arytenoid cartilages to the re-entering angle of the thyroid 
cartilage, and between them lies a slit-like passage, the 
glottis. This is covered by a cartilage, the epiglottis, attached 


104 THE ANATOMY OF VERTEBRATED ANIMALS. 


to the re-entering angle of the thyroid, and to the base of 


thetongue. Folds of mucous membrane, extending from the | 


epiglottis to the arytenoid cartilages, are the aryepiglottic — 
ligaments. The inner surfaces of these end below in the false | 


vocal cords, between which and the true chorde vocales, lie re- 
cesses of the mucous membrane, the ventricles of the larynx. 

The chief accessory cartilages are the cartilages of San- 
torimi, attached to the summits of the arytenoid cartilages, 
and the cartilages of Wrisberg, which lie within the ary- 
epiglottic ligaments. 

Birds possess a larynx in the ordinary position; but it is 
another apparatus, the lower larynx or syrinx, developed 
either at the end of the trachea, or at the commencement 
of each bronchus, which is their great vocal organ. 

The Mechanism of Respir ation. —The mechanism by ae 
the acérating medium is renewed in these different respira- 
tory organs is very various. Among branchiated Vertebrata, 
Amphiowus stands alone in having ciliated branchial organs, 
which form a network very similar to the perforated pharyn- 
geal wall of the Ascidians. Most Fishes breathe by taking 
aérated water in at the mouth, and then shutting the oral 
aperture, and forcing the water through the branchial clefts, 
when it flows over the branchial filaments. 

Pulmonated Vertebrata which have the thoracic skeleton 
incomplete (as the Amphibia), breathe by distending their 
pharyngeal cavity with air; and then, the mouth and nostrils 
being shut, pumping it, by the elevation of the hyoidean ap- 
paratus and floor of the pharynx, into the lungs. A Frog, 
therefore, cannot breathe properly if its mouth is kept wide 
open. 

In most Reptilia, and in all Aves and Mammalia, the 
sternum and ribs are capable of moving in such a way, as 
alternately to increase and diminish the capacity of the 
thoracico-abdominal cavity, and thereby to give rise to an 
inspiratory and expiratory flow of air. 

In the Reptilia, the elastic lungs dilate with the inspira- 
tory, and contract with the expiratory, act; but in Aves, 
the air rushes through the principal bronchial passages of 


ee 


oaies. 


THE RENAL ORGANS. 105 


the fixed and little distensible lungs, into the very dilatable 
and compressible air-sacs. From these the act of expira- 
tion expels it back through the principal bronchial pas- 
sages to the trachea, and so out of the body. 

Both in Reptilia (e. g. Chelonia) and in Aves, muscular 
fibres pass from the ribs to the surface of the lungs beneath 
the pleuroperitoneal membrane, and this rudimentary dia- 
phragm acquires a very considerable development in the 
Ratite, or struthious birds. So far as the contraction of 
these fibres tends to remove the ventral from the dorsal 
walls of the lungs, they must assist inspiration. But this 
diaphragmatic inspiration remains far weaker than the 
sterno-costal inspiration. 

Finally, in the Mammalia, there are two equally important 
respiratory pumps, the one sterno-costal, the other dia- 
phragmatic. The diaphragm, though it makes its appear- 
ance in Sawropsida, only becomes a complete partition 
‘between the thorax and the abdomen in mammals; and 
as its form is such, that, in a state of rest, it is concave 
towards the abdominal cavity, and convex towards the 
thorax, the result of its contraction, and consequent flat- 
tening, necessarily is to increase the capacity of the thorax, 
and thus pump the air into the elastic lungs, which occupy 
a large part of the thoracic cavity. When the diaphragm 
ceases to contract, the elasticity of the lungs is sufficient to 
expel the air taken in. 

Thus, mammals have two kinds of respiratory mechanism, 
either of which is efficient by itself, and may be carried on 
independently of the other. 


The Renal Organs.—The higher Vertebrata are all provided 
with two sets of renal organs, the one existing only during 
the early fcetal state, the other persisting throughout life. 

The former are the Wolffian bodies, the latter the true 
Kidneys. 

The Wolffian bodies make their appearance very early, on 
each side of the ventral aspect of the spinal region of the 
embryo, as small transversely-disposed tubuli, opening into 


106 THE ANATOMY OF VERTEBRATED ANIMALS. 


a duct which lies upon their outer side, and enters, poste- 
riorly, into the base of the allantois, and thence into the 
primitive cloaca with which that structure is connected, 
The Wolffian duct is one of the first-formed structures in 
the embryo, and precedes the tubuli. 

The Kidneys appear behind the Wolffian bodies, and, appa- 
rently, independently of them; their ducts, the wreters, are 
also distinct, but likewise terminate in the pelvic part of the 
allantois. Thus the urinary secretion passes into the allan- 
tois, and it is that portion of this organ which lies within 
the abdomen, and becomes shut off from the rest by the 
constriction and obliteration of the cavity of an interme- 
diate part, and its conversion into the wrachus, that gives 
rise to the wrinary bladder. The ultimate secreting tubuli 
of both the Wolffian body and the kidney, are alike re- © 
markable for ending in dilatations which embrace con- 
voluted capillaries—the so-called malpighian tufts. Neither 
Wolffian bodies nor kidneys have been observed in Amphi- 
oxus. It is doubtful whether true kidneys are developed 
in Ichthyopsida, or whether the so-called kidneys of these 
animals are not, rather, persistent Wolffian bodies. 


The Reproductive Organs.—These, in vertebrated animals, 
are primitively similar in both sexes, and arise on the inner 
side of the Wolffian bodies, and in front of the kidneys, in 
the abdominal cavity. In the female the organ becomes an 
ovarium. This, in some few fishes, sheds its ova as soon as _ 
they are ripened into the peritoneal cavity, whence they 
escape by abdominal pores, which place that cavity in direct 
communication with the exterior. In many fishes, the 
ovaries become tubular glands, provided with continuous 
ducts, which open externally, above and behind the anus. 
But, in all other Vertebrata, the ovaries are glands without 
continuous ducts, and which discharge their ova from sacs, 
the Graafian follicles, successively developed in their solid 
substance. Nevertheless, these ova do not fall into the 
peritoneal cavity, but are conveyed away by a special appa- 
ratus, consisting of the Fallopian tubes, which result from 


a a ae ee 


THE REPRODUCTIVE ORGANS. 107 


the modification of certain embryonic structures called the 
Miillerian ducts. 

The Millerian ducts are canals which make their appear- 
ance alongside the ducts of the Wolffian bodies, but, through- 
out their whole extent, remain distinct from them. Their 
proximal ends lie close to the ovary, and become open and 
dilated to form the so-called ostia. Beyond these ostia they 
generally remain narrow for a space, but towards their 
hinder openings into the genito-urinary part of the cloaca, 
they commonly dilate again. In all animals but the didel- 
phous and monodelphous Mammalia, the Miillerian ducts 
undergo no further modification of any great morphological 
importance ; but, in the monodelphous Mammalia, they be- 
come united, at a short distance in front of their posterior 
ends; and then, the segments between the latter and the 
point of union, or still farther forward, coalesce into one. 
By this process of confluence the Miillerian ducts are 
primarily converted into a single vagina with two uteri 
Opening into it; but in most of the Monodelphia, the two 
uteri also more or less completely coalesce, until both 
Miillerian ducts are represented by a single vagina, a 
single uterus, and two Fallopian tubes. The didelphous 
Mammalia have two vagine which may, or may not, coalesce 
anteriorly for a short extent; but the two uteri remain 
perfectly distinct. So that what takes place in them is, pro- 
bably, a differentiation of each Miullerian duct into Fallo- 
pian tube, uterus, and vagina, with or without the union of 
the two latter, to the extent to which it is effected in the 
earlier stages of development in Monodelphia. The Wolffian 
ducts of the female either persist as canals, the so-called 


canals of Gaertner, which open into the vagina, or dis- 


appear altogether. Remains of the Wolffian bodies consti- 
tute the parovaria, observable in certain female mammals. 


In the male vertebrate embryo, the testis, or essential 
reproductive organ, occupies the same position, in front of 
the Wolffian body, as the ovary; and, like the latter, is 
composed of indifferent tissue. In Amphioxus and in the 


108 THE ANATOMY OF VERTEBRATED ANIMALS. 


Marsipobranchii, this tissue appears to pass directly into 
spermatozoa; but, in most Vertebrata, it acquires a saccular 


Wd if 


Fig. 27.— Diagram exhibiting the relations of the female (the left- 
hand figure, ¢), and of the male (the right-hand figure, 3) reproduc- 
tive organs to the general plan (the middle figure) of these organs in 
the higher Vertebrata. 

Cl, the cloaca; R, the rectum; B/, the urinary bladder; U, the 
ureter; K, the kidney; Uh, the urethra; G, the genital gland, ovary, or 
testis; W, the Wolffian body: Wd, the Wolffian duct; W/Z, the Miillerian 
duct ; Pst. prostate gland ; Cp, Cowper's gland; Csp, the corpus spon- 
giosum; Cc, the corpus cavernosum. 

In the female, V, the vagina; Ut, the uterus; Fp, the Fallopian 
tube; Gt, Gaertner’s duct; P.v, the parovarium ; A, the anus; Ce, C.sp, 
the clitoris. In the male, Csp, Cc, the penis; Ut, the uterus mascu- 
linus; Vs, vesicula seminalis; Vd, the vas deferens. 


| 
| 


or tubular structure, and from the epithelium of the sacs, or 
tubuli, the spermatozoa are developed. At first, the testis is _ 


MODIFICATIONS OF THE REPRODUCTIVE ORGANS. 109 


as completely devoid of any excretory canal as the ovary; 
but, in the higher vertebrates, this want is speedily supplied 
by the Wolffian body, certain of the tubuli of which become 
continuous with the tubuli seminiferi, and constitute the vasa 
recta, while the restabort. The Wolffian duct thus becomes 
the vas deferens, or excretory duct of the testis; and its 
anterior end, coiling on itself, gives rise to the epididymis. 
A vesicula seminalis is a diverticulum of the vas deferens, 
near its posterior end, which serves as a receptacle for the 
semen. 


If the Wolffian bodies, the genitalia, and the alimentary 
canal of a vertebrate embryo, communicated with the exterior 
by apertures having the same relative position as the organs 
themselves, the anus would be in front and lowest, the Wolf- 
fian apertures behind and highest, and the genital apertures 
would lie between the two. But the anal, genital, and uri- 
nary apertures are found thus related only among certain 
eroups of fishes, such as the Teleostei. In all other Verte- 
brata, there is either a cloaca, or common chamber, into 
which the rectum, genital, and urinary organs open; or, the 
anus is a distinct posterior and superior aperture, and the 
opening of a genito-urinary sinus, common to the urinary 
and reproductive organs, lies in front of it, separated by a 
| more or less considerable perineum. 
These conditions of adult Vertebrata repeat the states 
/ through which the embryo of the highest vertebrates pass. 
At a very early stage, an involution of the external integu- 
ment gives rise to a cloaca, which receives the allantois, the 
ureters, the Wolffian and Miillerian ducts, in front, and the 
rectum behind. But, as development advances, the rectal 
division of the cloaca becomes shut off from the other, and 
opens by a separate aperture—the definitive anus, which thus 
appears to be distinct, morphologically, from the anus of an 
osseous fish. For a time, the anterior, or genito-urinary part 
of the cloaca, is, to a certain extent, distinct from the rectal 
division, though the two have a common termination; and 
this condition is repeated in Aves, and in ornithodelphous 


110 THE ANATOMY OF VERTEBRATED ANIMALS. 


Mammalia, where the bladder, the genital ducts, and the | 
ureters, all open separately from the rectum into a genito- 
urinary sinus. 

In the male sex, as development advances, this genito- 
urinary sinus becomes elongated, muscular, and surrounded, 
where the bladder passes into it, by a peculiar gland, the 
prostate. Itthus becomes converted into what are termed the 
fundus, and neck of the bladder, with the prostatic and mem- 
branous portions of the urethra. Concomitantly with these 
changes, a process of the ventral wall of the cloaca makes 
its appearance, and is the rudiment of the intromittent 
organ, or penis. Peculiar erectile vascular tissue, developed 
within this body, gives rise to the median corpus spongiosum 
and the lateral corpora cavernosa, The penis gradually pro- 
trudes from the cloaca; and while the corpus spongiosum 
terminates the anterior end of it, as the glans, the corpora 
cavernosa attach themselves, posteriorly, to theischia. The 
under, or posterior, surface of the penis is, at first, simply 
grooved; by degrees the two sides of the groove unite, and 
form a complete tube embraced by the corpus spongiosum. 
The penial urethra is the result. 

Into the posterior part of this penial urethra, which is fre- 
quently dilated into the so-called bulbus urethre, glands. 
called Cowper’s glands, commonly pour their secretion; and 
the penial, membranous, and prostatic portions of the 
urethra (genito-urinary sinus) uniting into one tube, the — 
male definitive urethra is finally formed. . 

In sundry birds and reptiles, the penis remains in the © 
condition of a process of the ventral wall of the cloaca, — 
grooved on one face. In ornithodelphous mammals the 
penial urethra is complete, but open behind, and distinct 
from the genito-urinary sinus. In the Didelphia the penial 
urethra and genito-urinary sinus are united into one tube, 
but the corpora cavernosa are not directly attached to the 
ischium. 

Certain Reptilia possess a pair of eversible copulatory 
organs situated in integumentary sacs, one on each side of 
the cloaca, but it dees not appear in what manner these 


MODIFICATIONS OF THE REPRODUCTIVE ORGANS. 111 


penes are morphologically related to those of the higher 
Vertebrata. 

In the female sex, the homologue of a penis frequently 
makes its appearance asa clitoris, but rarely passes beyond 
the stage of a grooved process with corpora cavernosa and 
corpus spongiosum—the former attached to the ischium, and 
the latter developing a glans. But, in some few mammals 
(e.g. the Lemuride), the clitoris is traversed by an urethral 
canal. 

In no vertebrated animal do the ovaries normally leave the 
abdominal cavity, though they commonly forsake their 
primitive position, and may descend into the pelvis. But, in 
many mammals, the testes pass out of the abdomen through 
the inguinal canal, between the inner and outer tendons of 
the external oblique muscle, and, covered by a fold of peri- 
toneum, descend temporarily or permanently into “a pouch 
of the integument—the scrotum. In their course they be- 
come invested with looped muscular fibres, which constitute 
the cremaster. The cremaster retracts the testis into the 
abdominal cavity, or towards it, when, as in the higher 
mammals, the inguinal canal becomes very much narrowed 
or altogether obliterated. In most mammals the scrotal 
sacs lie at the sides of, or behind, the root of the penis, 
but in the Didelphia the scrotum is suspended by a narrow 
neck in front of the root of the penis. 

In most mammals the penis is inclosed in a sheath of 
integument, the preputium ; and in many, the septum of the 
corpora cavernosa is ossified, and gives rise to an os penis. 

In the female the so-called labia majora represent the 
serotal, the labia minora the preputial, part of the male 
organ of copulation. 

Organs not directly connected with reproduction, but in 
yarious modes accessory to it, are met with in many Verte- 
brata. Among these may be reckoned the integumentary 
pouches, in which the young are sheltered duving their 
development in the male Pipefish (Syngnathus), in some 
female Amphibia (Notodelphys, Pipa), and Marsupialia; to- 
gether with the mammary glands of the Mammalia. 


112 THE ANATOMY OF VERTEBRATED ANIMALS. 


CHAPTER III. 


THE PROVINCES OF THE VERTEBRATA—THE CLASS PISCES. 


THE Vertebrata are divisible into three primary groups or 
provinces: the Ichthyopsida, the Sawropsida, and the Mam-_ 
malia. 


I.—The Ichthyopsida 


1. Have the epidermic exoskeleton either absent, or very 
shghtly represented. 

2. The spinal column may persist as a notochord with a — 
membranous sheath, or it may exhibit various degrees of 
chondrification or ossification. When the vertebre are dis- 
tinct their centra have no epiphyses. 

3. The skull may be incomplete and membranous, more 
or less cartilaginous, or osseous. When membrane bones — 
are developed in connection with it, there is a large para- — 
sphenoid. The basisphenoid is always small, if it be not 
absent. 

4, The occipital condyle may be absent, or single, or 
double. When there are two occipital condyles they belong 
to the ex-occipital region, and the basi-occipital region is 
unossified or very imperfectly ossified. 

5. The mandible may be absent, or be represented only 
by cartilage. If membrane bones are developed in con- 
nection with it, there is usually more than one on each side. 
The articular element may be ossified or not, and may be 
connected with the skull by the intermediation of a quadrate 
and a hyomandibular element, or by a single fixed plate of 
cartilage representing both these and the: pterygo- a 
arch. A stapes may be present or absent. 


THE SAUROPSIDA. 1138 


6. The alimentary canal may or may not terminate in a 
cloaca. When there is no cloaca the rectum opens in front 
of the urimary organs. 

7. The blood-corpuscles are always maclented, and the 
heart may be tubular, bilocular, or trilocular. 

8. There are never fewer than two aortic arches in the 

adult. 

9. Respiration takes place by branchize during part, or 
the whole, of life. 

10. There is no thoracic diaphragm. 

11. The urinary organs are permanent Wolffian bodies. 

12. The cerebral hemispheres may be absent, and are 
never united by a corpus callosum. 

13. The embryo has no amnion, and, at most, a‘rudi- 
mentary allantois. 


14. There are no mammary glands. f 


Il.—The Sauropsida 


1. Almost always possess an epidermic exoskeleton in the 
form of scales or feathers. 

2. The centra of the vertebrx are ossified, but have no 
terminal epiphyses. 

3. The skull has a completely ossified occipital segment, 
and alarge basisphenoid. No separate parasphenoid exists 
in the adult. The pro-otic is always ossified, and either 
remains distinct from the epiotic and opisthotic through- 
out life, or unites with them only after they have anky- 
losed with adjacent bones. 

4. There is always a single, convex, occipital condyle, into 
which the ossified ex-occipitals and basi-occipital enter in 
yarious proportions. 

5. The mandible is always present, and each ramus con- 
gists of an articular ossification, as well as of several mem- 
brane bones. The articular ossification is connected with 
the skull bya quadrate bone. The apparent “ankle-joint” 
is situated, not between the tibia and the astragalus, as in 
all Mammalia, but between the proximal and the distal divi- 
sions of the tarsus. 

I 


114 THE ANATOMY OF VERTEBRATED ANIMALS. 


6. The alimentary canal terminates in a cloaca. 

7. The heart is trilocular or quadrilocular. Some of the 
blood-corpuscles are always red, oval, and nucleated. 

8. The aortic arches are usually two or more, but may be 
reduced to one, which then belongs to the right side. 

9. Respiration is never effected by means of branchie, 
but, after birth, is performed by lungs. The bronchi do 
not branch dichotomously in the lungs. 

10. A thoracic diaphragm may exist, but it never forms a 
complete partition between the thoracic and the abdominal 
viscera. 

11. The Wolffian bodies are replaced, functionally, by 
permanent kidneys. 

12. The cerebral hemispheres are never united by a corpus 
callosum. 

13. The reproductive organs open into the cloaca, and 
the oviduct is a Fallopian tube, which presents an uterine 
dilatation in the lower part of its course. 

14, All are oviparous, or ovoviviparous. 

15. The embryo has an amnion, and a large respiratory 
allantois, and is developed at the expense of the massive 
vitellus of the egg. 

16. There are no mammary glands. 


IiI.—The Mammalia 


1. Always possess an epidermic exoskeleton in the form of _ 
hairs. 

2. The vertebre are ossified, and (except in the Ornitho- 
delphia) their centra have terminal epiphyses. 

3. All the segments of the brain-case are completely | 
ossified. No distinct parasphenoid exists in the adult. 
The pro-otic ossifies, and unites with the epiotic and opis- 
thotic before these coalesce with any other bone. 

4. There are always two occipital condyles, and the basi- 
occipital is well ossified. 

5. The mandible is always present, and each ramus con- 
sists (at any rate, in the adult) of a single membrane bone, 
which articulates with the squamosal. The quadrate bone, 


THE CLASS PISCES, 115 


and the supra-stapedial element of the hyoidean arch, are 
converted into a malleus and an incus, so that, with the 
stapes, there are, at fewest, three ossicula auditis. 

6. The alimentary canal may, or may not, termmate in a 
cloaca. When it does not, the rectum opens behind the 
genito-urinary organs. 

7. The heart is quadrilocular. Some of the blood-cor- 
puscles are always red and non-nucleated. 

8. There is only one aortic arch, which lies on the left side- 

9. Respiration is never effected by means of branchiw, 
but, after birth, is performed by lungs. 

10. There is a complete diaphragm. 

11. The Wolffian bodies are replaced by permanent 
_ kidneys. : 

12. The cerebral hemispheres are united by a corpus cal- 
 losum. ; 

13. The reproductive organs may, or may not, open into 
a cloaca. The oviduct is a Fallopian tube. 

14. The embryo has an amnion and an allantois. 

15. Mammary glands supply the young with nourishment. 


The Ichthyopsida.—Class I.—PIsczs. 

The class of Fishes contains animals which vary so much 
in their grade of organization, and in their higher forms 
so closely approach the Amphibia, that it is difficult to 
draw up any definition which shall be at once character- 
istic and diagnostic of them. But they are the only ver- 
tebrated animals which possess median fins supported by 
fin-rays; and in which the limbs, when present, do not 
exhibit that division into brachium, antebrachium, and 
manus which is found in all other Vertebrata. 

The presence of the peculiar integumentary orgams con- 
stituting what is known as the system of mucous canals and 
the organs of the lateral line (supra, p. 86), is highly charac- 
teristic of Fishes, though these organs cannot be said to 
exist in the entire class. 

The class Pisces is divisible into the following primary groups :— 


A. The notochord extends to the anterior end of the body. There 
are no skull, brain, auditory, or renal organs, such as exist in the 


116 THE ANATOMY OF VERTEBRATED ANIMALS. 


higher Vertebrata. The heart is a simple tube, and the liver is 
saccular, (LeEprocarpiA. Haeckel). 


I.— Pharyngobranchii. 

B. The notochord ends behind the pituitary fossa. A skull, brain, au- 
ditory, and renal organs are developed. The heart is divided 
into auricular and ventricular chambers. The liver has the 
ordinary structure (PacnycarpiA. Hcek.). 

a. The nasal sac is single, and has a median external 
aperture. Neither mandibles nor limb arches are deve- 
loped (Monorhina., Hek.). 


Il.—Marsipobranchii. 

b. There are two nasal sacs with separate apertures. Mandibles 
and limb arches are developed. (Amphirhina. ck.). 
a. ‘The nasal passages do not communicate with the cavity 
of the mouth. There are no lungs, and the heart 

has but one auricle. 
a. The skull is devoid of membrane bones, 
Il.— Elasmobranchit. 
8, Membrane bones are developed in relation with 
the skull. 
1. The optic nerves form a chiasma, and there 
are several rows of valves in the aortic bulb. 


IV. Ganoidei. 
2. The optic nerves simply cross, and there is 
only one row of valves in the aortic bulb. 


V.— Teleostei. 
6. The nasal passages communicate with the oral cavity. 
‘There are lungs, and the heart has two auricles. 


VI.— Dipnoi, 


I, The PHARYNGOBRANCHII.—This order contains but — 
one species of fish, the remarkable Lancelet, or Amphiowus 
lanceolatus, which lives in sand, at moderate depths in the 
sea, in many parts of the world. It is a small semitrans- 
parent creature, poimted at both ends, as its name implies, 
and possessing no limbs, nor any hard epidermic or dermal 
covering. 

The dorsal and caudal regions of the body present a 
low median fold of integument, which is the sole represen- 
tative of the system of the median fins of other fishes. The 
mouth (Fig. 28, A, a) is a proportionally large oval aper-— 
ture, which lies behind, as well as below, the anterior ter-_ 
mination of the body, and has its long axis directed longi- 
tudinally. Its margins are produced into delicate ciliated 
tentacles, supported by semi-cartilaginous filaments, which 


THE PHARYNGOBRANCHII. ai U7 


are attached to a hoop of the same texture placed around 
the margins of the mouth (Fig. 29, f, g). These probably 
represent the labial cartilages of other fishes. The oral 
“aperture leads into a large and dilated pharynx, the walls 
of which are perforated by numerous clefts, and richly 
ciliated, so that it resembles the pharynx of an Ascidian 
(Fig. 28, B, f,g). This great pharynx is connected with 
a simple gastric cavity which passes into a straight intes- 


ee = 
EE RE JE 


Fig. 28.—Amphiorus lanceolatus.—a, mouth; 6, pharyngobranchial 
chamber ; c, anus; d, liver; e, abdominal pore.—B, the head en- 
larged: a, the notochord; 6, the representatives of neural spines, 
or fin-rays; c, the jointed oral ring; d, the filamentary appendages 
of the mouth; e, the ciliated lobes of the pharynx; f, g, part of the 
branchial sac ; /, the spinal cord. 


tine, ending in the anal aperture, which is situated at the 
root of the tail at a little to the left of the median line 
(Fig. 28, A, ce). The mucous membrane of the intestine is 
ciliated. 

An aperture called the abdominal pore (Fig. 28, A, e), 
placed in front of the anus, leads into a relatively spacious 


118 THE ANATOMY OF VERTEBRATED ANIMALS. 


cavity, which is continued forwards, on each side of the | 
pharynx, to near the oral aperture. The water which is 
constantly propelled into the pharynx by its cilia, and those 
of the tentacles, is driven out through the branchial clefts, 
and makes its exit by the abdominal pore. 

The liver (Fig. 28, A, d) is a saccular diverticulum of the 
intestine, the apex of which is turned forwards. 


Fig. 20.—Anterior end of the body of Amphioxus :— Ch, notochord ; 
My, myelon, or spinal chord, a, position of olfactory (?) sac ; b, optic 
nerve ; ¢, fifth (?) pair; d, spinal nerves; e, representatives of neu- 
ral spines, or fin-rays; f, g, oral skeleton. The iighter and darker 
shading represents the muscular segments and their interspaces. 


The existence of distinct kidneys is doubtful; and the re- 
productive organs are simply quadrate glandular masses, 
attached in a row, on each side of the walls of the visceral 
cavity, into which, when ripe, they pour their contents. 

The heart retains the tubular condition which it possesses 


THE PHARYNGOBRANCHII. 119 


in the earliest embryonic stage only, in other Vertebrata. 
The blood brought back from the body and from the ali- 
mentary canal enters a pulsatile cardiac trunk, which runs 
along the middle of the base of the pharynx, and sends 
branches up on each side. The two most anterior of these 
pass directly to the dorsal aorta; the others enter into the 
ciliated bars which separate the branchial slits, and, there- 
fore, are so many branchial arteries. Contractile dilata- 
tions are placed at the bases of these branchial arteries. 
On the dorsal side of the pharynx the blood is poured, by 
the two anterior trunks, and by the branchial veins which 
carry away the aérated blood from the branchial bars, into 
a great longitudinal trunk, or dorsal aorta, by which it is 
distributed throughout the body. 

Notwithstanding the extremely rudimentary condition of 
the liver, it is interesting to observe thata contractile trunk, 
which brings back the blood of the intestine, is distributed 
on the hepatic sac after the manner of a portal vein. The 
blood is collected again into another contractile trunk, which 
represents the hepatic vein, and is continued into the cardiac 
trunk at the base of the branchial sac. The corpuscles of 
the blood are all colourless and nucleated. 

The skeleton is in an extremely rudimentary condition, 
the spinal column being represented by a notochord, which 
extends throughout the whole length of the body, and ter- 
minates, at each extremity, in a point (Fig. 28). The in- 
vestment of the notochord is wholly membranous, as are 
the boundary-walls of the neural and visceral chambers, 
so that there is no appearance of vertebral centra, arches, 
orrvibs. A longitudinal series of small semi-cartilaginous 
rodlike bodies, which lie above the neural canal, represent 
either neural spines or fin-rays (Fig. 28, B, 6). Neither is 
there a trace of any distinct skull, jaws, or hyoidean appa- 
ratus; and, indeed, the neural chamber which occupies the 
place of the skull, has a somewhat smaller capacity than a 
segment of the spinal canal of equal length. 

There are no auditory organs, and it is doubtful if a 
ciliated sac, which exists in the middle line, at the front 


120 THE ANATOMY OF VERTEBRATED ANIMALS. 


part of the cephalic region (Fig. 29, a), ought to be con-! 
sidered as an olfactory organ. 

The myelon traverses the whole length of the spinal 
canal, and ends anteriorly without enlarging into a brain. | 
From its rounded termination nerves are given off to the 
oral region, and to the rudimentary eye or eyes (Fig. 29, 
b,c). 

According to M. Kowalewsky,* who has recently studied 
the development of Amphiowus, the vitellus undergoes com- 
plete segmentation, and is converted into a hollow sphere, the 
walls of which are formed of a single layer of nucleated cells. 
The wall of the one moiety of the sphere is next pushed 
in, as it were, until it comes into contact with the other, 
thus reducing the primitive cavity to nothing, but giving 
rise to a secondary cavity, surrounded by a double mem- 
brane. The operation is, in substance, just the same as that 
by which a double nightcap is made fit to receive the head. 
The blastoderm now acquires cilia, and becomes nearly 
spherical again, the opening into the secondary cavity being 
reduced to a small aperture at one pole, which eventually 
becomés the anus. M. Kowalewsky points out the resem- 
blance, amounting almost to identity, of the embryo at this 
stage with that of many Invertebrata. 

One face of the spheroidal blastoderm becomes flattened, 
and gives rise to lamine dorsales, which unite in the charac- 
teristically vertebrate fashion; and the notochord appears 
between and below them, and very early extends forwards, 
beyond the termination of the neural canal. The neural 
canal remains in communication with the exterior, for a 
long time, by a minute pore at its anterior extremity, The 
mouth arises as a circular aperture, developed upon the 
right side of the anterior end of the body, by the coalescence 
of the two layers of the blastoderm, and the subsequent 
perforation of the disc formed by this coalescence. The 
branchial apertures arise by a similar process, which takes 
place behind the mouth; and they are, at first, completely 


* “Mémoires de Académie Impériale des Sciences de St, Peters- 
bourg,’ 1867. 


: 


THE MARSIPOBRANCHII. 121 


exposed on the surface of the body. But, before long, a 


longitudinal fold is developed upon each side, and grows 


over the branchial apertures. The two folds eventually 


eoalesce on the ventral side, leaving only the abdominal 


pore open. One cannot but be struck with the resem- 
blance of these folds to the processes of integument which 
grow over the branchie of the amphibian larva; and, in 
like manner, inclosea cavity, which communicates with the 
exterior only by a single pore. 

In a great many of the characters which have been enu- 
merated—as, for example, in the entire absence of a distinct 
skull and brain, of auditory organs, of kidneys, of a cham- 
bered heart; in the presence of a saccular liver, of ciliated 
branchiz and alimentary canal; and in the extension of the 
notochord forwards to the anterior end of the body—Amphi- 
owus differs from every other vertebrated animal. Hence 
Professor Haeckel has proposed to divide the Vertebrata 
into two primary groups—the Leptocardia, containing 
Amphiowus; and the Pachycardia, comprising all other 
Vertebrata. The great peculiarities in the development of 
Amphioxus, and the many analogies with invertebrate ani- 
mals, particularly the Ascidians, which it presents, lend 
much support to this proposition. 

No fossil form allied to Amphiowus is known. 


II. The MarsrpopraNcutit.—In this order of the class 
Pisces the integument is devoid of scales or bony plates. 

The spinal column consists of a thick persistent notochord 
enveloped in a sheath, but devoid of vertebral centra. The 
neural arches and the ribs may be represented by carti- 
lages, and there is a distinct skull presenting cartilage at 
least in its base, and retaining many of the characters of 
the fetal cranium of the higher Vertebrata. _The notochord 
terminates in a point in the base of this cartilaginous skull 
behind the pituitary body; and the skull is not moveable 
upon the spinal column. There are no jaws; but the palato- 
pterygoid, the quadrate, the hyomandibular, and the hyoi- 
dean apparatus of higher Vertebrata, are imperfectly repre- 


122 THE ANATOMY OF VERTEBRATED ANIMALS. 


sented (Fig. 30, f, g, h). In some genera a basket-like carti-: 

laginous apparatus strengthens the walls of the oral cavity 5 

while, in others, such a framework supports the gill-sacs. 
The Marsipobranchii possess neither the pectoral nor the 


Fig. 30. 


Fig. 30.—A, the skull of a Lamprey, viewed from the side; B, from 
above :—a, the ethmovomerine plate ; b, the olfactory capsule ; c, the — 
auditory capsule ; d, the neural arches of the spinal column ; e, the 
palato-pterygoid portion, f, probably, the metapterygoid, or superior 
quadrate, portion, and g, the inferior quadrate portion, of the | 
subocular arch; h, stylohyal process; i, lingual cartilage; k, in- 
ferior, /, lateral, prolongation of the cranial cartilage ; 1, 2, 3, 
accessory labial cartilages; m, branchial skeleton, The spaces on 
either side of 1 are closed by membrane. 


pelvic pair of limbs, nor their arches. Horny teeth may be 
developed upon the roof of the palate, or upon the tongue, 
or may be supported by peculiarly developed labial carti- 


THE MARSIPOBRANCHII. 123 


lages. The alimentary canal is simple and straight, and 
the liver is not sac-like, but resembles that organ im other 
Vertebrata. 

The heart has the usual piscine structure, consisting of 
a single auricle preceded by a venous sinus, a single ven- 
tricle, and an aortic bulb, all separated from one another by 
valves. This heart is contained in a pericardium, the cavity 
of which communicates with that of the peritoneum. 

In Myxine the portal vein is rhythmically contractile. 

The cardiac aorta, which is continued from the bulb, 
distributes its branches to the respiratory organs. These 
consist of antero-posteriorly flattened sacs, which commu- 
nicate, directly or indirectly, on the inner side, with the 
pharynx, and, externally, with the surrounding medium. 

In the Lamprey there are seven sacs, upon each side, 
which open externally by as many distinct apertures. Inter- 
nally,they communicate witha long canal, which lies beneath 
the esophagus and is closed behind, while anteriorly it com- 
municates freely with the cavity of the mouth (Fig. 32, Pr). 

The kidneys are well developed, and have the ordinary 

yertebrate structure, while the ureters open behind the 
‘rectum. 
| The brain, though very small, is quite distinct from the 
myelon, and presents all the great divisions found in the 
higher Vertebrata—that is to say, a fore-brain, mid-brain, 
and hind-brain. The fore-brain is further divided into 
rhinencephala, solid prosencephalic lobes, and a thala- 
mencephalon; the hind-brain, into metencephalon and mye- 
lencephalon (Fig. 31). 
_ The auditory organ is simpler than in other fishes, possess- 
ing only two semicircular canals and a sacculated vestibule 
inthe Lamprey. In Mywine the whole organ is represented 
by a single circular membranous tube, without further dis- 
tinction into canals and vestibule. 

The Marsipobranchii differ remarkably, not only from the 
fishes which lie above them, but from all other vertebrate 
animals, in the characters of the olfactory organ, which 

consists of a sac placed in the middle line of the head, and 


124 THE ANATOMY OF VERTEBRATED ANIMALS. 


Fig. 31.—Side and upper views of the brain of Petromyzon fluviatilis, 
and an upper and inner view of the membranous labyrinth of 
P. marinus. The following letters refer to the figures of the brain :— 
I. the olfactory nerves, narrow anterior prolongations of the rhinen- 
cephalon (A); B, the prosencephalon ; C, the thalamencephalon ; D, 
the mesencephalon; E, the medulla oblongata; F, the fourth ven- 
tricle ; e, the narrow band whichis all that represents the cerebellum ; 
G, the spinal cord; II. the optic; III. the oculomotorius; IV. the pathe- 
ticus; V. the trigeminal; VI. the abducens; VII. the facial, and the 
auditory; VIII. the glossopharyngeal and pneumogastric; IX. the 
hypoglossal nerves; 1, 1’, 2, 2’, sensory and motor roots of the first 
two spinal nerves. In the figure of the membranous labyrinth: A, 
the auditory nerve; a, the vestibule ; c, the two semicircular canals, 
which correspond with the anterior and posterior vertical canals of 
other Vertebrata ; d, their union and common opening into the ves- 
tibule; 6, the ampulle. F 


THE MARSIPOBRANCHII. 125 


having a single, median, external aperture. In all other 
Vertebrata there are two nasal sacs. In the Lampreys, the 
nasal sac terminates blindly below and behind, but in the 
Hags (Myzine), it opens into the pharynx. In no other 
fishes, except Lepidosiren, does the olfactory apparatus com- 
municate with the cavity of the mouth. 

The reproductive organs of the Marsipobranchii are solid 
plates suspended beneath the spinal column, and they have 
no ducts, but shed their contents into the abdomen, whence 


Fig. 32.--Vertical and longitudinal section of the anterior part of the 
body of a Lamprey (Petromyzon marinus} :—A, the cranium with 
its contained brain; a, section of the edge of the cartilage marked 
a, in Fig. 30; O/f, entrance into the olfactory chamber, which is 
prolonged into the cecal pouch,o; Ph, the pharynx; Pr, the 
branchial channel, with the inner apertures of the branchial sacs ; 
M, the cavity of the mouth, with its horny teeth; 2, the cartilage 
which supports the tongue; 3, the oral ring. 


they pass out by an abdominal pore. In the early stages of 
their development the Lampreys present some singular re- 
semblances to the Amphibia. They also undergo a metamor- 
phosis, the young Petromyzon being so unlike the parent, 
that it was, until lately, regarded as a distinct genus— 
Ammocetes. But the young Lampreys never possess ex- 
ternal branchial filaments or spiracula. 

The Marsipobranchii are inhabitants of both fresh and 
salt water. The Myxinoids are remarkable for their parasitic 
habits—the Hag boring its way into the bodies of other 


126 THE ANATOMY OF VERTEBRATED ANIMALS. 


fishes, such as the Cod. No fossil Marsipobranchii ave§ 
known. This circumstance may, in part, be due to the 
perishableness of their bodies; though horny teeth, like 
those of the Lampreys, might have been preserved under 
favourable circumstances. 


IJ. The ELaAsMoBRANCHII.— This order contains the 
Sharks, the Rays, and the Chimera. 

The integument may be naked, and it never possesses 
scales like those of ordinary fishes; but, very commonly, it 
is developed into papillz, which become calcified, and give 
rise to toothlike structures: these, when they are very 
small and close-set, constitute what is called shagreen, When 
larger and more scattered, they form dermal plates or 
tubercles; and when, as in many cases, they take the form 
of spines, these are called dermal defences, and, in a fossil 
state, ichthyodorulites, All these constitute what has been 
called a “placoid exoskeleton ;” and, in minute structure, 
they precisely resemble teeth, as has been already explained. 
The protruded surfaces of the dermal defences are fre- 
quently ornamented with an elegant sculpturing, which 
ceases upon that part of the defence which is imbedded in 
the skin. The dermal defences are usually implanted in_ 
front of the dorsal fins, but may be attached to the tail, or, _ 
in rare cases, lie in front of the paired fins. 

The spinal column exhibits a great diversity of structure: 
from a persistent notochord exhibiting little advance upon 
that of the Marsipobranchii, or having mere osseous rings 
developed in its walls, to complete vertebre, with deep 
conical anterior and posterior concavities in their centra, 
and having the primitive cartilage more or less completely 
replaced by concentric, or radiating, lamelle of bone. In — 
the Rays, indeed, the ossification goes so far as to convert 
the anterior part of the vertebral column into one con-— 
tinuous bony mass. 

The neural arches are sometimes twice as numerous as 
the centra of the vertebrz, in which case the added arches 
are termed intercrural cartilages. 


THE ELASMOBRANCHII. 127 


The terminal part of the notochord is never enclosed 
within a continuous bony sheath, or wrostyle. The ex- 
tremity of the vertebral column is generally bent up, and the 
median fin-rays which lie below it are, usually, much longer 
than those which lie above it, causing the lower lobe of the 
tail to be much larger than the upper. Elasmobranchs with 
tails of this conformation are truly heterocercal, while those 
in which the fin-rays of the tail are equally divided by the 
spinal column, or nearly so, are diphycercal (p. 16). The 
Monkfish (Squatina) and many other Hlasmobranchii are 
more diphycercal than heterocercal. 

The ribs are always small, and may be quite rudimentary. 

The skull is composed of cartilage, in which superficial 

-pavement-like deposits of osseous tissue may take place, 
but it is always devoid of membrane bone. When move- 
able upon the spinal column, it articulates therewith by 
two condyles. 

In its general form and structure, the cartilaginous skull 
of an Hlasmobranch corresponds with the skull of the verte- 
brate fetus in its cartilaginous state, and there are usually 
more or less extensive membranous fontanelles in its upper 
walls. The ethmoidal region sends horizontal plates over 
the nasal sacs, the apertures of which retain their em- 
bryonic situation upon the under-surface of the skull. 

Neither premaxille nor maxille are present, the “jaws” 
of an Elasmobranch consisting, exclusively, of cartilaginous 
representatives of the primary palato-quadrate arch and of 
Meckel’s cartilage. 

The former of these, the so-called upper jaw, may either 
he represented, as in the Chimera (Fig. 33), by the anterior 
portion (B, D) of a triangular cartilaginous lamella, which 
stretches out from the sides of the base of the skull, and is 
continuous with the representative of the hyomandibular 
suspensorium; or there may be, on each side, a carti- 
laginous bar moveably articulated in front with the fore 
part of the skull; and, posteriorly, furnishing a condyle, 
with which the ramus of the lower jaw, representing Meckel’s 
cartilage, articulates. 


128 THE ANATOMY OF VERTEBRATED ANIMALS. 


In the latter case, which is that met with in the Sharks 
and Rays (Figs. 34 & 35), a single cartilaginous rod (9) is 
moveably articulated with the skull, in the region of the 
periotic capsule, upon each side; and, by its opposite ex- 
tremity, is connected by ligamentous fibres both with the 
palato-quadrate (h), and with the mandibular or Meckelian 
cartilage (Mn). This cartilaginous suspensoriwm represents 


Fig. 33. 


Fig. 33.—Vertical section of the skull of Chimera monstrosa, without 
the labial and nasal cartilages :—A, the basi-occipital region; P, 
the pituitary fossa; Ma, partition between the olfactory sacs; B, 
alveolus tor the anterior upper jaw tooth; C, D, the region of the 
triangular cartilage which answers to the hyomandibular and quad- 
rate; D, B, that which answers to the quadrate, pterygoid, and 
palatine ; Mn, the mandible; /Or, the interorbital septum; asc and 
psc, the anterior and posterior semicircular canals; IJ., Il., V., VIII, 
exits of the olfactory, optic, fifth and eighth pairs of nerves. 


the hyomandibular and the symplectic bones of the Teleostei, 
and gives attachment to the hyoidean apparatus (Hy). The 
latter consists of a lateral arch upon each side, united with 
its fellow, and with the branchial arches, by the intermedia- 
tion of medial basal elements below; and it is succeeded 
by a variable number of similar arches, which support the 
branchial apparatus. 


THE ELASMOBRANCHII. 129 


From the hyoidean and from the branchial arches carti- 
laginous filaments pass directly outwards, and support the 
walls of the branchial sacs. Superficial cartilages, which 
lie parallel with the branchial arches, are sometimes super- 
imposed upon these. There are no opercular bones, though 

cartilaginous filaments which take their place (Fig. 34, Op) 
may be connected with the hyomandibular cartilage; and, 
in the great majority of the Elasmobranchii, the apertures 
of the gill-sacs are completely exposed. But in one group, 
the Chimera, a great fold of membrane extends back from 
the suspensorial apparatus, and hides the external gill- 
apertures. 

Large accessory cartilages, called labial, are developed at 
the sides of the gape in many Elasmobranchii. (Figs. 34 & 
35, 1, k, 1.) 

The pectoral arch consists of a single cartilage on each 
side. The two become closely united together in the ventral 
median line, and are not directly connected with the skull. 
The pelvis is also represented by a pair of cartilages, which 
may coalesce, and are invariably abdominal in position. 

There are always two pairs of lateral fins corresponding 
with the anterior and posterior limbs of the higher Verte- 
brata. The pectoral fins, the structure of which has already 
been described, are always the larger, and sometimes attain 
an enormous size relatively to the body. 


In these fishes, teeth are developed only upon the mucous 
membrane which covers the palato-quadrate cartilage and 
the mandible. They are never implanted in sockets, and 
they vary greatly in form and in number. 

In the Sharks they are always numerous, and their crowns 
are usually triangular and sharp, with or without serrations 
and lateral cusps. As a rule, the anterior teeth on each side 
haye more acute, the posterior more obtuse crowns. In the 
Port Jackson shark (Cestracion), however, the anterior teeth 
are not more acute than the most obtuse teeth of the others, 
while the middle teeth acquire broad, nearly flat, ridged 
crowns, and the hindermost teeth are similar but smaller. 

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THE ELASMOBRANCHII. 131 
The Rays usually have somewhat obtusely-pointed teeth, but 
‘in Myliobates, the middle teeth have transversely elongated, 
and the lateral ones hexagonal, flat crowns, and the various 
‘teeth are fitted closely by their edges into a pavement. In 
Aetobatis only the middle transversely elongated teeth re- 
main. Inthe Sharks and Rays the teeth are developed from 
‘papille, or ridges, situated at the bottom of a deep fold 
“within the mucous membrane of the jaw. The teeth come 
to the edge of the jaw, and, as they are torn away or worn 
down by use, they are replaced by others, developed, in suc- 
cessive rows, from the bottom of the groove. No such 
successive development takes place in the Chimera. 

As in other fishes, there are no salivary glands. The 
wide esophagus leads into a stomach which is usually 
spacious and sac-like, but sometimes, as in Chimera, may 
be hardly distinct from the rest of the alimentary canal. 
No diverticulum filled with air, and constituting a swim- 
ming-bladder, as in Ganoid and many Teleostean fishes, is 
connected with either the esophagus, or the stomach, 
though a rudiment of this structure has lately been dis- 
covered in some Elasmobranchs. 

The intestine is short, and usually commences by a 
dilatation separated from the stomach by a pyloric valve. 
This duodenal segment of the intestine is usually known as 
the Bursa Entiana. It receives the hepatic and pancreatic 
ducts, and, in the foetus, the vitelline duct. Beyond this 
part, the absorptive area of the mucous membrane of the 
small intestines is increased by the production of that 
membrane into a fold, the so-called spiral valve, the fixed 
edge of which usually runs spirally along the wall of the 
intestine. In some sharks (Carcharias, Galeocerdo) the fixed 
edge of the fold runs straight and parallel with the axis of 
the intestine, and the fold is rolled up upon itself into a 
cylindrical spiral. 

The short rectum terminates in the front part of a cloaca, 
which is common to it and the ducts of the renal and the 
reproductive organs. The peritoneal cavity communicates 

with that of the pericardium in front, and, behind, opens 


132 THE ANATOMY OF VERTEBRATED ANIMALS. 


externally by two abdominal pores. The heart presents a 
single auricle, receiving the venous blood of the body from 
a sinus venosus. There is a single ventricle, and the walls 
of the aortic bulb contain striped muscular fibres, and are 
rhythmically contractile, pulsating as regularly as those of 
the auricle and ventricle. 

The interior of the bulb exhibits not merely a single row 
of valves at the ventriculo-bulbous aperture, but several other 


Fig. 36. 


Fig. 36.—The aortic bulb of a Shark (Lamna), laid open to show the 
three rows of valves, v, v, v, and the thick muscular wall, m. 


transverse rows of semilunar valves, which are attached to 
the walls of the bulb itself, and at its junction with the 
aorta. These valves must be of great importance in 
giving full effect to the propulsive force exerted by the 
muscular wall of the bulb. 

In a good many Elasmobranchii there is a spiracle, or aper- 
ture leading into the cavity of the mouth, on the upper side 
of the head, in front of the suspensorium. From this 
aperture (which, according to the observations of Professor 
Wyman, is the remains of the first visceral cleft of the 


THE ELASMOBRANCHII. 133 


embryo), as well as from the proper branchial clefts, long 
branchial filaments protrude, in the fetal state. These 
disappear in the adult, the respiratory organs of which 
are flattened pouches, with transversely-plaited walls, from 
five to seven in number. They open by external clefts 
upon the sides (Sharks and Chimera), or under-surface 
(Rays), of the neck, and, by internal apertures, into the 
pharynx. 

The anterior wall of the anterior sac is supported by the 
hyoidean arch. Between the posterior wall of the first, and 
the anterior wall of the second sac, and between the ad- 
jacent walls of the other sacs, a branchial arch with its 
radiating cartilages is interposed. Hence the hyoidean 
arch supports one series of branchial plates or laminz; 
while the succeeding branchial arches, except the last, bear 
two series, separated by a septum, consisting of the ad- 
jacent walls of two sacs with the interposed branchial 
skeleton. 

The cardiac aorta, a trunk which is the continuation of 
the bulb of the aorta, distributes the blood to the vessels of 
these sacs; and it is there aérated by the water which is 
taken in at the mouth and forced through the pharyngeal 
apertures, outwards. 

The kidneys of the Elasmobranchii do not extend so far 
forward as those of most other fishes. The ureters gene- 
rally become dilated near theixy terminations, and open 
by a common urinary canal into the cloaca behind the 
rectum. 

The brain is well developed. It usually presents a large 
cerebellum overlying the fourth ventricle, the side-walls of 
which (corpora restiformia) are singularly folded (Fig. 37, 
A., a); and moderate-sized optic lobes, which are quite dis- 
tinct from the conspicuous thalamencephalon, or vesicle of 
the third ventricle. The third ventricle itself is a relatively 
wide and short cavity, which sends a prolongation forwards, 
on each side, into a large, single, transversely-elongated 
mass (Fig. 37, a), which is usually regarded as the result of 
the coalescence of the cerebral hemispheres, but is, perhaps, 


134 THE ANATOMY OF VERTEBRATED ANIMALS. 


Fig. 37. 


Fig. 37.—The brain of the Skate (Maia batis). A. From above; 
B. Aportion of the ventral aspect enlarged :-—s, the olfactory bulbs ; 
a, the cerebral hemispheres which are united in the middle line; 
6, the thalamencephalon ; c, the mesencephalon; d, the cerebellum; — 
aa, the plaited bands formed by the corpora restiformia; I., IL., 
IV., V., the cerebral nerves of the corresponding pairs; f, the me- 
dulla oblongata; w, a bloodvessel. In B.: ch, the chiasma of 
the optic nerves ; h, the pituitary body; n and », vessels connected 
with it; %, the saccus vasculosus; 8, the pyramids of the medulla 
oblongata. : 


THE ELASMOBRANCHII. 135 


more properly, to be considered as the thickened termina- 
tion of the primitive encephalon, in which the lamina ter- 
_minalis and the hemispheres are hardly differentiated. 
The large olfactory lobes are usually prolonged into pe- 
dicles, which dilate into great ganglionic masses where they 
come into contact with the olfactory sacs (Fig. 37, A., s). 
The latter always open upon the under-surface of the head. 
A cleft, which extends from each nasal aperture to the 
margin of the gape, is the remains of the embryonic sepa- 
ration between the naso-frontal process and the maxillo- 
palatine process, and represents the naso-palatine passage 
of the higher Vertebrata. The optic nerves fuse into a com- 
plete chiasma (Fig. 37, B., ch), as in the higher Vertebrata. 
In some Sharks, the eye is provided with a third eyelid or 
nictitating membrane, moyed by a single muscle, or by two 
muscles, arranged in a manner somewhat similar to that 
observed in birds. In both Sharks and Rays, the posterior 
surface of the sclerotic presents an eminence which articu- 
lates with the extremity of a cartilaginous stem proceeding 
from the bottom of the orbit. 

Except in Chimera, the labyrinth is completely inclosed 
in cartilage. In the Rays the anterior and_ posterior 
“semicircular” canals are circular, and open by distinct 
narrow ducts into the vestibular sac. In the other Elas- 
mobranchii they are arranged in the ordiary way. A 
passage leading from the vestibular sac to the top of the 
skull, and opening there by a valvular aperture, represents 
the canal by which, in the vertebrate embryo, the auditory 
involution of the integument is, at first, connected with the 
exterior. 

The testes are oval, and are provided with an epididymis 
and vas deferens, as in the higher Vertebrata. The vas 
deferens of each side opens into the dilated part of the 
ureter. Attached to the ventral fins of the male are pecu- 
liar appendages, termed claspers. 

The ovaria are rounded, solid organs. There are usually 
two, but in some cases, as in the Dogfishes and nictitating 
Sharks, the ovary is single and symmetrical. The oviducts 


136 THE ANATOMY OF VERTEBRATED ANIMALS: 


are true Fallopian tubes, which communicate freely with 


the abdominal cavity at their proximalends. Distally, they 


dilate into uterine chambers, which unite and open into the 
cloaca. 

The eggs are very large, and comparatively few. 

The Dogfishes, the Rays, and the Chimera are ovi- 
parous, and lay eggs enclosed in hard leathery cases; the 
others are viviparous, and in certain species of Mustelus 
(levis) and Carcharias, a rudimentary placenta is formed. 
the vascular walls of the umbilical sac becoming plaited. 
and interdigitating with similar folds of the wall of the 
uterus. 

The embryos of most Elasmobranchs are, at first, pro- 
vided with long external branchial filaments, which proceed 
from the periphery of the spiracle, as well as from most of 
the branchial arches. These disappear, and are function- 
ally replaced by internal gills as development advances. 


The Elasmobranchii are divided into two groups, the 
Holocephali and the Plagiostomi. 

In the Holocephali the palato-quadrate and suspensorial 
cartilages are united with one another and with the skull 
into a continuous cartilaginous plate; the branchial clefts 
are covered by an opercular membrane. The teeth are 
very few in number (not more than six, four of which are in 
the upper, and two in the lower jaw. in the living species) 
and differ in structure from those of the Plagiostomi. This 
suborder contains the living Chimera and Callorhynchus, 
the extinct Mesozoic Edaphodon and Passalodon ; and, very 
probably, some of the more ancient Elasmobranchs, the 
teeth of which are so abundant in the Carboniferous lime- 
stones. * 

In the Plagiostomi, the palato-quadrate and suspensoriai 
cartilages are distinct from one another, and are moveable 
upon the skull. The branchial clefts are not covered by 
any opercular membrane. The teeth are usually numerous. 

The Plagiostomi are again subdivided into the Sharks 
(Selachii or Squali), with the branchial apertures at the sides 


THE GANOIDEI. 137 


of the body, the anterior ends of the pectoral fins not con- 
nected with the skull by cartilages, and the skull with a 
‘median facet for the first vertebra; and the Rays (Rae), 
with the branchial clefts on the under-surface of the body. 
‘the pectoral fins united by cartilages to the skull, and no 
median articular facet upon the occiput for the first vertebra. 

The Elasmobranchii are essentially marine in their habits ; 
though Sharks are said to occur very high up in some of 
the great rivers of South America. 

Both divisions of the Plagiostomi oecur in the Mesozoic 
rocks. In the Paleozoic epoch, dermal defences and teeth 
of Elasmobranchii abound in the Permian and Carboni- 
ferous formations, and are met with in the Upper Silurian 
rocks. But, except in the case of Plewracanthus (a Selachian), 
it is impossible to be certain to what special divisions they 
belong. 


IV. The GanorpE1.—In former periods of the world’s 
history this was one of the largest and most important of 
the orders of fishes; but, at present, it comprises only the 
seven genera—Lepidosteus, Polypterus, Calamoichthys, Amia, 
Accipenser, Scapirhynchus, and Spatularia, which are either 
partially, or wholly, confined to fresh water, and are found 
only in the northern hemisphere. These fishes differ very 
widely from one another in many points of their organiza- 
tion, but agree in the following characters, some of which 
they possess in common with the Hlasmobranchti, and 
others with the Teleostei. Thus :— 

a. The bulbus aorte is rhythmically contractile, and pro- 
vided with several rows of valves, as in the Hlasmobranchi. 

b. The optic nerves unite in a chiasma, as in the Elasmo- 
branchii. 

c. There is a well-developed spiral valve in the intestine, 
as in the Elasmobranchii, in all but Lepidosteus, which pos- 
sesses only a rudiment of such a valve. 

On the other hand— 

a. The branchial processes are not fixed throughout their 
extent to the wall of a branchial sac, which extends beyond 


138 THE ANATOMY OF VERTEBRATED ANIMALS. 


them, as in the Elasmobranchii ; but their extremities project 
freely beyond the edge of the septum which separates each _ 
pair of branchial clefts, as in the Teleostei; and, as in the | 
Teleostei, they are covered by a bony operculum. : 

b. There is a large air-bladder connected by a perma- 
nently open pnewmatic duct with the esophagus, as in many 
Teleostei. 

c. As in the Teleostei, there is no cloaca. 

The ventral fins are always abdominal in position. The 
tailis diphycercal, or heterocercal, and the terminal portion 
of the notochord is not ossified. The cavity of the abdomen 


Fig. 38. 


i 


Fig. 38.— The brain of Lepidosteus semiradiatus. .A. From above; B. 
From below :—f, the medulla oblongata; d, the cerebellum ; c, the © 
optic lobes of the mesencephalon; g, the cerebral hemispheres ; 
h, the pituitary body; 7, the lobi inferiores. Ch, the chiasma; I., ol- 
factory ; II., optic nerves. 

is placed in communication with the exterior by abdominal 

pores. Finally, the ducts of the reproductive organs com- 

municate with those of the permanent urinary apparatus, 
which is, in part, an Hlasmobranch, in part, an Amphibian, 
character. 
The exoskeleton presents the most extreme variations in — 
the Ganoidei. Spatularia is naked; Accipenser and Scapi- 
rhynchus develope numerous dermal plates composed of true 
bone; Amia is covered with overlapping cycloid scales ; 
Lepidosteus and Polypterus have solid, rhomboidal, enamelled 


THE GANOIDEI. 139 


scales, which not only overlap, but are fitted together by 
pegs and sockets, where their anterior and posterior edges 
come into contact. 

The endoskeleton is not less diversely modified; and it is 
worthy of remark that no sort of relation, either direct or 
inverse, is traceable between the completeness of the endo- 
skeleton and that of the exoskeleton. Thus Spatularia, 
Scapirhynchus, and Accipenser have a persistent notochord, 
in the sheath of which mere cartilaginous rudiments of the 
arches of vertebre appear. The ribs, when present, are 
partially ossified. Polypterus and Amia have fully ossified 
vertebre, the centra of which are amphicelous. Lepidosteus 
also has fully ossified vertebree; but their centra are opis- 
thocelous, having a convexity in front and a concavity 
behind, as in some Amphibia. 

More or fewer of the anterior vertebra, or their cartila- 
ginous representatives, are united with one another, and 
with the posterior part of the skull. And the cranium may 
consist principally of cartilage, membrane bones being super- 
added; or the primordial cartilage may be largely super- 
seded by bone, as in the Teleostei. 

Spatularia, Scapirhynchus, and Accipenser have skulls of 
the former description. The cranium is one mass of car- 
tilage, continuous behind with the coalesced anterior spinal 
cartilages, so as to be immoveably connected with the spinal 
column. The notochord enters its base, and terminates in 
a point behind the pituitary fossa. In front, the cartilage 
is produced into a beak, which, in Spatularia, is very long, 
flattened, and spatulate. In the perichondium of the base 
of the skull, median bones, answering to the vomer and to 
the parasphenoid of Teleostean fishes, are developed; and, 
in that of its roof, ossifications, which represent the parie- 
tals, frontals, and other membrane bones of the Teleostei, 
appear. 

The framework of the jaws in Spatularia is very similar 
to that in the EHlasmobranchii. There is a partly carti- 
laginous, and partly ossified, suspensorial cartilage (A, B, 
Fig. 39), which gives attachment below, directly, to the 


140 THE ANATOMY OF VERTEBRATED ANIMALS. 


hyoidean arch (Hy) and, indirectly, to the jaws. The latter 
consist of a palato-quadrate cartilage (D) united by liga- 


ment with its fellow, and with the prefrontal region of the 
skull at F.; and presenting, at its posterior end, a con- | 


vex articular head to the cartilage of the mandible, or 
Meckelian cartilage, Mn. It is obvious that A, B corre- 
sponds with the hyomandibular, or suspensorial, cartilage 
in the Sharks and Rays ; D, with the palato-quadrate carti- 


Fig. 39, 


Fig. 39.—Side-view of the skull of Spatularia, with the beak cut away, 
and the anterior (asc), and posterior (psc), semicircular canals 
exposed :—Au, auditory chamber; Or, the orbit with the eye; WV, 
the nasal sac; Hy, the hyoidean apparatus; Br, the representatives 
of the branchiostegal rays; Op, operculum; Mn, mandible; 4, B, 
suspensorium ; D, palato-quadrate cartilage; #, maxilla. 


lage, or so-called “upper jaw,” and the cartilage of the 
mandible with the lower jaw in these animals. But, in 
the Ganoid fish, an osseous operculum (Op) is attached to 
the hyomandibular; and a branchiostegal ray (Br) to the 
more strictly hyoidean part of the skeleton of the second 
visceral arch; while a membrane bone (#) representing the 


maxilla, and another (Mn) the dentary, of the lower jaw in — 


Teleostei, are developed in connection with the palato-quad- 
rate and mandibular cartilages. 


THE GANOIDEI. 141 


In the Sturgeon (Fig. 40), the membrane bones of the 
roof of the skull are more numerous and distinct than in 
Spatularia, and large dermal bones (I, K, L) are united 
with them, to form the great cephalic shield. The suspen- 


Fig. 40. 


Fig. 40.—The cartilaginous skull of a Sturgeon, with the cranial bones. 
The former is shaded, and supposed to be seen through the latter, 
which are left unshaded :—a, ridge formed by the spinous processes 
of the anterior vertebre ; 6, 6, lateral winglike processes ; c, rostrum ; 
Au, position of the auditory organ; Na, position of the nasal sacs ; 
Or, that of orbit. The membrane bones of the upper surface are: A, 
the analogue of the supra-occipital ; B, B, of the epiotics; /, of the 
ethmoid ; G, G, of the postfrontals; H, H, of the prefrontals; C,C, 
the parietals; D, D are the frontals, and F, F the squamosals; K, 
the anterior dermal scute; J, J and L, L. dermal ossificatioas con- 
necting the pectoral arch with the skull. 


Fig. 41. 


Fig. 41.—Side-view of the cartilaginous cranium of Acczpenser : —a, ros- 
trum; 4, nasal chamber; Or, orbit; c, auditory region; d, coa- 
lesced anterior vertebre; e, ribs; f, g, A, suspensorium ; 4, palato- 
maxillary apparatus; Mn, mandible. : 


sorium (f, g, h, Fig. 41) is divided into two portions, to the 
lower of which (at hk) the proper hyoid is attached; and the 
palato-quadrate cartilages, with their subsidiary ossifications, 


142 THE ANATOMY OF VERTEBRATED ANIMALS. 


are so loosely connected with the floor of the skull, that — 
the jaws can be protruded and retracted to a considerable 
extent. 

In Lepidosteus, Polypterus, and Amia, the skull presents — 
not only membrane bones, but, in addition, basi-occipital, 
ex-occipital, and pro-otic ossifications of the primordial carti- 
lage, to which others may be added. The vomers are double, 
as in the Amphibia (? Polypterus). The apparatus of the 
jaws has become modified in accordance with the Teleos- 
tean type of structure. The suspensorium consists of two 
ossifications united by a cartilaginous intermediate por- 
tion. The upper—broad, and moveably articulated with the 
periotic capsule—is the hyomandibular ; the lower answers to 
the symplectic of osseous fishes. The cartilaginous palato- 
quadrate arcade is, in part, replaced by a series of bones: 
the palatine lies in front, and is connected with the pre- 
frontal region of the skull; behind it, lie representatives 
of the pterygoid, the sadist se goid, the ectopterygoid ; 
and, most posteriorly, of the quadrate bone. The last fur- 
nishes a condyle to the articular element of the mandible. 
The symplectic is either loosely connected with the quad- 
rate, as in Lepidosteus, or more closely united with it, as in 
the other genera. 

In Lepidosteus and Amia, a strong and long membrane 
bone, the preoperculum, is developed on the outer side of 
the hyomandibular and quadrate bones, and connects them 
still more firmly together. 

The maxilla is represented by a series of small separate 
ossifications in Lepidosteus. The proximal end of the 
mandibular cartilage ossifies, and becomes a distinct arti- 
culare. A dentary element is added on the outer, and a 
splenial one upon the inner side of the cartilage; and in 
Lepidosteus, angular, swpra-angular, and coronary elements 
are added, so that the components of the mandible are as 
numerous as in reptiles. Lepidosteus and Amia have bran- 
chiostegal rays, but Polypterus has none—at any rate, of the 
ordinary kind. A single jugular plate is developed between 
the rami of the mandible in Amia, and there are two such 


THE GANOIDEI. 143 


plates in Polypterus, which may possibly represent branchio- 
stegal rays. 

In Accipenser, Spatularia, and Amia, the pectoral arch 
presents two constituents: one, internal and cartilaginous, 
answers to the cartilaginous pectoral arch of the Elasmo- 
branchii, and to the scapula and coracoid of the higher 
Vertebrata ; the other, external, consists of membrane bones 
representing the clavicular, supra-clavicular, and post- 
‘clavicular bones of the Teleostei. In Lepidosteus one centre 
of ossification appears in the cartilage; in Polypterus, 
two. ‘The upper represents the scapula, and the lower the 
coracoid. 

It has been already stated (p. 39) that Polypterus comes 
nearest to the Hlasmobranchii in the structure of the rest 
of the limb. The numerous dermal fin-rays, all nearly 
equal in size, are connected with the rounded periphery of 
the broad and elongated disc formed by the skeleton of the 
fin; and the scaly integument is continued to the bases of 
the fin-rays, which thus seem to fringe a lobe of the integu- 
ment. Hence the fin is said to be lobate. Inthe other genera, 
only two of the basal cartilages are present, and some of the 
radialia come into contact with the shoulder-girdle between 
them. In addition, the anterior dermal fin-ray is much 
larger than the others, and becomes directly connected with 
the anterior basal cartilage. Thus, in the structure of their 
fins, as in so many other characters, the Gamoidei are inter- 
mediate between the Hlasmobranchii and the Teleostei. 

In certain Ganoids, as Lepidosteus, Accipenser, and many 
fossil genera, the anterior margins of the anterior fin-rays 
of the dorsal fins, bear a single or a double series of small 
scales, or spines, called fulera. 

In Accipenser and Polypterus, spiracula, or openings which 
communicate with the mouth, lie on the top of the head, in 
front of the suspensorium, as in many Elasmobranchs. 

_ Lepidosteus, Accipenser, and Scapirhynchus, have branchize 
attached to the hyoidean arch, as in the Elasmobranchii. 
They are now called opercular gills. 

In Polypterus the air-bladder is double and sacculated, 


144 THE ANATOMY OF VERTEBRATED ANIMALS. 


and the pneumatic duct opens upon the ventral aspect of 
the esophagus. The air-bladder thus becomes exceedingly 
like a lung; but its vessels are in communication with 
those of the adjacent parts of the body—not with the heart, | 
as in a true lung. 

In Lepidosteus, the ducts of the male and female repro- 
ductive organs are continuous with those bodies, and each 
duct opens into the dilated ureter of its side. In the other 


Fig. 42. 


Fig. 42.—The female reproductive organs of Amia calva: —ua, a, the 
open ends of the genital ducts; b, 6, oviducts; c,d, the right and 
left divisions of the urinary bladder; e, e, the openings of the 
ureters into the bladder; f, the anus; g,g, the abdominal pores; 
h, the urogenital aperture. 


Ganoids the proximal ends of the genital ducts, in both sexes 
open widely into the abdominal cavity. In Polypterus the 
united ureters open into the cavity of the confluent ovi- 
ducts, while, in the other Ganoids, the oviducts open into the 
dilated ureters. (Fig. 42.) 


THE GANOIDEI. 145 


When the fossil, as well as the existing Ganoidei, are 
taken into account, they form a large order, divisible 
into the following suborders :—1. Tee 2. Lepidosteide, 
3. Crossopter ygiden, 4. Chondrosteide, all of which have living 
_representatives ; while the other three—viz., 5. Cephalaspide, 
6. Placodermi, and 7. Acanthodide—have been extinct since 

the Paleozoic epoch, and are only ranged among the Ganoids 
provisionally, inasmuch as we have no knowledge of their 
“internal anatomy. 

1. The Amiade have a single living representative in the 
rivers of North America—Amia calva ; and it is not certain 
that any member of the group occurs in the fossil state. 
The cycloid scales, preoperculum, single median jugular 
plate, branchiostegal rays, non-lobate paired fins, and 
heterocercal tail, diagnose the suborder. 

2. The Lepidosteide have rhomboidal enamelled scales, 
a preoperculum, branchiostegal rays, non-lobate paired 
fins, and heterocercal tail. These are represented in the 
rivers of North America at the present day, and in tertiary 
formations, by Lepidosteus ; in the Mesozoic rocks, by a great 
variety of genera—Lepidotus, Hchmodus, Dapedius, &c.; and, 
in the Palzozoic epoch, by Paleoniscus in the Carboniferous, 
and probably hy Cheirolepis, in the Devonian, formation. 

3. In the Crossopterygide the scales vary in thickness and 
ornamentation, and may be thin and cycloid, or thick and 

ae 43.—Restoration of og 


) 
oy)) 
Be 


yyy) 
BEN YP ) 


rhomboid. The dorsal fins are either two in number, or, if 

single, very long, or multifid. The pectoral fins, and usually 

the ventrals, are lobate; they are sometimes rounded, as 
Ti 


146 THE ANATOMY OF VERTEBRATED ANIMALS. 


in Polypterus—sometimes greatly elongated and almost fili- 
form, as in Holoptychius (Fig. 43). There are no branchio- 
stegal rays, but two principal, and sometimes many smaller’ 
lateral, jugular plates. The tail may be either diphycercal or 
heterocercal. 

The only living representatives of this suborder are 
Polypterus and Calamoichthys, which inhabit the rivers of 
North Africa. Neither of these are known to occur in the 
fossil state. The only family of the suborder at present 
known among Mesozoic fossils is that of the Celacanthini, 
a remarkable group of fishes with a persistent notochord, 
rudimentary ribs, an air-bladder with ossified walls, and a 
single interspinous bone for each of the two dorsal fins. 
The Celacanthini also occur in the Carboniferous forma- 
tion; and the great majority of the Crossopterygide are 
found in this and the Devonian formations (Osteolepis, 
Diplopterus, Glyptolemus, Megalichthys, Holoptychius, Rhi- 
zodus, Dipterus, Phaneroplewron, &c,). Megalichthys, Di- 
pterus, and probably a few other of these fishes, have partially 
ossified vertebral centra; the rest possessed a persistent 
notochord. It is by the Crossopterygide that the Ganoids 
are especially connected with the Dipnoi, and, through 
them, with the Amphibia, 

4. The Chondrosteide are either naked, or have dermal 
plates of bone in the place of scales, Neither the pectoral 
nor the ventral fins are lobate, The branchiostegal rays 
ire few or absent, the tail is heterocercal, There are no 


cartilage bones in the brain-case, The teeth are very small, — 


or absent. 


The Sturgeons (Accipenser)—which inhabit the northern i 
rivers of Europe, Asia, and America, occasionally migrating — 


to the sea—Spatularia, and Scapirhynechus (found in the rivers 
of North America), are the recent members of this group, 


which is represented, in the older Mesozoic rocks, by Chon- — 


drosteus. 
5. The Cephalaspide are remarkable fishes, probably. 
allied to the Chondrosteide, which occur only in the Lower 


4 
4 


Devonian and the Upper Silurian rocks, and are some of — 


THE GANOIDEI. 147 


the oldest fish at present known. The head is covered by 
a continuous shield, which has the structure of true bone, 
in Cephalaspis, but more resembles certain piscine scales, 
in Pterapsis. The shield is prolonged into two horns 
at its posterolateral angles, and a median dorsal back- 
ward prolongation usually bears a spine, in Cephalaspis ; 
the body is covered with flat bony scales or plates, and 
possesses two large pectoral fins. The characters of the 
body and fins of Pterapsis are unknown. Notwithstand- 
‘ing the excellent preservation of many of the specimens of 
these fishes, they have, as yet, yielded no evidence of jaws 
or teeth. Should jaws be absent, the Cephalaspide would 
approach the Marsipobranchii more nearly than any of 
the other amphirhine fishes do. 
6. The Placodermi, comprising the genera Coccosteus, 
Pterichthys, Asterolepis,and some others, are known to occur 
only in the Devonian and Carboniferous formations. In 
these fishes the pectoral region of the body is incased in 
great bony plates, which, like those of the skull, are orna- 
mented with dots of enamel. The caudal region was covered 
with small scales in Pterichthys, while in Coccosteus it appears 
: to have been naked. The pectoral member of Pterichthys is 
exceedingly long, covered with suturally-united bony plates, 
and united with the thoracic plates by a regular joint. In 
Coccosteus the pectoral member seems to have had the ordi- 
nary construction. The bones of the head and thorax of 
Coccosteus nearly resemble those of certain Siluroid fishes 
(e.g. Clarias) in their form and arrangement, and it seems 
probable that the Placodermi were annectent forms between 
the physostome Teleostei and the Ganoidei. 

7. The Acanthodide, on the other hand, seem to have 
connected the Ganoidei with the Elasmobranchii. The scales 
of these fishes of the Devonian and Carboniferous formations 
are very small, and similar to shagreen; spines, resembling 
the dermal defences of the Elasmobranchii, are placed in 
front of more, or fewer, of the median and of the paired 
fins. The skull appears to have been unossified, and the 
pectoral arch seems to have consisted of a single bony hoop. 


148 THE ANATOMY OF VERTEBRATED ANIMALS. 


The Pycnodontide, which are commonly grouped among 
the Ganoids, are fishes with much-compressed bodies, like the ; 
John Dory or the Filefishes, covered with large rhomboidal 
enamelled scales, from which bony ridges projected inter- 
nally, and were imbedded in the integument. The noto- 
chord is persistent, but the neural arches and the ribs 
are ossified. The proximal ends of the ribs, imbedded in the 
sheath of the notochord, are but little expanded in the more 
ancient members of the group, while, in the more modern 
species, they enlarge, and at length unite by serrated su- 
tures, giving rise to spurious vertebre. The skull is high 
and narrow, as in Balistes; the premaxille are small, and 
there are no teeth in the maxille, but several longitudinal 
series of crushing teeth (the vomer and parasphenoid P) 
are attached to the base of the skull. These bite between 
the rami of the mandible, which are also armed with several 
rows of similar teeth. The teeth of the Pyenodonts have no 
vertical successors. The pectoral fins are small, the ventral, 
obsolete. The Pycnodonts are all extinct, but existed. 
formerly, for avery long period of time—their fossil remains 
occurring in rocks from the Carboniferous to the older 
Tertiary formations, inclusively. They present curious 
features of resemblance to the plectognath Teleostei. 

The remains of Ganoid fishes began to appear in the 
Upper Silurian rocks at the same time as those of the Hlas- 
mobranchii, with which they constitute the oldest Verte- 
brate Fauna; they abound in the Devonian formation, and | 
constitute, with the Hlasmobranchii, the whole of the Palzo- 
zoic Fish Fauna. We are in ignorance of the true affinities 
of Tharsis and Thrissops, and of the Hoploplewride ; but 
unless some, or all, of these are Teleosteans, Ganoids and 
Elasmobranchs, alone, constitute the Fish Fauna of the 
Mesozoic formations, as far as the bottom of the Cre- 
taceous series. i 


V. The TELEosTEI.—The osseous fishes are occasionally — 
devoid of any exoskeleton. Sometimes they present scat-_ 
tered dermal plates of true bone; or, as in the Trunkfishes — 


THE TELEOSTEI. 149 


(Ostracion), the body may be incased in a complete cuirass, 
which is calcified, but has not the structure of bone. Again, 
as in the Filefishes (Balistes), the skin may be beset with 
innumerable small spines, somewhat like those which form 
the shagreen of the Elasmobranchs in appearance, though 
they differ from them in structure. But, usually, the exo- 
skeleton of the Teleosteans takes the form of overlapping 
scales, which rarely exhibit the lacunze characteristic of true 
bone. The free portions of the scales are sometimes smooth, 
and rounded at the edge, when they are termed cycloid ; or 
they are roughened with ridges and minute spines, when 
they are called ctenoid. 

The spinal column always presents ossified vertebral 
centra, and the primordial cartilage of the skull is more 
or less replaced by bone. The centra of the vertebre are 
usually biconcave, each face presenting a deep conical 
hollow. In certain Eels (Symbranchus), the centra of most 
of the vertebre are flat in front and concave behind, the 
most anterior possessing a convexity in front. In many 
Siluroid fishes a certain number of the anterior vertebre 
are ankylosed together, and with the skull, into one mass, 
as in the Ganoids. 

The vertebre are distinguishable only into those of the 
trunk and those of the tail. The latter are provided with 
complete inferior arches, traversed by the caudal artery 
and vein. The former usually possess ribs, but these do 
not unite with one another, nor with any sternum, in the 
ventral median line, and they enclose the thoracico-abdomi- 
nal viscera. The vertebre are commonly united by zyga- 
pophyses, or oblique processes, placed above the centra; in 
addition to which, the lower margins of the centra are, 
not unfrequently, united by additional articular processes. 
Transverse processes commonly exist, but the ribs are articu- 
lated with the bodies of the vertebra, or with the bases of 
the transverse processes, not with their extremities. 

When a dorsal fin exists in the trunk, its rays are articu- 
Jated with, and supported by, elongated and pointed bones 
—the interspinous bones, which are developed around pre- 


150 THE ANATOMY OF VERTEBRATED ANIMALS. 


existing cartilages, and lie between, and are connected with, 
the spines of the vertebra. The fin-rays may be entire | 
and completely ossified, or they may be transversely jointed — 
and longitudinally subdivided at their extremities. Not | 
unfrequently, the articulation between the fin-rays and the 
interspinous bone is effected by the interlocking of two 
rings—one belonging to the base of the fin-ray and its 
included dermal cartilage, and the other to the summit of 
the interspinous bone—like the adjacent links of a chain. 

In all Teleostean fishes the extremity of the spinal 
column bends up, and a far greater number of the caudal 
fin-rays lie below than above it. These fishes are, therefore, 
strictly speaking, heterocercal. Nevertheless, in the great 

majority of them (as has been already mentioned, p. 16), the 
tail seems, upon a superficial view, to be symmetrical, the 
spinal column appearing to terminate in the centre of a 
wedge-shaped hypural bone, to the free edges of which the 
caudal fin-rays are attached, so as to form an upper and a 
lower lobe, which are equal, or subequal. This characteris- 
tically Teleostean structure of the tail-fin has been termed 
homocercal—a name which may be retained, though it 
originated in a misconception of the relation of this struc- 
ture to the heterocercal condition. 

In no Teleostean fish is the bent-up termination of the 
notochord replaced by vertebra. Sometimes, as in the 
Salmon (Fig. 6, p. 17), it becomes ensheathed in cartilage, 
and persists throughout life. But, more usually, its aheaitlt 
becomes calcified, and the urostyle thus formed coalesces 
with the dorsal edge of the upper part of the wedge-shaped 
hypural bone, foraied by the ankylosis of a series of ossicles, 
which are developed in connection with the ventral face of 
the sheath of the notochord. 

In the caudal region of the body, interspinous bones are 
developed between the spines of the inferior arches of the 
vertebre, and bear the fin-rays of the anal and, in part, of — 
the caudal fin. 

The Teleostei differ very much in the extent to which the 
primordial cranium persists throughout life. Sometimes, 


THE TELEOSTEI, 151 


as in the Pike (Figs. 44 & 45), it grows with the growth of 
the fish, and only becomes partially ossified ; in other cases 
it almost disappears. A basi-occipital (B.O.), ex-occipital 
(#.0.), and supra-occipital (S8.0.) bone are developed in it, 


Fig. 44. 


Fig 44.—The cartilaginous cranium of the Pike (Hsor lucvus), with its 
intrinsic ossifications ; viewed, A, from above; B, from below; C, 
from the left side :—V, N, nasal fosse ; I. Or, interorbital septum ; 
a, groeve for the median ridge of the parasphenoid; 6, canal for the 
orbital muscles. Sy., wrongly so marked, is the Pterotic. V. and 
VIII. mark the exits of the fifth and pneumogastric nerves; 3, 3, 
small ossifications of the rostrum. 


and form a complete occipital segment. The proper basi- 
sphenoid (BS) bone is always a very small, and usually 
somewhat Y-shaped, bone. The alisphenoids (AS.) some- 


152 THE ANATOMY OF VERTEBRATED ANIMALS. 


times are and sometimes are not developed. The pre- 
Fig. 45. 


= 
rs 


Fig. 45.—Longitudinal and vertical section of a fresh Pike’s skull.— 
The cut surface of cartilage is dotted. For 8.V.., and P.V.C., 


THE TELEOSTEI. 153 


read a.s.c., anterior, and p.s.c., posterior semicircular canal; 2, the 
parasphenoid ; y, the basisphenoid ; Vo, the vomer; P., the pituitary 
fossa. 


sphenoidal and orbitosphenoidal regions commonly, but 
not always, remain unossified. 

In most osseous fishes, the base of the skull in front of 
the basisphenoid is greatly compressed from side to side, 
and forms an interorbital septum (I. Or.). The anterior 
moiety of the cranial cavity is consequently reduced to a 
comparatively narrow passage above the septum (Fig. 45). 
In the Siluroid and Cyprinoid fishes, however, this septum 
is not formed, and the cranial cavity is of nearly equal size 
throughout, or gradually diminishesforwards. The ethmoidal 
cartilage usually remains unossified, but sometimes, as in 
the Pike, ossification may take place in it. (Fig. 44, 3,3.) The 
-antorbital, or lateral ethmoidal, processes of the primordial 
cranium ossify, and give rise to the prefrontal bones (Prf.). 
The postorbital processes also ossify as postfrontals 
(Pif.). The upper and posterior part of the primordial 
cranium exhibits five processes—one postero-median, two 
postero-lateral, and two postero-external. The postero- 
median ossifies as part of the supra-occipital (S.0.) The 
postero-lateral ossifies as part of the epiotic (Hp.0.), which 
lies upon the summit of the superior vertical semicircular 
canal. The postero-external closely corresponds with the 
squamosal of the higher Vertebrata in position; but, as a 
cartilage bone, it corresponds with an ossification of the 
capsule of the ear, called pterotic in the higher Vertebrata. 
Not unfrequently, as in the Cod, for example, the opisthotic 
(Op.O.) is a distinct bone, and enters into the formation of 
the postero-external process. The pro-otic (Pr.0.) is always 
a well-developed bone, and occupies its regular place, in 
front of the anterior vertical semicircular canal, and behind 
the exit of the trigeminal nerve. 

In addition to these cartilage bones, the brain-case of 
osseous fishes is additionally defended by numerous mem- 
brane bones. These are, on the roof of the skull— 

1. The parietal bones -(Pa.), which sometimes meet in a 


154 THE ANATOMY OF VERTEBRATED ANIMALS. 


sagittal suture, as in most of the higher Vertebrata, but are 
very generally separated by the junction of the frontals with | 
the supra-occipital. 

2. The large frontals (Fr.), which may or may not unite | 
into one. 

3. The nasal bones (Na.), apparently replaced in the Pike 
by the bones 1 and 2. 


Fig. 46. 


Prf, Ptf 
\ 


Fig. 46.—Side and upper views of the skull of a Pike ( sor lucius), — 
without the facial or supra-orbital bones:—y, the basisphenoid ; 
z, the alisphenoid; a, the articular facet for the hyomandibular 
bone. 


The under-surface of the skull possesses two membrane 
bones: in front the vomer (Vo.), and, behind, the huge para- 
sphenoid (x, «), which ensheathes all the basis cranii, from 
the basi-occipital to the vomer. 

A supra-orbital bone (S.Or.) is the only ae ane bone 
attached to the sides of the brain-case. Two premaxillary — 
bones (Pmz.) are attached, sometimes closely, sometimes — 
loosely, to the anterior extremity of the cranium; and behind 
these are the maxille (Mzw.), which are sometimes large and — 
single, as in the Cyprinoid fishes, but may become subdivided, 
or be reduced to mere styliform supports for cirri, as in 
many Siluroid fishes. In most osseous fishes the maxille 


THE TELEOSTEI. 155 


take little or no share in the formation of the gape, which 
is bounded above by the backwardly extended premaxille. 


/ 7 10 

Ar An SyPr0p Brg 

Fig. 47.—Side-view of the skull of a Pike (Hsor lucius) :—Prf, pre- 
frontal; H.M., hyomandibular bone; Op, opercuium; S.Op., sub- 

_ operculum; J.Op, interoperculum; Pr.Op, preoperculum; Brg, 
branchiostegal rays; Sy, symplectic; Mt, metapterygoid; PJ, 
palato-pterygoid arch; Qu, quadrate bone; Ar, articular; An, 
angular; D, dentary; S. Or, suborbital bone. 


Fig. 48, 


re 


Fig. 48.—Palato-quadrate arch, with the hyomandibular and sym- 
plectic of the Pike, viewed from the inner side; the articular piece 
(4nt). of the lower jaw, and Meckel’s cartilage (Mck.) of the Pike; 
seen from the inner side :—a, the cartilage interposed between the 
hyomandibular (H.M.), and the symplectic (Sy.); b, that which 
serves as a pedicle to the pterygo-palatine arch; c, process of 
the hyomandibular with which the operculum articulates; d, head of 
the hyomandibular which articulates with the skull. 


156 THE ANATOMY OF VERTEBRATED ANIMALS. 


The palato-quadrate and hyomandibular have essentially 
the same structure and arrangement as in Lepidosteus 


and Amia. The homologue of the suspensorium of the} 


EHlasmobranchii is articulated with a surface furnished to it 


by the postfrontal, pterotic, and pro-otic bones. Usually it 


moves freely upon that surface, but, in the Plectognathi, it 
may be fixed. It ossifies so as to give rise to two bones: an 
upper broad hyomandibular (H.M.), with which the operculum 
articulates; and a lower styliform symplectic (Sy.), which 
fits into a groove on the inner and posterior surface of the 
quadrate, and is firmly held there. 

The palato-quadrate arch is represented by several 
bones, of which the most constant are the palatine (P1.) 
in front, and the quadrate (Qu.) behind and below. Besides 
these there may be three others: an external, ectopterygoid 
(Hept.), an internal, entopterygoid (EHpt.), and a metaptery- 
goid (Mpt.). The last envelopes the upper and posterior 
portion of the primitive quadrate cartilage; and, fixing 
itself against the hyomandibular, contributes to the firm- 
ness of the union already effected by the symplectic. 

Meckel’s cartilage (Mck.) persists throughout life, but the 
ossification of its proximal end gives rise to an os articulare 
in the lower jaw. To these an angular (An.) and a dentary 
(D.) membrane bone are commonly added (Fig. 47). 


The hyoidean arch is usually composed of two large — 
cornua—connected with the cartilaginous interval between — 


the hyomandibular and the symplectic by a stylohyal ossi- 
fication, and abutting, in the middle line below, upon one or 
more median pieces, the anterior of which (entoglossal) sup- 
ports the tongue, while the posterior (wrohyal) extends back 
to join the median elements of the branchial apparatus. 
The cornua themselves are usually ossified into four pieces: 
an upper (epihyal) and a lower (ceratohyal) large ossification, 
and two small ones (basihyals) connected with the ventral 
ends of the lower large ossification. 

There are usually five pair of branchial arches connected 
by median ventral ossifications. The posterior pair are 
single bones, which underlie the floor of the pharynx, bear 


THE TELEOSTEIL. 157 


no branchial filaments, but commonly support teeth, and 
are called hypopharyngeal bones. In certain osseous fishes, 
thence called Pharyngognathi, they ankylose together into 
one bone. The anterior four pair are composed of several 
joints, and the uppermost articulations of more or fewer of 
them usually expand, bear teeth, and form the epipharyngeal 
‘bones. Sundry important membrane bones are connected 
with the mandibular and hyoidean arches. The preoper- 
culum (P.Op.), operculum (Op.), and branchiostegal rays (Br.). 
already met with among the Ganoidei, are the most constant 
ofthese. Beneath the operculum, lies a suboperculum (S.Op.), 
and below this an interoperculum (I.Op.), which is con- 
nected by ligament with the angular piece of the lower jaw, 
and is also united to the outer face of the hyoidean arch. It 
may be altogether ligamentous, as in the Siluroids. 

The branchiostegal rays are attached partly to the ner, 
and partly to the outer, surface of the hyoidean arch. They 
support a membrane, the branchiostegal membrane, which 
serves as a sort of inner gill-cover. 


Most Teleostei possess two pair of limbs, the pectoral and 
the ventral fins. But the latter are often absent, and the 
former are occasionally wanting. When the pectoral fins 
are absent, the pectoral arch usually remains, though it 
may be reduced to little more than a filament, as in Muren- 
ophis. The ventral fins are frequently situated in their nor- 
mal position beneath the posterior part of the trunk; but in 
considerable groups of these fishes they are immediately 
behind the pectoral fins (thoracic), or even in front of them 
(jugular). In the asymmetrical Plewronectide one pectoral 
fin may be larger than the other, or may alone remain, as 
in Monochirus. 

The pectoral arch always consists of a primarily cartila- 
ginous coraco-scapular portion—which usually ossifies in two 
pieces, a coracoid below, and a scapula above—and of sundry 
membrane bones. The chief of these membrane bones is 
the clavicula (Cl.), which meets its fellow in the middle line, 
and is usually joined to it by ligament, but sometimes, as 


158 THE ANATOMY OF VERTEBRATED ANIMALS. 


in the Siluroids, by sutural union. By its inner surface it 
gives attachment to the coraco-scapular—and sometimes _ 
above them, to a styliform bone which extends back among | 
the lateral muscles—the post-clavicula (p.cl.). 

Attached to the dorsal end of the clavicle, there is 
usually a second much smaller bone, the supra-clavicula 


Fig. 49. 


. 


Fig. 49.—The bones of the pectoral arch and fore-limb of the Pike 
(Esox lucius). A, a semi-diagrammatic view of these bones, to 
show their relative natural position. ‘Vhe clavicle ( C/) is supposed 
to be transparent. S.cl, supra-clavicula; p.cl, post-clavicula ; ¢, d, 
the posterior and anterior ends of the outer margin of the scapulo- 
coracoid.—B, the scapulo-coracoid and limb separate and on a larger 
seale; Sep, scapula; Cr, coracoid; a, basal cartilages; , fin-rays; 
e corresponds with c in the foregoing figure. 


(S.el.), and this is very generally connected with the skull 
by a superticial membrane bone, the post-temporal, which, — 
in front, becomes forked, and attaches itself by one prong 


THE TELEOSTEI. 159 


to the epiotic bone, by the other to the pterotic, or lower 
down to the side of the cranium. The base of the fin 
‘contains a series of not more than five. more or less ossi- 
fied, cartilages, which are placed side by side and articu- 
late with the coraco-scapular; to these succeed one or more 
rows of small cartilages, partially hidden by the bases 
of the exoskeletal fin-rays. The most anterior of these 
basal cartilages (the mesopterygial basale) is inclosed by 
the base of the anterior fin-ray, and effects that articula- 
tion with the shoulder-girdle which is so remarkable in 
many Siluroid fishes. The posterior cartilage, or bone, is 
the metapterygial basale, and the intermediate three are 
radialia (p. 40), 

Most Teleostei possess teeth, and, in the majority of these 
fishes, teeth are very widely distributed over the surface of 
the walls of the oral and pharyngeal cavities. The teeth 
vary very much in structure; ordinarily, they consist of 
dentine, capped with structureless enamel. The parietes 
of the tooth are not unfrequently longitudinally folded 
towards the base, but this folding never goes so far as in 
the Ganoids. The different kinds and modes of arrange- 
ment of the teeth may be classified as follows :— 

1. Isolated, more or less pointed teeth, developed from 
papillz of the mucous membrane, which do not become in- 
closed in sacs—frequently ankylosed to the subjacent bone, 
but not imbedded in alveoli, nor replaced vertically. 

The great majority of ordinary osseous fishes have teeth 
of this kind. 

2. Isolated teeth, which become imbedded in sockets, and 
are replaced vertically, 

Such teeth are seen in the premaxille of Sargus, where 
they curiously simulate the form of human incisors; and, 
imbedded in the coalesced hypopharyngeal bones, in Labrus. 

3. Isolated teeth, imbedded in the substance of the bone 
which supports them. The teeth and the supporting bone 
wear away in front, and are replaced by new teeth developed 
behind the others. This structure is seen in the coalesced 
hypopharyngeal bones of the Parrotfish (Scarus). 


160 THE ANATOMY OF VERTEBRATED ANIMALS. 


4, Beak-like compound teeth, attached to the premaxille 
and dentary bones of the mandible. 


These are of two kinds. In the Parrotfish (Scarus) the | 


beak is formed by the union of numerous separately de- 


veloped teeth into one mass. But in the Gymnodonts— 


(Tetrodon and Diodon) the beak is produced by the coales- 
cence of broad calcified horizontal lamellze thrown off from 
a subjacent pulp. 

5. In the Carp and its allies the basi-occipital sends down 
a median process, which expands at the end, and supports a 
broad, thick, horny tooth. 

The stomach is usually wide and sac-like, but sometimes 
(in Scomberesoces, Cyprinoids, and others) is not wider than 
the intestine. Occasionally, as in Mugil, it acquires thick 
walls and becomes gizzard-like. The commencement of 
the small intestine is very generally marked by the presence 
of more or less numerous cecal diverticula, the pyloric ceca. 
The small intestine has no spiral valve, though the mucous 
membrane may be raised into large transverse folds. The 
rectum does not terminate in a cloaca, and almost always 
opens quite separately from the urinary and genital ducts, 
and in front of them. 


In many Teleostean fishes an air-bladder underlies the — 
vertebral column, and is connected by an open pneumatic — 


duct with the dorsal wall of the esophagus, or even with 
the stomach, as in the Herring. In other Teleostei, the air- 
bladder occupies the same position, but is closed, the duct 
by which the air-bladder is primitively connected with the 
alimentary canal becoming obliterated. In a comparatively 
small number of the Teleostei—the Blennii, the Pleuronec- 
tide or Flatfishes, the Sand-eel (Ammodytes), the Loricarini, 


and Symbranchii, and some members of other families— 
there is no air-bladder. In those Teleostei in which it is © 


present, it may be divided into two parts by a constriction ; 
or it may be prolonged into diverticula; or retia mirabilia 


—" 


may be developed in its walls. Sometimes the air-bladder — 


is brought into direct relation with the membranous laby- 
ninth, as in Myripristis and Sparus, and the Herring, Shad, 


THE TELEOSTEI. 161 


and Anchovy—prolongations of the one organ being sepa- 
rated from the other only by a membranous fenestra in the 
wall of the skull. In the Stlwroidei, Cyprinoidei, and Cha- 
racimi, and in the Gymnotini, the anterior end of the air- 
bladder is connected with the membranous vestibule by the 
intermediation of a series of bones attached to the vertebral 
column, some of which are moveable. 

The vessels of the air-bladder are derived from, and empty 
themselves into, those of the adjacent parts of the body, in 
which respect, and in the dorsal position of the esophageal 

aperture of the pneumatic duct, this structure differs from 
a lung. 


The heart consists of a single auricle, receiving its blood 
from a venous sinus; and of a single ventricle, separated by 
a single row of valves from the bulbus aorte, which is not 
rhythmically contractile. 

The cardiac aorta divides into trunks to form the branchial 
arteries, which run upon the outer, or convex, side of the 
branchial arches, and are distributed to the branchial fila- 
ments. The blood is collected thence into a branchial 
vein, which also lies on the convex side of the arch; and, 
increasing towards its dorsal end, opens into one of the 
trunks of the original dorsal aorta. Of these there are two, 
a right and a left, which pass backwards and meet in the 
trunk of the dorsal aorta under the spinal column. 

The anterior branchial vein gives off, at its dorsal ter- 
mination, a considerable carotid trunk, which passes for- 
wards under the base of the skull; and this is united with 
its fellow by a transverse branch—so that a complete arterial 
circle, the circulus cephalicus, is formed beneath the base of 
the skull. Below, the anterior branchial vein gives off the 
hyoidean artery, which ascends along the hyoidean arch, 
and very generally terminates by one branch in the cephalic 
circle, and by another enters a rete mirabile, which lies 
in the inner side of the hyomandibular bone, and some- 
times has the form of a gill. This is the pseudobranchia. 
The branches of the rete mirabile unite again into the 

M 


162 THE ANATOMY OF VERTEBRATED ANIMALS. 


ophthalmic artery, which pierces the sclerotic, and breaks ' 
up into another rete mirabile, the choroid gland, before being » 
finally distributed. 


In the Lamprey, as has been seen, the respiratory organs | 
are pouches, the anterior and posterior walls of which are- 
raised into vascular folds. The walls of adjacent pouches 
are distinct and but loosely connected together; and con- 
siderable spaces of integument separate their rounded outer 
apertures, 

In the ordinary Elasmobranchii, the branchial pouches 
are more flattened from before backwards, and their outer 
apertures are more slithke. The integumentary spaces 
between the slits are correspondingly narrower, and the 
adjacent walls of successive pouches are more closely ap- 
proximated, so that they are divided only by septa; but 
the vascular plaits of the surface of the respiratory mucous 
membrane do not reach the outer edges of these septa. 

In Chimera, the free edges of the septa are exceedingly 
narrow, and the apices of the branchial processes extend 
outwards to them, 

In the Sturgeon, the septum is not more than three-fourths 
as long as the branchial processes, the apices of which are 
consequently free. 

The process of reduction is carried still further in the 
Teleostei—the septum not attaining to more than one-third 
the length of the branchial processes; and, as in the 
Ganoids, each process is supported by an osseous or cartila- ; 
ginous skeleton. 

The Teleostei have no functional hyoidean, or opercular, 
gill; and, as a general rule, each of their four branchial 
arches possesses a double series of branchial processes, 
making eight in all. Not unfrequently (Cottus, Cyclopterus, 
Zeus, &c.), the number is reduced to seven; the fourth bran- | 
chial arch having only one series, the anterior. In this © 
case, the gill-cleft, which should lie between this arch and — 
the fifth, is closed. Sometimes there are only six series of 
branchial processes. the fourth arch beg devoid of any 


ee 


THE TELEOSTEI. 163 


(e.g., Lophius, Diodon). In Malthea the number is reduced 
to five, only the anterior series of the third arch being 
developed; and in Amphipnous cuchia only the second bran- 
chial arch possesses branchial filaments, the first, third, 
and fourth being devoid of them. 

_ Many Teleostean fishes possess accessory respiratory 
organs. These may take the form of arborescent appendages 
‘to the upper ends of some of tae branchial arches, as in 
Clarias, Heterobranchus, and Heterotis; or, as in the Climb- 
ing Perch (Anabas) and its allies, the epipharyngeal bones 
Z, enlarge and acquire a labyrinthic honeycombed 
structure, and support a large surface of vascular mucous 
membrane; or, as in the Clupeoid (Iwtodeira chanos), an 
accessory gill may be developed in a curved cxcal prolonga- 
tion of the branchial cavity. Finally, in Saccobranchus 
singio and in Amphipnous cuchia, the membrane lining the 
branchial chamber is prolonged into sacs, which lie at the 
sides of the body, and receive the blood from the divisions 
of the cardiac aorta which supply the branchie, while they 
return it into the dorsal aorta. 

All these fishes (except Ivtodeira) are remarkable for 
their power of sustaining life out of the water. Many in- 
habit the marshes of hot countries, which become more or 
less desiccated in the dry season. 


The kidneys of Teleostean fishes receive a great part of 
their blood from the caudal vein, which ramifies in them. 
They vary greatly in length, sometimes extending along 
the whole under-surface of the vertebral column, from the 
head to the termination of the abdomen. The ureters pass 
into an urinary bladder which opens behind the rectum, 

The brain in the Teleostei has solid cerebral hemispheres, 
and, when viewed from above, the thalamencephalon is 
hidden by the approximation to the hemispheres of the large 
and hollow optic lobes of the mesencephalon, which has a 
pair of inferior enlargements, lobi inferiores. There is a 
peculiarity about the structure of the optic lobes, which has 
given rise to much diversity of interpretation of the parts 


164 THE ANATOMY OF VERTEBRATED ANIMALS. 


of the brain in osseous fishes. The posterior wall of these 
lobes, where it passes into the cerebellum, or in the 
region which nearly answers to the valve of Vieussens in 
mammals, is thrown forwards into a deep fold which lies 
above the crura cerebri, and divides the iter a tertio ad 
quartum ventriculum from the ventricle of the optic lobes 
throughout almost the whole extent of the latter. This fold 


is the “ fornix” of Gottsche. On each side of it the floor 


Fig. 50.—Brain of the Pike, viewed from above :—A, the olfactory 
nerves or lobes, and beneath them the optic nerves; B, the cerebral 
hemispheres; C, the optic lobes; D, the cerebellum. 


of the ventricle of the optic lobes is raised up into one or 
more eminences, which have the same relation to the optic 
lobes as the corpora striata have to the prosencephalic: 
vesicle. if 

The optic nerves simply cross one another, and form no’ 
chiasma. The cerebellum is usually large. 4 

The cephalic part of the sympathetic nerve is present, as 
in the higher Vertebrata. 


c ‘ 


4 
4 
"| 


THE TELEOSTEI. 165 


Each of the nasal sacs usually opens externally by two 
apertures. In some Gymnodonts a solid tentacle is said to 
take the place of a nasal sac. 

The eyes are abortive in the Blind-fish of the caves of 
Kentucky (Amblyopsis speleus). A fibrous band often 
passes from the back of the orbit to the sclerotic, and re- 
presents the cartilaginous pedicle of the Elasmobranchs. 
There is no nictitating membrane, but immoveable external 
eyelids may be developed. The choroidal gland, mentioned 
above, surrounds the optic nerve between the sclerotic 
and the choroid. Very generally, a falciform process of the 
latter membrane traverses the retina and vitreous humour to 
the crystalline lens. This represents the pecten of higher 
Vertebrata. As in other fishes, the lens is spheroidal, and 
the cornea flat. The sacculus of the auditory organ -con- 
tains large solid otoliths, which are usually two in number 
—the larger, anterior one, is termed Sagitta; the smaller, 
posterior, Asteriscus. There are always three large semi- 
circular canals. 

The reproductive organs are either solid glands which 
burst into the abdominal cavity, whence their reproductive 
elements are conveyed away by abdominal pores; or, as is 
more usual, they are hollow organs, and are continued back- 


wards into ducts which open beside, or behind, the urinary 


aperture. 
Some few Teleostei are ovoviviparous (e.g., Zoarces vivi- 


_parus), the eggs being retained in the interior of the ovary, 


and hatched there. In the male Syngnathus, and other 
Lophobranchii, integumentary folds of the abdomen grow 
down and form a pouch, into which the eggs are received, 
and in which they remain until they are hatched. 

The young of osseous fishes are not known to undergo 
any metamorphosis, nor are they provided with external 
gills, nor with spiracula, 


The classification of the Teleosteiis not yet in a thoroughly 
satisfactory state, and the following arrangement must be 


regarded as provisional ;— 


166 THE ANATOMY OF VERTEBRATED ANIMALS. 


1. The Physostomi.This group contains the Siluroidei, 
the Cyprinoidei, the Characini, the Cyprinodontes, the Salmon- 
ide, the Scopelini, the Esocini, the Mormyri, the Galawic, 
the Clupeide, the Heteropygii, the Murenoidei, Symbranchii, 
and Gymnotini. The air-bladder is almost always present, 
and, when it exists, has an open pneumatic duct. The skin 
is either naked, or provided with bony plates, or cycloid 
scales; the ventral fins, when present, are abdominal in 
position. The fin-rays (except in the pectoral and dorsal 
fins of sundry Siluroidei) are all soft and jointed. The 
inferior pharyngeal bones are always distinct. 

In all other Teleostean fishes the air-bladder is either 
absent, or devoid of an open pneumatic duct. Hence they 
are termed, collectively, Physoclisti by Haeckel. 

2. The Anacanthini—The body has cycloid or ctenoid 
scales, or is naked. The ventral fins, if present, are jugular 
in position. The fin-rays are all articulated. The inferior 
pharyngeal bones are distinct. (Ophidini, Gadoidei, Pleuro- 
nectide.) 

The Pleuronectide are the most aberrant of all Teleostean 
fishes, on account of the disturbance in the bilateral sym- 
metry of the body, skull, and fins, to which reference has — 
already been made (p. 30). 

3. The Acanthopteri have generally ctenoid scales, thoracic 
or jugular ventral fins, entire fin-rays in some of the fins, 
and distinct inferior pharyngeal bones. The Pereoidei, Cata- 
phracti, Sparoidei, Scienoidei, Labyrinthici, Mugiloidei, Nota- — 
canthini, Scomberoidei, Squamipennes, Teenioidei, Gobioidei, 
Blennioidei, Pediculati, Theuthyes, and Fistulares, belong to 
this great group. 

4. The Pharyngognathi is the name given by Miiller to a 
somewhat artificial assemblage of fishes, the only common 
characters of which are the ankylosis of the inferior pha- 
ryngeal bones and the closed pneumatic duct. They have — 
either cycloid, or ctenoid, scales. The ventral fins may be 
abdominal or thoracic. The anterior dorsal and ventral — 
fin-rays may be either unjointed, as in the Labroidei, Poma- 
centride, Chromide ; or articulated, as in the Scomberesoces. 


THE DIPNOI. 167 


The two remaining groups are very peculiar; but I con- 
fess I do not see upon what ground they can be regarded as 
of ordinal] value. 

5. The Lophobranchii—The body is covered with bony 
plates. The ventral fins are almost always absent. The 
inferior pharyngeal bones are distinct. The branchial pro- 
cesses have a clavate form, being larger at the free than at 
the attached ends, and are in this respect unlike those of 

any other fishes. (Pegaside, Syngnathide.) 

6. The Plectognathi—The body is covered with plates or 
spines. The ventral fins are absent, or represented only 
by spines. The inferior pharyngeal bones are distinct. 
The premaxille and, usually, the hyomandibular, are im- 
moveably united with the skull—a character of rare occur- 
rence among other fishes. (Gymmnodontide, Ostraciontide, 
Balistide.) 

The greater number of Teleostei are marine. No Anacan- 
thini, Plectognathi, or Lophobranchii, and only one family 
of Pharyngognathi (the Chromide), inhabit completely fresh 
water. Comparatively few Acanthopteri are fluviatile. On 
the other hand, by far the greater number of the Physostomi 
are, either temporarily or permanently, freshwater fish. 

If the Leptolepide (Thrissops, Leptolepis, Tharsis) are 
Ganoids, the Teleostei are not known before the Cretaceous 
epoch, when both Physostomi and Acanthoptert make their 
appearance, under forms, some of which (e.g., Beryx) are 

_ generically identical with fish living at the present day. 


VI. The Drpno1.—The “ Mudfishes” of the rivers of the 
east and west coasts of Africa and of eastern South America 
are nearly transitional forms between the Pisces and the 
Amphibia. 

The eel-like body, covered with overlapping cycloid 
scales, tapers to a point at its caudal extremity, and is 
provided with two pairs of long, ribbon-like, pointed ex- 
- tremities, and with a caudal fin. 

The spinal column consists of a thick notochord, invested 
by a cartilaginous sheath, without any osseous or cartila- 


168 THE ANATOMY OF VERTEBRATED ANIMALS, 


ginous vertebral centra. The proximal ends of ossified 
neural arches, of ribs, and, in the caudal region, of inferior 


arches, are imbedded in the sheath of the notochord. 


Fig. 52.—Skull of Lepidosiren annectens :-— A, the parieto-frontal bone ; 
8, the supra-orbital; C, the nasal; D, the palato-pterygoid; £, 
the vomerine teeth; £.Q., the ex-occipital ; Mn, the mandible; Hy, 
the hyoid; Br, the branchiostegal rays; Op, the opercular plate; x, 
the parasphenoid; y, the pharyngo-branchial; Or, the orbit; Av, 
the auditory chamber; J, the nasal sac. 


Fin-rays support the median fin. The skull, the palato- 
quadrate, and suspensorial apparatus, form, as in Chimera, 


THE DIPNOI. 169 


one continuous cartilaginous mass, into the base of which 
the notochord penetrates, terminating in a point behind 
the pituitary fossa. 

No cartilage bone is developed in the place of the basi- 
occipital, supra-occipital, basisphenoid, or presphenoid; 
and there are only two such ossifications, which represent 
the ex-occipitals (E.0.) in the side-walls of the cranium. 
A large parasphenoid (x) underlies the base of the skull. 
Upon its roof a great single bone (A), answering to the 
parietals and frontals, extends from the occipital to the 
ethmoidal regions. In front of this are two nasal bones (C). 


_ Fig. 53.—Longitudinal and vertical section of the skull of Lepidosiren. 
_ ‘The cartilage is dotted; the membranous and bony constituents are 
’ shaded with lines. A, B, C, D, EZ, Hy, as in the preceding figure ; 
x, x, the parasphenoid ; P.S', cartilaginous presphenoidal region ; ch, 
notochord ; Au, situation of auditory chamber ; 1, 2, first and second 
vertebre; JI., V., VIII., exits of optic, trigeminal, and vagus 
nerves; a, quadrato-mandibular articulation. 


There is no alisphenoid, but the fronto-parietal and para- 
sphenoid send processes towards one another, which unite 
in front of the exit of the third division of the fifth nerve. 
There is no interorbital septum, and the cavity of the 
skull remains of tolerably even diameter throughout. In 
front of the exit of the optic nerves, however, it is longi- 
tudinally divided by a membranous septum, 

The ethmovomerine cartilage is continued to the anterior 
extremity of the skull. It bears teeth, but no distinct 
yomer. 


170 THE ANATOMY OF VERTEBRATED ANIMALS. 


A great palato-pterygoid osseous arch (D) extends from } 
the middle line along the upper and the under surface of 
the palato-quadrate arch on each side to near the articular’ 
surface of the mandible. In the middle of the ruof of the 
mouth, divergent, cutting, dentary plates are developed upon 
it. An osseous nodule lies in the articular head of the palato- 
quadrate cartilage, and is continuous with the bone #. 

The mandible presents dentary plates corresponding with 
those of the palate, and biting between the latter. The 
hyoidean arch is attached to the posterior and lower edge 
of the suspensorium—which bears a bony ray representing 
an operculum—while the hyoidean arch itself carries a 
single branchiostegal ray (Br, Fig. 52). 

The pectoral arch is composed of a median cartilaginous 
part, with two lateral portions of cartilage, at once separated 
from, and connected with, the median cartilage by bone. 
The bone is separated from the cartilage by a layer of 
connective tissue, and seems to represent the clavicle, while 
the cartilage answers to the coalescent coraco-scapular 
cartilages of other fishes. 

The filiform fin is supported by a many-jointed carti- — 
laginous rod, articulated proximally with the coraco-scapular. — 
Upon this are disposed fine fin-rays like those of the Elas- — 
mobranchs, which support the marginal fringe of the fin. 
The ventral fin has the same structure as the pectoral. 

The intestine possesses a spiral valve, and the rectum 
opens into a cloaca. The lungs have remarkably stiff walls, 
and extend through the greater part of the body, beneath 
the spine. The glottis, opening upon the ventral wall of 
the gullet, places them in communication with the cavity 
of the mouth, into which the nasal sacs open by posterior 
apertures, which lie inside the upper lip and constitute true 
posterior nares. The heart has a small, but distinct, left 
auricle, into which the blood which has been aérated in the 
lungs is returned. In addition to lungs, Lepidosiren pos- 
sesses both internal and external gills, but the latter are 
rudimentary in the adult. 

The different species seem to differ in the manner in. which 


> 


THE DIPNOI. 171 


the primitive aortic arches are metamorphosed : but it may 
be said, generally, that the first has disappeared ; the second 
supplies an internal branchia developed upon the hyoidean 
arch; the third gives off the anterior carotid artery, and 
supplies neither internal nor external branchia; the fourth 
supplies only the first external branchia; the fifth and sixth 
supply both internal and external branchie; while the 
seventh is connected only with an internal branchia. The 
pulmonary artery seems originally to have been given off 
from an eighth aortic arch. 

It is a remarkable circumstance, that while the Dipnoi 
present, in so many respects, a transition between the piscine 
and the amphibian types of structure, the spinal column 
and the limbs should be not only piscine, but more nearly 
related to those of the most ancient Crossopterygian 
Ganoids than to those of any other fishes. 


172 THE ANATOMY OF VERTEBRATED ANIMALS. 


CHAPTER IV. 
THE CLASS AMPHIBIA. 


The IcHTHYOPSIDA.—Class I].—AMPHIBIA. 


The only clearly diagnostic characters of this class as 
compared with Fishes are the following :— 

1. Amphibia have no fin-rays. 

2. When limbs are present they contain the same skeletal 
elements as those of the higher Vertebrata. 

Certain other structural peculiarities are common to the 
whole of the Amphibia, and are very characteristic of them 
without being diagnostic. Thus :— 

1. The body is usually devoid of any exoskeleton, and 
when scales, or scutes, are present in recent Amphibia, they 
are concealed within the skin (Cecilia, Ephippifer). In the 
extinct Labyrinthodonta, the dermal armour is confined to 
the ventral region of the body. 

2. The vertebral centra are always represented by bone. 

3, The sacrum rarely consists of more than one vertebra, 
though there are individual exceptions to this rule, as in 
Menopoma. 

4, The suspensorial apparatus of the mandible is con- 
tinuous with the skull, which has two occipital condyles, 
and no completely ossified basi-occipital. 

5. There are no sternal ribs. 

The Amplibia are divisible into the following groups :— 

A. A distinct and often long tail; the vertebre amphiccelous or 
opisthoceelous; the proximal elements of the tarsus not 
elongated. 

A, ‘Iwo or four limbs; no scutes or scales. 
I. Saurobatrachia or Urodela. 
a, External branchiz or gill-clefts persistent, or disap- 


THE AMPHIBIA. 173 


pearing only in advanced age; no eyelids; vertebra 
amphiccelous ; carpus and tarsus cartilaginous. 


1. Proteidea. 


b, No branchie or branchial clefts in the adult; eyelids 
present; carpus and tarsus more or less ossified ; 
vertebree commonly opisthocelous. 


2. Salamandridea. 


B. Limbs absent, or all four present. Three large pec- 
toral osseous plates and an armour of small scutes on 
the ventral surface of the body ; vertebrae amphi- 
celous; walls of the teeth more or less folded. 


II. Labyrinthodontu. 


B. Tail obsolete in the adult. 
‘A. Limbs absent; numerous minute dermal scutes im- 
bedded in the integument of the serpentiform body. 


Ill. Gymnophiona. 


B. All four limbs present, and the proximal elements of 
the tarsus much elongated ; the body short. and the 
integument devoid of small scutes, though dermal 
osseous plates are sometimes developed in it. 


IV. Batrachia or Anura. 


The integument in most Amphibia is soft and moist, as in 
the Frog, where numerous glands open upon its surface. 
The Gymnophiona are exceptional, among existing Amphibia, 
in possessing small, rounded, flexible scales, like the cycloid 
scales of fishes, imbedded within the wrinkled integument. 

In certain Batrachia (Ceratophrys dorsata, Ephippifer 
aurantiacus), flat dermal bony plates are developed in the 
dorsal integument, and become united with some of the 
subjacent vertebre. Many of the extinct Labyrinthodonta, 
and probably the whole of the members of that group, pos- 
sessed an exoskeleton which appears to have been confined 
to the ventral surface of the body. Under the anterior part 
of the thorax there is a sort of plastron composed of one 
median and two lateral plates. The median plate is rhom- 
boidal. The lateral ones are somewhat triangular, and unite 
with the anterolateral margins of the median plate by one 
_ side, sending a process upwards and backwards from their 
- outer angles. The outer surfaces of all these plates exhibit 

a sculpture, which radiates from the centre of the median 
plate and from the outer angles of the lateral plates. These 


174 THE ANATOMY OF VERTEBRATED ANIMALS. 


plates are in close relation with the pectoral arch, and 
probably represent the interclavicle and clavicles. 

Minute bony plates cover the surface of the throat in a 
small African Labyrinthodont, Micropholis. I have not met 
with dermal ossicles in this position in other Labyrintho- | 
donts. But in Archegosaurus, Pholidogaster, Urocordylus, 
Keraterpeton, Ophiderpeton, Ichthyerpeton, the integument be-_ 
tween the thoracic plates and the pelvis presents regularly- 
disposed rows of small elongated ossicles, which, for the 
most part, converge from without, forwards and inwards, 
towards the middle line. No trace of these appears upon 
the tail, nor in any part of the dorsal region of the body, nor 
on the limbs. 

The endoskeleton of the Amphibia is least complete in 
Archegosaurus, where the centra of the vertebre are repre- 
sented only by bony rings, the ribs and the neural arches 
being well ossified. In other Labyrinthodonts of the same 
(Carboniferous) epoch, however, such as Anthracosaurus, the 
centra of the vertebre are completely ossified biconcave 
dises, very like the centra of the vertebre of Ichthyosawrus. 

In the existing Proteidea, and in the Gymnophiona, the 
vertebral centra are amphicelous. In the Salamandridea 
they are opisthocelous. In Pipa and Bombinator they are 
also opisthocelous, but in other Batrachia they are, for the 
most part, proccelous, but vary in different regions, some 
being biconvex and some biconcave. 

The first vertebra, or atlas, presents two articular cups 
to the condyles of the skull, but there is no specially modi- 
fied axis vertebra. 

The transverse processes may be simple, but in the Laby- 
rinthodonts, and in the existing Salamanders, they are 
divided into two processes—an upper tubercular, and a lower 
capitular, process. When the transverse process is thus 
divided, the proximal end of the rib is correspondingly split 
into a capitular and a tubercular process. 

In the Gymnophiona, the Sawrobatrachia, and the Laby- 
rinthodonta, the number of the vertebre in the trunk is con- 
siderable, and the members of the two latter groups have 


THE AMPHIBIAN SKELETON. 175 


long tails. But in the Batrachia, the total number of verte- 
bre does not exceed eleven, of which eight belong to the pre- 
sacral region, one to the sacrum, and two (modified vertebrz) 
to the coccygeal region. The transverse processes of some of 
the presacral vertebre are usually very long, but there are 
no separately ossified ribs. The transverse processes of the 
sacral vertebra are very large and expanded, and its centrum 
has usually a single concavity in front and a double convexity 
behind. 

The coccyx consists of a long, cylindroidal, basal bone 
proceeding from the ossification of the sheath of the termi- 
nation of the notochord, and corresponding with the urostyle 
of the Teleostei ; and of two neural arches, which lie over its 
anterior end, and become ankylosed with it, The anterior 
face of the coccyx usually presents two concave facets for 
articulation with the posterior convexities of the sacrum. 

The cavity of the cranium is not narrowed anteriorly by 
the development of an interorbital septum in any Amphi- 
bian. All existing Amphibia have ex-occipitals developed 
in the walls of the cartilaginous cranium; but it is not 
certain that any such ossifications existed in Archegosaurus, 
though they are present in other Labyrinthodonts. 

No Amphibian possesses a complete basi-occipital, supra- 
occipital, basisphenoid, alisphenoid, or presphenoid car- 
tilage bone. In existing Amphibia, a pro-otic ossification 
appears to be very constant. The constant existence of 
distinct opisthotic and epiotic elements is doubtful. 

The Frog’s skull is characterised by the development 
of a very singular cartilage bone, called by Cuvier the “ os 
en ceinture,” or girdle-bone. This is an ossification which 
invades the whole circumference of the cranium in the 
presphenoidal and ethmoidal regions, and eventually as- 
sumes somewhat the form of a dice-box, with one-half of its 
cavity divided by a longitudinal partition. The latter, cor- 
responding with the front part of the bone, extends into 
the prefrontal processes in some frogs, protects the hinder 
ends of the olfactory sacs, and is perforated by the nasal 
division of the fifth nerve, The septum, therefore, answers 


176 THE ANATOMY OF VERTEBRATED ANIMALS. 


Fig. 54, 
B 


; = i 


EO. 


Fig. 54.—The cartilaginous cranium of Rana esculenta. A, from 
above; B, from below :—y, the “os en ceinture” or girdle-bone. 


Fig. 55.—Skull of Rana esculenta. A, from above; B, from below; 
C, from the left side:—x, parasphenoid ; y, girdle-bone; Z, the “tem- 
' poro-mastoid.”’ 


: 


THE AMPHIBIAN SKULL. 177 


to the ethmoid, the anterior half of the girdle-bone to the pre- 
frontals, or part of them, and the posterior half of the girdle- 
bone to the orbitosphenoids of other Vertebrata. Turbinal 
ossifications are developed in the cartilage bounding the 
nasal capsules in some Amphibia. 

The membrane bones of the Amphibian skull are :— 
1. Frontals and parietals, which, in the Batrachia, may be 
fused together into one bone. 2. Nasals are generally pre- 
sent. 3. The vomers, always present, are two in number, 
one for each side, in all Amphibia but Pipa, Dactylethra, and 
Pelobates. 4, A great parasphenoid covers the base of the 
skull from the occipital to the ethmoidal region, as in Teleostet 
and Ganoidei. 5. A membrane bone (4), called ‘ temporo- 
mastoid” by Dugés, lies on the outer side of the suspen- 
sorium, extending from the side-walls of the skull to the 
articular head for the lower jaw. The relations of this 
bone in its upper part are similar to those of the squamosal 
of the higher Vertebrata, in its lower part to those of the 
bone F in Lepidosiren, to the preoperculum of fishes, and 
to the tympanic of the higher Vertebrata. 

Two premaxillz are always developed. The maxille are 
usually present, and may be connected, as in most Batrachia, 
by quadrato-jugal ossifications with the outer side of the end 
of the suspensorium, in which an ossification representing 
the quadrate bone is often developed. But the quadrato- 


_jugals (and even the maxillw) may be represented simply 


by more or less ligamentous fibrous tissue, as is the case in 


the Urodela. Pterygoid bones are developed in all Amphibia, 


and distinct palatine bones in most, but not all, of the Ba- 
trachia. The suspensorium, which is inclined downwards 
and forwards in the lower Urodela, passes almost directly 
downwards, or a little backwards, in the higher, and in the 
Batrachia slopes greatly backwards; and it undergoes the 


same modifications in direction, during the progress of any 


of the Batrachia from the larval to the adult state. 

In the mandible, the proximal end of Meckel’s cartilage is 
rarely, if ever, completely converted into a bony articular 
element, but the distal moiety is ossified in some Batrachia. 

N 


178 THE ANATOMY OF VERTEBRATED ANIMALS. 


The membrane bones of the mandible are a dentary and 
a splenial piece, with, perhaps, an angular element. 

The hyoidean arch is, in most Amphibia, connected with 
the suspensorial cartilage—sometimes quite close to its 


origin, sometimes near its distal end, in the Urodela. Its | 


cornua are stout and well ossified in the Proteidea. In the 
Batrachia they are slender, and their proximal ends may 
be free. Distally, they are connected with a broad lamellar 
body, from the posterior margin of which two processes which 
embrace the larynx are usually given off. In the peren- 
nibranchiate Proteidea, the hyoidean arches are united by 
narrow median entoglossal and urohyal pieces, as in Fishes. 

In the Batrachia, the branchial arches disappear in the 
adult; but in the Gymnophiona and in the Urodela, more 
or fewer of the larval branchial arches persist throughout 
life. 

In the Proteidea there are three or four branchial arches, 
each usually consisting of two cartilaginous, or ossified, 
pieces on each side. In the Salamandridea, there are, primi- 
tively, four branchial arches, but of these, portions of only 
the two anterior remain in the adult. Four are developed 
in the Cecilia, and three of these are permanent. 

Some peculiarities exhibited by the skulls of the Gymno- 
phiona, and by the Labyrinthodonta, are worthy of especial 
notice. 

In the former, e.g. in Ichthyophis glutinosa, the skull is 
covered by a complete bony roof, formed, mainly, by the 
ex-occipitals, parietals, frontals, prefrontals, nasals, and as- 
cending processes of the premaxillaries. Between the ex- 
occipitals, the parietal, and the frontal, above, the maxilla, 
in front, and the quadrate, behind and below, lies a bone 


which appears to answer to the bone (z) of the Frog, and to } 
its quadrato-jugal. Between the nostril and the maxilla, — 


the nasal bone and the premaxilla, there is a bone which 
seems to be an ossification of the cartilaginous ala nasi. 
Another bone nearly encircles the orbit, and, as a supra- 
and postorbital bone, has no analogue among existing 
Amphibia. The palatine bones surround the posterior and 


THE LIMBS OF AMPHIBIA. 179 


outer margins of the posterior nares, and then extend back 
on the inner side of the maxilla, in a manner unlike any- 
thing observed among other existing Amphibia. But in the 
Labyrinthodonta, both this disposition of the palatine and 
the complete roofing over of the skull by bone are repeated, 
and there is a postorbital bone. 


Fig. 56. 


Fig. 56.—Side and upper views of the skull of Trematosaurus. The 
sculpture of the cranial bones is not represented in the lower half 
of the upper view of the skull, in order to show the sutures more 
distinctly. 


The Labyrinthodont skull is further characterised by the 
development of distinct pointed epiotics, like those of 
fishes, and of paired ossifications, which take the place of 
the supra-occipital, asin many Ganoidet. Jn many Labyrin- 


180 THE ANATOMY OF VERTEBRATED ANIMALS. 


thodonts the articular element of the iower jaw is com- 
pletely ossified. 

Archegosawrus possessed branchial arches when young, 
and there can be little doubt that the other Labyrintho- | 
donts resembled it in this respect. 

The limbs and their arches are completely absent in the | 
Gymnophiona, and, apparently, in the extinct Ophiderpeton 
of the Carboniferous formation. In all other Amphibia the 
pectoral arch and limbs are present, and, in all but Siren, 
the pelvic arch and limbs. The anterior and posterior 
limb arches consist of a continuous cartilage on each side, 
divided by an articular surface into a smaller dorsal moiety, 
and a more expanded ventral portion. The dorsal moieties 
are, respectively, the scapula and the ilium. The ventral 
moieties are divided by notches, or fontanelles, into two 
portions—an anterior, precoracoidal, or pubic part, and a 
posterior, coracoidal, or ischial part. 

In the Urodela the scapula ossifies, and its ossification 
may be prolonged into the coracoid and precoracoid, but 
there is never more than one osseous mass. The clavicle 
is not developed. In Siredon, the Derotremata, and Sala- 
mandridea, the coracoids are received into grooves of the 
anterolateral edges of a cartilaginous sternum. 

The pectoral arch of the Labyrinthodonts seems to have 
possessed representatives of clavicles in the lateral thoracic — 
shields. The structure of the rest of the arch is not clear, 
but ossified coraco-scapular pieces seem to have existed. 

In the Batrachia, the coraco-scapular cartilages are some- 
times, as in the common Frog, firmly united in the middle 
line, and send forwards a median process, which becomes 
ossified, and is the omosternum (Fig. 57, o.st.). Behind, 
the coracoids articulate with a well-developed sternum (st.). 
Distinct ossifications arising on either side of the glenoidal 
cavity represent the scapula (sc.) and the coracoid (er.), and 
the upper moiety of the scapula may be distinctly ossi- 
fied as a supra-scapula (s.sc.). The coracoid is divided by a 
large membranous space or fontamelle into a proper cora- 
coid (cr.), which lies behind the fontanelle; a persistently 


THE LIMBS OF AMPHIBIA. 181 


cartilaginous epicoracoid (e.cr.), which bounds it internally ; 
and a precoracoid, which limits it in front. Closely applied 
to the precoracoid is an ossification in membrane, which 
represents the clavicle. 

The pelvic arch is attached (except in Proteus) to the 
extremity of the sacral rib. An iliac ossification is always 
developed; an ischial, in all but Proteus. The pubis does not 


Fig. 57. 


Fic. 57.—The sternum and pectoral arches of a Frog, seen from above. 
The left supra-scapula is removed :—se. scapula ; s.s¢. supra-scapula ; 
p.se. prescapular process ; cr. coracoid ; e.cr. epicoracoid ; cr.f. cora- 
coid fontanelle. The bar which bounds this in front is the precora- 
coid, and bears the clavicle: 0.s¢. omosternum ; st. sternum; z.st. 
xiphisternum. 


appear to be regularly represented by a distinct ossification. 
In the Batrachia the applied flat faces of the expanded 
ventral divisions of the pelvic arch coalesce into a dise. 

In the genus Amphiwma, the limbs have each either two 
or three digits. In Siren, the anterior limbs, which alone 
exist, are three or four-toed. In Proteus, the anterior 


182 THE ANATOMY OF VERTEBRATED ANIMALS. 


limbs are tridactyle, the posterior didactyle. Menobranchus 
has tetradactyle feet, while in the other Urodela the anterior 
limbs are tetradactyle, the posterior pentadactyle. The 
Batrachia have four digits, with or without a rudiment of 
another, in the fore-limb, and five in the hind-limb. In 
the perennibranchiate Urodela, the cartilages of the carpus 
and tarsus, which, except in Proteus, present little deviation 
from the typical number and arrangement (Fig. 11, p. 32), 
remain unossified ; in the other Urodela, and in the Batrachia, 
they are for the most part ossified. 

In the Batrachia, the posterior limbs are much longer 
than the anterior. The radius and the ulna in the fore- 
limb, and the tibia and fibula in the hind-limb, are fused 
together into one bone. The carpal bones no longer present 
the typical arrangement; and, in the tarsus, there are two 
proximal, greatly elongated, cylindrical bones, which take 
the place of a caleaneum and an astragalus, while the distal 
series is reduced. 

The limbs of the Labyrinthodonts were feeble in com- 
parison with the size of the body. In the genera Archego- 
saurus, Keraterpeton, Urocordylus, Lepterpeton, each foot 
possessed five digits, and the carpus and tarsus were un- 
ossified. 


The Amphibia usually possess teeth on the vomers, pre- 
maxille, maxille, and dentary pieces of the mandible, but 
rarely on the palatine and pterygoid bones. The premaxillary 
and vomerine teeth are disposed in concentric semicircles, 
an arrangement which is very characteristic of the group. 
In the larve of the Batrachia, and in Siren, the premaxille 
and mandibles are ensheathed in horny beaks, as in the 
Chelonia and Aves. In addition, Siren has teeth in the 
vomers, and on the splenial piece of the mandible ; Meno- 
branchus and Siredon have pterygoid teeth. Many of the 
Labyrinthodonts possess palatine teeth. In some Gymno- 
phiona the mandible has a double row of teeth, and there is 
an approximation to this structure in the Labyrinthodonts. 

The teeth usually become ankylosed with the adjacent 


THE HEART IN THE AMPHIBIA. 183 


bones. In existing Amphibia their structure is simple, but 
in the Labyrinthodonts, the parietes of the teeth, at a 
certain distance below the summit, become longitudinally 
folded, and each fold may be again longitudinally plaited, 
so that the transverse section of the tooth acquires a very 
complicated structure, the pulp-cavity being subdivided 
into a great many radiating and branching segments. The 
structure is similar in principle to that exhibited by the 
teeth of many of the Ganoidei. In many of the Labyrin- 
thodonts, again, two of the anterior mandibular teeth take 
on the form of long tusks, which are received into fosse, or 
foramina, of the upper jaw, as in most existing Crocodilia. 
The tongue is fixed to the floor of the mouth in Urodela and 
Gymnophiona, and remains undeveloped in the genera 
Pipa and Dactylethra, which have thence been termed 
Aglossa. In other Batrachia, the tongue, which is usually 
long, and fixed by its anterior end to the symphysis of the 
mandible, can be rapidly protruded and used as an organ 
of prehension. No distinct salivary glands have been ob- 
served in the Amphibia. Many male Batrachia have the 
mucous membrane of the floor of the mouth produced into 
pouches which can be distended with air. 

The simple alimentary canal is usually short, and much 
longer in the larve (which are vegetable feeders) than in 
the adults. A gall-bladder is always present. 


The heart presents two auricles, a single ventricle and a 
bulbus arteriosus. A venous sinus, the walls of which are 
rhythmically contractile, receives the venous blood from the 
body, and opens into the right auricle. In Proteus, Menobran- 
chus, and Siren, the septum of the auricles is less complete 
than inthe other Amphibia. The left auricle is much smaller 
than the right, and a single pulmonary vein opens into it. 
The interior of the ventricle is more like a sponge than a 
chamber with well-defined parietes. The walls of the long 
bulbus arteriosus contain striated muscular fibres, and are 
rhythmically contractile. Valves are sometimes placed at 
each end of it, and it may be imperfectly divided into two 


184 THE ANATOMY OF VERTEBRATED ANIMALS. 


cavities by an incomplete longitudinal partition. It termi-— 


nates, upon each side, in either three, or four, trunks, which 
ascend upon the branchial arches. The most anterior of 


these trunks give off the carotid arteries, the most posterior | 
the pulmonary arteries, and arteries to the integument; © 
the middle trunks form the principal roots of the dorsal 


aorta. 

In Proteus, where there are three branchial arches, the 
bulb of the aorta splits into two trunks; each of these 
divides, at first, into two branches, and then the posterior 
branch, on each side, again subdivides into two others. 
Thus, three pairs of aortic trunks are formed, which ascend 
upon the branchial arches. The two anterior pairs of aortic 
trunks pass directly into the roots of the dorsal aorta, but 
each gives off a vessel which enters one of the external gills, 
the blood from which is brought by an efferent canal into 
a higher part of the same aortic arch. The third aortic 
trunk, on each side, is interrupted, its lower part becoming 
the branchial artery of a gill-tuft. The blood is carried out 
of this branchia by a venous trunk, which opens into the 
root of the dorsal aorta, and is, in reality, merely the upper 
part of the third aortic trunk. The facts may be expressed 
in another way, by saying that the bases of the branchial 
artery and vein anastomose in the first two gills, but not in 
the third. 

The adult Axolotl (Siredon) has four pairs of aortic 
trunks (Fig. 25, E, p. 91); the hindermost pair (v1.) gives off 


the pulmonary arteries, the three next (v., Iv., 111.) supply _ 


the external branchiz; and the anterior trunk passes, above, 
into an artery which divides into hyoidean and carotid 
branches. 

In Salamandra there are four pairs of aortic trunks in 
the adult, but the upper moiety of the first, on each side, 
is obliterated, and remains as a mere ductus Botalli. The 
fourth trunk gives off the pulmonary artery; some twigs 
for the esophagus, and a few cardiac branches, next arise 
from it; and it then unites with the second and third to form 
the root of the dorsal aorta. The basal moiety of the first 


THE CIRCULATION OF THE FROG. 185 


trunk enlarges at its extremity, close to the angle of the 
mandible, into a spongy organ, the carotid gland, from 
which the carotid artery, and that for the supply of the 
hyoidean and oral regions, are given off. 

In the adult Frog, the aortic bulb is separated by an 
incomplete longitudinal septum into two passages; and, 
at its extremity, divides into two trunks, each of which 
is partitioned internally into three passages. The middle, 
or systemic, passage passes directly into a trunk, which 
unites with its fellow beneath the spinal column into the 
dorsal aorta. The anterior, or carotid, passage ends, as in 
Salamandra, in a carotid gland and ductus Botalli; carotid, 
hyoidean, and oral branches being given off from the former. 
The hindermost, or pulmo-cutaneous, passage ends in the 
pulmonary and the cutaneous arteries, the anastomoses of 
these with the roots of the dorsal aorta being obliterated. 
The middle pair of aortic trunks thus exclusively constitute 
the origins of the dorsal aorta, and are the permanent aortic 
arches. The right aortic arch is wider than the left, espe- 
cially towards their junction ; as the left gives off, just before 
this point, a large cceliaco-mesenteric artery to the ab- 
dominal viscera. Each aortic arch gives off the subclavian 
and vertebral arteries of its side. Only venous blood 
passes into the pulmonary arteries of a Frog; while mixed 
blood enters the aortic arches, and is of a brighter arterial 
hue at the end, than at the beginning, of the systole. The 
blood in the carotid passages is always bright. The me- 
chanical arrangements by which this is brought about 
have been beautifully analysed by Briicke, who shows :— 
first, that the spongy interior of the ventricle contains, 
in its base, a transversely elongated cavity, into which 
the auricles open, and which, by its right extremity, com- 
municates with the ventricular opening of the aortic bulb; 
secondly, that the aortic bulb is imperfectly divided by a 
longitudinal septum, the upper left edge of which is at- 
tached, while its lower right edge is free; thirdly, that, of the 
two passages into which the aortic bulb is thus divided, the 
one on the right side of the septum ends in a chamber, in 


186 THE ANATOMY OF VERTEBRATED ANIMALS. 


which the carotid and systemic passages commence, while 
that on the left side similarly leads to the entrance to the 
pulmo-cutaneous passages; fourthly, that the carotid gland, 
in which the carotid passage ends, presents a mechanical ob- 


stacle to the flow of the blood through it; fifthly, that there’ 


is a valvular fold open towards the heart, in each systemic 


passage, which also offers a certain amount of mechanical 


resistance to the blood ; and, sixthly, that after the blood has 
begun to flow through the bulb, it will gradually force the 


Fig. 58. 


Fig. 58.—The Axolotl (Siredon). 


septum over to the left side, and so impede the flow into the 
pulmo-cutaneous passage. 

Thus, when the auricular systole takes place, the right 
auricle sends its venous blood into that division of the ventri- 
cular cavity which lies nearest the opening of the bulb ; and, 
when the ventricle contracts, the blood first driven into the 
bulb is wholly venous. This blood fills the passages on both 
sides of the septum, but finds a very much greater resistance 
to its exit on the right than on the left side. It therefore 
flows, at first, exclusively into the left division, and makes 
its way through the short pulmonary arteries into the lungs. 


THE RESPIRATORY ORGANS OF AMPHIBIA. 187 


But, as the pulmonary vessels fill, the pressure on the two 
sides of the septum becomes equalized, and the systemic 
passages, which offer the next least resistance, fill with blood, 
which is now mixed, as it comes from the middle of the 
‘yentricle. Next, the septum, being driven over to the left 
side, prevents any more blood from going into the pulmo- 
eutaneous passage. At the end of the systole, the blood 
driven out by the ventricle is almost wholly that of the left 
auricle; and, by this time, the resistance in the systemic is as 
great as that in the carotid passages. Hence the latter fill, 
and send arterialized blood to the head. 


The organs of respiration of the Amphibia, in the adult 
state, are either external branchiz, combined with lungs, as 
in the perennibranchiate Urodela; or lungs only, as in the 
other Urodela, the Batrachia, the Gymmnophiona, and, pro- 
bably, the majority of the Labyrinthodonta. 

In the perennibranchiate Urodela, the branchial arches 
(or some of them) are separated by open clefts (the number 
of which varies from four to two), throughout life, and 
three, branched, gills are continued by single stems into the 
integument, at the dorsal ends of the branchial arches. An 
opercular fold of the integument, in front of the gill-clefts, 
attains a considerable size in Siredon (Fig. 58), but does not 
cover the gills. The branchial arches themselves bear no 
branchial filaments. Other Urodela are devoid of external 
gills, but (as is the case in Menopoma and Amphiuma) 
present one or two small gill-clefts on each side of the 
neck, and are thence called Derotremata. The rest of the 
Urodela, and all the Batrachia and Gymnophiona, are devoid 
of both external gills and gill-clefts, in the adult state. 

In all the Amphibia, a glottis, placed on the ventral wall 
of the esophagus, opens into a short laryngo-tracheal cham- 
ber with which two pulmonary sacs are connected, either 
directly, or by the intermediation of bronchi (as in the 
Aglossa), or by a trachea (as in the Gymnophiona). The 
walls of the pulmonary sacs are more or less sacculated. 
In most Amphibia the lungs are equal in size; but in the 


188 THE ANATOMY OF VERTEBRATED ANIMALS. 


snake-like Gymnophiona, the right is much smaller than the 
left. In Proteus, the pulmonary blood is not all returned 
to the heart, some of it entering the veins of the trunk. 
Aérial respiration is effected, in the Amphibia, by pumping — 
the air from the oral cavity into the lungs. To this end — 
the mouth is kept shut, and ingress and egress to the air is — 
given by the nasal passages, which always open immediately 
behind the vomers, at the anterior part of the roof of 
the mouth. These passages being open, and the hyoidean 


Fig 59.—The brain of Rana esculenta, from above, magnified four 
times :—L. ol., the rhinencephalon, or olfactory lobes, with,I., the — 
olfactory nerves ; Hc., the cerebral hemispheres ; Fh. o., the thala- 
mencephalon with the pineal gland, Px.; L. op., optic lobes; C., 
cerebellum; S. rh., the fourth ventricle; JZo., medulla oblongata. 


apparatus depressed, the air fills the cavity of the mouth. 
The external nostrils are then shut, and the hyoidean appa- 
ratus being raised, the air is forced, through the open glottis, 
into the lungs. 

All Amphibia possess an urinary bladder, which opens into 
the cloaca, and does not receive the ureters. The kidneys of 
the Amphibia appear, like those of fishes, to be persistent 
Wolffian bodies. 


THE REPRODUCTIVE ORGANS OF AMPHIBIA. 189 


In the brain of the Amphibia the cerebellum is always 
very small, and represented by a mere band; the cerebral 
hemispheres are elongated, and contain ventricles. In 
Proteus the mesencephalon is very inéistinctly marked. 
The optic nerves form a chiasma. 

As in fishes, the pneumogastric gives off a lateral nerve, 
which runs along the sides of the body. 

The eyes are very small, and covered by the integument, 
in Proteus, the Gymnophiona, and the genus Pipa. The 
perennibranchiate and derotreme Urodela have no eyelids ; 
but most Batrachia have not only a well-developed upper 
eyelid, but a nictitating membrane, moved by special muscles. 

All Amphibia possess a fenestra ovalis with a cartilagimous, 
or osseous, columelliform stapes, the expanded proximal 
end of which is fixed to the membrane of the fenestra. In 
many Batrachia, if not in all, there is a fenestra rotunda, 
though the presence ‘of a distinct cochlea has not been as- 
certained. The Urodela, the Gymnophiona, and the Peloba- 
tidea, among the Batrachia, have no tympanic cavity, nor 
membrane. In the other Batrachia there are tympanic 
cavities communicating freely with the throat. Hach is 
closed externally by a tympanic membrane, with which the 
outer extremity of the stem of the stapes is connected. 
In the Aglossa, the two tympanic cavities communicate 


with the mouth by a single Eustachian aperture; and the 
outer end of the stapes expands into a great cartilaginous 


plate coextensive with the tympanic membrane. 

The ducts of the reproductive organs of the Amphibia, 
like those of the Ganoidei, always communicate directly with 
the urinary ducts: and, as in most Ganoidei and all Hlasmo- 
branchii,the proximal end of the oviduct is open, and commu- 
nicates with the peritoneal cavity. The male has no penis, 
unless a papillary elevation of the wall of the cloaca may 
represent such an organ. The testes of the male Amphibia 
are composed of tubules, and vasa efferentia convey the con- 
tents of these away. In the Urodela, the vasa efferentia of 
each testis enter the inner side of the corresponding kidney, 
and traverse it, leaving its outer side to enter a genito- 


190 THE ANATOMY OF VERTEBRATED ANIMALS. 


urinary duct, which lies on the outer side of the kidney, 
ends blindly in front, and opens behind into the cloaca. 
The uriniferous tubuli also pass directly from the outer mar- 
gin of the kidneys into the genito-urinary duct. In the 
Batrachia there is likewise a genito-urinary duct, and the 
vasa efferentia run to the inner edge of the kidney and 
enter it. In Bombinator igneus and Discoglossus pictus, the 
genito-urinary duct receives the urinary products and the 
spermatozoa, in the same way as in the Urodela. But, in the 
Frogs and Toads, the urinary tubuli are gathered together 
into a special small canal which opens into the genito-urinary 
duct near its termination in the cloaca, and the vasa effe- 
rentia pour their contents into this canal. Under these 
circumstances, the part of the genito-urinary duct which 
lies beyond the renal canal may become obliterated, as in 
the Frogs; or may persist, and play the part of a vesicula semi- 
nalis, as in the Toads. 

In the female Amphibia, the kidneys have, as in the male 
Frogs and Toads, a renal canal which opens into the lower 
part of the oviduct. | 

It would appear from these facts that the oviduct in the © 
female, and the genito-urinary ducts in the male, Amphibia — 
represent both the Wolffian and the Miillerian ducts of the 
higher Vertebrata, 


In most Amphibia the ova are impregnated and hatched 
outside the body, but internal impregnation and incubation 
occur in some of the Urodela. In Pipa the eggs are hatched 
in pouches of the dorsal integument, while the male Alytes 
carries them twisted in strings round his legs. 

When hatched, the young are devoid of respiratory organs 
and of limbs, and are provided with a long tail, by means 
of which they swim about. Branchial clefts soon make their 
appearance; and ciliated external branchial plumes, like those 
of the perennibranchiate Urodela, are developed. A pair of 
suckers are sometimes formed upon the under-surface of 
the mandibular region, and the jaws acquire horny sheaths. 

A broad opercular membrane is developed in front of the 


THE DEVELOPMENT OF AMPHIBIA. 191 


branchial aperture, and, in the Batrachia, extends over and 
eventually covers the gills, a rounded aperture persisting 
for a certain time only on the left side. The anterior pair 
of limbs is developed before the posterior, but in the Frog 
they are not so soon visible, being hidden by the opercular 
membrane. 

The lungs make their appearance as diverticula of the 
ventral wall of theceesophagus. The nasal sacs are at firstmere 


Fig 0. 


Fig. 60.—A. B., Tadpoles with external branchizw: n, nasal sacs; a, 
eye; 0, ear; £b, branchie ; m, mouth; z, horny jaws; s, suckers ; 
d, opercular fold. 

C., a more advanced Frog’s larva: y, the rudiment of the hind limb ; 4s, 
the single branchial aperture. The figure has not been reversed, so 
that this aperture appears to lie on the right side instead of the left. 


excal involutions of the integument, but nasal passages com- 
municating with the mouth are soon formed, and both 
aérial and aquatic respiration are completely established. 

In the Batrachia, as development proceeds, the external 
branchie disappear, and are succeeded, functionally, by 
short branchial filaments developed upon the whole length 
of each of the branchial arches, of which there are four. 


192 THE ANATOMY OF VERTEBRATED ANIMALS. 


Before the development of the lungs the heart has only 
a single auricle ; afterwards, the auricle becomes divided into 
two. The aortic arches, at first, pass along the visceral and 
branchial arches to the dorsal aorta, as in other vertebrate | 
embryos. When external gills are developed, each receives — 
a loop from the corresponding arch, much as in Proteus. 

When the internal gills of the Batrachia appear, each aortic - 
arch which belongs to a branchial arch splits into two trunks, 
—one which remains directly connected with the cardiac 
aorta, and another which opens into the dorsal aorta. The 
vessels of the branchial filaments constitute loops between 
these afferent and efferent trunks, which always remain 
united by anastomoses. When branchial respiration ceases, 
and the branchial processes and their vessels disappear, 
the anastomoses dilate; the direct communication between 
the afferent and efferent trunks of the second pair of in- 
ternal branchie is re-established; and they become the 
permanent arches of the aorta. The anterior branchie are 
replaced by the carotid glands, and their afferent vessel is 
the carotid passage of the adult. The afferent and efferent 
trunks of the third pair of branchiz are converted into the © 
stem of the cutaneous artery, and the afferent trunk of the © 
fourth pair of branchiz into that of the pulmonary artery. © 
The diagram (Fig. 25, p. 91) is intended to make these 
changes, and the relations of the various trunks to the 
embryonic aortic arches, intelligible. 

The alimentary canal of the Tadpole is, at first, long, and 
coiled up into a close spire, like a watch-spring, in the 
abdomen, but its length becomes relatively less as age ad- 
vances. At the same time, the diet changes from vegetable — 
to animal—the young tadpole being chiefly herbivorous, the 
adult, insectivorous. 

In the Urodela the tail persists, and developes complete ver- — 
tebrz; but, in the Batrachia, the caudal part of the spinal — 
column disappears, for the most part, together with the 
rest of the tail, and only the basal portion of the notochord 
becomes converted into the urostyle, which eventually 
ankyloses with the two hindermost neural arches. 


193 


CHAPTER V. 


THE CLASSIFICATION AND THE OSTEOLOGY OF THE 
REPTILIA. 


The province Sauropsida is divisible into the two classes. 
Reptilia and Aves. 


All Reptilia, so far as their organization is known to us, 
are distinguished from Aves by the following characters :— 

1. The exoskeleton is composed of horny plates (scales), 
_or bony plates (scutes), never of feathers. 

2. The centra of the vertebree may be amphiccelous, pro- 
ecelous, opisthocelous, or may have nearly flat articular 
faces; but these faces are spheroidal or oval, and are never 
eylindroidal, even in the cervical region.* 

3. When reptiles possess a sacrum, the sacral vertebrx 
have large expanded ribs, with the ends of which the ilia 
articulate. 

4, The sternum is rhomboidal; and, when many ribs ave 
connected with it, the hindermost of these are attached to 
a single, or double, median backward prolongation (except, 
perhaps, in the Péerosawria). The sternum may be con- 
verted into cartilage bone, but (with the possible exception 
of the Pterosawria) is never replaced by membrane bone, 
and does not ossify from two, or more, definite centres. 

5. When an interclavicle exists, it remains distinct from 
the clavicles. 

6. The manus contains more than three digits (? Dino- 
sauria), and the three radial digits, at fewest, have claws. 


* The articular faces of the are very much elongated trans- 
vertebre of some Ptercsauria versely. 


Oo 


194. THE ANATOMY OF VERTEBRATED ANIMALS. 


7. In all existing reptiles, the ilia are prolonged further 
behind the acetabulum, than in front of it; and the inner 
wall of the acetabulum is wholly, or almost completely, 
ossified. The pubes are directed downwards and for- 


wards, and, like the ischia, meet in a ventral symphysis. | 


In the extinct Dinosauria, the pelvis exhibits forms tran- 


sitional between the reptilian and the ornithic arrange- 


ment. 

8. The digits of the pes are not fewer than three; and 

the metatarsal bones are not ankylosed together, or with 
the distal tarsal bones. 
' 9. In existing reptiles not fewer than two aortic arches (a 
right and a left) persist. Two arterial trunks are given 
off from the right ventricle, or the part of the single 
ventricle which answers to it. The venous and arterial 
currents of the blood are connected, either in the heart 
itself, or at the origins of the aortic arches. 

10. The blood is cold. There are usually two semilunar 
valves at the origins of the aortic and pulmonary trunks. 

11. The corpora bigemina lie upon the upper surface of 
the brain. 


In Aves, on the contrary :— 


’ T. The exoskeleton consists of feathers. Ossifications of — 


the dermis are rare, and never take the form of scutes. 

' 2. Tn all recent birds. the centra of the cervical vertebra, 
at least, have subcylindrical articular faces. If, as in some 
birds, the faces of the centra of the other vertebre are 
spheroidal, they are opisthocceelous, which is the rarest 
arrangement among reptiles. 

3. The proper sacral vertebre of birds—that is to say, 

those between, or through, the arches of which the roots of 
the sacral plexus pass—have no expanded ribs abutting on 
the ilia. 
4. The sternum has no costiferous median backward 
prolongation, all the ribs being attached to its sides. The 
cartilaginous sternum is replaced, in the adult, by mem- 
brane bone, and ossifies from two, to five or more, centres. 


THE DIVISIONS OF THE REPTILIA. 195 


- § When an interclavicle exists it is confluent with the 
clavicles. 

6. The manus does not contain more than three digits, and 
not more than the two radial digits have claws. 

7. The ilia are greatly prolonged in front of the aceta- 
bulum, the inner wall of which is membranous. The pubes 
and ischia are directed backwards, more or less parallel 
with one another, and the ischia never meet in a ventral 
symphysis. 

8. The astragalus sends up a process on to the front face 
of the tibia, and early ankyloses with the latter bone. In 
this character, Birds differ from all existing Reptiles. The 
foot contains not more than four digits. The first meta- 
tarsal is, almost always, free, shorter than the rest, and 
incomplete above. The other three are ankylosed together, 
and with the distal tarsal bone, to form a tarso-metatarsus, 

Some of the extinct Dinosauria closely resembled birds 
in the form of the tibia and astragalus, the immoveable 
union of the two bones, and the reduction of the number 
of the digits. 

9. Only one aortic arch, the right, is present. Only one 
arterial trunk, the pulmonic, is given off from the right 
ventricle. The arterial and venous currents communicate 
_ only by the capillaries. 

10. The blood is hot, There are three semilunar valves 
at the origins of the aortic and pulmonary trunks. In all 
existing birds the extremities of the chief pulmonary 
passages terminate in air-sacs. There is a rudiment of this 
structure in the Chameleons, and the extinct Pterodactyles 
very probably possessed such sacs. 

11. The corpora bigemina are thrown down to the sides 

and base of the brain. 


The Reptilia.—This class is divisible, by well-detined 
characters, into the following groups :— 
A. The dorsal vertebree (which, like all the other vertebrae, are 


devoid of transverse processes) are not moveable upon one another, 
nor are the ribs moveable upon the vertebrae (Pleurospondylia). Most 


196 THE ANATOMY OF VERTEBRATED ANIMALS. 


of the dorsal vertebre and ribs are restrained from motion by the 
union of superficial bony plates, into which they pass, to form a 
carapace. 

Dermal bones, usually nine in number, one of which is median and 
symmetrical, and the others lateral and paired, are developed in the 
ventral walls of the thorax and abdomen, forming a plastron. 


I.— Chelonia. 

B. The dorsal vertebrze (which have either complete, or rudimentary, 
transverse processes), are moveable upon one another, and the rlbs 
upon them. ‘There is no plastron. 

a. The dorsal vertebrae have transverse processes, which are 
either entire, or only very imperfectly divided into terminal 
facets ( Erpetospondylia). 

a, The transverse processes are long ; the limbs well developed, 
with the digits united by the integument into a paddle; the 
sternum and sternal ribs are absent or rudimentary. 

II,-— Plesiosauria. 

6. The transverse processes are short, and sometimes rudi- 
mentary; the limbs present or absent; when they are fully 
developed, the digits are free, and there is a well-developed 
sternum with sternal ribs. 

a. A pectoral arch and urinary bladder. 
WI.—Lacertilia. 

4. No pectoral arch, and no urinary bladder. 
IV .— Ophidia. 

b. The dorsal vertebra have double tubercles in the place of | 
transverse processes (Perospondylia). 'Yhe limbs are paddle- 
like. 

V.—Ichthyosauria. . 
¢. The anterior dorsal vertebrx have elongated and divided trans- 7 
verse processes, the tubercular being longer than the capitular 
division (Suchospondylia). 
a. With only two vertebrz in the sacrum. 
VI.—Crocodilia. 


0. With more than two vertebra in the sacrum. 
a. Tl:e manus without a prolonged ulnar digit. 
1. The hind limb saurian. 


VII.— Dicynodontia, 
2. The hind limb ornithic. 


VIII.— Ornithoscelida. 
4, The manus having an extremely prolonged ulnar digit. 


1X.—Pterosauria. 


I shall describe the exoskeletal. endoskeletal. and dental — 
systems of the chief groups of the Reptilia, under the — 
several heads here enumerated, and I shall then give an 


THE CHELONIA. 197 


account of these systems in Aves. But modifications in the 
myology, neurology, splanchology, and development of the 
_ two classes may be conveniently considered together, under 
those several heads, in another chapter. 


I. The CHELoNIA.—The Tortoises and Turtles are those 
reptiles which most nearly approach the Amphibia, though 
they depart very widely not merely from the amphibian, but 
from the ordinary vertebrate type, in some respects. 

A horny epidermic exoskeleton is absent in the soft Tor- 
toises (Trionyx), the bodies of which are covered by a soft 
integument; but, intheother Chelonia, the epidermis is modi- 
fied into horny plates, which constitute the so-called “ Tor- 
toiseshell,” and have in generala very definite arrangement, 
The dorsal surface of the body presents three series of 
central plates, of which five are in the middle and four upon 
each side (4,5, 4). The margins of the dorsal shield are 
guarded by twenty-four or twenty-five plates: one on the 
middle line in front, called nuchal ; one or two behind, pygal ; 
and eleven on each side, marginal. The ventral shield some- 
times presents an anterior median scale ; but, more usually, 
there are six pairs, disposed symmetrically. It will be seen, 
presently, that these epidermic plates by no means corre- 
spond with the bony dermal ossifications. In addition to 
these principal plates, smaller scale-like patches of horny 
epidermis are developed on other parts of the body, and on 
the limbs. 

The dermal ossifications may best be described in con- 
nection with the endoskeleton. 

The presacral vertebre are few in number. In the 
Green Turtle (Chelone midas) there are eight cervical, and 
ten dorsal, in front of the sacrum, which is composed of 
twovertebre. In all the cervical vertebre the neurocentral 
sutures persist ; there are no transverse processes, or ribs, 
and the spines are low or obsolete. The first vertebra, or 
atlas, is a ringlike bone, composed of three pieces, one 
basal and two superolateral. The second is a true axis 
vertebra, the central part of the centrum of the atlas ossify- 


198 THE ANATOMY OF VERTEBRATED ANIMALS. 


ing apart, as an odontoid bone, and attaching itself to the 
front face of the centrum of the second vertebra. 

The other cervical vertebrx are remarkable for the singular 
variety in the disposition of their articular cups and balls. 


Fig. 61.—The Alligator Terrapene (Chelydra Serpentina). 


Thus, the third is opisthocelous; the fourth, biconvex ; 
the fifth, proccelous; the sixth, also procclous, but the 
posterior face is nearly flat, and very broad; in the seventh, 
both the anterior and the posterior faces are very broad 
and flattened, the posterior being the more convex. The 
eighth cervical vertebra is procelous, and differs from the 
rest by the expansion of its neural spine, and by the 
arching backwards of its postzygapophyses over the convex 
prezygapophyses of the first dorsal vertebra, upon which 
the former play backwards and forwards. 

All the cervical vertebre are very freely moveable upon 
one another, and confer great flexibility on the neck, In 
striking contrast with this arrangement, the ten following 
vertebre have flattened faces, firmly united by cartilage. 
If any one of these vertebra, from the second to the ninth, 
be examined, it will be found that the elongated centrum is 
only loosely united with the neural arch, and that the 
summit of the neural arch is continuous with a broad flat 
plate of bone, which forms one of the eight median elements 
of the carapace, or neural plates (Fig. 62, V). 

There are no transverse processes, nay a rib is articulated 


THE CARAPACE OF THE CHELONIA. 199 


between the centrum and the neural arch. Ata short dis- 
tance from its attachment, this rib passes into a broad 
plate of bone, which extends upwards to unite suturally 
with the neural plate; and, in front and behind, becomes 
similarly connected with preceding and succeeding costal 
plates. The rib may be traced.along the under-surface 
of the costal plate, beyond the outer margin of which it 
protrudes; and its free extremity is received into a pit. in 
an elongated prismatic dermal ossification, which forms one 
of a series of marginal plates (Fig. 62, M). 

The first dorsal vertebra differs from the others in many 
respects. The anterior face of its centrum is concave, and 
looks downwards and forwards, while its prezygapophyses 


Fig. 62.—Transverse section of the skeleton of Chelone midus in the 
dorsal region:—(’, centrum; V, expanded neural plate; C, costal 
plate; R, rib; 7, marginal plate ; P, lateral element of the 
plastron. 


are much prolonged, in order to articulate with the convex 
posterior face of the centrum and prolonged postzygapo- 
physes of the last cervical vertebra. The spmous process 
of this vertebra does not pass into the bony nuchal plate of 
the carapace, which lies above it (Fig. 63, Nw), and its rib 
does not expand into a costal plate, but becomes connected 
with the costal plate of the second dorsal vertebra. The 
neural arch of this vertebra is shorter, from before back- 
wards, than its centrum; andthe neural arch of the second 
dorsal vertebra extends forwards and overlaps the centrum 
of the first, for the space thus left unoccupied. The rb of 
the second vertebra is also carried forward, and articulates 


200 THE ANATOMY OF VERTEBRATED ANIMALS. 


not only with its own centrum and neural arch, but with the 


posterior edge of the centrum of the first vertebra. 


These arrangements are repeated by the other dorsal — 


vertebre and ribs, up to the ninth inclusive; but, in the 


tenth, the neural arch occupies only the anterior half of the — 
centrum of its own vertebra, and the rib is very small, and 


has no costal plate. 
The union of the neural and costal plates of the eight 


Fig. 63.—Dorsal view of the carapace of Chelone midas :— Nu, nuchal 
plate; M, marginal plates; 2, ribs; 1—8, neural plates; C.1—C.8, 
costal plates; Py, pygal plates. 

dorsal vertebrx, from the second to the ninth inclusively, 

gives rise to the principal part of the carapace, or dorsal 

moiety of the bony shell of the Chelonian. The first and 
the tenth dorsal vertebree contribute nothing to the cara- 
pace, their small ribs merely becoming attached to the 
costal plates behind and before them. 

In front of the first neural plate, and joined with it by a 


THE PLASTRON OF THE CHELONIA. 201 


serrated suture, lies a large nuchal plate (Fig. 63, Nu), 
-which forms the anterior median boundary of the carapace. 
This nuchal plate sends down from its under-surface a 
median process, which is joined by ligament with the ex- 
panded neural spine of the eighth cervical vertebra. Be- 
hind the eighth neural plate, three other median pygal plates 
(Fig. 63, Py) succeed one another. The anterior two of 
these are united by sutures with the eighth neural and 
costals, and with one another; but the bhi is connected 
externally only with the marginal plates. All three are 
perfectly distinct from the subjacent vertebre. 

The sides of the carapace are completed, between the 
nuchal and pygal plates, by eleven marginal plates (Fig. 
63, M) on each side. Eight of these receive the ends of 
the ribs of the second to the ninth dorsal vertebra, in the 
way already described. 

There is no doubt that the nuchal, the pygal, and the 
marginal plates of the carapace are membrane bones, de- 
veloped in the integument, quite independently of either 
the vertebre or the ribs. But it appears that the neural 
plates and the costal plates exist, as expansions of the 
cartilages of the neural spines and ribs of the primitive ~ 
yertebre, before ossification takes place. This being the 
case, the neural and costal plates are vertebral and not 
dermal elements, however similar they may seem to be to 
the nuchal, pygal, and marginal plates. But this ultimate 
similarity of bones of totally distinct origin is not more 
remarkable here, than in the case of the skull, where the 
parietal and frontal bones stand in the same relation to the 
supra-occipital bone, as the nuchal and pygal plates do to 
the neural plates of the carapace. 

There are no sternal ribs, and no trace of a true sternum 
has yet been discovered in the Chelonia. The plastron is 
wholly composed of membrane bones, which are developed 
in the integument, and lie, in part, in front of, and, in part, 
behind, the umbilicus of the fetus. The latter, at least, 
therefore belong to the abdomen, and the plastron is a 
thoracico-abdominal structure. 


202 THE ANATOMY OF VERTEBRATED ANIMALS. 


In the Turtle the plastron consists of nine pieces—one 
median and anterior, four lateral and paired (Fig. 64). These 
pieces may be named—the median, entoplastron; the first 
lateral, epiplastron ; the second, hyoplastron; the third, hypo- 
plastron; and the fourth, wiphiplastron.* The entoplastron 
and the two epiplastra correspond with the median and 
lateral thoracic plates of the Labyrinthodont Amphibia, 


Fig. 64. 


Fig. 64.—The plastron of the Green Turtle (Chelone midas) :—I.cl, 
interclavicle; cl, clavicles; Hy.p., hyoplastron; Hp.p, hypoplas- 
tron; Xp, xiphiplastron., 


and very probably answer to the interclavicle and clavicles 
of other Vertebrata. 

The sacrum consists of two vertebre. The expanded — 
sacral ribs are not ankylosed with the centra and arches 
of their vertebre. 

The tail is flexible, and consists of procelous vertebre. 
The anterior caudal vertebre have no transverse processes, _ 


* Believing the plastron to  plastron entosternum, episternum, 
answer to the sternum of other hyosternum, hyposternum, and 
Vertebrata, anatomists~ have siphisternum. 
termed these elements of the. 


THE CHELONIAN SKULL. 203 


but possess ribs which may not become ankylosed with 
the centra. Thus the tail and the neck are the only regions 
of the spinal column of a Chelonian which are flexible. 

In the skulls of the Chelonia all the bones, except the 
mandible and the hyoidean arch, are immoveably united 
together. 

In the occipital segment of the adult, the supra-occipital 
is united with the epiotic, but the ex-occipital usually re- 
mains perfectly distinct from the opisthotic. The basi- 


Fig. 65.— External view of asection of the auditory region of the skull 
in a Turtle (Chelone midus) :—f.o., fenestra ovalis; f.7., fenestra ro- 
tunda; esc, asc, psc, external, anterior, and posterior semicircular 
canals. 

sphenoid is large and distinct. The alisphenoidal region 

remains unossified; but the large parietals send down a 

prolongation on each side, which plays the part of an 
alisphenoid. Neither the presphenoid nor the orbito- 
sphenoids are represented by bone, but there are large 
frontals. In the periotic capsule the large pro-otic and 
the opisthotic (Cuvier’s occipitale eaterne) remain distinct 
bones, but the epiotic unites with the supra-occipital. 

The naso-ethmoidal cartilage largely persists; but it 


204 THE ANATOMY OF VERTEBRATED ANIMALS. 


becomes covered above and at the sides by a large bone, 
which meets with its fellow in the middle line, and occu- 
pies the position of the lachrymal, prefrontal, and nasal. 


Fig. 66. 


— 


net cen 
\ me) A 
‘ | 


Fig. 66.—Longitudinal sections of the skull of the Turtle. The upper 
figure represents the entire skull with the outline of the brain in 
situ ; the lower gives a larger view of the inner face of the bones of 
the posterior moiety of the skull. 


The premaxille are small, and usually united together. — 
There is a single vomer, produced downwards into a median — 


THE CHELONIAN SKULL. 205 


internasal plate, which expands below, and joins the pala- 
tine plate of the palatine bone. 

Above the posterior and upper part of the orbit lies a 
postfrontal, and, behind this, a squamosal is placed at the 
sides of the periotic capsule, and above the large quadrate 
bone. The postfrontal and squamosal occupy the upper 
part of the temporal region of 
the skull. Below these, a quad- 
rato-jugal and a jugal connect 
the quadrate bone with the large 
maxilla. 

Insome genera, as Chelone and 
Chelydra, the skull possesses a 
sort of false roof, formed by the 
expansion of a median ridge, de- 
veloped from the parietal bones, 
into a broad plate, which becomes 
suturally united with the post- 
frontals and squamosals. 

The quadrate bone is firmly 
fixed to the sides of the periotic 
region of the skull, and ends 
below in a strong condyle for 
the mandibles. The long and 
broad pterygoid bones unite with 
one another in the middle line, 
and are firmly fixed to the base 
of the skull, as in Plesiosawria 
and COrocodilia. They unite 
only with the upper part of the Fig. 67.—The left half of the 
quadrate bone, as in the latter eee We pone 
reptiles. 

The palatines are firmly united with the pterygoids. 
behind, and with the vomer above and in front. They 
are prolonged downwards, and develope a short palatine 
plate, which unites with the produced and expanded lower 
edge of the vomer, to bound the posterior nares. (Fig. 67, 
Vo, N'.) 


Fig. 67. 
Pm 


206 THE ANATOMY OF VERTEBRATED ANIMALS. 


The dentary pieces of the two rami of the mandible are: 


represented by one bone, as in Birds. 


The hyoidean apparatus consists of a broad plate of car- | 


tilage with two longer anterior, and two shorter posterior, 


ossified cornua. The cornua have no direct connection | 


with the skull. 


The pectoral and pelvic arches appear, at first sight, to 


have a very anomalous position in the Chelonia, inasmuch 
as they seem to be situated inside, and not outside, the 
skeleton of the trunk. But since the plastron does not 
answer to the sternum of other Vertebrata, but to part of 
the dermal skeleton,the anomaly does not really exist on the 
ventral side. And, as to the dorsal side, the pectoral and 
pelvic arches of the foetal Chelonian are at first situated in 
front of, or behind, and external to, the ribs, as in other 
Vertebrata. It is only as development advances, that the 
first costal plate extends over the scapula, and the hinder 
costal plates over the ilium. 


The pectoral arch is ossified in such a manner that the 


scapula and precoracoid form one bone, while the coracoid 
remains distinct. The free ends of the coracoid and pre- 


coracoid are usually connected together by a fibro-carti-_ 


laginous band, representing the epicoracoidal cartilage in 
Lacertilia. There is no clavicle, unless the epiplastra and 
entoplastron represent that bone. 

The carpus of the Chelonia contains nine primary ossicles, 
as in the Urodela—three in the proximal row, one central, 
and five distal—and these almost always remain distinct. 

There are five digits, the numbers of the phalanges of 
which present no constancy. 

The pelvis contains the usual bones. The pubes (which 


tvs 


are very large) and the ischia meet respectively in a long 


symphysis; and, sometimes, the foramina obturatoria are 
completed, internally, by the meeting of the bony pubes and 
ischium of each side in the middle line. 

The pelvis is not usually united with either the carapace 
or the plastron, but in Chelys, Chelodina, and some other 


THE DIVISIONS OF THE CHELONIA. 207 


genera, the ilia unite by synchondrosis, or ankylosis, with 
he last costal plate, and the pubis and ischium with the 
xiphisternal plates, so that the pelvis becomes firmly fixed 
between the carapace and plastron. 

The proximal row of the tarsal bones consists usually of 
an astragalus, formed by the union of the tibiale and in- 
termedium, and of a fibulare or caleaneum. In Chelydra 
there is a centrale. In Chelone, Emys, Testudo, and 
Trionyx, the centrale is united with the astragalus ; and in 
Emys, the calcanewm coalesces into the astragalus, so 
that the proximal portion of the tarsus consists of one 
bone. In the distal series the two fibular tarsals are united 
into a cuboid bone. There are five digits, and the fifth 
metatarsal has a peculiar form, as if bent upon itself at 
right angles, in the middle of its length. 

In the Testudinea there are only two phalanges in each 
digit of the pes. 


- The Chelonia are divisible into the Testudinea, the 
Emydea, the Trionychoidea, and the Euereta. 

- 1. The Testudinea have the horny jaws naked and cutting, 
or denticulated. The eyes are lateral, the tympanic mem- 
brane is exposed, the short and thick limbs have the toes 
(all of which have nails) bound together by the integument. 
The horny plates of the carapace and plastron are well 
developed. 

The Land Tortoises belong to this division. The cara- 
pace is usually very convex, and sometimes (as in the genus 
Pyzis) the anterior part of the plastron is moveable, and 
ean be shut up like a lid. In Cinyzis, the hinder part of 
the carapace is similarly mobile. 

2. The Emydea have, usually, horny cutting jaws, un- 
covered by lips; the tympanum exposed, and the limbs more 

slender than in the Testudinea, with five-clawed digits, 
which are only united by a web. The horny plates of the 
earapace and plastron are well developed. 

These are the River and Marsh Tortoises. Theyarefurther 
divisible into two groups, in the one of which, the Terrapenes, 


208 THE ANATOMY OF VERTEBRATED ANIMALS. 


the pelvis is free, the neck bends in a vertical plane, and the 
head is almost completely hidden by the carapace when 
retracted (Hmys, Cistudo, Chelydra). In Cistudo, Cinoste- 
num, and Staurotypus, the hinder part of the plastron is— 
mobile. In the other division, the Chelodines, the pelvis © 
is fixed to the carapace and plastron, the neck bends side- — 


ways, and the head cannot be completely retracted under } 


the carapace (Chelys, Chelodina). 

3. In the Trionychoidea (Mud or Soft Tortoises), the jaws — 
have an external cutaneous lip; the nasal organ is pro- — 
longed into a kind of snout, and the head is covered by a | 
soft skin without any visible tympanic membrane. The © 
limbs are flattened, somewhat finlike, and pentadactyle ; 
but only three digits have nails. The integument developes — 
no horny plates, but is quite soft. The costal plates are 
shorter than in other Chelonia, and the marginal ossicles 
are either rudimentary or absent. 

The genera Gymnopus, Cryptopus, and Cycloderma, con- 
stitute this division; they all inhabit the fresh waters of 
hot latitudes. 

The Euereta, or Turtles, have an exposed, hooked, horny 
beak, with a blunt snout. The tympanum is hidden by the 
integument. The limbs, of which the anterior pair are 
much the longer, are converted into paddles, the digits being 
much flattened and elongated, and immoveably united 
together by the integument; only one or two nails are 
developed. The skin of the body is either rugose (Sphargis). 
or covered with thick epidermic plates (Chelone). 

The two genera composing this group inhabit the seas of 
warm climates. 

The Chelonia are first known to occur, with certainty, in 
the Lias. The older forms are, in many respects, interme- 
diate between the Huereta and the Trionychoidea, but present 
no approximation to any other order of Reptilia. 


II, The PLestosaurr1a.—In some of the Plesiosawria, 
the head, not more than one-twelfth or one-thirteenth of 
the length of the body, is mounted upon a neck as long, in 


THE PLESIOSAURIA. 209 


proportion, as that of a Swan; but in others, the head is 
large and massive, and the neck much shorter. The hind 
limbs are longer than the fore limbs, and there is a compa- 
ratively short tail. The integument was certainly devoid 
of any scutes; and was, probably, smooth and possessed no 
scales. 
The cervical vertebre may exceed forty in number, though 
they are generally fewer; and as none of the ribs appear to 
have been connected with the sternum, or if such connec- 
tion existed it cannot now be traced, it becomes difficult to 
distinguish between cervical and dorsal vertebrae, and one is 
obliged to have recourse to some method of separating the 
two, differing from that already adopted. Now, in these 
animals, the neurocentral suture persists for a consider- 
able period, if not throughout life; and the surfaces for 
the articulation of the cervical ribs, which are at first alto- 
gether below the neurocentral sutures, eradually rise, in 
the posterior parts of the neck, until they first are cut by, 
and then rise above, the suture. It is very convenient, and 
harmonizes very well with some facts to be mentioned by- 
and-by in the structure of the Crocodilia, to take the last 
of the vertebre in which the costal articular surface is 
cut by the neurocentral suture, as the last of the cervical 
series. 
- The two anterior cervical vertebra, as thus defined, con- 
stitute the atlas and axis, and are frequently ankylosed 
together. The centra of the other cervical vertebre have 
slightly concave anterior and posterior surfaces; well-de- 
veloped neural arches; anterior and posterior oblique pro- 
cesses, or zygapophyses, of the ordinary character; and stout, 
but somewhat short, spinous processes. The centrum pre- 
sents, upon each side, an oval rugose pit, sometimes more 
or less divided into two facets. This is the costal articular 
surface, which has been already adverted to. Into it fits 
the thickened head of a costal rib, which may have corre- 
sponding facets, but is otherwise undivided. The rib is 
continued backwards into a short and straight body, and 
the angle, 01 the part at which the neck and the body of 
P 


210 THE ANATOMY OF VERTEBRATED ANIMALS. 


= 


Fig. 68.—Diagram showing the structure of the most important parts 
of the skeleton of Plesiosaurus.—A, the skull: Wa, nasal aperture.— 
B, the left fore limb: H, humerus; U, ulna; R, radius; 7. 7. w., 
radiale, intermedium, and ulnare, in the proximal row of carpal bones 
1, 2, 3, distal carpal bones; Mc, metacarpus; Ph, phalanges.— 
C, a dorsal vertebra with ribs (#.), and ventral ossifications ( V.o). 
—D, the left hind limb: F, femur ; 7, tibia; F, fibula; ¢. ¢. f., tibiale, 


THE PLESIOSAURIA. 211 


intermedium, and fibulare, in the proximal row of tarsal bones; 
1, 2, 3, distal tarsal bones; Mt, metatarsus; Ph, phalanges.—E, 
the pectoral arch: Sc, scapula ; Co, coracoid ; a, clavicles and inter- 
clavicle (?).—F, the pelvic arch: Pé, pubis; Z/, ilium; Js, ischium. 


the rib join, is produced forwards, so that the cervical ribs 
of the Plesiosawria have a strong general resemblance to 
those of the Crocodilia. In the posterior part of the neck 
and the anterior part of the dorsal region, the ribs become 
somewhat longer, and lose their anterior processes, gradually 
acquiring the rounded and curved form of ordinary ribs. 
Their proximal ends remain simple, and the facets, with 
which they articulate, become raised, and thrown outwards: 
as transverse processes, developed from the arches of the 
vertebre. (Fig. 68, C.) 

In the anterior dorsal vertebre, these transverse processes 
rapidly acquire their full length; and they are continued 
under this form, descending somewhat lower upon the arches 
of the vertebrz towards the sacrum, to the end of the dorsal 
region. The neural spines acquire greater length, the 
zygapophyses are well developed, and the articular sur- 
faces of the centra retain the form which they possessed 
in the cervical region. There are usually between twenty 
and twenty-five dorsal vertebra. The sacral vertebre are 
two, and resemble the others, except that the sacral 
ribs are large and broad for the attachment of the ilium. 
The caudal vertebre, usuaily between thirty and forty 
in number, become, as usual, reduced to little more than 
centra at the end of the tail; but, in the fore part of the 
tail, they have well-developed spimes and articular pro- 
cesses, with ribs which become ankylosed to the bodies of 
the yertebre, only late in life. Well-developed chevron 
bones are attached between the ventral margins of succes- 
sive centra of the caudal vertebre. 

As has been mentioned, there appear to be no sternal 
ribs, but there is a well-developed system of ossifications of 
the wall of the abdomen, arranged in transverse rows from 
before backwards; each row consists of a median bone, 
slightly bent upon itself, thick in the middle, and thin at 


212 THE ANATOMY OF VERTEBRATED ANIMALS. 


each end—and of six other bones, three on each side, which 
are elongated and pointed at each end, and so disposed 
that their pointed ends overlap one another. (Fig. 68, C.) 

In some Plesiosauria, as already stated, the skull (Fig. 68, A) 
is very small in proportion to the body, not having more than 
a twelfth, or a thirteenth, of the length of the latter; but, in 
other species, the skullis much larger. The snout is taper- 
ing and depressed, and the nasal apertures are situated, 
not at its extremities, but just in front of the orbits—the 
latter, like the supra-temporal fosse, being wide. The 
occipital condyle is almost wholly developed from the stout 
basi-occipital. The ex-occipitals give off elongated parotic 
processes, and the basisphenoid is a thick bone, which ends 
in front in a long rostrum. 

There is a well-marked parietal foramen, and the parie- 
tals send off comparatively short processes backwards, which 
become connected with the large squamosals. The latter 
unite with the postfrontals, which separate the orbits from 
the temporal fossa, and the orbit is completed behind by 
the junction of the postfrontal with the jugal. The jugal 
bone is continued backwards into a slender bar, which 
extends as far back as the lower end of the quadrate, and 
probably contains a quadrato-jugal, so that there is a 
distinct infra-temporal fossa. The most obvious circum- 
stance in which the skull of Plesiosuwrus differs from that 
of most Reptilia is in the great size of the premaxillaries, 
which constitute a large proportion of the snout. 

The under-surface of the skull is rarely well exposed in 
its anterior part; posteriorly, it exhibits a broad and long 
expansion, formed by the pterygoid bones, which unite in 
the middle line, and send processes outwards and backwards 
to the quadrate bone. On each side of the middle line of 
this region of the skull, is seen an ovoidal fossa or depres- 
sion. The pterygoids are continued forwards, and are 
united externally with transverse bones, and more an- 
teriorly with flattened palatine bones. When the forepart 
of the under-surface of the skull is exposed, two other fosse 
are visible, one on each side of the middle line, bounded 


THE PLESIOSAURIA. : 213 


behind by the palatine bones, and separated by what appear 
to be the vomers. I conceive that these are the true pos- 
terior nares, and that the posterior apertures are simply 
spaces left between the pterygoid bones and the basis eranit. 

At the sides of the base of the skull, specimens of Ple- 
siosaurus occasionally exhibit two styliform bones, which lie 
parallel with the axis of the skull; these may be parts of 
the hyoidean apparatus. No trace of any sclerotic ring has 
been found. i 

The teeth of the Plesiosawria are sharp-pointed, curved, 
and the outer surfaces of their crowns striated. Hach 
tooth is lodged in a distinct alveolus, with which, as in the 
Crocodilia, it does not become ankylosed. 

The pectoral arch (Fig. 68, E) is one of the most remark- 
able parts of the organization of the Plesiosawria. It con- 
sists, in the first place, of two very large coracoids, the long 
axes of which are parallel with one another, while their in- 
ner edges meet, without overlapping, throughout the greater 
part of their extent. In this respect they differ from any 
of the Lacertilia, which are provided with well-developed 
limbs. In these the long axes of the coracoids always cut 
one another at a large angle, open posteriorly—a circum- 
stance which results from the manner in which the cora- 
coids are received into grooves in the anterolateral edges of 
the rhomboidal part of the sternum. Hence it would 
appear that the Plesiosawria, like the Chelonia, did not 
possess anything corresponding to this rhomboidal part of 
the sternum, but that the intercoracoid part of the sternum 
was either absent, or reduced to a mere band, as in some 
Batrachia. 

The scapulz are unlike the corresponding organs in any 
other reptile. The glenoidal end, stout and strong, is 
continued horizontally forwards and inwards, as a bony 
prism, with a somewhat concave inner edge, and flat inferior 
surface. The outer surface, rismg up at right angles to 
the ventral surface, gives rise to a well-defined edge; at 
a short distance from the glenoidal end, the part of the 
pone which bears this surface is produced upwards and 


214 THE ANATOMY OF VERTEBRATED ANIMALS. 


backwards, into a low recurved plate. This part appears to 
represent the proper body of the scapula in other Reptiles, 
while the horizontal prolongation answers to that pre- 
glenoidal process of the scapula, which extends forwards and 
inwards as a free bony bar in many Lacertilia—for example, 
Iguana. 

In well-preserved specimens, a broad hoop of substance 
(Fig. 68, EH, a), which seems to have been but imperfectly 
ossified, extends across the middle line of the body, from 
the preglenoidal process of one scapula to that of the 
other, and is continued backwards in the middle line, to 
the junction of the two coracoids. This corresponds very 
nearly in form and position to the epicoracoidal ossifica- 
tions of the Lacertilia, combined with the clavicles and 
interclavicles; but I have never been able to detect any 
distinct clavicular, or interclavicular, elements in any Plesio- 
saurus, though they appear to have been well developed in 
Nothosaurus. 

The humerus is a stout bone—prismatic, and with a 
rounded head at its proximal end, flattened and broad 
distally. (Fig. 68, B.) Its anterior margin is nearly straight, 
or even slightly convex, while the posterior is concave. 
Distally, it presents two facets, meeting at an angle, with 
which the broad and short radius and ulna articulate. The 
ulna differs in shape from the radius, beimg convex pos- 
teriorly, and concave in front. The two bones are of equal 
length, and much shorter than the humerus. There are 
six rounded carpal bones,* arranged in two rows; and to 
these succeed five digits, composed of metacarpals and 
phalanges, which are elongated and constricted in the 
middle. The middle digits have numerous phalanges. 

The pelvic arch has very large dimensions, in correspon- 
dence with thesize of the hind limb, which is usually longer 
than the fore limb. (Fig. 68, F and D.) The ilium is a 


* Tt may be a question whe- tarsus, or to metacarpus and 
ther the fourth distal bone in the metatarsus; or whether it is 
carpus and tarsus (Fig. 68, B formed by the confiuence of ele- 
and D) belongs to carpus and ments belonging to both regions, 


THE PLESIOSAURIA. 215 


vertically elongated bone, narrower below than above, 
where it becomes connected with the sacral nbs. In- 
feriorly, it unites with the pubis and with the ischium, to 
form the acetabulum. The pubes are very broad quadrate 
bones, much larger than the ischia, and they meet in a 
median symphysis. The ischia, triangular and expanded, 
also unite in a ventral symphysis. The femur resembles the 
humerus in its general form, although both its sides are 
straighter, and the other bones of the hind limb are so like 
those of the fore limb, as to need no special description. 

There can be little doubt that all the bones of the limbs 
were, like those of the Cetacea, enclosed within a common 
sheath of integument, so as to form a paddle. 

Such is the general organization of the skeleton of the 
Plesiosauria, which are long extinct animals, entirely con- 
fined to the Mesozoic Rocks, from the Trias to the Chalk, 
inclusive. They may be divided into two groups, according 
as they are Triassic, or Post-Triassic, in age. 

The Post-Triassic group contains the genera Plesiosawrus 
and Pliosaurus, the different species of which appear to 
differ in little more than the proportions of the head to the 
trunk, and the relative length and degree of excavation of 
the centra of the vertebra. In the species which have been 
named Pliosaurus, the vertebre are wide in proportion to 
their length, and deeply excavated in front and behind. 
Pliosawrus attained gigantic dimensions, paddles of some 
individuals reaching a length of not less than six feet. 

The Triassic genera, Nothosawrus, Simosawrus, Pisto- 
saurus (for a knowledge of the organization of which we are 
chiefly indebted to the labours of Hermann Von Meyer), 
appear to have differed from Plesiosawrus principally in the 
following respects :— 

The connection of the neural arches with the centra of 
the vertebra seems to have been looser. The supra-tem- 
poral fosse in the skull appear to have been larger in 
proportion. In these animals, the under-surface of the 
skull has the same structure as in Plesiosawrus, but appa- 
rently lacks the posterior fosse; while there is no doubt 


216 THE ANATOMY OF VERTEBRATED ANIMALS. 


whatsoever that the true posterior nares are situated far 
forwards, in the position assigned to them in Plesiosaurus. 

The pectoral arch of Nothosaurus, again, presents a very 
interesting deviation from the Plesiosaurian type. The 
coracoids, indeed, are greatly expanded, and meet by their 
inner edges, so that the rhomboidal part of the sternum 
seems to have been wholly absent, and the scapule have a 
horizontal prolongation, not quite so long as in Plesio- 
saurus, with an upstanding proper scapular part of corre- 
sponding shape. But then the ends of these preglenoidal 
processes are connected together by, and indeed suturally 
united with, a stout, curved, transverse bar of bone, con- 
sisting of three pieces, one small and median, and two very 
large and lateral, all united firmly together by sutures. 
There can be little doubt that the constituents of this bony 
bar correspond with the interclavicles and clavicles of 
Lacertilia and Ichthyosauria. 


III. The Lacrertin1aA.—Some few Lacertilia, like the Cha- 
meleons and the Amphisbene, are covered by a soft integu- 
ment; but, in the majority, there is an epidermic exoskeleton_ 
composed of horny plates, tubercles, or spines, or over- 
lapping scales. In some forms (e.g. Scineus, Cyclodus) the 
dermi beneath the horny scales is ossified, and the body 
has a complete armour of bony scutes, corresponding in 
form with the scales. The dermal ossifications of the head 
may coalesce with the subjacent bones, but this union of 
dermal bones with subjacent parts does not occur in other 
parts of the body. 

The spinal column always contains a considerable number 
of vertebre; and, except in the Amphisbene and some few 
other Lizards, the tail is long. Those Lizards which possess 
hind limbs have a sacrum, into which not more than three 
vertebre, and rarely more than two, enter. The presacral 
vertebre are distinguishable, when sternal ribs are present, 
into cervical and dorsal. All those vertebrae which lie in 
front of the first sternal rib are cervical; and if, as sometimes 
happens, the last two or three dorsal vertebrz are devoid of 


THE LACERTILIA. 217 


ribs, they become lumbar. Not more than nine vertebra 
are met with in the cervical region of existing Lacertilia, 
and this number is rare. The number was greater in some 
extinct Lacertilia. 

The atlas is composed of three pieces, one inferior and 
two superolateral. The odontoid bone is closely united with 
the second vertebra, and its anterior face may be cylin- 
droidal. A separate ossification is sometimes formed on 
the under-surface of the spinal column at the junction of 
each pair of vertebre. Such a separate ossification, or sub- 
vertebral wedge-bone, is commonly developed beneath and 
between the odontoid bone and the body of the second 
vertebra. 

The centra of the vertebre are either proccelous, or amphi- 
ceelous; the former being by far the more common condition 
in existing Lacertilia, all of which, except the Geckos and 
Sphenodon, have proceelous vertebre, The cups and balls 
are usually ellipsoidal, the long axis of the ellipsoid being 
transverse. In the Geckos, the centra of the vertebre are 
conically excavated at each end; and, except in the centre of 
each vertebra, where it is ossified, the notochord persists 
throughout the spinal column. 

The sacral vertebre of existing Lacertilia are not anky- 
losed together, nor are their articular faces modified, the two 
being connected by a free cup-and-ball articulation. The 
movements of the two vertebrae, however, are restrained by 
the strong ligaments which connect their neural spines and 
arches, and by the fibro-cartilage which connects and covers 
the free ends of their expanded ribs. 

In the anterior part of the tail of the Lacertilia there are 
usually well-developed subvertebral chevron bones, which 
are commonly attached to the bodies of the several verte- 
bre, and not in the intervals between adjacent vertebre. 
In many Lacertilia (Lacerte, Iguane, Geckos) the caudal 
vertebre have a very singular structure, the middle of each 
being traversed by a thin, unossified, transverse septum. The 
vertebra naturally breaks with great readiness through the 
plane of the septum, and when such Lizards are seized by 


218 THE ANATOMY OF VERTEBRATED ANIMALS. 


the tail, that appendage is pretty certain to part at one of 
these weak points. 

The arches of the vertebrz of the Lacertilia are articulated 
together by the ordinary oblique processes, or zygapophyses. 
In the Iguane they are additionally connected by a process 
of the front part of each arch (zygosphene), which fits into 
a fossa on the posterior face of the preceding arch (zygan- 
trum). These Lacertilian vertebre thus nearly approach 
the vertebre of the Ophidia. 

The transverse processes of the vertebrze are very short, 
and are, at most, divided into two indistinct facets, with 
which corresponding facets on the proximal ends of the ribs 
articulate. 

Ribs may be developed in all the cervical vertebree except 
the atlas, and they usually increase in length towards the 
dorsal region, where more or fewer of them become con- 
nected with the sternum. The dorsal moiety of the primi- 
tive cartilage of the rib becomes ossified, and the primitive 
cartilage bone is finally replaced by membrane bone. The 
ventral moiety becomes converted only into cartilage bone, 
and may pass directly and without articulation, on the one 
hand into the sternum, and on the other into the vertebral 
rib. Processes are sometimes developed from the posterior 
margins of certain of the ribs, which are termed processus 
uncinati. The sternum, when fully formed, consists of a 
rhomboidal anterior portion, from the posterior angle of 
which a single, or double, backward prolongation is con- 
tinued into the wall of the abdomen. Two or three pairs 
of the sternal ribs are connected with the posterolateral 
edges of the rhomboid, while the rest may be attached to 
the abdominal prolongations ; or, behind these, they may be 
continued into one another, to form complete hoops across 
the wall of the abdomen (Geckos, Chameleons, Scincoids). 

The Flying Lizard (Draco volans) is remarkable for the 
elongation of many of its posterior ribs, which are con- 
tinued into, and support, the parachute-like expression of 
the integument by which it is enabled to perform its 
flights. 


THE LACERTILIA. 219 


The skull of the Lacertilia resembles that of the Chelonia 
in the development of an interorbital septum (except in 
the Amphisbene), and in the absence of alisphenoids, or of 
any complete ossification of the presphenoidal or orbito- 
sphenoidal regions. The premaxille and maxille are firmly 
united with one another and with the skull, and there are 
two vomers. An unossified space, the parietal foramen, 
usually remains in the roof of the skull in the course of the 
sagittal suture, or between the parietals and the frontals. 


Fig. 69. 


lgpammid 
MUL 


Fig. 69.—The skull of Cyclodus, entire and longitudinally bisected. 


In the principal group of the Lacertilia, a column-like 
membrane bone, called the colwmella (but which is not to 
be, by any means, confounded with the stapes, to which the 
same name is often applied in Reptiles), extends from the 


220 THE ANATOMY OF VERTEBRATED ANIMALS. 


parietal to the pterygoid on each side, in close contact 
with the membranous or cartilaginous wall of the skull. 
Hence they have been called “ Kionocrania,” or “column 
skulls.” This columella (Fig. 69, Co) appears to correspond 
with a small independent ossification, which is connected 
with the descending process of the parietal and with the 
pterygoid, in some Chelonia. 

In the great majority of the Lacertilia (as in the Chelonia), 
the side-walls of the skull, in the region of the ear, are pro- 
duced into two broad and long parotic processes, into the 
composition of which the opisthotic, ex-occipital, and pro- 
otic bones enter. Hach quadrate bone is articulated with the 
outer end of one of these processes (in which a small separate 
pterotic ossification sometimes appears), and is usually move- 
able. The parietal bones do not unite suturally with the occi- 
pital segment of the skull, or with the pro-otic bones, but 
are connected with them only by fibrous tissue. And as the 
presphenoidal region remains unossified, or incompletely 
ossified, it follows that the fronto-parietal portion of the 
skull is, in most Lizards, slightly moveable upon the occi- 
pito-sphenoidal part. 

Each parietal bone is prolonged backwards into a process 
which articulates with the upper part of the parotic pro- 
longation of the skull; and to the outer side of the posterior 
extremity of the parietal process the squamosal is attached. 
The squamosal may be continued forward to the post- 
frontal, which is sometimes subdivided into two. The post- 
frontal may unite below with the jugal, and thus bound the 
orbit. Only in Sphenodon, among recent Lizards, is the 
jugal connected with the distal end of the quadrate by 
bone. As a general rule the quadrato-jugal is represented 
only by a ligament. 

In consequence of the structure which has been described, 
the posterior region of the ordinary Lacertilian skull pre- 
sents a number of distinct fosse in the dry state. A supra- 
temporal fossa lies between the parietal, the postfrontal, 
and the squamosal, on the upper face of the skull; a post-tem- 
poral, between the parietal, the occipital, and the parotic 


THE LACERTILIA. 


221 


apophysis on the posterior face; a lateral-temporal, between 
the squamosal and postfrontal above, the jugal and quad- 
rate in front and behind, and the quadrato-jugal ligament 


below. 

The palatine and pterygoid bones 
are firmly connected both with the 
facial bones, and with the floor of 
the skull, Thus the basisphenoid 
gives off two basipterygoid processes, 
the outer ends of which articulate 
with the inner sides of the pterygoid. 
The posterior ends of the pterygoids 
are usually connected with the inner 
surfaces of the distal ends of the quad- 
rate bones. Their anterior ends are 
firmly united with the palatines ; and, 
from the junction of the two, a trans- 
verse bone (Fig. 70, Tr) usually passes, 
to unite the palatine and pterygoid 
with the maxilla. 

The anterior ends of the palatines 
unite with the maxilleand the vomers; 
but, in existing Lacertilia, they do not 
meet one another, or come into contact 
with the basisphenoid or presphenoid 
in the middle line. The palatine aper- 
tures of the nostrils are placed between 
the palatine bones, on the outer side, 
and the vomer, on the inner. In only 
a few Lacertilia do the palatine bones 
send down processes which bend to- 


Fig. 70.— Under-view of 
the skull of Cyclodus : 
NN’, posterior nasal 
aperture. 


wards one another in the middle line, and so form a posterior 
nasal passage, partially separated from the oral cavity. 
The two rami of the lower jaw are usually, though not 
invariably, firmly connected at the symphysis—and each is 
composed of five ossifications in addition to the articulare. 


The hyoidean apparatus consists of 


an elongated median 


rod, the anterior part of which supports the base of the 


222 THE ANATOMY OF VERTEBRATED ANIMALS. 


tongue; and, usually, of two long cornua on each side of 
this. The cephalic ends of the anterior cornua may be per- 
fectly free, and lie upon the sides of the neck, as in Psam- 
mosaurus; or they may be traceable to, and be connected 
with, the stapes and the parotic processes, as in Sphenodon. 

The limbs may be completely developed; or only one pair 
(either the anterior or the posterior) may be present; or they 
may be entirely absent. When present, they may be mere 
styliform rudiments, or may possess any number of digits 
from two to five. Even when the lmbs are altogether 
absent, the pectoral arch remains, though the pelvic arch 
seems to vanish. When the pectoral arch is complete, it con- 
sists of a suprascapula, scapula, coracoid (with precoracoid 
and epicoracoid elements), and two clavicles, united by an 
interclavicle, which hes in a groove of the sternum. (Figs. 
12 & 13, pp. 35 & 36.) 

The coracoids articulate with grooves in the anterolateral 
edges of the sternum, and usually more or less cross and 
overlap one another, in front. 

In the genus Lialis, in which not a trace of a fore-limb is 
discernible, there is a small sternum, consisting of a flat, 
somewhat pentagonal, plate of cartilage, in which there is a 
little coarsely granular calcareous deposit; but this sternum 
is connected with nu ribs, nor, though it les between the 
coracoids, does it articulate with them. Hach coraco- 
scapular arch is a continuous cartilage, narrow in the 
middle, but expanded at its dorsal, and still more at its 
sternal, end, where the right overlaps the left, and both are 
connected by fibrous tissue with the sternum. The narrow 
middle part of the coracoid is invested, and in part replaced, 
by a sheath of membrane bone, which expands above and 
below, and represents both scapula and coracoid, though it 
presents no trace either of division, or of a glenoidal cavity. 
Beyond the extremities of this central ossification the carti- 
lage merely presents scattered granular calcification. Along 
the front edge of each coraco-scapular arch, and closely con- 
nected with its ossified part, is a long curved clavicle, en- 
tirely composed of membrane bune, and united with its fellow 


THE LACERTILIA. 223 


in the ventral median line, by ligamentous fibres. There is 
no interclavicle. The pectoral arch in other snakelike 
Lizards, such as the Blind Worm (Anguis) and the Shelto- 
pusik (Pseudopus), is in much the same condition as in Lialis. 

When the hind limbs are well developed there is a com- 
plete pelvis. The ilia are moveably articulated with the 
fibro-cartilages which cover the ends of the sacral ribs. 
The pubes and the ischia meet in median symphyses, and 
the anterior margin of the pubis usually, as in the Chelonia, 
gives off a strong curved process. In many Lacertilia a 
partially ossified or cartilaginous rod (os cloacw) is con- 
tinued back from the symphysis of the ischia, and supports 
the front wall of the cloaca. 

In most Lacertilia the manus possesses five digits; and, 
when this is the case, there are usually eight bones in the 
carpus—one for each metacarpal on the distal side, one 
radial, one ulnar, and one central. As a very general rule, 
the pollex has two phalanges, the second digit three, the 
third four, the fourth five, and the fifth three (2, 3, 4, 5, 3). 
The pes. also, generally possesses five digits, which increase 
in length to the fourth, the fifth being smaller than the rest, 
and divergent in direction. Two large bones, very closely 
united, or completely fixed together, represent the calca- 
neum and the astragalus, and are articulated, in a manner 
which allows of very little motion, with the tibia and fibula. 
Tn the distal row there is usually a large bone, representing 
the cuboid. The fifth metatarsal* is bent, as in the Chelonia, 
and may articulate with the caleaneum as well as with the 
cuboid. One or two of the cuneiform bones may be present, 
or the inner ones may be represented merely by fibrous 
membrane, or by cartilage; in which latter case the inner 
metatarsals appear to articulate directly with the astra- 
galus in the skeleton. The number of the phalanges is 
very generally the same as in the manus for the four tibial 
toes, but one more for the fibular (2, 3, 4, 5, 4). 


* The bone thus named may metatarsal, but the corresponding 
perhaps contain a tarsal element, _ distal tarsale, 
and represent not only the fifth 


224, THE ANATOMY OF VERTEBRATED ANIMALS. 


The Lacertilia all possess teeth, which may be confined 
to the premaxille, maxille, and dentary piece of the man- 
dibles ; or may, in addition, be developed on the palatine and 
pterygoid bones. These teeth are simple in structure, and 
their crowns have very various forms, being sometimes 
sharp and conical (Monitor); or bladelike, with serrated 
edges (Iguana); or with broad, crushing, and spheroidal 
crowns (Cyclodus). As a general rule, the teeth become 
ankylosed to the adjacent bone with age; and in the 
upper and lower jaws they thus become attached, either by 
their sides to the parapet of the jaw, when the dentition is 
said to be plewrodont; or by their bases to the summit of 
the parapet, when the dentition is acrodont. The extinct 
Protorosauria are said to be thecodont, or to have the teeth 
lodged in alveoli. New teeth are usually developed at the 
bases of the old ones. 


The Lacertilia are divisible into numerous groups, the leading dis- 
tinctive characters of which are exhibited in the following table :— 
J.—The pterygoid and quadrate bones united. 
A. A columella and an interorbital septum in the skull. 
Kionocrania (Stannius). 
a. Amphiccelous vertebrae (AK. Amphicalia.) 
a. Dentition acrodont or pleurodont. 
1. Ascalabota. 
2. Rhynchocephala. 
3. Homaosauria.* 
b. Dentition thecodont (?). 
4. Protorosauria.* 
b. Proceelous vertebrae (K. procelia.) 
a. Not more than nine cervical vertebre. 
a. The nasal bone, single. 
5. Platynota. 
b. The nasal bones, two. 
1. The integument of the head not 
covered with epidermic plates. 
6. Eunota. 
2. The integument of the head 
covered with epidermic plates. 
7. Lacertina. 
8. Chalcidea. 
9. Scincoidea. 
6. More than nine cervical vertebre. 
10. Dolichosauria.* 
11. Mosasauria. 


* The columella has not been observed in these groups. 


THE RHYNCHOCEPHALA. 225 


B. No columella ; no interorbital septum. 
12. Amphisbenoida. 
II.—The pterygoid and quadrate bones disunited. 
13. Chameleonida. 


1. The Ascalabota.—The Geckos, which constitute this 
group, are Lizards of small size, which inhabit the hotter 
parts of both the Old and the New Worlds, and have always 
attracted attention by their habit of running with exceeding 
swiftness along the walls and ceilings of rooms. They are 
enabled to maintain their hold under these circumstances, in 
part by the sharpness of their curved, and, in some cases, 
retractile claws; and, in part, by laminated expansions of 
the integument of the under-surfaces of their digits, which 
appear to act in somewhat the same fashion as the sucker 
of the Remora, or Sucking-fish. 

The most important and distinctive characters of these 
Lizards are :-— 

Their vertebrz are amphicelous. 

Neither the upper nor the lower temporal arcades are 
ossified, the postfrontal being connected with .the squa- 
mosal, and the maxilla with the quadrate, by ligament. 

The jugal is rudimentary, and the squamosal very small. 

There are no eyelids, but the tegument becomes trans- 
parent as it is continued over the eyes. The integument is 
soft, or coriaceous, not scaly. 


2. The Rhynchocephala.—This division contains only the 
very remarkable genus Sphenodon (otherwise Hatteria, or 
Rhynchocephalus). The vertebrz are biconcave. Some of 
the ribs have recurrent “uncinate” processes, as in Birds 
and Crocodiles. The sternal and vertebral ribs are con- 
nected by an articulation, and there is a very peculiar 
system of abdominal ribs. The infra-temporal arcade is 
completely osseous in this, but in no other recent, lizard. 
The quadrate bone is immoveably fixed, not merely by an- 
kylosis with the squamosal, quadrato-jugal, and pterygoid, 
but by the ossification of the strong membrane, which, in 
Lizards in general, extends between the quadrate, the ptery- 


Q 


2236 THE ANATOMY OF VERTEBRATED ANIMALS. 


goid, and the skull, and bounds the front walls of the 
tympanum. The dentary pieces of the mandible are not 
suturally united. The premaxille are not ankylosed to- 
gether, and, as in some other Lizards (e. g. Uromastix), have 
a beak-like form, the large premaxillary teeth becoming 
completely fused with the bony substance of the pre- 
maxille. There is a longitudinal series of teeth upon the 
palatine bone running parallel with those on the maxilla, 
and the mandibular teeth are received into the deep longi- 
tudinal groove which lies between the maxillary and the 
palatine teeth. By mutual attrition, the three series of 
teeth wear one another down to the bone in such a way, 
that the mandibular teeth are ground to an edge, while the 
maxillary and palatine teeth are worn upon their inner and 
outer faces respectively. 

The extinct Lizards of the Triassic age, Rhynchosaurus 
and Hyperodapedon, appear to have been very closely allied 
to Sphenodon. 


3. The Homeosauria.—The remains of Lizards of small size, 
and agreeing in the most important points of their osteology 
with the ordinary Lacertilia, but having amphiccelous ver- 
tebre, have been found in the older Mesozoic rocks, from 
the Solenhofen slates to the Trias inclusively. They cannot 
be identified with either the Rhynchocephala, or the Ascala- 
bota, and may be provisionally grouped as Homeosawria. 
The genera’ Homeosaurus, Sapheosawrus, and Telerpeton 
belong to this group. 


4. The Protorosauria.—These are the oldest known Sau- 
ropsida, their remains occurring in the Kupferschiefer of 
Thuringia, which is a part of the Permian formation, and 
in rocks of corresponding age in this country; but no more 
modern representatives of this group are known. 

The Thuringian Lizard (Protorosawrus) does not appear to 
have attained a length of more than six or seven feet. 
The neck is remarkably long, the cervical region being 
equal to the dorsal in length, and it bears a skull of mode- 


THE PROTOROSAURIA. 227 


rate size. The tail is long and slender, and the limbs well 
developed, as in the existing Monitors. Notwithstanding 
the length of the neck, it contained not more than nine, 
possibly not more than seven, vertebr, which, except the 
atlas, are remarkably stout and strong. There are about 
eighteen or nineteen dorsal, two (or not more than three) 
sacral, and more than thirty caudal vertebre. In all these 
vertebrz the neurocentral suture is completely obliterated, 
and the centra are slightly concave at each end. The side 
of each cervical vertebra, after the atlas, presents, near its 
anterior edge, a small tubercle, with which the head of a 
slender styliform rib articulates. The transverse processes 
of the dorsal vertebree are very short, antero-posteriorly 
flattened, plates, and the strong ribs are articulated with 
them by undivided heads. The sternum has not been 
preserved. In the abdominal region of some specimens, 
numerous short and filiform bones appear to represent, 
and correspond with, the abdominal ribs of Plesiosawria 
and Crocodilia. 

The spinous processes of the caudal vertebre, up to near 
the middle of the tail, have the ordinary structure; but 
beyond this point they bifureate, so that each vertebra 
seems to have two spinous processes, a peculiarity unknown 
in other Lacertilia. 

The large chevron bones are articulated between the 
bodies of the caudal vertebre, as in the Crocodilia, but also 
as in some Lacertilia, such as the Geckos. The skull is 
preserved in one specimen only, and in that it is in such an 
imperfect condition that the details of its structure cannot 
be made out. The teeth, however, are nearly straight, 
conical, and sharply pointed, and seem to have been im- 
planted in distinct sockets, though there may be some doubt 
upon this point. 

The pectoral and pelvic arches are large and strong. The 
fore limbs are shorter than the hind limbs, and each hmb 
bears five digits. The manus contains certainly eight, pos- 
sibly nine, carpal bones, five of which correspond with the 
metacarpals. The number of phalanges is exactly the same 


228 THE ANATOMY OF VERTEBRATED ANIMALS. 


asin most existing Lacertilia (2, 3,4,5,3). In the pes, again; 
the number of the phalanges is characteristically Lacertilian 
(2, 3, 4, 5, 4), and so is the form of the fifth metatarsal; but the 
two proximal tarsal bones appear to have been less closely 
connected together than im existing Lacertilia, and there 
were, at fewest, three distal tarsal bones with which the 
metatarsals articulated, and by which they were completely 
separated from the proximal tarsals. Among existing 
Lacertilia an arrangement similar to this is met with only 
in the Ascalabota. 


5—9. The great majority of existing Lacertilia belong to 
_ the procelous Kionocrania, with not more than nine cervical 
vertebre, and they deviate but little in their osteology from 
the general type of organization which has been described. 

The skull in the Platynota, or Monitors of the Old World, 
with the American genus Heloderma, differs from that of 
any other Lacertilia in the circumstance that the nasal 
bones are represented by a single narrow ossification. 

In the genus Lacerta the bones of the roof of the skull 
become continued into dermal ossifications, which roof 
over the supra-temporal fosse. In the Chalcidea and Scin- 
coidea, in which the body sometimes becomes elongated and 
snakelike, and the limbs rudimentary, the supra- and infra- 
temporal arcades are apt to be ligamentous, and the post- 
frontals and squamosals small. 


10. The Dolichosawia.—A very singular Lacertilian found 
in the Chalk, and resembling an eel in form and size, has been 


bat-crmmarnte 


described by Professor Owen under the name of Dolicho- — 


saurus. It possesses an exceedingly elongated body, but is 
provided with limbs and with a distinct sacrum, consisting of 
two vertebre. Its most remarkable peculiarity, however, 
lies in the number of its cervical vertebree, which were not 
fewer than seventeen. 


11. The Mosasawria.—The cretaceous rocks of Hurope 
and America have yielded another remarkable long-bodied 


THE MOSASAURIA. ; 229 


marine Lacertilian, which attained a great size. This is 
the genus Mosasaurus, remains of which were first obtained 
from the Chalk near Maestricht. 

Highty-seven vertebre belonging to one individual of this 
genus have been discovered, and when put together had a 
length of thirteen-and-a-half feet. But there were certainly 
many more vertebre than these, as those of the end of the 
tail are wanting, and there are gaps in the series of the 
rest. The centres of all these vertebre are concave in 
front and convex behind; but the concavities and con- 
vexities are less marked in the posterior, than in the an- 
terior, vertebre. The atlas and axis are not well preserved 
in this series of vertebrz, but the nme following all have 
inferior spinous processes, which become shorter in the 
posterior vertebre, and, in the last two, are represented 
only by a pair of low elevations. They have short trans- 
verse processes, each terminated by a simple costal facet. 
It is probable that these are cervical vertebre. In the 
dorsal vertebre, of which there must have been at fewest 
twenty-four, the transverse processes, which are strong in 
the anterior, gradually diminish in size in the posterior, 
vertebre. There are no inferior processes. All the verte- 
brz which have been mentioned hitherto have the circum- 
ference of the centrum rounded, and are articulated to one 
another by zygapophyses. But a series of eleven, which 
follow them, have no zygapophyses, and the centra assume 
a more or less triangular prismatic form. The transverse 
processes of these are long, thin, and bent a little downwards 
and backwards. These seem to have been lumbar vertebre. 
No sacrum has been discovered, but there are numerous 
caudal vertebre with transverse processes, pentagonally 
prismatic centres, and chevron bones attached to the middle 
of the under-surface of each. In the nine posterior of these 
caudal vertebre the bodies are cylindrical, the transverse 
processes are obsolete, and the chevron bones, ankylosed to 
the undersides of the centra, are long, inclined backwards, 
and overlap one another. And, in the hindermost caudals, 
the spinous processes and the chevron bones disappear. 


230 THE ANATOMY OF VERTEBRATED ANIMALS. 


There were strong ribs, but nothing is known with cer- 
tainty of the sternum, limb-arches, or other bones. 

The very complete specimens of the skull that have been 
discovered prove that its structure was very similar to that 
of the Old World Monitors in the large size of the nasal 
apertures, and the fusion of the nasals into a narrow bone. 
But sharp recurved teeth are ankylosed by thew bases, 
not only to the premaxillary, maxillary, and dentary bones, 
but also to the pterygoid bones; and these pterygoid 
bones are unlike those of other Lacertilia, not only m 
form, but because they articulate together in the middle 
line for a considerable distance behind the posterior nasal 
aperture. 


12. The Amphisbenoida.—These lizards have completely 
snakelike bodies; one genus of the group (Chirotes) has 
a pau of small pectoral members, but the rest are apodal. 
The integument of the body is not scaly, but its surface is 
divided into small rectangular aree arranged in transverse 
rows. The tail is exceedingly short, so that the vent is 
close to the end of the body. 

The numerous procelous vertebre have less elliptical 
articular faces than those of the typical Lacertilia. There 
isno sacrum, and all the precaudal vertebre, except the one 
or two of the most anterior, have ribs. The representatives 
of the chevron bones in the tail are firmly united with the 
centra of the vertebre. The vertebre have no zygantrum 
nor zygosphene. Amphisbena has no sternum. Chirotes has 
a sternum, but it is not united with the ribs. 

The skull, unlike that of Lacertilia in general, developes no 
interorbital septum. In this respect, and in the complete 
closure of its anterolateral walls by bone, it resembles the 
Ophidian cranium. There is no columella. Postfrontals 
are absent, and the squamosal is very small. The quadrate 
bone is small, and inclined not only downwards, but for- 
wards, in a manner unknown in other Lacertilia. The two 
rami of the mandible are firmly united by suture. 

In Amphisbena the premaxille bear two rows of teeth, 


THE CHAMALEONIDA. 231 


one behind the other, and one tooth lies upon the symphysis 
of the premaxiile. 


13. The Chameleonida.—The Chameleons are distin- 
guished from the Kionocrania not only by the negative 
character of the absence of the columella, which they share 
with the preceding group, but by a number of very im- 
portant positive features. Among these I may mention 
the soft and tuberculated skin, with its changing hues; the 
absence of any tympanum; the prehensile tail; and the 
very peculiarly modified feet. The digits are arranged in 
bundles of two and three, the manus having the pollex, the 
index, and the medius, syndactylous and turned inwards; 
while, in the foot, it is the hallux and index only which are 
thus united and turned inwards, the three other toes being 
similarly connected together by integument, as far_as the 
ungual phalanges, and directed outwards. To these cha- 
racters may be added the remarkable tongue, capable of 
protrusion and retraction with almost lightning rapidity. 

The vertebre of the Chameleons are similar in their 
characters to those of the procelous Kionocrania. The 
sacrum is composed of only two vertebre. Only a few of 
the anterior ribs are united with the sternum. A large num- 
ber of the posterior ribs, as we have already seen to be the 
case in the Gecko, unite together in the mid-line, and form 
continuous hoops across the ventral wall of the abdomen. 

But it is in the structure of the cranium that the 
Chameleonida depart most completely from the ordinary 
Lacertilian type. The parietal bone is not moveable 
upon the occipital, the supra-occipital sending up a median 
ridge, which unites with the base of a corresponding crest 
or process extending backwards for a considerable dis- 
tance from the middle line of the parietal bone. The 
summit of this sagittal crest is Jomed by two curved pro- 
longations of the squamosal, the three giving the occipital 
region of the Chameleon its remarkable casque-like form. 
The frontal bone is comparatively small and single, and 
the nasals are very narrow, and do not bound any part of 


232 THE ANATOMY OF VERTEBRATED ANIMALS. 


the anterior nasal apertures. These apertures, in fact, are 
situated upon the sides of the forepart of the skull, and are 
separated from the nasal bones, in part, by a membrane 
which stretches outwards from the nasal bones; and external 
to this by a prolongation forwards of the prefrontal bone, 
which unites with the maxilla, and in some specimens of 
Chameleons is prolonged forwards into a great osseous horn, 
projecting from the sides of the front part of the snout. 

The orbit is closed behind by the ascending process of 
the jugal bone, but there is no quadrato-jugal. The quad- 
rate bone itself is not, as in most other Lacertilia, move- 
able upon the sides of the skull, but is firmly ankylosed 
with the bones which le adjacent to its upper end. The 
pterygoid bones are produced downwards; and, by a very 
exceptional peculiarity, do not articulate with the quadrate 
bones, but are connected with them only by fibrous tissue. 
In the lower jaw, the dentary piece takes up a very much 
larger proportion of the ramus than is the case in other 
Lacertilia. The basal portion of the hyoid is represented 
by a long median cylindrical entoglossal bone, and its pos- 
terior cornua are much stronger and longer than the anterior 
pair. In the pectoral arch the scapula and coracoid are 
remarkably longer and narrower than in other Lacertilia. 
There are no clavicles, and the interclavicle is wanting, the 
sternum being represented only by its rhomboidal ossified 
cartilage. Again, in the pelvic arch, the ilium is long and 
narrow, and its long axis is directed nearly vertically to 
that of the trunk—in which respect the Chameleons differ 
very much from the ordinary Lacertilia. There is no os 
cloace. 

The carpus and the tarsus have a very singular structure. 
In the carpus there are two proximal bones, articulated with 
the radius and the ulna respectively. A single spheroidal 
bone is articulated with these, and with the five proximal 
constituents of the digits. Besides these, there is an ossicle 
representing the pisiform. In the tarsus there are also four 
bones, two articulated with the tibia and fibula respectively, 
a third below and between them, and a fourth distal bone 


THE OPHIDIA. 233 


articulating with the five proximal bones of the digits. In 


both manus and pes the number of the phalanges, count- 
ing from the preaxial to the postaxial side, is 2, 3, 4, 4, 3. 


TV. The Opuip1a.—This order of Reptiles has been 
divided as follows :— 


A. The palatine bones widely separated, and their long axes 
longitudinal; a transverse bone; the pterygoids united 
with the quadrate bones. 

a. None of the maxillary teeth grooved or canaliculated. 


1. Aglyphodontia. 
b. Some of the posterior maxillary teeth grooved. 
2. Opisthoglyphia. 
ce. Grooved anterior maxillary teeth succeeded by solid teeth. 


3. Proteroglyphia. 
d. Maxillary teeth few, canaliculated, and fanglike. 


4, Solenoglyphia. 


B. The palatine bones meet, or nearly meet, in the base of the 
skull, and their long axes are transverse; no transverse 
bone; the pterygoids are not connected with the quadrate 
bone. 


5. Typhlopide. 


All the Snakes possess a scaly epidermic investment, 
which is usually shed in one piece, and reproduced at defi- 
nite intervals. Asa general rule these scales are flat, and 
overlap one another; but sometimes, as in Acrochordus, 
they become more tubercle-like, and do not overlap. In the 
Rattlesnakes (Crotalus) the body is terminated by several 
loosely-conjoined rings of horny matter, which consist of 
the modified epidermis of the end of the tail. 

The derm does not become ossified in the Ophidia. 


The number of the vertebre in the snakes is always con- 
siderable, and in some cases becomes very great, amounting 
to more than four hundred in some of the large Pythons. 
The spinal column is divisible only into caudal and pre- 
caudal regions, as there is no sacrum, nor any distinction 
between cervical, dorsal, and lumbar vertebre. The atlas 


234 THE ANATOMY OF VERTEBRATED ANIMALS. 


and the odontoid vertebra are similar to those of the 
Lizards, and the atlas is the only precaudal vertebra which 
is devoid of ribs. The centra have nearly hemispherical 
articular surfaces, and thus differ from those of ordinary 
Lacertilia, while the superadded articular processes found 
only in certain Lizards attain a great development in the 
Snakes. The zygapophyses are broad and flattened, and the 
outer surfaces of the anterior pair are commonly prolonged 
into a process. The anterior surface of the arch above the 


Fig, 71. 


Fig. 71.—Anterior and posterior views of the dorsal vertebra of a 
Python :—z. s., zygosphene; z.a., zygantrum; p. z., prezygapo- 
physes ; pt. z., postzygapophyses ; ¢. p., transverse processes. 


neural canal is produced into a strong wedge-shaped zygo- 
sphene, which fits into a corresponding zygantrum of the 
next preceding vertebra; and, on the posterior surface of 
the arch, there is a zygantrum for the zygosphene of the 
next preceding vertebra. (Fig. 71.) 

The transverse processes are short and tubercle-like, and 
the heads of the ribs which articulate with them are simple. 
Each rib usually gives off a short upward process at a little 
distance from its head; it is curved, usually hollow, and 
terminates, inferiorly, in a cartilage which is always free, no 
trace of a sternum existing. Strong descending processes 
are given off from the undersides of many of the presacral 


THE OPHIDIA. 235 


vertebre. In the caudal region, elongated transverse pro- 
cesses take the place of the ribs. Chevron bones, like those 
of the Lacertilia, do not exist, but the caudal vertebre pos- 
sess bifurcated descending processes, which bear similar 
relations to the caudal vessels. 

The skull differs from the ordinary Lacertilian cranium 
in the following points :— 

1. That vertical elevation and lateral compression of the 
presphenoidal region, which give rise to the interorbital 
septum, is wanting; the floor of the cranium being nearly 
flat, and the vertical height of its cavity diminishing gra- 
dually in front, so that it remains spacious between the 
eyes, and in the frontal region generally. The periotic 
region is not produced into parotic processes. 

2. The boundary-walls of the front half of the cranial 
cavity are as well ossified as those of its posterior moiety, 
and the bones which constitute the brain-case are firmly 
united together. 

3. On the other hand, the nasal segment is less com- 
pletely ossified, and may be moveable. The premaxille are 
usually represented by a single small bone, which very 
rarely bears teeth. It is connected with the maxillz only 
by fibrous tissue. 

4, The palatine bones never unite directly with the vomer, 
or with the base of the skull, but they are usually connected 
with the maxille by transverse bones; and, by the ptery- 
goids, with the mobile quadrate bones. Hence the connec- 
tion of the palato-maxillary apparatus with the other 
bones of the skull is always less close in Ophidia than in 
Lacertilia, and sometimes it is exceedingly lax. 

5. The two rami of the mandible are united at the sym- 
physis only by ligamentous fibres, which are often extremely 
elastic. 

6. The hyoidean apparatus is very rudimentary, consist- 
ing only of a pair of cartilaginous filaments, which are 
united together in front, and lie parallel with one another 
beneath the trachea. They have no connection with the 
skull. 


236 THE ANATOMY OF VERTEBRATED ANIMALS. 


These are the most apparent differences between the 
Ophidian and the Lacertilian skull. But there are others, 
of a less obvious but more remarkable character, by which 
the skulls of the Ophidian depart not only from’ that of the 
Lizard, but from that of other Vertebrata. Thus the basi- 
sphenoid passes in front of the sella turcica, into a great 
rostrum, which extends forwards to the ethmoidal region, 
and probably results from a parasphenoidal ossification. In 
many adult Ophidia two cartilaginous rods lie in grooves on 


Fig. 72.—The skull of a Python, viewed from the left side, and in 
longitudinal section: Cm, stapes; 7, turbinal bone. 


the upper face of this rostrum, and pass behind into the 
basisphenoid, while in front they are continued into the 
cartilaginous ethmoidal septum. These rods are the tra- 
becule cranii of the foetus, which do not become united in 
Snakes, as they do in all the other abranchiate Vertebrata. 
The roof and side-walls of the Ophidian skull are com- 
pleted in front of the occipital segment, by two pairs of 
bones, which appear to be parietals and frontals. The 
“frontal” bones not only completely wall in the sides of 


THE OPHIDIA. 237 


the frontal region, but extend inwards below, and meet in 
the middle line, above the basisphenoidal rostrum and the 
persistent trabecule. The “ parietals ” unite suturally 
with the basisphenoid. These relations are not usual 
in true frontals or parietals (though the latter unite with 
the basisphenoid in Chelonia, and the frontals unite in 
the middle line of the floor of the skull in some Mammals) ; 
and as there are only two bones in the place of four in 
this region of the skull, it becomes a matter for inquiry 
whether the two bones, on each side, respectively repre- 
sent orbitosphenoids + frontals, and alisphenoids + 
parietals; or whether they represent overgrown frontals 
and parietals only; or whether, lastly, they are the result 
of an excessive development of the orbitesphenoids and 
alisphenoids, true frontals and parietals being absent. 
According to Rathke’s elaborate investigation into the 
development of the skull in Coluber natrix, the two bones 
on each side are formed from single centres of ossifi- 
cation, which appear in patches of “cartilage,” which 
are situated, at first, in the superolateral regions of the 
skull, in the place normally occupied by orbitosphenoids 
and alisphenoids, and that these grow up and meet in the 
middle line. In this case the bones in question are orbito- 
sphenoids and alisphenoids, and Ophidia have no true 
frontals or parietals; but the existence of so remarkable a 
deviation from the ordinary construction of the vertebrate 
skull cannot be admitted until the development of the 
Snake’s skull has been carefully re-examined. 

The Ophidia usually possess well-developed postfrontals, 
and they have large membrane bones in front of the orbit, 
which lie upon the cartilaginous nasal chambers, and are 
ordinarily regarded as lachrymals. Large nasals lie upon 
the upper surface of the nasal capsule between the lachry- 
mals; and, forming the floor of the front part of the nasal 
chamber, on each side, is a large concavo-convex bone 
(71, Fig. 72), which extends from the ethmoidal septum to the 
maxilla, protects the nasal gland, and is commonly termed 
a turbinal, though, if it be a membrane bone, it does not 


238 THE ANATOMY OF VERTEBRATED ANIMALS. 


truly correspond with the turbinals of the higher Verte- 
brata. The squamosals are usually well developed. There 
is no jugal, or quadrato-jugal. 

Though the general conformation of the skull in the 
Ophidia is that which has now been described, it presents 
remarkable modifications in different members of the 
order, especially in the form and disposition of the bones 
of the jaws. In the great majority of the Ophidia, the 
elongated palatine bones have their long axes longitudinal, 
lie on the outer sides of the internal nasal apertures, and 
do not enter into the formation of the posterior boundaries 
of those apertures. Hach is connected by a transverse bone 
with the maxilla, which lies at the side of the oral cavity; 
and the pterygoids diverge posteriorly towards the quadrate 
bones, with which they are connected by ligaments. 

But, in the remarkable group of the Typhlopide, the 
slender palatine bones meet upon the base of the skull in 
the middle line, and are directed transversely, in such a 
manner as to bound the posterior nasal apertures behind, 
as in the Batrachia. There is no transverse bone. The 
pterygoids lie parallel with one another under the base of 
the skull, and are not connected with the quadrate bones. 
The maxille are short plates of bone which are connected 
with the outer extremities of the palatine bones, and are 
directed obliquely towards the middle line of the oral cavity, 
into which their free edges, armed with teeth, depend. 

Again, the first-mentioned, or typical, form of Ophidian 
skull exhibits two extreme modifications, between which lie 
all intermediate gradations. At the one end of the scale 
are the non-venomous Snakes, and especially Python and 
Tortrix (which belong to the division Aglyphodontia) ; at the 
other the poisonous Snakes, and especially Crotalus (Soleno- 
glyphia). 

Thus, Python (Figs. 72 & 73) has well-marked premaxille, 
large maxillary bones, palatine bones which are firmly united 
with the pterygoids, and transverse bones which bind the 
maxillaries and palato-pterygoid bars into one solid frame- 
work. 


THE OPHIDIA. 239 


The maxillaries give attachment to a long series of re- 
curved teeth, which are not very unequal in size. And 
Python (like Tortrix, but unlike all other Ophidia) pos- 
sesses teeth in the premaxille. 

The squamosal bones are very long, and adhere to the 
skull, upon which they are slightly 
moveable, only by their anterior 
ends; and the quadrate bones are 
borne upon the posterior ends of 
the squamosals, and are thus, as 
it were, thrust away from the 
walls of the skull. The rami of the 
mandible are loosely connected by 
an elastic symphysial ligament. 
Thus, not only can these rami be 
widely separated from one another, 
but the squamosal and quadrate 
bones constitute a kind of jointed 
lever, the straightening of which 
permits of the separation of the 
mandibles from the base of the 
skull. And all these arrangements, 
taken together, allow of that im- 
mense distension of the throat 
which is requisite for the passage 
of the large and undivided prey of 
the serpent. 

In Tortriz, this mechanism does 
not exist, the short quadrate bone Fig. 73.—Under-view of 
being directly articulated with the the left half of the skull 
skull, while the squamosal, like the meee te ee 
postfrontal, is rudimentary. The 
maxillary bones are also almost fixed to the skull. 

In the Rattlesnakes (Crotalus, Fig. 74), the premaxille 
are very small and toothless. ‘The maxillary bone has 
no longer the form of an elongated bar, but is short, 
subeylindrical, and hollow; its cavity lodges the fossa 
formed by the integument in front of the eye, which is so 


240 THE ANATOMY OF VERTEBRATED ANIMALS. 


conspicuous in these, and sundry other, poisonous Snakes. 
The upper and inner part of the maxilla articulates with a 


pulleylike surface furnished to it by the lachrymal, so that 


the maxilla plays freely backwards and forwards upon that 
bone. The lachrymal, again, has a certain amount of motion 
upon the frontal. The upper edge of the posterior wall of 
the maxilla is articulated by a hingelike joint with the 
anterior end of the transverse bone, which has the form of 
an extremely elongated and flattened bar connected pos- 
teriorly with the pterygoid. 


Fig. 74.—A, the skull of Crotalus, viewed from the left side; B, a 
transverse section taken at the point Bin Fig. A, showing 7, the 
persistent cartilaginous trabeculae. ‘The maxilla is supposed to be 
transparent, and the anterior half of the palatine bone is seen 
through it. 


The latter is long and stout, and, as usual, is united, be-- 
hind, with the distal end of the quadrate bone. In front of, 
and internal to, its union with the transverse it is prolonged 
forwards, and becomes united, by a moveable joint, with the 
short palatine bone, which is flattened from side to side, 


THE OPHIDIA. 241 


and lies on the outer side of the posterior nasal aperture. 
Its anterior end is connected only by fibrous tissue with the 
base of the skull. The inferior edge of the palatine bears 
a few small teeth, and other sharp, recurved, solid teeth are 
attached to the under-surface of the anterior moiety of 
the pterygoid. 

When the mouth is shut, the axis of the quadrate bone 
is inclined downwards and backwards. The pterygoid, 
thrown as far back as it can go, straightens the pterygo- 
palatine joint, and causes the axes of the palatine and 
pterygoid bones to coincide. The transverse, also carried 
back by the pterygoid, similarly pulls the posterior part of 
the maxilla, and causes its proper palatine face, to which 
the great channeled poison-fangs are attached, to look 
backwards. Hence these fangs lie along the roof of the 
mouth, concealed between folds of the mucous membrane. 
But, when the animal opens its mouth for the purpose of 
striking its prey, the digastric muscle, pulling up the angle 
of the mandible, at the same time thrusts the distal end 
of the quadrate bone forwards, This necessitates the 
pushing forward of the pterygoid, the result of which is 
twofold: firstly, the bending of the pterygo-palatine joint; 
secondly, the partial rotation of the maxillary upon its 
lachrymal joint, the hinder edge of the maxillary being 
thrust downwards and forwards. In virtue of this rota- 
tion of the maxillary, through about a quarter of a circle, 
the dentigerous face of the maxilla looks downwards, and 
even a little forwards, instead of backwards, and the fangs 
are erected into a vertical position. The snake “strikes ;” 
by the simultaneous contraction of the crotaphite muscle, 
part of which extends over the poison-gland, the poison 
is injected into the wound through the canal of the fang; 
and, this being withdrawn, the mouth is shut, all the pre- 
vious movements are reversed, and the parts return to 
their first position. 


No Ophidian possesses any trace of anterior extremities, 
but the Typhlopide, the Pythons, Boas, and Tortrices, have 
R 


242, THE ANATOMY OF VERTEBRATED ANIMALS. 


rudiments of a pelvis, and the latter Snakes even possess 
very short representatives of hind limbs terminated by 
claws. 

The teeth of the Ophidia are short and conical, and 
become ankylosed to the bones by which they are sup- 
ported. They may be developed in the premaxillaries, max- 
illaries, palatines, pterygoids, and the dentary piece of the 
mandible, but their presence in the premaxillaries is excep- 
tional. In Uropeltis and some other genera, there are no 
palatine teeth ; and in the egg-eating African snake, Rachio- 
don, the teeth are small and rudimentary upon all the bones 
which usually bear them. But the inferior spines of eight 
or nine of the anterior vertebre are long, and tipped, at 
their apices, with a dense enamel-like substance. These 
project through the dorsal wall of the esophagus into its 
cavity, and the eggs, which are swallowed whole, are thus 
broken in a position in which all their contents must neces- 
sarily be saved. 

In the majority of the non-venomous Snakes the teeth are 
simply conical, but in the others, and in all the poisonous 
Snakes, some of the maxillary teeth (which are usually 
longer than the rest) become grooved in front. In the 
Solenoglyphia, or Vipers and Rattlesnakes, the maxillary 
teeth are reduced to two or three long fangs, the groove in 
the front of which is converted into a canal open at each 
end, by the meeting of its edges. The teeth of the Snakes 
are replaced by others which are developed close to the 
bases of the old ones. 

Ophidia are not known in the fossil state before the 
older tertiaries. 


V. The IcutTHyosavurRiA.—In its general form Ichthyo- 
saurus presents a good deal of resemblance to a Cetacean. 
The head is enormous, and passes at once into the trunk, 
so that there is no more appearance of a neck than in a 
Porpoise, and the body tapers off behind, much as would 
happen in the latter animal were it devoid of a caudal fin. 
Indeed, there is some reason to suspect that the tail of 


2 


THE ICHTHYOSAURIA. 243 


Tehthyosawrus may have been provided with a sort of finlike 
expansion of the integument. This fishlike body was pro- 
pelled, like that of the Plesiosaurus, by four paddles; but 
the anterior paddles were placed close behind the head, and 
were, generally, very much larger than the posterior ones. 


iy, ive 
VIEL ivorieunince 


Fig. 75.—A restoration of Ichthyosaurus. The existence of the caudal 
fin is doubtful. 


The spinal column is only distinguished into two regions, 
caudal and precaudal, inasmuch as the ribs, beginning at the 
anterior part of the neck, are continued, without being 
connected with the sternum, to the posterior end of the 
body; andthereis nosacrum. Thecaudal region, however, 
is distinguished by the chevron bones which are attached 
beneath its vertebre. The vertebre of Ichthyosawia in 
general have certain characters by which they differ from 
those of all other Vertebrata. (Fig. 76, C.) Not only are 
the centra flattened discs, very much broader and higher 
than they are long, and deeply biconcave (circumstances 
in which they resemble the vertebre of some Labyrintho- 
donts and Fishes), but the only transverse processes they 
possess are tubercles, developed from the sides of these 
centra; and the neural arches are connected with two flat 
surfaces, one on each side of the middle line of the upper 
surface of the vertebra, by mere synchondroses. The neural 
arches themselves are forked bones, with only rudiments of 
zygapophyses, and in the greater part of the body do not 
become articulated with one another at all. 

In the cervical region, if one may call “neck” the most 
anterior part of the vertebral column, the front part of 
the lateral surface of each vertebra presents two separate 


Fig, 76.—Different parts of the skeleton of Ichthyosaurus intermedius, 
drawn to the same scale. A, the skull; B, the fore limb:—H, 
humerus; #, radius; U, ulna; 7. z. v., radiale, intermeduim, ulnare ; 
Cp, carpalia; 1, 2, 3, 4,5, digits; m.7. m.w. radial and ulnar marginal 
ossicles.—C, a dorsal vertebra, with the ribs (2) and ventral ossifi- 
cations (V.O).—D, the hind limb: F, femur; 7; tibia; 6, fibula ; 
t, i, f, tibiale, intermedium, fibulare; 7s, tarsalia; Jt, metatarsalia ; 
Ph, phalanges ; m, th, tibial marginal ossicles.—E, the pectoral arch, 
seen from the ventral side; F, the same aspect of the pelvic arch. 


THE ICHTHYOSAURIA. 245 


elevations, or articular surfaces, which are at first situated in 
the upper half of the lateral surface. Towards the posterior 
half of the dorsal region they descend, and, gradually 
approaching one another, coalesce into one in the caudal 
vertebre. The form of the proximal ends of the ribs cor- 
responds with the arrangement of these tubercles; for, 
where they are separate, the proximal end of the rb is 
forked. The lower fork, or capitulum, goes to the capitular, 
or lower, tubercle, and the upper branch, or tuberculum, to 
the upper, or tubercular, elevation. In the caudal region, 
where the articular surface is single, the proximal end of 
the rib is alsoundivided. In the caudal region the ribs are 
short and straight, but in the precaudal region they are 
stout and curved, and much longer in the middle than at 
either end of the series. The atlas and axis resemble the 
other vertebrz in their general form: but a wedge-shaped 
bone is, as it were, let in between their opposed lower edges ; 
and a similar bone, attached to the under-part of the con- 
cave face of the centrum of the atlas, serves to complete the 
cup for the occipital condyle. 

The skull of Ichthyosaurus (Fig. 76, A) is remarkable for 
the great elongation and tapering form of the snout, the 
huge orbits, the great supra-temporal fossz, and the closing 
over of the infra-temporal fossz by plates of bone. Again, 
the two rami of the mandible are united in a symphysis, 
which, for length, is comparable to that observed in the 
modern Gavials and in the ancient Teleosawria. The basi- 
occipital bone furnishes the rounded articular condyle to 
the first vertebra, and becomes very stout and thick in front. 
It appears to have been ankylosed neither with the basi- 
sphenoid nor with the basi-occipital. The latter bones are 
adapted to its sides, and, together with the supra-occipital, 
which is interposed between them above, circumscribe the 
occipital foramen. The basisphenoid, a deep and stout 
bone, is produced in front into a long and slender para- 
sphenoidal rostrum. There do not appear to have been 
any ossified alisphenoids. The parietals remain separate 
throughout life; and, in some species, not merely present 


246 THE ANATOMY OF VERTEBRATED ANIMALS. 


a great parietal foramen close to the coronal suture, but 
are completely divided by a median fissure. Ossified pre- 
sphenoids and orbitosphenoids appear to have been alto- 
gether absent, and the frontal bones are relatively small. 
The pro-otic bones are, as usual, situated in front of the 
ex-occipitals; and between the latter and them there may 
sometimes be discerned a conical bone with a broad base, 
which appears to be fitted in between the ex-occipital and 
the pro-otic. If this bone were not so large, it might well 
be regarded as a stapes, but it is possible that, as Cuvier 
suggests, it answers to the separate opisthotic of the 
Chelonia. 

In the naso-premaxillary segment, the nasal bones, con- 
tinuing the direction of the frontals, attain considerable 
size, but the premaxille make up by far the greater part 
of the snout. The maxille are reduced, as in birds, to 
comparatively small and slender rodlike bones, bounding 
only a fraction of the gape. The vomers are elongated, 
and situated in the middle line on the underside of the 
snout. 

The nostrils are small apertures close to the orbits, 
bounded by the nasal, lachrymal, and premaxillary bones. 

On each side of the frontal there is a large prefrontal, 
which passes back above to meet the postfrontal, and thus 
bound the orbit. Below, the maxilla is connected with a 
jugal. From the postfrontal to the jugal, the posterior 
margin of the orbit is constituted by a distinct, curved, 
postorbital bone (Fig. 76, A, Pt.0). A broad and flat 
quadrato-jugal (Q.j.) passes from the end of the jugal to 
the lower end of the quadrate, and covers in the lower 
and posterior part of the infra-temporal fossa. The space 
between this bone, the postorbital, the postfrontal, and 
the squamosal is occupied by another flattened bone (Fig. 
76, A, St.), which Cuvier calls the temporal, but which 
does not appear to have any precise homologue among 
other Reptilia. The squamosal bone is very large and 
stout, and forms the postero-external angle of the skull. 
From this point it sends a process forwards to meet the 


THE ICHTHYOSAURIA. 247 


postfrontal, inwards to unite with the parietal, and down- 
wards to become connected with the pterygoid. A strong 
and stout quadrate bone is connected with the exterior of 
the skull, and presents a pulley-like surface to the articular 
piece of the mandible. 

On the under-surface of the skull the long and slender 
palatine bones are seen, bounding the posterior nares, which 
are situated far forwards. Behind, and separated by an 
interval traversed by the rostrum of the basisphenoid 
bone, the very large pterygoids commence, by slender and 
pointed ends, which le on the inner side of the palatine 
bones at the level of the posterior nares. They then widen, 
and passing backwards with a slight outward curvature, 
on each side of the sphenoidal rostrum, end in three pro- 
cesses—one of which connects itself with the basisphenoid, 
another passes outwards and backwards to the quadrate, 
while the third runs upwards to the squamosal bone. 

The lower jaw is composed of two rami, which unite, 
anteriorly, in a very long symphysis. Hach ramus is com- 
posed of the normal six pieces, the splenial being remark- 
ably long, and entering extensively into the symphysis. 

We have no very clear knowledge of the structure of the 
hyoidean apparatus in this reptile. 

The pectoral arch (Fig. 76, E) consists, upon each side, 
of a narrow scapula (Sc.), having the direction usual in 
Lacertilia, and a broad coracoid (Co.), the inner edge of 
which does not overlap its fellow, but meets it throughout 
in the middle line, as in Plesiosawrus ; so that, in this genus 
also, the rhomboidal part of the sternum appears to have 
been absent or very small. 

But there is a very distinct T-shaped interclavicle (I.C1.), 
the backward prolongation of which is received between 
the anterior ends of the coracoids, while its horizontal bar 
is very closely united with the inner ends of two stout 
curved clavicles (Ol.), the outer extremities of which abut 
against, and are no less closely connected with, the upper 
part of the anterior edge of each scapula. This arrange- 
ment of the clavicles and interclavicle presents interesting 


248 THE ANATOMY OF VERTEBRATED ANIMALS. 


conditions intermediate between those observed in Nothosau- 
rus, on the one hand, and those common in the Lacertilia, on 
the other. 

The scapula and coracoid give rise by their junction to a 
glenoidal cavity, into which the thick head of the very short 
prismatic humerus (Fig. 76, B, H) is received. The distal 
end of the humerus presents two facets, which articulate 
with a couple of short flattened polygonal bones, which 
represent the radius and the ulna (BR, U). To these succeed 
two rows of smaller polygonal ossicles in the place of a 
carpus: three, representing the radiale, intermedium, and 
ulnare (r. i. u.), lie in the proximal row, and three or four 
carpalia (Cp.) in the distal row. With the distal carpal 
bones are connected, by means of the metacarpal ossicles 
(Mce.), longitudinal series of very numerous polygonal bones, 
adapted together by their edges, and becoming gradually 
smaller towards the distal extremity of each series. The 
number of complete series does not exceed five, and may be 
reduced to three—so that the paddle may be pentadactyle, 
tetradactyle, or tridactyle. An apparent multiplication of 
the number of digits arises from two causes: first, the 
occasional bifurcation of some of the digits; secondly, the 
superaddition of marginal bones* to the radial and to the 
ulnar edges of the manus (m.u.,m.r.). There is thus formed 
a paddle, which is unlike either that of a Cetacean, or that 
of a Plesiosaurus, or that of a Turtle—departing more than 
any of these structures from the ordinary form of verte- 
brate limb. 

There is no trace of any sternum behind the pectoral 
arch, but the abdominal walls were strengthened by a num- 
ber of transverse arcuated bones, similar to those observed in 
the Plesiosauria, though not so strong. Hach is composed of 
a median piece with pointed ends, and of some three, or more, 
lateral pieces, overlapping each other’s ends, on each side. 
(Fig. 76, C, V.O.) 


* T leave open the question of a polydactyle manus, such as 
whether these series of marginal _ exists in the Elasmobranch fishes. 
ossicles are remains of the digits 


THE CROCODILIA. 949 


The pelvis (Fig. 76, F) is not connected by bone with the 
vertebral column. It consists of an ilium (J/.), an ischium 
(Is.), and a pubis (Pb.), uniting together to form an aceta- 
bulum, while the pubis and ischium of each side meet in 
the middle line. The ischium is a narrow and almost rod- 
like bone, the pubis is somewhat broader, especially at its 
symphysial end. 

The hind limb (Fig. 76, D) has substantially the same 
structure as the fore limb, but is always smaller, and gene- 
rally of much less size. 

The only other bony structure appertaming to Ichthyo- 
saurus that need be noticed, is a circle of plates developed 
in the sclerotic of the enormous eye, which is frequently 
met with in a very perfect state of preservation. 

It is possible that the Ichthyosawria occur in the Trias; 
they abound in the Lias and in other rocks of Mesozoic 
date, up to, and including, the Chalk. 

Some attain gigantic dimensions, and many species have 
been founded by the differences in form and proportion of 
the body and of the teeth; but no one form is sufficiently 
different from the rest to justify its separation as a distinct 
genus. They may be roughly grouped into such as have 
relatively short snouts and short paddles, with four carpalia 
(I. intermedius, communis, &c.); and such as have longer 
snouts, long paddles, and three carpalia (I. longirostris, 
tenuirostris, platyodon). 


VI. The CrocopiL1a.—Crocodiles, the highest living 
Reptilia, are Lacertilian in form, with long tails and four 
well-developed limbs, the anterior pair being the shorter, 
and possessing five complete digits, while the hind feet are 
four-toed. With a single exception, the living species have 
nails on the three preaxial (radial and tibial) digits, so 
that two digits are without nails on the forefoot, and one 
on the hind-foot. The feet are webbed, but the degree to 
which the web is developed varies greatly. The nostrils are 
situated at the end of the long snout, and can be closed. 
The tympanic membranes are exposed, but a cutaneous 


250 THE ANATOMY OF VERTEBRATED ANIMALS. 


valve, or earlid, lies above each, and can be shut down 
over it. All are partially aquatic in habit, and some (the 
Gavials) are completely so. None of the existing genera 
are marine, though many ancient Crocodilia inhabited the 
sea. 

The dermal armour is composed of scutes covered by 
epidermic scales of corresponding form. When the armour 
is complete—as in Caiman and Jacare alone among existing 
Crocodilia, in Teleosaurus and Stagonolepis among extinct 
forms—it consists of transverse rows of quadrate bony plates, 
disposed so as to form a distinct dorsal and ventral shield, 
separated by soft integument, in the trunk, but united into 
continuous rings on the tail. The scutes of the same row 
are united suturally; those of each row overlap their suc- 
cessors, which present smooth facets to receive their under- 
surfaces. In existing Crocodilia, in the extinct Crocodilus 
Hastingsie, and in Stagonolepis, each ventral scute consists 
of two pieces, a small anterior and a large posterior, united 
by a suture. The scutes always exhibit a pitted sculpture, 
and those of the dorsal region are ridged longitudinally, 
while the ventral scales are always flat. More or fewer 
dorsal scutes exist in all crocodiles, and those upon the 
neck sometimes form distinct “nuchal” and “cervical” 
groups, distinct from the dorsal shield. The dorsal scutes 
do not always overlap, and the ventral scutes are absent, or 
incompietely ossified, in most existing Crocodilia. 

In these reptiles the vertebral column is always thoroughly 
ossified, and marked out into distinct cervical, dorsal, lumbar, 
sacral, and caudal regions. The number of the presacral ver- 
tebre is twenty-four; that of the sacral, two, in all the recent 
forms, and probably in the extinct genera also. The num- 
ber of the caudal vertebre varies, but is not less than 
thirty-five. The number of the cervical, dorsal, and lum- 
bar vertebrz varies; but there are usually nine of the first, 
eleven or twelve of the second, and four, or three, of the 
third description. 

In existing Crocodilia all the vertebre, except the atlas 
and axis, the two sacrals, and the first caudal, are procelous, 


THE CROCODILIA. 251 


The majority of the pre-cretaceous Crocodilia have the cor- 
responding vertebra amphiccelous, the concavities of the 
centra being very shallow. One genus, Streptospondylus, 
which is perhaps Crocodilian, has the anterior vertebre 
opisthoceelous. It is characteristic of the Crocodilia, that 
the centra of the vertebre are united by fibro-cartilages, 
and that the neurocentral sutures persist for a long time, 
or throughout life. 

The atlas is composed of four pieces, an upper median 
piece—which is sometimes divided into two, and is developed 
in membrane apart from the rest—being added to the 
three pieces found in Lacertilia and Chelonia, A large 
odontoid bone is closely united to, but not ankylosed with, 
the anterior flat face of the second vertebra. A pair of 
elongated, single-headed ribs are attached to the inferior 
piece of the atlas, and another similar pair to the os odon- 
toidum and to the second vertebra, by distinct capitular 
and tubercular processes. The other cervical vertebre all 
possess ribs with distinct and long capitula and tubercula— 
the latter attached above the neurocentral suture to the 
neural arch, the former to the centrum below the neuro- 
central suture. The body of each cervical rib, after the 
second, and as far as the seventh or eighth, is short, and 
prolonged in front of, as well as behind, the junction of the 
capitulum with the tuberculum; and the several ribs lie 
nearly parallel with the vertebral column, and overlap one 
another. The ribs of the eighth and ninth cervical vertebree 
are longer, and take on more the character of the dorsal ribs, 
the ninth having a terminal cartilage. 

The points to which the capitula and tubercula of the 
ribs are attached are raised into tubercles; and, by degrees, 
these become elongated into distinct capitular and tuber- 
cular processes, between which, in the third to the ninth 
vertebrz, the neurocentral suture passes. But in the tenth 
and in the eleventh vertebre, the capitular process, which 
lies nearer the neurocentral suture in the posterior than 
in the anterior cervical vertebre, rises upon the body of 
the vertebra to the level of the neurocentral suture, by 


252, THE ANATOMY OF VERTEBRATED ANIMALS. 


which it is traversed, and the tubercular process becomes 
longer thanit. (See Fig.5,p. 15.) The terminal cartilage is 
united with the sternum by a sternal rib, which may be- 
come more or less completely converted into a cartilage 
bone, and is articulated with the vertebral rib. 

In the twelfth vertebra a sudden change in the character 
of the transverse processes takes place. There is no longer 
a capitular, distinct from a tubercular, process, but one 
long “ transverse process ” takes the place of both. A sort 
of step in the base of this process bears the capitulum 
of the rib, and answers to the capitular process of the cer- 
vical vertebre, while the outer end of the process articulates 
with the tubereulum of the rib, and represents the tubercular 
process. The neurocentral suture, in this and the succeed- 
ing dorsal vertebree, lies below the root of the transverse 
process, which, therefore, is wholly a product of the neural 
arch. Neither the capitular processes, nor that part of the 
dorsal transverse process which represents them, have dis- 
tinct centres of ossification.* 

In the succeeding dorsal vertebre the “step” of the 
transverse process gradually moves outwards, until at length 
it becomes confounded with the tubercular facet, and a cor- 
responding change takes place in the proximal ends of the 
ribs, in the hindermost of which the distinction between 
capitulum and tuberculum is lost. 

The lumbar vertebre have long transverse processes which 
arise from the neural arches, 7.e., above the neurocentral 
suture. 

The centra of the two sacral vertebre have their applied 
and firmly united faces flat, their free faces concave; conse- 
quently, the first has the anterior face concave and the 
posterior flat, while the second has the anterior surface flat 
and the posterior concave. Hach sacral vertebra has a 
strong rib expanded at its distal end; and wedged in, at its 

* Thus, if it be a part of the part of the definition of a “‘ para- 
definition of a ‘‘parapophysis,’ pophysis”’ that it arises from the 
that it is antogenous, there are centrum, the dorsal vertebre of 


no parapophyses inthe vertebre the Crocodilia have no parapo- 
of the Crocodilia; and, if it be physes. 


THE CROCODILIA. 253 


proximal end, between rough sutural surfaces furnished by 
the neural arch above and the centrum below. 

The first caudal vertebra is biconvex, but all the others are 
procelous ; those of the anterior moiety of the tail have long 
ribs fixed in between the neural arches and centra, as in the 
sacrum, and becoming ankylosed in that position. Chevron 
bones are attached to the posterior edges of the centra of 
the vertebre, except that of the first, and those of the pos- 
terior part of the tail. 

From seven to nine of the anterior dorsal ribs are united 
with the sternum by sternal ribs, the form of which varies 
a good deal in different Crocodilia, being sometimes narrow, 
sometimes broad and flattened. An elongated plate of 
cartilage, which may be partially converted into cartilage 
bone, is attached to the hinder margin of several of the 
most anterior ribs, above the junction between the ossified 
and the cartilaginous part of the vertebral rib. (Fig. 5, P.w.) 
These are the so-called “uncinate processes,” which also 
exist in Hatteria, and reappear in Birds. 

The sternum consists of a rhomboidal plate of cartilage 
bone, with the posterolateral edges of which two pairs of 
sternal ribs articulate. The posterior angle of the plate is 
continued into a median prolongation, which, at length, 
divides into two curved divergent cornua. From five to 
seven pairs of sternal ribs are united with the prolongation 
and its cornua. A long and slender interclavicle lies in a 
groove of the middle of the ventral face of the rhomboidal 
part of the sternum. 

In the ventral wall of the abdomen, superficial to the 
recti muscles, lie seven transverse series of membrane hones, 
which are termed “abdominal ribs;” though it must be 
recollected that they are quite distinct from true ribs, and 
rather correspond with the dermal ossicles of the Labyrin- 
thodonta. ach series is composed of four elongated and 
more or less curved ossicles, pointed at each end, and so 
disposed that inner ends of the imner pair meet at an 
angle, open backwards in the middle line, while their outer 
ends overlap the inner ends of the outer pair. The most 


254, THE ANATOMY OF VERTEBRATED ANIMALS. 


posterior of these ossicles are stronger than the others, and 
are closely connected with the pubic cartilages. 

In the Crocodilian skull the following are the chief pecu- 
liarities which are worthy of especial notice :— 

1, There is an interorbital septum, and the presphenoidal 


Fig. 77.—Longitudinal and vertical section of the hinder part of the 
skull of a Crocodile :—£u, Eustachian tube; P N, posterior nares 
P, pituitary fossa. 


and orbitosphenoidal regions remain cartilaginous, or very 
incompletely ossified. 

2. All the bones of the skull (except the mandible, stapes, 
and hyoid) are firmly united by sutures, which persist 
throughout life. 

3. There are large parotic processes. Both the upper 
and the lower temporal arcades are completely ossified, and 
formed by postfrontal, squamosal, jugal, and quadrato-jugal 


THE CROCODILIA. 255 


bones; supra-temporal, lateral-temporal, and post-temporal 
fossz are formed, as in the Lacertilia, though their relative 
sizes are very different. 

4, The maxillary and.the palatine bones develope palatine 
plates, which unite suturally in the middle line, and sepa- 
rate the nasal passages from the cavity of the mouth, as in 
Mammalia; and in all existing Crocodiles, but not in Teleo- 
saurus or Belodon, the pterygoids are also modified in the 
same way (as in Mymercophaga among Mammals), so that 
the posterior nares are situated very far back beneath the 
base of the skull. 

5. In consequence of the development of these palatine 
plates of the maxillary and palatine bones, the two vomers 
are, in most Crocodiles, invisible upon the under-surface 
of the bony roof of the mouth. 

6. There are large alisphenoids, but the orbitosphenoids 
are absent or rudimentary. 

7. There is no parietal foramen. 

8. The quadrate bone is very large, and fixed immoveably 
to the walls of the skull, as in the Chelonia; and, as in the 
latter, the pterygoid bone is firmly connected with the base 
of the skull, and united only with the upper and inner sur- 
face of the quadrate bone. 

9, The pterygoid sends down a large free process, against 
the broad outer edge of which the inner surface of the 
mandible plays. 

10. The tympanic cavity is completely bounded by bone. 
The pro-otic and opisthotic (which is united with the 
ex-occipital) form its inner walls, the quadrate its outer 
- wall, the squamosal and postfrontal its roof, and the quad- 
rate, the basi-occipital, and basisphenoid its floor. The 
two tympana are placed in communication with the cavity 
of the mouth by three canals—one large, opening in the 
middle line; and two smaller ones at the sides, on the base 
of the skull, behind the posterior nares. The large canal 
passes up between the basisphenoid and basi-occipital, and 
divides between those bones into a right and left lateral 
canal. Hach lateral canal subdivides into an anterior 


256 THE ANATOMY OF VERTEBRATED ANIMALS. 


branch, which traverses the basisphenoid, and a posterior, 
whick passes up in the basi-occipital. The posterior branch 
receives the narrow lateral canal of its side (which runs 
vertically up to it), and then opens-into the posterior part 
of the floor of the tympanum. The anterior branch opens 
into its anterior wall. 

The tympanic cavities of embryonic Crocodiles communi- 
cate with the mouth by wide and simple apertures, and the 
complicated arrangement of canals just described results 
from the great downward development of the basisphenoid 
and basi-occipital, and their encroachment upon these aper- 
tures on the inner side, while the quadrate bone narrows 
them on the outer. 

In adult Crocodilia, air-passages extend from each tym- 
panum to that of the opposite side, through the bones 
which form the roof of the posterior region of the skull. 
On the other hand, they excavate the quadrate bone, from 
whence the air passes through a membranous tube into the 
hollow articular piece of the mandible. The hyoidean 
apparatus is greatly simplified, consisting only of a broad 
plate of cartilage, which may become partially ossified, 
and of two ossified cornua which are not directly connected 
with the skull. A minute styliform cartilage, which lies in 
close proximity with the portio dwra, on the upper part of 
the posterior face of the quadrate bone, represents the stylo- 
hyal, or proximal end of the hyoidean arch. 

The pectoral arch has no clavicle, and the coracoid has no 
distinct epicoracoidal element, nor any fontanelle. The 
carpus consists proximally of two elongated and somewhat 
hourglass-shaped bones, articulated respectively with the 
radius and the ulna. The radial is the larger, and is par- 
tially articulated with the ulna. Behind these, and directed 
transversely, lies another carved ossification, the upper 
concave face of which articulates with the ulna. It is united 
with the latter bone on the one hand, and with the fifth 
metacarpal, on the other, by strong ligaments, and represents 
a pisiform bone. Distally, there lies on the ulnar side the 
so-called lenticular bone, an oval ossicle interposed between 


THE CROCODILIA. 257 


the ulnar proximal carpal and the second, third, fourth, 
and fifth metacarpals, the three last of which it supports 
altogether. On the radial side, a disk of cartilage, which 
never becomes completely ossified, is connected by ligament 
with the lenticulare, and is interposed between the radial 
proximal bone and the head of the metacarpal of the pollex. 
From the ulnar side of the head of this bone a cartilagi- 
nous ligamentous band proceeds, over the head of the 
second metacarpal, to the radial side of the lenticulare. 

The three radial digits are much stronger than the two 
ulnar, and the numbers of the phalanges are 2, 3, 4, 4, 3. 
counting from the radial to the ulnar side. 

The pelvis (Fig. 78, C) possesses large ilia, which are firmly 
united with the expanded ends of the strong ribs of the 

sacrum. The ischium unites with its fellow in a median 
Peentral symphysis, and, with the ilium, forms almost the 
whole of the acetabulum. 

The pubes take hardly any share in the formation of the 
latter cavity in the adult. Their axes are directed forwards 
and inwards, and they coalesce in the middle line; but as the 
inner, or median, moiety of each pubis remains cartilaginous, 
or imperfectly ossified, the bones, in imperfectly prepared 
skeletons, appear as if they formed no symphysis. 

The tarsus presents, proximally, an astragalo-navicular 
bone and a calcaneum, which are less closely united than in 
the Lizards. The latter bone has a large calcaneal process 
on its posterior face, the Crocodile being the only Sauropsid 
vertebrate in which suchaprocess is developed (Fig. 78, C. Ca.) 

Two rounded distal tarsal bones, of which the fibular is 
much the larger, lie between the calcaneum and the third, 
fourth, and rudimentary fifth, metatarsals. A thin plate of 
cartilage is interposed between the distal end of the astra- 
galo-navicular and the second metatarsal, and unites with 
the head of the first metatarsal. 

As in the manus, the three, pre-axial, clawed, digits are 
stronger than the others. The fifth is represented only by 
an imperfect metatarsal. The numbers of the phalanges are 
2, 3, 4, 4, counting from the tibial to the fibular side. 

8 


958 THE ANATOMY OF VERTEBRATED ANIMALS. 


In the Crocodilia the teeth are confined to the premaxille, 
maxille, and dentary part of the mandible. They are ° 
simple in structure, have large pulp cavities, are lodged in 
distinct alveoli, and are replaced by others developed upon 
their inner sides. The development of the new tooth causes 
absorption of the inner wall of the base of the old one, and 
the replacing tooth thus comes to lie within the pulp cavity 
of its predecessor. The teeth vary much in shape, having 
either long, curved, and acute, or short and obtuse, or almost 
globular and straight, crowns. Very often they possess 
sharp anterior and posterior edges, which may be finely 
serrated. 

The Crocodilia are to be found in the rivers of all con- 
tinents and the larger islands in the hotter parts of the 
world. None of the existing species are truly marine.) ~ 
though many of the extinct species were. They are first . 
known to cccur in strata of Triassic age, and abound, 
under forms which differ but little from some of those 
which now exist, in the Mesozoic and Cainozoic formations. 

They may be divided into the following groups :— 


A. With proccelous presacral vertebra, and posterior nares bounded 
below by the pterygoids. (All existing Crocodilia, and the fossil 
forms of cretaceous and later formations, are included in this 
division.) 

a. The nasals enter into the formation of the nasal aperture. 

a. The head short and broad, The teeth very unequal; the 
first and fourth of the mandibles biting into pits of the 
upper jaw. The premaxillo-maxillary suture straight or 
convex forwards. ‘the mandibular symphysis not ex- 
tending beyond the fifth tooth, and the splenial ele- 
ment not entering into it. The cervical scutes distinct 
from the tergal. 

1. Alligatoride. 
Alligator. Caiman. Jacare. 


b. The head longer. The teeth unequal. The first mandi- 
bular tooth biting into a fossa ; the fourth, intoa groove, 
at the side of the upper jaw. The premaxillo-maxillary 
suture straight or convex backwards. ‘The mandibular 
symphysis not extending beyond the eighth tooth, and 
not involving the splenial elements. The cervical scutes 
sometimes distinct frem the tergal, sometimes united 
with them. 

2. Crocodilide. 
Crocodilus. Mecistops. 


Ms 


THE DICYNODONTIA. 259 


b. The nasals are excluded from the external nasal aperture, The 
head very long; the teeth subequal. oth the first and the 
fourth mandibular teeth bite into grooves in the margin of the 
upper jaw. The premaxillo maxillary suture acutely angulated 
backwards. he mandibular symphysis extends to at least 
the fourteenth tooth, and the splenials enter into it. The 
cervical and tergal scuies form a continuous scries. 

3. Gavialide. 
Tihynchosuchus. Gavialis. 


B. With the presacral vertebree amphiccelous (the anterior vertebre 
sometimes opisthoccelous (?) ); and the posterior nares bounded 
by the palatines, the pterygoids not being united below. (All 
these Crocodiles are extinct and pre-cretaceous.) 

a. With the external nares terminal. 

4, Teleosauride. 
Teleosaurus. _Goniopholis. 
Streptospondylus. Siayonolepis. Galesaurus (?). 


b. With the external nares on the upper part of the base of the 
snout near the orbits. 
5. Beloduntide. 
Belodon. 


There is a large number of extinct Reptilia which re- 
semble the Crocodilia in the characters of their pre-sacral 
vertebre, but differ from them, and resemble Lacertilia 
Chelonia, or Birds, in other respects. 

These are the Dicynodontia, the Ornithoscelida, and the 
Pierosauria. 


VII. The Dicynopont1A.— Dicynodon and Oudenodon 
are lacertiform animals. sometimes of large size, with 
erocodilian vertebrx, four or five of which are ankylosed 
together to form a strong sacrum. The skull is massive 
and lacertilian in most of its characters; but the jaws are 
like those of the Chelonia, and were doubtless cased in a 
horny beak. Nevertheless, most of the species possess two 
great tusks, which grow from persistent pulps, lodged in 
a deep alveolus of either maxilla. The limbs appear to 
have been subequal and massive, with short and stout feet. 
The scapula and coracoid are simple and expanded, and 
there seems to have been no clavicle. The pelvis is very 
strong, with widely expanded ilia, ischia, and pubes. The 
two latter meet in a median ventral symphysis, and the 
pubis and ischium of each side meet and obliterate the 


260 THE ANATOMY OF VERTEBRATED ANIMALS. 


obturator foramen. The limb-bones are lacertilian in 


character. 


Fig. 78. 


Fig. 78.—The pelvis and hind limb of, A., Dromeus ; B., an ornithos- 
celid reptile, such as Iguanodon, or Hypsilophodon ; and C., a Croco- 
dile. he bird’s limb is in its natural position, as is that of the 
Ornithoscelid, though the metatarsus of the latter may not, in nature, 


THE ORNITHOSCELIDA. 261 


have been so much raised. The Crocodile’s limb is purposely repre- 
sented in an unnatural position. In nature, the femur would be 
turned out nearly at right angles to the middle vertical plane of the 
body, and the metatarsus would be horizontal. ‘The letters are the 
same throughout. J/, ilium ; Js, ischium; Pb, pubis; a, anterior pro- 
cess, 6, posterior process, of the ilium; 77, inner trochanter of the 
femur; 7. tibia; /, fibula; As, astragalus; Ca, calcaneum. J., IJ., 
ITT., IV., the digits. 


Remains of these Reptiles have hitherto been found only 
in strata, which probably belong to the Triassic formation, 
in India and South Africa, and the Ural mountains. 


VIII. The OrniTHoscELIDA.—The very remarkable ex- 
tinct reptiles which constitute this group, present a large 
series of modifications intermediate in structure between 
existing Reptilia and Aves. 

This transitional character of the Ornithoscelidan skeleton 
is most marked in the pelvis and hind limbs. 

If the pelvis of any existing reptile be compared with 
that of any existing bird, the following points of difference 
will be observed :— 


1. In the reptile (Fig. 78, C.), the ilium is not prolonged 
in front of the acetabulum; and the acetabulum is either 
wholly closed by bone, or presents only a moderate-sized 
fontanelle, as in the Crocodilia. 

In the bird (Fig. 78, A.), the ilium is greatly prolonged 
in front of the acetabulum, and the roof of the acetabular 
cavity is a wide arch, the inner wall of that cavity re- 
maining membranous. The anterior pier of the arch, or 
pre-acetabular process, extends further downwards than 
the posterior pier, or post-acetabular process. 

But, in all the Ornithoscelida, the ilium extends far in 
front of the acetabulum, and furnishes only a widely arched 
roof to that cavity, as in birds. It retains a reptilian 
character in the further proportional extension of the post- 
acetabular process downwards (Fig. 78, B.). 

2. The ischium, in the reptile (Fig. 78, C.) is a moderately 
elongated bone, which becomes connected with the pubis in 
the acetabulum, and extends downwards, inwards, and some- 


262 THE ANATOMY OF VERTEBRATED ANIMALS. 


what backwards, to unite with its fellow ina median ventral 
symphysis. The obturator space is not interrupted by 
any forward process of the outer and anterior half cf the 
ischium. 

In all birds (Fig. 78, A.), the ischium is elongated and 
inclined backwards, the backward direction being least 
marked in Apteryx, and most in Rhea. The ischia never 
come together directly in a median ventral symphysis, 
though they unite dorsally in Rhea. The anterior edge of 
the external, or acetabular, half of the ischium very gene- 
_ rally sends off a process which unites with the pubis, thus 

dividing the obturator space. 

In all the Ornithoscelida (Fig. 78, B.), in which I have been 
able to identify the bone (Vhecodontosawrus, Teratosaurus, 
Megalosaurus, Iguanodon, Stenopelyx, Hadrosawus, Hypsilo- 
phodon), the ischium is greatly elongated. In Iguanodon it 
has the obturator process characteristic of the same bone in 
Birds; and I imagine that the same process is seen in 
Compsognathus. In Hypsilophodon there can be no mistake 
about the matter, and the remarkable slenderness and pro- 
longation of the ischium give it a wonderfully ornithic 
character. In Iguancdon the slenderness and prolongation 

_are even carried beyond what is to be seen in Birds. I am 
disposed to think, however, that, as was certainly the case 
in Hypsilophodon, the ischia united in a median ventral 
symphysis in all the Ornithoscelida, 

3. Inall reptiles the pubis is inclined forwards, as well as 
downwards, towards the ventral median line. In all, except 
the Crocodile, it takes a considerable share in the formation 
of the acetabulum; and the ossified pubis unites directly 
with its fellow in the middle line. 

The pubes of Compsognathus are, unfortunately, obscured 
by the femora. They seem to have been very slender; and 
to have been directed forwards and downwards, like those 
of lizards. Some lizards, in fact, have pubes which, if the 
animal were fossilized in the same position as Compsogna- 
thus, would be very similar in form and direction. Hypsilo- 
phodon, however, affords unequivocal evidences of a further 


THE ORNITHOSCELIDA. 963 


step towards the bird. The pubes are not only as slender 
and elongated as in the most typical bird, but they are 
directed downwards and backwards parallel with the ischia, 
thus leaving only a very narrow and elongated obturator 
foramen, which is divided by the obturator process. 

It remains to be seen how far the hypsilophodont modi- 
fication extended among the Ornithoscelida. The remains 
of Compsognathus and of Stenopelyx tend to shew that it was 
by no means universal. 

As to the hind limb, in existing reptiles :— 

1. The proximal end of the tibia has but a very small, or 
quite rudimentary, cnemial crest, and it presents no ridge 
for the fibula on its outer side. 

2. The flattened sides of the distal end of the tibia look, 
the one directly forwards, or forwards and inwards; and 
the other backwards, or backwards and outwards. And 
when the posterior edges of the two condyles of the 
proximal end of the tibia rest on a flat surface which looks 
forwards, the long axis of the distal end is either nearly 
parallel with that surface, or is inclined obliquely from in 
front and without, backwards and inwards. 

3. There is no depression on the anterior face of the tibia 
for the reception of an ascending process of the astragalus. 

4. The distal end of the fibula is as large as, or larger 
than, the proximal end, and articulates largely with a facet 
on the outer part of the astragalus. 

5. The astragalus is not depressed and flattened from 
above downwards, nor does it send a process upwards in 
front of the tibia. 

6. The astragalus remains quite free from the tibia. 

In all these respects the leg of any existing bird (see 
Fig. 78), is very strikingly contrasted with that of the reptile. 

1. The proximal end of the tibia is produced forwards and 
outwards into an enormous cnemial crest, in all walking and 
swimming birds (Fig. 78, A.); and, on the outer side, there 
is a strong ridge for the fibula. 

2. When the posterior edges of the condyles of the tibia 
rest upon a flat surface, the one flat face of the distal end 


264 THE ANATOMY OF VERTEBRATED ANIMALS. 


of the bone looks outwards as well as forwards, and the 
other inwards as well as backwards. Further, the long axis 
of the distal end is inclined, at an angle of 45° to the flat 
surface, from within and in front, backwards and outwards, 
thus exactly reversing the direction in the reptile. 

3. There is a deep longitudinal depression on the anterior 
face of the distal end of the tibia, which receives an ascend- 
ing process of the astragalus. 

4, The distal end of the fibula is a mere style, and does 
not articulate with the astragalus. 

5. The astragalus is a much-depressed bone, with a con- 
cave proximal, and a convex, pulley-like, distal, surface. A 
process ascends from its front margin in the groove on the 
front face of the tibia. This process is comparatively short, 
and perforated by two canals for the tibialis anticus and 
extensor communis, in the Fowl; while in the Ostrich and 
Kmeu it is extremely long and not so perforated. 

6. The astragaius becomes ankylosed with the tibia 
(though it remains distinct for a long time in the Ostrich 
and Rhea, and in some breeds of fowls). 

In the Ornithoscelida :— 

1. There is a great cnemial crest and aridge for the fibula. 

2. The disposition of the distal end of the tibia is literally 
that observed in the Bird. 

3. There is a fossa for the reception of the ascending pro- 
cess of the astragalus. 

4, The distal end of the fibula is much smaller than the 
proximal, though not so slender as in Aves. 

5. The astragalus is altogether similar to that of a bird, 
with a short ascending process. 

6. The astragalus appears to have remained distinct from 
the tibia throughout life in Iguanodon, Megalosawrus, and 
many other genera; but it seems to have become ankylosed 
in Compsognathus, Ornithotarsus, and Euskelosaurus. 


The reptiles belonging to this group are for the most part 
of very large size, and some of them, as the Iguanodon, are 
among the largest of known terrestrial animals. They 


THE ORNITHOSCELIDA. 265 


occur throughout the whole range of the Mesozoic forma- 
tions, being represented by Thecodontosaurus, Paleosau- 
rus, Teratosaurus, Plateosaurus, and other genera in the 
Trias; by Scelidosaurus in the Lias: by Megalosaurus, 
Poikiloplewron, Euskelosawrus, Hylcosawrus, Polacanthus, 
Acanthopholis, Igquanodon, Hadrosawrus, Trachodon, and 
Laelaps in the middle and upper Mesozoic strata. 

There is no evidence that Megalosawrus, or Iguanodon, 
possessed any dermal armour; but several genera (¢.g., 
Scelidosaurus, Hyleosawrus, and Acanthopholis) had osseous 
dermal scutes, sometimes produced into prodigious spines. 

The faces of the centra of the vertebre are slightly 
amphiccelous, or nearly flat; but those of the anterior dorsal 
and cervical regions seem, in some cases, to have been opis- 
thocelous. The sacrum seems to have consisted of at 
fewest four vertebre, which in some (Scelidosawrus) are cro- 
codilian, in others (Megalosaurus) take on a somewhat or- 
nithie character. The caudal region had many and long 
vertebrz, between which the chevron bones are attached. 
The rami of the chevron bones have their vertebral ends 
united by bone. 

The thoracic vertebral ribs are very strong; but the 
sternal ribs and sternum are unknown. However, there is 
some reason to think that the sternum was broad and ex- 
panded. Abdominal dermal ribs are developed in some 
species, if not in all. 

The structure of the skull seems to have been interme- 
diate, in many respects, between the crocodilian and the 
lacertilian types. In Iguanodon and Hypsilophodon, the 
extremities of the premaxille appear to have been edentu- 
lous and beak-like; and the symphysis of the mandible is 
excavated to receive the beak, almost as in the mandible of 
a Parrot. 

The teeth vary extremely, from the sharp, recurved, ser- 
rated fangs of Megalosawrus, to the broad grinders, wearing 
down by mutual attrition, of Iguanodon. Their mode of 
implantation varies, but they are not ankylosed to the jaws. 

The scapula is vertically elongated, narrow, and devoid of 


266 THE ANATOMY OF VERTEBRATED ANIMALS. 


any acromial process; the coracoid rounded and without 
fontanelles or processes. 

No Ornithoscelidan is known to have possessed a clavicle. 

The fore-limb is shorter, and often much shorter, than 
the hind-limb. The structure of the manus is not certainly 
known. 

The femur usually has a strong inner trochanter ; and its 
distal end is particularly bird-like, in the development of a 
strong ridge, which plays between the tibia and the fibula. 

The metatarsals are elongated, and fit together in such a 
way that they can hardly, if at all, move on one another. 
The inner and outer digits are either shorter than the rest, 
or quite rudimentary ; and the third digit is the longest, as 
in birds in general. 

The Ornithoscelida are divisible into two sub-orders, the 
Dinosauria and the Compsognatha. The type of the latter 
division is the wonderful little extinct reptile, Compsogna- 
thus, which differs from the Dinosawria in the great length 
of the centra of the cervical vertebra, and in the femur 
being shorter than the tibia. It has a light bird-like head 
(provided with numerous teeth), a very long neck, small 
anterior limbs, and very long posterior limbs. The astra- 
galus appears to have been ankylosed with the tibia, as in 
birds. A single specimen only of this reptile has been 
obtained, in the Solenhofen slates. 


IX. The PrrErosaurta.—The flying Reptiles, which be- 
long to this group, and are commonly known as Ptero- 
dactyls, are, and long have been, extinct, their remains 
oecurring only in Mesozoic rocks, from the Lias to the 
Chalk inclusively. 

They are all remarkable for their proportionally long 
heads and necks, and for the great size of the anterior 
limb, the ulnar finger of which, enormously elongated and 
devoid of a claw, appears to have supported the outer edge 
of an expansion of the integument, like the patagium of a 
Bat (Fig. 79). 

The vertebral column is distinctly divided into cervical, 


THE PTEROSAURIA. 267 


dorsal, sacral, and caudal regions, the cervical vertebra 
being, as in Birds, the stoutest of all. The atlas and axis 


Fig. 79. 


VA Ny 


Fig. 79.—The nearly entire skeleton of Pteroductylus spectabilis (Von 
Meyer) as shown by the two halves of a split block of lithographic 
slate. a, the left pre-pubic bone: on the right side this bone is 
not shown and the ilium is exposed. 


are ankylosed together, at least in the cretaceous species. 
The other cervical vertebra, apparently not more than six 


268 THE ANATOMY OF VERTEBRATED ANIMALS. 


or seven in number, have low, or obsolete, spinous processes ; 
and, like the vertebrze of the rest of the spine, are proccelous, 
and have the neuro-central suture obliterated. The exist- 
ence of cervical ribs is doubtful. From fourteen to sixteen 
vertebree intervene between the cervical and the sacral 
regions; and not more than one or two of the hindermost 
of them, if any, are devoid of ribs. The number of vertebree 
ankylosed together to form the sacrum, is not fewer than 
three, nor more than six. 

The tail is very short in Pterodactylus, and, in this genus, 
all the vertebree are moveable upon one another; but, in 
Rhamphorhynchus, it is extremely long, and the vertebre are 
immoveably fixed by what appear to be ossified hgamentous 
fibres. : 

The vertebral ribs are slender, and the anterior ones, at 
any rate, have distinct capitula and tubercula. There are 
ossified sternal ribs, and splint-like abdominal ribs. The 
sternum is broad, and, unlike that of other Reptilia, is very 
completely ossified, and bears a strong median crest on the 
anterior part of its ventral surface. No median posterior 
prolongation has been observed in connection with it. 

The brain case is more rounded and bird-like than in the 
other Reptilia, and, im many other respects, the skull ap- 
proaches that of birds. Thus, the occipital condyle is on 
the base of the skull, not on its posterior face; the cranial 
bones ankylosed very early; the orbits are very large, and the 
external nares ure situated close to them. The premaxille 
are very large, the maxillz slender, and the dentary pieces 
of the mandible are fused together into one bony mass, with- 
out any trace of a symphysial suture. 

The resemblance to birds is still further increased, in 
some species, by the presence of wide Jachrymo-nasal fosse 
between the orbits and the nasal cavities, and by the pro- 
longation of the extremities of the premaxille and of the 
symphysial part of the mandible into sharp, beak-like pro- 
cesses, which appear to have been covered with horny 
sheaths. But the reptilian type is kept up by the presence 
of a distinct postfrontal, which unites with the squamosal, 


THE PTEROSAURIA. 269 


and thus gives rise to a supra-temporal fossa. The post- 
frontal and the jugal unite behind the orbit, in Lacertilian 
fashion; and both the upper and the lower jaws contain 
teeth. The sclerotic is supported by a ring of bones, as in 
many other Sauropsida. 

The scapula and the coracoid are wholly unlike these 
structures in any other Sauropsida, but are extremely 
similar to the same parts in birds, and imdeed to the 
shoulder girdle of the less reptilian Carinate. The scapula 
is slender and blade-like, and its long axis is inclined, at 
less than a right angle, to that of the coracoid. The 
glenoidal surface is cylindroidal, concave from above down- 
wards, convex from side to side. The coracoid, elongated 
and comparatively narrow, is devoid of fontanelle, epico- 
racoid, or procoracoid. 

No trace of any clavicle has been discovered. 

The humerus has a great deltoid ridge or process. The 
radius and ulna are equal in size and separate. There are 
four distinct metacarpal bones, that on the ulnar side being 
very much stronger, though not longer, than the others. 
Another styliform bone attached to the carpus does not 
appear to have belonged to the metacarpal series. The 
radial metacarpal bears two phalanges; the second, three; 
the third, four, so that these represent the pollex and 
the succeeding digits of the Lizard’s manus. The ter- 
minal phalanx of each of these digits is strong and 
eurved, and was doubtless ensheathed in a horny claw. 
The fourth, like the corresponding digit in the Crocodile, 
has four phalanges, the last of which is straight and bears no 
nail. But these phalanges are enormously elongated and of 
great relative strength. A strong process projects from the 
dorsal side of the proximal end of the first phalanx, and 
doubtless gave attachment to the tendon of a correspond- 
ingly powerful extensor muscle. The articular surface 
below and behind it, is concave, and plays over the convex 
distal pulley of the fourth metacarpal. 

The pelvis is remarkably small. The ilia are elongated 
bones, produced both anteriorly and posteriorly, as in Birds; 


270 THE ANATOMY OF VERTEBRATED ANIMALS. 


but the rest of the pelvis is not at all ornithic. The flat 
and broad ischia appear to be united with the pubes into 
wide bony plates, which pass, at right angles with the ilia, 
to their median ventral symphysis. A large spatulate bone 
articulates with each pubis near the symphysis, and seems 
to be an exaggeration of the pre-pubic process of Lacertilia 
and Chelonia. Or it may be (though I do not think this 
very probable) that the broad flat plates correspond almost 
altogether to the ischia, and that the spatulate ossifications 
are the pubes; in which case the structure of the pelvis 
would bea sort of extreme exaggeration of that observed in 
the Crocodilia. 

The hind limb is small compared with the fore limb. The 
fibula is imperfect, and appears to coalesce with the tibia at 
its distal end. The structure of the tarsus requires fur- 
ther elucidation. In some Pterosawria there seem to be only 
four digits, with, perhaps, a rudiment of a fifth, in the pes; 
but others, such as Rhamphorhynchus Gemmingi, have five 
digits in the foot. Where there are only four, each digit is 
terminated by a curved and pointed ungual phalanx, and 
the number of the phalanges from the tibial to the fibular 
side is 2, 3, 4, 5. These digits, therefore, are the hallux, and 
the three which immediately follow it ; and the rudimentary 
digit is the fifth. 

The long bones of the Pterosawria have thin walls, in- 
closing a large cavity, which appears to have contained air, 
as in many birds; and pneumatic foramina are visible on 
the sides of the vertebre. 

The remains of more than twenty species of Pterosauria 
have been discovered. Some of them are exquisitely preserved 
in the fine matrix of the lithographic stone of Solenhoten. 

They are thus grouped into genera :— 


A. With two joints in the ulnar digit of the manus. 
Ornithopterus. 


B. With four joints in the ulnar digit. 

a. The jaws strong, pointed, and toothed to their anterior 
extremities. The tail very short. The metacarpus 
usualiy longer than half the length of the antebrachium. 

Pierodactylus. 


THE PTEROSAURIA. 271 


b. The extremities of the jaws produced into toothless beaks, 
probably ensheathed in horn. ‘The tail very long. The 
metacarpus shorter than balf the length of the ante- 
brachium. 

a. All the mandibular teeth similar. 
Rhamphorhynchus. 


b. The posterior teeth for the most part very short, 
The anterior long. 
Dimorphodon. 


IT am much inclined to suspect that the fossil upon which 
the genus Ornithopterus has been founded, appertains to a 
true Bird. 


272, THE ANATOMY OF VERTEBRATED ANIMALS. 


CHAPTER VI. 


THE CLASSIFICATION AND THE OSTEOLOGY OF BIRDS. 


THE class Aves.— Though this class contains a great 
number of specific forius, the structural modifications which 
they present are of comparatively little importance; any 
two birds which can be selected differing from one another 
far less than the extreme types of the Lacertilia, and hardly 
more than the extreme forms of the Chelenia,do. Hence the 
characters by which the following groups are separated 
appear almost insignificant when compared with those by 
which the divisions of the Reptilia are indicated. 


A. The metacarpals not ankylosed together. The tail longer than 
the body. 
I.—Savrur =. 
1. Archaopterygide. 
B. The metacarpals ankylosed together. The tail considerably shorter 
than the body, 
A. The sternum devoid of a keel. 


I.—Rartirz. 
a, The wing with a rudimentary, or very short, humerus 
and with not more than one ungual phalanx. 
a. A hallux. 
2. Apterygide (The Kiwis). 
B. No hallux. 
8. Dinornithide (The Moas), 
4. Casuaride (‘The Cassowaries). 
6. The wing with a long humerus and with two ungual 
phalanges. 
a. The ischia uniting immediately beneath the 
sacrum, and the pubes free. 
5, Rheide (The American Ostriches). 
B. The ischia free and the pubes uniting in a 
ventral symphysis. 
6. Struthionide (‘The Ostriches). 
s. The sternum provided with a keel.* 


* The keel is rudimentary in the singular Parrot Sirigops. 


CLASSIFICATION OF BIRDS. 


bo 


73 


Ill. Carat. 


a. The vomer broad behind, and interposing between 
the pterygoids, the palatines, and the basisphe- 
noidal rostrum, 


(Dromeognathe.) 
7. Tinamomorphe (The Tinamous). 


b. The vomer narrow behind: the pterygoids and pala- 
tines articulating largely with the basisphenoidal 
rostrum. 

a. The maxillo-palatines free.* 
i. The vomer pointed in front. 


(Schizognathe.) 
8. Charadriomorphe (The Plovers). 
9. Cecomorphe (‘The Gulls). 
10. Spheniscomorphe (The Penguins). 
1l. Geranomorphe (The Cranes). 
12, Turnicimorphe (The Hemipods). 
13. Alectoromorphe (The Fowls). 
14, Pteroclomorphe (The Sand-grouse), 
15. Peristeromorphe (The Pigeons). 
16. Heteromorphe (The Hoazin). 


ii. The vomer truncated in front. 
( digithognathe.) 
17. Coracomorphe (‘The Passerines). 
18. Cypselomorphe (The Swifts). 
19. Celeomorphe (The Woodpeckers). 


g. The maxillo-palatines united. 
(Desmognathe.) 
20. Aetomorphe (he Birds of Prey). 
21. Psittacomorphe (‘The Parrots). 
22. Coccygomorphe (The Cuckoos, King- 
fishers, ‘l'rogons). 
23. Chenomorphe (The Anserine Birds). 
24. Amphimorphe (The Flamingoes). 
25, Pelargomorphe (The Storks). 
26. Dysporomorphe (The Cormorants). 


* With the exception of Dicholophus and some species of Craz. 
} The subjoined Table, which shows with which of the above groups 
the old orders of Birds correspond, may be useful to the student :— 


ess) 


or ‘ = Aetomorphe, 
Raprrores | 
IT.—Scansorrs. . . . . =Psittacomorphe,  Coccygomorphe 


(in part), 
Coracomorphe, Cypselomorphe, 
=| Celeomorphe, Coceygomorphe. 
(in part). 
T 


or 


IIT.— Passeres 
INSESSORES 


274 THE ANATOMY OF VERTEBRATED ANIMALS. 


The exoskeleton of Birds consists almost entirely of ep1- 
dermic structures in the form of horny sheaths, scales, 
plates, or feathers. No bird possesses dermal ossifications, 
unless the spurs which are developed upon the legs and 
wings of some species may be regarded as such. 

The feathers are of various kinds. Those which exhibit 
the most complicated structure are called penne, or contour 
feathers, because they lie on the surface and determine the 
contour of the body. In every penna the following parts 
are to be distinguished :—l. A main stem (scapus) forming 
the axis of the feather, and divided into a proximal hollow 
cylinder, partly embedded in a sac of the derm, called the 
calamus, or quill; and a distal veaillum, or vane, consisting 
of a four-sided solid shaft, the rachis, which extends to the 
extremity of the feather, and bears a number of lateral pro- 
cesses, the barbs. The calamus has an inferior aperture 
(umbilicus inferior), into which the vascular pulp penetrates; 
and a superior aperture (wmbilicus superior), situated on the 
under surface of the feather at the junction of the calamus 
with the scapus. The barbs are narrow plates, tapering to 
points at their free ends, and attached by their bases on 
each side of the rachis. The edges of these barbs are 
directed upwards and downwards, when the vewillum of 
the feather is horizontal. The interstices between the 
barbs are filled up by the barbules ; pointed processes, which 
stand in the same relation to the barbs, as the barbs do 
to the rachis. The barbules themselves may be laterally 
serrated and terminated by little hooks, which interlock with 
the hooks of the opposed barbules. In very many birds 
each quill bears two vexilla ; the second, called the aftershaft 
(hyporachis), being attached on the under side of the first 


IV.—Gawuinm (with Cotumpx)= Alectoromorphe, Peristeromorphe, 
Pterociomorphe, Turnicimorphe. 


V.—Cursores . . . . . = Ratite. 
VI.—GrRALL& . . « . « =Charadriomorphe, Geranomorphe, 
Amphimorphe, Pelargomorphe. 
VII.—PawtMipeDES . . . . =Cecomorphe,  Spheniscomorphe, 


Chenomorphe, Dysporomorphe. 


THE FEATHERS OF BIRDS. . 275 


close to the superior umbilicus. The aftershaft is generally 
much smaller than the chief vexillum; but in some birds, 
as the Casuaride, the two are of equal size, or nearly so. 
Muscles pass from the adjacent integument to the feather 
sac, and by their contraction erect the feather. The other 
kinds of feathers differ from the penne, in having the barbs 
soft and free from one another, when they constitute penno- 
plume, or plumule (down), according as the scapus is much 
or little developed. When the scapus is very long, and the 
vexillum very small or rudimentary, the feather is termed 
a filopluma. 

The contour feathers are distributed evenly over the body 
only in a few birds, as the Ratite, the Penguins, and some 
others. Generally, the penne are arranged in definitely 
circumscribed patches or bands, between which the integu- 
ment is either bare, or covered only with down. These 
series of contour feathers are termed pteryle, and their 
interspaces, apteria. 

In some birds, such as the Herons, plumule of a peculiar 
kind, the summits of which break off into a fine dust, or 
powder, as fast as they are formed, are developed upon 
certain portions of the integument, which are termed powder 
down patches. 

The integument of birds is, for the most part, devoid of 
glands; but many birds have a peculiar sebaceous gland 
developed in the integument which covers the coccyx. This 
uropygial gland secretes an oily fluid, which the bird 
spreads over its feathers by the operation of “ preening.” 
The excretion passes out by one or two apertures, commonly 
situated upon an elevation, which may or may not be 
provided with a special circlet of feathers. 

In various birds (e¢.g., the Turkey) the integument about 
the head and neck develops highly vascular and sometimes 
erectile processes (combs, wattles). 


The spinal column of birds contains numerous and well 
ossified vertebre, a considerable number of which (more 
than six) are ankylosed together to form a sacrum. Of 


276 THE ANATOMY OF VERTEBRATED ANIMALS. 


the vertebree which enter into the composition of this com- 


plex bone, however, not more than from three to five can | 


be regarded as the homologues of the sacral vertebre of a 
Crocodilian or Lacertilian reptile. The rest are borrowed, in 
front, from the lumbar and dorsal regions ; behind, from the 
tail. The cervical region of the spine is always long, and 
its vertebra, which are never fewer than eight, and may 
be as many as twenty-three, are, for the most part, large iz 
proportion to those of the rest of the body. 

The atlas is a relatively small, ring-like, bone; and the 
transverse ligament may become ossified and divide its 
aperture into two—an upper, for the spinal cord, and a 
lower, for the odontoid process of the axis vertebra. The 
os odontoidewm is always ankylosed with the second ver- 
tebra, and constitutes a peg-like odontoid process. 

The spines of the succeeding cervical vertebre are often 
obsolete, and are never very prominent in the middle region 
of the neck. The anterior faces of their elongated vertebral 
centra are cylindroidal, slightly excavated from above down- 
wards, and convex from side to side; while the posterior 
faces are convex from above downwards, and concave from 
side to side. Hence, in vertical section, the centra appear 
procelous; in horizontal section, opisthoccelous; and this 
structure is exceedingly characteristic of birds. The under 
surfaces of the centra frequently give off median inferior 
processes. In the Ratite, it is obvious that the cervical 
vertebre have short transverse processes and ribs, disposed 
very much asin the Crocodilia. For, in young birds, the ante- 
rior end of the lateral face of each vertebra bears two small 


processes, an upper and a lower; and the expanded head of — 


a styliform rib is articulated with these by two facets which 
represent the capitulum and the tuberculum. With age, 
the cervical ribs may become completely ankylosed; and 
then they appear like transverse processes, perforated at the 
base by a canal, which, as in the Crocodilia, contains the 
vertebral artery and vein, and the main trunk of the sympa- 
thetic nerve. The cervical ribs and transverse processes 
are similarly disposed in very young Carinate ; but in these 


i =~ 


THE VERTEBRZ IN BIRDS. 277 


birds their form frequently becomes much modified in the 
adult; and they develope prolongations, which extend down- 
wards and inwards, and protect the carotid artery or 


arteries. 


The neural arches have well developed pre- and post- 
zygapophyses. The ribs of one or two of the posterior 
cervical vertebre become elongated and freely moveable in 
the Carinate, as in the Ratite. 

The first dorsal vertebra is defined as such, by the union 
of its ribs with the sternum by means of a sternal rib; 
which not only, as in the Crocodilia, becomes articulated 
with the vertebral rib, but is converted into complete bone, 
and is connected by a true articulation with the margin of 
the sternum. 

The number of the dorsal vertebre (reckoning under that 
head all the vertebre, after the first dorsal, which possess 
distinct ribs, whether they be fixed or free) varies. The 
centra of the dorsal vertebrz either possess cylindroidal 
articular faces, like those of the neck, as is usually the 
case; or, more or fewer of them may have these faces 
spheroidal, as in the Penguins. In this case, the convex 
face is anterior, the concave, posterior. They may, or may 
not, develope inferior median processes. They usually pos- 
sess well marked spinous processes. Sometimes they ares 
slightly moveable upon one another; sometimes they be- 
come ankylosed together into a solid mass. 

It is characteristic of the dorsal vertebre of Birds that 
the posterior, no less than the anterior, vertebre present a 
facet, or small process, on the body, or the lower part of the 
arch, of the vertebra for the capitulum of the rib, while 
the upper part of the neuralarch gives off amore elongated 
transverse process for the tuberculum. Thus the trans- 
verse processes of all the dorsal vertebre of a bird resemble 
those of the two anterior dorsals of a crocodile, and no 
part of the vertebral column of a bird presents transverse 
processes with a step for head of the rib, like those of the 
great majority of the vertebre of Crocodilia, Dinosauria, 
Dicynodontia, and Pterosauria. 


278 THE ANATOMY OF VERTEBRATED ANIMALS. 


The discrimination of the proper lumbar, sacral and 
anterior caudal vertebre, in the ankylosed mass which consti- 
tutes the so-called “sacrum” of a bird, is a matter of consider- 


Fig. 80. 


Fig. 80.—The “Sacrum” of a Chick. dl., dorso-lumbar; s., sacral; 
c., caudal vertebre. 


able difficulty. The general arrangement is as follows :— 
The most anterior lumbar vertebra has a broad transverse 
process, which corresponds in form and position with the 
tubercular transverse process of the last dorsal. In the 
succeeding lumbar vertebre this process extends down- 
wards; and, in the hindermost, it is continued from the 
centrum, as well as from the arch of the vertebra, and 
forms a broad mass which abuts against the ilium.* This 
process might well be taken for a sacral rib, and its ver- 
tebra for the proper sacral vertebra. But, in the first 
“place, I find no distinct ossification in it; and, secondly, 
the nerves which issue from the intervertebral foramina in 
front of and behind this vertebra enter into the lumbar 
plexus, which gives origin to the crural and obturator nerves, 
and not into the sacral plexus, which is the product of the 
nerves which issue from the intervertebral foramina of the 
proper sacral vertebree in other Vertebrata. Behind the last 
lumbar vertebra follow, at most, five vertebrze, which have 
no ribs, but their arches give off horizontal, lamellar, trans- 
verse processes, which unite with the ilia. The nerves which 
issue from the intervertebral foramina of these vertebre 


* Tt would be more proper to cess, like other processes, exists 
say that ossification extends into before the centrum is differen- 
it from the centrum as well as tiated from the arch by ossifi- 
from the neural arch, The pro- cation. 


THE VERTEBRZ IN BIRDS. 279 


unite to form the sacral plexus, whence the great sciatic 
nerve is given off; and I take them to be the homologues 
of the sacral vertebre of Reptilia. The deep fosse between 
the centra of these vertebre, their transverse processes, and 
the ilia, are occupied by the middle lobes of the kidneys. 

Tf these be the true sacral vertebre, it follows that their 
successors are anterior caudal. They have expanded upper 
transverse processes, like the proper sacral vertebre; but, 
in addition, three or four of the most anterior of these ver- 
tebre possess ribs which, like the proper sacral ribs of rep- 
tiles, are suturally united, or ankylosed, proximally, with 
both the neural arches and the centra of their vertebre, 
while, distally, they expand and abut against theilium. The 
ankylosed caudal vertebre may be distinguished as wro- 
sacral. The caudal vertebre which succeed these may be 
numerous and all distinct from one another, as in Archeop- 
tery and Rhea ; but, more generally, only the anterior caudal 
vertebrz are distinct and moveable, the rest being ankylosed 
into a ploughshare-shaped bone, or pygostyle, which supports 
the tail feathers and the uropygial gland, and sometimes, as 
in the Woodpeckers and many other birds, expands below 
into a broad polygonal disc. 

The centra of the moveable presacral vertebre of Birds 
are connected together by fibro-cartilaginous rings, which 
extend from the circumference of one to that of the next. 
Hach ring is continued inwards into a disc with free 
anterior and posterior faces—the meniscus. The meniscus 
thins towards its centre, which is always perforated. The 
synovial space between any two centra is, therefore, divided 
by the meniscus, into two very narrow chambers, which com- 
municate by the aperture of the meniscus. Sometimes the 
meniscus is reduced to a rudiment; while, in other cases, it 
may be united, more or less extensively, with the faces 
of the centra of the vertebre. In the caudal region, the 
union is complete and the meniscus altogether resembles an 
ordinary intervertebral cartilage. 

A ligament traverses the centre of the aperture in the 
meniscus; and, in the chick, contains the intervertebral por- 


280 THE ANATOMY OF VERTEBRATED ANIMALS. 


tion of the notochord. As Jaiger* has shewn, it is the 
homologue of the odontoid ligament in the cranio-spinal 
articulation ; and of the pulpy central part of the interver- 
tebral fibro-cartilages in Mammalia. 

All the vertebral ribs in the dorsal region, except, per- 
haps, the very last free ribs, have widely separated capitula 
and tubercula. More or fewer have well ossified uncinate 
processes attached to their posterior margins, as in the 
Crocodilia. The vertebral ribs are completely ossified up to 
their junction with the sternal ribs. The sternum in birds, 
is a broad plate of cartilage, which is always more or less 
completely replaced in the adult by membrane bone.f It 
begins to ossify by, at fewest, two centres, one on each side, 
as in the Ratite. In the Carinate it usually begins to 
ossify by five centres, of which one is median for the keel, 
and two are in pairs, for the lateral parts of the sternum. 
Thus the sternum of a chicken is at one time separable into 
five distinct bones, of which the central keel-bearing ossi- 
fication (7. to m. «. in Fig. 81) is termed the lophosteon, the 
antero-lateral piece which articulates with the ribs, pleu- 
rosteon (pl. 0.), and the posterolateral bifurcated piece, met- 
osteon. ‘ 

Though the sternum, in most birds, seems to differ very 
much in form from that of the Reptilia, itis rhomboidal in 
the Casuaride, where it differs from the reptilian sternum 
chiefly in the greater proportional length of its posterior 
sides, the absence of median backward prolongations, and 
the convexity of its ventral surface. But in other birds, and 
notably in many Carinate, the antero-lateral edges, which 
are grooved to receive the coracoids, form a much more 
open angle than in the Reptilia, while the postero-lateral 
edges become parallel, or diverge; and a wide, straight or 
convex, transverse edge takes the place of the posterior 
angle. Two, or four, membranous fontanelles may remain 

* “ Das Wirbelkérpergelenk sternum, like those further on 
der Vogel.”  Sitzungsberichte touching the skull. do not apply 
der Wiener Akademie, 1858. to Arheepteryz, in which all these 


+ These statements respecting parts are unknown or imperfectly 
the vertebral column, ribs, and known. 


THE STERNUM IN BIRDS. 281 


in the posterior moiety of the sternum when ossification 
takes place, and give rise to as many holes, or deep notches, 
separating slender processes in the dry skeleton. All these 
correspond with so many divisions of the xiphoid process 
of the sternum in Mammalia, and hence are called middle, 


™. x. 


Fig. 81.—Frent and side views of the sternum of a Fowl. ., rostrum, 
or manubrium ; ¢. p., costal process ; pl. o., pleurosteon (the line from 
the letter goes to the point of junction between the pleurosteon and 
ie oo ; m. x., the middle xiphoid process; ca., the carina or 

eel. 


internal, and external xiphoid processes. Sometimes, a median 
process, rostrum or manubriwm (r., Fig. 81), is developed from 
the anterior angle of the sternum, and its antero-lateral 
angles are frequently produced into costal processes (¢. p., 
Fig. 81), which may bear the articular surfaces for more or 


282 THE ANATOMY OF VERTEBRATED ANIMALS. 


fewer of the ribs. The two last-named structures are very 
distinct in the Coracomorphe, or Passerine Birds. 

The extent to which the keel of the lophosteon is de- 
veloped in the carinate birds varies very much. In Strigops 
it is rudimentary ; in birds of powerful flight, as well as in 
those which use their wings for swimming, it is exceedingly 
large. 

In the bird’s skull (Fig. 82), the brain-case is more arched 
and spacious, and is larger, in proportion to the face, than 
in any Reptilia, with the exception of the Pterosauria. 
There is a well-marked interorbital septum, but the extent 
to which it is ossified varies greatly. As a general rule, 
the superior temporal bar is incomplete, and there is no 
distinct post-frontal bone. The inferior temporal bar, 
formed by the jugal and quadrato-jugal, on the other hand, 
is always complete. There are no long parotic processes, 
nor any post-temporal fosse, the whole of each parietal 
bone being, as it were, absorbed in the roof of the skull. 

The nasal apertures are almost always situated far back 
near the base of the beak. In the dry skull (above Ma. 
in Fig. 82), there is a lachrymo-nasal fossa, or interval 
unoccupied by bone, between the nasal, lachrymal, and 
maxillary bones, such as exists in some Teleosawria, Dino- 
sauria, and Pterosauria, 

The posterior nares le between the palatines and the 
vomer; and the nasal passage is never separated from the 
cavity of the mouth by the union of palatine plates of the 
palatine or pterygoid bones. 

The Hustachian tubes generally traverse the basisphenoid, 
and have a common aperture upon the middle of the under 
surface of the skull. 

The bones of the brain-case, and most of those of the face, 
very early become ankylosed together into an indistinguish- 
able whole in most birds, but the sutures remain distinguish- 
able longer in the Chenomorphe and Spheniscomorphe; and 
especially in the Ratite. 

All the constituents of the occipital and parietal seg- 
ments of the skull are represented by distinct bones, but 


THE SKULL IN BIRDS. 223 


the frontal segment varies a good deal in this respect. 
The basisphenoid has a long rostrum, which represents 
part of the parasphenoid of the Ichthyopsida. Large frontal 


Fig. 82.—Lateral, upper, and under views of the skull of a common 
Fowl (Phasianus gallus). mxp.,the maxillo-palatine process. Qu., the 
quadrate bone. The dotted line accidentally stops at the angular 
process of the mandible. 


bones always exist, but the pre-sphenoidal and orbito- 
sphenoidal regions are not so regularly ossified. 

The ethmoid is ossified, and frequently appears upon the 
surface of the skull, between the nasal and the frontal 


284. THE ANATOMY OF VERTEBRATED ANIMALS. 


bones; and the internasal septum, in front of the ethmoid, 
may present very various degrees of ossification. Very 
frequently, the interspace between the ethmoidal and the 
internasal ossifications is simply membranous in the adult, 
and the beak is held to the skull only by the ascending 
processes of the premaxillary bones, and by the nasal 
bones, which are thin and flexible. By this means a sort 
of elastic joint is established, conferring upon the beak a 
certain range of vertical motion. In the Parrots, and some 
other birds, this joint is converted into a true articulation, 


Fig. 83, 


Fig. 83.—A longitudinal and vertical section of the posterior half of 
the skull of an Ostrich. P., the pituitary fossa; asc., psc., anterior 
and posterior vertical semicircular canals of the ear. 


and the range of motion of the upper beak becomes very 
extensive. 

The periotic capsule is completely ossified, and, as in 
other Sauropsida, the epiotic and the opisthotic are anky- 
losed with the occipital segment before they unite with the 
pro-otic. In the primordial skull of the bird the olfactory 
organs are surrounded by cartilaginous capsules, the lateral 
walls of which send in turbinal processes of very various 
degrees of complexity. When the posterior wall of this 


THE SKULL IN BIRDS. 285 


capsule is ossified, the bone thus formed represents the 
prefrontal, or lateral mass of the ethmoid, of the mammal. 
It is largely developed in the Apteryz, in the Casuaridae, 
and many other birds, but is absent in the Struthionide ; and, 
in other birds, is often represented by a mere bar of bone 
standing out from the ethmoidal ossification. 

The lachrymal is, usually, a distinct and large bone articu- 
lated with the nasal and frontal above, with the prefrontal 
internally, and with the maxilla, below; but sometimes it 
becomes undistinguishably fused with the prefrontal. Some- 
times, on the contrary, as in the Parrots, it acquires a large 
size, and sends a process backwards beneath the orbit, 
which may join with a post-orbital process of the frontal, 
and so circumscribe the orbital cavity. Opisthocomus ex- 
hibits the peculiarity of the complete ankylosis of the nasal 
with the lachrymal, which is quite free from the frontal 
and moves with the hinged beak. A supra-orbital bone, or 
chain of bones, may be developed in connection with the 
orbital margin of the frontal bone; and, occasionally, infra- 
orbital bones, appear below the orbit, parallel with the jugal 
arch. A post-orbital process may be developed from the 
frontal, or from the alisphenoid; and, in the latter case, 
may be separately ossified. 

The squamosal is closely applied to the skull, and is, 
usually, ankylosed with the other bones. It often sends a 
process downwards over the quadrate bone, and it may be 
united by bone with the post-orbital process of the frontal, 
as in the Fowl. 

The frame of the tympanic membrane not unfrequently 
contains distinct ossifications, which represent the tympanic 
bone of the Mammalia. 

The premaxille are modified in a manner which finds 
a partial parallel only among the Reptilia. They are 
tri-radiate bones of great size, which, usually, give off 
three processes; an ascending process to the frontal; a 
palatine process, along the middle of the palate, to the 
palatine bones; and an external, or maxillary process, 
which forms the greater part of the margin of the beak, 


286 THE ANATOMY OF VERTEBRATED ANIMALS. 


and unites with the maxilla. The two bones are very early 
represented by one continuous ossification. 

The vomers vary more than almost any other bones of the 
skull. They underlie and embrace the inferior edge of the 
ethmo-presphenoidal region of the basis cranii, and, in all 
birds in which they are distinctly developed, except the 
Ostrich, they are connected behind with the palatine bones. 
In most birds, they early unite into a single bone; but 
they remain long distinct in some Coracomorphe, and seem 
to be always separate in the Woudpeckers. The coalesced 
vomers constitute a very large and broad bone in most 
Ratite, and in the Tinamomorphe; anarrow elongated bone 
pointed in front in Schizognathe ; a broad bone deeply cleft 
behind, and abruptly truncated in front, in Coracomorphe. 
In most Desmognathe the vomer is small; and, sometimes, 
it appears to be obsolete. 

The maxille of birds are usually slender, rod-like bones, 
articulating by squamous suture, in front, with the pre- 
maxillz, and, behind, with the equally slender jugals. In 
the great majority of birds the maxilla sends inwards a 
maaillo-palatine process (Fig. 82, map.), which, sometimes, 
is mere thin lamella of bone, sometimes, becomes swollen 
and spongy. In the Ratite and the Desmognathe (Fig. 84), 
the maxillo-palatine processes unite with the vomer, or with 
one another, and form a complete bony roof across the 
palate. In the Schizognathe (Fig. 82), and githognathe, 
the maxillo-palatines remain quite distinct both from one 
another and from the vomer. 

The quadrato-jugal is usually a slender rod of bone, the 
hinder extremity of which presents, on its inner side, an 
articular head which fits into a fossa in the outer face of 
the distal end of the quadrate bone. 

The palatine bones are generally long and concave on 
their palatine faces. In front, they pass beneath (7.e., on 
the ventral side of) the maxillo-palatines and unite with 
the premaxill2, sometimes by a squamous suture, some- 
times by ankylosis, rarely, as in the Parrots, by a flexible 
joint. Posteriorly, they always unite with the ptery- 


THE SKULL IN BIRDS. 287 


goids. In most birds, the palatines converge, posteriorly, 
towards the basi-sphenoidal rostrum, and unite with it by 
an articular surface, which allows of a sliding motion of the 
palatines upon the rostrum. Such an articulation does not 
exist in Ratite, or in the Tinamous, among the Carinate. 
In these, (with the exception of Struthio), the palatines are, 
as it were, borne off from the rostrum by the divergent 
ends of the great vomer, and the disposition of the parts 


Fig. 84.—The under surface of the cranium of the Secretary bird ( Gy- 
pogeranus), as an example of the Desmognathous arrangement. Mzp., 
maxillo-palatine process; Bpt., basi-pterygoid processes. 


is more lacertillian than in other birds. The outer, or 
posterior, end of the pterygoid bone presents a fossa for an 
articular head, which is developed upon the inner side of 
the distal end of the quadrate. The inner, or anterior, ends 
of the pterygoids meet in almost all birds, and may become 
articulated with the basi-sphenoidal rostrum. In all em- 
bryonic birds, in all the Ratite, and in many Carinate, such 
as the Tinamomorphe, Charadriomorphe, Alectoromorphe, 


288 THE ANATOMY OF VERTEBRATED ANIMALS. 


Peristeromorphe, Chenomorphe, longer or shorter pro- 
cesses extend from the basi-sphenoid, and present terminal 
articular facets to corresponding facets upon the inner 
sides of the pterygoids. These are basi-pterygoid pro- 
cesses, similar to those which occur in Lacertilia and some 
Ophidia. 

The quadrate bone is almost always moveable upon the 
skull, articulating with the pro-otie, alisphenoid, and 
squamosal, by a single, or double, head. The distal head 
articulates with the mandible below, the quadrato-jugal on 
the outer, and the pterygoid on the inner, side. Hence, 
when the ethmo-nasal joint is developed, any forward move- 
ment of the distal end of the yuadrate, such as must take 
place when the mandible is depressed by the digastric 
muscle, causes the maxillo-jugal bar to thrust the pre- 
maxilla upwards and forwards; the palatine and pterygoid 
bones, at the same time, sliding forward upon the rostrum 
of the basisphenoid. Thus it comes about that the upper 
jaw of such a bird as a Parrot rises, when, in opening the 
mouth, the mandible is depressed. Each ramus of the man- 
dible consists primitively of six pieces, as in other Sau- 
ropsida, but the dentary pieces of each side are, as in the 
Chelonia, very early united, if indeed they are not ossified 
from one centre. Very often, a fontanelle remains between 
the dentary and the other elements, as in COrocodilia; and 
the dentary long remains readily separable from the rest; 
or, as in the Goatsuckers, is united with the others only by 
fibrous tissue, so that it is moveable. The angle of the 
mandible may be truncated or produced backwards into a 
long curved process, as in Fowls (Fig. 82), Ducks, and 
Geese. 

The hyoid is composed of basal elements, the anterior of 
which, usually composed of two portions, lies in the tongue ; 
and of two short, anterior, and two long, posterior, cornua, 
which are never united with the periotic region of the 
skull, and commonly remain quite free. In some of the 
Woodpeckers, however, the long posterior cornua are im- 
mensely elongated, and curve upwards and backwards over 


THE PECTORAL ARCH IN BIRDS. 289 


the skull (the frontal bones being grooved to receive them), 
and their free ends are inserted between the ascending and 
maxillary processes of the right premaxilla. 


Fig. 84.* 


Fig. 84.—The right scapula (Sc.), and coracoid (Co.) of a Fowl ; gi, 
the glenoidal cavity ; f, the right clavicle, or right half of the fur- 
culum ; Ap, the hypocleidium. 


The pectoral arch presents a long, narrow, and recurved 
scapula (Sc. Fig. 84*), without any supracapula; and a 
coracoid (Co.), fitted by its proximal end into the groove 
in the anterolateral edge of the sternum. The inner ends 
of the coracoids occasionally overlap, as in Lacertilia ; other- 
wise, the shoulder girdle is unlike that of any of the 
Reptilia, except the Pierosauria. The coracoid is usually 
completely ossified, and presents no fontanelle. There is 
no distinct epicoracoid. The two bones take nearly equal 
shares in the formation of the glenoidal cavity, and usually 
remain unankylosed and distinct in this region. 

In the Ratite the long axis of that part of the scapula 
which lies near the glenoid cavity is parallel or coincident 
with that of the coracoid, and the two bones become com- 
pletely ankylosed. But, in all the Carinatw, the long axis 
of the scapula forms an acute, or only slightly obtuse 
angle (Ocydromus, Didus) with that of the coracoid. A 
small bone, the scapula accessoria, is developed on the outer 

U 


290 THE ANATOMY OF VERTEBRATED ANIMALS. 


side of the shoulder-joint in most Coracomorphe and 
Celeomorphe. 

In the Carinate, the glenoidal end of the scapula is 
divided into two portions; a glenoidal process, which expands 
to form the upper part of the glenoidal cavity, and to unite 
with the coracoid—and an acromial process, which gives 
attachment to the outer end of the clavicle. The glenoidal 
end of the coracoid is in like manner divided into two por- 
tions; a glenoidal process, which unites with the scapula, and 
a clavicular process, which articulates with the outer surface 
of the clavicle, near its outer end. 

The clavicular process of the coracoid probably represents 
the procoracoid of Lacertilia. In the Ratite there is no 
distinct clavicular process, but the anterior part of the 
coracoid, near the glenoid cavity, may be produced and 
separated by a notch, or fontanelle, from the rest, as a 
lacertilian procoracoid. There is no trace of clavicles in 
the Apteryx and in some Parrots. In the Kmeu, and in 
sundry Carinate (some Parrots and Owls), the clavicles 
remain distinct from one another, or connected only by 
fibrous tissue; but, in the majority of birds, they are very 
early ankylosed together, and with the representative of 
the interclavicle, in the middle line, into a single bone, the 
furculum, the strength of which bears a pretty close re- 
lation to the exertion required of the wings in flight, or 
in natation. In the passerine birds the scapular end of 
the clavicle is usually expanded, and ossifies separately, 
as an epicleidiwm. A median process (hypocleidium) is 
frequently developed from the interclavicular part of the 
furculum, and this may be united with the carina of the 
sternum by strong fibrous tissue, or even by continuous 
ossification. In Opisthocomus, the furculum is ankylosed 
with the manubrial part of the sternum, on the one hand, 
and with the coracoids on the other. Ankylosis of the fur- 
eulum with the coracoids has also been observed in Didus. 

The fore limb of a bird, when in a state of rest, exhibits a 
great change of position if it be compared with that of an 
ordinary reptile ; and this change is of a character similar to, 


THE FORE LIMB IN BIRDS. 291 


but in some respects greater than, that which the arm of a 
man presents, when compared with the fore-limb of a quad- 
rupedal mammal. The humerus lies parallel with the axis 
of the body, its proper ventral surface looking outwards. 
The fore arm is in a position midway between pronation and 
supination, and the manus is bent back upon the ulnar side 
of the fore arm, in a position, not of flexion, but of abduc- 
tion. 

In ordinary birds, the proximal end of the humerus is 
expanded, and its articular head transversely elongated ; its 
ventral face is convex, and provided with a strong preaxial 
ridge, which gives attachment to the pectoral muscle. The 
proper dorsal face is concave from side to side, especially 
towards the postaxial margin, where the pneumatic aperture 
occurs in those birds which have the humerus hollow. The 
distal end is expanded, and the articular surface for the 
radius is a convex facet, directed obliquely inwards, on its 
ventral face. In this respect the bird’s humerus exaggerates 
a feature of that of the Lizards. 

In the Ratite these peculiarities are very feebly, or not 
at all, marked, the humerus being a slender, cylindrical, 
slightly curved, bone. In the Casuaride, Dinornithide, 
and Apterygide, the fore-limb is extraordinarily reduced, 
and may become rudimentary. In the Penguins and, toa 
less degree, in the great Auk, the humerus becomes flat- 
tened from side to side; the proximal end is singularly 
modified, and, at the narrow distal end, the articular sur- 
face for the radius lies completely in front of, and rather 
above, that for the ulna. 

The ulna, which often presents a series of tubercles, 
indicating the attachment of the secondary quill feathers, 
is usually a stronger, and a longer, bone than the radius. 
There are only two carpal bones, one radial and one 
ulnar. 

In the Apterygide and in the Casuaride, there is but one 
complete digit in the manus. It appears to answer to the 
second of the pentadactyle limb, and is provided with a claw. 
In the Struthionide and Rheide, and in all Carinate, there are 


292 THE ANATOMY OF VERTEBRATED ANIMALS. 

three digits in the manus, which answer to the pollex and the 
second and third digits of the pentadactyle fore limb; and 
the metacarpal bones of these digits are ankylosed together. 
Asa rule, the metacarpal of the pollex is 
much shorter than the other two; that of 
the second digit is strong and straight, 
that of the third is more slender and 
bowed, so as to leave an interspace be- 
tween itself and the second, which is 
often filled up by bony matter. The 
pollex has two phalanges, and the second 
of them is, in many birds, pointed, curved, 
and ensheathed in a horny claw. The 
second digit has three phalanges, and 
the terminal phalanx is similarly pro- 
vided with a claw in sundry birds, In 
the ostrich, both the pollex and the second 
» £9» digit are unguiculate. The third digit 
never possesses more than one or two 
phalanges, and is always devoid of a 
claw. 

It is a singular circumstance that the 
relative proportions of the humerus and 
the manus should present the most 
marked contrast in two groups of birds, 
which are alike remarkable for their 
powers of flight. These are the Swifts 
and Humming-birds, in which the hu- 
merus is short and the manus long; and 
the Albatrosses, in which the humerus is 
long and the manus relatively short. 

In the Penguins, the pollex has no 


Fig. 85. 


Fig. 85.—The radius 
(r); ulna(~); ra- 
dial and ulnar car- 
pal bones (7’, u’); 
with the three di- 


gits (i., ii., iii.), of 
the right fore limb 
of a Fowl. The 
terminal pha- 
langes of both the 
first and the se- 
cond digits were 
incomplete in the 
specimen figured. 


free phalanges, and its metacarpal bone 
seems to be ankylosed with that of the 
second digit. The third metacarpal is 
slender and straight. The bones of the 
manus are singularly elongated and 
flattened, 


THE PELVIS IN BIRDS. 293 


The pelvis of a bird (Fig. 86), is remarkable for the great 
elongation, both anteriorly and posteriorly, of the iliac 
bones (Z/.), which unite with the whole length of the edges 
of the sacrum (sm.) and even extend forwards, over the pos- 


Fig. 86.—A, lateral; and B, dorsal, view of the pelvis of a Fowl. 
Sm., sacrum; J/., ilium ; /s.,ischium ; Pb., pubis ; Am., acetabulum. 


terior ribs of the dorsal region. Below, each iliac bone 
forms awidearch over the upperpart of the acetabulum (Am.), 


294. THE ANATOMY OF VERTEBRATED ANIMALS. 


the centre of which is always closed by fibrous tissue, so that, 
in the dry skeleton, the bottom of the acetabulum is per- 
forated by a wide foramen. An articular surface on the 
ilium, on which the great trochanter of the femur plays, is 
called the antitrochanter. In all ordinary birds, the ischium 
(Fig. 86, Is.), which broadens towards its hinder end, extends 
back, nearly parallel with the hinder part of the ilinm, and 
is united with it by ossification, posteriorly. The iliosciatic 
interval is thus converted into a foramen. The pubis (Pb.) 
enters, by its dorsal or acetabular end, into the formation of 
the acetabulum, and then passes backwards and downwards 
as a comparatively slender, curved, bone, nearly parallel 
with the ischium. It is united with its fellow only by 
fibrous tissue. Neither the ischia, nor the pubes, unite 
directly with the sacrum. Very few birds present any im- 
portant deviation from this structure of the pelvis. In 
Tinamus, Casuarius, Dromeus, Apteryx, Dinornis, the ischium 
is not united with the backward extension of the ilium by 
bone. In Rhea, the ischia unite with one another beneath 
the vertebral column, and the vertebre in this region are 
very slender and imperfectly ossified. In Struthio, alone, 
among birds, do the pubes unite in a median ventral sym- 
physis. Another, not less remarkable circumstance, in the 
ostrich, is, that the 3lst to the 35th vertebre inclusively 
(counting from the atlas) develope five lateral tuberosities. 
The three middle tuberosities are large, and abut against 
the pubis and the ischium. In these vertebre, as in the 
dorsal vertebree of Chelonia, the neural arch of each ver- 
tebra shifts forward, so that half its base articulates with 
the centrum of the next vertebra in front; and the tube- 
rosities in question are outgrowths, partly of the neural 
arch, partly of the juxtaposed vertebral centra, between 
which it is wedged. Hence, in young ostriches, the face of 
each tuberosity exhibits a triradiate suture. 

The upper articular head of the femur is rounded, and its 
axis is almost at right angles with the body of the bone; a 
structure which is not found in ordinary Reptilia, but exists 
in the Iguanodon and other Ornithoscelida. The shaft is re- 


THE HIND LIMB IN BIRDS. 295 


latively short and thick, and the two terminal condyles are 
large and elongated antero-posteriorly. A prominent ridge, 
which plays between the proximal ends of the tibia and the 
fibula is apparent upon the posterior and inferior surface 
of the outer condyle. A similar ridge is faintly developed 
in some Lacertilia, and is well marked in the Dinosaurian 
reptiles. A patella is usually present, but it is sometimes 


absent, and may be double. 

The fibula of birds is always im- 
perfect, ending in a mere style 
below. Generally it is decidedly 
shorter than the tibia, but it has 
the same length as that bone in 
some Penguins. The tibia, or 
rather tibio-tarsus, is a highly cha- 
racteristic bone. Its proximal end 
is expanded and produced ante- 
riorly, into a great cnemial process 
(which may be variously subdi- 
yided) as in Dinosauria. The distal 
end is terminated by a well-marked 
pulley-like articular surface which 
is inclined somewhat forwards as 
well as downwards. Not unfre- 
quently there is an oblique bar of 
bone on the anterior face, just 
above the pulley, beneath which 
the long extensor tendons pass. 

The extremity of the cnemial 
process in Struthio and Rhea is 
ossified as an epiphysis; and, in 
young birds, the whole of the dis- 
tal articular end of the bone is 
separated from the rest by a su- 
ture, and also appears to be an epi- 


Fig. 87, 


AX, b. 

Fig. 87,—The right tibia 
and fibula of a Fowl. A, 
front view; B, external 
lateral view. ‘T., tibia; 
F., fibula; Cr., enemial 
process; As., astragalus. 


physis. But it is, in fact, as Professor Gegenbaur has 
proved, the proximal division of the tarsus (apparently 
representing only the astragalus of the other Vertebrata), 


296 THE ANATOMY OF VERTEBRATED ANIMALS. 


which exists in the embryo as a separate cartilage, and, as 
it ossifies, ankyloses with the tibia. The so-called tibia of 
a bird is therefore, properly speaking, a tibio-tarsus (see 
p. 263, Fig. 77, A, and Fig. 88). 

In all birds, even in Archeopteryx, the fifth digit of the 
pes remains undeveloped; and the second, third, and fourth 
metatarsals are ankylosed together, 
and, by their proximal ends, with a 
bone, which is a distinct cartilage in 
the foetus, and represents the distal 
division of the tarsus. Thus a tarso- 
metatarsus is formed. The distal ends 
of the metatarsals remain separate, and 
offer convex articular. surfaces to the 
proximal phalanges of the digits. 

In the Penguins, large apertures lie 
‘ between the several metatarsals of the 

} ee adult tarso-metatarsus; and, in other 
Fig. 88.—The distal hina : cal ideeible 7 

end of the left tibia birds, more or less considerable pa 

(7b.) with the as- sages persist between the middle and 

ieee is fee the lateral metatarsals proximally, and 

Fowl. Viewed from the middle and the outer, distally. In 

pe a aes from most birds, the middle metatarsal does 

: not remain parallel with the others, but 
its proximal end inclines a little backwards, and its distal 
end a little forwards. Hence the two apertures on each side 
of its proximal end may lie at the bottom of a fossa, or run 
into one, in front, while they remain distinct behind. 

Again, im most birds, the posterior face of the proximal 
end of the middle metatarsal, and the adjacent. surface of 
the tarsal bone, grow out into a process, which is commonly, 
but improperly, termed “ calcaneal.” The inferior surface 
of this hypo-tursus is sometimes simply flattened, sometimes 
traversed by grooves or canals, for the flexor tendons of the 
digits. 

When a hallux exists, its metatarsal bone is usually 
incomplete above, and is united by ligament to the inner, 
or the posterior, surface of the tarso-metatarsus. In the 


Fig. 88. 


THE FOOT IN BIRDS. 297 


Frigate-bird (Phaethon) and in Steatornis, the hallucal 
mnetatarsal is remarkably long. The genus Phaethon stands 
alone, so far as I know, in having the Fig. 89. 
hallucal metatarsal ankylosed with . 

the others. 

In many of the Alectoromorphe, a 
spur (calcar), consisting of a bony 
core ensheathed in horn, is developed 
on the inner side of the metatarsus, 
and becomes ankylosed with the me- 
tatarsal of the second digit. In afew 
birds, similar spurs (Palamedea), or 
osseous excrescences (Pezophaps), are 
developed in relation with the meta- 
carpus. 

The normal number of the pedal 
phalanges in birds is (as in ordinary 
Lacertilia) 2,3, 4, 5, reckoning from ~ A ‘ RB. 
the hallux to the fourth digit. Among Fig. 89, ernie eeu 
the few birds which constitute excep- _tarso-metatarsus of a 
tions to the rule are the Swifts, in ek onsite _of 
which the third and fourth toe have iv, anbeloced ae 
only three phalanges each (2, 3, 3,5), one another, and with 
and the Goatsuckers and the Sand- ne al Pag ce 
grouse, in which the fourth toe only aspect; B., inner as- 
has the number thus reduced (2, 3, 4,3). pect 

Many birds have only three toes, by suppression of the 
hallux. In the Ostrich, not only the hallux, but the pha- 
langes of the second digit, are suppressed; and the distal 
end of the second metatarsal is reduced to a mere rudiment. 
Hence the ostrich has only two toes (which answer to the 
third and fourth of the pentadactyle foot), with four pha- 
langes in the inner and five in the outer, though the inner 
toe is far the longer and the stronger. 

In most four-toed birds the hallux is turned more or less 
completely backwards, and the other three digits forwards. 
But in many Aetomorphee (especially the Owls), the outer toe 
can be turned outwards, or even backwards, at will. And in 


298 THE ANATOMY OF VERTEBRATED ANIMALS. 


the Parrots, Toucans, Cuckoos, Woodpeckers, and other so- 
called “ scansorial ” birds, the outer toe is permanently re- 
versed. Under these circumstances the distal end of the 
outer metatarsal may be divided into two distinct articular 
surfaces. In the Trogons, there are two toes in front and two 
behind, as in the Parrots, but it is the second toe which is 
turned backwards. Lastly, in the Swifts, the Dysporomorphe 
and the Spheniscomorphe, the hallux is directed more or less 
forwards, so that all four toes are turned to the front. 

As a general rule, the osseous tissue of birds is remark- 
ably dense and hard. Before hatching, the bones are solid 
and filled with vascular medulla; but, after birth, more or 
fewer of the bones are always excavated by prolongations 
of cavities containing air, which lie in their neighbourhood, 
Such air cavities are always found in the skull, in connec- 
tion with the nasal and auditory passages, and they may 
extend through all parts of the skull, with the exception of 
the jugal arch. In many birds, such as the Apteryx, Pen- 
guins, Divers, Gulls, and the smaller song-birds, no other 
bones than those of the skull are pneumatic; but, in most 
birds, the air sacs of the lungs send off prolongations into the 
bones of the rest of the skeleton, and thus the whole skeleton 
in some cases (as in the Hornbills) becomes pneumatic. 
It is proper to remark, that the amount of pneumaticity of 
the bones by no means follows the development of the 
power of flight. In the Ostrich, for example, the bones are 
far more extensively pneumatic than in the Gull. 

In some cases, prolongations of the air sacs extend he- 
neath the integument. 


CHAPTER VIL. 


THE MUSCLES AND THE VISCERA OF THE SAUROPSIDA. 


THE most important deviations from the ordinary ar- 
rangement of the muscular system occur, as might be 
expected, in the Ophidia, in the Chelonia, and in Aves. In 
the first-mentioned group, the numerous muscles-of the 
limbs are, of course, absent, and the mobility of the 
vertebre, ribs and jaws, is accompanied by a corre- 
sponding differentiation of the muscles of those parts. 
The episkeletal muscles form a continuous series (divis- 
ible into spinalis, semispinalis, longissimus dorsi, levatores 
costarum, and other muscles) from the end of the tail to 
the head; and, in the region of the back, constitute a thick 
mass which extends outwards to the ends of the caudal ribs 
(the so-called transverse processes), and over the dorsal thirds 
of the other ribs. Beyond these points it is continued, as a 
thinner layer of muscular fibres, over the ventral half of the 
tail and trunk, passing from rib to rib in the latter region, 
where the more dorsal fibres are directed obliquely, only a 
longitudinal band running along the extremities of the ribs 
and representing arectusabdominis. This muscle is continued 
forwards to the hyoidean apparatus, and thence to the man- 
dible. Superficial muscular bundles pass from the ribs to 
the scales. The hyposkeletal muscles are better developed 
than in most other Vertebrata, and also extend from the head 
to the end of the tail. A median dorsal set are connected with 
the subvertebral processes in the trunk, and with the bases 
of the representatives of the chevron bones in the tail, and 
pass to the caudal and dorsal ribs. One set of these, in the 
trunk, act as retractors of the ribs. The muscles which 


300 THE ANATOMY OF VERTEBRATED ANIMALS. 


correspond with the transversus abdominis, commence in the 
tail by transversely directed bundles of fibres, which arise 
from the roots of the caudal ribs (transverse processes) and 
meetin a median aponeurosis. In the trunk, similar bundles 
arise from the under surfaces of the ribs, and form two 
layers of oblique fibres, which also meet in the middle line. 

In the Chelonia, the episkeletal muscles are always weakly 
developed, and may be altogether abortive in the dorsal 
region, while those of the abdominal walls are small. The 
rectt are very weak, but muscles answering to the pyrami- 
dales extend from the pubes to the inner surface of the 
plastron. A muscular expansion analogous to a diaphragm 
may be attached to the bodies and ribs of the third and 
fourth dorsal vertebree, whence it expands over the surface 
of the lungs. No muscles pass from the head to the 
shoulder girdle. The pectoral arch is protracted, and 
the neck retracted, by a muscle attached to the cervical 
vertebree and to the procoracoid. There is also a single 
retractor of the pectoral arch, apparently representing a 
serratus magnus, and passing from the first costal plate to 
the scapula. The pectoralis major arises from the inner 
surface of the plastron. The representative of the latis- 
simus dorsi arises from the inner side of the first costal 
plate. 


The cutaneous muscles of birds are well developed, and 
form bread expansions in various parts of the body. Special 
bundles of muscular fibres pass to the great quill feathers of 
the tail and wings, and others to the patagiwm, a fold of in- 
tegument which extends between the trunk and the brachium 
behind, and between the brachium and ante-brachium in 
front. In correspondence with the slight mobility of the 
dorsal vertebrez, the episkeletal and hyposkeletal muscles of 
the spine attain a considerable development only in the 
neck and in the tail. Owing to the great size of the 
sternum, the abdominal muscles are usually small, and the 
internal oblique may be absent. A diaphragm, consisting 
of bundles of muscular fibres, which pass from the ribs to 


- NEUROLOGY OF THE SAUROPSIDA. 301 


the aponeurosis covering the ventral face of the lungs, is 
developed in all birds, but attains the greatest degree of 
completeness in the Ratitw, and especially in Apteryx. 

The muscles of the limbs are remarkably modified by the 
excessive development of some of those found in other 
Vertebrata, and the suppression of others. 

Thus in all birds possessing the power of flight, the 
pectoralis major, as the chief agent of the downward stroke 
of the wing, is very large and thick, taking its origin from 
the whole length, and a great part of the depth, of the keel 
of the sternum. 

The elevation of the wing is chiefly effected by the 
pectoralis tertius, which arises beneath the foregoing muscle, 
and passes over the inner side of the scapulocoracoid 
articulation, as over a pulley, to reach the humerus, The 
muscles of the forearm and digits are reduced, in accordance 
with the peculiar modification of the skeleton of these parts. 
In the hind limb of most birds there is a singular extensor 
muscle, which arises from the pubis, ends in a tendon which 
passes to the outer side of the knee-joint, and terminates 
in the leg by uniting with the flexor digitorum perforatus. 
The result of this arrangement is, that the toes are flexed 
whenever the leg is bent upon the thigh, and, consequently, 
the roosting bird is held fast upon his perch by the weight 
of his own body. 


In all the Sawropsida the cerebro-spinal axis is angulated 
at the junction of the spinal cord with the medulla oblongata, 
the latter being bent down towards the ventral side of the 
body. The region in which the nerves of the anterior and pos- 
terior extremities originate may be enlarged in reptiles, as 
in birds; but, in the former, the posterior columns of the 
cord remain parallel in the lumbar enlargement, while, in 
the latter, they diverge and give rise to the sinus rhom- 
boidalis, which is a sort of repetition of the fourth ventricle, 
the dilated central canal of the spinal cord being covered 
merely by a thin membrane consisting chiefly of the 
ependyma and arachnoid, 


302 THE ANATOMY OF VERTEBRATED ANIMALS. 


Fig. 90. 


Fig. 90.—A, C, the brain of a Lizard (Psammosaurus bengalensis), and 
B, D, of a bird (Meleagris gallopavo, the Turkey), drawn as if they 
were of pe Sa) lengths. A, B, viewed from above; C, D, from the left 
side. O/f., Olfactory lobes; Pn., Pineal gland; Hmp., cerebral 
hemispheres; J/Z6., optic lobes of the mid-brain ; ; Cb., cerebellum ; 
M. O., medulla oblongata; ii., Wv., vt., Second, fourth, and sixth pairs 
of cerebral nerves; Py., pituitary body. 


The brain (Big: 90) fills the cavity of the skull in the 
higher Sauropsida,and presents a well-developed cerebellum; 
a mesencephalon divided above into two optic lobes; and 
relatively large prosencephalic hemispheres, which attain a 
considerable size in Crocodilia and Aves, but never conceal 
the optic lobes. In Crocodilia the cerebellum presents a 
distinct vermis, with transverse fissures. In birds the 
latter are more distinct, and the lateral appendages of the 
cerebellum, or floceuli, become well defined, and are lodged, 
asin many of the lower Mammalia, in cavities of the side 
walls of the skull, arched over by the anterior vertical 
semicircular canal. 

There is no pons Varolii, in the sense of transverse fibres 
connecting the two halves of the cerebellum, visible upon 
the ventral surface of the mesencephalon. The optic lobes 
contain ventricles. In Reptilia, the optic lobes usually lie 
close together upon the dorsal side of the mesencephalon, 


NEUROLOGY OF THE SAUROPSIDA. 303 


but in Aves (Fig. 90 B, D) they are thrown down to the: 
sides of the base of the brain, and are connected over the 
aqueductus Sylvii by a broad commissural band. 

Each prosencephalic lobe contains a lateral ventricle 


Fig. 91. 


Fig. 91—The brains of a Lizard (Psammosaurus bengalensis) and of a 
bird (Meleagris gallopavo), in longitudinal and vertical section. The 
upper figure represents the lizard’s brain; the lower (taken, like 
fig. 90, B, D, from Carus’ “ Erlauterungs-Tafeln”’) that of the bird. 

The letters as in the preceding figure, except L. t., lamina termi- 
nalis, or anterior wall of the third ventricle; f. 1, foramen of 
Munro; a., anterior commissure; Zh. E., thalamencephalon; 
s., soft commissure; p., posterior commissure; iv., indicates the 
exact point of exit of the fourth pair from that part of the brain 
which answers to the valve ot Vieussens. 


304 THE ANATOMY OF VERTEBRATED ANIMALS. 


(continuous through the foramen of Munro with the third 
ventricle), which is little more than a fissure between the 
very thin inner wall of the lobe and its thick outer part, 
which contains the corpus striatum. The corpora striata 
are united by an anterior commissure, which is not of large 
size. The thinning of the inner wall of the lobes, from the 
margin of the foramen of Munro backwards, which gives 
rise to the fissure of Bichat in the Mammalia, extends for a 
very short distance in the Sawropsida, even in birds. 

The olfactory lobes are usually elongated, and contain 
ventricles continuous with those of the prosencephalic 
hemispheres. 

In all Sawropsida the motor nerves of the tongue pass 
through a foramen in the ex-occipital bone. Hence, twelve 
pairs of cranial nerves are present, except in the Ophidia, 
which possess no spinal accessory nerve. 

The lateral cutaneous branches so generally sent to the 
trunk by the pneumogastric in the I[chthyopsida are absent, 
but the pneumogastric gives a recurrent branch to the 
larynx. The third, fourth, and sixth nerves arise quite 
independently of the fifth. 

The sympathetic is well developed, except in the Ophidia, 
where it is not distinct from the spinal nerves, in the 
greater part of the trunk. 


The Ophidia, many Sawria, and Aves, possess nasal 
glands, which, in birds, attain a large size, and lie more 
usually upon the frontal bone, or in the orbits, than in the 
nasal cavity. 

The eye, rudimentary in some Ophidia and Lacertilia, is 
usually large; and, sometimes, as in many birds and in the 
extinct Ichthyosawria, attains very great absolute and rela- 
tive dimensions. 

In the Ophidia and some Lacertilia (the Amphisbeenoidea, 
some Scincoidea, all Ascalobota), the integument is con- 
tinued over the eye, and becomes transparent. These 
reptiles are commonly said to possess no eyelids; but it 
must be remarked that this is not true of them in the 


THE EYE-MUSCLES IN SAUROPSIDA. 305 


sense in which it is true of most osseous fishes, as the 
transparent covering of the eye really represents the 
two eyelids of the higher Vertebrata, and is separated 
from the eyeball by a chamber lined by conjunctiva, 
which communicates with the nose by a lachrymal canal. 
In the other Sauropsida two lids are developed, and each 
generally possesses a special palpebral muscle, which 
acts as an elevator of the upper, and a depressor of the 
lower, lid. In some Scincoidea the middle of the lower lid 
is transparent. In many Lacertilia it contains a cartilage 
or an ossification. 

Most lizards, all Chelonia, Crocodilia, and Aves, possess 
a nictitating membrane moved by special muscles, which 
present three different arrangements. 

In the lizards a short thick muscle (bursalis) is attached 
to the inner and posterior wall of the orbit, and ends in a 
fibrous sheath. A tendon, one end of which is attached to 
the presphenoidal region of the inner wall of the orbit, 
passes backwards through the sheath, and then forwards to 
be attached to the nictitating membrane. When the muscle 
contracts, it necessarily pulls the latter over the eye. A 
Harderian gland is always developed, and alachrymal gland 
very generally, though not always. 

In the Chelonia, muscular fibres (forming the so-called 
pyramidalis muscle) arise from the inner side of the eye- 
ball, and, arching over it and the optic nerve, are inserted 
partly into the outer edge of the nictitating membrane, 
partly into the lower eyelid. The Crocodilia have a py- 
ramidalis muscle taking the same origin and course; but it 
sends no fibres to the lower eyelid, its tendon being inserted 
altogether into the nictitating membrane. 

The third arrangement, which in a manner combines 
together the first and the second, is that seen in birds. A 
pyramidalis muscle, arising from the inner and under surface 
of the eyeball, soon ends in a tendon which sweeps round 
the upper and outer surfaces of the sclerotic to the nicti- 
tating membrane, as in the crocodiles. But there is also a 
bursalis muscle, which however arises, not, as in lizards, 

x 


306 THE ANATOMY OF VERTEBRATED ANIMALS. 


from the wall of the orbit, but from the upper surface 
of the sclerotic itself, whence it passes backwards and 
ends in a fibrous sheath which incloses the tendon of 
the pyramidalis. The contraction of this muscle neces- 
sarily tends to draw the tendon of the pyramidalis away 
from the optic nerve. A tubercle is sometimes developed 
from the sclerotic above the entrance of the optic nerve, 
and prevents the tendon of the pyramidalis from shifting 
forwards and inwards. 

The eyeball is always moved by four recti and two 
obliqui. The superior oblique does not pass over a pulley. 
The Chelonia and most Lacertilia have a more or less com- 
pletely developed retractor, or choanoid, muscle. 

A ring formed of bony plates is developed in the fore 
part of the sclerotic in Lacertilia, Chelonia, Ichthyosauria, 
Dicynodontia, Pterosawria and Aves, but not in Ophidia, 
Plesiosawria, or Crocodilia. 

The iris and the tensor choroidei contain striated mus- 
eular fibres. 

A pecten is very generally developed. It attains a large 
size, and becomes much plaited, in most Aves. 


Only Crocodilia and Aves possess a rudiment of an exter- 
nal ear. 

The Ophidia and the Amphisbenoidea have no tympanic 
cavity. In some Chelonia, in Sphenodon, and in the Chame- 
leons, the tympanic membrane is covered by the integu- 
ment, but a tympanic cavity exists. In Lacertilia, the 
tympanic cavities communicate by wide openings with the 
pharynx; but in Chelona, Crocodilia, and Aves, the com- 
municating passages, reduced in size, become Eustachian 
tubes. In the Chelonia, these curve backwards, downwards, 
and inwards, round the quadrate bones, and open separately 
on the roof of the mouth. In the Crocodilia there are, as 
has been described above (p. 255), three Eustachian tubes 
—one median and two lateral. In Aves, there is but one 
Eustachian aperture, answering to the median of the Croco- 
dilia; and, as in the latter group, each Eustachian tube 


THE ALIMENTARY CANAL IN SAUROPSIDA. 307 


usually traverses the osseous base of the skull, to join with 
its fellow in the common aperture. 

The stapes is a columelliform bone, the outer end of which 
is attached to the tympanic membrane, where the latter is 
developed; but lies among the muscles when there is no 
tympanic cavity. 

All Sauropsida possess a fenestra rotunda, as well as a 
fenestra ovalis, and all have a cochlea, which is never coiled 
spirally, and is more rudimentary in the Chelonia than in 
other groups. Three semicircular canals, an anterior and 
posterior vertical, and an external horizontal, are connected 
with the membranous vestibule. In Aves. the anterior 
vertical canal is very large in proportion to the others, and 
the adjacent crura of the two vertical canals overlap before 
they unite with one another. 


Labial and buccal glands are developed insome Sawropsida, 
and one of them, on each side, attains a large development in 
the poison glands of the venomous snakes. Well-developed 
sublingual, submaxillary, and parotid glands appear in 
Birds, and the sublingual glands attainanimmense size in the 
Woodpecker. The tongue varies greatly, being sometimes 
obsolete, as in the Crocodile and some birds (e.g. the Peli- 
cans), sometimes horny and even spinose, sometimes fleshy. 
Tn the snakes, and some lizards, the tongue is forked, and 
capable of retraction into a basal sheath. In the Cha- 
meleons, it is clubbed at its extremity, and can be retracted 
or protruded by the invagination or inversion of its hollow 
stem. 

The alimentary canal of the Sawropsida is generally 
divided into an csophagus, a simple stomach, a small 
intestine and large intestine, which last always terminates 
in a cloaca. It is invested by a peritoneal coat, which 
generally follows all the curvatures of the intestine. But 
in the Ophidia, the folds of the small intestine are united 
by fibrous tissue, and enclosed by a common sheath of 
peritoneum. 

The stomach is usually a simple dilatation of the alimen. 


308 THE ANATOMY OF VERTEBRATED ANIMALS. 


tary canal, the cardiac and pyloric apertures of which are 
remote from one another; but, in the Crocodiles, and in 
most Birds, the pyloric and cardiac apertures are approxi- 
mated. In many Crocodilia and Aves, there is a pyloric 
dilatation before the commencement of the duodenum. 

In the Crocodilia, and in Aves, the walls of the stomach 
are very muscular, and the muscular fibres of each side 
radiate from a central tendon or aponeurosis. The thick- 
ening of the muscular tunic of the stomach attains its 
maximum in the graminivorous birds; and it is accom- 
panied by the development of the epithelium into a dense and 
hard coat, adapted for crushing the food of these animals. 
Birds commonly aid the triturating power of this gastric 
mill by swallowing stones; but this habit is not confined to 
them, crocodiles having been observed to do the same thing. 

Birds are further remarkable for the development of a 
broad zone of glands in the lower part of the esophagus, 
which is usually dilated, and forms a proventriculus, 
connected by a narrow neck with the above-mentioned 
muscular stomach or gizzard (gigerium), 

Some Ophidia have a cecum at the junction of the small 
intestine with the large; and two such ceca, which some- 
times attain a large size, are very generally developed in 
Aves. In this class also, the small intestine, not unfre- 
quently, presents a cecal appendage, the remains of the 
vitelline duct. The duodenum of Birds constantly makes 
a loop, within which the pancreas lies, as in Mammalia. 

The liver in the Sawropsida almost always possesses a 
gall bladder, which is usually attached to the under surface 
of the right lobe, but in the Ophidia is removed to some 
distance from it. 

A peculiar glandular sac, the Bursa Fabricii, opens into 
the anterior and dorsal region of the cloaca in birds. 


Three forms of heart are found in the Sauropsida. The 
first is that observed in the Chelonia, Lacertilia, and Ophidia; 
the second, that in the Crocodilia; and the third, that in Aves. 

1. In the Chelonia, Lacertilia, and Ophidia, there are two 


THE HEART IN SAUROPSIDA. 309 


auricles. Generally, a distinct sinus venosus, with contractile 
walls, and communicating by a valvular aperture with the 
auricle, receives the blood from the vene cave, and pours 
it into the right auricle. The pulmonary veins usually 
open by a common trunk into the left auricle. 

The interauricular septum is rarely (in some Chelonia) 
perforated. Its ventricular edge spreads out on each side 
into a broad membranous valve, the edge of which, during 
the systole, flaps against a ridge, or fold, developed, on one, 
or both, sides, from the margin of the auriculo-ventricular 
aperture, and constituting a rudiment of a second valve. 
The ventricle contains only one cavity, but that cavity is 
imperfectly divided into two or three chambers, by septa 
developed from its muscular walls. 

In the Turtle (Fig. 92), a partly muscular, and partly 
cartilaginous, septum extends from the front wall of the 
ventricular cavity towards its right-hand end. It im- 
perfectly divides the common ventricular cavity into a 
right small, and a left large, moiety. The latter of these 
receives the blood from the auricles. In consequence of 
the elongated form of the ventricular cavity, and the pro- 
jection into it of the large auriculo-ventricular valves, 
especially of that of the right side, this left and larger 
moiety of the common ventricle is virtually divided into 
two, a left and a right, at the time of the auricular systole. 
The left portion becomes filled with arterial blood from the 
left auricle, and is distinguished as the cavum arterioswm ; 
the right receives the venous blood from the right auricle, 
and is the cavwm venosum. 

No arterial trunk arises from the cavum arteriosum, but two 
arterial trunks arise from the right-hand end of the cavum 
venosum ; these are the two aortic arches, One of these 
passes to the left and the other to the right side, and they 
cross one another as they do so, because the origin of the 
left arch lies more to the right, than does the origin of the 
left arch. The ostia of both arches are guarded by semi- 
lunar valves; and that of the left arch is placed below and 
to the right of that of the right arch. As no arterial trunk 


310 THE ANATOMY OF VERTEBRATED ANIMALS. 


arises from the cavum arteriosum, the red blood can be 
driven out of the latter, during the systole, only into the 
cavum venosum. 


Fig. 92.—The Heart of a Turtle (Chelone midas).— A, a drawing from 
nature: the ventral face of the ventricle being laid open, B, a 
diagram explanatory of the arrangement of the cavities and vessels. 
R.A., L. A. right and left auricles. w, x, arrows placed in the 
auriculo-ventricular apertures to indicate the course of the blood at 
the auricular systole. v, the right, and v!, the left median auriculo- 
ventricular valves. C v., cavum venosum. C. p.. cavum pulmonale. 
a, the incomplete septum which divides the cavum pulmonale from 
the rest of the cavity of the ventricle’ P.A., pulmonary artery. 
R. Ao., L. Ao., right and left aorte. s, arrow showing the course of 
the blood in the left aorta; ¢, in the right aorta; z, in the pulmo- 
nary artery; y, between the cavum venosum and cavum pulmonale ; 
x, in the left, and w, in the right auriculo-ventricular aperture. 


THE HEART IN SAUROPSIDA. 311 


The right, comparatively small, moiety of the ventricle 
is separated from the cavum venosum by the already 
mentioned septum, which is attached between the origin 
of the left aortic arch, and that of the pulmonary artery, 
its free edge looking towards the dorsal face of the heart. 
Thus the pulmonary artery arises from what is, virtually, a 
separate subdivision of the ventricle, or a cavum pul- 
monale, 

When the systole of the ventricle takes place, the prac- 
tical result of these arrangements is, that the pulmonary 
artery, and the aortic arches, at first, receive wholly venous 
blood from the cavwm venosum and cavum pulmonale, But 
as the arterial blood of the cavum arterioswm is driven into 
the cavum venosum, the venous blood of the latter tends to 
be excluded from the mouths of the aortic arches, and 
to be driven into the cavum pulmonale, while the aortic 
arches receive arterialised blood. The left arch receives 
a larger proportion of venous blood than the right. As the 
ventricle contracts, the free edge of the muscular septum 
approaches the dorsal wall of the ventricle, and gradually 
closes the access to the cavum pulmonale, which thus finally 
expels the venous blood which it received from the cavum 
venosum, but admits none of the arterialised blood; con- 
sequently none of this reaches the lungs. 

2. In the Croccdilia, the cavum venosum and the cavum 
arteriosum are converted into perfectly distinct right and 
left ventricles. The right ventricle gives off the pulmonary 
artery, and, in addition, an aortic arch which crosses over 
to the left side. From the left ventricle only a single trunk 
arises, and this, crossing to the right side, becomes the 
right aortic arch, of which the dorsal aorta is the direct 
continuation. The walls of the two aortic arches are in 
contact where they cross one another; and, at this point, 
a small aperture, situated above the semilunar valves, places 
the cavities of the two arches in communication. 

Thus, in the Crocodilia, the venous and the arterial 
currents communicate only outside the heart, not within it, 
as in the foregoing groups. 


312 THE ANATOMY OF VERTEBRATED ANIMALS. 


The septum of the cavum pulmonale remains as a small 
muscular band, and the fold of the outer lip of each 
auriculo-ventricular aperture, has become a distinct mem- 
branous valve. 

3. In Aves, the venous and arterial blood currents, com- 
municate only in the pulmonary and systemic capillaries. 
The auricular and ventricular septa are complete, as in 
the Crocodilia ; but the right ventricle gives off only the 
pulmonary artery, the left aortic arch having disappeared. 
The septum of the cavum pulmonale becomes a great 
muscular fold, and takes on the function of an auriculo- 
ventricular valve. At the origin of the pulmonary artery, 
and at that of the aortic arch, three semilunar valves are 
developed. 


In Reptiles there are usually only two aortic arches, one 
on each side, answering to the fourth pair of arches of the 
embryo. The right gives off the carotid and subclavian 
arteries, and passes directly into the trunk of the dorsal 
aorta. The left commonly gives off visceral arteries, and 
becomes a good deal diminished in size before joining the 
common trunk. 

In many Lacertilia, four aortic arches, (answering to the 
third and fourth pairs of the embryo,) persist, two anterior 
arches, from which the carotids are given off, springing, by 
a common trunk, from the right ordinary aortic arch. 

In the Reptilia, most of the blood of the hind limbs and 
tail passes through one or other of two “portal systems” 
before reaching the heart, the one portal system lying in 
the kidney, the other in the liver. The portion which goes 
to the liver is carried to it mainly by the anterior abdominal 
veins, which are represented by two trunks in most Reptilia, 
by one in the Ophidia. 

In Aves there is no renal portal system, and the anterior 
abdominal vein opens into the inferior vena cava close 
to the heart. Nevertheless a median trunk, which is given 
off from the caudal vein, carries a considerable proportion 
of its blood directly into the hepatic portal system. 


THE LARYNX IN SAUROPSIDA. 313 


All the Sawropsida possess a larynx, a trachea, and one 
or two lungs. The bronchi do not divide dichotomously, as 
they do in Mammalia. 

In Chelonia and Crocodilia the larynx consists of a 
circular cartilage, apparently corresponding with both the 
thyroid and the cricoid of the higher Vertebrata; and of 
the arytenoid cartilages, articulated with its anterior and 
dorsal edge. 

The Lacertilia have, for the most part, a similar larynx, 
but the circular cartilage is often interrupted by round, 
or elongated, membranous fontanelles. In the Chameleons, 
the mucous membrane of the larynx between the circular 
cartilage and the first rig of the trachea protrudes in the 
form of an air sac. 

In the Amphisbeenoidea, and in the Ophidia, the skeleton of 
the larynx consists of two lateral longitudinal bands of carti- 
lage, united by from four to sixteen transverse bands. In 
other words, the structure which answers to the circular 
cartilage is greatly elongated, and has many transversely 
elongated fontanelles. There is a single arytenoid car- 
tilage, which is sometimes represented by a process of the 
anterior dorsal margin of the circular cartilage. An 
epiglottis is rarely present. 

Tn Birds there are distinct thyroid, cricoid, and arytenoid 
cartilages, which may be more or less completely ossified. 
Sometimes an epiglottis is added. 

The voice of Birds, however, is not formed in the larynx, 
but im the syrinwz, or lower larynx, which may be developed 
in three positions:—l. At the bottom of the trachea, from 
the trachea alone. 2. At the junction of the trachea and 
bronchi, and out of both. 3. In the bronchi alone. The 
syrinx may be altogether absent, asin the Ratite and the 
Cathartidee, or American vultures. 

The commonest form of syrinx is the second mentioned 
above, or the broncho-tracheal syrinw. It is to be met with 
in all our common song birds, but is also completely deve- 
loped in many birds, such as the crows, which have no song. 
In its commonest condition this form of syrinx presents 


314 THE ANATOMY OF VERTEBRATED ANIMALS. 


the following characters. The hindermost rings of the 
trachea coalesce, and form a peculiarly shaped chamber, 
the tympanum. Immediately beyond this, the bronchi 
diverge, and from their posterior wall, where one bronchus 
passes into the other, a vertical fold of the lining membrane 
rises, in the middle line, towards the tympanum, and forms 
a vertical septum between the anterior apertures of the two 
bronchi. The anterior edge of this septum is a free and 
thin membrana semilunaris, but in its imterior a car- 
tilaginous or osseous frame is developed, and becomes 
united with the tympanum. The base of the frame is 
broad, and sends out two cornua, one along the ventral, 
and the other along the dorsal, edge of the inner wall of 
the bronchus of its side; which, in this part of its extent, 
is membranous and elastic, and receives the name of the 
membrana tympaniformis interna. 

The bronchial “rings” opposite this are necessarily in- 
complete internally, and have the form of arches embracing 
the outer moiety of the bronchus. The second and third 
of these bronchial ares are freely moveable, and elastic 
tissue accumulated upon their inner surfaces, gives rise to 
a fold of the mucous membrane, which forms the outer 
boundary of a cleft, bounded, on the inner side, by the mem- 
brana semilunaris. The air forced through these two clefts 
from the lungs sets their elastic margins vibrating, and 
thus gives rise to a musical note, the character of which is 
chiefly determined by the tension of the elastic margins and 
the length of the tracheal column of air. The muscles, by 
the contraction of which these two factors of the voice are 
modified, are extrinsic and intrinsic. The former are pos- 
sessed by birds in general, and are usually two pair, passing 
from the trachea to the furcula and to the sternum. Some 
birds possessing a broncho-tracheal syrinx such as has been 
described, as the Alectoromorphe, Chenomorphe, and Dy- 
sporomorphe, have no intrinsic muscles. Most others have 
one pair, attached, one on each side, to the rings of the 
trachea above, and to the tympanum, or the proximal 
bronchial ares, below. The majority of the Coracomorphe 


THE RESPIRATORY ORGANS IN SAUROPSIDA. 315 


have five or six pairs of intrinsic syringeal muscles, which 
pass from the trachea and its tympanum to the moveable 
bronchial arcs. The Parrots have no septum, and only 
three pairs of intrinsic muscles. 

The tracheal syrinw occurs only in some American Cora- 
comorphe. The hinder end of the trachea is flattened, and 
six or seven of its rings above the last are interrupted at 
the sides, and held together by a longitudinal hgamentous 
band. These rings are excessively delicate, so that this 
part of the trachea is in great part membranous. 

The bronchial syrinx occurs only in Steatornis and Croto- 
phaga. 

In the genus Cinyxis, among the Chelonia, and in some 
species of Crocodilus (C. acutus,e.g.) the trachea is bent upon 
itself. Similar flexures attain an extraordinary development 
in many birds, and may lie outside the thorax under the in- 
tegument (Tetrao wrogallus, some species of Craw and Pene- 
lope) ; in the cavity of the thorax (some Spoonbills); on the 
exterior of the sternum (some Swans and Cranes); or even 
in a sort of cup formed by the median process of the 
fureula (the Guinea-fowl). In the Emenu some of the rings 
of the trachea are incomplete in front, and bound the 
aperture of an air sac which lies in front of the trachea, 
Some birds (Aptenodytes, Procellaria) have the trachea 
divided by a longitudinal septum, as in Sphargis among the 
Chelonia. The tracheal tympanum is greatly enlarged in 
Cephalopterus, and in many Ducks, Geese, and Divers; and 
in these aquatic birds the enlargement is more marked in 
the males, and is usually asymmetrical, the left side bemg 
generally the larger. 

In the Ophidia, the bronchus opens at once into the lung; 
and the latter is an elongated sac, the walls of which are 
produced into numerous septa, which render the cavity 
highly cellular near the bronchus, while, at the opposite end, 
they become smooth and but little vascular. In this latter 
region the lung may receive its blood from the systemic and 
not from the pulmonary circulation. The lungs are always 
unequal in size, and the left is usually the smaller. Very 


316 THE ANATOMY OF VERTEBRATED ANIMALS. 


frequently, especially among the poisonous snakes, one lung 
is rudimentary or altogether absent; and the posterior 
portion of the trachea may take on the structure of a lung. 

The lungs of Lizards much resemble those of the Ophidia, 
and they are elongated and unequal in size in the snake- 
like Lacertilia. In the ordinary lizards they are more 
rounded and the trachea and bronchi are shorter. In many 
Chameleons, and in some Geckos, the posterior half of 
each lung is produced into narrow diverticula, which le 
among the abdominal viscera, and foreshadow the air sacs 
of birds. 

In the Crocodilia each bronchus traverses its lung, and 
at first retains, but soon loses, its cartilaginous rings. 
Lateral apertures in the walls of the bronchus lead into 
sacculated pouches, each of which resembles the lung of an 
ordinary Lacertilian. 

The Chelonia have similar lungs; but while, in the fore- 
going groups, the two lungs are free and invested on all 
sides by the peritoneum, in this they are fixed against the 
inner periosteum of the carapace, and are covered by peri- 
toneum on their ventral face only. This resemblance to 
the arrangement of the lungs in birds is increased by the 
presence of a muscular diaphragm, the fibres of which 
spread over the ventral faces of the lungs. 

In Aves the lungs are firmly fixed on each side of the 
vertebral column, the dorsal surface of each lung being 
moulded to the superjacent vertebrz and ribs. The muscular 
fibres of the diaphragm arise from the ribs outside the 
margins of the lungs, and from the vertebral column, and 
end in an aponeurosis upon the ventral surface of the 
lungs. 

Each bronchus enters its lung nearer the centre than 
the anterior edge ; and, immediately losing its cartilaginous 
or bony rings, dilates, and then traverses the lung, gradually 
narrowing, to the posterior edge of that viscus, where it 
terminates by opening into the posterior air sac, which 
generally lies in the abdomen. From the inner side of the 
bronchus canals are given off, one near its distal end, and 


THE AIR SACS IN BIRDS. 317 


others near its entrance into the lung, which pass directly 
to the ventral surface of the lung, and there open into other 
air sacs. Of these there arefour. Two, the anterior and the 
posterior thoracic, lie on the ventral face of the lung in the 
thorax. The other two are situated in front of its anterior 
end, and are extra-thoracic. The external and superior is 
the cervical, the internal and inferior, the interclavicular. 
This last unites into one cavity with its fellow of the oppo- 
site lung. Thus there are altogether nine air sacs; two 
posterior or abdominal, four thoracic, two cervical, and 
one interclavicular. Other large canals given off from the 
bronchus do not end in air-sacs, but those which pass from 
the inner side of the bronchus, run along the ventral sur- 
face, and those on the outer side, along the dorsal surface, 
of the lung. Here they give off, at right angles, series of 
secondary canals, and these similarly emit still smaller ter- 
tiary canals; and thus the whole substance of the lung be- 
comes interpenetrated by tubuli, the walls of the finest of 
which are minutely sacculated. The different systems of 
tubuli are placed in communication by perforations in their 
walls. 

In most birds, the air-sacs (except the anterior and pos- 
terior thoracic, which never communicate with any cavity 
but that of the lungs) are in connection with a more or less 
extensively ramified system of air passages, which may ex- 
tend through a great many of the bones, and even give off 
subcutaneous sacs. Thus the interclavicular air-sac gene- 
rally sends a prolongation into each axilla, which opens 
into the proximal end of the humerus, and causes the 
cavity of that bone to be full of air. When the sternum, 
the ribs, and the bones of the pectoral girdle are pneumatic, 
they also receive their air from the interclavicular air-sacs. 
The cervical air-sacs may send prolongations along the ver- 
tebral canal of each side, which supply the bodies of the 
cervical vertebre, and communicate with elongated air- 
chambers in the spinal canal itself. When the dorsal ver- 
tebra are pneumatic, they communicate with the system of 
the cervical air-sacs. The abdominal air-sacs send pro- 


318 THE ANATOMY OF VERTEBRATED ANIMALS. 


longations above the kidneys to the sacral vertebre and 
to the femora, whence these bones, when they are pneu- 
matic, receive their air. 

The pulmonary air-sacs and their prolongations do not 
communicate with the air cavities of the skull, which re- 
ceive their air from the tympana and the nasal chambers. 
In some birds, the air is conducted from the tympanum 
to the articular piece of the mandible by a special bony 
tube, the siphonium. 

In all Sawropsida, the ureters open directly into the 
cloaca, which is provided with a urinary bladder in the 
Lacertilia and the Chelonia, but not in other Reptilia, nor in 
Aves. 

Organs of copulation present themselves under three 
forms :— 

1. In the Chelonia, the Crocodilia, and the Ostrich, a 
simple solid penis, grooved upon its posterior aspect, is at- 
tached to the anterior wall of the cloaca, and contains 
erectile tissue. In the ostrich this penis lies in a sac of the 
cloaca, into which it can be retracted somewhat as in the 
Menotremata. 

2. In many birds, such as the Rheide, Casuaride, 
Apterygide, Tinamomorphe ; Penelope, and Crazx, among the 
Alectoromorphe ; and in many aquatic birds, there is also 
a single penis attached to the front wall of the cloaca, 
grooved on its dorsal side, and supported by two fibrous 
bodies coated with more or less erectile tissue. But the 
distal end of the penis is invaginated, and the involution 
held in this position, except during erection, by an elastic 
ligament. 

3. In Lacertilia and Ophidia, two copulatory organs are 
developed at the sides of the cloaca. The integument is 
prolonged inwards, on each side, into a blind sac, which 
lies upon the inferior caudal muscles. The imner surface 
is often armed with spiny developments of the epidermis, 
and presents a groove, which is continued on the parietes 
of the cloaca to the aperture of the vas deferens. The 
wall of the blind sac contains erectile tissue, and it can be 
erected or retracted by appropriate muscles. 


319 


CHAPTER VIII. 


THE CLASSIFICATION AND ORGANIZATION OF THE 
MAMMALIA. 


THE class Mammalia is divisible into the following 
groups :— 

A. There are large and distinct coracoid bones, which articulate 
with the sternum. 

The ureters and the genital ducts open into a cloaca, into 
which the urinary bladder has a separate opening. 

The penis is traversed by an urethral canal which opens into 
the cloaca posteriorly, and is not continuous with the cystic 
urethra. 

There is no vagina. 

The mammary glands have no teats. 


I, OnnITHODELPHIA. 


1. Monotremata. 


B. The coracoid bones are mere processes of the scapula in the adult, 
and do not articulate with the sternum. 
The ureters open into the bladder; the genital ducts, into an 
urethra or vagina. 
The cystic urethra is continuous with the urethral canal of 
the penis. 
There is a single or a double vagina. 
The mammary glands have teats. 
A, The embryo does not become connected with the 
wall of the uterus by an allantoic placenta. The 
vagina is double. 


Il. DivELrura. 
; 2. Marsupialia. 


B. The embryo has an allantoic placenta, The vagina 
is single. 


Til.—Monopevpnia.* 
a, Median incisor teeth are never developed in either jaw. 


* The manner in which the Monodelphia are here subdivided must 
be regarded as merely provisional. 


320 THE ANATOMY OF VERTEBRATED ANIMALS. 


3. Edentata. 
6. Median incisor teeth are almost always developed in 


one or both jaws, 
;. The uterus developes no decidua (Noti-decidteada): 


4. Ungulata. 
5. Touodontia (?).* 
6. Sirenia (2).* 
7. Cetacea. 
zi. The uterus developes a decidua (Deciduata). 
a. The placenta is zonary. 
8. Hyracoidea. 
9. Proboscidea. 
10. Carnivora. 
g. The placenta is discoidal. 
11. Rodeutia. 
12, Insectivora. 
13. Cheiroptera. 
14. Primates. 

I. The ORNITHODELPHIA are those mammals which 
approach nearest to the Sawropsida, although separated 
from them by all the essential characters of the Mammalia 
which have already been defined. 

The two genera Echidna and Ornithorynchus, which con- 
stitute this division, agree with one another, and differ from 
all other Mammals, in the combination of the following 
characters :— 

In the spinal column, the centra of the vertebre are 
devoid of epiphyses. The os odontoidewm, or so-called 
“ odontoid process” of the second cervical vertebra remains 
for a long time, if not throughout life, umankylosed with 
the body of that vertebra, as is the case in many Reptiles. 
And some of the cervical ribs, in like manner, long persist 
in a separate condition. 

A striking Saur opsidan and Amphibian feature, peculiar 
to the Ornithodelphia, is seen in the fact that the coracoid, 
which is a large bone, articulates with the sternum directly. 
In front of it is another considerable ossification called the 
epicoracoid, which corresponds in position, though not in 
the manner of its ossification, with the ossified cartilage So 
termed in reptiles. In these mammals alone, again, there 


is a T-shaped interclavicle, which supports the clavicles. 


* The placentation of the Toxodontia and Sirenia is unknown. 


THE ORNITHODELPHIA. 321 


The central portion of the acetabulum remains unossified, 
and hence, in the dry skeleton, appears perforated, as in 
Aves, Ornithoscelida, and Crocodilia. 

The inner tendons of the external oblique muscles are 
ossified for a considerable distance; and these ossifications 
appear in the dry skeleton as bones, which are articulated 
with the inner portions of the anterior margins of each 
pubis. These bones correspond with those which exist in 
a like position in the Didelphia, and are called marsupial 
bones; though the term is peculiarly inappropriate, inas- 
much as they have nothing to do with the marsupiwn, 
or pouch, in which the young are sheltered in most of the 
Didelphia. 

In the upper view of the brain the cerebellum is left 
completely uncovered by the cerebral hemispheres. The 
latter are connected by only a very small corpus callosum. 
The anterior commissure, unlike that of any of the Sawrop- 
sida, attains a very great size, and the hippocampal sulcus 
is prolonged forwards to the corpus callosum. 

In the internal ear, the cochlea is only slightly bent upon 
itself, not coiled into a spiral, as in other Mammalia. The 
stapes is imperforate and columelliform, and the malleus is 
very large, while the incus is singularly small. 

There is a spacious cloaca common to the rectum, genital 
and urinary organs, as in the Sawropsida and many Ichthy- 
opsida. In both sexes a long urogenital canal opens into 
the front part of the cloaca. At its anterior end there are 
five distinct apertures—one in the middle line for the 
bladder, and two on each side, which are the openings of 
the genital ducts and of the ureters. Thus in these Mam- 
malia, and in these only, the ureters do not open into the 
urinary bladder. The testes remain in the abdomen through- 
out life. The penis is attached to the front wall of the 
cloaca, and is not united directly with the ischia. It is 
traversed by an urethral canal, which opens into the cloaca 
posteriorly, but is not directly connected with either the 
seminal or the urinary passages. It is probable that during 
copulation, the posterior aperture of the penial urethra is 

¥ 


322 THE ANATOMY OF VERTEBRATED ANIMALS. 


applied to the anterior aperture of the urogenital canal, so 
as to form a continuous passage for the semen. 

The ova of the female are very large and project from the 
surface of the ovary, as in the Sawropsida. The mouths of 
the Fallopian tubes are not fimbriated. There is no vagina 
distinct from the urogenital chamber. The mammary 
glands are situated, one upon each side of the middle line, 
in the hinder part of the abdominal wall. The various 
ducts of the gland open upon a small area of the integu- 
ment which is not raised up into a teat, so that, m the 
strict etymological sense of the word, these animals are not 
Mammalia. The mammary gland is compressed by the 
panniculus carnosus, and not by any prolongation of the 
eremaster. 

There is no sufficient evidence of the nature of the fetal 
appendages; but the embryo is born in an imperfect con- 
dition, and may be provided with a knob or caruncle upon 
the premaxille, such as is found in the Sawropsida. In the 
adult the heart exhibits a fossa ovalis. 

Both genera of the Ornithodelphia are restricted to Aus- 
tralia, including Tasmania under that name. 

The one of them, Hcehidna, has the body covered with 
spines, like a porcupine. It possesses strong digging feet, 
and a narrow toothless mouth, from which the long tongue, 
with which it licks up the ants upon which it preys, is 
protruded. 

The other genus, Ornithorhynchus, has soft fur; a flattened 
muzzle resembling the beak of a duck, and covered with a 
leathery integument; and clawed, but strongly webbed feet, 
fitting it for its altogether aquatic mode of life. The Orni- 
thorhynchus, in fact, frequents fresh water pools and rivers, 
very much like a water rat, sleeping and breeding in 
burrows excavated in the bank. 

In these animals the angle of the mandible is not in- 
flected. They are devoid of any external ear; and in the 
males, a kind of spur, which is perforated, and gives exit to 
the secretion of a gland, is attached to the astragalus. The 
function of this organ is unknown. In each genus the 


THE DIDELPHIA. 323 


heart is provided with two superior cave. In Hehidna the 
right auriculo-ventricle valve is membranous, but, in Or- 
mithorhynchus, it is more or less fleshy. 

The hemispheres of the brain are abundantly convoluted 
in Eehidna, but are smooth in Ornithorhynchus. The 
Ovaries are of equal size in Hchidna ; but, in Ornithorhynchus, 
the right is much smaller than the left, as in Birds. As 
has already been stated, Hchidna is entirely devoid of teeth, 
while Ornithorhynchus has four large horny teeth. 


IJ. The DiprnpHi1a.—In the Didelphia, the “ odontoid 
_ process” early becomes completely ankylosed with the body 
of the second vertebra; and, usually, all the cervical ribs 
speedily lose their distinctness, as in Mammals in general. 

The coracoid is reduced to a mere process of the scapula 
and does not come near the sternum. There is no epi- 
_coracoid, such as exists in the Ornithodelphia. There is no 
T-shaped interclavicle, but the clavicles, which are always 
present (except in Perameles) articulate with the manu- 
brium of the sternum, in the same way as in ordinary Mam- 
malia. The floors of the acetabula are completely ossified, 
and consequently are imperforate in the dry skeleton. The 
cochlea is coiled upon itself. 

There is a shallow cloaca, the sphincter muscle being 
common to the urinary and genital apertures, but there is 
no such urogenital chamber as in the Monotremata. The 
ureters open directly into the bladder. 

In the male, the urogenital part of the urethra, and that 
which traverses the penis, form one continuous canal, which 
opens outwards only at the extremity of the penis. 

In the female, the vaginal, is perfectly distinct from the 
urinary, passage. The mouths of the Fallopian tubes are 
fimbriated, and the ova are not larger than those of the 
Monodelphia. 

The mammary glands are provided with long teats. 

In all the preceding characters the Didelphia agree with 
the Monodelphia, and differ from the Ornithodelphia. 

But they agree with the Ornithodelphia, and differ from 


324 THE ANATOMY OF VERTEBRATED ANIMALS. 


the Monodelphia in possessing either bones, or cartilages, 
attached to the pubes, in the position of the so-called 
marsupial bones of the Ornithodelphia. 

Again, the brain, the cerebral hemispheres of which may 
or may not have a convoluted surface, is provided with a 
very small corpus callosum, and a large anterior com- 
missure. The hippocampal sulcus is prolonged forwards 
over the corpus callosum. 

The crura of the corpus cavernosum of the penis are not 
fixed to the ischium. 

The embryo does not become connected with the parentby 
villi developed from the allantois, and it is born in avery - 
imperfect condition. 

Certain characters are peculiar to the Didelphia. Thus, 
the testes of the male pass into a scrotum, which is sus- 
pended in front of the penis. In the female, the cremaster 
muscle is largely developed, and spreads over the surface of 
the mammary gland, which it compresses, so as to drive 
the milk out of the projecting teat. There is no fossa 
ovalis on the right side of the septum of the auricles. 
Very generally, though not invariably, the Didelphia possess 
what is termed a marsupial pouch, which is a sort of bag, 
formed by a fold of the integument of the abdomen, into 
which muscular fibres of the panniculus carnosus extend. 
These support the ventral wall of the pouch, and are 
capable of closing its mouth, which may be directed either 
forwards or backwards. The mammary glands lie in the 
dorsal wall of this pouch, into which the teats project. 

There is no direct communication between the female 
generative organs and the pouch; but the minute young 
are transported, in the blind and imperfect state in which 
they are born, into the interior of the marsupiuwm, and each 
becomes attached to a nipple, which exactly fills its mouth. 
To this it remains attached for a considerable period, the 
milk being forced down its throat by the contraction of the 
cremaster muscle. The danger of suffocation is averted 
by the elongated and conical form of the upper extremity 
of the larynx, which is embraced by the soft palate, as in 


THE DIDELPHIA. 325 


the Cetacea; and thus respiration goes on freely, while the 
milk passes, on each side of the laryngeal cone, into the 
cesophagus. 

Tt very commonly happens among the Didelphia that the 
two long vaginz are bent upon themselves, their proximal 
ends becoming applied together and dilated, and these 
dilated portions not unfrequently communicate. Another 
very general peculiarity of the Didelphia is the inflection 
of the lower margin of the angle of the mandible inwards 
into a strong horizontal process. In the genus Tursipes, 
however, this process is absent. 

There are further anatomical characters which are well 
worthy of notice, though they are not so important as the 
foregoing. 

The integument is always furry, never spiny or scaly, nor 
provided with dermal scutes. The pinna of the external 
ear is well developed. In the skull the carotid arteries 
pierce the basisphenoid to enter the cranial cavity. The 
tympanic cavity is, in front, bounded by the alisphenoid; 
and, very generally, the jugal furnishes part of the articular 
surface for the mandible. 

Many of the cranial sutures, especially in the occipital 
region, persist throughout life; and the squamosal, the 
united periotic ossifications, and the tympanic bones remain 
distinct from one another. 

The jaws are always provided with true teeth; and, 
usually, these teeth are readily distinguished into incisors, 
canines, false molars, and true molars. The canines, how- 
ever, are absent in some genera, either in both jaws or in 
the mandible. There are usually four true molar teeth, 
and, as Professor Flower has recently discovered, only one 
grinder succeeds another vertically. It represents the last 
premolar. The molars never possess a complex structure. 

No didelphous mammal has three incisor teeth upon each 
side above and below; and none but Phascolomys has an 
equal number of incisors in each jaw, the number of the 
upper being, usually, in excess of that of the lower jaw. 

The number of the dorso-lumbar vertebre is almost 


326 THE ANATOMY OF VERTEBRATED ANIMALS. 


always nineteen ; and, of these, six are usually dorsal. The 
atlas is generally incompletely ossified in the ventral 
median line. The manus usually possesses five digits, but 
in Perameles and Cheropus the outer digits become rudi- 
mentary. 

The fibula is always complete at its distal end. In some 
cases it becomes ankylosed with the tibia, while in the 
Wombat (Phascolomys), the Phalangers (Phalangistide), and 
the Opossums (Didelphide), it is not only free, but is capable 
of a rotatory movement upon the tibia, similar to the move- 
ment of pronation and supination of the radius upon the 
ulna in Man. The rotation of the fibula towards the ventral 
side of the tibia is effected by a muscle which, in great 
measure, occupies the place of the interosseous ligament, 
and is analogous to the pronator quadratus in the fore limb. 
This muscle is antagonised by the extensors of the digits, 
so far as they arise from the fibula. 

The digits of the pes vary remarkably in their form and 
relative development among the Marsupialia; the different 
subdivisions of the order being very well distinguished by 
the modifications of the hind foot. 

Thus in the especially carnivorous marsupials—the Didel- 
phide, of America, and the Dasyuride, of the Australian 
province—the second and third digits of the pes are not 
united together by the integument. In the Didelphide, the 
hallux is nail-less, but large and opposable, so as to convert 
the pes into a prehensile organ like that of many Primates ; 
in the Dasywride, on the other hand, the hallux is rudi- 
mentary or absent. In all the other marsupials, the second 
and third digits of the pes are syndactyle, or united together 
by integument. In the Wombat, the fourth toe is bound 
together with the other two, and the small hallux is devoid 
of anail. In the Phalangers, only the second and third 
toes are syndactyle, and they are slender, compared with 
the other digits, while the hallux is well developed and | 
opposable. In the Peramelide (Bandicoots) and Macro- 
podide (Kangaroos), the metatarsus is much elongated, and 
the second and third digits united and slender, while the 


THE DIDELPHIA. 320 


fourth toe is very large. The hallux is reduced to its 
metatarsal bone in the Peramelide, and the fifth digit is 
small or rudimentary. In the Kangaroos, the hallux dis- 
appears altogether, but the fifth digit remains well de- 
veloped, though not so large as the fourth. 

There is a great range of variation in the characters 
of the brain. The carnivorous marsupials (Didelphys, 
Dasyurus, Thylacinus) exhibit the lowest type of cerebral 
structure, the olfactory lobes being very large and com- 
pletely exposed, while the cerebral hemispheres are com- 
paratively small and quite smooth. In the Kangaroos, on 
the other hand, the cerebral hemispheres present numerous 
convolutions and are much larger in proportion to the 
olfactory lobes, which they cover. 

The stomach may be simple, as in most Marsupialia, or 
provided with a cardiac gland (Phascolarctos, Bhascolomys). 
In the Kangaroos, it becomes immensely elongated, with 
longitudinal muscular bands and transverse sacculations, 
so that it resembles the human colon. The cecum, which is 
large in the Kangaroos, but absent in the Dasyuride, is 
provided, in the Wombat, with a vermiform appendix lke 
that of Man. 

The liver always possesses a gall-bladder. There are two 
vence cave superiores, and they receive the ven azygos of 
their respective sides. The tricuspid valve in the heart is 
membranous. There is no inferior mesenteric artery, and 
the external and internal iliacs arise separately from the 
aorta. 

There are no vesicule seminales, and the glans penis is 
bifurcated in many species. The marsupial pouch is absent 
in some Opossums and Dasywride. When it is present, its 
mouth is usually directed forwards, but in Thylacinus and 
in some Peramelide it looks backwards. In Thylacinus also 
the “marsupial bones” remain cartilaginous. The con- 
dition of the fetus is known only in the Kangaroos, and 
further observations on the embryology of the Didelphia 
are much needed. The fetus is said to possess a large 
umbilical sac, the vessels of which extend on to the plaited 


328 THE ANATOMY OF VERTEBRATED ANIMALS. 


chorion; and a small allantois; and to be devoid of a thymus 
gland. 

The Didelphia are at present confined to the Australian 
and the Austro-Columbian provinces, some few species 
stretching beyond the borders of the latter into the northern 
parts of North America. The Didelphide alone are found 
in Austro-Columbia, all the other groups being Australian. 

Gigantic, Kangaroo-like, or Phalangistic, forms (Notothe- 
rium, Diprotodon, Thylacoleo), have been found in post-tertiary 
deposits and caves in Australia. In Europe, Didelphide 
occur in Eocene strata; Didelphide, Dasywride, and Ma- 
cropodide (Phascolotherium, Amphitherium, Plagiaulax), in 
middle Mesozoic rocks; and Macropodide (?) (Microlestes) in 
the Trias. 


III. The MonopreLpu1A.—In the Monodelphia, the os 
odontoidewm very soon becomes ankylosed with the second 
cervical vertebra, of which it appears merely as the odontoid 
process; and the cervical ribs early become inseparably 
united with their vertebre. The coracoid is reduced to a 
mere process of the scapula, and there is no epicoracoid 
similar to that of the Ornithodelphia. 

Clavicles may be present or absent. When completely 
developed they articulate directly, or by the intermediation 
of more or less modified remains of the sternal end of the 
coracoid, with the sternum, and not with any interclavicle. 
The acetabula are imperforate. The pelvis is devoid of 
marsupial bones; though, in some Carnivora, there are small 
cartilages in the inner tendons of the external oblique 
muscle, which have a corresponding form and relations. 

The anterior commissure and the corpus callosum, no less 
than the cerebral hemispheres themselves, vary greatly, the 
brains of some Hdentata very closely approaching those of 
the Didelphia in respect of the corpus callosum and an- 
terior commissure; while, as regards the hemispheres 
themselves, they may either be so small as to allow the cere- 
bellum to be completely exposed on the dorsal aspect, or so 
large, as completely to cover it and project beyond it. The 


THE MONODELPHIA. 329 
external surface of the hemispheres again, may be either 
perfectly smooth or extremely convoluted. 

The cochlea is coiled spirally. The reproductive and 
urinary apertures, as a general rule, open quite separately 
from the rectum. The ureters always open into the bladder. 
The testes may remain in the abdomen throughout life, 
or may pass into a scrotal pouch. But, when this scrotum 
forms a distinct sac, it lies at the sides of, or behind, the 
penis, and not in front of it. The cystic urethra is always 
continuous with that part of the urethra which traverses 
the penis. 

The ova are small, and the mouths of the Fallopian tubes 
are fimbriated. The vagina is a single tube, which may 
however be partially divided by a longitudinal partition. 
The cremaster has no relation to the mammary glands, 
which are provided with distinct teats. 

The allantois is always well developed, and gives rise to a 
placenta; and the young are born of large size, and 
active. 

The great majority of the Monodelphia, as thus defined, 
are divisible according to the characters of their placenta 
into non-deciduata ee deciduata. 

In the non-deciduata the fetal villi of the placenta are, 
at birth, simply withdrawn from the uterine fosse, into 
which they are received, and no part of the maternal 
substance is thrown off in the form of decidua, or maternal 
part of the placenta. In the deciduata, on the other hand, 
the superficial layer of the mucous membrane of the uterus 
undergoes a special modification, and unites, to a greater 
or less extent, with the villi developed from the chorion 
of the fetus; and, at birth, this decidual and maternal 
part of the placenta is thrown off along with the fcetus, 
the mucous membrane of the uterus of the parent being 
regenerated during, and after, each pregnancy. 

There are, however, two orders of existing monodelphous 
Mammalia, the nature of the placentation of which is not 
yet fully made out. One of these is the Sirenia, the pla- 
centation of whichis unknown. ‘The other is the ill-defined 


330 THE ANATOMY OF VERTEBRATED ANIMALS. 


and heterogeneous assemblage called Hdentata. Some of 
the members of this group certainly possess deciduate pla- 
cent, while, in others, it appears questionable whether 
the decidua is, or is not, developed. And as this group, 
the Hdentata, is decidedly the lowest of the whole division, I 
shall take it first in order, while the Sirenia are arranged, 
provisionally, among the Non-deciduata. 


The EpENnTATA, or Bruta.—In these Mammals the 
teeth are by no means always wanting, as the name of the 
group would seem to imply; but, when teeth are present, 
incisors are either altogether absent, or, at any rate, the 
median incisors are wanting in both jaws. The teeth are 
always devoid of enamel, consisting merely of dentine and 
cement. As they grow for an indefinite period they never 
form roots; and, so far as our knowledge at present 
extends, those which first appear are displaced by a 
second set only in some of the Armadillos. The ungual 
phalanges of the digits support long and strong claws. 

There are mamme upon the thorax, and sometimes, in 
addition, on the integument of the abdomen; or, in the 
inguinal region. 

The brain varies greatly, its hemispheres being some- 
times quite smooth, with a very small corpus callosum and 
large anterior commissure; while, in other cases, the cor- 
pus callosum is much larger, and convolutions appear upon 
the surface of the brain. 

The Hdentata are divided into the Phytophaga, or vege- 
table feeders, and the Entomophaga, or insect-eating forms. 
Leaves are the chief food of the former group, while the 
latter delight chiefly in ants, though some take, in addition, 
worms and carrion. 

1. In the Phytophaga the long bones are without me- 
dullary cavities. The lateral part of the zygomatic arch 
sends down a remarkable vertical process. The acromial 
process of the scapula coalesces with the coracoid. In the 
carpus, the scaphoid and the trapezial bones ankylose and 
form one. The ischia become united with the anterior 


THE EDENTATA PHYTOPHAGE. 331 


caudal vertebre, and these ankylose with the proper sacrals 
to form the long sacrum. 

The ankle joint has the character of a peg and socket, 
and the hind foot is, more or less completely twisted, rest- 
ing upon its outer edge, and not upon its sole. 

Vascular canals connected with the pulp cavity traverse 
the dentine of the teeth. 

The Phytophaga are divisible into two groups, one exist- 
ing, and the other extinct. The former consists of the 
Sloths, or Tardigrada ; remarkable animals, which are con- 
fined to the great forests of South America, where they 
lead a purely arboreal life, suspended by their strong, hook- 
like, claws to the branches of the trees. 

Their distinctive characters are these :—The tail is short, 
and the limbs exceedingly long and slender, the anterior, 
beimg longer than the posterior, pair. In both the fore and 
the hind limbs the internal and the external digits are 
rudimentary, but the hind foot always has the three middle 
toes completely developed; while, in the fore foot, it some- 
times happens that only two remain. The ungual pha- 
langes are very long and hooked. 

The zygomatic arch is incomplete posteriorly, not being 
united by bone with the squamosal. The cervical vertebree 
in this remarkable group sometimes exceed, and sometimes 
fall short of, the number (seven) which is so characteristic 
of the Mammalia in general; some species of Sloths having 
nine, and others only six, vertebre in the neck. 

The pelvis is exceedingly spacious, and the acetabula are 
directed backwards as well as outwards. The femur is de- 
void of a ligamentwmn teres. The distal end of the fibula 
sends inwards a process which fits into a fossa situated 
upon the outer surface of the astragalus, giving rise to that 
kind of peg and socket ankle-joint which is peculiar to these 
animals. 

A good deal of confusion prevails respecting the structure 
of the ankle-joint in the Sloths. Cuvier (‘ Ossemens fossiles,’ 
t. viii. p. 143), writes of the Ai, or three-toed Sloth: 

“In the greater number of animals, the principal articu- 


302 THE ANATOMY OF VERTEBRATED ANIMALS. 


lation of the astragalus connects it with the tibia, by means 
of a more or less loose ginglymus, which allows the foot to 
be bent on the leg. But here the principal and superior 
facet of the astragalus is a conical fossa, into which the 
pointed extremity of the fibula penetrates, like a pivot. 
(See Pl. 208, fig. 2a.) The inner edge of this fossa turns 
against a very small facet, which occupies only a third of 
the lower head of the tibia. The result of this arrange- 
ment is that the foot turns on the leg, like a weathercock 
on its support, but that it cannot be flexed. It further 
follows that the plane of the sole of the foot* is almost 
vertical when the leg is so, and that the animal can only 
place the plantar surface of its foot on the ground by 
spreading out the leg so as to make it almost horizontal.” 
Meckel,+ has already justly remonstrated against Cuvier’s 
assertion that only abduction and adduction are possible 
to the pes of the Ai, affirming that it is capable of flexion 
and extension, though only to a limited extent. A. Wagner 
follows Meckel, but Rapp (‘Edentaten, p. 46) adopts 
Cuvier’s statement in its fulness: ‘“ Extension and flexion 
of the foot cannot take place, but only abduction and 
adduction.” However, it is easy to demonstrate on the 
uninjured dead animal, or still better, on the limb from 
which the muscles have been removed, while the ligaments 
have been left intact, that the pes of the three-toed Sloth 
is capable of extensive motion in three directions; Ist, in 
abduction and adduction; a movement in azimuth, when 
the leg is vertical; 2ndly, in flexion and extension; a more 
extensive movement in altitude, under the same circum- 
stances; and 3rdly, in rotation upon its own axis, by means 
of which the sole can be moved through 90° from a position 
perpendicular to the axis of the leg to one parallel with it. 
The anatomical arrangements upon which the execution 
of these movements depend are the following. The astraga- 


* Cuvier’s words are: “Il en résulte encore que le plan, le corps du 
pied, est presque vertical quand la jambe l’est.”’ 

+ ‘System der vergleichenden Anatomie,’ 2te Theil., 2te Abthei- 
lung, p. 457. 


THE ANKLE-JOINT OF THE SLOTHS. 300 


lus presents two facets to the bones of the leg, one of which 
(when the pes is in the position usual in other quadrupeds) 
looks inwards and upwards, while the other looks outwards 
and upwards. The former, convex from before backwards, 
as well as from side to side, is by no means a mere rim, 
though it is not so wide as the other. It is the proper 
proximal surface of the astragalus, and articulates with the 
tibia. The other surface is excavated by a deep conical pit. 
Into this is received a correspondingly conical process of 
the distal end of the fibula, which is directed from above 
and without, downwards and inwards—unot vertically, there- 
fore, but very obliquely. Hence, even if the pivot fitted 
its socket quite accurately, there would still be abundant 
opportunity for flexion and extension, though the movement 
of the pes would be obliquely inwards, as well as upwards, in 
the former case; and obliquely outwards, as well as down- 
wards, in the latter. But the socket fits the pivot loosely, 
and hence, as experiment demonstrates, the movement 
of the pes in flexion and extension is but very slightly 
oblique. 

The true movement of abduction and adduction is so 
much less extensive than the movement in flexion and 
extension, because it is checked by the short and strong 
internal and external lateral ligaments of the ankle-joint. 

With respect to the rotation of the foot on its own axis— 
it is to be observed, in the first place, that the calcanewm, 
cuboides, naviculare, the three cuneiformia, the three com- 
plete and the three rudimentary metatarsals, and the three 
basal phalanges of digits 7., iii., and iv., are ankylosed to- 
gether into one bony mass; while, as in the manus, there 
is hardly any motion between the basal and the middle 
phalanges. Practically, in fact, the only bones of the pes 
which are movable upon one another are: J. The distal 
phalanges, which have a movement of extension and flexion 
through 180° upon the middle phalanges. 2. The tarso- 
phalangeal synostosis above described is freely movable on 
the astragalus; and the joint is disposed in such a manner 
as to allow the sole of the foot to be rotated from the 


34 THE ANATOMY OF VERTEBRATED ANIMALS. 


plantigrade position in which it is perpendicular to the 
axis of the leg, to the scansorial position, in which it lies 
parallel with the axis of the leg. It may be doubted, how- 
ever, whether the former position can be given to the sole 
by the living animal. The tibialis anticus and the extensor 
hallucis longus are extremely strong muscles, and have no 
efficient antagonists; so that their tonic contraction must 
pull the nayicular metatarsal tuberosity into which they are 
inserted as far upwards as it will go, causing the tarso- 
phalangeal synostosis to rotate upon the astragalus, and 
thus obliging the sole of the foot to look inwards. 

In the two-toed Sloth, or Unau (Cholepus), the general 
structure of the ankle-joint is the same, but the fossa of 
the astragalus looks almost directly outwards, and the pivot 
of the fibula is more nearly horizontal, when the leg is 
vertical. The tibial facet of the astragalus looks directly 
upwards. Hence, the movement of the pes is more ex- 
clusively one of flexion and extension than in the Ai. No 
ankylosis of the tarsal, metatarsal, and phalangeal bones 
occurs, but the rotation of the distal moiety of the tarsus 
upon the astragalus is much more complete and permanent 
than in the Ai. The calcaneum is twisted round under the 
astragalus, in such a manner that its proper external face 
becomes inferior, while the articular surface for the cuboid 
is not only below, but is partially internal to, the navicular 
facet of the astragalus. Asa result of this position of the 
cuboid, the outer metatarsals, which it supports, are placed 
directly beneath the inner ones, and the pes rests absolutely 
upon its outer edge, the plane of the sole being vertieal. 

The Sloths, it thus appears, are naturally club-footed; 
but neither in the Ai, nor in the Unau, does this depend in 
any way on the structure of the ankle-joint. On the con- 
trary, it results, in the Unau, from the manner in which 
the calcanewm and naviculare articulate with the astragalus ; 
and, in the Ai, from the action of the muscles on the tarso- 
phalangeal synostosis. Neither in the Ai, nor the Unau, 
is there anything to interfere with free flexion and exten- 
sion of the pes. 


THE EDENTATA ENTOMOPHAGA. 300 

The teeth are five in number on each side above, and 
four below, and become sharpened by mutual attrition into 
a chisel-like form. The stomach is remarkably complex. 

The Gravigrada are, for the most part, ike the Sloths, 
South American forms, but they are entirely extinct; and 
while, in most respects, they resemble the Sloths, in others 
they present an approximation to Ant-eaters. 

The jugal arch may be complete or incomplete. The 
articular surfaces of the dorsal vertebre are sometimes 
complicated in a manner similar to that observed in the 
Ant-eaters. The tail is very long and strong. The limbs 
are short and sub-equal, while the fore foot has the ulnar 
digit imperfect, as in the Ant-eaters. The fibula has 
no inward process, and the astragalus is consequently de- 
void of any fossa upon its outer surface. But another 
kind of peg and socket ankle-jomt is produced by the 
interlocking of the surfaces of the tibia and of the astra- 
galus. 

The great extinct animals, Megatherium, Mylodon, Me- 
galonyx, &c., the remains of which have been found almost 
wholly in later tertiary deposits of America, belong to this 
group. 

2, The Hntomophaga.—In this group of Hdentata the zy- 
goma sends down no process from its lateral region, 
although, in some rare cases, the anterior part of the arch 
has a descending prolongation. The acromion and the 
coracoid do not become united. The scaphoid and the 
trapezium remain distinct; and the sole of the hind foot 
rests upon the ground by a greater or lesser extent of its 
whole surface, and not merely by its outer edge. 

The insectivorous edentates are divisible into four groups 
—a. the Mutica, b. the Squamata, c. the Tubulidentata, and 
d. the Loricata. 

a. The group of the Mutica contains the genera Myrme- 
cophaga and Cyclothurus, the Ant-eaters of South America. 
The bodies of these animals are covered with hair, and they 
are provided with very long tails, which are sometimes pre- 
hensile. The skull is greatly elongated, and the small pre- 


336 THE ANATOMY OF VERTEBRATED ANIMALS. 


maxille are but loosely connected with it. The jugal arch ~ 


is incomplete. In Myrmecophaga, the pterygoids, which are 
very long, stretch back to behind the level of the tympanic 
bull, with the whole inner edges of which they are united 
either by bone or by membrane; and as, at the same time, 
they unite in the middle line, the roof of the palate is greatly 
prolonged, and the posterior nares are bounded below and 
at the sides, by the pterygoid bones. This arrangement 
is to be found in no other Mammals, except some Cetacea, 
nor in any other Vertebrata, except the Crocodiles. The 
mandible is very slender, the ascending ramus, coronoid pro- 
cess, and angle of the jaw, being obsolete. The articular 
surface of the condyle is flat. The hyoid is placed far back 
beneath the posterior cervical vertebre, and is connected with 
the skull only by muscles. The thyroid and the cricoid car- 
tilages are ossified. The dorso-lumbar vertebre are com- 
plicated by the presence of accessory articular processes. 
Well-developed clavicles are present in the climbing Cyclo- 
thurus didactylus, but they are incomplete, or absent, in 
the other species. In the manus, the outer digit, or digits, 
are devoid of claws, and the weight of the body, when 
the animal walks, is supported upon its outer edge, which 
is frequently thick and callous. The pes has five digits, 
each provided with a strong nail, and the sole rests upon 
the ground. 

The tongue is extraordinarily long and protractile; it is 


not connected to the hycid by the ordinary hyo-glossus | 


muscles; but long muscles, which are attached to the ster- 
num (sternoglossi), retract it, while it is protracted by the 
genio-glossi and stylo-hyoidet. 

Immense submaxillary glands extend back over the tho- 
rax, and cover the tongue with a viscid secretion, when it is 
thrust into the nests of the ants, upon which the Myrme- 
cophaga preys. The insects, entangled by thousands in 
this substitute for birdlime, are then dragged back into the 
mouth of the Ant-eater, and swallowed. The pyloric 
portion of the stomach is so exceedingly thick and mus- 
cular as to be comparable to a gizzard. The brain presents 


) 


THE EDENTATA SQUAMATA. 337 


numerous convolutions, and has a large corpus callosum. 
The anterior commissure is also remarkably large. In the 
female, the uterus is simple, but has a double os uteri. 
The placenta is said to be discoidal in form in Myrme- 
cophaga didactyla. 

b. The group of the Squamata contains the single genus 
Manis, species of which are found both in Africa and 
Southern Asia. In these singular animals, the body is 
covered with overlapping, horny scales, and they have the 
power of rolling up like hedgehogs. In walking, the long 
claws of the fore foot are bent under, so that their dorsal 
surfaces rest upon the ground, while the weight of the 
hinder part of the body is thrown upon the flat soles of the 
hind feet. 

_ The skull is elongated, the premaxilla is small, and the 
zygoma usually incomplete. The pterygoids are much 
elongated and extend backwards beyond the bullate tym- 
panic bones, but they do not unite in the middle line. The 
mandible has no ascending ramus, and its condyle is flat. 
Air passages in the walls of the skull place one tympanum 
im communication with the other and extend into the 
squamosal: bone. There are no clavicles. The “xiphoid ” 
extremity of the sternum is large, and may be produced 
into two long cornua, as in Lizards. The mouth is toothless. 

The large salivary glands extend on to the thorax. The 
stomach is divided into a thin-walled cardiac sac, lined by a 
dense epithelium, and a thick muscular pyloric portion. It 
is always found to contain numerous stones. The placenta 
appears to be diffuse and non-deciduate. 

e. The Tubulidentata are also represented only by a single 
genus, Orycteropus, which is a native of South Africa. The 
body is hairy, provided with thoracic and inguinal teats, 
and the ears are long, not short or rudimentary, as in the 
preceding genera. In both the fore and the hind limbs, 
the foot rests evenly upon the ground and mainly upon the 
plantar surfaces of the strong claws. The fore foot has 
only four digits, in consequence of the absence of the 
pollex, while the hind foot is pentadactyle. 

Z 


338 THE ANATOMY OF VERTEBRATED ANIMALS. 


The skull has a complete zygoma and well-developed pre- 
maxille. The lachrymal bone is large, and the lachrymal 
foramen is situated upon the face. The tympanic bone is 
annular, and the periotic mass so large, and enters so 
much into the lateral walls of the skull, as to remind one 
of its proportions in the Sawropsida. The mandible has 
an ascending ramus. The clavicles are complete. 

The jaws are provided with teeth, the substance of which 
is traversed by a great number of parallel vertical canals. 
These teeth are rootless molars, and the greatest number 


which has been observed is — but the small anterior ones 
fall out, reducing them to as The hindermost, and the 
small anterior ones, are simple cylinders, but the middle 
teeth present a longitudinal groove, on each side. 

The submaxillary glands are very large. The stomach 
is divided into a right and a left portion; the former 
having very thick and muscular walls. The intestine 
has a cecum. It is stated that the ductus arteriosus long 
remains open. 

The two uteri open separately into the vagina. The pla- 
centa is deciduate and discoidal 

d. In the Loricata, the dorsal region of the body is 
covered by a carapace, composed of epidermal scales, and 
of suturally united quadrate, or polygonal, scutes, which 
are dermal ossifications, so that the whole structure is 
strictly comparable to the dorsal shield of a crocodile. These 
are the only mammals in which such scutes exist. When 
fully developed, the dorsal armour of one of these animals 
presents five distinct shields, the edges of which permit of a 
certain amount of motion between them. One of these 
covers the head, and is called cephalic; another, nuchal, 
protects the back of the neck; a third, scapular, covers 
the shoulders like a great cape; a fourth, usually consisting 
of a number of free and movable segments, covers the 
posterior dorsal and lumbar region, as the thoraco-ab- 
dominal shield; and the fifth, the pelvic, is attached by its 


THE EDENTATA LORICATA. 339 


deeper surface to the ilia and ischia, and arches over the 
rump like a half dome. The tail may further be invested 
by a series of incomplete bony rings and scattered scales ; 
and scutes are distributed over the limbs. In one genus, 
Chlamydophorus, the scutes are developed only in the pelvic 
region. 

In the skull the premaxille are well developed, and the 
zygoma is complete. The mandibular ramus usually has a 
well-developed ascending portion and coronoid process. 
Clavicles are present. The fore and the hind feet rest 
upon the ground evenly, and indeed the hind lmbs are 
usually plantigrade, or nearly so; but, in the singular 
genus Tolypeutes, the fore foot is supported upon the ex- 
tremities of the long nails. The pollex is always present 
in the fore foot, but the fifth digit sometimes becomes rudi- 
mentary. There are always five toes in the hind foot. 

In the genus Huphractes, each premaxilla contains a 
single tooth, which, consequently, is an incisor. 

This group contains two divisions, the Dasypodide and 
the Glyptodontide; both are South American, but the 
former is chiefly composed of living animals, while the 
latter only contains an extinct genus. 

The Dasypodide are what are commonly known by the 
name of Armadillos. In this division the thoraco-abdominal 
shield, when present, as it is in all the genera except Chla- 
mydophorus, consists of, at fewest, three, and, at most 
thirteen, transverse movable zones of scutes. 

In the skull, the ends of the nasal bones project beyond 
the level of the premaxille, so that the nasal aperture looks 
more or less downwards. The premaxille have a consider- 
able size, and articulate largely with the nasals. The 
anterior part of the jugal arch offers, at most, a rudimentary 
downward prolongation. The mandibular symphysis has 
but a moderate length, and the posterior alveoli of the 
mandibles do not extend along the inner face of the 
ascending portion of the ramus of the jaw. 

The teeth of the upper and lower jaws alternate, and 
hence their grinding surfaces wear down into ridges. 


340 THE ANATOMY OF VERTEBRATED ANIMALS. 


The odontoid vertebra is ankylosed with a greater or 
smaller number of its successors. The cervical vertebre 
which follow these have peculiar accessory articular sur- 
faces; and the hinder dorsal and the lumbar vertebre are 
also provided with accessory articular facets and processes. 
A number of the anterior caudal vertebre are always 
ankylosed with one another, and with the true sacrals, to 
form the long sacrum; and the transverse processes of 
some of these caudal vertebre abut against the inner sur- 
faces of the ischia, and become ankylosed therewith. 

The first rib is broad and flattened, and the anterior piece 
of the sternum is expanded. The succeeding vertebral ribs 
are connected by ossified sternal ribs with the sternum, 
and these are articulated, not only with the sternum, but 
with one another. 

In the carpus, the cuneiform bone bends round the unci- 
form, and articulates with the fifth metacarpal, when that 
bone is present, The ungual phalanges of the manus are 
long and pointed. The femur has a third trochanter, and 
the four inner metatarsals are much longer than they are 
broad. 

The division of the Glyptodontide contains the single 
genus Glyptodon, which is essentially a large armadillo; 
but it departs, in some respects, not only from all these 
animals, but from all other Mammalia, and even stands 
alone among the Vertebrata, 

The carapace covers the whole body, but presents no 
movable thoraco-abdominal zones, inasmuch as it consists 
of polygonal plates firmly united together, and fringed by 
a margin of scutes with raised conical surfaces. 

The nasal bones are short and broad, and their free 
ends do not project so far as the premaxille; whence the 
anterior nasal aperture looks slightly upwards as well as 
forwards. The premaxille, however, are very small bones, 
and if they unite with the nasals at all, do so for a very 
short distance. The anterior portion of the jugal arch 
gives off a great downward process. The mandibular sym- 
physis is very long, and the posterior alveoli of the man- 


THE UNGULATA. 341 


dible are situated upon the inner face of the very high per- 
pendicular part of the ramus. The teeth are trilobed, two 
deep grooves excavating their inner and their outer sur- 
faces. And, as the crowns of those of each jaw are placed 
opposite each other, they are worn flat. 

The last cervical and the anterior dorsal vertebre are 
ankylosed together into a single “ tri-vertebral” bone, which 
moves by a hinge joint upon the third dorsal. This and 
the succeeding dorso-lumbar vertebre are 1mmovably 
united, and, for the most part, ankylosed, together. The 
head of the first rib is engaged in the socket furnished to 
it by the tri-vertebral bone in such a manner as to be 
Immovable, and the rib is not flat, but rounded and co- 
lumnar. 

In the carpus, the cuneiform bone articulates with the 
fourth, as well as with the fifth metacarpal, the latter bone 
being entirely supported by the cuneiform. The metacarpals 
and phalanges are all very short and broad. The pollex is 
rudimentary, while the fifth digit is fully developed. 

The supra-condyloid ridge of the femur is not distinct 
from the third trochanter, even if the latter can be said to 
exist at all. The metatarsal bones are as broad as they are 
long, or broader; and, as in the fore foot, the majority of 
the phalanges are comparatively short and truncated. 

THe Non-pDecipuATE Mammaria.—I. UneuLata.—A 
large number of the non-deciduate Mammalia are con- 
veniently comprehended under the title of the Ungulata, 
though it may be open to question whether the group 
thus named represents a single order, or more than one. 

In all the Ungulata the placenta is either diffuse, that is 
to say, the villi are scattered evenly over the surface of the 
chorion; or it is cotyledonary, in which latter case, the villi 
are accumulated in distinct patches on the chorion. These 
patches are called cotyledons. 

All Ungulata have milk teeth, succeeded vertically by 
teeth of the permanent set. The teeth consist of enamel, 
dentine and cement, and the grinders have broad crowns, 
with tuberculated, ridged, or folded enamel. 


342 THE ANATOMY OF VERTEBRATED ANIMALS. 


Clavicles are never present. The limbs have not more 
than four complete digits. The ungual phalanges are 
clothed in obtuse horny sheaths, which are commonly very 
thick and go by the name of hoofs. Upon these the weight 
of these quadrupeds is usually supported, whence they have 
been called wnguligrade. Some few, however, rest the 
weight of the body upon the under surfaces of the pha- 
langes, or are digitigrade. The metacarpal and metatarsal 
bones are elongated, and take a vertical, or much inclined 
position. 

In the female, the mamme are either few in number, 
when they are inguinal in position; or numerous, when 
they are disposed in two rows along the abdomen. 

The intestine is very generally provided with a cecum 
of considerable size. 

The cerebral hemispheres always exhibit convolutions, 
which are usually very numerous; and, when the brain is 
viewed from above, the surface of the cerebellum is largely 
uncovered. 

The Ungulata are divisible into the Perissodactyla and 
the Artiodactyla, though it is probable that the attempt to 
define these groups will break down with the increase of 
our knowledge of fossil forms. 

1. In the Perissodactyla, the number of the dorso-lumbar 
vertebre is not fewer than twenty-two. The third digit 
of each foot is symmetrical* in itself, and the toes of the 
hind foot are odd in number (Fig. 93, B). The femur 
has a third trochanter (Fig. 100-*). The two facets upon 
the front face of the astragalus are very unequal; the less 
articulating with the cuboid bone. 

In the skull, the tympanic bone is small; and, as im 
sundry other mammals, the root of the pterygoid process 
of the sphenoid is perforated by an aperture or canal. 

The posterior premolar teeth are, generally, very like the 
molars. The stomach is simple, and the cecum exceedingly 
large. 

The teats are inguinal, or situated in the groin. When 

* Or at least very nearly so. 


THE PERISSODACTYLA. 343 


the head is provided with horny appendages, they are en- 
tirely epidermal and devoid of a bony core; and they are 
placed in the middle line of the skull. 


Fig. 93. 


Fig. 93.—A, Front aspect of the left tarsus of a Horse. 1. Calcaneum. 
2. Astragalus. 3. Naviculare. 4. Ectocuneiform. 5. Cuboides. 
B, Posterior aspect of the left metatarsus of a Horse. 1. The me- 

tatarsal of the third digit. 2,3. The metatarsals of therudimentary 

digits. 

The Perissodactyla consist of the existing families Hquide, 
Rhinocerotide, and Tapiride, and of the extinct Paleotheride 
and Macrauchenide. 


a. The Equide, or Horses and Asses, have one toe on 


344 THE ANATOMY OF VERTEBRATED ANIMALS. 


each foot—the third—much longer and larger than the 
rest. The latter are represented only by their metacarpal 
or metatarsal bones, the inner and outer toes being absent, 
or represented by mere ossicles (as rudiments of their meta- 
carpals or metatarsals) in all existing Equide. But, im the 
extinct Hipparion, the second and fourth digits were com- 
plete, though small and like dew claws; while the mio- 
cene Anchitherium, which most nearly approaches the 
Paleotheride, has the lateral toes much larger, and taking 
their share in supporting the weight of the body. 


See page 345. *, 


Fig. 94.—A, right fore foot of a Horse. 1. Radius. 2. Groove in the 
front face of the radius. 3. Scaphdides. 4. Lunare. 5. Cunei- 
forme. 6. Pisiforme. 7. Magnum. 8. Unciforme. 9. Metacar- 
pale, ziz. 10. Metacarpale, iv. 11. Sesamoid bones in the ligaments 
at the back of the metacarpo-phalangeal articulation. 12. Proximal 
phalanx (fetter bone). 13. Middle phalanx (coronary). 15. Distal 
phalanx (coffin bone). 14. Sesamoid bone in the tendon of the flezor 
perforans (called “ navicular” by Veterinarians). 

B, left hind foot of a Horse. 1. Tibia. 2. Caleaneum. 3. Astragalus. 
4. Cuboid. 5, Navicular,or scaphoid. 6. Ectocuneiform. 7. Me- 
tatarsale, ziz, 8. Metatarsale, iv. 9,11, 12. Phalanges. 10, 14. Se- 
samoids. 


The dental formula is 7. 5 c _ p.m. aa m.=—. The 
tooth here counted as the first premolar may be a milk tooth, 
as it appears to have neither predecessor nor successor, and 
soon disappears. 

The molar teeth present an outer wall, which is bicrescentic 
in transverse section; and two inner ridges, which are 
curved more or less inwards and backwards, and correspond 
respectively with the anterior and the posterior crescents of 
the outer wall. The valleys may be more or less com- 
pletely filled up with cement, which also coats the tooth. 
The incisors are similar in form in each jaw, and in Equus 
and Hipparion their crowns present a wide and deep median 
cavity, formed by a fold of the enamel. 

These are the distinctive characters of the Equide. It 
may be useful to add some special details respecting the 
anatomy of the Horse as a familiar example of the peris- 
sodactyle group. 


THE PERISSODACTYLA. 345 
Fig. 94. 


346 THE ANATOMY OF VERTEBRATED ANIMALS. 


The Horse has seven cervical vertebre, twenty-four 
dorso-lumbar (eighteen or nineteen of which are dorsal), 
five sacral, and about seventeen caudal vertebre. The 


Fig. 95. 


Fig. 95.-A cervical vertebra of a Horse. 1. The rudimentary spine. 
2, 3. The pre- and post-zygapophyses. 5. The convex anterior face 
of the centrum. 9. Its concave posterior face. 6,7. The trans- 
verse processes and rudimentary ribs. 

atlas has very wide lateral processes, the faces of which 
look obliquely downwards and forwards, and upwards and 
backwards. The centra of the other cervical vertebre are 
much elongated, strongly convex in front, and correspond- 
ingly concave behind. The neural spines are obsolete in all 
but the seventh. The ligamentum nuche is a great sheet of 
elastic tissue, which extends from the spines of the anterior 
dorsal vertebrz to the occiput, and is fixed, below, into the 
neural arches of the cervical vertebre. 

In the dorsal region, the opisthoccelous character of the 
centra of the vertebre gradually diminishes, though the 
anterior face of the centrum of the last lumbar is still dis- 
tinctly convex. The spines of these vertebre increase in 
length to the fourth or fifth. The spine of the sixteenth is 
vertical, those in front inclining backwards, and those be- 
hind a little forwards. 

In none of these vertebra do the prezygapophyses bend 
round the postzygapophyses of the vertebra in front, as is 
often the case in the Artiodactyla. The transverse pro- 
cesses of the penultimate, and of the last, lumbar vertebre 
present concave facets upon their posterior margins, which 


THE HORSE. 347 


% 
iy 
~~ 
Ww 
~~ 
Spas 
Aer) 
Fed 
\=] 
Gh 
A 
i= 
(ps 


we 


Fig. ¢6.—The skeleton of the Horse. 


348 THE ANATOMY OF VERTEBRATED ANIMALS. 


articulate with convex facets developed upon the anterior 
margins of the last lumbar and first sacral vertebrx re- 
spectively. 

In the skull, the plane of the supra-occipital is inclined 
upwards and forwards, and gives rise to the middle part 
of a transverse ridge which is continued at the sides into 
the squamosal. The ridges which limit the origins of the 
temporal muscles above, unite in the middle line poste- 
riorly, and thus produce a low sagittal crest. The orbit is 
bounded behind by the united postorbital processes of the 
frontal and the jugal. The lachrymal aperture lies in the 
orbit. The nasal bones unite, for a short distance only, 
with the premaxilla. There is no prenasal bone. The pos- 
terior margin of the palate is opposite the penultimate molar 
tooth. The glenoidal surface is transversely elongated and 
convex from before backwards. 

The tympanic bulla is not very large, and is rugose 
inferiorly. It is not ankylosed with the surrounding bones. 
The post-tympanic process of the squamosal does not 
approach the postglenoidal process of the same bone, below 
the meatus auditorius. 

The proper mastoid process is distinct, but short. There 
is a long and strong paramastoid developed from the ex- 
occipital. 

The rami of the mandible are ankylosed at the symphysis. 
The perpendicular part of each ramus is long, the condyle 
transverse and convex from before backwards, and the narrow 
coronoid process rises far above the level of the condyle. In 
a longitudinal section of the skull the cerebral chamber lies 
almost altogether in front of that for the cerebellum. 

The structure of the limbs of the Horse is such as 
might be expected from its pre-eminent cursorial powers. 

That excessive development of the epidermis which gives 
rise to a nail takes place, in the Horse, not only upon the 
dorsal surface of the terminal joint of the digit, but upon 
its ventral surface and sides, and thus produces a hoof. 

The animal is supported by these greatly-developed nails, 
and hence is said to be wnguligrade. The long axes of its 


THE HORSE. 349 


phalanges are greatly inclined to the surface upon which it 
stands, while those of the metacarpals and metatarsals are 
Fig. 97. 


Fig. 97.—Longitudinal median section of the foot of a Horse, 13, 14, 
18. The three phalanges. 16. The navicular sesamoid. 5. The 
flexor perforatus. 6. The flexor perforans. 19. The hoof, 


perpendicular and greatly elongated. The wrist of the 
Horse thus comes to occupy the middle of the length of 
its fore-leg, and constitutes what is improperly called the 
“knee.” The heel is similarly raised to the middle of the 
hind leg, and is termed the “hock.” The forearm and the 
leg are free, but their motions are almost restricted to an 
antero-posterior plane. The fore arm is fixed in the prone 
position. The arm and thigh are closely applied to the 
sides of the body and inclosed in the common integument, 
so as to be capable of very little proper motion. At the 
same time, the axis of the humerus is inclined obliquely 
backwards and downwards, at right angles with the long axis 


350 THE ANATOMY OF VERTEBRATED ANIMALS. 


of the scapula; and that of the femur obliquely forwards 
and downwards at right angles with that of the os innomi- 
natum ; and the long axes of both these bones make a great 
angle with those of the fore-arm and leg respectively. Hach 
limb thus forms a sort of double C spring, upon the top of 
which the weight of the body is supported—in the hind 
limbs by means of the solid connection of the ilia with the 
sacrum; in the fore limbs, by the great muscular slings 
formed by the serratus magnus and the levator anguli scapule. 
Fig. 98, The scapula is long and 
vs Gt narrow; the low spine has no 
acromion ; the coracoid process 
is small, and there is no clavicle. 
The head of the humerus 
looks backwards, and the distal 
articular surface of the bone 
is completely ginglymoid. The 
two bones of the antibrachium 
are ankylosed; the shaft of 
the ulna becomes exceedingly 
slender, and its small distal end 
is distinguishable only with diffi- 
culty. The articular surface for 
the carpal bones is, therefore, 
almost wholly furnished by the 
radius. There are seven carpal 
bones, the trapezium being ob- 
solete. A line prolonging the 
axis of the third metacarpal 
and that of the os magnum does 
not pass through that of the 
Fig. 98.—Front view of the “are, but corresponds more 
right carpus of a Horse, nearly with the junction be- 

1. Cuneiforme. 2. Lunare. tween scaphiides and lunare. 
5. Unsiforme, 6, Maguum, ‘The pollex and the fifth digit 
7. Trapezoides. are suppressed, or represented 
only by minute nodules of bone, and the only complete digit 
is the third; the second and the fourth being represented 


THE HORSE. Bol 


only by the splint-like metacarpal bones. The third meta- 
carpal, which is somewhat flattened from before backwards, 
is nearly symmetrical in itself. Careful observation, how- 
ever, shows the inner moiety to be rather the broader. 

There are two large sesamoid bones (the greater sesamoids) 
developed in the ligaments which connect the metacarpal 
with the basal phalanx; and one transversely elongated 
sesasmoid gives attachment to the tendon of the perforating 
flexor, and lies upon the ventral aspect of the joint between 
the middle and the distal phalanx. 

The ossa innominata are elongated, and their long axes, 
on the length of which depends the proportional size of the 
“quarter ” of a Horse, form an acute angle with the spine. 
The crests of the ilia are wide and directed transversely, 
and the symphysis pubis is very long. 

Fig. 99. 
Zz 


Fig. 99.—The ossa innominata of a Horse viewed from the left side 
and behind. 1. The crest of the ilium. 2. Tne surface by which it 
articulates with the sacrum. 4. The acetabulum. 6. The ischium. 


The femur has a large third trochanter (°, Fig. 100), into 
which the gluteus mawimus is inserted. Its head presents a 


352 .THE ANATOMY OF VERTEBRATED ANIMALS. 


deep pit for the round ligament, and there is a peculiar and 
very characteristic fossa ('°) on the imner and posterior 
face of the distal moiety of the bone. ‘ ; 
Fig. 100. The proximal end of the fibula 
- is reduced to a mere rudiment ; its 
shaft is not represented by bone; 
and its distal end is ankylosed 
with the tibia, and has the ap- 
pearance of being an external 
malleolar process of that bone. 
The distal end of the tibia pre- 
sents two deep, obliquely-directed 
concayities, which correspond 
with the convexities of the astra- 
galus. 

There are six or seven tarsal 
bones, according as the ento- and 
meso-cuneiform bones remain dis- 
tinct or become ankylosed. The 
astragalus (Fig. 93 A, 94 B) is ex- 
tremely characteristic. It presents 


deep fossa, and directed obliquely 
from behind and within, forwards 
and outwards, to the tibia; and it 
has a nearly flat distal face, 
not borne upon any distinct neck. 
which articulates almost wholly 
with the naviculare, presenting 
only a very small facet to the 
cuboid. 
The naviculare and the ecto- 
Fig. 100.—A, Left femur of cuneiform are peculiarly broad and 
a Horse, posterior view. flattened in form (Fig. 93 A, 94 B). 
ane Bs oe ia The metatarsus and digits repeat 
chanter. 4 Lesser tro- the arrangements of the fore limb ; 
chanter. 5. Pitforround y+ the principal metatarsal is 


ligament. 10, Fossa, “cask : 
11. Condyles. more slender in its proportions, 


two convex ridges separated by a | 


THE MUSCLES OF THE HORSE. 353 


and is flattened from side to side rather than from before 
backwards (Fig. 93 B, 94 B). 

As might, be expected, the principal peculiarities of the 
muscular system of the Horse are to be observed in the 
limbs. 

The serratus magnus and the levator anguli seapule (which 
really form one muscle), together with a sterno-scapularis, 
form the great sling already mentioned, by which the weight 
of the fore part of the body is transmitted to the anterior 
extremities. The power of abduction is hardly needed by 
a purely cursorial animal; hence the deltoid is reduced 
to its scapular portion, which is very small. On the other 
hand, the pro- and re-tractors, the flexors and extensors, are 
well developed. The supra- and infra-spinatus are large. 
There is a great cephalo-humeralis, answering to the clavi- 
cular portions of the human sternomastoid and of the 
deltoid, which run into one another, in consequence of the 
total absence of the clavicle. The anterior portion of the 
sternomastoid is fixed to the mandible, and thus becomes 
“ sternomaxillary.” 

The latissimus dorsi and teres muscles are very large, as 
are the flexors and extensors of the antibrachium. 

The supinators and pronators are wanting; but there is 
a distinct eatensor minimi digiti, the tendon of which unites 
with that of the extensor communis. Radial and ulnar 
extensors of the carpus are also present. The flexor per- 
foratus has only a single tendon, which splits, and is attached, 
as usual, to the sides of the middle phalanx. The flexor per- 
forans also has only a single tendon, which pierces the 
former, and is inserted into the lesser sesamoid and the 
distal phalanx. 

The interossei of the third digit are represented only by 
the ligaments which connect the greater sesamoid bones 
with the metacarpai, and in which a few muscular fibres are 
sometimes found. There are said to be two others, one for 
each lateral metacarpal, and a lumbricalis. 

In the hind limb, the femoral muscles are in the Horse 
the same as in Man, but enormously developed. There is 

2A 


304 THE ANATOMY OF VERTEBRATED ANIMALS. 


no tibialis anticus, peronceus longus, or brevis, nor any tibialis 
posticus. 

The extensor longus digitorum has a head which arises 
from the external condyle of the femur; there is a simple 
extensor brevis. 

The flexor hallucis and flexor digitorum perforans unite into 
the single perforating flexor tendon for the distal phalanx; 
while the perforated tendon is the termination of that of 
the plantaris, which passes over a pulley furnished by the 
calcaneum. 

The deciduous or milk dentition of the Horse has the 
following formula: d.i. _ d.c. pas d.m. = It is com- 
plete at birth, with the exception of the outer incisors, which 
appear before the foalis nine monthsold. The incisors have 
the same structure asin the adult. The canines and first deci- 
duous molars are simple and very small, the canines being 
smaller than the molars. In the upper jaw, the other 
deciduous molars all have the same structure. The outer 
wall of the tooth is bent in such a manner as to present, 
from before backwards, two concave surfaces separated by a 
vertical ridge. From the anterior end, and from the middle, 
of this outer wall, two lamine of the crown pass inwards 
and backwards, so as to be convex inwards and concave 
outwards, and thus to include two spaces between them- 
selves and the outer wall. From the inner surface of the 
hinder part of each of these crescentic lamin a vertical 
pillar is developed, and the inner surface of the pillar is 
grooved vertically. The outer wall, the lamine, and the 
pillars are all formed of dentine and enamel, thickly coated 
with cement. The attrition which takes place during mas- 
tication wears down the free surfaces of all these parts, so 
as, in the long run, to lay bare a surface of dentine in the 
middle of each, surrounded by a band of enamel, and, outside 
this, by the cement with which the interspaces are filled. 
The band of enamel is simple and unplaited. The general 
pattern of the worn surface may be described as consisting, 
externally, of two longitudinal crescents, one behind the 


THE TEETH OF THE HORSE. 355 


other, and with their concavities turned outwards, which 
arise from the wear of the wall; internal to these, of two 
other crescents, partly transverse in direction, and con- 
nected by their anterior ends with the wall, which arise 
from the wear of the laminz; and attached to the inner 
surface of these, two hour-glass-shaped surfaces, produced 
by the wear of the grooved pillars. 

In the mandible, the structure of the molars and the 
resulting pattern are quite different. The outer wall pre- 
sents two convex surfaces separated by a longitudinal 
depression, and thus reverses the conditions observable in 
the upper molars. The result of the wear of this is, ne- 
cessarily, two crescents, the concavities of which are turned 
inwards. A vertical pillar, longitudinally grooved on its 
inner face, is developed on the inner face of the tooth at 
the junction of the anterior and posterior crescents, and 
gives rise to a deeply bifurcated surface when worn. A 
second smaller pillar appears in connection with the inner 
face of the posterior end of the outer wall. 

Thus the grinding surface of the upper molars may be 
represented by four crescents with two inner pillars; and 
that of the lower molars by two crescents with two inner 
pillars. The upper crescents are concave outwards; the 
lower concave inwards; and by this arrangement, together 
with the unequal wear of the dentine, enamel, and cement, 
a permanently uneven triturating surface is secured. 

As is the general rule among Mammals, the first per- 
manent molar is the first permanent tooth which appears 
(unless the eruption of the inner incisor be contemporary 
with it), and it comes into place and use long before the 
deciduous molars are shed and replaced by the premolars. 
Hence, when the last premolar comes into place as a fresh 
and unworn tooth, the first molar, which lies next to it, is 
already considerably worn. This disparity of wear is main- 
tained for a long time, and furnishes a very useful means 
of distinguishing the last preniolar from the first molar in 
the adult, when, as in the Horse, the premolars and molars 
are very similar. 


306 THE ANATOMY OF VERTEBRATED ANIMALS. 


The first deciduous molar usually falls out when the 
first premolar appears, and is not replaced; but it is occa- 
sionally retained. All the other milk teeth have successors, 
and there are three permanent molars, Consequently the 
dental formula of the adult Horse is 


= Bee Be 3.3 3°3 _ 40 
Be Bagi Oe eg 3a ae 


The permanent canines are the last teeth to be fully 
developed, and, in the mare, they often do not make their 
appearance. The upper canines are distant from the outer 
incisors, while the lower canines are quite close to them. 
In both jaws there is a wide interval, or diastema, between 
the canines and the premolars. 

The deep valley of the incisor teeth becomes filled up 
with masticated matter, and thus the dark “ mark” is pro- 
duced. As the incisors wear down, the mark changes its 
form in consequence of the differences in the transverse 
section of the valley at different points; and eventually, 
when the wear has extended beyond the bottom of the 
valley, it disappears. The presence or absence of the 
“mark ” thus serves as an indication of age. The structure 
and patterns of the grinding surfaces of the permanent 
molars are essentially the same as those of the milk molars; 
but the enamel becomes more or less plaited; and, at an 
advanced period of life, the development of the long teeth 
is completed by the formation of roots. It is important to 
notice that the last molar of the Horse is not more complex in 
its structure than the other molars, and that the last milk 
molar is not more complex than the premolar which suc- 
ceeds it. 

The alimentary canal of the Horse is about eight times 
as long as the body. The stomach, simple in its form, 
presents a cardiac and a pyloric division, which are sharply 
distinguished by the dense epithelium which lines the inner 
surface of the former. 

The cecum is enormous, having fully twice the volume 
of the stomach. There is no gall-bladder. A cartilage 
is developed in the septum of the heart. There is no 


THE VISCERA OF THE HORSE. 307 


Eustachian valve, and only one anterior cava remains. The 
aorta divides immediately after its origin into an anterior 
and a posterior trunk; the latter becomes the thoracic 
aorta; the former is the source of the arteries for the 
head and the anterior extremities, giving off first the left 
subclavian, and then as an “innominata” supplying the right 
subclavian and the carotids. 

The trachea divides into only two bronchi, no accessory 
bronchus being given off to the right lung, In the brain 
the following points are worthy of notice. The medulla 
oblongata presents corpora trapezoidea. The flocculi do 
not project at the sides of the cerebellum, and the vermis 
and lobes of the cerebellum are unsymmetrically convo- 
luted. The cerebral hemispheres are elongated and sub- 
cylindrical, and do not overlap the cerebellum when the 
brain is viewed from above. The sulci are very deep, and 
separate numerous gyri, upon the upper and outer surfaces 
of the hemispheres. The uncinate gyrus (or natiform pro- 
tuberance) and the region which answers to the insula, are 
not hidden by the overlapping of the convolutions in the 
lateral aspect of the brain. The sylvian fissure is indi- 
cated. The corpus callosum is large, and the anterior com- 
missure is of moderate size. The posterior cornu of the 
lateral ventricle is wanting. 

Large air sacs are connected with the Eustachian tubes. 

The testes pass into a scrotum, but the inguinal canal 
remains permanently open. 

The prostate is single. Cowper’s glands are present, and 
there is a large uterus masculinus. The large penis is 
sheltered within a prepuce and is retracted by a special 
muscle, which arises from the sacrum. 

The uterus is divided into two cornua, and the vagina of 
the virgin mare is provided with a hymen. The period 
of gestation is eleven months. The yelk sac of the fetus. 
is small and oval. The allantois spreads over the whole 
interior of the chorion and covers the amnion, which is 
vascular. The minute villi which it supplies with vessels 
are evenly scattered over the whole surface of the chorion. 


308 $$ THE ANATOMY OF VERTEBRATED ANIMALS. 

The existing Hquwide are naturally restricted to Europe, 
Asia, and Africa; and are distinguished into the Horses, 
which have horny patches on the inner sides of both pairs of 
limbs—above the wrist in the fore limb and on the inner 
side of the metatarsus in the hind limb; and the Asses, 
which possess such callosities only on the fore limbs. 

Fossil remains of Equide are abundant in the later ter- 
tiary deposits of Europe, Asia, and the Americas; but the 
group is not known to be represented earlier than the 
miocene, or later eocene, epoch. 

The EHquide are among the very few groups of Mam- 
malia, the geological history of which is sufficiently well 
known, to prove that the existing forms have resulted from 
the gradual modification of very different ancestral types. 
The skeleton of the older pliocene and newer miocene 
Hipparion very closely resembles that of an Ass, or a mo- 
derate-sized Horse. There is a curious depression on the 
face in front of the orbit, somewhat like that which lodges 
the “larmier” of a stag (traces of which are observable in 
some of the older species of Equus); otherwise the cranium 
is altogether like that of a Horse. Again, the shaft of the 
ulna is very slender, but it is larger than in the Horse, and 
is distinctly traceable throughout its whole length although 
firmly ankylosed with the radius. The distal end of the 
fibula is so completely ankylosed with the tibia, that, as in 
the Horse, it is difficult to discern any trace of the pri- 
mitive separation of the bones. But, as has been already 
mentioned, each limb possesses three complete toes—one 
strong, median, and provided with a large hoof, while the 
two lateral toes are so small that they do not extend beyond 
the fetlock joint. In the fore limb, rudiments of the first 
and fifth toes have been found. 

The teeth are exceedingly like those of the Horse, but the 
crowns of the molars are shorter; and, in the upper jaw, 
that which, in the true Horses, is a large fold of the inner 
face of the tooth becomes a detached pillar. The smaller 
plications of the enamel are also more numerous, close-set, 
and complicated. On the outer face of the lower milk 


HIPPARION AND ANCHITHERIUM. 309 


molars there is a column such as exists in the Stags. Of 
this a rudiment exists, as a fold, in the corresponding teeth 
of the existing Horse. 

In the genus Anchitherium, all the known remains of 
which are of older miocene (and, perhaps, newer eocene) 
age, the skeleton in general is still extraordinarily like 
that of a Horse. The skull, however, is smaller in pro- 
portion than in the Horse, and the jaws are more slender. 
The hindermost molar tooth is situated farther back under 
the orbit, and the orbit itself is not completely encircled by 
bone, as it is in the Horses and Hipparions. 

The shaft of the ulna is stouter than in Hipparion, 
and is less closely united with the radius. The fibula 
appears, at any rate in some cases, to have been a complete 
though slender bone, the distal end of which is still closely 
united with the tibia, though much more distinct than in 
the Hipparions and the Horses. In some specimens, how- 
ever, the middle of the shaft seems to have been-incom- 
pletely ossified. Not only are there three toes in each foot, 
as in Hipparion, but the inner and the outer toes are so 
large that they must have rested upon the ground. Thus, 
so far as the limbs are concerned, the Anchitherium is just 
such a step beyond the Hipparion, as the Hipparion is 
beyond the Horse, in the direction of a less specialized 
quadruped. The teeth are still more divergent from the 
Equine type. The incisors are smaller in proportion, and 
their crowns lack the peculiar pit which characterizes those 
of Equus and Hipparion. The first grinder is proportion- 
ately much larger, especially in the upper jaw, and like the 
other six has a short crown and no thick coat of cement. 
The pattern of their crowns is wonderfully simplified. 
The fore and hind ridges run with but a slight obliquity 
across the crown, and the pillars are little more than en- 
largements of the ridges, while in the lower jaw these 
pillars have almost disappeared. But the foremost of the 
six principal grinders is still somewhat larger than the 
rest, and the posterior lobe of the last lower molar is small, 
as in the other Hquide. 


360 THE ANATOMY OF VERTEBRATED ANIMALS. 


In all those respects in which Anchitherium departs from 
the modern Equine type, it approaches that of the extinct 
Paleotheria; and this is so much the case that Cuvier 
considered the remains of the Anchitheriwm with which he 
was acquainted to be those of a species of Palwotherium. 

b, In the Rhinocerotide the second, third, and fourth 
toes are nearly equally developed in both the fore and the 
hind feet. 

I'l 00 00 4:4 393 


The dental formula is 7. ai O8 % ag & ong Bale gat aes: 


But the teeth differ from those of the Horse in many 
other respects besides the number of the incisors and the 
absence of canines. Thus, the upper incisors differ greatly 
in form from those which are situated in the lower jaw; 
and, in some species, incisors are absent. Their crowns are 
not folded as in the Horse. The peculiarities of the 
grinding teeth will be mentioned below. 

The skin is very thick and may he converted into a 
jointed armour; the hair is scanty. The upper lip is 
much produced and is very flexible. In some species one, 
or sometimes two, horns are attached in the middle line to 
the nasal or frontal bones. But these horns are formed, as 
it were, by agglomeration of a great number of hair-like 
shafts. 

The distal phalanges of the tridactyle feet of the Rhi- 
noceros are invested by small hoofs; but these do not 
entirely support the weight of the body, which rests, in 
great measure, upon a large callous pad developed from the 
under face of the metacarpal and metatarsal regions; these 
are much shorter than in the Horse. 

The dorsolumbar vertebrz are twenty-two or twenty-three, 
of which twenty are dorsal. There are four sacral and 
twenty-two caudal. The cervical vertebre, as in the Horse, 
are strongly opisthocelous, and the transverse processes 
of the last lumbar articulate with those of the penultimate 
lumbar and with the sacrum. 

The skull differs from that of the Horse in the absence 
of any frontal or zygomatic processes, in consequence of 


THE RHINOCEROTID&. 361 


which the orbit and temporal fossa form one cavity. The 
nasals are immense, and are separated from the premaxille 
by a wide extent of the maxilla on each side. The pre- 
maxille are relatively small, and reduced to little more 
than their palatine portions. The glenoidal surface of the 
mandible is transverse and convex. The squamosal sends 
down an immense post-glenoidal process, which is longer 
than either the post-tympanic or the paramastoid. It unites 
with the post-tympanic to form a kind of false auditory 
meatus, in the absence of any proper ossified canal of that 
kind. The periotic and the tympanic bones are ankylosed, 
the tympanic being a mere irregular hoop of bone. The 
pars mastoidea is completely hidden by the junction of the 
short post-tympanic with the long paramastoid. The hinder 
margin of the bony palate is opposite the middle of the 
antepenultimate molar. 

The mandibular condyle is transverse and convex. The 
perpendicular portion of the ramus is large, and the coro- 
noid process ascends slightly above the condyle. In a 
- vertical and longitudinal section of the skull, the form of 
the cerebral cavity is seen to be similar to that of the 
Horse. The inner and outer tables of the bony roof of the 
skull are separated by great air-cavities. 

The spine of the scapula has no acromion, but gives 
off a strong recurved process from the middle of its 
length. 

The radius and ulna are complete, but are ankylosed. 

The carpus has the eight ordinary bones. In the manus 
the digits ii. iii. iv. are complete, and a bony tubercle 
articulated with the outer facet of the cwneiforme repre- 
sents digit v. The digit iii. is largest and longest, and its 
phalanges are symmetrical in themselves; those of the 
digits ii. and iv. are not symmetrical in themselves. The 
terminal phalanges have somewhat the form of the coffin 
bone of the Horse. 

The ilia have wide transversely directed crests, as in the 
Horse. The femur is provided with a very strong third 
trochanter. The tibia and the fibula are complete, and 


362 THE ANATOMY OF VERTEBRATED ANIMALS. 


the tarsus has the ordinary seven bones. The pulley of the 
astragalus is not very deeply grooved, and is hardly at all 
oblique. The facet for the cuboid is very small. The 
metatarsals resemble the metacarpals in their number and 
symmetry, but there is no rudiment of the fifth. 

In some species of Rhinoceros there are pi incisors in the 
milk dentition, and aa or os incisors in the permanent 
dentition. In the latter the upper incisors are large, 
long-crowned teeth, very unlike the lower ones, of which 
it seems probable that only one pair, in any case, are 
permanent teeth. In some Rhinoceroses, as has been 
already stated, the adult is devoid of incisor teeth. 

There are no canines in either dentition. Of the 
four milk molars, the first, as in the Horse, is smaller than 
the others, and is not replaced. The structure of both the 
upper and the lower molars is substantially the same as in 
the Horse, but the roots are developed much sooner; 
the laminz of the upper molars take a much more trans- 
verse direction; the lamine of the upper molars do not 
develop pillars, though accessory crests may be developed 
from the two faces of the posterior lamina; the lower 
molars have no pillars; and the cement does not fill up 
the valleys between the wall and the laminz. 

The cardiac division of the simple, though large, stomach 
is lined by a white callous epithelium, as in the Horse. The 
small intestine presents large processes or tags, half an inch 
long or more, upon which the true villi are borne. The 
cecum is very large, and the colon enormous. There is no 
gall-bladder. The heart and brain are very similar to 
those of the Horse. 

The male can hardly be said to have a scrotum, as the 
testes lie close to the abdominal ring, A prostate, vesicule 
seminales, and Cowper’s glands are present. The long penis 
has a mushroom-shaped glans, and the animal is retro- 
mingent. The cornua uteri are proportionately longer than 
in the mare. The teats are two and inguinal in position. 


THE TAPIRIDZ. 363 


The characters of the fetal membranes and the nature 
of the placentation are unknown. 

At the present day the genus Rhinoceros is confined to 
Africa and Asia. The African species all have two horns, 
a nearly smooth skin, and the adult has no incisors. The 
Asiatic species have one horn only (except that of Sumatra, 
which has two). The skin is marked out by deep folds into 
shields, and the adults have well-developed incisors. 

Rhinoceroses are known in the fossil state as far back 
as the miocene epoch. R. tichorhinus, with the nasal 
septum ossified, and a covering of long woolly hair, in- 
habited Europe and Asia during the cold of the glacial 
epoch. RK. incisivus had four digits in the manus, and 
larger incisor teeth than any existing species. R. hexa- 
protodon had more numerous incisors than any other 
species. 

ce. In the Tapiride there are four toes on the front foot, 
though the ulnar digit does not reach the ground. The 
hind foot has three toes. 


The dental formulais 7. oe @ — p. li th, 


The molar teeth each eee is He transverse, or slightly 
oblique, ridges, connected by a low wall externally. 

The skin is soft and hairy, and the muzzle and snout are 
prolonged into a short proboscis. 

The Tapirs have twenty-three or twenty-four dorsolumbar 
vertebre, of which nineteen, or twenty, are usually dorsal. 
The centra of these vertebre, and the transverse processes of 
the last lumbars, have the same peculiarities as those of the 
Horse and Rhinoceros. There are seven sacral and about 
twelve caudal vertebre. The skull is partly Rhinocerotic, 
partly Equine in its characters. Thus there is a sagittal 
crest—the post-tympanic processes are large, but they are 
not so long as the paramastoids, and they do not unite with 
the post-glenoidal processes beneath the meatus. In these 
respects the Tapir is Horse-like, but in the following it is 
more Rhinocerotic. 

Thus the tympanic is quite rudimentary; the post- 


364 THE ANATOMY OF VERTEBRATED ANIMALS. 


glenoidal process is larger than in the Horse; the orbit is 
not separated from the temporal fossa; the nasals are 
widely separated from the premaxille; the premaxille are 
very small, and are early ankylosed. 

The hinder margin of the osseous palate is opposite the 
anterior edge of the penultimate molar. The mandibular 
rami unite in a very long symphysis; the ascending portion 
of the ramus is large, and projects backwards with a convex 
edge in aremarkable manner. There is a high coronoid 
process. 

In the fore limb, the scapula has no acromion, and the 
coracoid is a mere tubercle. The supraspinous fossa is 
very much larger than in the Horse or Rhinoceros. The 
radius and the ulna are complete, but not movable upon 
oneanother. Although, by the completion of the fifth digit, 
in addition to the second, third, and fourth, there are four 
digits in the manus, the Perissodactyle character is mani- 
fested by the fact that the third is longest, and symmetrical 
in itself, while the others are asymmetrical. The femur has 
a strong third trochanter; the fibula is complete; the as- 
tragalus more Rhinocerotic than Equine. There is no 
trace of a hallux, but the fifth digit of the pes appears to 
be represented by an osseous rudiment. 

In the presence of the full complement of incisors and 
canines the Tapir is more Horse-like than Rhinocerotic, 
but is still very peculiar; for the outer upper incisors are 
larger than the canines, while the outer lower incisors are 
much smaller than the canines, and are apt to fall out at a 
certain age. The canines, are still more closely approxi- 
mated to the incisors than in the Horse, especially in the 
lower jaw, and, consequently, the diastema is very large. 
The six posterior molars in the upper jaw, and the five 
posterior molars in the lower, present nearly the same 
structure. There is a low outer wall with two shghtly 
marked concavities (in the maxillary teeth) or convexities 
(in the mandibular teeth) on its outer face. From this two 
ridge-like lamine run inwards and a little backwards across 
the crown of the tooth. The valleys are broad and shallow: 


THE PALHOTHERIDA. 365 


and the coat of cement very thin. The molar tooth of the 
Tapir thus represents the plan of structure common to 
the Perissodactyla in its simplest form. Deepen the valleys, 
increase the curvature of the wall and laminz, give the 
latter a more directly backward slope; cause them to de- 
velop accessory ridges and pillars, and increase the quantity 
of cement; and the upper molar of the Tapir will gradually 
pass through the structure of that of the Rhinoceros to 
that of the Horse. 

In the anterior upper premolar (or milk molar?) the 
anterior moiety of the crown is incompletely developed. 
In the anterior lower premolar the anterior basal process, 
which exists in all the molars, is excessively developed, so that 
the crown of the tooth assumes the bicrescentic pattern of 
the Rhinoceros’ lower grinder. This probably indicates 
the manner in which the Tapiroid form of inferior molar 
is converted into the Rhinocerotic, or Equine, form. 

The stomach is simple and oval, the cardiac and pyloric 
orifices being closely approximated. The cecum is pro- 
portionally smaller than in the Horse or Rhinoceros. There 
is no gall-bladder. The heart is devoid of a septal bone 
and of a Eustachian valve. There is only a single vena 
cava anterior, and the aorta divides into an anterior and a 
posterior trunk. There is no third bronchus. No distinct 
scrotum is present. There are vesicule seminales and 
prostatic glands, but no Cowper’s glands. The placentation 
is diffuse. The teats are two, and inguinal. 

There are two or three species cf Tapir at present living 
in South America and one in South-west China, Malacca, 
and Sumatra. The genus Tapirus has been found fossil in 
Europe in rocks of miocene age. The closely allied extinct 
genera Lophiodon (and Coryphodon?) carry the Tapiride 
back through the eocene epoch. 

d. The Paleotheride.—These are all extinct animals, the 
remains of which are found in the older tertiary rocks; 
and which are closely allied, on the one hand, with the 
Horses and, on the other, with the Tapirs, 

The type of the family, Palcotheriwm, resembles the Tapir 


366 THE ANATOMY OF VERTEBRATED ANIMALS. 


in most respects, but has only three digits in the manus as 


well as in the pes. The dental formula, however, is 
a. = @ pa p.m. Mm. 28" The diastema is smaller than in 
the Tapir, and the patterns of the grinding teeth of both 
jaws are more like those of the Rhinoceros. 

e. The Macrauchenide.—The genus Macrauchenia is also 
an extinct form, which occurs in later tertiary or quater- 
nary deposits in South America. 

The feet are tridactyle, and the dental formula is 
4 OE gil 5°53 3:3 


1. Soy Ce ay PM. Tag Fg The teeth are disposed in a nearly 


continuous series. The crowns of the incisors present a 
deep fossa, as in the Equide. The molars are in part 
Equine, in part Rhinocerotic in character. The skullis, on 
the whole, Equine, but the nasal bones are very short and 
tapiroid. The vertebre of the long neck are extraor- 
dinarily similar to those of the Camelide, and especially of 
the Llamas. 

2. The Artiodactyla—The number of the dorso-lumbar 
vertebre in this group is always fewer than twenty-two, 
and rarely exceeds nineteen. 

The third digit of each foot is asymmetrical in itself, 
and usually forms a symmetrical pair with the fourth 
digit; and the functional toes of the hind foot are even in 
number—that is to say, either two or four. 

The femur is devoid of any third trochanter; the facets 
upon the distal face of the astralagus are subequal, that 
for the cuboid being nearly as large as that for the navicular 
bone. The tympanic is large, and the pterygoid process 
of the sphenoid is not perforated. 

The posterior premolar teeth usually differ a good deal 
from the succeeding molars, being simpler in pattern. The 
last milk molar in the lower jaw is trilobed; but this is also 
the case in some Perissodactyla. 

The stomach is more or less complex. The cecum, though 
well developed, is smaller than in the Perissodactyla. 

The mamme are inguinal or abdominal. When horns are 


THE SUID. 367 


present, they are double, supported, wholly or partly, by 
the frontal bone and provided with an osseous core, which 
is almost always an outgrowth from that bone. 

The Artiodactyla are divisible into the Non-Ruminantia and 
the Ruminantia. 

A. The Non-Ruminantia usually have more than one pair 
of incisors in the upper jaw. The molar teeth have either a 
mamuillate, a transversely ridged, or a rhinocerotic pattern. 
In only one genus, Dicotyles, are any of the metatarsal or 
metatarsal bones ankylosed together. They are devoid of 
horns, and the stomach has rarely more than two divisions. 

The Non-Ruminantia are divisible into three families :— 
The Suide, the Hippopotamide, and the Anoplotheride ; but 
more or fewer of the members of this last group may have 
ruminated. 

a. The Suide have the skin of moderate thickness and 
hairy; the limbs slender, and the third and fourth toes 
considerably longer than the second and fifth. The teats 
are abdominal, and there is a scrotum. The dental formula 
varies considerably, but the molars have a multituberculate 
or transversely ridged grinding surface. 


Share a ie 

In the genus Sus, the dental formula is 7. —3¢. — p.m. 
4-4. '3°3 
eae 33 


By way of contrast with the Horse, I add some more 
detailed statements regarding the anatomy of the Pig as a 
common and very good example of an Artiodactyle. The 
Pig has seven cervical vertebrz, nineteen* dorsolumbar, of 
which fourteen are dorsal, four sacral, and twenty to twenty- 
three caudal. The atlas has wide oblique ale, as in the 
Horse. The centra of the other cervical vertebre are short, 
with nearly flat articular surfaces, and this flatness is 
retained in the dorsolumbar region. The cervical and 
dorsal vertebre are provided with long spines, that of the 
first dorsal vertebra being the longest of all. Up to the 
twelfth dorsal the spines all slope backwards; beyond it they 
slope forwards, if at all. 

* Exceptionally, the number may be increased to twenty-two. 


368 THE ANATOMY OF VERTEBRATED ANIMALS. 


In the ninth dorsal vertebra the postzygapophysis pre- 
sents an articular surface on its dorsal side, and the pre- 
zygapophysis of the tenth vertebra bends round so as to 
overlap this surface. This character is continued in the 
succeeding vertebre as far as the first sacral. The trans- 
verse processes of the penultimate and last lumbar vertebre 
are tolerably long, but they are inclined forwards as well as 
outwards, and do not articulate with one another, or with 
the first sacral. 

In the skull the supraoccipital is inclined upwards and 
forwards into a great transverse crest, to which the parietals 
contribute but little. The parietals are early ankylosed. 
The temporal ridges remain widely separated in the middle 
of the roof of the skull. ? 

The frontal bone has a post-orbital process, and so has 
the jugal, but the two do not meet so as to bound the orbit. 
The lachrymal is very large, and its two canals open on the 
face. The nasals are very long, and the premaxillz unite 
with them for a great distance. There is a prenasal bone, 
or ossification of the cartilaginous septum of the nose. The 
bony palate extends back beyond the level of the last molar. 
The base of the external pterygoid process is not perforated. 
The surface for the articulation of the lower jaw is trans- 
versely elongated, convex from before backwards, and 
bounded behind and internally, by a post-glenoidal ridge. 

The tympanic bulla is very large, and the exceedingly 
long bony meatus curves upwards and outwards, between 
the squamosal and the mastoid, with both of which it is 
ankylosed, to the root of the zygoma, where its aperture 
looks almost directly upwards. The post-tympanic is 
closely appressed to the post-glenoidal process, so as, with 
the latter, to encircle the meatus. The proper mastoid is 
distinct, though short, but there is a very long paramastoid 
developed from the exoccipital and extending behind and 
below the mastoid. 

The rami of the mandible are completely ankylosed at 
the symphysis. There is a long perpendicular portion of 
the ramus. The condyle is transversely elongated and 


THE OSTEOLOGY OF THE PIG. 369 


convex, antero-posteriorly; the coronoid process ascends 
hardly higher than it. In a longitudinal section, the 
cavity of the cerebral hemispheres is more rounded than in 
the Horse, and lies above, as well as in front of, that for 
the cerebellum. 

The scapula is long and narrow. It is devoid of acromion, 
and has but a small coracoid process. 

The radius and ulna are complete, but are ankylosed to- 
gether in the prone position. The distal end of the ulna 
articulates with the cuneiform bone. 

The carpus contains eight bones, but the radial bone in 
the distal series may be either the trapezium, or a rudiment 
of the pollex. The lunare, and the axis of the third meta- 
carpal have the same relation as in the Horse. The third 
and fourth digits are larger than the other two, and form 
a symmetrical pair. There are sesamoid bones on the 
ventral face of the articulations between the metacarpal and 
the basal phalanx, and of that between the middle and the 
distal phalanges. Hach distal phalanx is incased in a small 
hoof. The femur has a round ligament. There is no third 
trochanter. The fibula is complete, and its distal end 
articulates with the caleaneum. There are the usual seven 
tarsalbones. The tibial end of the astragalus has the form 
of a deeply-grooved pulley, the direction of the groove 
corresponding nearly with the length of the foot. The 
distal end presents a convex subcylindrical surface divided 
by a ridge into two facets, of which one is somewhat less 
than the other, and articulates with the cuboid. 

The metatarsus and phalanges of the pes are disposed like 
the corresponding bones in the manus. 

The fore part of the body is supported upon the anterior 
extremities by a muscular sling composed of the serratus, 
levator anguli scapule, and sternoscapularis, much as in the 
Horse, with which the Pig exhibits a general correspondence 
in its myology. The muscles which move the digits, how- 
ever, have undergone less modification. Hach digit of the 
manus, for example, has its proper extensors, and there is 
an eatensor ossis metacarpt pollicis which ends on the basal 

2B 


: 


370 THE ANATOMY OF VERTEBRATED ANIMALS. 


phalanx of the second digit. A pronator teres is inserted 
into the lower half of the radius. The flexor perforatus has 
only two tendons, which go to the third and fourth digits. 
The flexor perforans sends two large tendons to the third 
and fourth, and two small ones to the second and fifth 
digits. There is a large interosseus muscle on the radial 
side of the third digit, and another on the ulnar side of the 
fourth; but the interossei of the interspace between these 
digits are represented only by fibrous tissue. The second 
and fifth digits have each two interossei. There is no 
soleus. The strong and fleshy plantaris arises from the 
outer condyle, beneath the gastrocnemius; and, inclosed 
between the two heads of the latter, passes to the inner 
side of the tendo Achillis; its tendon curves round this 
tendon, passes over the end of the caleaneum as over a 
pulley, enters the sole, and finally divides into the two 
perforated tendons of the third and fourth digits. The 
inner and outer digits of the pes, like those of the manus, 
have no perforated tendons. 

A large and fleshy flexor hallucis longus arises from the 
fibula and the interosseous ligament, and its broad tendon 
passes into the sole and coalesces with the tendon of the 
smaller flexor longus digitorum. The conjoined tendons 
divide into four slips—two large, median, and two small, 
inner and outer. These go to the distal phalanges and 
sesamoids of the respective digits. 

The tibialis posticus is absent, but there is a small tibialis 
anticus. 

A very complicated muscle represents the extensor longus 
digitorum and the peroneus tertius. It arises by (a) a strong 
round tendon from the outer condyle of the femur, just in 
front of the external lateral ligament. From this tendon 
proceed two fleshy bellies, one of which supplies tendons to 
the third, fourth, and fifth digits, while the other ends in a 
broad band of tendinous fibres, which is inserted into the 
third metatarsal and the ectocuneiform. Into this band is 
inserted (b) the second fleshy head which arises from the 
upper part of the tibia; and it is traversed by the tendon 


THE DENTITION OF THE PIG. 371 


of (c) the third head, which is slender, arises from the 
fibula, and sends its long and delicate tendon to the 
dorsum of the second digit. 

The peroneus longus is present, and its tendon is inserted 
into the entocuneiform and the second metatarsal. There 
is no peroneus brevis. A peroneus 4ti et 5ti digiti arises from 
the upper part of the fibula, behind the peroncus longus, 
and ends in a tendon which passes behind, and on the inner 
side of, that of the latter muscle, to the dorsum of the foot, 
where it divides into two branches which join the extensor 
sheaths of the fourth and fifth digits. 

The extensor brevis goes to the two middle digits, and is 
connected with the middle tendon of the extensor longus. 

The interossei are similar to those of the manus. 


The formula of the milk dentition of the Pig (which is 
complete at the third month after birth) is di. [> die. => 
dm. —. 

rom 

The outer upper incisors are directed obliquely outwards 
and backwards. In the upper jaw, the anterior two molars 
present sharp longitudinal edges, while the posterior two 
have broad crowns with two transverse ridges. In the 
mandible the anterior three molars have sharp longitudinal 
edges, while the hindermost has a broad, three-ridged crown. 

The first permanent molar is the first tooth of the per- 
manent set which comes into place (at about six months 
after birth), and the permanent dentition is completed in the 
third year, at which time the first deciduous molar, which 
is not replaced, falls out. Hence the formula of the per- 


373 1—1 33 88 
manent dentition isi. > ¢.7— p.m. 730 = 40. 


The permanent incisors in the upper jaw have short, 
broad, vertically-disposed crowns, and lie in a longitudinal 
series, the external being separated by an interval from 
the others. The elongated inferior incisors lie side by side, 
are greatly inclined forwards and upwards, and are grooved 
upon their upper or inner faces. The strong, angulated 


372 THE ANATOMY OF VERTEBRATED ANIMALS. 


crowns of the canines are bent upwards and outwards in 
both jaws. They work against one another, in such a 
manner, that the upper wears on its anterior and external 
face, the lower on the posterior aspect of its apex. The 
crowns of the premolars are all brought to a cutting longi- 
tudinal edge, while the molars have broad crowns with 
transverse ridges subdivided into tubercles. Of these ridges 
there are two in the anterior two molars of each jaw, while 
the posterior molar is more complex, having at fewest three 
distinct ridges. The molar teeth all develop roots; but the 
canines continue to grow for so long a time, in the Boar, 
that they might be said to be rootless. 

The alimentary canal is ten or twelve times as long as 
the body. 

The stomach is less simple in structure than it appears 
to be at first sight. The cardiac end presents a small 
cecum, in which is a spiral fold of the mucous membrane ; 
and, at the entrance of the esophagus, the epithelial lining 
is folded so as to form a sort of valve. Folds of the mucous 
membrane, between which there les a groove, extend from 
the cardia towards the pylorus, and foreshadow the more 
developed structure observable in Ruminants. 

The cecum has not above one-sixth the capacity of the 
stomach, and the ilium projects into it, so as to form a 
very efficient iliocecal valve. The liver is provided with a 
gall-bladder. The heart is devoid of an Eustachian valve, 
and sometimes, but not always, possesses a septal ossifi- 
cation. 

There is only one anterior cava. The aorta gives off an 
innominata, from whence the right subclavian and the two 
carotids arise, and a left subclavian. This is an arrange- 
ment midway between that observed in the Horse and that 
in Man. 

The trachea, before it divides, gives off a third bronchus, 
which passes to the right lung; and the lungs are deeply 
lobed. 

In the brain the cerebral hemispheres rise above the cere- 
bellum much more than they do in the Horse. 


THE SUID. 373 


In the male, the penis is contained in a long prepuce, and, 
like that of the Horse, is devoid of a bone and provided 
with retractor muscles. The prostate islobed. Thereisa 
large uterus masculinus and well-developed vesicule semi- 
nales. The ducts of Cowper’s glands open into a cecal 
cavity contained in the muscular bulb. The testes descend 
into a scrotum. In the Sow, a pair of Gaertner’s canals, or 
persistent Wolffian ducts, open into the vestibule beside 
the urinary meatus. The uterine cornua are very long, and 
the ovaries are lobulated. The period of gestation is sixteen 
to twenty weeks. The ovum, at first spherical, retains that 
form until it attains a diameter of nearly half an inch. 
it then rapidly elongates into a coiled filiform body, as much 
as twenty inches long. Both the allantois and the um- 
bilical vesicle at the same time assume a spindle-shape. 

The allantois soon becomes divided into an internal epi- 
thelial and an external vascular layer; the latter becoming 
united with the chorion, through the extremities of which 
the allantois eventually passes. The villi are very nu- 
merous, minute, and spread over the whole surface of the 
ovum. 

The Suide exhibit great variations in their dentition and 
in the structure of the stomach. 


In Porcus (the Babyrussa) the dental formula is 7. _ 


1-1 55 
C. Ty p-m.m. = 5 


kid, and the pharynx is provided with peculiar air 
sacs. 

The stomach is divided into three chambers, and the 
groove leading from the esophagus towards the Le goa is 
more distinctly marked than in Sus. 

In Dicotyles (the Peccaries) the upper incisors are also 
reduced to two on each side, and the molar teeth present 
transverse ridges, which are more distinct and less tuber- 
culated than in Sus. 

The stomach is divided into three sacs, and is provided 
with an cesophageal groove as in the preceding genus. 

The middle metatarsals and metacarpals. coalesce into a 


the canines are enormously elongated and 


374 THE ANATOMY OF VERTEBRATED ANIMALS. 


cannon bone, and the fifth digit of the pes is represented 
only by its metatarsal. 

In Phacocherus (the Wart-hog) the upper incisors are re- 
duced to one pair, and the hindermost molars, which are 
the only ones which are not shed in the old animal, are OL 
great size, and possess a complicated, tubereulated, struc- 
ture. 

The Suide are represented by one genus or another in 
all the great distributional provinces except the Australian* 
and Novo-Zelanian. Porcus is peculiar to part of the 
Malay Archipelago, Dicotyles to South America, and Pha- 
cocherus to South Africa. 

A great variety of Swine-like Ungulata existed during the 
deposition of the older tertiary strata, and are the earliest 
known members of the group. 

b. The Hippopotamide are represented at present only 
by the genera Hippopotamus and Cheropus. These animals 
have a huge head, a heavy body, covered with a thick in- 
tegument, provided with scanty hairs, and short, stout, 
tetradactyle limbs, all the four toes of which rest on the 
ground. The female has inguinal teats, and the male is 
devoid of a scrotum. 

; npn OFS 

The dental formula of the adult Hippopotamus is 1. >> 
c. = p.m. os m. = while Cheropus has only two incisors 
in the lower jaw. The tubercles of the molar teeth, when 
ground down by mastication, present a double trefoil 
pattern, and the hindermost inferior molar is trilobed. 
The incisors are straight and tusk-like. The very large 
and curved canines are directed downwards in the upper 
jaw, upwards in the lower. Their mutual attrition wears 
the anterior face of the extremity of the upper, and the 
posterior face of that of the lower, flat. 

44 


The milk dentition consist of d.1. - d.c. a d.m. 73. The 
last lower deciduous molar is trilobed, and the first deciduous 
molar persists a long time, and seems not to be replaced. 

* The Papuan pig may have been introduced from the westward. 


THE HIPPOPOTAMID. BY) 


The stomach is divided into three or four compartments, 
and there is no cecum. The liver has a gall-bladder, and 
the kidneys are lobulated. 

The skeleton is very pig-like, but in some respects ap- 
proaches the Ruminants. The ceutra are slightly convex 
in front, and concave behind, in the cervical region, but not 
elsewhere. The prezygapophyses overlap the postzygapo- 
physes in the posterior dorsolumbar vetebre. On the other 
hand, the transverse processes of the last lumbar vertebre 
articulate with those of the preceding and succeeding ver- 
tebrze, as in the Horse and other Perissodactyles. 

In the skull the orbits are nearly complete posteriorly, 
and they become almost tubular by the outward production 
of the frontal and lachrymal bones. 

The nasals and premaxille unite for a great extent. The 
osseous palate is long; the large tympanic bone is 
ankylosed with the approximated post-glenoidal and post- 
tympanic processes. 

The mandible is extremely massive, and has a backwardly 
produced angle. 

The scapula has a short acromion. The radius and ulna 
are complete and ankylosed, and there are eight bones in 
the carpus. The fibula is complete, and the tarsus, which 
has seven bones, much resembles that of the Pig. 

The Hippopotamide are at present confined to Africa; 
but a species abounded in the rivers of Hurope in the later 
tertiary times. 

Merycopotamus of the miocene Fauna of the Sewalik 
Hills appears to have been a Hippopotamid, with upper 
molars haying a quadri-crescentic, ruminant-like, pattern, 
and lower molars bi-crescentic and rhinocerotic in character. 

In the Suide and Hippopotamide, it is interesting to 
remark the tendency to the coalescence of the metacarpals 
and metatarsals in Dicotyles; the disappearance of the upper 
incisors by pairs in Dicotyles, Porcus, and Phacocherus ; and 
the great complexity of the stomach in Dicotyles and Hippo- 
potamus ; as they are so many approximations towards the 
structure of the Ruminant Artiodactyla. And the tran- 


376 THE ANATOMY OF VERTEBRATED ANIMALS. 


sition from the non-Ruminant to the Ruminant groups, 
or rather the common stem of both, is furnished by the 
Anoplotheride. 

c. The family of the Anoplotheride exclusively contains 
extinct Mammals belonging to the eocene and miocene 
epochs. ‘They are most conspicuously distinguished by the 
circumstance that the teeth, of which there are eleven on 
each side, above and below, in the adult dentition, are not 
interrupted by any gap in front of and behind the canine, 
as they are in the preceding genera, but form an uninter- 
rupted and even series, as in Man. 

The dental formula of the adult Anoplotheriwm is 
PIRSee) (isles 44 

7 St aaa “44 
molar is really such, and not a persistent milk molar. 

The upper and lower molars have the general structure 
of those of the Rhinoceros; but the lamine of the upper 
are bent more backwards into parallelism with the outer 
wall, and a strong conical pillar is developed on the inner 
side of the anterior lamina. The skull resembles that of 
the Ruminant Tragulide in structure, but the orbit is in- 
complete behind. The rest of the skeleton partly resembles 
that of the Pigs, and partly that of the Ruminants.* 

In Xiphodon and Cainotheriwn, which are ordinarily com- 
prised among the Anoplotheride (though, in all probability, 
they are true Ruminants of the Traguline group), the orbit 
is complete, and both upper and lower molars put on the 
Ruminant characteristics. In dentition, Cainotheriwm differs 
from a Ruminant only in possessing all the upper incisors, 
while no existing adult Ruminant has more than the outer 
upper incisors. We are of course unacquainted with the 
structure of the stomach in these animals, but they so 
closely resemble Ruminant Artiodactyla that it is highly 
probable they may have possessed the faculty of rumination 
in a more or less perfect degree. 


mu. i supposing that the first pre- 


* In Anoplotherium secundarium the digit zi. is developed in each 
foot, though not nearly so long as #i., which is nearly symmetrical in 
itself. There is an approach to the same structure in the manus of 
Cainotherium. 


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‘(sog) XO UB Jo WOJO]OIS OT, “LOT “SLT 


a ie aa 


oo eee 


THE RUMINANTIA. BY aA 


B. The Ruminantia—In the commonly recognised mem- 
bers of this division of the Artiodactyla there is never 


SS 
VF 
q Y 
ay 
i 
~ Va 
; 
ft 
vit 
Mh 
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SS 
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378 THE ANATOMY OF VERTEBRATED ANIMALS. 


more than one pair of incisors, and that the outermost, in 
the upper jaw of the adult. Canines may or may not exist 
in the upper jaw; they are always present in the lower 
jaw, and are generally inclined forwards and closely 
approximated to the incisors, which they usually resemble 
in form. It consequently happens that they are often 
reckoned as incisors, and Ruminants are said to possess 
eight cutting teeth in the lower jaw. 

With one exception (Hycemoschus), the metacarpal and me- 
tatarsal bones of the third and fourth digits early become 
ankylosed together into a single, so-called, cannon bone. 
There is a peculiar bone called malleolar, which takes the 
place of the distal end of the fibula, articulating below 
with the calcaneum and above with the astragalus. 

The great majority of the Ruminantia possess horns, the 
bony supports, or cores, of which are developed on each 
side of the middle line; and, except in the Giraffe, are 
outgrowths of the frontal bones. 

The stomach has, at fewest, three divisions; and, in the 
majority of the Ruminantia, it has four compartments. 

If the stomach of a typical Ruminant, such as a Sheep or 
an Ox, be examined, it will be found to be divisible into two 
principal moieties, the one cardiac and the other pyloric, 
while each of these is again subdivided into two others. 
Thus the extreme cardiac end of the cardiac moiety is 
dilated into an enormous sac of irregular form, the mucous 
membrane of which is raised up into a vast number of close- 
set papille. This chamber is the Rumen, or Pawnch. It 
communicates, by a wide aperture, with a much smaller 
chamber, which constitutes the second sub-division of the 
cardiac moiety. This is called the Reticulum, or Honeycomb 
stomach, from the fact that its mucous membrane is raised 
up into a great number of folds, which cross one another 
at right angles, and, in this way, inclose a multitude of 
hexagonal-sided cells. The reticulum communicates by a 
narrow aperture with the first subdivision of the pyloric 
moiety, which is somewhat more elongated in form. The 
mucous membrane of this subdivision is produced into a 


THE RUMINANT STOMACH. 379 


yast number of longitudinal folds of various heights, but 
the majority of them are sufficiently large to extend almost 


Fig. 102.—A, the stomach of a Sheep. B, that of a Musk-deer (Tra- 
gulus). 

@., _—_ Rn., rumen; Ret., reticulum; Ps., psalterium; 4., 
Ab., abomasum; Du., duodenum; Py., pylorus. 

completely across the cavity of the chamber; they thus 

reduce that cavity to a series of narrow radiating clefts 

interposed between the lamellz. When this portion of the 

stomach is slit open, longitudinally, the lamelle fall apart 

like the leaves of a book, whenceit has received the fanciful 

name of the Psalteriwm from anatomists, while butchers give 


380 THE ANATOMY OF VERTEBRATED ANIMALS. 


it that of Manyplies. The fourth segment of the stomach, 
or second subdivision of the pyloric moiety, is termed the 
Abomasum, or Rennet stomach. This portion is compara- 
tively slender and elongated, and its mucous membrane has 
a totally different character from that of the other three 
segments, being soft, highly vascular, and glandular, and 
raised into only a few longitudinal ridges. 

It will be observed that the psalterium is so constructed 
as to play the part of a very efficient strainer between the 
reticulum and the abomasum; nothing but very finely 
divided, or semi-fluid matter, being capable of traversing 
the interstices of its lamellez. 

The gastric aperture of the esophagus is situated at the 
Junction of the paunch and the reticulum; the margins of 
its opening are raised into muscular folds, and are pro- 
duced, parallel with one another, along the roof of the 
reticulum to the opening which leads into the psalterium. 
When the lips of this groove are approximated together, 
a canal is formed, which conducts directly from the ceso- 
phagus to the psalterium, 

A Ruminant, when feeding, crops the grass rapidly and 
greedily, seizing it with its tongue and biting off the bundle 
of blades thus collected, by pressing the lower incisors 
against the callous pad formed by the gum which covers 
the pre-maxillz. The bunches of grass are then hastily 
swallowed, accompanied by abundant saliva. After grazing 
until its appetite is satisfied, the Ruminant lies down, usually 
inclining the body to one side, and remains quiescent for a 
certain space of time. A sudden movement of the flanks is 
then observed, very similar to that which might be produced 
by a hiccough ; and careful watching of the long neck will 
show that something is, at the same time, quickly forced up 
the gullet into the cavity of the mouth. This is a bolus of 
grass, which has been sodden in the fluids contained in the sto- 
mach, and is returned, saturated with them, to be masticated. 
In an ordinary Ruminant this operation of mastication is 
always performed in the same way. The lower jaw makes a 
first stroke, say in the direction from left to right, while the 


THE ACT OF RUMINATION. 381 


second stroke, and all those which follow it until the bolus 
is sufficiently masticated, takes place from right to left, or 
in the opposite direction to that of the first. While the 
mastication is going on, fresh quantities of saliva are 
poured into the mouth, and when the grass is thoroughly 
ground up, the semifluid product is passed back imto the 
pharynx and swallowed once more. These actions are 
repeated until the greater portion of the grass which 
has been cropped is pulpified. 

The precise nature of the operation, the external features 
of which have now been described, has been the subject of 
much investigation and discussion. The following points 
appear to have been clearly established: 

1. Rumination is altogether prevented by paralysis of 
the abdominal muscles, and it is a good deal impeded by 
any interference with the free action of the diaphragm. 

2. Neither the paunch, nor the reticulum, ever becomes 
completely emptied by the process of regurgitation: The 
paunch is found half full of sodden fodder, even in animals 
which have perished by starvation. 

3. When solid substances are swallowed, they pass indif- 
ferently into the rumen, or reticulum, and are constantly 
driven backwards and forwards, from the one into the other, 
by peristaltic actions of the walls of the stomach. 

4. Fluids may pass either into the paunch and the re- 
ticulum; or into the psalterium, and thence at once into 
the fourth stomach, according to circumstances. 

5. Rumination is perfectly well effected after the lips 
of the esophageal groove have been closely united by wire 
sutures. 

It would appear, therefore, that the cropped grass passes 
into the reticulum and rumen, and is macerated in them. 
But there is no reason to believe that the reticulum takes 
any special share in modelling the boluses which have to be 
returned intothe mouth. More probably, a sudden and simul- 
taneous contraction of the diaphragm and of the abdominal 
muscles, compresses the contentsof the rumen and reticulum, 
and drives the sodden fodder against the cardiac aperture of 


382 THE ANATOMY OF VERTEBRATED ANIMALS. 


the stomach. This opens, and then the cardiac end of the 
cesophagus, becoming passively dilated, receives as much of 
the fodder as it will contain. The cardiac aperture now 
becoming closed, the bolus, thus shut off,is propelled, by 
the reversed peristaltic action of the muscular walls of the 
cesophagus, into the mouth, where it undergoes the thorough 
mastication which has been described. 

The sodden fodder is prevented from passing out of the 
psalterial aperture of the reticulum, in part by the narrow- 
ness of that aperture, and in part by the fine grating 
formed by the edges of the psalterial lamine. But when 
the semifluid matter, returned after mastication, once more 
reaches the cardia. it is compelled to pass towards the psal- 
terial end of the reticulum (even apart from the guidance 
afforded by the lips of the esophageal groove) on account 
of the direction of the esophagus and the bounding of 
the cardiac aperture, on the side of the rumen, by a raised 
ridge. The chewed matter thus flowing over the surface 
of the more solid contents of the reticulum reaches the 
psalterium; and, in consequence of the fine state of 
division of its solids, readily traverses the interspaces of 
the lamelle of that organ, and passes into the fourth 
stomach, there to be submitted to the action of the 
gastric juice and to undergo the digestion of the protein 
compounds, which have remained unaffected by the previous 
mastication and insalivation. 

The Ruminantia are divided into three groups: a. the 
Tragulide, b. the Cotylophora, and c. the Camelide. 

a. The Tragulide are a remarkable family, formerly 
united with the genus Moschus, and still commonly known 
under the name of Musk Deer, though they are devoid 
of the musk sac and, in other respects, are totally different 
from Moschus. They are at present restricted to southern 
Asia and Africa; and they are particularly interesting, 
as affording, in many respects, a connecting link between 
the typical Ruminants and the other Artiodactyla, especially 
the Anoplotheride. Thus, the second and fifth digits are 
complete in both fore and hind feet, and the metacarpals 


ee ee 


ee ell ee 


THE TRAGULIDA. 383 


and metatarsals of the third and fourth digits unite very 
late, or, as in one genus, Hycemoschus, not at all. The 
canines are well developed in both jaws, and the premolar 
teeth are sharp and cutting. 

The cesophagus opens at the junction of the rumen with 
the reticulum, the communication between the two being 
yery wide (Fig. 102 B). The epithelium of the rumen is papil- 
late, and there are two csophageal folds, as im ordinary 
Ruminants, but the psalterium is represented only by a very 
short and narrow tube, the liming membrane of which is 
devoid of folds. 

The surface of the hemispheres of the brain has fewer 
convolutions than in any other Ruminants, though this may 
very possibly be connected with the small size of the 
animal; as it is a general rule that, within the same group, 
the brain is less convoluted in small than in large animals. 

The blood corpuscles, small in all Ruminantia, are 
remarkably minute in the Tragulide, not exceeding +5155 
of an inch in diameter. They have circular contours. 

The placenta is very nearly diffuse, the fetal villi being scat- 
tered over the chorion in bands, not collected into cotyledons. 

As further remarkable peculiarities of this group may 
be mentioned the ankylosis of the malleolar bone with the 
tibia, and the tendency to ossification in the pelvic liga- 
ments and of the aponeurosis of the muscles of the back, 
in adult males. Finally, the navicular, cuboid, and ecto- 
cuneiform bones in the tarsus are all ankylosed together. 
If, as is probable, Xiphodon is one of the Tragulide, the 
group has existed since the eocene epoch. 

b. The Cotylophora are, like the preceding group, unguli- 
grade, but the outer metacarpals aud metatarsals are in- 
complete at their proximal ends, and the middle ones are 
early ankylosed into a cannon bone. The malleolar bone is 
always distinct. The navicular and the cuboid bones of 
the tarsus are ankylosed together, but rarely with any other 
tarsal bone. The premaxilla is devoid of teeth in the adult. 
The stomach has the structure which has been described as 
typical. 


384. THE ANATOMY OF VERTEBRATED ANIMALS. 


The blood corpuscles are circular, and may have a 
diameter of as little as =,',, of an inch. 

The fetal villi are gathered together into bunches or 
cotyledons, which may present either a convex or a concave 
face towards the uterus. They are received into persistent 
elevations of the mucous membrane of the uterus, the sur- 
faces of which present a reverse curvature. 

All the Cotylophora except Moschus, the true Musk Deer, 
are provided with horns, but these horns are of two kinds. 
The bony core, in the one case, is ensheathed in a strong 
horny epidermic case; while, in the other, the epidermis of 
the integument which covers the core does not become so 
modified. In the former kind of horn, the core becomes 
excavated by the extension into it of the frontal sinuses, 
whence the ruminants which possess such horns are not un- 
frequently called Cavicornia (Antelopes, Sheep, Goats, Oxen). 
As a general rule, the horny sheath persists throughout 
life, growing with the growth of the core. But in the 
remarkable Prong-horned Antelope of North America 
(Antilocapra), the horny sheath is annually shed and replaced 
by a newly-formed one. 

Of the second kind of horn, or that which acquires no 
horny sheath, there are also two kinds. In the Giraffe, 
the horn cores are attached over the coronal suture, at the 
junction of the frontal and parietal bones, with which they 
are not ankylosed; they persist throughout life, and are 
always covered by a soft and hairy integument. 

In the Deer, on the other hand, the frontal bones grow 
out into solid processes, which are, at first, covered by 
soft and hairy integument; generally they are developed 
in the male sex only, but both sexes have them in the Rein- 
deer. The horns attain their full size very rapidly, and 
then a circular ridge, which makes its appearance at a 
short distance from the root of the horn and is called 
the “burr,” divides the horn into the “pedicel” on the 
skull side of the burr, and the “ beam” on the opposite side. 
The circulation in the vessels of the beam now gradually 
languishes, its integument dies and peels off, and the dead 


THE TYLOPODA. 385 


bony substance beneath is exposed. Absorption and 
sloughing next occur at the extremity of the pedicel, just 
as might happen in any other case of necrosis. The beam 
and burr are shed, and the end of the pedicel scabbing 
over, fresh integument gradually grows up under the scab, 
and eventually restores to the extremity of the pedicel its 
pristine smooth and hairy covering. 

The rapidity with which the development of bony matter 
into Deer horn takes place is wonderful, horns weighing 
72 lbs. having been produced in ten weeks. 

The Cotylophora are represented in all parts of the world 
except the Australian and Novo-Zelanian provinces. They 
have not yet been traced back further than the miocene 
epoch. 

ce. The Camelide or (Tylopoda) are devoid of horns; and, 
unlike the other Ruminants, they walk upon the palmar 
and plantar surfaces of the phalanges of the third and 
fourth toes, which are alone developed. Broad integu- 
_ mentary cushions form a sole to the foot; while the nails 
are flattened and can hardly be called hoofs. 

The arches of the cervical vertebree, and not their trans- 
verse processes, are perforated by the canal of the vertebral 
artery; a character which the camels share with the 
Macrauchenide. 

The metacarpals are separated by a deep cleft, and the 
distal phalanges of the digits are nearly symmetrical in 
themselves. The distal facets of the astragalus are more 
unequal than in the other Ruminantia, and the navicular 
and cuboid bones are not ankylosed together. 

The premaxille have a single strong outer incisor on 
each side. Large curved and pointed canines are developed 
in each jaw, and are quite distinct from the series of the 
incisors in the mandible. There are not more than five 
grinding teeth in a continuous series above and below. 

The stomach is unlike that of the typical Ruminants. 
The csophagus opens directly into the paunch, which is 
lined by a smooth, not papillose, epithelial coat. From its 
walls, at least two sets of diverticula, with comparatively 

2c 


386 THE ANATOMY OF VERTEBRATED ANIMALS. 


narrow mouths, are developed. These, the so-called “ water 
cells,” serve to strain off from the contents of the paunch, 
and to retain in store, a considerable quantity of water. 
The reticulum is sharply defined from the rumen, and com- 
municates with it by a comparatively small aperture. The 
cesophageal groove is bounded by only one ridge, which lies 
upon its left side. The psalterium is reduced to a mere 
tubular passage, without laminz; and the abomasum is 
large, and has the ordinary structure. The pyloric end 
of the duodenum is considerably dilated, and has been 
taken for a division of the stomach. The ccecum is short 
and simple. By a remarkable exception among the Mam- 
malia, the red blood corpuscles are elliptical. The feetal 
villi are scattered evenly over the chorion, so that the 
placenta is diffuse. 

While the Tragulide connect the typical Ruminants with 
the non-ruminant Artiodactyles, the Camelide, on the 
other hand, link them with Macrauchenia and the Perisso- 
dactyles. 

The Camelide are at present represented by two very 
distinct groups—the Camels of the old world and the 
Llamas of the new. They occur in the fossil state as far 
back as the miocene epoch. 

II. The ToxopontT1a.—This order has been founded for 
the reception of the large extinct Mammal (Toxodon), remains 
of which have been discovered in the later tertiary deposits 
of South America. 

The supraoccipital surface of the massive skull slopes 
obliquely upwards and forwards. There are supraorbital 
prolongations. The zygomata are very strong and arched, 
and the bony palate is very long. 

In the upper jaw there are two small, inner, and two 
large, outer, incisors. In the lower jaw there are six incisors. 
In the mandible there are canines in the middle of the in- 
terval between the incisors and the grinders. In the upper 
jaw of the adult, only indications of the former existence of 
alveoh for canines remain, The grinding teeth are seven 
on each side above, and six on each side below. They are 


THE SIRENIA. 387 


greatly bowed (whence the name of the genus), so as to 


_be convex outwards and concave inwards. They grow 


from persistent pulps, and the enamel is absent upon their 
inner faces. 

The centra of the cervical vertebre have flattened arti- 
cular faces. The dorsolumbar vertebre and the sacrum 


are not known. The ribs are spongy internally, like those 
_ of ordinary Mammals, not compact, as in the Sirenia. 


The scapula has a very large supraspinous fossa, as in 
Tapiwrus. There is no acromion, and the coronoid is very 
small. The humerus and the ulna are very massive, but 
the rest of the fore-limb is unknown. The femur is devoid 
of any third trochanter, and, like the tibia and astragalus, 
presents a good many points of resemblance to the corre- 
sponding bone in the Elephants. 

It is a curious comment upon the pretension to recon- 
struct animals from mere fragments of their bones and 


_ teeth which some have put forward, that although we know 
_ the skull, the dentition, and the most important of the limb 
_ bones of Toxodon, no one ventures to predict the characters 


of its feet, still less to say anything about its internal 


organization. Even its zoological affinities are extremely 


doubtful, and it is hard to say whether Toxodon is merely 
an aberrant Ungulate, or whether it is the type of a new 
order. 

iil. The Stren14.—As has been already said, nothing is 
known of the placentation of this small but important 
group of Mammalia, all the existing forms of which are 
aquatic in their habits, frequenting great rivers and their 
estuaries; and are devoid of hind ibs while the integu- 
ment of the caudal end of the body is produced itd a 
flattened horizontal fin. No dorsal fin is ever present. 
The demarcation between the head and neck is but ob- 
securely marked, and the forelimbs are converted into 
paddles, upon which only rudimentary nails are developed. 
Scanty bristles cover the surface of the body. The snout 
is fleshy and tumid, and the valvular nostrils, which are 


perfectly distinct from one another, are situated consider- 


388 THE ANATOMY OF VERTEBRATED ANIMALS. 


ably above its termination. There is a well-developed 
third eyelid, the pinna of the ear is absent, and the 
mamme are thoracic; a circumstance which has probably 
not a little contributed to the origination of the myths 
respecting the existence of mermaids. 

The Sirenia were formerly united with the Whales and 
Porpoises as Cetacea herbivora. But their organization 
differs from that of the true Cetaceans in almost every 
particular, while they are closely allied with the Ungulata. 

The cervical vertebree are reduced to six in one genus— 
Manatus. The bodies of these vertebre are always com- 
pressed from before backwards, but they are never all 
ankylosed together (it is rare for any of them to be thus 
united), and the second has a distinct odontoid process. 
The dorsal vertebra have broad and depressed spines, and 
may be as many as seventeen or eighteen in number, while 
there are not more than three lumbar vertebre; and the 
hindermost of these even is probably to be regarded as 
sacral. There are twenty or more caudal vertebre. the 
terminal ones being not polygonal, but depressed, with 
well-developed processes. 

The zygopophyses of successive vertebre articulate to- 
gether in the dorsal region; but, in the lumbar and caudal 
regions, the postzygapophyses disappear and the prezygo- 
pophyses are small, and neither overlap, nor embrace, the 
spine of the antecedent vertebra. The posterior moiety 
of the spine thus acquires considerable flexibility. There 
is no true sacrum, the vertebra called “sacral” being only 
determined as such by its connection with the rudimentary 
pelvis. Strong subvertebral chevron bones are placed 
beneath the interarticular cartilages of the caudal vertebra. 
The heads of the ribs articulate with the centra of all 
the vertebre. The bodies of the ribs are very thick, 
rounded, and have a remarkably dense and laminated struc- 
ture. The narrow and elongated sternum is an undivided 
mass of bone, and is connected by ossified sternal ribs with 
the anterior three pairs of vertebral ribs. 

In the skull the elongated and subcylindrical form of the 


2 


THE SIRENIA. 389 


cranial cavity is worthy of notice, as it strongly contrasts 
with the form of the brain-case in the Cetacea. The supra- 
occipital is very large and slopes upwards and forwards 
a long way on to the upper surface of the skull; but it does 
not separate the parietal bones; which, as usual, unite in 
the sagittal suture. The frontals are prolonged into broad 
supra-orbital processes. The nasal bones are abortive, and, 
in the dry skull, the external nares are very wide and look 
upwards. The tympanic bone is a thick hoop, ankylosed 
with the periotic bones, and readily comes away from the 
skull with them, The zygoma is enormously stout. The 
premaxille constitute a large portion of the boundary of 
the gape; and the lower jaw has a high ascending portion, 
with a large coronoid process. 

The scapula has a distinct spine occupying the ordinary 
position. There are no clavicles. The humerus has its 
distal end fashioned into articular surfaces, upon which the 
radius and ulna are freely movable. The pollex is rudi- 
mentary, and the other digits have no more than three 
phalanges each. 

The pelvis is rudimentary, the bones which represent 
the ossa innominata being connected by their proximal 
ends with the transverse processes of the last of the pre- 
caudal vertebre. They are disposed vertically to the axis 
of the body. No trace of the hind limbs has been observed 
in any of the existing Sirenia. 

The premaxillary region of the palate, and the corre- 
sponding surface of the mandible, are coated with mam- 
millated and rugose horny plates formed of hardened 
epithelium ; and, in the extinct genus Rhytina, these plates 
were the only masticating organs, as there were no teeth. 
In Halicore (the Dugong), there are teeth which have no 
vertical successors, form no roots, and are devoid of 
enamel; while, in Manatus, there are milk molars, and the 
grinding teeth are enamelled, and present crowns with 
double transverse ridges. 

The adult Manatee has no incisors. In the Dugong 
there are no incisors in the mandible of the adult. The 


390 THE ANATOMY OF VERTEBRATED ANIMALS. 


male has two tusk-like incisors which project from their 
sockets in the premaxille; while, in the female, the tusks 
remain concealed in their alveoli. 

In the fetal state, both Halicore and Manatus have in- 
cisors in the mandible as well as in the premaxille. 

The stomach is divided into two portions by a median 
constriction, and its cardiac end is provided with a peculiar 
gland. Its pyloric end, in some species, gives off two ceca. 

There is a cecum at the junction of the large and small 
intestine. Salivary glands are well developed. The apical 
portion of the septwm ventriculorum is deeply cleft, so that 
the ventricles are separated from one another through 
about half their extent. 


Fig. 103. 


Fig. 103.— Dorsal view of the heart of a Dugong ( Halicore), its cavities 
being laid open. R. v., right ventricle; L.v., left ventricle. V.c.s.s., 
left superior vena cava. V.c.s. d., right superior vena cava. V. c. i., 
vena cava inferior. F.o.v., the inner end of a cecal diverticulum 
of the right auricle, into which a style is introduced, and which 
represents the foramen ovale. O., the auricular septum, 

There are two superior cave and a Hustachian valve. 
Extensive arterial and venous retia mirabilia are developed 
in Manatus. In consequence of the great length of the 
thoracic region and the brevity of the sternum, the dia- 
phragm takes a very unusual course, extending very 
obliquely from before backwards, and causing the upper 


THE CETACEA. 391 


part of the thoracic cavity to extend posteriorly over 
almost the whole of the abdomen. The greatly elongated 
lungs fill this part of the thoracic chamber, while the broad 
heart lies in its anterior and sternal portion. 

The arytenoid cartilages are not prolonged as in the 
Cetacea. A broad and high epiglottis is capable of covering 
the glottis completely. 

There is no third bronchus. 

The cutaneous muscle is largely inserted into the hu- 
merus, and the sub-caudal muscles extend forward as far 
as the posterior lumbar vertebra. The chief muscles of the 
antibrachium and manus are present. 

The male Sirenia possess vesicule seminales. The uterus 
is two-horned. 

There are two living genera of Sirenia—the Dugong 
(Halicore), which is found upon the shores of the Indian 
Ocean and of Australia; and the Manatee (Manatus), which 
is confined to the South American and African borders of 
the Atlantic. 

A third genus, Rhytina, which had a coriaceous integu- 
ment almost devoid of hair, and possessed no teeth, 
abounded in Behring’s Straits less than a century ago. 
Tt is now altogether extinct. 

The Miocene genus, Halitheriwm, appears to have pos- 
sessed distinct, though small, hind limbs. 


IV. The Cetacea.—In this order of Mammalia the form 
of the body is still more fish-like than in the Sirenia. 
There is no trace of a neck, the contour of the head 
passing gradually into that of the body. A horizontally 
flattened caudal fin is always present; and, very generally, 
the dorsal integument is produced into a median, laterally 
compressed, dorsal fin. The body is encased in a thick 
smooth integument, beneath which a very thick layer of 
fat is deposited. Hairs are almost entirely absent in the 
adult state. 

As in the recent Sirenia, the anterior limbs alone are 
present. Externally they do not present any indication of 


392 THE ANATOMY OF VERTEBRATED ANIMALS. 


division into brachium, antebrachium, and manus, but have 
the form of a broad flattened paddle, without any vestiges 
of nails. 

The one or two apertures by which the cavity of the 
nose opens externally, are always situated at the top of the 
head, and far removed from the extremity of the snout. 
There is no third eyelid, and the very small auditory aper- 
tures are totally devoid of any pinna. The teats are two, 
and, in the female, are lodged in depressions on each side 
of the vulva. 

The articular surfaces of the centra of the vertebre are 
flat, and the epiphyses usually remain distinct for a long time. 

The spinal. column, as a whole, is remarkable for the 
shortness of its cervical, and the leneth of its lumbar region, 
there being sometimes a greater number of lumbar than of 
dorsal vertebre. There is no sacrum. The caudal vertebree 
-are only distinguishable from the posterior lumbo-sacral 
vertebre by their chevron bones. The second vertebra of 
the neck is devoid of any odontoid process; and it very 
commonly happens that more or fewer of the cervical 
vertebra, the bodies of which are often so short as to be 
mere discs, are ankylosed together, either by their arches, 
or by their centra, or by both. The centra of all the suc- 
ceeding vertebre are large in proportion to their arches, 
and the inter-vertebral fibro-cartilages are exceedingly 
thick, so as to confer great flexibility and elasticity on the 
spine. The arches of the hinder dorsal vertebre, and of 
those of the lumbar and caudal regions, are not articulated 
together by zygapophyses. The centra of the posterior 
caudal vertebre lose their processes and become polygonal. 

Very few of the ribs become connected with the sternum 
at their distal ends; and, in contradistinction to what 
happens in most Mammalia, the proximal ends of the 
majority of the ribs are connected only with the transverse 
processes of the vertebre, and not with their bodies. 

The skull is even more remarkably modified than the 
vertebral column. The brain case itself has a spheroidal 
form; while the jaws are greatly prolonged, the principal 


THE CETACEA. 393 


enlargement of the upper jaw taking place in the region 
which lies in front of the nasal aperture. The basis cranii, 
as a whole, is remarkably broad, and its upper surface 
concave from before backwards, the sella turcica being very | 
slightly indicated. The parietal bones are comparatively 
small, and do not meet in a sagittal suture, as they do in 
other Mammalia; the supraoccipital, with an interparital 
bone, being interposed between them, and extending for- 
wards so as to unite with the frontals. Hach frontal 
bone is produced outwards into a great bony plate which 
covers the orbit. The squamosal bone sends a very large 
and stout zygomatic process forwards to meet this supra- 
orbital prolongation of the frontal. The proper jugal 
bone, on the other hand, which bounds the orbit below, 
is exceedingly slender. The very large maxilla extends 
backwards and outwards in contact with the frontal, or 
even overlapping the greater part of its surface; and it 
stretches forwards to very near the anterior end of the 
snout, so that almost the whole of the gape is bounded by 
the maxilla. 

The premaxille, on the other hand, though very long, 
imasmuch as they occupy the whole length of the jaw in the 
middle line, from the anterior nasal aperture to the end of 
the snout, are almost entirely excluded from the gape. 

The nasal bones are always short; and, sometimes, are 
mere bony tuberosities united with the frontal bones behind 
the anterior nasal aperture. The turbinal bones are almost 

_ always rudimentary, and the nasal passages are nearly ver- 
_ tical, in consequence, for the most part, of the rudimen- 
tary condition and shortness of the nasal bones. 

The periotic bones are loosely connected with the squa- 
mosal and tympanic, and are usually united with the other 
bones of the skull only by cartilage, so that they fall out 
very readily in the dry skull. The tympanic bones are 
commonly of very considerable size, thick and _ scroll- 
shaped. ; 

The lower jaw has hardly any coronoid process, and its 
ramus has no perpendicular portion, the condyle being 


394 THE ANATOMY OF VERTEBRATED ANIMALS. 


situated upon its posterior extremity. The body of the 
hyoid is a very broad plate of bone, and has two pair of 
stout well-ossified cornua. 

The Cetacea are devoid of clavicles. If the spine of the 
scapula is present, itis a low ridge situated close to the 
anterior edge of the bone; but it commonly terminates in a 
long acromion process, and, sometimes, there is a con- 
spicuous, straight, and flattened, coracoid. The humerus is 
short, and the articular surfaces at its distal end are, in 
all recent Cetacea, flat facets inclined to one another at 
an angle. The ulna and the radius are short, laterally 
compressed bones, without any movement upon one another ; 
and, in all recent Cetacea, they are not freely movable upon 
the humerus. The carpus is often imperfectly ossified. 
When the carpal bones are complete, they are polygonal 
and imbedded in a fibrous tissue; not united by articu- 
lations provided with synovial membranes. The digits do 
not exceed five in number, but there are always more 
than three phalanges in some of them. 

The pelvis is represented by two bones which lie parallel 
with the axis of the vertebral column, give attachment to 
the corpora cavernosa in the male, and, therefore, probably 
represent the ischia. They are elongated, convex upwards 
and concave downwards, and are connected with the verte- 
bral column only by fibrous tissue. In some few Cetacea 
(Balenoidea) ossicles, which lie on the outer side of the 
pelvic bone, appear to represent the femur, but no further 
indication of a hind limb has been discovered. 

In most of the Cetacea, the muscles which, in other 
Mammalia, move the antebrachium and the manus, are 
absent, those which move the humerus upon the shoulder- 
blade being, alone, represented. 

In no recent Cetacean have the teeth any vertical suc- 
cessors, nor more than a single root. The alveoli are often 
incompletely separated from one another. The number of 
the teeth varies very greatly, but they are almost always 
nearly uniform in character. There appear to be no salivary 
glands. The stomach is complicated, being divided into, 


THE CETACEA. 395 


at fewest, three chambers, of which the first is a kind of 
paunch lined by a thick epithelium, while the second and 
the third are more elongated, the last stomach being that 
in which digestion takes place. 

The arteries and veins form great plexuses, or retia mi- 
rabilia, and these are especially conspicuous in the cavity 
of the thorax, upon each side of the vertebral column, and 
in the intercostal spaces. 

The soft palate is remarkably long and muscular. The 
epiglottis and the arytenoid cartilages are more or less 
produced, so as to give the glottis the shape of a funnel, 
the apex of which is embraced by the soft palate, in such 
a manner as to form a continuous air-passage from the 
posterior nares to the larynx, on each side of which the 
food passes. The very short trachea, before it divides 
into the bronchi, gives off the so-called “third bronchus” to 
the right lung, as in the Bears, Walruses and Ruminants. 

The kidneys are deeply subdivided into lobules. In the 
male the testes always remain in the abdomen, and there 
are no vesicule seminales. The penis is devoid of a bone. 
The uterus of the female is deeply divided into two horns, 
and the villi of the fetus are scattered over its chorion, 
as in other mammals with a diffuse placentation. 

The Cetacea are divisible into three groups; the Bale- 
noidea, the Delphinoidea, and the Phocodontia.* 

a. In the Balenoidea the nasal chambers communicate 
with the exterior by two apertures, which are capable of 
being shut at the will of the animal, and are called spira- 
cles. These are not connected with any saccular dilata- 
tions of the nasal passages, situated between the skull and 
the integument. 

In the spinal column, no rib has a complete neck and 
capitulum, the heads of even the most anterior ribs being 
united with the bodies of the vertebre only by ligament. 
The chief connection of all the ribs therefore, and the only 


* For further information respecting the characters of the recent 
Cetacea, 1 refer the reader to Prof. Flowers’ very valuable memoir 
‘*Qn the Osteology of Inia and Pontoporia,” published in the ‘‘ Trans- 
actions of the Zoological Society for 1867.” 


396 THE ANATOMY OF VERTEBRATED ANIMALS. 


connection of most of them, is with the transverse pro- 
cesses of the vertebre. The short and broad sternum 
Fig. 104. 


Mn 
Tin 


7 
TON 


maT TN 
eC it ii SAGU ALANNA 


Fig. 104.—Lateral and superior views of the skull of a foetal Whale 
(Balena australis). The jugal bones are absent, and the figure does 
not sufficiently indicate the outward curvature of the ramus of the 
mandible (Mn ). 


——_-_- = 


- 


THE BALH/NOIDEA. 397 


unites only with the first rib, and the union is direct, so 
that there are no sternocostal ribs. 


Fig. 105. 


ANT 
if amis p 


Ul] 


Fig. 105.—“‘ Ear bones” of the adult Balena australis. Seen from 
within in the upper figure ; from without in the lower. Zuw., Eus- 
tachian canal; Aw., external auditory meatus; Sty., ossified root 
of the styloid process. 

The skull (Fig. 104) is exceedingly large in proportion to 
the body, and nearly symmetrical. The nasal bones, Na., 
though short, are longer, and more like those of ordinary 
mammals, than is the case in other Cetacea. The maxilla, 
Mz., extends outwards in front of the great supraorbital 
process of the frontal, Fr., but it does not cover the frontal 
bone. There is a distinct lachrymal. Hach ramus of the 
mandible, Mn., is convex outwards and concave inwards; 


398 THE ANATOMY OF VERTEBRATED ANIMALS. 


and the space between the rami of the mandible is very 
much greater than the width of the maxillo-premaxillary 
part of the skull, which tapers to its anterior end, and 
is more or less convex upwards and concave inferiorly. 
The two rami of the mandible are connected only by 
ligament at the symphysis. 

Minute teeth are developed in fetal Balenide, but are 
very soon lost, and their place taken by the so-called Whale- 
bone, or Baleen plates. Hach of these is triangular, with a 
thick, smooth outer edge, somewhat concave from above 
downwards, which, in the natural position of the plates, is 
nearly vertical, and is covered by the great lower ip. The 
upper edge of the plate, also slightly concave, is attached 
to a transverse elevation of the gum covering the palate. 
Vascular papille extend from this ridge into cavities of cor- 
responding dimensions, which lie, parallel with one another, 
inthe baleen plate. The third side of the triangular baleen- 
plate, somewhat convex and sloping from the middle line 
above, downwards and outwards, gives origin to a number 
of filamentous processes, into which the baleen appears to 
be, as it were, frayed out. When the mouth is shut, these 
frayed edges of the numerous and close set baleen plates, 
which are longest in the middle of each series, and shortest 
at each end, enclose a cavity, the bottom of which is occu- 
pied by the large and fleshy tongue. By raising the 
tongue, whatever solid matters are inclosed in the mouth 
can be forced back into the pharynx and swallowed; while 
the water in which they were suspended is driven out 
between the baleen-plates. The Whale feeds by putting 
this gigantic strainer into operation, as it swims through 
the shoals of minute molluscs, crustaceans and fishes, which 
are constantly found at the surface of the sea. Opening 
its capacious mouth, and allowing the sea water, with its 
multitudinous tenants, to fill the oral cavity, the Whale 
shuts the lower jaw upon the baleen plates, and straining 
out the water through them, swallows the prey stranded 
upon its vast tongue. 

In some of the Balenoidea, e. g., Balena rostrata, the 


— 


SEE 


THE DELPHINOIDEA. 399 


ericoid cartilage and the rings of the trachea are incom- 
plete in front, and a large air sac is developed in the 
ericothyroid space. The Balenoidea possess olfactory 
nerves and a distinct, though small, olfactory apparatus. 
The sclerotic coat of the eyeball is enormously thick, and 
the optic nerve is surrounded by a rete-mirabile. The tym- 
panic membrane is connected with the malleus by ligament. 
The semicircular canals are very small, but the cochlea is 
large, and makes only 1; turns. The muscles of the 
antebrachium and manus are not altogether absent. 

The Right Whale (Balena), and the Fin-fishes (Mega- 
ptera, Balenoptera, &c.), belong to this division. 

b. In the Delphinoidea the nasal chambers open by only 
a single spiracle on the top of the head; and saccular 
dilatations, of various dimensions, are developed from the 
walls of the passage which connects this aperture with the 
bony naso-palatine passages, and lie between the integu- 
ment and the outer surface of the skull. 

More or fewer of the anterior ribs have heads and necks, 
the capitula articulating with the bodies of the vertebra, as 
in other Mammalia. The elongated sternum is, almost 
always, composed of several pieces arranged in a longi- 
tudinal series; and cartilaginous, or ossified, sternal ribs 
are present in greater or smallernumber. The nasal bones, 
which are very short, and have their upper surfaces tubercle- 
like, are more or less asymmetrically developed, as are also 
the maxille; so that the facial part of the skull appears 
distorted. The maxille are expanded behind, and cover 
the orbital process of the frontal bone wholly, or par- 
tially. The lachrymal bone is usually small and confluent 
with the slender jugal, but it may be large and distinct. 
The rami of the mandible are not arcuated outwards, and 
they become united in a longer, or shorter, symphysis. 
The mandible, as a whole, is not sensibly broader than the 
corresponding portion of the maxillo-premaxillary part of 
the skull. 

Teeth always exist after birth, and are never replaced by 
baleen plates. They are usually numerous, but sometimes 


400 THE ANATOMY OF VERTEBRATED ANIMALS. 


few and deciduous. Occasionally, only one or two teeth 
persist, and these, as in the Narwhal, may take the form of 
immensely elongated tusks. 

To this division belong the Physeteride, Platanistide and 
Delphinide. 

The ‘Physeteride possess functional teeth only in the 
lower jaw. The asymmetry of the skull is strongly pro- 
nounced ; and, in the adult, the maxillary and frontal bones 
are produced, so as to form a sort of basm upon the upper 
and anterior surface of the skull. The pterygoids meet 
in the middle line below, and the mandibular symphysis 
is sometimes extremely long. 

The greater number of the cervical vertebra are anky- 
losed. The hinder ribs lose their tubercular, but retain 
their capitular articulation with the vertebre. The costal 
cartilages are not ossified. The pectoral limbs are small, 
and a dorsal fin is usually present. 

The proper Sperm Whales (Physeterine) have an enor- 
mous head, with a quadrate, truncated snout, at the anterior 
superior angle of which the spiracle is placed. The teeth 
become fully developed only in the lower jaw. The cranial 
basin is immense, and is filled by a loose connective tissue, 
in which the peculiar fat known as spermaceti is contained. 
Ambergris is a sort of bezoar, found in the alimentary 
canal of the Cachalot, and seemingly derived from the fatty 
matter contained in the Cephalopoda on which the Cetacean 
feeds. In the other group of the Physeteride—the Ziphiine 
or Rhynchoceti—to which the Bottlenosed Whale (Hyperoo- 
don) belongs, there are only one or two pairs of fully formed 
teeth in the mandible. Some recent and many fossil 
(middle and later tertiary) genera of these Cetaceans are 
remarkable for the elongated rostrum formed by the solid 
ossification and ankylosis of the ethmoid, premaxille and 
maxille. 

The Platanistide are fluviatile or estuarine Cetacea, which 
occur in the Ganges and in the rivers of South America. 
The cervical vertebre are not ankylosed, and the costal car- 
tilages are not ossified. The tubercula and capitula of the 


THE DELPHINOIDEA, 401 


Fig. 106. 


Fig. 106.—Upper (A), under (B), and lateral (C) views of the skull 
of a foetal Cachalot (Physeter). The nasal bones are not represented 
in the upper view, and the hinder end of the jugal is displaced 
from its natural connection with the squamosal in (C). 


2D 


402 THE ANATOMY OF VERTEBRATED ANIMALS. 


ribs blend together posteriorly. The symphysis of the 
mandibles is extremely long and the jaws are narrow. Nu- 
merous teeth with compressed fangs are found in both jaws. 
The eyes are small, and in Platanista they are rudimentary. 

In the Delphinide lastly (Dolphins, Porpoises, Gram- 
puses), the teeth are usually numerous in both jaws, though 
the Narwhal is an exception to this rule, as has already 
been mentioned. 

The anterior cervical vertebre are generally ankylosed 
together. The posterior ribs lose their capitula and become 
articulated only with the transverse processes of the ver- 
tebre. The costal cartilages are well ossified. The sym- 
physis of the mandible does not exceed one-third of the 
rami in length, and the frontal and maxillary bones are 
not especially produced upwards at their edges. 

As the common Porpoise (Phocena communis), which 
is a member of this group, is the Cetacean which is most 
likely to come within reach of the student, it may be useful 
to speak at some length of its more interesting anatomical 
peculiarities. 

The adult animal is usually about five feet long, and is 
covered with a smooth integument upon which no hair 
is to be discovered, though a few hairs are visible about 
the mouth in the young animal. The contour of the 
anterior part of the head is very convex, and presents, in 
the middle line, the spiracle or blow-hole, which has the 
form of a crescent with the points turned downwards and 
forwards. The eyes are small and placed low down, close 
to the posterior end of the gape of the mouth, which is 
bounded by dense and rigid lips. The aperture of the ear 
lies about an inch and three-quarters behind the eye, and 
is so minute as to be discovered with difficulty. The 
genital aperture is placed a long way in front of the anus 
in the male; while, in the female, the interval, in which the 
fossee which lodge the teats are situated, is much less. 
There is a conspicuous vertical dorsal fin in addition to the 
flattened caudal fin. Immediately beneath the skin is a 
thick layer of blubber, as in other Cetacea, 


THE SKELETON OF THE PORPOISE. 403 


In the spongy texture of all the bones, the absence of 
medullary cavities in those of the limbs, and in the long 
persistent separability of the epiphyses of the centra of the 
vertebre, the Porpoise resembles other Cetacea; as it does 
in the shortness of the cervical, and the length of the 
lumbar, region of the spinal column. 

The seven cervical vertebre are all ankylosed together, 
and the atlas, which is very large in proportion to the rest, 
overlaps them above and at the sides. The centra of the 
hinder cervicals are so short and broad that they are mere 
plates of bone. There are twenty-eight dorso-lumbar verte- 
bree, of which fifteen are dorsal. In all but the most anterior 
of these vertebre, the zygapophyses are abortive ; and long 
accessory processes, developed from the front part of the 
neural arches, loosely embrace the spine of the vertebra in 
front. This arrangement, together with the thickness of 
the intervertebral ligaments, gives great flexibility to the 
spinal column. ‘The transverse processes of the hinder 
dorsal, and of the lumbar, vertebrz are very long. There 
are five pairs of true ribs. The sternebre ankylose into 
an elongated sternum. The anterior caudal vertebre are 
provided with large chevron bones, and their transverse 
processes exhibit notches through which branches of the 
aorta pass. 

In consequence of the globular form of the brain-case, 
and the prolongation of the jaws, the skull has a flask-like 
shape. There is a slight want of symmetry about the 
base of the upper jaw, but it is hardly appreciable. 

In a longitudinal section, the flatness and the upwardly 
eoncave contour of the base of the skull; the extreme 
shallowness of the sella turcica; the presence of an ossified 
tentorium; and the broad imperforate anterior wall, in the 
place of the cribriform plate of the ethmoid, are striking 
features. The synchondrosis between the basi- and pre- 
sphenoid is persistent. On the base of the skull the basi- 
occipital gives off great processes outwards and downwards, 
to form, together with a paramastoid prolongation of the 
exoccipital, and the squamosal, a chamber in which the 


4.04. THE ANATOMY OF VERTEBRATED ANIMALS. 


ankylosed tympanic and periotic bones are contained. 
The ex- and supra-occipitals, together with the inter- 
parietals, form the whole back wall and middle of the roof 
of the cranium, separating the parietals completely, and 
the frontals largely, and reaching the nasal bones. 

The basi-sphenoid is ankylosed with the small and almost 
horizontal alisphenoids, and there are no sphenoidal ptery- 
goid processes. The parietals are small, and occupy only 
the under and lateral portions of the brain-case. The 
frontal bones are very broad and expanded, and are com- 
pletely ankylosed together, where they form the front wall 
of the brain-case. Posteriorly and above, they diverge to 
receive the interparietal. The supra-orbital processes are 
extremely large, and are directed forwards and outwards, 
not backwards and outwards, as in the Whalebone Whales. 
The greater part of the superior surface of the frontals 
and of their orbital processes is rough and covered over by 
the expanded maxillary bones, which allow only a narrow, 
transverse, smooth, band-like surface, formed by the frontals, 
to be seen on the upper and anterior region of the skull. 
The rough surface is marked by two shallow grooves 
which pass from below upwards, and are convex towards 
one another and to the middle line. Corresponding grooves 
exist on the under side of the expanded proximal ends of 
the maxillaries; and when these are in their natural positions, 
the coadapted grooves form two canals, which are blind in 
front and above. These, in the natural state, are full of 
air and communicate with the air chambers at the base of 
the skull and with the Eustachian tubes. 

The narrow premaxille are ankylosed with the inner 
margins of the maxille, and contribute only a very small 
portion of the alveolar margin of the upper jaw. The 
alveoli are not completely separated from one another. 
The pterygoid bones do not unite in the palate. They have 
a peculiar excavated form, and are notched for the passage 
of the ends of the Eustachian tubes into the nasal passages. 
These are nearly vertical and are separated by the large 
and strong vomer. Their superior apertures are left quite 


THE SKELETON OF THE PORPOISE. 405 


uncovered in consequence of the small size, tubercular form, 
and backward position of the nasal bones. The squamosal 
is relatively small, but has the characteristically cetacean, 
large, zygomatic process; this extends forwards nearly to 
the posterior end of the supra-orbital process, and gives 
attachment to the slender jugal. 

The periotic bones form a dense osseous mass, which is 
ankylosed with the no less heavy and thick, scroll-shaped, 
tympanic. The pars mastoidea of the periotic mass fits 
pretty accurately into a recess of the chamber which has 
already been described; and is thus held in position in the 
dry skull, though it is very easily detached. 

When the tympano-periotic bone and all the facial bones 
are removed, only two pair of foramina are visible in the 
base of the skull. The anterior pair give exit to the second, 
third, fourth, the anterior division of the fifth and the sixth 
nerves, and these answer to the optic and sphenorbital fora- 
mina. The posterior pair take the place of the oval, 
posterior lacerated, and jugular foramina, and the pre- 
condyloid foramina open into them posteriorly. The rami 
of the mandibles are only united by a short symphysis. 
The body of the hyoid is broad and hexagonal, and has two 
slender, anterior, and two broad and flat, posterior, cornua. 

Tn the natural position the fore limbs stand out from the 
body with their flat surfaces looking upwards and down- 
wards; the upper surface being directed a little backwards, 
and the lower, a little forwards. The tuberosity of the short 
humerus is directed forwards. The carpus contains six or - 
seven ossifications. The number of phalanges in the digits 
is two, eight, six, three, two, counting the pollex as the first. 

The pelvic bones are elongated, slightly curved, osseous 
styles. They lie with their long axes parallel to the vertebral 
column, their convex sides upwards, and their smaller ends 
forwards, within an inch of the centra of the vertebre, 
their hinder ends being close to the third chevron bone 
of the tail. The front ends are about an inch apart. 
Behind its centre, each bone presents a flattened thickening 
for the attachment of the corpus cavernosum of its side. 


406 THE ANATOMY OF VERTEBRATED ANIMALS. 


The cutaneous muscle is very largely developed and lies 
between two layers of blubber, the thick superficial one 
separating it from the skin, and the thin deep layer from 
the subjacent muscles. It may be said to be disposed in two 
broad layers, a dorsal and a ventral, on each side; these 
extend from the occipital crest, and from the rami of the 
mandibles, to the tail. Both these divisions send off strong 
bundles to the humerus, which act as powerful adductors, 
abductors, protractors, and retractors of the fin. There is 
no trapezius, and the representative of the latissimus dorsi 
is very small. A strong occipito-hwmeralis, from the para- 
mastoid to the tuberosity of the humerus, seems to repre- 
sent the cleido-mastoid and clavicular deltoid. A costo- 
humeralis extends from the sternum to the inner tuberosity 
of the humerus. A small coraco-brachialis extends from 
the apex of the coracoid to the inner tuberosity of the 
humerus. The pectoralis major seems to be represented by 
a muscle which arises from the sternum, close to the attach- 
ment of the third and fourth ribs, and is inserted into the 
ulna. The triceps extensor is represented by tendinous fibres 
in which muscle cannot always be detected, which extend 
from the posterior face of the humerus to the ulna. The 
other muscles of the fore-arm and all those of the manus 
are absent. The dorsal muscles form a thick continuous 
mass from the end of the tail to the occiput; and, on the 
ventral side of the spinal column, the subcaudal muscles 
are similarly continued forwards, as far as the middle of the 
thorax. An ischio-caudalis passes, on each side, from the 
anterior chevron bones to the ischium. Between their 
attachments is an aponeurosis which supports the anus; 
ischio-cavernous muscles pass from the ischia to the corpora 
cavernosa. 

The diaphragm has no tendinous centre. Its pillars are 
very thin, and, extending between the kidneys and the spine, 
become tendinous, and are attached to the ventral faces of 
the vertebre, as far as the ninth lumbar. A strong fibrous 
aponeurosis is continued back over the subvertebral muscles 
to the pelvic bones. Between these bones and the ends of 


THE STOMACH OF THE PORPOISE. 407 


the transverse processes of the twenty-eighth and twenty- 
ninth vertebre (counting from the first dorsal) the apon- 
eurosis is so stout as to form an almost distinct fibrous 
band, which occupies the place of an ilium. The ureter lies 
between the ischio-vertebral fascia and the peritoneum. 

The teeth are small and numerous, and their crowns are 
obtuse and constricted. The passage of the pharynx is 
divided in the middle, the soft palate being prolonged into 
a muscular funnel, the opening of which closely fits the 
constricted neck of the long cone into which the epiglottis 
and the arytenoid cartilages are produced. Thus the 
arrangement which is transitory in the Marsupial is per- 
manent in the Cetacean. 

The stomach is divided into three sacs. The first is large, 
conical, and lined by a coarse white epithelial coat. The 
gullet opens directly into it. The second stomach com- 
municates with the first by an aperture which is close to 
the cardiac end of the gullet, and is surrounded by a very 
prominent rugose lip. A curved passage about one inch 
long and capable of admitting the finger, lined by a white 
epithelium similar to that of the first, leads into the second 
stomach. The second stomach is lined by an extremely 


vascular and soft mucous membrane, with about ten strong 


longitudinal folds, separated by deep sulci, interrupted by 
transverse ridges. A narrow and curved canal leads from 
this into the third stomach, which has a tubular form and 
is bent upon itself. Its lining membrane is quite smooth. 
A small, circular, pyloric aperture places this in com- 
munication with the dilated commencement of the duo- 
denum, which has sometimes been regarded as a fourth 
stomach. Its lining membrane presents longitudinal ruge 
continuous with those of the duodenum itself. The con- 
joined pancreatic and biliary ducts open just beyond the 
dilated part of the duodenum. There is no cecum, or 
demarcation between the large and small intestines. The 
bilobed liver has no gall bladder. 

In the heart the fossa ovalis is distinct, but there is 
neither Eustachian nor Thebesian valve. The vena cava 


408 THE ANATOMY OF VERTEBRATED ANIMALS. 


inferior is long and wide, but is not especially dilated near 
the heart. Muscular fibres are not continued on to it from 
the diaphragm. The aorta and pulmonary arteries are not 
dilated at their origins. The arteries have a great tendency 
to break up into plexuses. Thus the internal carotids 
form great networks which communicate with vertebral 
plexuses, extending throughout the entire spinal canal. 
The brachial artery divides into two branches, and these 
subdivide into innumerable parallel twigs. The intercostal 
arteries are the chief source of the large thoracic plexuses, 
which lie at the sides of the vertebral column in the 
dorsal half of the thorax. Finally, an arterial rete mirabile 
surrounds the caudal aorta. The veins form plexuses cor- 
responding to, and mixed up with, those of the arteries; 
and a very large venous plexus lies on the subvertebral 
muscles in the abdomen and thorax. 

The respiratory apparatus of the Porpoise presents many 
remarkable peculiarities. The contour of the front part 
of the head, as bounded by the integument, is very convex— 
the corresponding facial region of the skull, on the con- 
trary, is very concave. The interval between the two is 
occupied, in part, by fibrous and fatty tissue; and, in part, by 
a singularly sacculated spiracular chamber, which connects 
the single spiracle with the double external nares of the skull. 
Two valves, an anterior and a posterior, lie immediately 
above these external nares and close the communication 
between them and the chamber, except at such times as it — 
is forced open from below. Each nasal passage remains 
distinct from the other as far as the valves, the middle of 
each of the latter being fastened to the septum, so that there 
may be said to be a pair of valves for each opening between 
the passages and the spiracular chamber. Hach nasal pass- 
age, after it ceases to be surrounded by bone, sends off two 
diverticula, one forwards and one backwards. The anterior, 
which les between the anterior valve and the premaxilla, 
is a simple sac, lined with a thin, black, smooth membrane. 
The posterior diverticulum lies between the posterior valve 
and the ethmoid and nasal bones. It is incompletely 


OE 


THE MECHANISM OF SPOUTING. 409 


divided by a sort of shelf, is prolonged forwards, round, 
and in front of, the anterior valve, and ends blindly in the 
middle line above the anterior sac. The spiracular chamber 
itself is produced, on each side, into a large lateral sac, the 
walls of which are raised in strong parallel ridges, and 
covered with a black papillose integument. The walls of 
these sacs are strong and elastic. Layers of muscular 
fibres pass from the occipital ridge to the posterior lip of 
the spiracle, and from the edges of the maxille to its an- 


~ terior lip. Their action is necessarily to open the spiracle 


and compress the sacs. There is no sphincter, the form of 
the spiracle causing it to be naturally shut by the fitting to- 
gether of its walls, and the pressure of the water upon them. 

When a Porpoise comes to the surface to “blow,” the 
shape of the posterior, concave, lip of the crescentic spiracle 
does not sensibly alter; but the anterior, convex, lip is 
pwled downwards and forwards, its surface becoming some- 


what depressed, and its free edge nearly straight—so that 


the aperture, when fully dilated, assumes the form of a 
half-moon. At the same time, the air is expelled with a 
rushing sound. The inspiratory act must be very rapid, as 
the spiracle remains open for only a very short time after 
expiration ends. When the larger Cetacea come up to 
breathe, the expired vapour suddenly condenses into a 
cloud; and, if expiration commences before the spiracle is 
actually at the surface, a certain quantity of spray may be 
driven up along with the violent current of the expelled 
air. This gives rise to the appearance termed the “ spout- 
ing” of Whales, which does not arise, as it is commonly 
said to do, from the straining off of the sea-water swal- 
lowed with the food, and its expulsion by the nostrils. 

The epiglottis, in front, and the arytenoid cartilages be- 
hind, are prolonged into a tapering tube, dilated at its sum- 
mit into a knob. The muscular soft palate embraces the 
neck of this knob so closely that it cannot be withdrawn 
without considerable effort. And thus, during life, the nasal 
air-passages and the glottis are kept perfectly continuous; 
while the Porpoise dashes through the water, open mouthed, 


410 THE ANATOMY OF VERTEBRATED ANIMALS. 


after its prey. The point at which the extra bronchus tothe 
right lung is given off is separated by four rings from the 
bifurcation of the trachea. The lungs are not lobed and 
their tissue is very dense and elastic. 

The cerebral hemispheres are, taken together, broader 
than they are long. In the upper view they leave not more 
than a seventh of the length of the cerebellum exposed, while 
they overlap it largely at the sides. The outer surface of 
the hemispheres is extremely convoluted, the gyri being 
numerous and separated by deep sulci. There is a well- 
marked Sylvian fissure, with a central lobe, or insula, A 
rudiment of a posterior cornu has been observed in the 
lateral ventricle. The corpus callosum is small, relatively 
to the size of the hemispheres, and the anterior commissure 
is almost obsolete. The medulla oblongata has corpora 
trapezoidea. The olfactory nerves are wanting—a circum- 
stance which agrees with the entire absence of ethmoidal 
turbinals. The eye has a thick sclerotic, and there is a 
choanoid muscle; no nictitating membrane is present. 

The external auditory aperture is so small as to be easily 
overlooked. The meatus auditorius is a narrow undulating 
tube about two inches long. The tympanic membrane is con- 
cave externally ; and, as is usual in the Cetacea, is connected 
by a ligament with the handle of the malleus. There is 
only a small aperture in the stapes. The tensor tympani 
arises, as in Carnivores, from a fossa in the periotic ossifi- 
cation. 

The Eustachian tube passes through the notch in the 
pterygoid and opens into the nasal passage on the inner 
side of that notch. Close to its commencement it com- 
municates, by an oval aperture, with a remarkable air 
chamber, which extends backwards between the periotic mass 
and the basis cranit, and forwards to the under side of the 
expanded part of the maxilla, where it opens into the canal 
between the maxilla and the frontal already described. 
These chambers, like the bronchi, are generally full of 
nematoid worms. The testes and penis of the male are 
enormous in proportion to the size of the body. The penis 


THE DECIDUATE MAMMALIA. 411 


is devoid of a bone, and, ordinarily, is bent up in the long 
preputial sheath. 

ce. The Phocodontia are represented only by Zeuglodon, 
Squalodon, and other large extinct cetaceans of the tertiary 
epoch. These remarkable fossil forms constitute con- 
necting links between the Cetacea and the aquatic Carni- 
vora. The cervical vertebre are distinct and unanky- 
losed, nearly resembling those of the Rhyncoceti. The 
caudal vertebre have their transverse processes perforated 
vertically, as in many Cetacea. The distal ends of the 
ribs are enlarged somewhat as in the Sirenia. The skull 
is symmetrical, and the nasal bones, though still short, are 
longer than those of any other cetacean. The zygomatic 
processes of the sqyuamosal are large and thick, and the 
supraorbital processes of the frontals wide and expanded 
as in the Cetacea. 

The scapula appears to have had a spine and acromion 
like that of Manatus. The humerus is compressed from 
side, and has true articular surfaces upon its distal end, 
although they are of small size. 

The molar teeth have laterally compressed crowns with 
serrated edges and two fangs, resembling those of many 
seals, and Zeuglodon differs from all the other Cetacea in 
the circumstance that some of its teeth have vertical suc- 
cessors. 

The DrecipuaTE Mammaria.—These may be subdivided 
according to the form of the placenta, into two groups: 
the Zonaria and the Discoidea. In the former the placenta 
surrounds the chorion like a hoop, leaving its ends free of 
villi, or nearly so. 

In the Discoidea, on the other hand, the placenta takes the 
form of a thick disc, which is sometimes more or less lobed. 

The mammalia which possess a zonary placentation are 
the Carnivora, the Proboscidea, and the Hyracoidea. 

Each of these divisions is very closely related to one of 
the foregoing. Thus the Carnivora approach the Cetacea ; 
the Proboscidea, the Strenia; and the Hyracoidea, the 
Ungulata. 


412 THE ANATOMY OF VERTEBRATED ANIMALS. 


The Zonarta. 1. The Carnivora.—In this order the 
head, relatively to the body, is of moderate or small size; 
and hair is abundant. 

The cervical vertebrz are free and unankylosed, and their 
centra are elongated. The odontoid process of the second 
is well developed. The dorso-lumbar vertebra are almost 
always twenty in number, rarely twenty-one or nineteen. 
The number of dorsal and lumbar vertebre, respectively, 
varies between sixteen dorsal and four lumbar, and thir- 
teen dorsal and seven lumbar. The dorso-lumbar vertebree 
are always articulated together by their zygapophyses, and 
there is a complete sacrum. 

The sternebre are numerous and laterally compressed. 

In the skull the nasal bones are well developed, and have 
the ordinary form. When supraorbital enlargements of the 
frontal exist, they are of moderate size. The parietals unite 
in a long sagittal suture. The orbit and the temporal 
fossa communicate freely, the posterior boundary of the 
orbit never being completed by bone. The jugal bone is 
large and unites by a broad surface with the maxilla. There 
is a distinct coronoid process, and the long axis of the 
articular surface which receives the head of the mandible 
is transverse. 

The hyoid has a small body and many-jointed anterior 
cornua. 

Both pairs of limbs are fully developed, and the tail is not 
provided with a horizontal fin. Clavicles may be absent, 
and, when ossified, they do not occupy more than half the 
interval between the acromion and the sternum. The 
scapula has a distinct spine, and a large supra-spinous fossa. 

Neither the hallux nor the pollex are opposable. The 
carpal and tarsal bones have the ordinary number and 
arrangement; except that, in the carpus, the scaphoid and 
lunare are united into one bone. The terminal phalanges 
of the digits, which never fall below four in number, are 
almost always provided with sharp and pointed claws. 

The teeth are always distinguishable into incisors, canines 
and molars; they are lodged in distinct sockets, and their 


THE CARNIVORA. ' A413 


crowns are covered with enamel. There are always two 
sets of teeth, a milk and a permanent dentition. As 
a very general rule, there are six incisors above and an 
equal number below. The canines are long, curved, and 
pointed. 

The stomach is simple and undivided, and the cecum, 
which is never large, may be altogether absent. 

The liver is deeply subdivided and there is a gall bladder. 

In the brain, the cerebellum is never completely covered by 
the cerebral hemispheres, which are connected by a large 
corpus callosum, and, except in the aquatic forms, by a 
well-developed anterior commissure. On the exterior of 
each hemisphere, there are usually three distinct convolu- 
tions surrounding the sylvian fissure. But, in the aquatic 
Carnivora, the gyri are much more numerous and com- 
plicated; the cerebral hemispheres are much broader and 
longer in proportion to the length of the brain; and they 
may even exhibit a rudiment of the posterior cornu. In all 
these respects they approach the Cetacea. 

The inferior turbinal bones are always large and have 
a complicated form. 

There are no vesicule seminales, and an os penis is very 
generally present. The ovary is inclosed in a peritoneal sac. 

The Carnivora are divisible into the Pinnipedia, or aquatic 
Carnivores ; and the Fissipedia, which are mainly terrestrial 
and cursorial. 

a. In the Fissipedia the incisors are, with one exception 


(Enhydris, the Sea-otter, with 7. =). six In number in each 
jaw. 

The hind limbs have the position usual in mammals, and 
the tail is free to its root. The pinna of the ear is fully 
developed. The middle, or outermost, digits of the pes are 
longest, the hallux being shorter than the others. 

Almost invariably, the distal phalanges of both limbs are 
provided with claws; and, in the most thoroughly carnivorous 
forms, these claws are very strong, curved and pointed. The 
phalanx which supports the claw has a similar form, and a 


414. THE ANATOMY OF VERTEBRATED ANIMALS. 


plate of bone rises from its base as a short sheath, An 
elastic ligament connects the base of the ungual phalanx 


"LOL ‘Sty 


' 
ra 


"(097 say) UOLT 8} JO UOJO[aYS—" LOL “SLT 


THE ANATOMY OF THE DOG. 415 


with the middle phalanx, so that when the flexor pro- 
fundus digitorum is not in action, the ungual phalanx is 
pulled back upon the middle phalanx, and the claw which it 
bears is retracted into an integumentary sheath. 

The olfactory lobes are usually large and the cerebral 
hemispheres elongated. 


As the Dog (Canis familiaris) is an excellent and easily 
accessible example of a fissipede carnivore, it may be 
useful to mention some of the more important points in its 
anatomy. 

The vertebral column contains twenty dorso-lumbar ver- 
tebre, of which thirteen are dorsal and seven lumbar, three 
sacral, and eighteen to twenty-two caudal vertebre. The 
atlas has broad and rounded ale, the anterior margins 
of which are deeply excavated near the roots. The pos- 
terior edge of the spinous process of the axis vertebra is 
almost perpendicular and very thick. 

Nine pairs of ribs are usually connected by sterno-costal 
cartilages with the sternum, which is composed of eight 
laterally-compressed sternebre. Only two of the three 
ankylosed sacral vertebre articulate with the ilia. 

As in the Carnivora in general, the occipital foramen is 
placed at the posterior end of the skull, and looks almost 
directly backwards. The sagittal and lambdoidal crests 
are greatly developed and meet in a prominent occipital 
spine; the zygomata are very wide and arched outwards; 
and the coronoid process of the mandible is very large. 
The size of these parts is in relation to the magnitude of 
the muscles of the neck and jaws. 

The ramus of the mandible is nearly straight, the proper 
angle of the jaw being obsolete. A swpra-angular process 
projects outwards from the ascending portion of the ramus, 
and takes the place of the proper angle. The articular 
condyle is much elongated transversely, narrow and convex 
from before backwards; and the pre- and post-glenoidal pro- 
' cesses of the squamosal are produced downwards so as to 
convert the joint into a complete ginglymus and to restrict 


416 THE ANATOMY OF VERTEBRATED ANIMALS. 


the motion of the jaw to the vertical plane. The supra- 
orbital processes of the frontals are small and pointed. The 
root of the alisphenoid is traversed by a longitudinal canal. 
The tympanum is bounded below by a convex osseous 
wall, which is termed the bulla. It opens externally by the 
short external meatus, at the inner end of which is a cir- 
cular elevation for the attachment of the tympanic mem- 
brane. A short distance internal to this frame for the 
membrane of the drum, a low crest rises from the floor 
of the bulla and imperfectly divides it into an outer and 
anterior portion which communicates with the Eustachian 
tube, and an inner blind spheroidal cavity which occupies 
the greater part of the bulla. The part of the bulla which 
forms the floor of this cavity is the result of the ossification 
of a process of the periotic cartilage, while the other part 
is furnished by the tympanic bone. The low crest is 
produced by the conjunction of both. Posteriorly and 
internally, the periotic region of the bulla presents a canal, 
through which the internal carotid artery passes. The 
posterior opening of the carotid canal looks into the fora- 
men lacerum posticum, and is not visible without dissection. 
There is a large paroccipital process, with a prominent free 
extremity; but, for the greater part of its length, it is closely 
applied to the back of the bulla. The condyloid foramen 
is quite distinct from the foramen lacerwm posterius. A 
large foramen behind the glenoidal cavity transmits a vein 
from the interior of the skull. In the nasal cavity, the 
ethmoidal turbinals are very large; the superior turbinals 
are prolonged into the great frontal sinus, and the inferior 
turbinals unite, in the middle line, with the septum. 

The clavicles of the Dog are always rudimentary and 
are generally represented only by a gristly intersection of 
the muscles which represent the sterno-mastoid and deltoid, 

The olecranar fossa of the humerus is perforated. The 
hallux is much shorter than the other digits. When 
the Dog stands, the metacarpal bones of these digits are 
nearly vertical; the basal phalanges are horizontal; the 
middle and the distal phalanges are inclined in the form of 


THE MYOLOGY OF THE DOG. 417 


a V with the apex (the articulation between the two) 
downwards. The claws are, consequently, raised from the 
ground, the foot resting partly on a thick integumentary 
pad, which les beneath the basal phalanges; and, partly, on 
the under surfaces of the joints between the middle and 


_ the distal phalanges. The distal phalanges are kept bent 


=. 


upon the middle ones by elastic ligaments, which pass from 
one to the other, and which antagonise the action of the 
long flexors. The Dog, therefore, possesses the mechanism 
for the retraction of the claws, but its action is not suffi- 
cient to protect them from wear. Fuabelle, or sesamoid 
bones developed in the tendons of the gastrocnemius, lie 
behind the condyles of the femur. The fibula is thin and 
closely applied to, but not ankylosed with, the tibia. The 
hallux is usually rudimentary; only the metatarsal, and 
the basal phalanx, being represented by two small ossicles. 
In some breeds of dogs, however, the hallux is fully deve- 
loped. ; 

In the myology of the Dog the insertion of the tendon 
of the external oblique muscle of the abdomen presents 
some interesting peculiarities. The outer and posterior 
fibres of this muscle end in a fascia which is partly con- 
tinued over the thigh as fascia lata, and partly forms an 
arch (Poupart’s ligament) over the femoral vessels; by its 
inner end it is inserted into the outer side of a triangular 
fibro-cartilage, the broad base of which is attached to the 
anterior margin of the pubis, between its spine and the 
symphysis, while its apex lies in the abdominal parietes. 
The internal tendon of the external oblique unites with the 
tendon of the internal oblique to form the inner pillar of 
the abdominal ring, and is inserted into the inner side of 
the triangular fibro-cartilage. The pectineus is attached to 
the ventral face of the cartilage; the outer part of the 
tendon of the rectus into its dorsal face; but the chief 
part of that tendon is inserted into the pubis behind it. 


_ This fibro-cartilage appears to represent the marsupial bone, 


or cartilage, of the Monotremes and Marsupials. 
The trapezius and the sternomastoid coalesce into a single 
25 


418 THE ANATOMY OF VERTEBRATED ANIMALS. 


muscle; and, in the absence of a complete clavicle, the outer 
fibres of the latter and those of the anterior part of the 
deltoid are continuous. In this way a muscle which has 
been called levator humeri proprius is formed. The omo- 
hyoid and the subclavius are absent. There is a trachelo- 
acromialis and a dorso-epitrochlearis. The supinator longus 
is absent, but there is a pronator quadratus. The extensor 
communis digitorum mantis divides into four tendons, in 
which sesamoid bones are developed over the articulations 
between the first and second phalanges. The extensor 
primi internodii pollicis is absent. The extensor secundi 
internodii is one muscle with the ewtensor indicis. The 
extensor minimi digiti sends tendons to the third, fourth, 
and fifth digits. All these deep extensors have sesamoid 
bones over the metacarpo-phalangeal articulations. The pal- 
maris longus appears to be absent; but all the other flexors 
of the manus, even the palmaris brevis, are represented. 
The tendons of the flewor pollicis longus and flexor digi- 
torum perforans are united. The divisions which the 
common tendon sends to the five digits develope sesamvid 
bones, just before their insertions into the bases of the distal 
‘phalanges. The fifth digit has its abductor, flexor brevis, and 
opponens; the pollex, an abductor, adductor, flexor brevis, and, 
perhaps, an opponens. The second, third, and fourth digits 
have each a pair of flewores breves, which represent the 
interossei, and are inserted into the bases of the proximal 
phalanges, a relatively large sesamoid being developed in 
each. Hach sends off a fine tendon dorsad to the extensor 
sheath. The plantaris is large, and, as in the Pig, its 
tendon passes into the representative of the flexor brevis 
digitorum pedis. The tendons of the flewor hallucis longus 
and flexor perforans unite into a common tendon, which 
subdivides into slips for the digits. 
3:3 1—1 


The dental formula of the Dog is 1. 53 ¢. — p.m. =~ 


2°2 . . . . 
M.s5 =42. Thetwo upper inner incisors, on each side, have 


distinctly trilobed crowns—the lateral cusps of the crown 
arising from outgrowths of the cingulwn at its base. The 


THE DENTITION OF THE DOG. 419 


outer incisor is larger than the others, and its middle 
cusp is very large, while the outer is rudimentary. The 
large canine has a strong, curved, pointed crown, with a 
longitudinal ridge along its posterior face. The crowns of 
the anterior three premolars are triangular, with a smooth- 
cutting anterior edge; the hinder edge is also sharp, but is 
divided by a notch into two lobes, of which the hinder 
is the smaller. These teeth are two-fanged. The fourth 
premolar is a large tooth. In form, its crown has a general 
similarity to that of the foregoing; but, firstly, the pos- 
terior lobe is relatively much larger, and pointed, so as 
to form an obvious second cusp; and, secondly, a strong 
process of the crown projects inwards from its anterior 
end, and is supported by a distinct fang—so that this pre- 
molar is three-fanged. It is termed a carnassial, or sec- 
torial, tooth, as it bites like a scissor-blade against a cor- 
responding tooth in the mandible. The preceding teeth 
have cutting crowns; but those of the molars are broad and 
erushing. They exhibit an outer division, formed by two 
large subequal cusps, and an inner division, also presenting 
two cusps, the posterior of which is much smaller than 
the anterior. In addition, the cingulum sends up a strong 
process on the inner side of the crown. 

In the lower jaw, the crowns of the incisors, the outer of 
which is the largest, are all trilobed. The outer cusp is 
stronger than the inner in all, and particularly in the outer, 
incisors. The canines resemble those of the upper jaw. 
Each premolar has two fangs and a sharp triangular crown, 
the posterior edge of which is trilobed, as in the upper 
premolars; but the posterior lobe is small in the fourth, 
which differs but little from the rest. The first molar, on 


_ the other hand, is a large tooth, with a blade-like crown, 


et DL aS 


_ which bites against the inner side of the upper fourth pre- 
molar, and is called the carnassial or sectorial tooth of the 


lower jaw. The crown is elongated, and presents a large 
anterior external cusp, divided into two lobes by a deep 


notch. On the inner side of this is a small internal 
_¢usp. The two posterior cusps are very much lower than 


420 THE ANATOMY OF VERTEBRATED ANIMALS. 


the anterior ones, and form a sort of heel to the blade-like 
anterior portion of the crown. An oblique ridge connects 
the outer and larger of the two posterior cusps with the 
small inner and anterior cusp. The second molar has a 
broad quadricuspidate crown, the inner posterior cusp being 
almost obsolete. The crown of the last-molar is small, 
simple, and obtusely conical. 

It thus appears that the sectorial, or carnassial, teeth in the 
two jaws differ in their nature, the upper being the last pre- 
molar, and the lower the anterior molar. The milk dentition 


of the Dog is d.t. 3 d.c. = d.m. — the “first premolar” 


of the adult dentition having no deciduous predecessor; so 
that, in this, as in so many other cases, it is doubtful whether 
it ought to be counted in the milk, or in the adult, denti- 
tion. The middle deciduous molar in both jaws resembles 
the hindermost premolar of the adult dentition, and the 
hindermost, the first molar of the adult. The so-called “first 
premolar” of the adult, and the anterior molars, appear 
before any of the deciduous molars are shed. 

The cecum of the Dog is long, and folded upon itself, in 
which respects it is unlike that of other Carnivores. The 
arch of the aorta gives off an anonyma and a left sub- 
clavian. 

In the brain, the olivary bodies are inconspicuous, the 
corpora trapezoidea large, and the corpora mammillaria 
distinctly double. The olfactory lobes are very large, and 
expand posteriorly on the sides of the brain into a broad 
mass continuous with the gyrus wncinatus, or hippocampal 
lobule. The cerebral hemispheres extend for a considerable 
distance over the cerebellum, in the upper view, and overlap 
it laterally. The Sylvian fissure does not extend more 
than half-way to the median fissure. The surface which 
answers to the insula is quite smooth. The,anterior ends 
of the calloso-marginal sulci pass on the upper surfaces 
of the hemispheres, and give rise to the “ crucial ” sulcus. 
There are three principal gyri upon the outer surfaces of 
the hemispheres; one which immediately bounds the Sylvian 


"wma = =~ 


CLASSIFICATION OF THE CARNIVORA. 421 


fissure, one which runs along the upper margin of the 
hemisphere, and one between these two. The corpus cal- 
losum is long, and the anterior commissure well developed. 

There is a musculus choanoides in addition to the usual 
ocular muscles, and the rudimentary nictitating membrane 
is said to possess a muscle. 

The tensor tympani arises from a deep pit above the pro- 
montory, and its tendon passes directly outwards to the 
malleus. 

The male is devoid of Cowper’s glands. The penis has a 
bone, and the glans becomes swollen during copulation, so 
as to prevent the withdrawal of the penis from the vagina 
of the female. The ovary of the female is enclosed in a sac 
of the peritoneum, and the uterus has long cornua. The 
umbilical sac is drawn out to a point at each end. 


The Dogs (including the Wolves, Jackals, and Foxes 
under this head) form the most central group of the 
Carnivora, which may be termed the Cynoidea.* From 
these the Bears, Weasels and Procyonide depart, on the one 
hand, and the Cats, Civets, and Hyznas on the other. The 
former group (Arctoidea) have the cavity of the bulla tym- 
pan undivided by a septum. The paroccipital process is 
not applied to the posterior wall of the bulla. The mastoid 
process is widely separated from the paroccipital. The 
condyloid foramen is not merged in a common opening 
with the foramen lacerwm posticum. The intestinal canal is 


devoid of a cecum. The large penis has a bone which is 


not grooved; there are no Cowper’s glands, and the pros- 
tate is small. 
In the latter group (Ailuroidea) the bulla tympani is large 


and rounded, and the septum, which is rudimentary in the 


Cynoidea, is so much enlarged as to leave only a narrow 
‘aperture of communication between the two chambers. The 


_ paroccipital is closely applied to the posterior wall of the 


bulla. The mastoid process is often obsolete. The con- 


* See Professor Flower’s important memoir on the Classification of 
the Carnivora in the Proceedings of the Zoological Society for 1869. 


429 THE ANATOMY OF VERTEBRATED ANIMALS. 


dyloid foramen opens into a fossa common to it and the 
foramen lacerum posticwm. All have a short cecum. The 
penis is small, and its bone small, irregular, or absent. 
They have Cowper’s glands and a well-developed prostate. 

The Cynoidea are all digitigrade, and resemble the Dog 
in their dentition. The Arctoidea are plantigrade, while 
the Ailuroidea are for the most part digitigrade, but may be 
plantigrade. In dentition, each of these groups presents 
forms such as the Bears on the one hand, and the Cats on 
the other, which may be regarded as extreme modifications, 
in opposite directions, of the type exhibited by the Dog. 

In the Bears, the dental formula is the same as in the 
Dogs, but the crowns of the teeth are all more obtuse. The 
sectorial teeth lose their marked characters, and the molars 
have flat and tuberculated crowns. The anterior pre- 
molars fall out as age advances. It is a remarkable cir- 
cumstance that the teeth of frugivorous and carnivorous 
Bears exhibit no such differences as would lead to a sus- 
picion of their complete difference of habit, if we were 
acquainted with these animals only in the condition of fossils. 


The Cats have the dental formula 7. _ €. is p.m. me 
m. = = 30. The canines are very long and sharp. The 


premolars are like the Dogs’, except that they are sharper, 
and that the hindermost (the sectorial tooth) has hardly 
any internal process.. The single upper molar is a small 
tooth with a flat transversely elongated crown, and it lies 
within, as well as behind, the great sectorial premolar. In 
the lower jaw, the sectorial, or first, molar is the last 
tooth in the series. The crown is a deeply bifurcated blade 
representing the antero-external cusp of the corresponding 
tooth in the Dog. The “heel” is obsolete. 

While the Bears are among the most completely planti- 
grade of the Carnivora, the Cats are most entirely digiti- 
grade, and the apparatus for the retraction of the ungual 
phalanges is so well developed that the claws are com- 
pletely retracted within sheaths of the integument, when 
the animal does not desire to use them. To this end the 


ee er LEE 


025 


THE PINNIPEDIA. 423 


elastic ligaments are very strong, and the median phalanx 
is excavated, in order to allow of the lodgment of the 
retracted phalanx on one side of it. 

b. The Pinnipedia, or Seals and Walruses, are those Car- 
nivora which come nearest the Cetacea. The tail is united, 
by a fold of skin which extends beyond its middle, with the 
integument covering the hind legs. These are, in most 
species. permanently stretched out in a line with the axis of 
the trunk. The pinna of the ear is small or absent. The toes 
are completely united by strong webs, and the straight nails 
are sometimes reduced in number, or even altogether abor- 
tive. The inner and the outer digits of the pes are very 
large. The incisors vary in number and lose their cutting 
form. The premolar and molar teeth are similar in cha- 
racter, and never have more than two fangs. There is no 
lachrymal bone or canal. 

The brain-case of the cranium is generally much more 
rounded than that of other Carnivora; and, in some genera, 
the supra-orbital processes of the frontals are very largely 
developed. In both of these characters, and in the great 
breadth and complication of the convolutions of their cere- 
bral hemispheres, as well as in their relatively small olfactory 
nerves and anterior commissure, the Pinnipedia approach 
the Cetacea. 

There are three groups of Pinnipedia: the Otaride, the 
Trichechide, and the Phocide. 

1. The Otaride, or Hared Seals, are so termed because 
the ear possesses a distinct though almost rudimentary 
pinna. These Seals have long necks, and can stand or 
walk upon all fours, the hind limbs being capable of sup- 
porting the body in the ordinary way. 

In many respects, these animals are closely allied with the 
Bears; and by no part of their organization is this more 
clearly shown than by the skull, which in its general 
form, its large supra-orbital processes, the small and rugged 
bulla tympani, the perforation of the alisphenoid by a 
canal, and the presence of a crest on the inner surface of 
the parietals, is extremely ursine. 


424 THE ANATOMY OF VERTEBRATED ANIMALS. 


2. The Trichechide, or Walruses, are devoid of external 
ears, but resemble the Otaride in their mode of standing 
and walking. The skull resembles that of the Bear in the 
same respects, but the muzzle is distorted by the enormous 
development of the superior canines. The Walruses re- 
semble the Bears in another point, namely, in the pre- 
sence of a supplementary bronchus; the right bronchus, 
before it reaches the lung, dividing into two trunks, a large 
anda small. The thyroid cartilage is deeply excavated, in 
front, by a triangular fissure; and the epiglottis is extremely 
small. 

In the brain, the remarkably large and richly convoluted 
hemispheres cover the cerebellum, and present a rudi- 
mentary posterior cornu. The anterior commissure is very 
small, as are the olfactory nerves. 

The dentition of the Walrus is extremely peculiar. In 
the adult, there is one simple conical tooth in the outer 
part of the premaxilla, followed by a huge tusk-like canine, 
and three, short, simple-fanged, teeth. Sometimes, two other 
teeth, which soon fall out, lie behind these, on each side of 
the upper jaw. In the mandible there are no incisors, but 
a single short canine is followed by three, similar, simple 
teeth, and by one other, which is caducous. 


‘ - Id 11 2 
The dental formula is therefore i. [= ¢. Ta P.M.m. 3.5 


+22 = 24, 

3. The Phocide, or ordinary Seals.—The pinna is alto- 
gether absent. The hind limbs are permanently stretched- 
out, parallel with the tail ; and, consequently, they are unable 
to support the body, or assist in locomotion on land. 

The space between the orbits is extremely narrow, and 
supra-orbital processes are absent. The bulla tympani is 
very large and thick-walled; and the middle, are much 
shorter than the outer, digits of the pes. 

The common Seal (Phoca vitulina) is a native and acces- 
sible member of this group. It has a rounded head and 
a neck which is well marked, though shorter in proportion 
than that of the Hared-seals. The nasal apertures are slit- 


THE PHOCIDZ. 425 


like and can be closed at will, the eyes large and bril- 
liant, and the auditory apertures small and devoid of a 
pinna. The limbs are large, and their distal, longer than 
their proximal, divisions. The fore limb is buried beyond 
the elbow in the common integument, but the flexible 
wrist allows the weight of the body to be supported by the 
palmar surface of the manus. The hind limbs, on the 
contrary, are permanently extended and turned backwards 
parallel with the tail, which lies between them, and with 
which they form a sort of terminal fin. When the Seal 
swims, in fact, the fore limbs are applied against the sides 
of the thorax, and the hinder moiety of the body being 
very flexible, the conjoined hind limbs and tail are put to 
the same use as the caudal fin of aCetacean. The Seal has 
twenty dorso-lumbar vertebre, of which five are lumbar. 
There are four sacral vertebre, but only one of these unites 
with the ilia. Eleven vertebre enter into the formation of - 
the short tail. There are ten true ribs and nine sternebre, 
the manubrium being prolonged forwards into a long carti- 
laginous process. 

The brain-case is smooth, rounded, and spacious, but 
the cranium narrows rapidly in the interorbital region. 
Its floor is remarkably flattened from above oad and 
_ very thin, the broad basi-occipital sometimes presenting a 
perforation in the dry skull. The falx is partially, and 
the tentorium is wholly, ossified. The occipital segment 
is very large, and the supra-occipital advances between 
the parietals, but does not separate them completely. The 
alisphenoids are small and almost horizontal, and the syn- 
chondrosis between the basisphenoid and presphenoid 
persists. In all these respects the Seal’s skull is strikingly 
cetacean. In fact, if the supra-orbital processes were sawn 
off, a Porpoise’s brain-case would closely resemble a Seal’s. 
But the nasal bones and the parietals are large, and the 
ethmoidal region is very peculiar. The lamina perpen- 
dicularis is largely ossified, and the vomer soon becomes 
ossified into one mass with it. The two ethmoidal tur- 
binals (or the superior and middle) are small and flattened, 


426 THE ANATOMY OF VERTEBRATED ANIMALS. 


and the latter ankyloses with the vomer on each side. 
The inferior, or maxillary, turbinal is extremely large and 
complicated, and it blocks the nasal passage in front of the 
others like a sieve, or strainer. There is no lachrymal 
bone, but the jugal is large. The squamosal is ankylosed 
with the periotic and tympanic. The latter is massive and 
shell-shaped, somewhat as in the Cetacea, but it has rather 
different relations to the auditory meatus. The periotic 
is very large, and its tumid pars mastoidea appears largely 
on the exterior of the skull. The fossa under the superior 
vertical semicircular canal is prolonged into this tumid 
part of the periotic. 

The alveolar portions of the premaxille are very small, 
but these bones extend far up the sides of the anterior 
nares. The maxillz do not extend over the frontals. The 
mandible has a well-developed coronoid process. 

The pollex is the longest and strongest digit, the others 
gradually decreasing in length. The fifth metacarpal arti- 
culates with the cuneiform bone, as well as with the unci- 
form. 

The ilium is short, and the long pubis and ischium are 
greatly inclined backwards, so that the long diameter of 
the os innominatwm makes only an acute angle with the 
spine. The femur is much shorter than the humerus. 
The tibia and fibula are ankylosed, and more than twice as 
long as the femur. The pes is longer than the tibia. The 
astragalus has a peculiar, roof-shaped, tibial surface, and 
sends a process backwards which contributes to the forma- 
tion of the very short heel. The hallux is the strongest 
of the digits ; while this and the fifth digit are the longest 
of those of the pes. 

The cutaneous muscle is largely developed and inserted 
into the humerus. The pectoralis major is very large, and 
arises from each side of the prolonged manubrium, and 
even in front of it, beneath the neck; the fibres of the 
muscles of opposite sides are continuous. The palmaris 
longus is a strong muscle, but the proper digital muscles are 
weak or absent, as in the case of the abductor, adductor, 


THE PHOCID®. 427 


flexor brevis, and opponens of the fifth digit. A special long 
abductor of this digit, however, passes from the olecranon to 
the distal phalanx. The iliacus is wanting, and there is no 
psoas major ; but muscles which represent the psoas minor 
and the subvertebral muscles of the Cetacea are very large 
and play an important part in effecting the locomotion of the 
Seal. The pectineus is very small, and the other adductors 
are inserted, not into the femur, but into the tibia. The 
gluteus maximus is inserted into the whole length of the 
femur. The semi-membranosus and semi-tendinosus are re- 
placed by a caudo-tibialis, which arises from the anterior 
caudal vertebrze and is inserted into the tibia, some of its 
tendinous fibres extending to the plantar aspect of the 
hallux. The popliteus and gastrocnemius are strong, but 
there is no soleus. The tendon of the plantaris passes over 
the caleaneum and ends on the plantar fascia of the per- 
forated tendon of the fourth digit. The other perforated 
tendons seem to arise from the fascia attached to the cal- 
caneum. 


~ . 83-8 1-1 5—5 
The dental formula is i. ——5 ¢. j= m.p.m. —- = 34. 


The grinding teeth have triangular crowns with notched 
edges, and at most two fangs. 

The milk teeth are shed during fcetal life, and at this 
period there are three molars above and below on each side, 
which appear to be replaced by the second, third, and 
fourth of the adult set. If such be the case, only the hinder- 
most of these last will be a true molar. 

The tongue is bifid at the extremity. The esophagus, 
very wide and dilatable, passes without any very well 
marked line of demarcation into the stomach, which is 
a great pyriform sac with its pyloric end bent upon itself. 
The intestine is about twelve times as long as the body. 
The colon is short, and is provided witha ccecum. The liver 
is divided into a great number of lobules, which are, as it 
were, set upon the inferior cava. The latter vessel, just below 
the diaphragm, presents a great dilatation, into which 
the vene hepatice of the several lobules open. After tra- 


428 THE ANATOMY OF VERTEBRATED ANIMALS. 


versing the diaphragm, the vena cava is surrounded, for 
about an inch, by a layer of red circular muscular fibres. 
The aorta and the pulmonary artery are both dilated at 
their commencements. 

The penis of the male is contained within a prepuce, 
supported by a loop of the cutaneous muscle. There is a 
large os penis, which presents a groove for the urethra 
inferiorly. The prostate is small, and there are no vesicule 
or Cowper’s glands. The testes lie just outside the inguinal 
canal, Theanus and the vulva of the female are surrounded 
by a common fold of integument. The clitoris has no 
bone. The body of the uterus is divided by a longitudinal 
septum. 

II. The Proboscidea.—These are massive animals, walking 
upon the extremities of the five toes, with which each foot 
is provided, and upon a great tegumentary cushion which 
unites these, and forms a flat sole behind them. 

The nose is prolonged into a flexible proboscis, which is 
at once a strong, and a delicate, organ of prehension. The 
hairy covering is scanty im the recent species; but there 
was abundant long hair, and an undercoat of wool, in at 
least one extinct Proboscidean, the Mammoth (Hlephas pri- 
migenius), which ranged over Northern Hurope and Asia 
during the glacial epoch. The pinna of the ear is large 
and flat. The testes of the male remain in the abdomen, and 
the mamme of the female are placed between the fore 
limbs. 

The dorso-lumbar vertebre amount to as many as twenty- 
three, and not more than three of these are lumbar, so that 
the dorsal region is, proportionally, exceedingly long. There 
are four sacral vertebre, followed by a comparatively short 
tail. The centra of the vertebre are far more flattened, 
from before backwards, than those of any other terrestrial 
mammal, and this is particularly the case in the cervical 
region, whence it follows that the neck is extremely short. 

The skull is enormous, even in proportion to the body, 
its size arising, in great measure, from the development of 
air cavities in the diploe. The interspace between the ~ 


429 


THE PROBOSCIDEA. 


‘(snupndfy uopoxoT) yueyda[y uvolypy oY} Jo u0j9[oxs OYT—"gOT “SLT 


430 THE ANATOMY OF VERTEBRATED ANIMALS. 


inner and the outer tables of the skull is often, in an old 
elephant, considerably greater than the diameter of the 
cerebral cavity itself. The cranial cavity is elongated and 
subcylindrical. The supra-occipital rises far upon the roof 
of the skull, so that the parietals are much narrower at 
the sagittal suture than elsewhere. The premaxille are 
very large, and the nasal bones short, the nasal passages 
being nearly vertical. The jugal bone forms only the 
middle part of the jugal arcade. The rami of the mandible 
have a high perpendicular portion, and they are largely 
ankylosed at the symphysis, which is produced into a sort 
of spout. 

The acromion of the scapula has a recurved process, 
such as is frequently found in the Rodents, to which order 
the Proboscidea present many curious approximations. 
There are no clavicles. In the antebrachium, the radius 
is permanently fixed (though not ankylosed) in the prone 
position, crossmg the ulna obliquely. The carpal and 
metacarpal bones, and the phalanges, are remarkable for 
their short and thick form, and the manus is larger than 
the pes. 

The ilia are immensely expanded transversely. The 
femur, which is not connected by any round ligament to 
the acetabulum, is relatively long and slender; and, when 
the animal is at rest, is directed perpendicularly to the 
axis of the trunk, not bent up, so as to form an acute angle 
with that axis, as it is in ordinary quadrupeds. The ham 
consequently occupies the middle of the length of the hind 
leg; the flexion of which, at this point, when the animal 
walks, gives an elephant a gait which is strikingly dif- 
ferent from that of other quadrupeds. The tibia is rela- 
tively short. The fibula is distinct and complete, and the 
bones of the pes have the same broad and short form as 
those of the manus. The hallux has only a single phalanx 
in some species. 

The Proboscidea have only two kinds of teeth, incisors 
and molars, canines being entirely absent. The incisors 
are composed of dentine and cement, with or without a 


THE PROBOSCIDEA. 431 


longitudinal belt of enamel, and, in the recent Hlephants, 
are developed only in the upper jaw. As their growth 
continues for a long period, or throughout life, they 
usually take the form of long tusks, which project on each 
side of the upper jaw. The molar teeth are composed of 
dentine, enamel, and cement, and their crowns, when un- 
worn, are always ridged, the ridges very often being made 
up of distinct tubercles. The intervals between the ridges 
are sometimes, as in the Asiatic Elephant, exceedingly deep, 
narrow, and completely filled up with cement; or, as in 
the African Elephant, they may be shallow and open, the 
cement forming only a thin coat. In the recent Elephants, 
only the two incisors are preceded by milk teeth. The 
molars are, altogether, six on each side, above and below; 
they come into place and use successively, the hinder ones 
moving forward, in proportion as the anterior ones are 
worn down by the attrition of those which are opposed to 
them. 

The stomach is simple and elongated, and there is a very 
wide cecum. The trilobed liver has no gall bladder. The 


heart has two anterior cave. 


The cerebellum is left uncovered by the cerebral hemi- 
spheres; which, in the existing Hlephants are large, and 
have greatly convoluted surfaces. 

The male reproductive organs exhibit two very large 
vesicule seminales, and four prostates. The uterus of the 
female has two cornua. 

Some, if not all, species of the extinct genus Mastodon 
were provided with a pair of short tusks in the man- 
dible, in addition to the large ones in the premaxille. And 
in some of these animals, as in certain other extinct Ele- 
phants, the anterior grinding teeth had vertical successors. 
The Miocene genus, Dinotherium, possessed two large, down- 
wardly-directed, tusks, one on each side of the symphysis 
of the mandible, while there were none in the upper jaw. 
The second and the third anterior grinding teeth had 
vertical successors. 

The Proboscidea are, at present, restricted to Asia and 


432 THE ANATOMY OF VERTEBRATED ANIMALS. 


Africa, where they are represented by two very distinct 
forms, to which the names of Lowodon (LH. africanus) and 
Huelephas (EH. indicus) proposed by the late Dr. Falconer 
may be very properly applied. The oldest rocks in which 
their remains occur are of Miocene age. Fossil remains of 
elephants occur not only in the old world, but also in both 
North and South America. 

III. The Hyracoidea.—The genus Hyraw, which is the 
sole member of this group, was referred by Pallas to the 
Rodents; and by Cuvier, who demonstrated that it could 
not be a Rodent, it was placed among the Ungulata, in the 
immediate neighbourhood of Rhinoceros, without any better 
evidence than that afforded by the characters of the molar 
teeth. Professor Brandt of St. Petersburg, in an elaborate 
memoir just published, arrives at the conclusion that it is 
a “gliriform Ungulate,” intermediate, in a certain sense, 
between the Rodents and the Ungulata; but, still, more 
Ungulate than Rodent. It appears to me to be neither 
Ungulate nor Rodent, but the type of a distinct order, in 
many respects intermediate between the Ungulata, on the - 
one hand, and the Rodentia and Insectivora, on the other. 

The small, Rabbit-like, animals comprised in the genus 
Hyraz are plantigrade, and provided with four visible toes 
in front and three behind. The nails are not hoof-like, 
but nearly flat, except the innermost of the hind foot, which 
is peculiarly curved. The body is covered with fur, and 
the muffle, or snout, is split, as in the Rodents. There is 
a pendulous penis, but no scrotum; and there are four 
inguinal and two axillary teats. 

There are from twenty-nine to thirty-one dorso-lumbar 
vertebre, which is the greatest number known in any ter- 
restrial mammal. Twenty-one or twenty-two of these 
are dorsal. No mammal, except Cholepus, the two-toed 
Sloth, possesses so large a number of dorsal vertebre as 
this. The transverse processes of the last lumbar vertebra 
articulate with the sacrum, as is the case in many Ungulate 
Mammals. In the skull, the post-orbital processes, which are 
chiefly furnished by the parietal and the jugal, nearly meet. 


THE HYRACOIDEA. 433 


Part of the articular facet for the mandible is formed by 
_ the jugal, which extends forwards until it comes into 
contact with the lachrymal bone. The base of the external 
pterygoid process is perforated by a canal, as in Perisso- 
dactyla and Lemuride. There are large pre- and post- 
tympanic processes, and the post-tympanic is much shorter 
than the par-occipital process. The premaxillx are large. 
and unite extensively with the nasal bones; the perpen- 
dicular ramus of the mandible is very wide, and somewhat 
like that of the Tapir in shape. The posterior margin of 
the bony palate is opposite the anterior edge of the last 
molar tooth. 

The scapula is devoid of an acromion process, as in the 
Perissodactyla. There are no clavicles, but the coracoid 
process is well developed. The ulna is complete, and a 
rudiment of the pollex is present. In the carpus, a line 
prolonging the axis of the third metacarpal bisects the os 
magnum and the lunare, which is not the case in any 

Ungulate Mammal. 
| In the hind limb, the femur possesses a small third tro- 
_ chanter, which is not nearly so conspicuous as in some 
Rodents. The tibia and fibula are complete. The ex- 
tremity of the inner malleolus articulates with a shelf-like 
process of the astragalus, the distal face of which bone has 
on facet for the cuboid. The digits 7. and v. are not repre- 
sented even by rudiments. The terminal phalanx of ii. is 
longitudinally cleft. 

The dentition of the adult is i. — c. — ‘p.m. — and 

33 

. 3°3° 
fall out; the inner, which are very large, curved, and have 
a thick coat of enamel on their anterior faces, continue to 
grow throughout life, as in Rodents. The lower incisors 
have crowns denticulated at the edges, like those of Galeo- 
pithecus and some Bats. They bite upon a callous pad 
which lies behind the upper incisors. The patterns of the 
upper and lower molar teeth are very similar to those of 
the corresponding teeth in Rhinoceros. As in the Horse, 

2F 


The outer upper incisors are very small, and soon 


434. THE ANATOMY OF VERTEBRATED ANIMALS. 


part of the Hustachian tube is dilated into a thin-walled 
sac extending on the inner side of the bulla tympani from 
the pterygoid processes to the exit of the ninth nerve. 

A slight constriction marks off the cardiac from the 
pyloric division of the stomach. The cardiac portion is 
lined by a dense epithelium. The intestine is provided with 
three cceca—one in the ordinary position, and two placed 
much lower down on the colon, opposite one another, and 
terminating by pointed ends. There is no gall-bladder. 
The ureters open, not near the neck of the bladder as in 
Mammals generally, but near the fundus, as in some few 
Rodents. 

The male has vesicule seminales, prostatic and Cowperian 
glands. The uterus is two-horned, and the vulva and anus 
are surrounded by a common fold of integument. 

In the feetus the yelk sac and the vitello-intestinal duct 
early disappear. The amnionis not vascular, The allantois 
spreads over the interior of the chorion, and gives rise to 
the broad zone-like placenta, which is composed of both 
maternal and fetal parts. The maternal vessels pass 
straight through the thickness of the placenta towards its 
feetal surface, on which they anastomose, forming meshes, 
through which the vessels of the fetus pass towards the 
uterine surface of the placenta. 

The species of the genus Hyrax are found only in Syria 
and Africa. No fossil Hyracoidea are known. 

Tue DiscoripEA—The Mammalia with discoidal placentz 
are the Rodentia, the Cheiroptera, the Insectivora, and the 
Primates. 

1. The RopentTrA.—This large group of Mammalia is 
most definitely characterized by its dentition. There are 
no canines, and the mandible never contains more than 
two incisors, which are placed one on each side of the 
symphysis, and continue to grow throughout life. They 
are coated with enamel much more thickly upon their front 
surfaces than elsewhere; so that by attrition they acquire 
and retain a chisel-shaped edge, the enamel in front wearing 
away less rapidly than the rest of the tooth. 


—" - 


—_— = = 


THE RODENTIA. 435 

With the exception of one group of Rodents, there are only 
two teeth in the premaxille; and these have the same cha- 
racters as the incisors of the mandible. The Lagomorpha, or 
Hares and Rabbits, however, have a second pair of incisors 
of small size, behind the first, in the upper jaw. The molars 
are from two to six in number, in each half of the upper 
jaw, and two to five, in the lower jaw. They consist of 
enamel, dentine, and cement, and their crowns may be 
tuberculate or laminate in pattern. Sometimes they form 
roots, but, in other cases, they grow throughout life. 
Where there are more than three grinding teeth, the 
one which precedes the three hindermost has displaced a 
milk tooth; but where the grinding teeth are fewer than 
three, or only three, none of them displaces a milk tooth. 


_ Even when milk teeth exist they may be shed before birth, 


as in the Guinea-pig. 

The premaxillary bones are always large, and the orbits 
are never shut off by bone from the temporal fossa. Very 
generally, the condyle of the mandible is elongated from 
before backwards. 

With the exception of one group, the Dormice (Myow- 
ine), all Rodents have a large cecum. 

The cerebral hemispheres leave the cerebellum largely 
uncovered, when the brain is viewed from above. They 
are either smooth externally, or very moderately convoluted. 
The corpus callosum is well developed. 

With the exceptions noted, the foregoing characters are 
universal among the Rodentia. There are other peculiari- 
ties which are generally present, and when they exist, are 
very characteristic, though they are not universal. 

Thus the dorso-lumbar vertebre are usually nineteen in 
number. There is a large interparietal ossification. The 
jugal bone is comparatively short, and occupies only the 
middle of the zygomatic arch. 

The clavicles are very generally present; though wholly 
absent in some genera, as, for example, the Guinea-pig, 
(Cavia). The acromion commonly sends a process back- 
wards over the infra-spinous fossa. There is a ninth bone 


436 THE ANATOMY OF VERTEBRATED ANIMALS. 


in the carpus intercalated between the proximal and the 
distal series. The digits are five, ungulate, and provided 
with small claws. 

There is a bone in the penis. The testes do not leave the 
abdomen, but come down into the groin in the breeding 
season. Vesicule seminales and prostatic glands are 
present. In the female the uterus is, in many genera, 
completely divided into two cornua, each of which opens 
separately into the vagina; but, in the rest, the cornua 
unite into a corpus uteri. 

Some genera depart widely from the rest in particular 
points; for example, in the Porcupines, the hairs on the 
dorsal region of the body are very much enlarged, acquire 
a peculiar structure, and form the so-called “ quills.” Some 
of the Porcupines have prehensile tails. 

In Cavia and Hydrocherus the toes are reduced to three, 
and the nails have almost put on the character of hoofs. 

The Squirrels have the short pollex almost opposable. 

The femur in some Rodents has a well-developed third 
trochanter; and in Dipus, the Jerboa, the long metatarsals 
become ankylosed together into a cannon bone. 

In the Porcupines, the suborbital foramen is enormous, 
and an anterior fasciculus of the masseter muscle arises 
from the maxilla, and traverses the foramen to its insertion. 

The Hamster (Cricetus) has great cheek pouches, pro- 
vided with special retractor muscles connected with the 
spines of two lumbar vertebre. 

In some genera, the stomach, which is usually simple, 
tends to become complex. Thus the cardiac division of 
the stomach of the Beaver is provided with a special glan- 
dular mass. The cardiac end of the csophagus of the 
Dormouse is glandular and dilated like the proventiculus 
of a bird. And, in Arvicola, the stomach becomes deeply 
constricted, and a groove leads from the esophagus towards 
the pyloric end, reminding one of certain Artiodactyla. 

In some few genera, the ureters open into the fundus of 
the bladder, or near it. 

Although the genera and species of the Rodentia are 


THE ANATOMY OF THE RABBIT. 437 


more numerous than those of any other mammalian order ; 
and although they are adapted to very different modes of 
life—some, like the “Flying Squirrels,” floating through 
the air by means of a parachute-like expansion of the in- 
tegument between the fore and hind limbs; others being 
arboreal, like the ordinary Squirrels; or among the swiftest 
of runners, as the Hares; or strong burrowers, as the 
mole-like Bathyergus ; or aquatic, like the Water-vole—their 
structural differences are comparatively insignificant, and 
the subdivision of the order into large groups is proportion- 
ately difficult. 

Brandt has divided the Rodents according to their 
cranial characters into Sciwromorpha, Myomorpha, Hystri- 
comorpha, and Lagomorpha ; or, Squirrels, Rats, Poreupines, 
and Conies, if we use these English names in a broad and 
tribal sense. 

The student will find the Rabbit, one of the Lagomorpha, 
to be a conveniently sized and easily obtained subject for 
study. The following are the most important points to be 
noted in its structure. The hairy covering of the body 
extends over the palmar and plantar regions of the feet, and 
into the interior of the mouth, so that there is a band of 
hair on the inside of each cheek. There are five digits on 
the fore foot, or manus; but the pollex is smaller than the 
others. The pes has only four digits, and the hind limb is 
longer than the fore limb. The upper lip is large, flexible, 
and cleft in the middle line; the large eyes are provided 
with a third eyelid, and the pinne of the ears are very 
long and mobile. The tail is short and recurved. The 
male has a recurved penis, and on each side of it a scrotal 
sac. The female has five pair of abdominal teats. In both 
sexes perineal glands are present, consisting of a saccular 
involution of the integument with rugose walls, into which 
the duct of a special gland lodged at the side of the penis, 
or of the clitoris, opens. 

There are nineteen dorso-lumbar vertebrx, of which twelve 
are dorsal. Of the four sacral vertebre only the first unites 
with the ilia. The dorsal vertebre have well-developed 


438 THE ANATOMY OF VERTEBRATED ANIMALS. 


spinous and transverse processes. At about the eighth, a 
mammillary process, or metapophysis, becomes obvious; 
and, in the succeeding vertebre this increases in length and 
strength, tillin the lumbar region it becomes as long as 
the spinous process. In the last lumbar, it is short, and 
in the sacrum, it is obsolete, but it is traceable through 
the series of the anterior caudal vertebre. Accessory pro- 
cesses, or anapophyses, are observable in the last dorsal 
and fowr or five anterior lumbar vertebra. The trans- 
verse processes of the lumbar vertebre are exceedingly long, 
and that of the first lumbar is bifurcated at its extremity. 
These transverse processes give attachment above, to the 
sacro-lumbalis, and below, to the psoas major, both which 
muscles are very large; while the heads of the longissimus 
dorsi are attached to the long metapophyses. The great 
mass of these extensor and flexor muscles of the spine, and 
the leverage afforded by the mode of their attachment to 
the long processes of the vertebrae, would seem to be re- 
lated to the leaping and scratching movements of the 
Rabbit. Strong median processes are developed from the 
ventral faces of the centra of the three anterior lumbar 
vertebre; these give attachment to the crura of the 
diaphragm. 

The tubercles of the second to the eighth ribs inclusively 
are prolonged into spiniform processes, which give attach- 
ment to the tendons of the longissimus dorsi. There are 
five sternebrze anda long xiphoid process. The manubrium 
is long, narrow, deep, and keeled inferiorly. 

In the skull, the great supra-orbital processes of the 
frontal are to be noted. The presphenoid is high and 
greatly compressed from side to side, so as to form a thin 
septum between the orbits, and the optic foramina run into 
one, aS in some Seals. The tympanic and the periotic are 
ankylosed together, but remain distinct from the adjacent 
bones, and are merely held in position by abutting against 
the basi-sphenoid on the inner side and by the post-tym- 
panic hook of the squamosal on the outside. The tympanic 
is prolonged upwards and outwards into a tubular meatus. 


THE MYOLOGY OF THE RABBIT. A439 


The glenoid cavity is elongated from before backwards. 
The suture between the jugal and the maxillary becomes 
obliterated, and there is no orbital process given off from 
the zygoma. A considerable extent of the outer wall of the 
maxilla remains incompletely ossified. The premaxilla is 
extremely large and trifurcated. 

The ascending portion of the ramus of the mandible is 
long, and the coronoid process well developed. The long 
axis of the condyle is antero-posterior, and the angular 
process has a slight inward projection. In the palate, the 
prepalatine, or incisive, foramina are enormous; and partly 
in consequence of this, partly by the posterior excavation 
of the palatal plate of the palatine, the roof of the palate is 
reduced to little more than a transverse bar of bone. 

The scapula is long and narrow, and the backward process 
of the acromion, to which reference has already been made, 
gives attachment to a slip of the trapezius. A bony clavicle 
is present, but it is incomplete at both ends. There is a 
supra-condyloid foramen in the humerus. The radius and 
ulna are complete, but are fixed in the attitude of pro- 
nation. 

The femur has a small third trochanter. The tibia and 
fibula are ankylosed. The internal cuneiform bone is 
wanting, and the plantar surface of the naviculare gives off 
a large process. The inner side of the base of the second 
metatarsal sends a process along the inner face of the meso- 
cuneiform to articulate with the naviculare. This may 
represent a rudiment of the hallux with the ento-cuneiform. 

In the myology of the Rabbit the vast size of the flexors 
and extensors of the back has already been noted. The 
muscles moving the fore, and especially the hind, limbs, 
and the masseter, are not less remarkable for their dimen- 
sions. In the fore limb, the supinator longus is absent. The 
extensor indicis and secundiinternodii pollicis form one muscle. 
The extensor minimi digiti goes to the fourth and fifth digits. 
The flexor perforans and the flexor pollicis longus unite in 
a common tendon which divides into five slips, one for each 
digit. There are three lumbricales from the radial sides 


440, THE ANATOMY OF VERTEBRATED ANIMALS. 


of the tendons for the third, fourth, and fifth digits. The 
flexor sublimis, or perforatus, for digits i., ii7., and iv. arises 
from the inner condyle as usual; but that for the fifth digit 
springs from the pisiform bone—thus simulating the or- 
dinary arrangement of the perforated flexor in the pes. 
There is no pronator quadratus; but the palmaris longus 
is distinct, and its slender tendon expands into the palmar 
aponeurosis. Hach digit, except the pollex, has a pair of 
fleores breves, or interossei, which lie on the palmar faces of 
the metacarpal bones. 

In the hind limb, the soleus has only a fibular origin. The 
plantaris is very large and ensheathed in the gastrocnemius ; 
it ends in a tendon nearly as large as the tendo Achillis, 
which passes over the end of the calcaneum, being con- 
nected with this and the tendo Achillis by a strong fascia 
laterally, but being, otherwise, separated from it by a 
synovial sac. In the sole of the foot it divides into four 
tendons, which become the perforated tendons of the 
four digits. The flexor perforans and flexor hallucis are 
fused into one muscle, the tendon of which divides in 
the sole into the four perforating tendons. There are 
three lumbricales, and four pair of interossei (flexores breves). 
There is no proper tibialis posticus, but a muscle arises 
from the upper part of the inner face of the tibia, internal 
to, and in front of, the insertion of the popliteus, becomes 
tendinous about the middle of the leg, passes behind the 
inner malleolus, and runs along the inner and dorsal aspect 
of the second metatarsal to be inserted into the extensor 
tendons. It seems to stand in the same relation to the 
second digit as the peroneus quinti, on the opposite side of 
the pes, to the fifth digit. The peroneus longus is inserted 
into the base of the second metatarsal: a peroneus brevis, 
p. quarti, and p. quinti digiti are present. There is no 
extensor hallucis longus, nor any extensor brevis digitorum. 

The principal characters of the brain of the Rabbit have 
already been described (see p. 64, and Figs. 21 and 22). 
There is a single large corpus mammillare. Of the corpora 
quadrigemina, the nates are larger than the testes, There 


THE DENTITION OF THE RABBIT. 441 


is a very large and completely exposed flocculus, and the 
vermis is large in proportion to the lateral lobes of the 
cerebellum. The corpora trapezoidea are well marked. 

The membrana nictitans is very large, has a convex free 
edge, and contains a triangular cartilage. There are no 
puncta lachrymalia, but a crescentic aperture leads into the 
lachrymal canal. The large lachrymal gland lies above and 
external to the eyeball, and there is a well-developed 
Harderian gland on its lower and inner side. 

The dental formula is 7. se oot p.m. = m. == = 28. 

The lower, and the inner upper, incisors are very large and 
long; they grow continuously from persistent pulps, and they 
are coated with enamel only in front, so that wear keeps 
them constantly sharp. The second pair of small incisors 
exists only in the upper jaw. A great diastema separates 
the incisors from the first premolar above and below. The 
grinding teeth all grow from persistent pulps, and do not 
form fangs; they have transversely ridged crowns, the 
patterns of which are very similar throughout, the first and 
the last only presenting some differences. The young 
Rabbit has three incisors and three milk molars on each 
side, in the upper jaw. In the lower jaw, there are only 
two milk molars on each side. 

The stomach is simple, and there is a large cecum, 
Special glands pour their secretions at the side of the anus. 

The pancreas is very large, and its duct enters the in- 
testine nearly a foot from the pylorus, and far distant 
from the biliary duct. 

There are two anterior cave ; and the external jugular vein 
is very much larger than the internal. 

In the male, the inguinal canal remains permanently 
open, and there is a large uterus masculinus. In the female, 
the uteri are quite separate, and each opens by a distinct 
os tince into the vagina. 

The distribution of the Rodentia is almost world-wide, 
Madagascar being the only considerable island in which 
indigenous Rodents are unknown. The Austro-Colum- 


442, THE ANATOMY OF VERTEBRATED ANIMALS. 


bian province may be regarded as the headquarters of the 
group. 

Remains of Rodents have been found, in the fossil state, 
as far back as the eocene formation. 

II. The Insecttvora.—It is exceedingly difficult to give 
an absolute definition of this group of mammals. But all 
the Insectivora possess more than two incisors in the man- 
dible; and their molar teeth, which are always coated with 
enamel, have tuberculated crowns, and form roots. 

The fore limbs have the structure usual among ungul- 
culate mammals; and, in both limbs, the digits are provided 
with claws. The hallux is not opposable, and, like the 
other digits, it is provided with a claw. 

In addition to these distinctive characters there are 
others which are met with in all members of the group. 

The Insectivora are, almost all, either plantigrade or semi- 
plantigrade. The clavicles are completely developed in all, 
except Potamogale. The stomach is simple. The testes 
of the male are either inguinal or abdominal, and do not 
descend into a scrotum. The female has a two-horned 
uterus. 

The cerebral hemispheres leave the cerebellum uncovered, 
in the upper view of the brain; and are almost, or wholly, 
devoid of sulci and gyri. The corpus callosum is sometimes 
exceedingly short. 

No Insectivore attains a large size, and some, such as the 
Shrew Mice, are the smallest of the Mammalia. 

The Insectivora present a great diversity of organization, 
the common Hedgehog being an almost central form. The 
Shrews tend towards the Rodentia, the Tupaye towards 
the Lemurs; while the Moles, on the one hand, and the 
Galeopitheci on the other, are aberrant modifications. Re- 
lations of a more general character connect them with the 
Carnivora and the Ungulata. 

The Hedgehog (Erinaceus Europeus) is pentadactyle and 
plantigrade. It has a long flexible snout. The eyes are 
small; the pinmne of the ears are rounded, and the integu- 
ment lining the concha is produced into a transverse, shelf- 


OE a eS ee 


THE ANATOMY OF THE HEDGEHOG. 443 


like, fold. The under surface of the body bears hairs of 
the ordinary kind; but, on the dorsal aspect of the head 
and trunk, the hairs are conyerted into strong fluted spines. 
There are twenty-one dorso-lumbar vertebre (of which 
fifteen are dorsal, and six lumbar), three or four sacral, and 
twelve to fourteen caudal. Accessory processes, or meta- 
pophyses, are developed on several of the dorso-lumbar ver- 
tebre. The sternebre are laterally compressed, except the 
manubrium, which is broad; and eight of the fifteen pair of 
ribs are connected with the sternum. 

The occipital foramen is placed completely at the hinder 
extremity of the skull, in the lower part of the perpen- 
dicular occipital face of the cranium, and looks backwards. 
There are large paramastoid processes. The glenoidal 
surface for the mandible is flattened. The zygoma is stout, 
and the jugal bone is, as it were, applied upon the outer 
side of it. The orbit has no posterior osseous boundary. 
The lachrymal foramen lies upon the face. There are 
unossified spaces in the bony palate, and the posterior 
margins of the palate are thickened, as in the Lemurs. 
The large and bullate tympanic bone does not ankylose 
with the squamosal, or the periotic, and is readily lost from 
the dry skull. The alisphenoid contributes largely to the 
formation of the front wall of the tympanum; and a large 
portion of the inner wall of the tympanic cavity is formed 
by a broad process of the basisphenoid, the outer and lower 
edge of which joins, by a sort of harmonia, with the inner 
and lower edge of the tympanic. 

The ascending portion of the ramus of the mandible is 
short, and the angle is slightly inflected. The two rami 
are not ankylosed at the symphysis. The supra-scapular 
fossa is wider than the infra-scapular. The spine is strong, 
and the acromion bifurcates, sending a prolongation back- 
wards. The clavicles are long and convex forwards. The 
humerus has an intercondyloid foramen; but there is no 


_ foramen above the inner condyle, and this circumstance 


is unusual among the Insectivora. The bones of the anti- 
brachium are fixed in the prone position. There is an os 


444, THE ANATOMY OF VERTEBRATED ANIMALS. 


centrale in the carpus, so that it has nine bones. The 
scaphoid and lunare are ankylosed, as in the Carnivora, and 
the pisiform bone is much elongated. The pollex and the 
fifth digit are the shortest. 

The pelvis is remarkably spacious. The symphysial 
union of the pubes is always small, and, sometimes, the 
bones remain separate. The subpubic arch is much rounded. 
The ilium is narrow, and a mere ridge separates the iliac 
fossa from the gluteal surface. The femur has a round 
ligament, and a prominent ridge represents a third tro- 
chanter. The distal ends of the tibia and fibula are anky- 
losed together. 

One of the most notable peculiarities of the Hedgehog 
is its power of rolling itself up into a ball, from all sides of 
which the spines protrude. This is effected, for the most 
part, by the contraction of the greatly developed cutaneous 
muscle, the chief fibres of which are disposed as follows. A 
very broad band, the orbicularis panniculi, encircles the body 
laterally. In front, it, partly, arises from the nasal and 
frontal bones, and, partly, is the continuation of a thick 
mass of fibres which pass over the occiput. Posteriorly, 
each lateral division of the muscle spreads out into a very 
broad band, which is thick ventrally and thin dorsally, and 
adheres closely to the skin, from the line at which the hairy 
and spinigerous surfaces join, to near the median line of 
the back. Posteriorly, the two lateral halves of the orbi- 
cular muscle pass into one another upon the distal half of 
the short tail. 

The action of this muscle will depend upon the attitude 
of the animal when it contracts. If the head and tail are 
fully extended, the orbicularis can only diminish the dimen- 
sions of the spinigerous region of the skin and erect the 
spines. But if the head and tail be more or less flexed, as 
they always are in the ordinary attitude of the Hedgehog, 
the orbicularis will play the part of a powerful sphincter, 
approximating the edges of the spinigerous area towards 
the centre of the ventral side of the body, and forcibly 
enfolding the trunk and limbs within the bag thus formed: 


THE MYOLOGY OF THE HEDGEOG. 445 


It is, in fact, the chief agent in coiling the body up, and 
keeping it so coiled. 

Numerous muscular bundles take a radiating direction 
on the dorsal aspect of the body, and antagonize the orbi- 
cularis: 1. A pair of slender occipito-frontales arise from the 
occipital crest, and are inserted into the integnment over 
the frontal and nasal bones. 2. A pair of occipito-orbiculares 
arise from the same crest, and pass into the anterior part 
of the orbicularis. 3. A pair of brcader cervico-orbiculares 
arise from the fascia of the neck, and pass to the dorsal 
part of the anterior fourth of the orbicularis. 4. Slender 
dorso-orbiculares arise close to the hinder ends of the tra- 
pexii and spread out above the foregoing. 5. Two stout 
muscles, coccygeo-orbiculares, arise from the middle caudal 
vertebre, and after receiving fibres from the ventral region, 
end in the dorsal margins of the orbicularis. 6. Two 
muscles attached to the pinne of the ears (awriculo-orbicu- 
lares) pass backwards to the orbicularis on each side. 

On the ventral aspect are certain muscles which assist 
the orbicularis: 1. Two broad muscles (sterno-faciales) arise 
in the middle line, over the anterior part of the sternum, 
and pass outwards and forwards to the sides of the lower 
jaw and the integument of the face and ears. Muscular 
slips from these are sent up over each shoulder to the 
orbicularis. 2. A humero-abdominalis arises from each 
humerus beneath the insertion of the pectoralis major, and, 
passing backwards over the sides of the abdomen, these 
become connected with the ventral edges of the orbicularis. 
The external fibres of these muscles are continued round the 
ischial region to the coccygeo-orbicularis; the internal fibres 
pass to the prepuce, and over the middle line of the ab- 
domen, in front of it. 3. A humero-dorsalis arises from the 
humerus close to the foregoing, and passing upwards and 
backwards through the axilla, spreads out in the mid- 
dorsal integument and the orbicularis. 

The contraction of all these muscles must tend to bring 
together the edges of the integumentary bag, and to tuck 
the head, tail, and limbs into it. 


446 THE ANATOMY OF VERTEBRATED ANIMALS. 


In the myology of the limbs the following points are 
noteworthy: The supinator longus, pronator teres and pal- 
maris longus are absent. The palmaris brevis is present. A 
single muscle takes the place of the extensor secundi internodii 
pollicis and extensor indicis, and sends a third tendon to the 
middle digit. The extensor minimi digiti supplies the other 
two digits. The flewor perforans and flexor pollicis longus are 
represented by five distinct muscular heads, each with a 
tendon of its own; but all the tendons unite in the middle 
of the forearm, and the common tendon again subdivides 
into only four slips, the pollex receiving no tendon. There 
are no lumbricales. The pollex has only a rudimentary flexor 
brevis and an abductor. The other digits have each two 
interossei, or flewores breves, inserted into the metacarpo- 
phalangeal sesamoids. 

In the leg, the soleus has only a fibular head, and the 
jlexor brevis digitorum arises wholly from the calcaneum. 
The flexor hallucis and flexor perforans have a common 
tendon, which, in the sole, divides into five tendons, one for 
each digit. There ar eno lumbricales, nor flewor accessorius. 
The tibialis posticus seems to be represented by two small 
muscular bellies, one of which arises from the prominent 
end of the tibia, and the other from that of the fibula. The 
tendons of both pass behind the inner malleolus, and that 
of the former muscle goes to the tibial and plantar surface of 
the hallucal metatarsal, while the latter is inserted into the 
ento-cuneiform bone. The interossei pedis are represented 
by a pair of flewores breves for each digit except the hallux. 

The adult Hedgehog has thirty-six teeth, of which twenty 
are in the upper, and sixteen in the lower jaw. The dental 
formula is 7. ~ ie = p.m. — m. _ = 36. 

The grinding surface of the crowns of the first and second 
upper molars exhibits a pattern fundamentally similar to 
that of the corresponding teeth in Man, the Anthropo- 
morpha, and’ the majority of the Lemurs; that is to say, 
there are four cusps, and the antero-internal is connected 
with the postero-external cusp by an oblique ridge. The 


, 


— © 


ee eee ee ee ee —— SC me ele Url eee 


THE BRAIN OF THE HEDGEHOG. 447 


cusps are remarkably sharp and pointed, and the outer sur- 
face of the postero-external one alone is somewhat inflected. 
In the lower jaw, the corresponding molars are each 
marked, as in most Lemurs, by two transverse ridges. In 
front of the anterior ridge is a basal prolongation of the 
tooth, on to which a curved ridge is continued inwards and 
forwards from the anterior principal ridge, giving rise to 
an imperfect crescent with its convexity outwards. 
According to Rousseau there are twenty-four milk teeth, 


oe dim: = which fall out seven weeks after birth. 


The brain of the Hedgehog is remarkable for its low 
organization. The olfactory lobes are singularly large, and 
are wholly uncovered by the cerebral hemispheres ; which, on 
the other hand, do not extend back sufficiently far to hide 
any part of the cerebellum. Indeed they hardly cover the 
corpora quadrigemina. Only a single shallow longitudinal 
sulcus marksthe upper and outer surface of each hemisphere. 
On the under surface, a rounded elevation corresponds 
with the base of each corpus striatum. Behind this, another 
elevation represents the end of the uncinate gyrus and the 
termination of the hippocampus major; and therefore 
answers, in a manner, to the temporal lobe. The inner face 
of the hemisphere presents neither convolution nor sulcus, 
except behind and below, where a very broad depression fol- 
lows the contour of the fissure of Bichat and the fornix, and 
represents the dentate sulcus. Above, this sulcus ends be- 
hind the posterior margin of the corpus callosum. The 
latter is remarkably short, and directed obliquely backwards 


and upwards. It has no genu, and the pre-commissural fibres 


of the ventricular wall spread out, beneath its anterior 
end, upon the face of the hemisphere. The part of the 
corpus callosum which answers to the lyra is very thick in 
proportion, and is inclined at an acute angle to the rest. 
_ Ina transverse section, the corpus callosum is seen to be 
very thin, and to curve upwards and outwards into the 
roof of the ventricular cavity. The inner walls of the 
“eral ventricles, which answer to the septum lucidum. are 


% 
; 


448 THE ANATOMY OF VERTEBRATED ANIMALS. 


thick, while the fornix is comparatively thin and slender. 
The anterior commissure is very stout. In this circum- 
stance, as in the small corpus callosum, the brain of the 
Hedgehog closely approaches that of the Didelphia and 
Ornithodelphia. There is no trace of a posterior cornu, or 
calearine fissure, and the lateral ventricle extends forwards 
into the olfactory lobe. The optic nerves are very slender ; 
the corpora geniculata externa are large and prominent; the 
nates are smaller than the testes, and transversely elongated. 
The cerebellum has a large vermis and small lateral lobes; 
the flocculi are prominent and are lodged in fosse of the 
periotic bones. The pons Varolii is very small; the corpora 
trapezoidea proportionally large. 

The spinal cord is remarkable for its thickness, and, at 
the same time, for its brevity, as it ends in the middle of 
the dorsal region. As a consequence of this arrangement 
the cauda equina is particularly large and long. 

The stomach is simple, but the mucous membrane of the 
considerable cardiac dilatation is thrown into numerous, 
and very strong, longitudinal rug. The intestine is about 
six times as long as the body, and presents no distinction 
into small and large; nor is there any cecum. The liver 
is divided by deep fissures into six lobes; a central one which 
bears the gall-bladder, a bifid spigelian lobe, and, on each 
side of these, two other lobes. The pancreas is a large and 
irregularly ramified gland; and the spleen is elongated and 
trihedral. 

The pericardium is extremely thin. The arteries arise 
from the arch of the aorta, as in Man, by an anonyma, a 
left carotid and left subclavian. The course of the internal 
carotid is remarkable. When it reaches the base of the 
skull it enters the tympanum and there divides into two 
branches, of which one traverses the stapes, and passing 
forwards in a groove of the roof of the tympanum, enters 
the skull and gives rise to the middle meningeal and 
ophthalmic arteries. The other branch passes over the 
cochlea, enters the skull by a narrow canal near the sella 
turcica, and unites with the circle of Willis. 


THE SPLANCHNOLOGY OF THE HEDGEHOG. 449 


The external jugular vein is very much more capacious 
than the internal, the latter being very small and hardly 
traceable to the internal jugular foramen. It is by the 
external jugular vein, in fact, that the great mass of the 
blood within the skull is carried away, a foramen in the 
squamosal bone allowing of a free communication between 
the external jugular vein and the lateral sinus. There is a 
left superior vena cava, which winds round the base of the 
left auricle, receives the coronary vein, and opens into the 
right auricle. The vascular system thus retains many 
embryonic characters. 

The right lung is four lobed; the left may possess from 
one to three lobes. 

Two ossifications, one on each side of the opening for the 
aorta, occur in the diaphragin. 

The testes of the male do not leave the cavity of the 
abdomen, but they descend as far as the inner side of the 
_ inguinal ring, to which they are connected by a short 
gubernaculum and cremaster. The vasa deferentia de- 
scend to the base of the bladder and then enter a hollow 
muscular sheath on their way to a “ chamber,” which is 
lodged in the distal end of that sheath. This “ chamber” 
passes into the penial urethra; the cystic urethra opens 
into it by a narrow slit in its front wall; and it receives the 
ducts of three pair of appendages. The proximal pair 
consist of a multitude of ramified tubuli, which have been 
found to contain spermatozoa, and are usually regarded as 
vesiculz seminales. The middle pair (the so-called “ pro- 
static glands”) have a similar structure and have also been 
observed to contain spermatozoa. The lowermost pair are 
Cowper's glands. The “chamber ” appears to represent the 
_ urogenital sinus of the embryo, which has not become 
y differentiated into prostatic and bulbous urethra. 

__ The ovaries are inclosed in wide-mouthed peritoneal sacs, 

_ and a ligamentous band, the diaphragmatic ligament, ex- 

_ tends from the ovary to the posterior surface of the dia- 

phragm. The cornua uteri are large and long. There 

are five pair of teats; the anterior pair being axillary and 
26 


Se rr ee 


450 THE ANATOMY OF VERTEBRATED ANIMALS. 


the posterior inguinal. The other three pair are equidistant, 
and lie along the ventral surface, internal to the edge of the 
orbicularis panniculi. 

Like the Rodentia, the Insectivora have a great diversity 
of habit; some Galeopithecr flitting through the air after 
the fashion of the flymg Squirrels; some arboreal, as the 
Tupaye ; some terrestrial and cursorial, like the majority 
of the order. A few are swimmers; and some, like the 
Mole, are the most completely fossorial of mammals. 

The most aberrant form of the Insectivora is the genus 
Galeopithecus, essentially an Insectivore of arboreal and 
frugivorous habit, with very long and slender limbs. These 
are connected with one another, with the sides of the neck 
and body, and with the tail, by a great fold of the integu- 
ment, which is called patagium; and, unlike the web of the 
Bat’s wing, is hairy on both sides, and extends between the 
digits of the pes. By the help of this great parachute- 
like expansion, the Galeopithecus is enabled to make float- 
ing leaps, from tree to tree, through great distances. When 
at rest, the Galeopithect suspend themselves by their fore 
and hind feet, the body and the head hanging downwards; 
a position which is sometimes assumed by the Marmosets 
among the Primates. 

The fore limbs are slightly larger than the hind limbs. 
There are four axillary teats. The male has a pendent 
penis and inguinal scrotal pouches. The pollex and the 
hallux are short, and capable of considerable movement in 
adduction and abduction, but they are not opposable; and 
their claws are like those of the other digits. 

. The occipital foramen is in the posterior face of the 
skull. The orbit is nearly, but not quite, encircled by 
bone. Thelachrymal foramen isin the orbit. The bony roof — 
of the palate is wide and its posterior margin is thickened. 
There is a strong curved post-glenoidal process of the 
squamosal, which unites with the mastoid, beneath the | 
auditory meatus, and restricts the movement of the man- 
dible to the vertical plane. A longitudinal section of the 
skull shows a large olfactory chamber projecting beyond 


GALEOPITHECUS. 451 


that for the cerebral lobes, and two longitudinal ridges upon 
the inner face of the latter, prove that these lobes must 
have possessed corresponding sulci. The tentorial plane is 
nearly vertical and the floccular fosse are very deep. 
The ulna is very slender inferiorly, where it becomes 
_ ankylosed to the distal end of the radius, which bears the 
carpus. When the ilia are horizontal, the acetabula look 
a little upwards and backwards as well as outwards. The 
fibula is complete. As in the Sloths and most Primates, 
the navicular and cuboid readily rotate upon the astra- 
galus and caleaneum, so that the planta pedis is habitually 
turned inwards. 


220 1 5—5 
The dental formula is 7. == ¢.  P. m.m. —— = 34. 


The outer incisor, in ie upper jaw, has two roots, a 

peculiari ity which is not known to occur elsewhere. The 
canines of both jaws also have two roots, as in some other 
Insectivora. The lower incisors are single-fanged; and 
their crowns are broad, flat, and divided by numerous 
deep longitudinal fissures, or “ pectinated.” 
_ The length of the whole alimentary canal from mouth to 
_ anus is not more than six times that of the body. The 
 sacculated ccecum is as long as the stomach, and its capacity 
_ must be greater than that of the latter organ. 

Galeopithecus has, at one time, been placed among the 
Lemurs, and at another, among the Bats. But the resem- 
blances with the former are general and superficial, and 
the differences in the form of the brain, the dentition, the 
structure of the limbs and of the skull, exclude it from 
the order of the Primates. 

Galeopithecus agrees with the Bats in the disposition of 
the tail, and in the existence of a patagium provided with 
special muscles. Further, in a slight obliquity of the 
-acetabula, such as is seen in its extreme development in 
‘the Bats; in the imperfect condition of the ulnx; and in 
‘the pectoral position of the teats and the pendent penis. 
‘Both of these last, however, it must be recollected, are also 
Primatic characters. Finally, the somewhat similarly pec- 


452 THE ANATOMY OF VERTEBRATED ANIMALS. 


tinated lower incisor teeth are found in the Cheiropteran 
genera, Diphylla and Desmodus. 

But Galeopithecus differs from the Bats completely in 
the structure of the fore limbs; in the position of the hind 
limbs and the absence of a calcar; in the two-fanged outer 
incisors and canines; and in the presence of a ccecum. 

On the other hand, the peculiarities of the skull and 
brain are mainly insectivorous, as is the two-fanged canine; 
and I see no reason for dissenting from Prof. Peters’ view 
that Galeopithecus belongs neither to the Primates, nor to 
the Cheiroptera, but that it is an aberrant Insectivore. 

With respect to other Insectivora, it is worthy of note, 
that Macroscelides has the radius and the ulna ankylosed. 
The Tupaye possess a large cecum. Chrysochloris has 
pectoral mammary glands; Centetes and the Moles have the 
penis pendent. 

The Tupaye are soft-furred, long-tailed, tree-loving 
animals, with complete bony orbits and a large ccecum, 
and are those Insectivora which most nearly approach the 
Lemurs. 

The Shrews (Sorices) most nearly resemble Rodents out- 
wardly, being very like small mice. The zygoma is 
imperfect, the tibia and fibula are ankylosed, and the pubic 
bones do not meet in the symphysis. There are sixteen to 
twenty teeth in the upper jaw and twelve in the mandible. 
Canines are absent, and there are six incisors above and 
four below. The inner lower incisors are greatly elongated 
and proclivous, and some of the teeth not unfrequently 
become ankylosed with the jaws. There is no cecum, and 
peculiar musk glands are sometimes developed at the sides 
of the body. 

The Moles (Talpine) have no external ears, and the eyes 
are rudimentary. The fore limbs are much larger than the 
hind, and are inclosed within the integument up to the 
carpus. The palmar surface of the broad manus is turned 
outwards and backwards. 

The manubrium of the sternum is very broad, and its ven- 
tral surface gives rise to a strong median crest. The scapula 


THE INSECTIVORA. 453 


is as long as the humerus and the radius together. It is 
triquetral and possesses an acromial process, but no distinct 
coracoid. The clavicle, which is very strong, is perforated 
by a great foramen, and at the middle of its posterior mar- 
gin sends off a truncated re-entering process. Proximally, 


_ it furnishes an articular surface for the humerus. In the 


a ae a eS ee, 


carpus there is a distinct centrale, and a large accessory 
C-shaped bone lies on its radial side. The pubes are sepa- 
rate at the symphysis, and an accessory styloid bone is 
connected with the naviculare of the foot. 

The distribution of the Insectivora is singular in this 
respect, that although they are met with, under very various 
climatal conditions, throughout the Old World and North 
America, there are none in South America or Australia. 

In the fossil condition they are not certainly known to 
occur in strata older than the tertiary. 


Fig. 109, 


Fig. 199.—The skeleton of a Flying Fox (Pteropus). 


454 THE ANATOMY OF VERTEBRATED ANIMALS. 


III. The Cuutroprera—The Cheiroptera may be re- 
garded as exceedingly modified Insectivora, having their 
nearest ally in Galeopithecus. 

They possess one or two pair of pectoral teats; and the fore 
limbs are very long, some of the digits particularly being 
immensely elongated. There is a patagiwm, or expansion 
of the integument, uniting the fore limbs with the body, 
and extended, as a membranous web, between the elongated 
fingers. Of these the third, fourth and fifth, and very 
frequently the second, are devoid of nails. The pollex 
always has a claw-like nail. When the animal is resting 
upon the ground, the thigh is twisted upwards and back- 
wards, in such a manner, that its extensor face looks 
forwards, and its flexor face backwards. In consequence 
of this the knee looks upwards and backwards, and the 
toes are turned backwards and slightly outwards. Under 
the same circumstances, all the digits of the manus are 
flexed upon their metacarpal bones; and the folded-up wing 
rests against the side of the body, whilst the pollex, with 
its claw, is extended forwards. In this position the animal 
shuffles along, with considerable rapidity; hauling itself 
forward by the claws on the pollices, and shoving itself 
along, by extending the hind limbs. 

The favourite attitude of a Bat, when at rest, however, 
is that of suspension by the claws of one or both legs, with 
the head downwards, and the patagiwm folded over it like a 
cloak. The most active movement of the Bat is effected by 
flight, the fore limbs being extended, and the patagiwm, 
which they support, playing the part of the feathers of a 
bird’s wing. 

The cervical vertebre are remarkably large in proportion 
to the others, but, as in the rest of the vertebral column, 
the spimous processes are very short. The ribs are long 
and curved, so as to include a relatively capacious chest. 
The manubrium of the sternum is very wide, and the 
middle of its under surface raised into a crest. In the 
lumbar region, the vertebral column is bent, so as to be 
concave forwards and to describe almost the quarter of a 


f 


a ae FR 


THE CHEIROPTERA. 455 


circle. As a consequence, the axis of the sacrum is at 
right angles to that of the anterior thoracic vertebre. 

In the skull, the orbit is not divided by bone from the 
temporal fossa, and the premaxillz are relatively small, and 
sometimes altogether rudimentary. 

The clavicles are remarkably long and strong, and the 
broad scapula has a strong spine. The ulne are imper- 
fect distally, the carpus being borne altogether by the 
radius. There is only a single bone in the proximal row 
of the carpus, the pisiform being absent. Those digits of 
the manus which are devoid of nails, possess not more 
than two phalanges. 

The pelvis is very narrow and elongated, and the pubic 
bones are widely separated at the symphysis, as in some 
Insectivora. The anterior caudal vertebre and the ischia 
are frequently united. The axes of the acetabula are 
directed towards the dorsal side of the body as well as 
outwards; whence, in part, arises the peculiar position of 
the thigh, which has already been described. The fibula is 
rudimentary, its upper part being represented only by 
ligament, and there is an elongated bone, or cartilage, 
attached to the inner side of the ankle-joint which lies 
in and supports the patagiwm, and is called the calcar. 
The distal moiety of the tarsus readily rotates upon the 
astragalus and calcaneum, permitting the sole to turn 
inward with much ease. 

All Cheiroptera possess three kinds of teeth, incisors, 
canines, and molars; and the intestine is devoid of a ccecum. 

The heart is provided with two superior cave, a right and 
left ; and the smooth cerebral hemispheres leave the cere- 
bellum completely exposed. 

The testes are abdominal throughout life, or may 
descend into the perineum, but there is no true scrotum. 
The penis is pendent. There are vesiculz seminales. The 
form of the uterus varies, beimg sometimes rounded and 
sometimes two-horned. 

The Bats are ordinarily divided into the Frugwora and 
the Insectivora. 


456 THE ANATOMY OF VERTEBRATED ANIMALS. 


a. The Frugivora live, as their name implies, exclusively 
upon fruits. With the single exception of Hypoderma, all 
the genera embraced in this group have a nail on the second 
digit of the manus, and the crowns of the molar teeth, 
which soon wear down, are, when entire, divided by a 
longitudinal furrow. 


a 5 2°2 
The incisors do not exceed aa 


The pyloric portion of the stomach is immensely elon- 
gated. 

The nose has no foliaceous appendages, and the well- 
developed pinna of the ear has the ordinary form, neither 
the tragus, nor any other part, being unusually developed. 

These Bats are confined to the hotter parts of the Old 
World and of Australia, where, from their dog-like heads 
and reddish colour, they are known as “Flying Foxes”- 
(Pteropus, Harpyia, &e.) 

b. The division of the Insectivora contains Bats which, for 
the most part, live upon insects, though some delight in 
fruits, and others suck the blood of larger animals. 

The second digit of the manus is devoid of a nail, and 
sometimes is without any bony phalanges. 

The stomach is usually pyriform, with a moderate cardiac 
enlargement. The molar teeth almost always have such a 
pattern as is observed in the typical Insectivora, and do not 
exceed six, or fall below four, on each side above and below. 

The incisors are ordinarily — or — but their number 
may be much reduced. 

The integument of the nose is developed into an appen- 
dage which is sometimes very large and leaf-like, and the 
tragus of the large ears is often similarly modified. The 
tail is often long, and sometimes prehensile. 

The genera Desmodus and Diphylla (of which the group 
Hematophilina has been formed) are the most completely 
blood-sucking of all the Bats in their habits. They have a 
pair of enormous, sharp-poimted, upper incisors, while 
the four lower incisors are small and pectinated. The 


THE PRIMATES. 457 


canines are very large and sharp, and the molars, which 
are reduced to two above and three below, on each side, 
have their crowns converted into sharp longitudinally dis- 
posed ridges, like the edges of scissors. In Desmodus, the 
very narrow esophagus leads into a stomach which would 
be of extremely small dimensions, were it not that its 
cardiac end is dilated into a great sac, which is longer 
than the body, and lies, folded up on itself, within the 
cavity of the abdomen. Into this sac it would appear 
that the blood swallowed by the animal at first passes, to 
be thence slowly drawn along the intestine. 

Mr. Darwin* thus speaks of the habits of Desmodus 
D Orbignyi : 

“The Vampire Bat is often the cause of much trouble 
by biting the horses on their withers. The injury is gene- 
rally not so much owing to the loss of blood as to the in- 
flammation which the pressure of the saddle afterwards 
produces. The whole circumstance has lately been doubted 
in England. I was therefore fortunate in being present 
when one was actually caught on a horse’s back. We were 
bivouacking late one evening near Coquimbo, in Chili, 
when my servant, noticing that the horses were very rest- 
less, went to see what was the matter, and fancying he 
could distinguish something, suddenly put his hand on the 
beast’s withers and secured the Vampire. In the morning 
the spot where the bite had been inflicted was easily distin- 
guished, from being slightly swollen and bloody. The 
third day afterwards we rode the horse without any ill 
effects.” 

IV. The Primates.— The Primates have two pectoral 
mamme, and, rarely, additional ones upon the abdomen, 
Incisor and molar teeth are always present, and, with one 
exception, canines. The incisors are never more than two, 
nor are there more than three premolars and three molars, 
on each side, above and below. 

Saving individual exceptions, which occur in one genus, 
and may be regarded as abnormal, the hallux possesses a 
; * “ Voyage of the Beagle,” Mammalia, p, 2. 


458 THE ANATOMY OF VERTEBRATED ANIMALS. 


flat nail. The hallux differs in form from the other digits 
of the foot, and is so disposed as to be capable of more 
or less extensive motion in adduction and abduction; and, 
very generally, it is opposable to the other digits of the foot. 

The Primates are divisible into—a. the Lemuwride, b. the 
Simiade, and c. the Anthropide. 

a. The first of these divisions, the Lemuride, is more 
widely separated, anatomically, from the other two, than 
these are from one another,* and it contains some forms 
which very closely approximate to the Insectivora, while 
others are nearly affined to the Rodentia. 

All the Lemwride are habitually quadripedal, have the 
integument furry, and are usually provided with long tails 
which are never prehensile. They are devoid of cheek 
pouches and of callous patches upon the integument cover- 
ing the ischia. 

The fore limbs are shorter than the hind limbs. In 
the foot, the hallux is large and opposable, and the second 
digit differs from the rest in size, and in the claw-like 
form of itsnail. The fourth digit is usually longer than the 
others, the difference being especially marked in the pes. 

In the skull, the brain-case is small relatively to the face, 
and is contracted anteriorly. If a straight line drawn from 
a point midway between the occipital condyles, through the 
median plane of the skull, to the junction of the ethmoid 
and presphenoid, in the floor of the cerebral cavity, be 
termed the basi-cranial avis; and if the planes of the 
cribriform plate of the ethmoid, of the tentorium cerebelli, 
and of the occipital foramen, be respectively termed the 
ethmoidal, tentorial, and occipital planes ; then, the greatest 
length of the cerebral cavity hardly exceeds the length 
of the basi-cranial axis; and the ethmoidal, tentorial, and 
occipital planes are very much inclined to that axis. The 
upper aperture of the lachrymal foramen lies upon the 


* On the strength of these differences M. Gratiolet relegated the 
Lemurs to the Insectivora; and Mr. Mivart, in his valuable paper 
“On the Axial Skeleton in the Primates,” published in the Proceedings 
of the Zoological Society for 1855, divides the Primates into two sub- 
orders, Lemuroidea and Anthropoidea. 


THE LEMURIDA. 459 


face, outside the front margin of the orbit. The frontal and 
the jugal bones are united behind the orbit, but a mere 
bar of bone results from their union; and it is so narrow 
that the orbit and the temporal fossa are in free com- 
munication. The bony palate is elongated and, in many 
species, its posterior free edge is thickened. 

The lateral processes of the atlas are, usually, expanded. 
The lumbar region of the spine is elongated; the vertebra 
composing it, in some cases, being as many as nine. There are 
nine bones in the carpus. The ilia are narrow and elongated, 
and the ischia are not everted. In most Lemurs, the tarsal 
bones resemble those of the other Primates; but, in Otolicnus 
and Tarsius, they have undergone a modification, a parallel 
to which is not to be found among Mammals, but must 
be sought among the Batrachia. When the distance he- 
tween the heel and the digits is great in other Mammalia, 
the elongation affects the metatarsal bones and not the 
tarsus; but, in these Lemurs, the caleaneum and the navi- 
culare are prolonged, as they are in the Frogs. 

The sublingua, a process of the mucous membrane of the 
floor of the mouth, developed between the apex of the 
tongue and the symphysis of the mandible, acquires a 
considerable size, and is often denticulated, or comblike, at 
its free end. The stomach is simple, with the cardiac and 
pyloric apertures approximated. The cecum is long, and 
has no vermiform appendage. 

In many Lemurs (Stenops, Nycticebus, Perodicticus, Arcto- 
cebus, Taursius) the great arteries and veins of the limbs 
break up into retia mirabilia formed of parallel branches. 

The ventricles of the larynx may be enlarged, but there 
are no great air sacs, such as exist in many other Primates. 

In the brain, the cerebral hemispheres are relatively small 
and flattened, and have narrow and pointed frontal lobes. 
They are so short as to leave the cerebellum largely un- 
covered. The gyri and sulci are scanty, or absent, upon the 


_ outer surface of the hemispheres, but the internal face 


" exhibits the calearine sulcus. The large olfactory lobes 
_ project forwards beyond the cerebral hemispheres. 


460 THE ANATOMY OF VERTEBRATED ANIMALS. 


The pendent penis of the male commonly contains a 
bone; the testes are lodged in a more or less complete 
scrotum ; and vesiculz seminales are generally present. 

In the female, the uterus has two long cornua, and the 
urethra traverses the clitoris. Sometimes there are one or 
two pairs of teats on the abdomen, in addition to the ordi- 
nary pectoral pair. 

The Lemuride are distinguishable into two families, the 
Lemurini and the Cheiromyini. 

In the Lemwrini, the pollex is large, opposable, and almost 
always has a broad, flat nail. 

55 66 
55 66 

The upper incisors are vertical, and the pairs of opposite 
sides are generally separated by an interval. The upper 
canines are large and pointed, and very different from the 
incisors. The lower incisors are close set, laterally com- 
pressed, long and proclivous, and the canines, which re- 
semble them in form and direction, are closely applied to 
the outer incisors. When six grinders are present, the 
anterior three are premolars. The anterior premolars, and 
sometimes all of them, have triangular and sharp-pointed 
crowns; the first premolar of the lower jaw, in fact, re- 
sembles a canine, but its true nature is shown by its biting 
behind the upper canine, not in front of it. 

Very generally the crowns of the upper molars are qua- 
dricuspidate, and an oblique ridge passes from the antero- 
external to the postero-internal cusp, as in the highest 
Primates; while, in the lower jaw, there are either two 
transverse ridges, or longitudinal crescents. The cusps of 
the molars are usually much produced, as in the Insectivora. 

In the Cheiromyini, the pollex is not truly opposable, and 
its nail is claw-like and resembles that of the other digits. 
All the digits of the pes, except the hallux, have compressed, 
claw-like, nails. The middle digit of the manus is much 
more slender than any of the others, and is longer than the 
fourth. The long axis of the articular head of the mandible 
is antero-posterior. The dentition differs from that of all 


sien, hae 
The usual dental formula is 7. 5 c. 34 p.m. mM. 


THE SIMIADZ. 461 


the other Lemurs (and indeed from that of all the other 
Primates), and resembles that of the Rodents. 

Thus there is only one pair of incisors in each jaw,* and 
these grow from persistent pulps and have a thick layer of 
enamel on their anterior faces, whence they wear to sharp 
chisel edges, like the incisors of the Rodentia. No canines 
are developed, and there are four grinders with simple 
crowns on each side above and below. 


face formula of the milk dentition is di. 5 —— 5d. ar 1 dm. 


| 
“| bo 


i 


out 

The Lemwride are confined to Hastern Asia, Madagascar, 
and South Africa; Madagascar presenting the greatest 
number and diversity of genera and species. 

b. In the great group of the Simiade, which contains the 
Apes and Monkeys, the attitude is sometimes habitually 
quadrupedal, the axis of the body being horizontal; but, 
in a few species, the trunk is habitually Belg 4 im a more in- 
clined position, and the animals readily assume the erect 
attitude. 

The Simiade are sometimes terrestrial in habit, and 
good runners, but they are always excellent climbers, and, 
in some cases, they are necessitated by their organi- 
zation to be almost as thoroughly arboreal as the Sloths. 

The hallux 3s always much shorter than the second digit 
of the foot, and capable of very free movement in adduction 
and abduction. 

The series of the teeth, in each jaw, is interrupted by a 
diastema in front of the canine in the upper jaw, and 
behind it, in the lower; and the canine teeth are longer 
than the others, the points of their crowns projecting for 
a greater or less distance beyond the rest. 

In the skull, the length of the basi-cranial axis equals 
more than half the extreme length of the cavity which 
contains the brain. The absolute capacity of the cranium 
* Among the Lemurida, the outer and upper incisors of Nyecticebus 


_ and Tarsius soon fall out. Lichanotus and Tarsius have only one pair 
of incisors in the mandible. 


462 THE ANATOMY OF VERTEBRATED ANIMALS. 


is less than forty cubic inches; and, if there is any differ- 
ence in the length and abundance of the hair which covers 


Fig. 110. 
Fig. 110,—The skeleton of a Catarrhine Monkey (Cercopithecus). 


the body, it is longest on the back. The uterus is un- i 
divided, and the clitoris is not perforated by the urethra. — 
The teats are only two in number, and they are pectoral. 
The Simiade are divisible into three families—the Arcto- — 
pithecini, the Platyrrhini, and the Catarrhini. . 
1. The Arctopithecini, or Marmosets, are small, thickly 


THE ARCTOPITHECINI. 463 


- furred, long-tailed, habitually quadrupedal, Squirrel-like, 
animals, which are found only in South America. None 
of them are provided with cheek pouches, nor possess bare 
and callous patches of integument over the ischia. The 
ears are large and hairy, and the nose is flat and broad, as 
_ in the Platyrrhini. 
_ The fore limbs are shorter than the hind limbs. The 
 pollex is not opposable, nor susceptible of extensive abduc- 
_ tion from the other digits, which it resembles in being pro- 
vided with a sharp curved claw. The manus, conse- 
_ quently, is a mere paw, and the term “hand” is not appli- 
cable to it. The hallux of the foot is very small and is pro- 
_ vided with a flat nail. The nails of all the other digits of 
| the pes are faleate. The plantar surface is very long, and 
the digits are very short. It follows from these facts that 
: the term ‘‘ quadrumanous” is not applicable, in any sense, 
_to the Marmosets. 

The skull is remarkable for the smooth and rounded 
surface and relatively large size of the _ brain-case. 
Although the orbits are large, the brow ridges are incon- 
spicuous, and the occipital region of the skull projects sc 
far backwards that the occipital foramen may le com- 
pletely upon the under surface of the skull, towards the 
junction of its middle and posterior thirds; and have its 
plane almost horizontal, when the face looks forwards. The 
orbit is almost completely shut off from the temporal fossa 

by bone. 

_ The hyoid resembles that of the Lemurs, its body being 
narrow and much arched from side to side, while the anterior 
_cornua are strong. 

There are eeene nineteen dorsolumbar vertebrz, and 
the transverse processes of the atlas are somewhat broad 
and flattened. 

3°23 


; The dental formula is 7. —; 56. = - p. M. 55 We 55 = 92. 
Thus the number of the ae 1s ns same as in Me and the 
Catarrhini ; but in the number of the premolars and molars 


the Arctopithecini differ from both the Catarriimi and the 


AG4 THE ANATOMY OF VERTEBRATED ANIMALS. 


Platyrrhini, haying one premolar more than the former and 
one true molar fewer than the latter. In Hapale, the lower 
incisors are proclivous; and the canines are approximated 
to them, and similarly inclined, as in the Lemurs. | 

Although the manus is a paw and the pollex is not 
opposable, this digit has its proper abductor, adductor, and 
long and short flexors. The existence of a proper opponens 
of the pollex is doubtful, but there is an opponens minimi 
digiti. The flexor longus is completely united with the flexor 
profundus digitorum, but the tendon for the pollex comes 
off on the radial side instead of on the ulnar side, as it does 
in some of the higher Simiade. The extensor secundi inter- 
nodii pollicis is united with the extensor indicis, and the 
extensor minimi digiti gives off slips to the third, fourth, 
and fifth digits, so that there is a complete set of deep ex- 
tensors. The four dorsal and three palmar interossei are not 
distinctly subdivided, but they send slips to the extensor 
tendons. 

There are four peronei: p. longus, p. brevis, p. quarti, and 
p. quinti digiti. The flexor brevis digitorum of the pes has 
one division which arises from the calcaneum and goes to 
the second digit; the other three heads arise from the 
tendons of the flexor perforans. The flexor accessorius fur- 
nishes almost the whole of the long flexor tendons of the 
hallux, the flexor longus digitorum supplying the perforating 
tendons of the second and fifth digits; while the flexor hal- 
lucis longus gives of the corresponding tendons of the 
third and fourth digits. The inéerossei, in the pes, appear 
to be represented only by the pairs of muscles which act 
as short flexors of the basal phalanges, and these He al- 
together upon the plantar aspect of the five metatarsal 
bones. The hallux has no special adductor, nor is there 
any transversus pedis. In fact, the pes is almost as com- 
pletely a “ paw” as is the manus. 

The brain has long and relatively large cerebral hemi- 
spheres, the posterior lobes of which project far beyond 
the cerebellum, and thus completely hide it, in the upper 
view of the brain. The external surfaces of the hemi- 


THE PLATYRRHINI. 465 


_ spheres are almost smooth, but the Sylvian fissure is well 
marked, and there is a trace of that of Rolando. On the 
inner face of each hemisphere, the calcarine fissure is deep 
and gives rise to a well-marked hippocampus minor within 
the posterior cornu of the lateral ventricle. The corpus 
callosum has about a third the length of the hemispheres. 
The septwm lucidum is very thick, and the precommissural 
fibres abundant. The vermis projects beyond the lateral 
lobes of the cerebellum, and the flocculi are large. 

2. The Platyrrhini are essentially quadrupedal and planti- 
grade, though some, like the Spider Monkeys (Afeles), occa- 
sionally assume the erect posture. They all possess tails, 
and in some genera (e.g. Ateles) this organ becomes very 
flexible and muscular, and the under surface of its extremity 
is devoid of hair and highly sensitive. The tail, thus modi- 
fied, is a powerful prehensile organ, and serves as a fifth 
hand. The partition between the nostrils is broad and 
separates them widely, so that the nose is remarkably wide 
and flat, whence the name of the group. The ears are 
rounded and bare. There are no cheek pouches, nor ischial 
callosities, in any Platyrrhine Monkey. In most, the fore 
limbs are shorter than the hind limbs, but the reverse is 
the case in the Spider Monkeys. The pollex differs less 
from the other digits than it does in the Catarrhini. It is 
more nearly parallel with, and in the same plane as, the 
other digits of the manus; and though capable of extensive 
adduction and abduction, can hardly be said to be truly 
opposable. The hallux is large, and susceptible of exten- 
sive movements in abduction and adduction. 

The number of the dorso-lumbar vertebre varies from 
seventeen to twenty-two, the greatest number being pos- 
sessed by Nyctipithecus, which has 22 (14 + 8 or 15 + 7). In 
those forms which have prehensile tails the terminal caudal 
yertebre are flattened from above downwards. The arti- 
eular surface of the head of the humerus looks more back- 
wards than inwards; and, not unfrequently, there is a 
foramen above the inner condyle. The carpus contains 

nine bones. The pollex is generally complete, but, in Ateles, 
2H 


466 THE ANATOMY OF VERTEBRATED ANIMALS. 


it isreduced to asmall metacarpal (to which, usually, a single 
minute nodular phalanx is articulated), and is completely 
hidden beneath the integument. The pelvis is, generally, 
elongated, and the anterior ramus of the pubis hes at right 
angles with the long axis of the narrow ium. The tuber- 
osities of the ischia are everted, but not rugose. In Aleles, 
the pelvis is broader, and the pubis forms a more open 
angle with the ilium. The calcaneal process is always very 
short, and compressed from side to side. ; 
The brain-case is rounded and devoid of strong crests. 
There is no distinct mastoid process, and the styloid is not 
ossified. The coronal suture is generally V-shaped, the 
apex of the frontal bone extending far back on the vertex 
of the skull. The alisphenoid and the parietal bones unite 
upon the side walls of the skull. The external auditory 
meatus is not ossified, the tympanic bone retaining its fetal 
hoop-like form. The frontal bones approach one another 
on the floor of the skull, but rarely unite over the junction 
of the presphenoid with the ethmoid. On the inner sur- 
face of the periotic bone there is a fossa overarched by the 
anterior vertical semicircular canal, in which the docculus 
rests. In Ateles the greater part of the tentorium is ossified. 
In other respects, the skull presents extraordinary variations 
among the Platyrrhini ; the two extremes being presented by 
the Howling Monkeys (Mycetes) and the Squirrel Monkeys 
(Chrysothrix). In the former, the face is very large and 
prominent, with a low facial angle. The roof of the brain- 
ease is depressed; the plane of the occipital foramen is 
almost perpendicular to the basi-cranial axis; and that 
of the tentorium is very much inclined. The occipital 
condyles are, consequently, situated at the posterior end 
of the basis cranii, and the basi-cranial axis is as long as 
the cerebral cavity. In Chrysothrix, on the contrary, the 
face is relatively small, with a high facial angle; the 
brain-case is moderately arched; the plane of the ten- 
torium is horizontal, like that of the occipital foramen, 
which lies but little behind the middle of the base of the 
skull. The basi-cranial axis is much shorter than the 


THE PLATYRRHINI. 467 


cerebral cavity. The premaxillo-maxillary suture disappears 


early in Cebus. 
The formula of the adult dentition is 7. = e. — p.m. — 


m. a5 = 36. The crowns of the molar teeth usually have 
two transverse ridges, ending in four cusps. In the upper 
molars of Ateles and Mycetes an oblique ridge crosses the 
crown from the antero-external to the postero-internal 
cusp. The permanent canines usually make their appear- 
ance before the last molar. 

The stomach is simple, the cecum large, and devoid of 
any vermiform appendix; the liver is usually five lobed; 
and the kidney has a single papilla. 

The ventricles of the larynx are not usually developed 
into air-sacs. In Ateles, however, a median air-sac is deve- 
loped from the posterior wall of the windpipe between the 
ericoid cartilage and the first ring of the trachea. A very 
remarkable modification of the hyoid and larynx takes 
place in Mycetes. The cornua of the hyoid are rudi- 
mentary, but its body is converted into a large thin-walled 
bony drum, the cavity of which communicates, beneath the 
large epiglottis, with that of the larynx. The thyroid 


cartilage is very large, and the cartilages of Wrisberg and 


Santorini are replaced by a fibrous mass, which is united 
posteriorly with its fellow of the opposite side. In addition 
to the hyoidean air-sac the ventricles of the larynx are 
dilated and prolonged upwards, coming into contact above 


_ the larynx; two pharyngo-laryngeal pouches may be added 
to these. Mycetes is famous for the distance to which its 


howling voice can be heard in the South American forests. 
Although the pollex is rudimentary and apparently func- 
tionless in Afeles, all its characteristic muscles (abductor, 
adductor, flecor brevis, and opponens) are present, except the 
long flexor. 
In Nyctipithecus the pedal interossei are jlewores breves, and 
lie on the plantar surfaces of the metatarsal bones, as in 


the Marmosets; but both the adductor hallucis and the 


transversus pedis are well developed. 


468 THE ANATOMY OF VERTEBRATED ANIMALS. 


The brain varies remarkably in different Platyrrhini. In 
Chrysothrix, the cerebral hemispheres project beyond the 
cerebellum to a greater relative extent than in any other 
Mammal, namely, by one-fifth of their total length. On 
the other hand, in Mycetes, the cerebral hemispheres 
hardly hide the cerebellum, when the brain is viewed from 
above. 

In Cebus, the outer surface of the brain is almost as 
much convoluted as in the Catarrhine Apes. Ateles has the 
external perpendicular fissure almost obliterated by the 
annectent gyri, and, so far, exhibits a higher type of brain 
than the Catarrhini; but, in Pithecia, Chrysothrie and 
Nyctipithecus, the external sulci gradually disappear, until 
the brain is almost as smooth as in the Marmosets. On 
the inner faces of the hemispheres, however, the internal 
perpendicular, the calloso-marginal, the calcarine, and 
the collateral sulci remain, while, in the interior of the 
hemispheres, the posterior cornu and the hippocampus minor 
are always present. 

The vermis of the cerebellum is large and projects beyond 
the level of the posterior margins of its hemispheres; the floc- 
culus is large and lodged in a fossa of the periotic ossifica- 
tion, as in the Marmosets. The upper ends of the pyramids 
are separated by corpora trapezoidea from the pons Varolit. 

The penis is usually terminated by a large button-shaped 
glans. The cavity of the tunica vaginalis is not shut off 
from the abdomen, and the testes lie at the sides of, rather 
than behind, the penis. The female Ateles has a long 
clitoris, which depends from the vagina. 

The Platyrrhini occur only in the Austro-Columbian pro- 
vince, and are known in the fossil state only in certain 
caves of that region. 

3. The Catarrhini—The Simiade of this division present 
a great range of variation in most respects, but they agree 
in having the partition between the nostrils narrower than 
in the Platyrrhini; in possessing a bony meatus auditorius; 


: ogee Tee 2°2 3 F 
in the dental formula 7. ag & pq P.M. 55 Mm. Sp and in 


THE CYNOMORPHA. 469 


being inhabitants of the old world. They fall into two very 
distinct groups, the Cynomorpha and the Anthropomorpha. 

a. The Cynomorpha are distinguished from the other 
group by being essentially quadrupedal and, usually, pro- 
vided with a tail, which is never prehensile. The femur and 
tibia, taken together, are longer than the humerus and the 
radius. The outer inferior incisors are not larger than the 
inner ones, but are often smaller. The crowns of the 
molar teeth present two transverse ridges, a third being 
present, in some genera, on the last inferior molar. 

All the Cynomorpha have ischial callosities, which some- 
times attain a very large size, and are brightly coloured. 

The dorsolumbar region of the spinal column is concave 
towards the ventral aspect, and the lumbo-sacral angle is 
very large. The atlas has narrow transverse processes. 
The ordinary number of dorsolumbar vertebre is nineteen, 
of which twelve, or thirteen, are dorsal; and seven, or six, 
lumbar. The middle cervical vertebre have short spines, 
which are not bifurcated at their extremities. In the pos- 
terior dorsal, and anterior lumbar, vertebre, the mammillary 
and accessory processes may be enlarged and interlock. 
The long transverse processes of the lumbar vertebre bend 
forwards. The sacrum usually contains only three an- 
kylosed vertebre. The caudal vertebre vary in number, 
from three in Inwus (where they form little more than a 
coccyx), to as many as thirty-one. In the anterior part of 
the tail the vertebre are provided with subvertebral, or 
chevron, bones. 

The thorax is laterally compressed, and the manubrium 
of the sternum is broad; but the six or seven sternebre 
which follow it are compressed and constricted. 

The skull presents a considerable range of variation. In 
the Semnopithecit and Colobi, the frontal region is rounded, 
the facial angle is comparatively large, and the ascending 
portion of the ramus of the mandible is high. In the 
Macaci and Cynocephali, on the other hand, the supra- 
orbital ridges become so much enlarged as to hide the 
forehead; and the horizontal portion of the ramus of the 


470 THE ANATOMY OF VERTEBRATED ANIMALS. 


mandible is much larger than the ascending portion, in 
accordance with the great production of the upper jaw, and 
the consequent low facial angle. In many of the Cyno- 
cephali, longitudinal osseous ridges are developed upon the 
maxille, and greatly increase the brutishness of their 
aspect. Sagittal and lambdoidal crests may appear along 
the lines of the corresponding sutures. There is no dis- 
tinct mastoid process; and the styloid process is not 
ossified. The parietal bones do not unite with the alisphe- 
noids, being separated from them by the union of the 
squamosals with the frontals. The brain case is flattened 
and elongated, and the convex roofs of the orbits project 
into it and greatly diminish the capacity of its frontal 
portion. The olfactory fosse are very deep, and sometimes 
almost tubular. The two frontal bones send thick processes 
across the base of the skull, which unite over the junction 
of the presphenoid and the ethmoid, and thus narrow the 
entrance to the olfactory fosse. The basicranial axis is 
shorter than the cerebral cavity, but is still proportionally 
long. The occipital foramen lies in the posterior sixth of 
the base of the skull, and it looks obliquely backwards and 
downwards. The premaxillo-maxillary suture never dis- 
appears until long after the second dentition is complete, 
and may persist throughout life. The palate is long and 
narrow. The nasal bones are flat, and early ankylose into 
one bone. 

The scapula is relatively longer and narrower than that 
of Man; but the spine lies at right angles to the vertebral 
border, and the supra-spinous, is much smaller than the 
infra-spinous fossa. 

The axis of the articular head of the humerus is not 
directed upwards and inwards, but upwards and backwards; 
the bicipital groove lies on the inner side; and the shaft of 
the bone is so bent that it is convex forwards. In all these 
characters the fore limb shows its relation to the function 
of support. The radius exhibits modifications which have 
the same signification. Its proximal head is transversely 
elongated, and lies somewhat in advance of the ulna, 


THE OSTEOLOGY OF THE CYNOMORPHA. A471 


articulating more largely with the humerus than in the 
higher Apes. The neck of the radius (between the head and 
the bicipital tuberosity) fits more closely to the ulna, and 
hence the movements of pronation and supination are 
restricted. 

There are nine bones in the carpus. The pisiforme is 
much elongated, making a sort of heel for the manus. To- 
gether with the cuneiforme, it furnishes an’ articular face 
for the ulna. The distal articular surface of the trapezium 
is saddle-shaped, and the pollex is usually complete, though 
short relatively to the other digits. In Colobus it is rudi- 
mentary. : 

.The pelvis is long and narrow. The ilia are narrow bones 
with much-excavated posterior and outer faces. Their 
crests generally lie opposite the transverse processes of the 
penultimate lumbar vertebra. The long axis of the ilium 
and that of the anterior ramus of the pubis cut one another 
nearly at a right angle; while the long axis of the ilium 
and that of the posterior ramus of the ischium lie nearly in 
one straight line. The symphysis pubis is very long, and 
the subpubic arch correspondingly reduced. The posterior 
ends of the ischia are everted, broad and rough, for the 
attachment of the callous pads of integument. The femur 
has around ligament. The tarsus has not more than one- 
third the length of the foot. The calcaneal process is flat- 
tened from side to side, and has a pulley-like excavation 
upon its posterior extremity. The tibial facet of the astra- 
galus is inclined slightly inwards, as well as upwards, and 
its outer edge is raised. The distal division of the tarsus, 
consisting of the cuboid and navicular, with the cunei- 
form, bones, is capable of a considerable amount of rotatory 
motion upon the astragalus and the caleaneum. The ento- 
cuneiform bone is large, and has a transversely-convex 
articular surface for the metatarsal of the hallux. Conse- 
- quently the latter (which is short, reaching to only about 
the middle of the proximal phalanx of the second digit) is 
capable of free motion in abduction and adduction. 

In the Cynomorpha, and even in the so-called “ tail-less” 


472 THE ANATOMY OF VERTEBRATED ANIMALS. 


genus, Inwus, proper caudal muscles are present. In the limbs 
there is a levator clavicule which passes from the transverse 
process of the atlas to the acromion; a dorso-epitrochlearis, 
consisting of a muscular bundle detached from the latissimus 
dorsi near its insertion, and passing to the distal and inner 
end of the humerus, or even further down; a scansorius, from 
the ventral edge of the ilium to the great trochanter, which 
sometimes becomes confounded with the gluteus minimus ; a 
special abductor ossis metacarpi quinti; anda peroneus quinti 
digiti, arising from the fibula, between the peroneus longus 
and brevis, passing behind the external malleolus, and send- 
ing its tendon to the extensor sheath of the fifth digit. 

The extensor primi internodii pollicis and the peroneus 
tertius are absent in this, as in the preceding group. 

The biceps femoris usually possesses only an ischial head, 
and the soleus arises only from the fibula. The flexor brevis 
digitorum arises partly from the tendon of the plantaris, 
where this passes over the pulley on the posterior surface 
of the calcaneal process to become continuous with the 
plantar fascia, and partly from the tendons of the long 
flexor. The transversus pedis is usually fully developed, 
but has only two heads of origin from the distal ends 
of the second and third metatarsals. The interosset pedis 
are just visible on the dorsal aspect of the foot, but none 
are, properly speaking, dorsal. None of them are penni- 
form muscles arising from adjacent sides of the metatarsal 
bones ; but they are attached, in pairs, to the plantar and 
lateral aspects of the metatarsal bones of the digits to which 
they appertain. They are inserted into the sesamoid bones, 
of which each digit has two, and into the bases of the proxi- 
mal phalanges, and give off no distinct tendons to the 
extensor sheaths. Additional muscles may arise over the 
proximal ends of the metatarsal bones, and pass to the 
three fibular digits. 

The interossei maniis are very similar to those of Man, 
being divided into a dorsal and a palmar set, and sending 
slips to the extensor sheaths of the digits, without that 
complete subdivision which is seen in the Anthropomorpha. 


THE DENTITION OF THE CYNOMORPHA. 473 


There is a complete double set of extensors in the four 
ulnar digits of the manus, the extensor minimi digiti giving 
a tendon to the fourth digit, and the eatensor indicis one to 
the third digit. The extensor ossis metacarpi pollicis gives a 
distinct slip to the trapezium, and thus precisely corre- 
sponds with the tibialis anticus, which has two tendons, one 
for the ento-cuneiform, and one for the metatarsal of the 
hallux. The flexor digitorum profundus and flexor longus 
pollicis are represented by one muscle, a slip from the ulnar 
side of the tendon of which usually goes to the pollex. 

The tendons of the flexor perforans digitorwm and flexor 
hallucis unite to form the deep flexor tendons of the pedal 
digits in very variable proportions. The flewor accessorius 
is very generally present. 

The anterior upper premolar has its outer cusp peculiarly 
modified and sharpened. The anterior lower premolar has 
the anterior margin of its crown prolonged and cutting, so 
that it works, like a scissor-blade, against the posterior edge 
of the upper canine. In the upper jaw, the premolars have 
three roots; in the lower, two. The molars in both jaws 
have four cusps connected by two transverse ridges. Some- 
times there is “heel ” behind the posterior ridge of the last 
lower molar. 


The formula of the milk dentition is d.i. — d.c. = d.m. 
— = 20; and the anterior milk molar resembles the per- 
manent premolars, while the posterior is like a permanent 
molar. 

The permanent canines make their appearance before or, 
at latest, contemporaneously with, the hindermost molar in 
both jaws. They are large and long, and are separated, by 
a well-marked diastema, from the outer incisor above, and 
from the first premolar below. 

The Cynomorpha very generally possess cheek-pouches, 
which serve as pockets for the temporary stowage of food. 
The stomach is usually simple, with a globular cardiac 
extremity and an elongated pyloric portion ; but, in Semno- 
pithecus and Colobus, the stomach is divided into three com- 


474 THE ANATOMY OF VERTEBRATED ANIMALS. 


partments, the middle of which is saceulated. A groove 
with raised edges leads from the cardiac end of the gullet 
to the middle compartment. 

The cecum, though distinct, is relatively small, and has 
no vermiform appendage. 

The liver varies much in the degree of its subdivision 
into lobes, being least divided in the Semnopitheci, and most 
in the Baboons. The innominate artery generally gives 
origin to both carotids, as well as to the right subclavian, 
the left subclavian arising directly from the arch of the 
aorta. 

When laryngeal air sacs are developed, they are not formed 
by dilatations of the lateral ventricles of the larynx; but a 
single sac, with a median aperture, is formed in the thyro- 
hyoidean space immediately beneath the epiglottis. This 
median air sac is very large, extending down over the front 
of the neck, and sending processes into the axille, in some 
Semnopitheci and Cynocephali. The right lung is usually 
four-lobed, the left two-lobed. 

The kidney has only a single papilla. 

The posterior lobes of the cerebrum project beyond the 
cerebellum in all the Cynomorpha; they are shortest in the 
Semnopitheci, and longest in the Cynocephali. The prin- 
cipal sulei and gyri which are found in the human brain 
‘ are always indicated; but the external perpendicular fissure 
is strongly marked. The posterior cornu of the lateral ven- 
tricle is large, and there is a strongly-marked hippocampus 
minor. 

There is usually, if not always, a bone in the penis, which 
is provided with two special retractor muscles. The females 
are subject to a periodical turgescence of the sexual organs, 
sometimes accompanied by hemorrhage, and comparable to 
menstruation. The placenta is often bilobed. 

b. The Anthropomorpha differ from the Cynomorpha in the 
following characters: They are especially arboreal animals, 
which habitually assume a semi-erect posture, supporting 
the weight of the fore part of the body upon the ends of 
the fingers or, more usually, upon the knuckles, There is 


——S~ a” = 2 


so” 


THE ANTHROPOMORPHA. 475 


no tail. The thigh and the leg are, respectively, shorter than 
the arm and the forearm. The dorsolumbar vertebrex are 
seventeen or eighteen in number, and their spines are not 
inclined towards a common point. They develop no inter- 
locking mammillary and accessory processes. The sacrum 
contains more than three ankylosed vertebra. The thorax 
is rather broad than laterally compressed, and the sternum 
is flattened from before backwards, and wide. The axis of 
the head of the humerus is directed more inwards than 
backwards, and the upper part of the shaft is not bent as 
in the Cynomorpha. The radius is capable of complete 
pronation and supination. 

The relative proportions of the incisor teeth are the same 
as in Man; that is to say, the inner upper incisors and the 
outer lower incisors are larger than the others. The crowns 
of the upper and lower molars have the same patterns as 
those of Man. 

The caudal muscles are small or absent. When the pollex 
has a flexor tendon, that tendon is not a slip given off from 
one common to the flexor pollicis and flexor perforans, as in 
the Cynomorpha. The plantaris does not pass over a pulley 
furnished by the calcaneal process, as in the Cynomorpha; 
and the fle«or brevis has an origin from that process. The 
peroneus quinti digiti has not been observed. 

There are three well-marked genera of Anthropomorpha— 
Hylobates, Pithecus, and Troglodytes; and perhaps a fourth, 
Gorilla, may be advantageously separated from the last- 
named. 

Pithecus, the Orang, has the smallest distributional area, 
being confined to the islands of Borneo and Sumatra; Hy- 
lobates, the Gibbons, of which there are several species, is 
found over a considerable area of Hastern Asia and the 
islands of the Malay Archipelago. The Chimpanzee and 
Gorilla are met with only in the intertropical parts of West 
Africa. 

The Gibbons are those Anthropomorpha which are most 
nearly allied to the Cynomorpha. They possess ischial cal- 
losities, and the nails of the pollex and hallux, only, are 


476 THE ANATOMY OF VERTEBRATED ANIMALS. 


broad and flat. The arms are so long that the points of 
the fingers readily touch the ground when the animal stands 
upright, as it very readily and commonly does. The 
Gibbons also run with great swiftness, putting the sole of 
the foot flat on the ground and balancing themselves with 
their long arms. Nevertheless, they are essentially arboreal 
animals, leaping from bough to bough of the trees in the 
forests which they frequent with marvellous force and 
precision. The manus is longer than the pes, and the ante- 
brachium considerably longer than the brachium. The 
Gibbons do not exceed three feet in height; their heads 
are small, and their bodies and limbs remarkably slender. 

None of the other Anthropomorpha have callosities, and 
the nails of all the digits are flattened. They are all heavier 
in make, with proportionally shorter limbs and larger heads 
than the Gibbons. In the Orangs, which rarely attain a 
stature of more than four feet and a half, the arms are very 
long, their span, when outstretched, being nearly double the 
height of the animal. The brachium and the antebrachium 
are equal in length. The long and narrow pes is longer 
than the equally-narrow manus, and the sole cannot be 
placed flat upon the ground, but the animal rests upon the 
outer edge of the foot when it assumes the erect posture. 
This posture, however, is quite unnatural, and the Orangs 
cannot run as the Gibbons do, but swing themselves along 
upon their long arms, as it were upon crutches. 

The pollex and the hallux are both short, the latter 
remarkably so; and the hallux is not uncommonly devoid 
of anail. The palmar and plantar aspects of the digits 
are naturally concave, and they cannot be completely 
straightened. 

The Chimpanzee attains a stature somewhat greater than 
that of the average Orang. The span of the arms is about 
half as much again as the height. The antebrachium is 
about as long as the brachium. The manus is equal to, or 
a little longer than, the pes; and these parts of the limbs 
are not so elongated, or so curved, as the corresponding parts 
of the Orang. The sole can be readily placed flat upon the 


; 


ae ee eee eer 


THE ANTHROPOMORPHA. 477 


ground, and the Chimpanzee easily stands or runs erect. 
But his favourite attitude is leaning forward and supporting 
himself on the knuckles of the manus. Both the hallux and 
the pollex are well developed and possess nails. 

The Gorilla exceeds five feet in height and may reach 
five feet six inches. The span is to the height as about 
three to two. The brachium is much longer than the ante- 
brachium. The pes is longer than the manus, and both 
are much broader than in the other Anthropomorpha. In 
consequence of this circumstance and of the greater develop- 
ment of the heel, the erect posture is easily maintained, but 
the ordinary attitude is the same as that assumed by the 
Chimpanzee. The hallux and the pollex have well-deve- 
loped nails. The basal phalanges of the three middle 
digits of the foot are bound together by the integument. 

With respect to the skeleton in the Anthropomorpha, the 
Gibbons have the spinal column nearly straight, with 
a very open vertebro-sacral angle. In the Orangs the 
dorsolumbar vetebre form a curve, which is nearly as 
much concave forwards as in a new-born child. In the 
Chimpanzee the spinal column begins to exhibit the 
curvatures which are characteristic of the adult human 
subject ; and these are still more marked in the Gorilla. 

The spinous process of the second cervical vertebra is 
bifurcated in the Chimpanzee, but this human character 
does not appear in the others. 

In the Gibbons there are usually eighteen dorsolumbar 
vertebre; but in the other Anthropomorpha the number is 
ordinarily seventeen, as in Man, or may be reduced to 
sixteen. The Orang has the human number of twelve 
pairs of ribs; but the Chimpanzee and Gorilla have thirteen, 
and the Gibbons may possess fourteen pairs of ribs. The 
thorax is wide, and the sternum broad and flat. In the 
Orang it may ossify from a double longitudinal series of 
centres, as sometimes happens in Man. 

In the Gibbons the transverse processes of the last lumbar 
vertebra are not exceptionally broad, and do not unite with 
the ilia. But in both the Chimpanzee and Gorilla they 


478 THE ANATOMY OF VERTEBRATED ANIMALS. 


are wide, and become more or less closely connected with 
the ilia. The last lumbar vertebra may become ankylosed 
with the sacrum in the Gorilla. All these conditions of 
the last lumbar vertebra are occasionally met with in Man. 

The sacrum is broad, and contains not fewer than five 
ankylosed vertebre, but its length always exceeds its 
breadth (whereas its breadth is equal to, or exceeds, its 
length, in Man), and its anterior curvature is but slight. 
The short coccyx is made up of not more than four or five 
vertebre. In the skull, the proper form of the brain-case 
is always more or less disguised in the adult males, by the 
development of crests for muscular attachment, or of the 
orbits and the supraorbital ridges. In the Gibbons and 
Chimpanzees, the latter are large, but the sagittal crest is 
absent, and the lambdoidal small. In the Orang, the brow 
ridges are small, so that the true form of the forehead is seen 
better than in the other Apes, but the sagittal and lamb- 
doidal cfests are strong. In the old male Gorilla the sagittal 
and lambdoidal crests, and the supraorbital ridges, are 
alike enormous. The frontal sinuses are large, and extend 
into the brow ridges both in the Gorilla and Chimpanzee. 
The jaws are largest in proportion to the brain case in the 
Gorilla and the Orang; smallest in some varieties of Chim- 
panzee. 

In all the Anthropomorpha the transverse is much less 
than the longitudinal diameter of the cranial cavity. The 
roofs of the orbits project into the frontal portion of the 
brain case, and diminish its capacity by causing its floor to 
slope from the middle line obliquely upwards and outwards. 
The occipital foramen is situated in the posterior third of 
the base of the skull, and looks obliquely backwards and 
downwards. The frontals meet in the base of the skull 
over the ethmo-presphenoidal suture in the Gibbons and in 
the Gorilla, as in the Baboons; but not in the Chimpanzee 
or the Orang. The alisphenoids unite suturally with the 
parietals, as is the rule in Man, in the Gibbons and (usually) 
in the Orangs; but, in the Chimpanzee, the squamosal unites 
with the frontal and separates the alisphenoidfrom the parie- 


THE ANTHROPOMORPHA. 479 


tal, as happens, exceptionally, in Man. Thenasal bones are 
flat and early ankylosed together, in the Gibbons, Orangs, and 
Chimpanzees. In the Gorilla the nasal bonesare distinctly 
convex from side to side, and rise above the level of the face. 
None of these Apes has a spina nasalis anterior ; and, only in 
the Siamang, is there a rudimént of the mental prominence 
in the mandible. The premaxillo-maxillary suture persists 
beyond the completion of the second dentition in all but 
the Chimpanzee, in which it disappears before that period. 
The epiotic region is never developed into a distinct 
mastoid process; and there is an ossified styloid process 
only occasionally in the Orangs. The palate is long and 
narrow, the alveolar margins being nearly parallel, or even 
diverging anteriorly. The zygomatic arches are strong, 
wide, and curved in two directions. 

The proportion of the length of the basi-cranial axis to 
that of the cerebral cavity, does not fall lower than the ratio 
of 10 to 17 in any of the Anthropomorpha. 

The body of the hyoid approaches the form of that of 
Man most nearly in the Orang. In the other genera it is 
more excavated posteriorly. 

The scapula of the Orang is most like that of Maun, es- 
pecially in the proportion of the supra- and infra-spinous 
fosse, in the proportional length of the anterior and the 
posterior borders, and in the angle made by the spine with 
the vertebral margin. In the other genera the posterior 
border is longer in proportion than in Man, and the spine 

_ of the scapula cuts the vertebral margin more obliquely. 
_ After the Orang’s, the scapula of the Gorilla comes nearest 
_ to that of Man. 
_ On the other hand, the long and straight clavicle of the 
Orang is least like that of Man. 
The head of the humerus loses the backward inclination 
' which it has in the lower Apes, and becomes directed up- 
wards and inwards, as in Man. The radius and ulna are 
curved, and leave a wide interosseous space. There are 
nine bones in the carpus in both Hylobates and Pithecus, 
but only eight in the Chimpanzee and Gorilla. In Hylo- 


—_——— > |S 


480 THE ANATOMY OF VERTEBRATED ANIMALS. 


bates the articular surface presented by the trapezium 
for the pollex is almost globular. It is evenly convex in 
the Chimpanzee; but, in the Gorilla, it has the characteris- 
tically human saddle shape. The pollex is longest and 


strongest in proportion in Hylobates; its length in propor- | 


tion to that of the manus being in H. syndactylus as three 
to seven. In the Gorilla, the pollex has rather more than one- 
third the length of the manus; in the Orang and Chim- 
panzee it has about one-third the length of the manus. 

The pelvis differs but little from that of the Cynomorpha 
in Hylobates. In the other genera the pelvis is still 
elongated. The antero-posterior diameter of the brim of 
the pelvis greatly exceeds the transverse, the tuberosities of 
the ischia are strongly everted, and the pubic symphysis is 
very long, the arch being correspondingly reduced; but 
the ilia are wider and more concave forwards in the Chim- 
panzee, than in the Orang, and in the Gorilla than in either. 

In the female Chimpanzee, which is of about the same 
size as the male, the dimensions of the basin of the pelvis 
and of its outlets, are greater than in the male, though the 
general form and absolute length of the pelvis are the same 
in the two sexes. The female Gorilla is much smaller than 
the male, and the pelvis is shorter in proportion, but the 
intersciatic measurement of the outlet is absolutely as 
great as in the male, and the transverse diameter of the 
brim is nearly as great. As, at the same time, the antero- 
posterior diameter is much shorter, the brim of the pelvis of 
the female is much more round. The female Orangs, also, 
are smaller than the males. The basin of the pelvis is 
relatively, but not absolutely, larger in all its dimensions, 
and the brim rounder. 

The femur of the Orang has no round lgament, and 
differs in this respect from the same bone in the other An- 
thropomorpha. The femur of the Gorilla resembles that of 
Man, most especially in the projection of the articular surface 
of the inner condyle beyond the outer. 

The length of the whole foot to that of the tarsus is, in 
Hylobates, as thirty-five to ten, and the proportion is about 


THE FOOT IN THE ANTHROPOMORPHA. 481 


the same in the Orang; in the Chimpanzee it is as twenty- 
four to ten; and, in the Gorilla, about the same (twenty- 
three to ten in the specimen measured). 

The hallux has not more than one-fourth of the length 
of the foot in the Orang; in the Gorilla less than five- 
twelfths; in the Chimpanzee and in Hylobates a little more. 

In the second digit of the pes of the Orang and the 
Chimpanzee, the phalanges, taken together, are longer than 
the metatarsal bone of the digit; in the Gorilla, they are 
about equal in length to the metatarsal. The calcaneal 
process is longest, strongest, and broadest in the Gorilla. 
In the astragalus the articular surface for the tibia is 
broadest in the Gorilla; but, in this Ape, as in the others, it 
is inclined a little inwards when the foot is in its natural 
position; and the surface for the external malleolus is 
oblique, and looks upwards as well as outwards. 

It is a mistake, however, to suppose that the disposition 
of these surfaces has anything to do with the more or less 
marked tendency of the plantar surface to turn inwards, 
and of the outer edge of the pes to be directed downwards, 
which is observable in all the Anthropomorpha. This 
tendency is the result of the free articulation between the 
scaphoid and the cuboid, on the one hand, and the as- 
tragalus and the calcaneum on the other; the consequence 
of which is that the distal portion of the pes, with the first- 


mentioned bone, being pulled by the tibialis anticus, easily 


a 


rotates round its own axis, upon the surface presented by 
the astragalus and calcaneum. This ready inversion of the 
sole must as much facilitate climbing, as it must interfere 
with the steadiness of the foot in walking. 

The distal surface of the entocuneiform is much inclined 
inwards in all the Anthropomorpha, and is convex from side 
to side, or subcylindrical. The metatarsal bone of the 
hallux presents a corresponding articular concavity to this 
surface, and has a great range of motion in adduction and 
abduction. The inward inclination of the articular facet 
of the entocuneiform, and its consequent separation from 
the facet upon the mesocuneiform for the second digit, is 

21 


482 THE ANATOMY OF VERTEBRATED ANIMALS. 


greatest in the Orang, in which the hallux is habitually 
directed at right angles to the long axis of the foot. The 
distal phalanx of the hallux is not unfrequently absent in 
the Orang. 

All the Anthropomorpha possess certain muscles which 
are not usually found in Man, though they may occur as 
varieties in the human subject. These are the levator 
clawicule, the dorso-epitrochlearis, the scansorius,* and the 
abductor ossis metacarpi quinti digiti. They are also devoid 
of two muscles which are usually present in Man—the ev- 
tensor primi internodii pollicist and the peroneus tertius. 
The former of these is sometimes, and the latter frequently, 
wanting in the human subject. 

The flexor accessorius appears to be regularly absent in 
Hylobates and Pithecus, and, in the majority of cases, in the 
Chimpanzee. The transversus pedis seems to be absent in 
the Orang, but it is present in the other Anthropomorpha. 

Many muscles which exist both in these Apes and in Man 
have different origins in the former. Thus, the soleus 
has only a fibular head, and takes no origin from the | 
tibia. The flexor brevis digitorum pedis never arises 
altogether from the caleaneum, but a large proportion 
of its fibres spring from the tendons of the deep flexors. 
The calcaneal head furnishes the tendons for the second, 
or the second and third, digits. The interosseous muscle 
which lies on the tibial side of the middle digit of the 
pes, usually arises from the fibular side of the second 
metatarsal as well as from the tibial side of its own meta- 
tarsal, and its origin lies on the dorsal side of that of the 
fibular interosseous muscle of the second digit. Hence, of 
the so-called dorsal interossei (or interosset which are visible 
on the dorsal aspect of the pes) two belong to the middle 
digit, and one, to the second and fourth digits respectively ; 
which is the same arrangement as that which obtains in the 

* Not actually described in the Gorilla, and absent in some Chim- 
pt The former muscle is said to be present by several anatomists 


in the Chimpanzee and other Apes ; but what they have taken for it 
is the metacarpal division of the eatensor ossis metacarpi. 


THE MYOLOGY OF THE ANTHROPOMORPHA. 483 


manus. The flexor pollicis is more or less closely connected 
with the flexor communis perforans, or with that part of the 
muscle which goes to the index digit. The connection is 
slightest in Hylobates, the origins of the two muscles, only, 
being united. It is most extensive in the Orang, in which 
no tendon goes to the pollex. The same complete loss 
of the flexor pollicis, as a thumb muscle, occasionally takes 
place in the Gorilla; but in this animal, as in the Chimpan- 
zee, the rule appears to be, that the flexor pollicis unites at 
its origin with part of the flexor perforans, and that the 
fleshy fibres converge to a common tendon which divides into 
two, one for the pollex and the other for the index. In 
Hylobates, the short head of the biceps brachii arises from the 
pectoralis major, and the adductor hallucis and transversus 
pedis form but one muscle. 

The flexor longus hallucis takes an origin from the ex- 
ternal condyle of the femur in the Orang; and the pecto- 
ralis major arises by three distinct slips. 

Some of the muscles in the Anthropomorpha differ in 
their insertion, or in the extent to which they are sub- 
divided, from what is usual in the corresponding muscles of 
Man. Thus the extensor ossis metacarpi pollicis ends in two 

. distinct tendons; one for the trapezium, and the other for 
the base of the metacarpal bone of the pollex. That part 
of the tibialis anticus which goes to the metatarsal of the 
hallux is usually very distinct, and is sometimes reckoned 
as a separate muscle, the abductor longus hallucis. 

In the Gibbons and in the Orang, there is a complete set 
of deep extensors for the four ulnar digits, the tendons of 
the eatensor indicis and extensor minini digiti subdividing 

_ to supply the third and fourth digits. 

Inthe Gorilla and Chimpanzee each of these muscles have 

but a single tendon, as is the usual arrangement in Man, 

_ The interossey of the hand are each divided into two 

- muscles with distinct tendons—a flezor brevis primi inter- 
nodii and an extensor brevis tertii internodii. ‘The division is 

less obvious in the Orang than in the other Anthropo- 
morpha. 


—— 


484. THE ANATOMY OF VERTEBRATED ANIMALS. 


In Hylobates, the tendon of the flexor perforans pedis goes 
only to the fifth digit, and is not directly connected with 
that of the flexor longus hallucis, which supplies the other 
four digits. In the Orang, also, the tendons of the two 
muscles are separate; but the flexor perforans supplies the 
second and the fifth digits, and the flecor hallucis the third 
and fourth. It gives no tendon to the hallux. In both 
the Chimpanzee and the Gorilla, a very large tendon is 
given to the hallux by the flexor hallucis, and it also supplies 
the third and fourth digits. The tendon of flexor longus 
digitorum is but slightly connected with that of the flexor 
hallucis, and its divisions go to the second and fifth toes. 
In both the manus and the pes of Hylobates a muscle occurs 
which is not, at present, known in any other Mammal. It 
arises from the second metacarpal or metatarsal bone, and 
is inserted by along tendon into the pre-axial side of the 
ungual phalanx of the second digit; it may be termed “ ab- 
ductor tertii internodii secundi digiti.” 

The Orang, in like manner, stands alone in possessing a 
small, but distinct opponens hallucis.* 

The volume of the brain, in the Orang and in the Chim- 
panzee, is about twenty-six or twenty-seven cubic inches; or 
about half the minimum size of a normal human brain. In 
the Gorilla, the volume rises to near thirty-five cubic inches. 
In the Gibbons the brain is very much smaller; and the 
Siamang, among these, is remarkable for the short posterior 
lobes of the cerebrum, which, in this anthropomorphous Ape, 
do not overlap the cerebellum, as they do in all the others. 

The cerebral hemispheres are higher in proportion to 
their length in the Orang than in the other Anthropomorpha; 
but, in all, they are elongated and depressed, as compared 
with those of Man. The frontal lobes taper off anteriorly, 
and their inferior surfaces are excavated from without 
downwards and inwards, in correspondence with the pro- 

* It must be borne in mind that these statements respecting the 
myology of the Anthropomorpha are based upon my own dissections 
(sometimes supplemented by those of Duvernoy and other ana- 


tomists) of particular specimens. Endless varieties will no doubt be 
met with by those who carry their inquiries further. 


THE BRAIN IN THE ANTHROPOMORPHA. 485 


jection of the upwardly convex roofs of the orbits into 
the cranial cavity. The posterior cornu of the lateral 
ventricle is always well developed, and contains a pro- 
minent hippocampus minor and eminentia collateralis. An 
occipito-temporal or “external perpendicular” sulcus is 
always present. It is most nearly obliterated in the Orangs. 
All the gyri of the human brain are represented in the 
cerebral hemispheres of the Chimpanzee; but they are 
simpler and more symmetrical, and larger in proportion to 
the brain (See Figs. 21 and 22). The fissure of Sylvius is less 
inclined backwards, and that of Rolando is placed more 
forwards than in Man. The insula has simpler and fewer 
radiating sulci, and is not completely hidden by the temporal 
lobe. Only the second, third, and fourth annectent gyri 
appear upon the surface. The first remains folded upon 
itself, and gives rise to the characteristically simian occipito- 
temporal or external perpendicular sulcus. The occipito- 
parietal sulcus, on the inner face of the hemisphere, is 
much more nearly perpendicular than in the human brain. 
The corpus callosum is relatively smaller; the septum 
lucidum is very thick, and the pre-commissural fibres are 
well developed. The vermis is small in proportion to the 
lateral lobes of the cerebellum, and the flocculi are rela- 
tively small, and lie below the latter. 

The whole cerebellum is: larger in proportion to the 
cerebral hemispheres; the latter being to the former, as 
83 tol in Man, but as 5? to 1 in the Chimpanzee.* The 
nerves are larger in proportion to the brain than in Man. 
There are no corpora trapezoidea, such as exist in the lower 
Mammals, and the corpora albicantia are double. 

In all the Anthropomorpha, the inner incisors are larger 
than the outer, in the upper jaw; smaller, in the lower jaw. 
There is a diastema, though it is often but small in the 
female Chimpanzees. The canines are large and strong, 
and may be grooved longitudinally on their inner sides. 

* Tt must be recollected that the brains of young anthropomorphous 


Apes, only, have been examined. Perhaps this has to do with the 
absence ot mineral deposits in the pineal gland of the Apes. 


486 THE ANATOMY OF VERTEBRATED ANIMALS. 


The premolars have three roots in the upper jaw, two in the 
lower. The crowns of the middle molars, above, have four 
cusps, and an oblique ridge which extends from the antero- 
external to the postero-internal cusp; and those of the middle 
molar, below, have five cusps, asin Man. The crown of the 
anterior premolar in the lower jaw is pointed, and has a 
long, sharp, oblique anterior edge as in the Cynomorpha. 

In the Gibbons, the permanent canine emerges contem- 
poraneously with, or before, the last molar; but, in the other 
Anthropomorpha, the last permanent canine is cut, ordinarily, 
only after the appearance of the last molar. 

In the Orang the circumyallate papille of the tongue are 
arranged ina VY, as in Man. In the Chimpanzee they are 
disposed like a J, with the top turned forwards. The 
Chimpanzee and the Siamang have an uvula, but the Orang 
has none. The stomach of the Chimpanzee is very like that 
of Man; but in the Orang the organ is more elongated, 
with a round cardiac and more tubular pyloric portion. 
An appendia vermiformis is found in the cecum of all four 
genera. In the Chimpanzee and Gorilla, the origin of the 
great arteries from the arch of the aorta takes place as in 
Man. In the Orang, they are sometimes disposed as in 
Man; while in other specimens the left carotid comes off 
from the innominata, and only the subclavian of the left 
side arises directly from the aorta. In Hylobates, the latter 
arrangement appears to obtain. 

The kidney has only a single papilla in Hylobates and | 
Pithecus. 

Only one species of Hylobates, namely, the Siamang, is 
known to possess a laryngeal sac. This is globular, and 
communicates by two apertures, situated in the thyrohyoid 
membrane, with the larynx. In the Orang, Chimpanzee, 
and Gorilla, enormous air sacs result from the dilatation 
of the lateral ventricles of the larynx. These dilatations 
extend down, in front of the throat, on to the thorax and 
even into the axille, and sometimes open into one another 
in the middle line. 

In the adult male Chimpanzee the penis is small and 


RELATIONS OF ANTHROPOMORPHA TO MAN. 487 


slender, and terminates in a narrow and elongated glans. 
The testes are very large, and the communication between 
the tunica vaginalis and the peritoneum is completely closed. 
The glans penis of the Gorilla is button-shaped. In the 
Orang it is cylindrical, and the testes are situated close to the 
inguinal canal, which has been found open on one side, and 
closed on the other. An os penis is developed in the males. 

The females have the clitoris large, and the uterus, which 
is undivided into cornua, resembles that of the human sub- 
ject. The placenta of a Chimpanzee fetus, 113 inches long, 
was simple, rounded, 33 inches in diameter, and 0°6 inch 
thick in the centre. The umbilical cord was inserted near 
one of its edges. 

The proportions of the limbs to one another and to the 
body do not sensibly change after birth; but the body, 
limbs and jaws, enlarge to a much greater extent than the 
brain-case. 

The amount of variation in the characters of the skull 
among the Chimpanzees, Gorillas, and Orangs, is exceed- 
ingly remarkable, especially if taken in connection with 
their very limited areas of distribution. 

Of the four genera of the Anthropomorpha, the Gibbons 
are obviously most remote from Man, and nearest to the 
Cynopithecini. 

The Orangs come nearest to Man in the number of the 
ribs, the form of the cerebral hemispheres, the diminution 
of the occipito-temporal sulcus of the brain, and the ossified 
styloid process; but they differ from him much more widely 
in other respects, and especially in the limbs, than the Go- 
villa and the Chimpanzee do. 

The Chimpanzee approaches Man most closely in the 
character of its cranium, its dentition, and the proportional 
size of the arms. 

The Gorilla, on the other hand, is more Man-like in the 
proportions of the leg to the body, and of the foot to the 
hand; further, in the size of the heel, the curvature of the 
spine, the form of the pelvis, and the absolute capacity of 
the cranium. ; 


488 THE ANATOMY OF VERTEBRATED ANIMALS. 


ce. The Anthropide are represented by the single genus 
and species, Man, and they are distinguished from the 
Simiade, and especially the Anthropomorpha, by the follow- 
ing characters : 

In progression on the ground, the erect posture is the 
easiest, and no assistance is given by the arms, which are 
shorter than the legs. After birth, the proportions of the 
body alter in consequence of the legs growing faster than 
the rest of the body. In consequence, the middle point of 
the height of the body—which, at birth, is situated about the 
umbilicus—becomes gradually lower, until, in the adult 
male, it is as low as the symphysis pubis. 

In the manus, the pollex is strong and long, reaching to 
the middle of the basal phalanx of the index digit. In the 
pes, the tarsus takes up half the length of the foot; the 
ealcaneal process is long, and expanded posteriorly. The 
hallux has half the length of the foot, and is nearly as 
long as the second digit; and its mobility in adduction and 
abduction is slight, compared with that of the hallux of 
the other Primates. 

Hair is more abundant upon the crown of the head; 
and, usually, in the axille, the pubic region, and the front 
part of the thorax, than elsewhere. 

In the new-born infant the whole dorso-lumbar region of 
the spine is concave forwards, and the vertebro-sacral an- 
gulation is slight; but, in the adult, the spinal column is 
concave forwards in the thoracic, and convex forwards in 
the lumbar, region, mainly in consequence of the dispo- 
sition of the elastic ligaments which connect the faces and 
the arches of the vertebre. There is a strongly-marked 
vertebro-sacral angulation. Normally, there are twelve 
dorsal, five lumbar, five sacral, and four coccygeal vertebre, 
and the transverse processes of the last lumbar vertebra 
are not expanded or directly connected with the ilia; but, 
in these respects, variations occur. 

The spinous processes of the middle cervical vertebrae 
are much shorter than the seventh, and are usually bifur- 
cated. The breadth of the sacrum is greater than its 


THE ANTHROPIDZ. 489 


length. In the skull, the occipital condyles lie within the 
middle fifth of the base, and the occipital foramen looks 
downwards, and either a little forwards or but slightly back- 
wards. Neither sagittal nor lambdoidal crests are developed, 
but the mastoid processes are distinct, and generally con- 
spicuous. The supraorbital ridges are never so largely 
developed as in some of the Anthropomorpha. The orbits 
and the jaws are relatively smaller, and situated less in 
front of, and more below, the fore-part of the brain-case. A 
spina nasalis anterior is almost always present ;* and, in the 
profile view of the face, the nasal bones project more beyond 
the level of the ascending process of the maxilla than they 
do in any Ape. The palate is broader and its contour more 
arched than in any of the Anthropomorpha. Its posterior 
margin is ordinarily produced in the middle line into a 
spina nasalis posterior, and the palato-maxillary suture is 
directed transversely. 

The distance between the zygomata is either less than the 
greatest transverse diameter of the calvaria, or exceeds it 
but little. The malar, is deeper than the squamosal, portion 
of the zygoma, and the upper edge of the zygoma is but 
little curved. 

The post-glenoidal process of the squamosal is small, 
while the auditory foramen is vertically elongated, its 
anterior wall being more or less flattened. 

The interorbital space occupies about one-fourth of the 
interval between the outer walls of the orbits. 

The planes of the orbital surfaces of the ethmoid bones 
(ossa plana) are nearly parallel with one another. 

The symphysis of the lower jaw has a mental promi- 
nence. The length of the cerebral cavity is more than 
twice that of the basi-cranial axis. 

After birth, no trace of the premaxillo-maxillary suture 
remains upon the face, though it may persist in the palate. 


* The only human skull in which I have been able to find no trace 
of the existence of the anterior nasal spine, is that of an Australian, 
which, some years ago, I presented to the Museum of the Royal College 
of Surgeons, 


490 THE ANATOMY OF VERTEBRATED ANIMALS. 


The nasal suture usually persists, and the direction of the 
fronto-nasal suture is nearly transverse. 

The cranio-facial angle* does not exceed 120°, and in the 
higher races of mankind does not go much beyond 90°. 

The supra-orbital plates of the frontal bones project but 
little into the frontal region of the brain-case, and they are 
almost horizontal, instead of being strongly inclined up- 
wards and outwards, as they are in the Anthropomorpha. 
The cribriform plate is long and wide, and the ecrista galli is 
usually prominent. The capacity of the brain-case of a 
healthy adult is invariably more than forty cubic inches, 
and may rise to more than a hundred cubic inches. 

The scapula is broad in proportion to its length, and 
its spine cuts its vertebral edge nearly at right angles. 
The ilia are very broad; their inner faces present a well- 
marked concavity, and their crests an §-shaped curvature. 
A line drawn from the centre of the articular surface of 
the sacrum to the centre of the acetabulum makes nearly 
a right angle with the chord of the arc offered by the 
anterior face of the sacrum. In all the Anthropomorpha 
this angle is much more open. 

The tuberosities of the ischia are hardly everted. The 
symphysis pubis is comparatively short, and the subpubic 
arch well marked. The width of the whole pelvis, from 
one iliac crest to the other, is greater than its height, which 
is the reverse of what obtains in the Apes. The transverse 
diameter of the brim is usually not exceeded by the antero- 
posterior diameter, though the contrary proportion occa- 
sionally obtains. The female pelvis is more spacious, and 
has a wider subpubic arch than the male. 

The proximal articular surface of the astragalus looks 
almost directly upwards, and hardly at all inwards, when 
the sole is flat upon the ground; and the lateral facets are 
more nearly at right angles to this surface than in any 
Ape. The inner and outer malleoli are stronger and 
more downwardly produced. The calcaneal process is 
thick, strong, enlarged at its hinder end, and not incurved 

* See p. 496 for the explanation of this term. 


THE FOOT IN MAN. 491 


inferiorly, but produced into two tuberosities on which the 
heel rests. The form and disposition of the astragalar, 
navicular, and calcaneo-cuboid articulations are such that 
the distal moiety of the tarsus is capable of only a slight 
rotatory motion upon the proximal portion. 

The distal articular surface of the ento-cuneiform bone 
is very nearly flat, though it has a slight convexity from 
side to side, and is irregularly concavo-convex, from above 
downwards. The comparatively slight mobility of the 
metatarsal bone of the hallux arises partly from this circum- 
stance, partly from the fact that the proximal articular 
surfaces of the four outer metatarsal bones are not 
perpendicular to the axes of those bones, but are ob- 
liquely truncated, from the tibial side, backwards, to the 
fibular side. Hence the four outer metatarsal bones, instead 
of diverging widely from the hallux as they would do 
if their axes were perpendicular to the distal facets of the 
meso- and ento-cuneiform and cuboid bones, take a direc- 
tion more nearly parallel with the metatarsal of the hallux, 
and the base of the second metatarsal, as it were, blocks the 
latter, in adduction. The hallux thus loses most of its 
prehensile functions ; but, in exchange, it plays an important 
part in supporting the weight of the body, which, in the 
erect position, falls on three parts of the pes; namely, 
the heel, the outer edge, and the integumentary pad which 
stretches beneath the metatarso-phalangeal articulations, 
from the hallux to the fifth digit. 

In the infant, the sole naturally turns inwards, and the 
digits (especially the hallux) retain much of their mobility. 

The only muscles which exist in Man, but have not yet 
been found in any Ape, are the eatensor primi internodi 
pollicis and the peroneus tertius. 

The only peculiarities in the origin of muscles which 
ordinarily obtain in Man, and have not yet been found in 
the Apes, are—the complete separation of the flexor pollicis 
longus from the flexor digitorum perforans; the presence of a 
tibial, as well as of a fibular, origin of the soleus; the 
origin of all four heads of the flexor brevis digitorwm pedis 


492, THE ANATOMY OF VERTEBRATED ANIMALS. 


from the caleaneum; the origin of the fibular interosseus 
of the second digit of the pes from the middle metatarsal, 
on the dorsal side of the tibial interosseus of the middle 
digit. The result of the last-mentioned arrangement is 
that the second digit of the pes has two “ dorsal” interossei, 
like the third digit of the manus. In the Apes the interosset 
of the second digit are generally arranged in the same way 
in both manus and pes. 

The tendons of the flexor hallucis longus and flewor digi- 
torwm perforans are usually more closely connected in the 
sole of the foot in Man, than in the Anthropomorpha. But 
it is to be noted that all the apparently distinctive pecu- 
larities of the myology of the Anthropomorpha are to be 
met with, occasionally, as varieties in Man. 

In the brain of Man, the only distinctive features, apart 
from its absolute size (55 to 115 cubic inches), are the 
filling-up of the occipito-temporal fissure; the greater 
complexity and less symmetry of the other sulci and gyri; 
the less excavation of the orbital face of the frontal lobe; 
and the larger size of the cerebral hemispheres, as com- 
pared with the cerebellum and the cerebral nerves. 

There is no diastema, though the summits of the canines 
project, slightly, beyond the level of the other teeth. The 
premolars have not more than two roots, and the anterior 
edge of the crown of the anterior lower premolar is not 
prolonged andsharp. The permanent canine tooth emerges 
before the second molar. 

The penis is devoid of a bone (though a prismatic carti- 
laginous body has occasionally been found in the centre of 
the glans), and its glans has a different shape from that of 
any of the Anthropomorpha. The vulva looks downwards 
and forwards, and the clitoris is comparatively small. 

The changes in the proportions of the different parts of 
the body, at different periods of intra- and extra-uterine 
life, are very remarkable. In a fcetus an inch and a half 
long, from the vertex to the heel, the head takes up from 
one-third to one-fourth of the entire length. The arms and 
legs are of about the same length, and are shorter than the 


THE LAWS OF GROWTH IN MAN. 493 


spine. The fore arm is about as long as the upper arm, 
and the leg as the thigh. The manus and pes are very 
similar in size andform; and neither pollex, nor hallux, are 
so different from the other digits as at later periods. Ina 
fcetus rather more than five inches high, the head occupies 
afourth of the entire height; the arms are longer than the 
spine by one-sixth of their whole length, and are a little 
longer than the legs. The fore arm is about as long as the 
upper arm, and the thigh is a little longer than the leg. 
The manus and pes are about equal in length. Ina fetus 
eight and a half inches high, the head measures less than a 
fourth of the whole height; the arms are longer than the 
spine by a fourth of their whole length, and they are longer 
than the legs. ‘The extremities of the digits reach down 
to the knee when the body is erect. 

At full term, the height of the head of the human fetus 
is rather less than a fourth that of the whole body, and the 
legs are longer than the arms. The arm is longer than the 
fore arm, and the thigh than the leg. The hands and 
the feet are still about equal in length. 

Thus it would appear that, while the head grows more 
slowly than the rest of the body, throughout the period of 
gestation, after the embryo has attained more than two 
inches in length; the arms grow proportionally quicker 
than the body and legs, in the middle of gestation, when 
the proportions most nearly resemble those of the Anthro- 
pomorpha. Inthe latter part of the period of gestation the 
legs gain on the arms, and the proximal segments of the 
limbs on the distal ones. After birth these changes are con- 
tinued. The adult has, on the average, three and a half 
times the height of the new-born child, and his arms are 
elongated in the same proportion. But the head is only 
twice as large, while the legs of the adult are five times as 
long as those of the child. At all ages after birth, the 
distance between the extremities of the digits of the out- 
stretched arms is equal to the height in average Europeans. 

Sexual differences, independent of the genitalia, are per- 
ceptible at birth ; and the female infant is, as a rule, slightly 


A494, THE ANATOMY OF VERTEBRATED ANIMALS. 


smaller than the male. These differences become more 
marked at, and subsequent to, puberty ; and are seen in the 
smaller stature of the female, the larger size of the head 
in proportion to the stature, the shorter thorax, the longer 
abdomen, and the shorter legs; so that the middle point of 
the stature of the female is nearer the umbilicus than in 
the male. The hips are wider in proportion to the shoul- 
ders, whence the femora are more oblique. The ridges and 
muscular processes of all the bones are less marked, and 
the frontal contour of the skull is more sharply angulated. 
When the peculiarities of the female sex are not connected 
with reproduction, they may be said to be infantile. 

The different persistent modifications or “races” of man- 
kind present a very considerable amount of wariation in their 
anatomical characteristics. The colour of the skin varies 
from a very pale reddish brown—of the so-called “ white” 
races—through all shades of yellow and red browns, to olive 
and chocolate, which may be so dark as to look black. 

The hair differs much in its character, having sometimes 
a circular, sometimes an oval or flattened transverse section, 
and presenting all varieties, from extreme length and 
straightness to short, crisp wool. 

The hair on the scalp is longer than that elsewhere; and 
it is very often, but not always, longer in the female. Hair 
upon the face and body is scanty in most races, and almost 
absent, except in the eyebrows, in some; but in others it 
becomes greatly developed over the lips, chin, and sides of 
the face, on the thorax, abdomen, and pubes, in the axille, 
and sometimes, though more rarely, upon the rest of the 
body and limbs. When hair is developed upon the limbs 
the points of the hairs of the arm and fore arm slope 
towards the elbow, and those of the lee and thigh away 
from the knee, as in the Anthropomorpia. 

Enormous accumulations of fat take place upon the but- 
tocks of the Bosjesmen, especially in the females; and the 
nymphe of these and some other Negroid tribes become 
greatly elongated. 

It appears that in some of the lower races, e.g., Negroes 


THE RANGE OF VARIATION IN ANTHROPIDE. 495 


and Australians, the fore arm and hand, and the foot and leg, 
are often longer in proportion than in Huropeans. From not 
wearing shoes, the hallux is much more moveable in these 
races, and the foot is commonly employed for prehension. 

There is no proof of what is so commonly asserted, that 
the heel is longer, in proportion to the foot, in Negroes. 

The spines of the middle cervical vertebra sometimes 
cease, more or less completely, to be bifurcated in the lower 
races. Thirteen pair of ribs are sometimes present, and 
occasionally there is a sixth lumbar vertebra. There may be 
one more sacral vertebra than the normal number; and a 
modification of the last lumbar, so that it resembles a 
sacral vertebra, and becomes connected with the ilia, seems 
to be more common in Australians and Bushmen than 
in other stocks. 

In the lower races, the male pelvis is less in many of its 
dimensions, and seems to differ more from the female, 
especially in the tendency to equality of the transverse and 
antero-posterior diameters of the brim, and the narrowness 
of the intersciatic diameter, than in the higher races. This is 
particularly obvious among the Australians. The antero- 
posterior diameter of the brim of the pelvis is occasionally 
greater than the transverse, and this variety would seem 
to be commoner among the Bushwomen of South Africa 
than elsewhere. 

But it is in the skull that the different races of mankind 
present the most striking osteological differences. The 
proportions of the antero-posterior and the transverse 
dimensions of the brain-case vary extremely. Taking 
the antero-posterior diameter as 100, the transverse dia- 
meter varies from 98, or 99, to 62. The number which thus 
expresses the proportion of the transverse to the longitu- 
dinal diameter of the brain-case is called the cephalic indea. 
Those people who possess crania with a cephalic index of 
80 and above are called brachycephali; those with a lower 
index are dolichocephali. The brain-case also varies greatly 
in its relative height. The proportion of the length of the 
cerebral chamber to the basicranial axis (as 100) may rise 


496 THE ANATOMY OF VERTEBRATED ANIMALS. 


to 270 in the higher, and sink to 230 in the lower races; 
and there are great diversities in the extent to which the 
cerebral cavity is rotated backwards or forwards upon this 
axis. The position and the aspect of the occipital foramen 
vary considerably, as does the plane of that part of the 
squama occipitis which lies above the superior semicircular 
ridge. The supra-ciliary ridges vary greatly in their develop- 
ment, and in the extension of the frontal sinuses into them. 
They are nearly, or quite solid in many Australian skulls. 

In the size, form, and disposition of the facial bones 
the different races of mankind present great diversities. 
A line drawn from the anterior extremity of the pre- 
maxilla to the anterior extremity of the basicranial axis, 
may be taken to represent the facial avis, and the angle 
included between these two is the craniofacial angle. It 
varies with the extent to which the face lies in front of, or 
below, the anterior end of the cranium, from less than 90° 
to 120°. When it is great, the face is prognathous ; when it 
is small, the face is orthognathous. This is the fundamental 
condition of prognathism or orthognathism. A secondary 
condition is the form of the alveolar portion of the upper 
jaw, which, so far as it is vertical, tends towards ortho- 
gnathism; but, so far as it is oblique and produced, tends 
to prognathism. 

The arch formed by the teeth is, in the most orthogna- 
thous races, wide and evenly rounded; while, in the most 
prognathous, it is prolonged, and its sides are nearly parallel. 
The teeth themselves are much larger, the roots of the pre- 
molars and molars more distinct, and the hindermost molar 
not so small relatively to the others, in some of the lower 
races, notably the Australians. 

The mental prominence may project beyond the line of 
the vertical alveolar margin of the mandible, in the higher 
races, or it may be almost obsolete, and the alveolar margin 
may be greatly inclined forwards, in the lower. 

The ditferent races of mankind are divisible into two 
primary divisions; the Ulotrichi, with crisp or woolly hair, 
and the Leiotrichi, with smooth hair. 


THE ULOTRICHI AND THE LEIOTRICHI. 497 


a. The colour of the Ulotrichi varies from yellow-brown 
to the darkest hue known among men. The hair and eyes 
are normally dark, and, with only a few exceptions (among 
the Andaman Islanders), they are dolichocephali. The Ne- 
groes and Bushmen of ultra-Saharal Africa, and the Ne- 
gritos of the Malay peninsula and archipelago, and of the 
Papuan islands, are the members of this Negroid stock. 


b. The Leiotrichi are divisible into— 


1. The Australioid group, with dark skin, hair, and eyes, 
wavy, black hair, and eminently long, prognathous, skulls, 
with well-developed brow ridges, who are found in Australia 
and in the Dekhan. The ancient Egyptians appear to me 
to have been a modification of this race. 


2. The Mongoloid group, with, for the most part, yellowish 
brown, or reddish brown, skins and dark eyes, the hair being 
long, black, and straight. Their skulls range between the 
extremes of dolichocephaly and those of brachycephaly. 
These are the Mongol, Tibetan, Chinese, Polynesian, 
Hsquimaux and American races. 


3. The Xanthochroic group, with pale skins, blue eyes, and 
abundant fair hair. Their skulls, like those of the Mongo- 
loid group, range between the extremes of dolichocephaly 
and brachycephaly. The Slavonians, Teutons, Scandi- 
navians, and the fair Celtic-speaking people are the chief 
representatives of this division; but they extend into North 
Africa and Western Asia. 


4, The. dark whites, or Melanochroi,; pale-complexioned 
people, with dark hair and eyes, and generally long, but 
sometimes broad, skulls. These are the Iberians and “black 
Celts” of Western Europe, and the dark-complexioned 
white people of the shores of the Mediterranean, Western 
Asia, and Persia. I am disposed to think that the Melan- 
ochroi are not a distinct group, but result from the mixture 
of Australioids and Xanthochroi. . 
25 


498 THE ANATOMY OF VERTEBRATED ANIMALS. 


Fossil remains of Men or implements of human manu- 
facture have hitherto been found only in late Tertiary 
(Quaternary) deposits, and in caves, mingled with the re- 
mains of animals which lived during the glacial epoch. 


INDEX. 


—_—_————_ 


A. 

ACCIPENSER, cartilaginous cra- 
nium of, 141. 

Air sacs in birds, 317. 

Alimentary canal, 86. 

Alligator terrapene, 198. 

Amia, caudal extremity of, 17. 

calva, reproductive organs 
of, 144. 

Amphibia, general characteristics, 
172. 

— development, 190. 

— groups, 172. 

— heart, 183. 

—— limbs, 180. 

— muscles, 47. 

—— reproductive organs, 189, 

— respiratory organs, 187. 

— teeth, 182. 

Amphisbeenoida, 230. 

Ankle-joint of sloths, 331. 

Anoplotheride, 376. 

Antebrachium, muscles of, 51. 

Anthropide. See Man. 

Anthropomorpha, general charac- 
teristics of, 475. 

—— comparison of, with man, 487. 

—— divisions, 475. 

Aortic arches. See Arches, aortic. 

Apes. See Simiadz., 

Arch, pectoral, 34. 

—— pelvic, 37. 

—— pectoral and pelvic, of che- 
lonia, 206. 

—— pectoral and pelvic, of ple- 
siosauria, 213, 214. 

Arches, aortic, 91, 92. 

—— number of, belonging to 
skull, 77. 

—— pectoral, and sternum, of a 
frog, 181. 


Arches, visceral, skeletons of, 85. 

Arctopithecini (marmosets), gene- 
ral characteristics of, 462. 

—— brain, 464. 

—— limbs, 463. 

— muscles, 464. 

— skull, 463. 

—— teeth, 463. 

— vertebre, 463. 

Armadillos, general characteristics 
of, 339. 

Artiodactyla, 
367. 

—— ruminantia, 377. 

Ascalabota, 225. 

Australians, peculiarities of, 495. 

Aves. See Birds. 

Axolotl (Stredon), 186. 

—— aortic arch of, 92. 


non - ruminantia, 


B. 


BALAZNOIDEA, general character- 
istics of, 395. 

Baleen plates, or whalebone, 398. 

Bats. See Cheiroptera. 

Birds, general characteristics of, 
194. 

—— air sacs of, 317. 

— brain of Meleagris gallo- 
pavo, 303. 

— classification, 272. 

— digits, 292, 297. 

—— ear, 306. 

—— heart, 312. 

—— larynx and syrinx, 313. 

— limbs, 291, 295, 

—— lungs, 316. 

—— muscular system, 300, 

— organs of copulation, 318, 

—— pectoral arch, 289. 


500 


Birds, pelvis, 293. 
—— sacrum of a chick, 278. 
skull, 282. 
—— spur, 297, 
—— sternum, 280, 281. 
—— vertebre, 275. 
See also Fowl. 
Bears, teeth of, 422. 
Blood, circulation of, in frog, 185. 
— corpuscles, 99. 
Bloodsucking bats, 456. 
Bones of cetacea, 394. 
—— cynomorpha, 470. 
—— delphinoidea, 399. 
—— elephant, 430. 
—— the face, 25. 
—— fishes, 28, 85. 
—— galeopithecus, 450. 
—— hedgehog, 443. 
—— pig, 369. 
rhinoceros, 361. 
—— the skull, 22, 23. 
See also Os, Ossa. 
Bosjesmen, fat of, 494. 
Brain of anthropomorpha, 484. 
carnivora, 413. 
—— chimpanzee, 64-69, 
—— cynomorpha, 474, 
divisions of, 59. 
—— dog, 420. 
— frog, 188. 
—— hedgehog, 447. 
—— horizontal section, 60. 
— lemuride, 459. 
—— longitudinal 
section, 61. 
man, 492. 
—— marmoset, 464. 
—— modifications of, 63. 
pig, 64-69. 
pike, 164. 
—— platyrrhini, 468. 
—— porpoises, 410. 
—— rabbit, 64-69, 440. 
Brain-case. See Skull. 
Bruta, or Edentata. See Edentata. 


and vertical 


C. 


CacuHA tort, skull of, 401. 

Cainozoic formation, crocodiles in, 
258. 

Camelide or tylopoda, 385. 


INDEX. 


Canal, alimentary, 86. 

— spinal, and cord, 69. 

Canals of Stenson, 79. 

Carnivora, general characteristics 
of, 412. 

— classification, 421. 

— divisions, 413. 

Carpus, skeletal elements of, 31. 

Catarrhine monkey, skeleton of 
462. 

Catarrhini, characteristics of, 469. 

Cats, teeth of, 422. 

Caudal extremities of polypterus, 
amia, and salmo, 17. 

— vertebre, 16. 

Cerebral nerves, 71. 

Cetacea, general characteristics, 
392. 

—— groups, 395. 

Characters, distinctive, of ver- 
tebrata, 1. 

Chalk, ichthyosauria in, 249. 

lizards found in, 228, 229. 

Chamelonida, 231. 

Cheiroptera, general character- 
istics of, 454. 

—— digits, 34. 

—— position of limbs of bats, 33. 

Chelone midas, carapace of, 200. 

— section of skeleton of, 199. 

Chelonia, general characteristics, 
197. 


— divisions, 207. 

—— heart, 308. 

—— lungs, 316. 

— muscular system, 300. 

—— organs of copulation, 318. 

—— pectoral and pelvic arches, 
206 


—— plastron, 201. 

— skull, 203-205. 

Chelydra, forefoot of, 32. 

Chimera monstrosa, section of 
skull, 127, 128. 

Chimpanzee, 476. 

brain of, 64-69. 

Circulatory organs, 90. 

Cochlea, development of, 82-84. 

Comparison of man with anthro- 
pomorpha, 487. 

Corpuscles, blood, 99. 

—— lymph, 101. 

Corpus callosum in mammalia, 63. 


INDEX. 501 


Cotylophora, 383. 

Cranial nerves, 75. 

—— system, 18. 

Cranio-facial angle, 490, 496. 

Crocodile, segment of endoskeleton 
in thoracic region of, 15. 

Crocodilia, 249. 

— dermal armour, 250. 

—— ear, 306. 

—— groups, 258. 

— heart, 311. 

— lungs, 316. 

—— pelvis and hind limb, 260. 

—— reproductive organs, 318. 

— skull, 254. 

—— teeth, 258. 

— vertebrx, 250. 

Crus, muscles of, 51. 

Cutaneous muscle of hedgehog, 


— porpoise, 406. 


D. 


Deer, horns of, 384. 
Delphinoidea, characteristics of, 
399. 
Dental formule. See Teeth. 
Dentition. See Teeth. 
Development of amphibia, 189. 
— cochlea, $2-84. 
—— egg, 3. 
—— fowl, stages of, 6, 8, 12, 20. 
— lamb, 27. 
—— skull of fishes, 21. 
—— vascular system, 93-96, 
—— vertebrata, 3. 
DIAGRAMS :— 
Accipenser, skull, 141. 
Alligator terrapine, 198. 
Amia, caudal extremity, 17. 
Amia calva, reproductive 
organs, 144. 
Amphioxus lanceolatus, 117, 
118. 
Aortic arches, 91. 
Axolotl, 186. 
Bird and lizard, brain, 302, 
303. 
Cachalot, skull, 401. 
Catarrhine monkey, 462. 
Chelone, skeleton, shell, 199, 
200. 


DIAGRAMS—continued. 
Chelydra, foot, 32. 
Chimera, skull, 128. 
Chimpanzee, brain, 65, 67. 
Crocodile, anterior thoracic 
region, 15. 
—— pelvis and hind limb, 260. 
— skull, 254. 
Cyclodus (/acertilia), skull, 
219, 221. 
Dromeus, 
limb, 260. 
Dugong, heart, 390. 
Elephant, skeleton, 429. 
Fish, visceral arch, 85. 
Foetus, human, principal 
vessels, 94. 
Fowl, development, 6, 8, 12, 20. 
—— fore limb, 292. 
leg, 295, 296. 
—— pelvis, 293. 
—— sacrum of chick, 278. 
— scapula and  coracoid, 
289. 
—— skull, 283. 
—— spur, 297. 
—— sternum, 281. 
Flying fox, skeleton, 453. 
Frog, nervous system, 70. 
— skull and brain, 176, 188. 
—— sternum and pectoral 
arch, 181. 
Holoptychus, 145. 
Homo, pregnant uterus, 4. 
Horse, carpus, 350. 
— cervical vertebra, 346. 
— femur, 352. 
— foot, 345, 349. 
—— ossa innominata, 351. 
— skeleton, 547. 
—— tarsus, 343. 
Ichthyosaurus, 243, 244, 
Iguanodon, pelvis and hind 
limb, 260. 
Lamb, foetal, head, 27. 
Lamprey, skull and brain, 122, 
124, 125. 
Lepidosteus, 138, 
Lion, skeleton, 414. 
Lizards, pectoral arch and 
sternum, 35, 36. 
visceral arch, 85. 
Mammal, visceral arch, 85. 


pelvis and hind 


502 


D1acRrams—continued. 

Monkfish (squatina), pectoral 

member, 39. 

— skull, 130. 

Mudfish, skull, 168, 169. 

Orang, digit, 53. 

Os innominatum of man, 37. 

Ostrich, skull, 284. 

Ox, skeleton, 377. 

Pig, brain, 65, 67. 

Pike, brain, 164. 

— outline, 42. 

— pectoral arch and fore 

limb, 158. 
skull, 151, 152, 154,155. 
Plaice, skull, 29. 
Plesiosaurus, skeleton, 210. 
Polypterus, caudal extremity, 
17. 
Pterodactylus, skeleton, 267. 
Python, dorsal vertebrae, 234, 
— skull, 236, 239. 
Rabbit, brain, 65, 67. 
Rattlesnake, skull, 240. 
Reproductive organs in higher 
vertebrata, 108. 

Salamander, foot, 32. 
Salmo, caudal extremity, 17. 
Secretary bird, skull, 287. 
Shark, aortic bulb, 132. 
Sheep, stomach, 379. 
Skate, brain, 134. 
Spatularia, skull, 140. 
Sturgeon, skull, 141. 
Tadpoles, 191. 
Torpedo, 58. 
Trematosaurus, skull, 179. 
Turtle, heart, 310. 
—— plastron, 202. 
— skull, 203, 204, 205. 
Vertebrate brain, sections, 60, 


61. 
Whale, skull, 396, 397. 
Dicynodontia, 259. 
Didelphia, characteristics of, 323. 
—— peculiarities of, 324. 
stomach of, 327. 
Digits of anthropomorpha, 479, 
481. 
—— bat, 34, 454, 456. 
birds, 297. 
—— cynomorpha, 473, 
—— dog, 416, 


INDEX. 


Digits of lacertilia, 223. 

lemuride, 458. 

—— man, 31, 488. 

—— marsupialia, 326. 

— muscles of, 52. 

—— rabbit, 437. 

seal and turtle, 34, 426. 

Dinotherium, 431. 

Dipnoi, 167. 

Dog, anatomy of, 415. 

—— digits, 416. 

Dolichosauria, 228. 

Dromeus, pelvis and hind limb, 
260. 

Dugong, heart of, 390. 


EH. 


Ear, 81. 

— bones of whale, 397. 

—— in sauropsida, 306. 

See Hearing, organs of. 

Edentata entomophaga, groups 
and characteristics of, 335. 

—— extinct, 335. 

— loricata 338. 

—— mutica, 335. 

—— phytophaga, characteristics 
of, 330. 

—— squamata, 337. 

—— teeth of, 330, 335. 

— tubulidentata, 337. 

Egg, development of, 3. 

Elasmobranchii, 126. 

Electrical organs, 57, 58. 

Elephant, skeleton of, 429. 

See Proboscidea. 

Embryo of vertebrata, develop- 
ment of, 5. 

Encephalon, 59. 

Endoskeleton, segment of, in tho- 
racic region of a crocodile, 15. 

— of vertebrata, 10. 

Entomophaga, 335. 

Eocene strata, didelphide in, 
328. 

—— extinct mammals of, 376. 

— fossils of equide in, 358, 
359. 

— fossil rodents of, 442. 

Episkeletal muscles, 45. 

Equide, fossil, 358. 


INDEX. 


503 


Equidz (horses and asses), general | Fowl, scapula and coracoid, 289. 


characteristics of, 343. 
See Horse. 
Exoskeleton, 40. 
in birds, fishes, reptiles, and 
mammals, 41, 42, 43, 44, 194, 
274. 
—— of reptilia, 193. 
Eye muscles of sauropsida, 304. 
structure of, 79. 


F. 


Faces, bones of, 25. 

— of man, 489, 496. 

Facial muscles, 73. 

Feathers, 274. 

Femur of the horse, 352. 

Fins of fishes, 39, 40. 

Fishes, electrical organs of, 57. 

—— groups in class, 115. 

—— limbs, 38. 

— muscular system, 46. 

— raylike bones, 28. 

— skeleton of visceral arches of 
osseous fish, 85. 

— skull, 21, 30. 

Fissipedia, general characteristics 
of, 413. 

Flatfishes (plewronectide), 30. 

Flying fox, skeleton of, 453. 

Feetal appendages of vertebrata, 7. 

Fetus, human, arrangement of 
principal vessels in, 94. 

Foot of anthropomorpha, 480, 484, 

— horse, 345, 349. 

—— man, 490. 

Fossils in chalk, 228, 229, 249. 

— eocene strata, 328, 358, 359, 
376, 442. 

—— lias, 208, 249. 

—— human, 497. 

— mesozoic formation, 215, 217, 
226, 258, 265, 266, 328. 

— miocene formation, 358, 359, 
363, 365, 375, 376, 385, 386. 

—— permian formation, 226. 

—— post-triassic formation, 215. 

— triassic formation, 226, 249, 
258, 261, 328. 

Fowl, stages of development of, 6, 
12, 18, 20. 

—— pelvis, 293, 


— skull, 283. 

—— sternum, 281. 

— tibia and fibula, 295, 296. 

Frog, aortic arch of, 92. 

brain, 188. 

—  cerebro-spinal and sympa- 
thetic nervous system, 70. 

circulation of blood, 185. 

—— larva, 191. 

— skull, 175, 176. 

er sternum and pectoral arches, 
181. 


G. 


GALEOPITHECUS, general charac- 

* teristics of, 450. 

Ganoidei, existing and fossil, 145. 

genera of, 137. 

Gibbons, 475. 

Glyptodon, peculiar character of, 
340. 

Gorilla, 477. 

Growth in man, laws of, 493. 


H. 


Hacs (marsipobranchii), optic 
nerves of, 71. 

Hand of anthropomorpha, 476, 
483. 

Head and trunk, muscular system 
of, 45. 

—— of sperm whale, 400. 

Hearing, organs of, cases, 24. 

—— in cetacea, 410. 

Heart of amphibia, 183. 

— bat, 455. 

birds, 312. 

— crocodiles, 311. 

—— modifications of, 97. 

—— porpoise, 407. 

— sauropsida, 308. 

— teleostei, 161. 

turtle, 309, 310. 

Hedgehog, 442. 

Hippopotamidz, general charac- 
teristics of, 374. 

Homeeosauria, 226. 

Horns of deer, &c., 384. 

Horse, general characteristics of, 
343, 


504: 


Horse, cervical vertebra, 346. 

— femur, 352. 

' —— forefoot and hindfoot, 345, 
349. 

—— limbs, 348. 

—— muscles, 353. 

—— ossa innominata, 351. 

— skeleton, 347. 

—— skull, 348. 

— teeth, 344, 354. 

viscera, 356. 

Hyposkeletal muscles, 45. 

Hyracoidea, characteristics of, 
452, 


IP 


IcnrnyopsipA, characteristics of, 
112. 

Ichthyosauria, 242. 

— pectoral arch, 247. 

—— pelvis, 249. 

— skeleton, 244, 

—— skull, 245. 

—— vertebre, 243. 

Impregnation of vertebrata, 3. 


Insectivora, characteristics of, 442. 


J. 


JACOBSON, organs of, 79. 


K. 


KIoNOCRANIA, 228, 


L. 


LACERTILIA, 216, 

—— groups, 224, 

—— organs of copulation, 318. 
— skull, 219. 

Lamb, development of, 27. 
Lamprey, optic nerves of, 71, 73. 
—— sections of skull, 122, 125. 
— skull, 21. 

—— teeth, 87. 

Larva of frog, 191. 

Larynx, 103. 

—— platyrrhini, 467. 

—— sauropsida, 313. 
Leiotrichi, 497. 


INDEX. 


Lemuridz, general characteristics 
of, 458. 

— brain, 459. 

—— limbs, 458. 

—— organs of reproduction, 460. 

— skull, 459. 

— teeth, 460, 461. 

Lepidosiren, aortic arch of, 92. 

Lepidosteus semiradiatus, brain 
of, 138. 

Lias, chelonia in, 208. 

ichthyosauria in, 249, 

Limbs of amphibia, 180. 

birds, 291. 

carniyora, 412. 

— fishes, 38, 

— galeopithecus, 450. - 

—— hedgehog, 446. 

—— horse, 348. 

— hyrax, 433. 

— lemuride, 458. 

—— man, 488. 

— marmoset, 463. 

—— muscular system of, 48. 

—— pig, 369. 

— porpoise, 405. 

—— position of, 32. 

— seal, 425. 

—— vertebrated animals, 30. 

Lion, skeleton of, 414. 

Liver, 87. 

—— in sauropsida, 308. 

Lizard, brain of, 302, 303. 

— pectoral arch and sternum, 
35, 36. 

— skeleton of visceral arches, 
85. 

Lymphatic system, 100. 

Lymph corpuscles, 101. 


M. 


MACRAUCHENIDS, 366. 

Mammalia, general characteristics 
of, 114. 

—— classification, 319. 

—— deciduate, 411. 

—— dental formule, 89. 

—— development of heart, 99. 

— skeleton of visceral arches 
of mammal, 85. 


| —— teeth, 355. 


INDEX. 


Man, arrangement of principal 
vessels in human foetus, 94. 

— general characteristics of 488. 

—— comparison of anthropomor- 
pha with, 487, 

— digits of, 31. 

—— divisions of :— 

Leiotrichi, 497, 
Ulotrichi, 497. 

— fossil, 497. 

— laws of growth in, 493. 

—— muscles of digits, 52, 53, 54, 
55, 56. 

— muscles of limbs, 48. 

—— 08 innominatum, 37. 

—— position of limbs, 33. 

—— ‘races’ of, 494. 

—— section of pregnant uterus of 
a deciduate placental mammal, 

— sexual differences, 493. 

—— teeth, 89. 

Marmosets. See Arctopithecini. 

Marsipobranchii, 121. 

Marsupialia, digits of, 326. 

Mastodon, 431. 

et formation, crocodiles in, 
258. 

—— didelphide, &c., in, 328. 

lizards in, 226. 

— ornithoscelida in, 265. 

—— plesiosauria confined to, 215. 

pterosauria in, 266. 

Miocene epoch, cotylophora of,385, 

—— extinct mammals, 376. 

— fossil camelidex, 386. 

— fossil equide, 358, 359. 

— fossil hippopotamide, 376. 

—— fossil rhinoceros, 363. 

—— fossil tapirs, 365. 

— genus of sirenia, 391. 

Modifications of the brain, 63. 

—— of the heart, 97. 

—— of reproductive organs, 109. 

Moles (talpine), 452. 

Monkeys. Sce Simiade. 

Monkfish (squatina), 
member of, 39. 

— sections of skull, 130. 

Monodelphia, characteristics of, 
328. 

Mosasauria, 228, 

Mudfish, 168. 


pectoral 


505 


Muscles of amphibia, 47. 

antebrachium, 51. 

— anthropomorpha, 482. 

—— crus, 51. 

— cynomorpha, 472, 

——- the digits, 52. 

—— (ilo, cule 

—— eye in sauropsida, 304. 

—— fishes, 46. 

—— hedgehog, 444-446, 

—— horse, 353. 

—— the limbs, 48. 

—— man, 491. 

—— marmoset, 464. 

— ophidia, 299. 

pig, 369. 

—— platyrrhini, 467. 

—— rabbit, 439. 

— seal, 426. 

—— system of, in ophidia, che- 
lonia, and aves, 299. 

—— trunk and head, 45. 

Musk deer, stomach of, 379. 

Myelon, 69. 

Myxine, 123. 


N. 


NEGROES, peculiarities of, 495. 
Nerves, cerebral, 71. 

— of the eye, 79-81. 

—— sauropsida, 301. 

— spinal, 69. ‘ 

—— sympathetic, 77. 

Nervous system of frog, 70. 
Non-ruminating animals, 367. 


0. 


OLFAcTOoRY apparatus, 78. 
—— nerves, 71. 

Ophidia, groups of, 233. 
fossil, 242. 

— muscular system, 299. 
— organs of copulation, 318. 
— skull, 235. 

— teeth, 242. 

vertebra, 233. 

Optic nerves, 71, 80, 81. 
Orangs, 476. 

— middle digit of, 53. 


506 


Organs, circulatory, 90. 

—— of hearing, 81. 

— renal, 105. 

—— reproductive. See Reproduc- 
tive organs. 

—— respiratory, 101. 
Respiration. 

—— of sight, 79. 

—— of taste, 86. 

— of touch, 86. 

— of voice, 103. 

Ornithodelphia, characteristics of, 
320. 

Ornithoscelida, 261. 

——transitional character of 
skeleton of, 261. 

Os innominatum of man, 37. 

Ossa innominata of the horse, 351. 

Ossification of facial apparatus, 25. 

—— skull, 21. 

vertebre, 13. 

Ostrich, reproductive organs of, 
318. 

— skull, 284. 

Otaridz (eared-seals), 423. 

Ox, skeleton of, 377. 


See also 


12 


PALHOTHERIDA, 365. 

Palate of cetacea, 395. 

Pectoral arch, 34. 

in birds, 289." 

— chelonia, 206. 

—— crocodiles, 256. 

—— and fore limb of pike, 158. 

—— of plesiosauria, 213. 

Pectoral fins, 40. 

— member of monkfish (squa- 
tina), 39. 

Pelvic arch, 37. 

—— of chelonia, 206. 

—— of plesiosauria, 214. 

Pelvis of anthropomorpha, 480. 

—— bat, 455. 

—— birds, 293. 

— cetacea, 394. 

— crocodiles, 257. 

— cynomorpha, 471. 

—— hedgehog, 444. 

— man, 490; lower races of 
man, 495. 


INDEX. 


Pelvis of platyrrhini, 466. 

— porpoise, 405. 

—— pterosauria, 269. 

sirenia, 389. 

Permian formation, lizards of, 226. 

Perissodactyla, 342. 

Pharyngobranchii, 116. 

Phocide, general characteristics 
of, 424. 

Phocodontia, 411. 

Phytophaga, 330. 

Pig, anatomy of, 367. 

brain, 64-69. 

digital muscles, 56. 

Pike, brain of, 164. 

fins, 42. 

— pectoral arch and fore limb, 
158. 

— skull, 151, 152, 154, 155. 

Pinnipedia, characteristics of, 423. 

—— groups, 423. 

Pisces. See Fishes. 

“ Placoid exoskeleton,” 126. 

Plaice, skull of, 29. 

Plastron of the chelonia, 201. 

Platyrrhini, general characteristics 
of, 465. 

Plesiosauria, 208, 215. 

—— pelvic arch of, 214. 

— skeleton, 210. 

—— extinct, confined to Mesozoic 
rocks, 215. 

Pleuronectide (flat fishes), 30. 

Polypterus,caudal extremity of,17. 

Porpoise, general characteristics 
of, 402. 

—— heart, 407. 

— muscles, 406. 

—— pelvis, 405. 

—— respiratory apparatus, 408. 

— skull, 403. 

— stomach, 407. 

— teeth, 407. 

— vertebre, 403. 

Post-Triassic group of plesio- 
sauria, 215. 

Poupart’s ligament, 38. 

Primates, characteristics of, 457. 

—— divisions of, 458. 

Proboscidea, general character- 
istics of, 428. 

—— bones, 430. 

— fossil, 432. 


INDEX. 


Proboscidea, reproductive organs, 
431. 

— skull, 428. 

— stomach, 431. 

—— teeth, 430. 

—— vertebra, 428. 

Protorosauria, 226. 

Protovertebre, 11. 

Psalterium of ruminants, 379. 

Pterodactylus, skeleton of, 267. 

Pterosauria, 266. 

—— groups of, 270. 

— skull, 268. 

—— vertebrex, 267. 

Python, dorsal vertebra of, 234. 

— skull, 236, 239. 


R. 


RaBBit, anatomy of, 437. 

—— brain, 64-69, 440. 

— digital muscles, 56. 

— limbs, 439, 440. 

— muscles, 439. 

—— reproductive organs, 441. 

— skull, 438. 

— teeth, 441. 

— vertebra, 437. 

—— viscera, 441. 

Races of man, 494. 

Rana esculenta, cerebro-spinal and 
sympathetic nervous system of, 
70. 

Rattlesnake, skull of, 240. 

Rays, pectoral arch of, 34, 

— skull, 21. 

Renal organs, 105. 

Reproductive organs, 106. 

—— of amia calva, 144. 

—— amphibia, 189. 

—— anthropomorpha, 487. 

—— bat, 455. 

—— birds, 318. 

— dog, 421. 

—— hedgehog, 449. 

—— lemuride, 460. 

—— man, 490, 492. 

—— modifications of, 109. 

—— ostrich, 318. 

—— porpoise, 410. 

— Europa, 318. 

Reptilia, characteristics of, 193. 

—— groups, 195. 


507 


Respiration, mechanism of, 104. 

organs of, 101. 

—— in amphibia, 187. 

—— porpoises, 408. 

—— sauropsida, 315. 

— teleostei, 162. 

Rhinoceros, general characteris- 
tics of, 360. 

— bones, 361. 

— fossil, 363. 

—— reproductive organs, 362. 

— skin, 360. 

— skull, 360. 

—— teeth, 360, 362, 

—— vertebre, 360. 

—— viscera, 362. 

Rhynchocephala, 225. 

Rodentia, general characteristics 
of, 434, 

— brain, 435. 

—— digits, 436. 

—— reproductive organs, 436. 

— teeth, 434, 435. 

—— vertebre, 435. 

Ruminating animals, 377. 

act of feeding, 380. 

— act of rumination, 381. 

— groups of, 382. 


8. 


SALAMANDRA, hindfoot of, 32. 

Salmo, caudal extremity of, 17. 

Sacrum of birds, 278. 

Sauropsida, general characteristics 
of, 113. 

—— alimentary canal of, 307. 

—— brain, 302, 303. 

—— ear, 506. 

—— eye muscles, 304. 

—— heart, three forms of, 308. 

—— larynx, 313. 

—— liver, 308. 

— muscles and viscera, 299. 

—— nerves, 301. 

—— reproductive organs, 318. 

—— respiratory organs, 315. 

— stomach, 308. 

—— tongue of, 307. 

Seals. See Otarida, 
Pinnipedia. 

Secretary bird, skull of, 287. 


Phocide, 


508 


Sensory organs, 78. 
Sexual differences in man, 493. 
Sharks, aortic arch of, 92. 
aortic bulb, 132. 
pectoral arch, 34. 
Sharks, skull, 21. 
Sheep, stomach of, 379. 
Shrews (sorices), 452. 
Simiadz, general characteristics 
of, 461. 
—— divisions of, 462. 
skull, 461. 
— teeth, 461. 
Sirenia, characteristics of, 387. 
Skate, brain of, 134. 
Skeleton, amphibian, 174, 175. 
— of anthropomorpha, 477. 
—— catarrhine monkey, 462. 
—chelone midas, section of, 
199. 
—— elephant, 429. 
—— flying fox, 453. 
— fossil equide, 358, 359. 
—— horse, 347. 
—— icthyosauria, 244. 
—— limbs, 31. 
— lion, 414. 
— ornithoscelida, 
character of, 261. 
—— ox, 377. 
—— plesiosaurus, 210. 
—— porpoise, 403. 
—— pterodactylus, 267. 
—— the skull, 19. 
— visceral arches of lizard, 
mammal, and fish, 85. 
See also Endoskeleton, Exo- 
skeleton. 
Skull of accipenser, 141. 
—— amphibian, 177. 
— of anthropomorpha, 478. 
arches belonging to, 77. 
—— of bat, 455. 
—— birds, 282. 
— carnivora, 412. 
— common fowl, 283. 
— cetacea, 392. 
— chelonia, 203-205. 
—— cranial system, 18. 
— crocodile, 254. 
—— cynomorpha, 469. 
— dog, 415. 
—— elephant, 428, 


transitional 


INDEX. 


_ Skull of fishes, 30. 


— feetal cachalot, 401. 

— frog, 175, 176. 

— hedgehog, 443. 

— horse, 348. 

lacertilia, 219, 221. 

— lemuride, 458. 

—— man, 489; differences in, 495, 

—— marmoset, 463. 

—— modifications of, 21, 

—— mudfish, 168, 169. 

— nerves of, 71-77. 

—— ophidia, 235. 

— ornithoscelida, 265. 

—- ostrich, 284. 

osseous brain-case, 21-23. 

pig, 368. 

—— pike, 151, 152, 154, 155. 

—— plaice, 29. 

—— platyrrhini, 466. 

—— plesiosauria, 212. 

—— porpoise, 403. 

—— pterosauria, 268. 

—— rabbit, 438. 

—— rattlesnake (crotalus), 240. 

—— rhinoceros, 360. 

— seal, 425. 

secretary bird, 287. 

—— sirenia, 388. 

— spatularia, 140. 

—— sturgeon, 141. 

—— trematosaurus, 179. 

—— typical segment of, 28. 

—— walrus, 424. 

whale, 396, 397. 

Sloths, characteristics of, 331. 

ankle-joint, 331. 

—— limbs, 331. 

—— pelvis, 331. 

—— tongue, 335. 

— vertebrer, 331. 

Snakes. See Ophidia. 

Sorices (shrews), 452. 

Spatularia, skull of, 140. 

Spinal canal and cord, 69. 

—— system, 11. 

Spleen, 101. 

Spouting, mechanism of, in ceta- 
cea, 409. 

Spur of birds, 297. 

Squatina (monkfish), 
member of, 39. 

— sections of skull, 130, 


pectoral 


INDEX. 


Stenson, canals of, 79. 
Sternum in birds, 280, 281. 
— of frog, 181. 

— of lizard, 35, 36. 
Stomach, 87. 

— of camels, &e., 385. 
—— carnivora, 415. 

musk deer, 379. 

—— porpoise, 407. 
ruminating animals, 378, 379. 
—— sauropsida, 308. 

—— sheep, 379. 

—— teleostei, 160. 
Sturgeon, skull of, 21, 141. 
Suid, 367. 

—— variations in, 373. 
Sympathetic nerves, 77. 
Syrinx, 103. 

of birds, 513. 


dM 


TADPOLES, 191, 192. 
Tapirs, characteristics of, 363. 
Tarsus, skeletal elements of, 31. 
Taste, organ of, 86. 

Teeth, 87. 

— of amphibia, 182. 

— anthropomorpha, 485. 
— bat, 455, 456. 

— carnivora, 412, 

— cats, 422. 

— cetacea, 394. 

— crocodiles, 258. 

—— cynomorpha, 473. 
—— delphinoidea, 399. 
— didelphia, 325. 

—— dog, 418, 422. 

—— edentata, 330, 335. 
—— edentata tubulidentata, 337. 
— elephant, 450. 

—— extinct mammals, 376. 
—— fishes, 129, 159. 

—— galeopithecus, 451. 
— hedgehog, 446. 

—— hippopotamus, 374, 
—— horse, 344, 354. 

—— hyrax, 433. 

— lacertilia, 224. 

— lemuridx, 460. 

—— macrauchenide, 366. 
—— man, 492, 496. 

—— marmoset, 463. 


509 


Teeth of ophidia, 242. 

— ornithoscelida, 265, 

—— paleotheride, 366, 

— pig, 371. 

—— platyrrhini, 467. 

—— porpoise, 407. 

—— rabbit, 441. 

— rhinoceros, 360. 

—— rodentia, 454. 

—— seal, 427. 

—— sirenia, 389. 

—— suide, 367, 373. 

“tapirs, 363. 

— toxodontia, 586. 

— walrus, 424. 

— whale, or whalebone, 398. 

Teleostei, 148. 

— aortic arch of, 92. 

Tertiary epoch, extinct cetaceans 
of, 411. 

— late, fossil man in, 497. 

Thymus, 101. 

Tongue of amphibia, 183. 

—— sauropsida, 307. 

sloths, 336. 

a electrical apparatus of, 

8. 


Tortoises, 197. 

Touch, organs of, 86. 

Toxodontia, extinct, characteris- 
tics of, 386. 

Tragulide, 382. 

Transition of skeleton of ornitho- 
scelida, 261. 

Trematosaurus, skull of, 179. 

Triassic formation, crocodiles of, 
258. 

— extinct lizards, 226. 

—— dicynodontia, 261. 

ichthyosauria, 249. 

—— macropodide, &e., 328. 

tee groups of plesiosauria, 

15. 

Trichechide (walruses), 424. 

Trigeminal nerves, 74, 76. 

Trunk and head, muscular system 
of, 45. 

Turkey, brain of, 302. 

Turtles, 197. 

— heart, 309, 310. 

—— plastron, 202. 

— skull, 203-205. 

Tylopoda or camelidz, 385, 


510 INDEX. 


U. 


Uxorricut, 497. 
Ungulata, characteristics of, 341. 


¥, 


VAMPIRE bat, 457. 
Vascular system, 93-96. 
Veins, 93. 

Ventral fins, 40. 


Vertebree of anthropomorpha, 477. 


—— bat, 454. 

— birds, 275. 

—— caudal, 16. 

—— of carnivora, 412. 
—— cetacea, 392. 
crocodiles, 250. 
—— cynomorpha, 469. 
—— dog, 415. 

— hedgehog, 443. 
—— horse, 346. 

—— hyrax, 432. 

—— ichthyosauria, 243, 
—— lacertilia, 217. 
—— lemuride, 459, 


—— man, 488 ; lower races of, 495. 


—— marmoset, 463. 
—— ornithoscelida, 265. 
— ossification of, 13. 
— of pig, 367. 

—— platyrrhine, 465. 
—— porpoise, 403. 
—— proboscidea, 428. 
—— pterosauria, 267. 
—— rabbit, 437. 

—— rhinoceros, 360. 
—— rodentia, 435. 
—— seal, 425. 

—— sirenia, 388. 


LONDON : 


Vertebre of snakes, 233. 

—— tapirs, 363. 

— whales, 395. 

Vertebrata, distinctive characters 
of, 1 

— development, 3. 

—— feetal appendages, 7. 

—— impregnation, 3. 

limbs, 30. 

—— provinces or groups, 112. 

Vertebrate endoskeleton, 10. 

— exoskeleton, 40. 

Vescicles of the brain, 59. 

Viscera of anthropomorpha, 486. 

camelide, 386. 

— cynomorpha, 473. 

— elephant, 431. 

— hedgehog, 448. 

horse, 356. 

—— hyrax, 434. 

—— lemuride, 459. 

—— pig, 372. 

— platyrrhini, 467, 468. 

— rabbit, 441. 

— rodentia, 436. 

—— seal, 427. 

— tapirs, 365. 

Visceral arches and clefts, 9. 

arches, skeletons of, 85. 

Voice of birds, 313. 

organs of, 103. 


W. 


WHALEBONE, 398. 
Whale, ear-bones of, 397. 
skull of, 397. 

— skull of foetal, 396. 
— sperm, head of, 400. 


PRINTED BY WILLIAM CLOWES AND SONS, STAMFORD STREET 


AND CHARING CROSS. 


By the same Author, 


INTRODUCTION TO THE CLASSIFICATION 
OF ANIMALS. 


With Engrayings, 8vo. 6s. 


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BOUND BY 


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