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Full text of "A manual of the anatomy of vertebrated animals"

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THE 

CHARLES EDWARD VAN CLEEF 
MEMORIAL LIBRARY 



Froir!..Th9 D.epartitisnt ..of. .Ana* 
t..Qmy.,.St.iB:.8.on.Hal.l,.. Cornell 
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Cornell University Library 
QL 805.H98 
A manual of the anatomy of vertebrated a 




3 1924 002 903 627 




Cornell University 
Library 



The original of tliis book is in 
tine Cornell University Library. 

There are no known copyright restrictions in 
the United States on the use of the text. 



http://www.archive.org/details/cu31924002903627 



A MANUAL 



ANATOMY OF YERTEBEATED 
ANIMALS. 



BY 

THOMAS H. HUXLEY, LL.D., F.R.S., 

AUTHOR OF ''lay SBBHONS/^ "MAN'b PLACE IN NATURE," *' ORIGIN OF SPECIES,' 

ETC., ETC. 



NEW YOEK: 
D. APPLETON AND COMPANY, 

1898. 




PREFACE. 



The present work is intended to provide students of 
comparative anatomy with a condensed statement of the 
most important facts relating to the structure of verte- 
brated animals, which have hitherto been ascertained. 
Except in a very few cases, I have intentionally abstained 
from burdening the text with references ; and, therefore, 
the reader, while he is justly entitled to hold me respon- 
sible 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, Dug^s, Flower, Gegenbaur, 
Hyrtl, Yon Meyer, Miiller, Pander and DAlton, Parker, 
Quatrefages, and Traquair. 

A considerable portion of the book has been in type 
for some years ; and this circumstance must be my excuse 
for appearing to ignore the views of several valued eon- 
temporaries. I refer more especially to those contained 
in recently-published works of Professors Flower and 
Gegenbaur. 

London, September, 1871. 

* Namely, Figures 1, 6, 10, 11, 12, 13, 15, 18, 23, 26, 28, 29, 30, 31, 36, 39, 41, 
42, 46, 50, 51, 54, 55, 66, 57, 58, 59, 60, 61, 75, 79, 82, 101, 107, 108, 109, 110. 



CONTENTS. 



Chajp I. — A General View of the Organtzation of the Veetebeata — 

THE VeETEBEATE SKELETON, 7 

II. — The Muscles and the Viscera — A General Vikw of the 

Oeganization of the Veriebrata, . . . . 44 

ni. — The Provinces of the Veetebeata — The Class Pisces, . 100 

IV. — The Class Amphibia 149 

V. — The Classification akd the Osteology of the Reptilia, . 16Y 

VI. — The Classification and the Osteology of Birds, . . 233 

VII. — The Muscles and the Visceea of the Saueopsida, . . 2ro 

Vm. — The Classification and Organization of the Mammalia, . 273 




THE ANATOM'Y 



VEETEBEATED AI^IMALS. 



CHAPTER L 



A GENEEAl VIEW 01" THE OEGAlTIZATIOMr OF THE VBltTE- 
BEATA THE VEETEBEATE SKELETON. 

The Distinctive Characters of the Yertebrata. — The Verte- 
brata are distinguished from all other animals by the circum- 
etance that a transverse and vertical section of the body 
exhibits two cavities, completely separated from one another 
by a 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 ner- 
vous 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 
llie development and union of outgrowths of the blastoderm, 
which are not formed in the Invertebrata* 

Again, in the partition between the cerebro-spinal and vis- 

* It is possible that an exception to tliis rule may be found in the Ascid- 
«ns. The tails of the larva of these animals exhibit an axial structure, whioh 
vis a certain resemblance to a vertebrate notochord ; and the walla of the 
pharynx arc perforated, much as in Am/pMoxus, 



8 THE ANATOMY OF VERTEBKATED ANIMALS. 

ceral tubes, certain structures, wbich are not represented in 
iuvertebrated animals, are contained. During the embryonic 
condition of all vertebrates, the centre of the partition is occu- 
pied by an elongated, cellular, cylindroidal mass — the oioto- 
chord, or chorda dorsalis. And this structure persists through- 
out life in some Vertebrata ; but, in most, it is more or less 
completely replaced by a jointed, partly fibrous and cartilag- 
inous, 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 development, a 
series of thickenings, parallel with one another and trans- 
verse to the axis of the bodj', which may be five or more in 
number, and are termed the visceral arches. The intervals 
between these arches become clefts, which place the pharyn- 
geal cavity, temporarily or permanentlj', in communication 
with the exterior. Nothing corresponding with these arches 
and clefts is known in the Invertebrata. 

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 mov- 
ing the limbs are attached. The limbs of invertebrated ani- 
mals are commonly more numerous, and their skeleton is 
always external. 

When invertebrated animals are provided with masticatory 
organs, the latter are either hard productions of the alimentary 
mucous membrane, or are modified linabs. Vertebrated ani- 
mals also commonly possess hard productions of the alimen- 
tary 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 not communicate 
with the exterior — recalling, in the latter case, the "atrial cavi- 
ties of Mollusca. 

In all Vertebrata, except AmpMoxus, there is a single 
valvular heart, and all possess an he2Mtic portal system y the 
blood of the alimentary canal never being wholly rettu^ed di- 
rectly 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. 



9 



The Development of the Vertebrata. — The ova of Verte- 
brata have the same primary composition as those of other 
animals, consisting of a germinal vesicle, containing one or 
many germ,inal 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 
vietnhrane, and this may receive additional investments in the 
form of layers of alhum,en, and of an outer, coriaceous, or cal- 
cified sJieU. 

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




FiG. 1.— Dlagrammattc section of the pregnant nterns of a decldnate placental mammal 
(Homo): «, nterus; I, Fallopian tube; c, neck of the uterus; du, uterine decidua; rf*, 
decidual serotina; dr, decidua r^jiexa; iB,e,' villi; cA, chorion; am amnion; nb^ 
umbilical Teeicle; oZ, allantoie. 



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 3'oung may be completed 



10 THE ANATOMY OF VERTEBKATED ANIMALS. 

while the egg reinains 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 viviparoiis 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 vasctdar appendages in question constitute the chief 
part of what is called the placenta, and may be developed 
from the umbilical vesicle (as in Musfeliis 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 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 ordinarj' fishes ; but, 
among some reptiles and in most birds, the parent supplies 
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 cleuvage- 
mass contains a nucleus. The cleavage-masses eventually be- 
come 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 embryogenic tissue in which it 
results, very early exhibits two distinguishable strata — an 
iiniQr, the so-called mucous stratum [hypoblast), which gives 
rise to the epithelium of the alimentary tract ; and an outer, 
the serous stratum (epiblast), from which the epidermis and 
the cerebro-spinal nervous centres are evolved. Between 
these appears the intermediate stratutn (mesoblast), which 
gives rise to all the structures (save the brain and spinal inai-- 
row) which, in the adult, are included between the epidermis 



THE DEVELOPMENT OF THE VERTEBRATA. 



11 



of the integument and the epithelium of the alimentary tract 
and its appendages. 

A linear depression, the primitive groove (Fig. 2, A, c), 
makes it appearance on the surface of the blastoderm, and 



■a a 2.2 9 




12 THE ANATOMY OF VERTEBKATED ANIMALS. 

the substance of the mesoblast along each side of this groove 
grows up, carrj'ing with it the superjacent epiblast. Thus are 
produced the two dorsal laminw, the free edges of which arch 
over toward one another, and eventually unite, so as to con- 
vert 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 
Encephalon, in the region of the head; and of the spinal 
cord, or JHyelon, in the region of the spine. The rest of the 
epiblast is converted into the epidermis. 

The part of the blastoderm vrhich lies external to the dor- 
sal laminae forms the ventral laminae, ; and these bend down- 
ward and inward, at a short distance on either side of the 
dorsal tube, to become the vraUs of a ventral, or visceral, 
tube. The ventral laminag 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, extending 
over the yelk, encloses it in a kind of bag. This bag is the 
first-formed and the most constant of the temporary, or foetal, 
appendages of the young vertebrate, the umbilical 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 mean whUe, by histological differentiation of 
the axial indifferent tissue, immediately under the floor of the 
primitive groove), into two lam,elloe. One of these, the visceral 
lamella, remains closely adherent to the hypoblast, forming 
with it the splanchnopleure, and eventually becomes the proper 
wall of the enteric canal ; while the other, the parietallatnella, 
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 
Eoraatopleures eventually unite, is the umbilicus. 

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

The Foetal Appendages of the Vertebrata. — At its outer 
margin, that part of the somatopleure which is to be con- 
verted 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 ap- 
proach one another, and, ultimately uniting, the inner layer 
of the fold becomes converted into a sac filled with a clear 



THE F(ETAL APPENDAGES. 



13 



fluid, the Amnion y while the outer laj'er either disappears or 
coalesces with the vitelline membrane, to form the Chorion 
(Fig. 3). 





Flo. 8. —Later stages of the development of the body of a Fowl than those represented U 
Fig. 2. — E, embryo at the third day of incubation ; ^, heart ; A, eye ; z, ear ; A, viflceral 
arclies and clefts ; I, 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 ; lo, vesicle of the 
third ventricle. — F, embryo at the fifth day of incubation. The letters as before, except 
n, o, rudiments of the anterior and posterior extremities ; Am^ amnion ; All (the allan- 
tois, hanging down from its pedicle) ; Vm, umbilical vesicle. — G, under-vlew of the head 
of Uie foregoing, the first visceral arch being cut away. 



Thus the amnion encloses the body of the embryo, but not 
the umbilical sac. At most, as the constricted neck, 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, in- 
creasing in absolute and relative dimensions, and becoming 
distended with fluid, is reflected over it (Fig. 1). 

A third foetal appendage, the Allantois, commences as a 
single or double outgrowth from the under surface of the mcso- 



14 THE ANATOMY OF VEETEBKATED ANIMALS. 

blast, behind the alimentary tract ; but soon takes the fonn 
of a vesicle, and receives the ducts of the primordial kidneyn, 
or Wblffimi bodies. It is supplied with blood by two arteries, 
called hypogastria,'yi\A(ia 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 nutri- 
tive, processes of which it then takes an important share. 

The sphtting of the ventral laminae, and the formation of a 
pleuroperitoneal cavity, appear to take place in aHiVertebratii. 
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 foetal append- 
ages. 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 urachus, which 
connects the bladder with the front wall of the abdomen. The 
umbilical vesicle may either be cast off, or taken into the in- 
terior 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 Amphibia, 
throw out filamentous or lamellar processes, which receive 
branches from the aortic arches, and, as branchice, subserve 
respiration. In other Vertebrata all the visceral clefts become 
closed and, with the frequent exception of the first, obliterated ; 
and no branchise are developed upon any of the visceral arches. 

In 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 endosheleton. 

The Vertebrate Endosheleton. — 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 those heads. 
The endoskeleton is distinguishable into two independant por- 
tions — the one axial, or belonging to the head and trunk ; the 
other, appendicular, to the limbs. 

The axial endosheleton usually consists of two systems of 



THE VERTEBRATE ENDOSKELETON. 15 

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 lamin88 gradually close over (this process commen- 
cing in the anterior moiety of their length, in the future ce- 
phalic 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 dilatations 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 enlargement, or anterior cere- 
bral vesicle, as it is now called, lies in front of the end of the 
notochord ; the median enlargement, or the middle cerebral 
vesicle, above its extremity ; and the hin-der enlargement, or 
the posterior cerebral vesicle, behind that extremity (Fig. 4, D 
and E). The under surface of the anterior vesicle lies in a 
kind of pit, in front of, and rather below, the apex of the noto- 
chord, 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 primi- 
tively tubular spinal cord (Fig. 4, A). Where it does so, the 
head ends, and the spinal column begins ; but no line of de- 
marcation is at first visible between these two, the indifl'erent 
tissues which ensheath the notochord passing without inter- 
ruption from one region to the other, and retaining the same 
character throughout. 

The first essential differentiation between the skull and 
the vertebral column is efiected by the appearance of the proto- 
vertebrce. At regular intervals, commencing at the anterior 
part of the cervical region, and gradually extending backward, 
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). 
Each pair of these gradually unite above and below that struct- 
ure, and send arched prolongations into the walls of the spinal 
canal, so as to constitute a protovertebra. 

No protovertebrse appear in the floor of the skull, so that, 



It) 



THE ANATOMY OF YERTEBRATED ANIMALS. 



even in this early stage, a clear distinction is drawn between 
the skull and the spinal column. 




Y^a i. — Successive stages of the development of the "^ead of a Chick. I, II, III, first, sec- 
ond, and third cerebral vesicles ; /a, vesicle of the cerebral hemisphere ; 76, vesicle of 
the third ventricle; a, rudiments of the eyes and optic nerves; 6, of the ears; c of th« 
olfactory organs; d^ the infundibulum ; e, the pineal gland; c, protovertebrje ; h. noto- 
chord ; 1, 2, 8, 4, 5, visceral arches ; V, YII, VIII, the trigeminal portio dura, and ninth 
and tenth pairs of cranial nerves ; ^, the nasal process ; l^ the maxillary process ; ec, tlie 
first visceral clelt. A, B, upper and under views of the head of a Chick at the end of 
the second day. 0, side-view at the third day. D. side-view at seventy-five hours. 33, 
aide-view of the head of a Chick at the fifth day, which has been subjected to slight press- 
xire. F, head of a Chick at the sixth day, viewed from below. 



OSSIFICATION OF THE VERTEBRA. i7 

The Spinal System. — ^The protovertebrse consist at first 
of mere indifferent tissue ; and it is by a process of histologi- 
cal differentiation within the protovertebral masses that, from 
its deeper parts, one of the spinal ganglia and a cartilaginous 
vertebral centrum — from its superficial layer, a segment of the 
dorsal muscles, are produced. 

Chondrification extends upward into the walls of the dorsal 
tube, to produce the neural arch and spine of each vertebra ; 
and, outward, into the wall of the thoracic and abdominal part 
of the ventral tube, to give rise to the transverse 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 coa- 
lesce in the middle line to form a median subthoracic cartilage 
■ — the sternum. 

When ossification sets in, the centra of the vertebra are 
usually ossified, in great measure, from ringlike deposits which 
closely invest the notochord ; the arches, from two lateral de- 
posits, 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 cartilaginous. The sternum 
itself is variously ossified. 

Between the completely-ossified condition of the vertebral 
column and its earliest state, there are a multitude of grada- 
tions, most of which are more or less completely realized in 
the adult condition of certain vertebrated animals. The verte- 
bral column may be represented by nothing but a notochord 
with a structureless, or more or less fibrous, or cartilaginous 
sheath, -nath or without rudiments of cartilaginous arches and 
ribs. Or there may be bony rings, or enslieathing ossifications, 
in its walls ; or it may have ossified neural arches and ribs 
only, without cartilaginous or osseous centra. The vertebra3 
may be completely ossified, with very deeply biconcave bodies, 
the notochord remaining persistent in the doubly-conical inter- 
vertebral substance ; or, ossification may extend, so as to ren- 
der the centrum concave on one surface and convex on the 
other, or even convex at each end. 

Vertebra which have centra concave at each end have 
been conveniently termed amphicoelus ; those with a cavity 
in front and a convexity behind, procodus ; where the position 
of the concavity and convexity is reversed, they are opistho- 
codous. 



18 THE ANATOMY OF VERTEBEATED ANIMALS. 

In the Mammalia, the centra of the vertebras 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 vertebras may be united together by 
synovial joints, or by ligamentous fibres — the intervertebral 
ligaments. The arches are connected by ligaments, and gen- 
erally, in addition, by overlapping articular processes called 
zygapophyses, or oblique processes. 

In a great many Vertebrata, the first and second cervical, 
or atlas and axis, vertebrae 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 odontoideu7n,OT an chy losing 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 
vertebras, 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 anchylosed ribs. In front of the sacrum the ver- 
tebrge 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. Vertebrje without distinct ribs, 
between the last dorsal and the sacrum, are lumbar. Ver- 
tebras, with or without ribs, in front of the first dorsal are 
cervical. 

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

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 procoelous vertebral ce7itrum (C), 
united with which by the neurocentral suture is the neural 
arch, which rises into the neural spine (iV S.). Two pro- 
cesses, 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 ventrally, proceed from the posterior face of the 
neural arch, and are the postzyg apophyses {Z"). By these, 
which are often called oblique, or articular, processes, the ^er- 
tcbra articulates with the corresponding processes ofits prede 



A SEGMENT OF THE SKELETON. 



19 



cessor or successor in the series. The transverse processes are 
two on each side, one superior and one inferior. The former 
{l\t) articulates with the tuberculum of the rib, the latter 
( Gp.t) with its capitulum. They may, therefore, be called cw- 
pitular and tubercular transverse processes resjDectively. Each 




S^i- 



St.r 



Fig. 5. — A segment of the endoskeleton in tlie antenor thoracic region of the body of a croc- 
odile. — C, the centrum or body of the vertebra; K,8.^ the neural spine: Z^ the prezy- 
gapophysis; ^, the postzygapophysia; T.t^ the transverse process which articulates 
■with the tuberculum of the rib (0 ; QJ.^ that which articulates with the capitulum of 
the rib {Qpy^ V.r^ the ossified vertebral rib; V.r', the part of the vertebral rib which 
remains cai-tilaginous ; AY.r, the sternal rib ; *S^ an artificially-separated segment of the 
sternum ; P.u, the uncinate process. 



rib is divided by an articulation into a vertebral ( V.r) and a 
sternal {St.r) part. The former remains unossified for a con- 
siderable distance at its distal end ( Vir') ; the latter is more or 
less converted into cartilage bone. The proximal end of the ver- 
tebral rib bifurcates into a tuberculum, {t) and a capitulum ( Qj). 
The distal end of the sternal rib unites with the more or less os- 
sified but unsegmented cartilage, which forms the sternum (St). 
A cartilaginous, or partly ossi^ed, uncinate process (I^.u.) pro- 
jects from the posterior edge of the vertebral rib, over the in- 
tercostal space. The student will find it convenient to famil- 
iarize himself with the conception of such a spinal segment as 
this, as a type, and to consider the modifications hereafter 
described with reference to it. . 

In the majority of the. Vertebrata, the caudal vertebra 
gradually diminish in size toward the extremity of the body, 
and become reduced, by the non-development of osseous pro- 
cesses or arches, to mere centra. But, in many fishes, which 
possess well-ossified trunk-vertebrae, 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 embry- 



20 



THE ANATOMY OF VERTEBKATED ANIMALS. 



onio 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 as to form 




THE CRANIAL SKELETON. 21 

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 di- 
vision 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 hypural bones wnich 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 anchylosed with the 
last ossified vertebral centrum. The inferior fin-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, etc.), the sheath of the no- 
tochord becomes completely ossified and united with the cen- 
trum of the last vertebra, which then appears to be prolonged 
into a bony urostyle. 









J\ 



.•^■* 



•». , --S'l 



h] 



Co f Co 



Fig. 7. — ^The cartilaginoaB craninin of a Fowl at the sixth day of incabatloii, viewed from be- 
low. — P^ the pituitary space ; tr^ the trdbeaulcB^ tmltiiig in front, in the bifurcated eth- 
moTomerine plate; Qu^ the quadrate cartilage; ^, the semicircular canals; Co, Ha 
cochlea ; /i, the notochord Imbedded in the basilar plate. 

T7ie Cranial System. — As has been stated, no protover- 
tebrae appear on the floor of the skull ; nor is there any cra^ 
nium, nor any developmental stage of a cranium, in which sep- 
arate cartilaginous centres are known to occur in this region. 

On the contrary, when chondrification takes place, it ex- 
tends continuously forward, on each side of the notochord, 



22 THE ANATOMY OP TERTEBKATED ANIMALS. 

and usually invests the anterior termination of that body, 
more or less completely, as a basilar plate. 

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

On each side of the posterior boundary of the skull, the 
basilar cartilage grows upward, an^ 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 devel- 
oped 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 ethmovo- 
merine part of the skull ; while, in that of the eyes, it apper- 
tains to the organ, is fibrous, cartilaginous, or osseous, and 
remains distinct from the skull. In the case of the ear, it is 
cartilaginous, and eventually osseous : whether primitively dis- 
tinct or not, it early forms one mass with the skull, immedi- 
ately 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 parti- 
tion between them. The partition is the proper ethmoid, the 
lamina perpendicularis of human anatomy; the posterolat- 
eral parts of the ethmovomerine cartilages, on each side of the 
partition, occupy the situation of the prefrontals, or lateral 
masses of the ethmoid of human anatomy. The ingrowths of 
the lateral walls, by which the nasal mucous membrane ac- 
quires a larger surface, are the turbinals. 

Ribhke 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 CRANIAL SKELETON. 23 

The first visceral arch bounds the cavity of the mouth be- 
iiind, and marks the position of the mandible or lower jaw. 
The cartilage which it contains is termed MeckePs cartilage. 

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



«!. /lllii.. 



illlillli 




Fro, 8. — Tlnder-Tlew of the head of a Fowl at the Beventh day of incubation. — la^ the cere 
bral hemispheres causing the integument to bulge ; a, the eyes; o', the olfactory sacs 
k^ the fronto-nasal ])rocess ; I, the maxillary process ; 1, 2, the first and second yiscezal 
arches ; (c, the remains of the first viBceral cleft. 

the preceding, it unites with its fellow in the ventral median 
line, where the so-called " body " of t he hyoid arises. 

A ridge, continued forward from the first visceral arch to 
the olfactory sac (Fig. 4, F ; Fig. 8, I), bounds the mouth on 
each side, and is called the maxillary process. A cartilaginous 
palato-pten'ygoid rod, developed in this process, becomes con- 
nected with Meckel's cartilage behind, and with the prefirontal 
cartilage in front. 

The maxillary process is at first separated by a notch cor- 
responding with each nasal sac, from the boundary of the 
antero-median part of the mouth, which is formed by the free 
posterior edge of a, fronto-nasaZ process (Fig. 4, F ; Fig. 8, Jc). 
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 in- 
ternally, and then gives rise to the posterior nasal apertvre, 
by which the nasal cavity is placed in communication vnth 
that of the mouth. 



24 THE ANATOMY OF VERTEBRATED ANIMALS. 

The General Modifications of the Vertebrate Skull. — The 
lowest vertebrated animal, Amphioxus, 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 ; tVjat 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 repre- 
sented, 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 membrane bones, as in the 
Sturgeon ; or may be the result of the ossification of the car- 
tilaginous cranium itself, from definite centres, as well as of 
the development of superimposed membrane bones. 

The Osseous JBrain-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 floor. The 
ossific deposit, nearest the occipital foramen, becomes the ba-si- 
occipital bone ; that which takes place in the floor of the pitu- 
itary fossa becomes the hasisphenoid ; that which appears in 
the reunited trabeculae, in front of the fossa, gives rise to the 
presphenoid. Again, in front of, and outside, the cranial cav- 
ity, 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 supra-occipital. The four occipital ele- 
ments, uniting together more or less closely, compose the oc- 
cipital 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 maj 
appear on each side and give rise to the alisphenoid ; which, 
normally, becomes united below with the basisphenoid. 

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

In front of the occipital segment, the roof of the skull is 
formed by membrane ; and the bones which complete the two 



THE TYPICAL BONY SKULL. 



26 



seg:ments of which the basisphenoid and presphenoid form the 
basal parts, are membrane bones, and are disposed ia tvva 
pairs. The posterior are the parietals, the anterior the fron- 
tills y and the segments which they complete are respectively 









O i 



H 9 



Eh 

n 

O 
■< 

to 



I" 






Pbeteostal. 



Branchial apparatus. 



Hyoldean apparstos. 



Eh 



Mandibular Suspenaorium. 






4 
s 

□Q 



o 
to 



to 



to Lg 



26 THE ANATOMY OF VERTEBRATE!) ANIMAI,S. 

called parietal and frontal. Thus the walls of the cranial cgv 
iiy in the typical ossified skull are divisible into three segment." 
—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., ii., v., and x.), in the manner shown in the 
diagram * on the preceding page. 

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 opcipital and the parietal segments 
of the skull. Each of them may have three principal ossifi- 
cations of its own. The one in front is the prootic ; the one 
behind and below, the opisthotio • and the one which lies 
above, and externally, the epiotic. The last is in especial re- 
lation 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 
constitute the petrosal and mastoid parts of the temporal bone 
of human anatomy ; or the epiotic, or the opisthotio, or both, 
may coalesce with the adjacent supra-occipital and ex-occipi- 
tals, leaving the prootio distinct. The proQtic is, in fact, one 
of the most constant bones of the skull in the lower Vet'tebra- 
ta, though it is commonly mistaken, on the one hand for the 
alisphenoid, and on the other for the entire petro-mastoid. 
Sometimes a iourth, pter otic ossification, is added to the three 
already mentioned. It lies on the upper and outer part of the 
ear-capsule between the prootio and the epiotic (see the fig- 
ure of the cartilaginous cranium of the Pike, infrd). 

In some Vertehrata the base of the skull exhibits a long 
and distinct splint-like membrane bone f — the parasphenoid, 

* The nam-es of the purely membrane bones in this diagram are in large 
capitals, as PAEIETAL ; whila tiiosu of the bones which are preformed in 
cartilage are in smaller type, as Basisphenoid. 

+ Bones may bo formed in two ways. They may be preceded by cartilage, 
and the ossiflo deposit in the place of the future bone may at first be deposited 
iu the matrix of that cartilage, or the ossiflc deposit may take place, from the 
first, in indifferent, or rudimentary connective, tissue. In this case the bone 
is not prefigured by cartilage. In the skulls of Elasmobraneh fishes, and in 
the sternum and epicoracoid of Lizards, the bony matter is simply ossified car- 
tilage, or cartilage bone. The parietal or frontal bones, on the other hand 
are always devoid of cartilaginous rudiments, or, in other words, are memimne 
bones. 

In the higher Vertehrata the cartilage bones rarely, if ever, remain as such : 
but the p"iniitive ossified cartilage bcoomea, in great measure absorbed and 
'■eplaeed by membrane bone, derived from the perichondrium. ' 



THE EONES OF TUE EACE. 27 

whicli un(]erlics it from tlie basi-occipital to the pre-splienoidal 
region. In ordinary fishes and Amjihibia, 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 
l)one 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 surface of the audi- 
tory capsule a membrane bone, the squamosal, is very com- 
monly developed ; and another pair of splint-bones, the nasals, 
cover the upper part of the ethmovomerine chambers, 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 with- 
in the various processes and visceral arches which have been 
enumerated. Thus, the premaxillm 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 anterior gives 
rise to the palatine bone, the posterior to the j)terygoid. 
Outside these, several membrane bones may make their ap- 
pearance in the same process. The chief of these is the max- 
illa, which commonly unites, in front, with the premaxilla. 
Behind the maxilla there may be a second, the jugal ; and 
0(>casionally behind this lies a third, the quadrato-jugal. 

Between the maxilla, the prefrontal and the premaxilla, 
another membrane bone, called lachrymal, from its ordinary 
relation to the lachrymal canal, is very generally developed ; 
and one or more suprororhital and post-orhital ossifications 
may be connected veith the bony boundaries of the orbit. 

When these and the postfrontal membrane bone are si- 
multaneously 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 lachrymal. The 



28 THE ANATOMY OF VERTEBRATED ANIMALS. 

upper series (lachrj'mal, supra-orbital, post-frontal, squamosal), 
teriuiiiates posteriorly over the proximal end of the quadrate 
hone, or inandibular suspensorium. The lower series (lacliry- 
mal, maxillary, jugal, quadrato-jugal) ends over the distal end 
of that bone, vs^ith 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 Ichthy- 
osauria, Chelonia, Groeodilia, 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, 
tlie prefrontal above and externally, and the palatine behind, 
to open into the forepart 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 communi- 
cates laterallj', 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 lachry- 
mal bone may be developed in especial relation with it. 

In the higher Vertebrata, the nasal passages no longer 
communicate with the forepart of the cavity of the mouth ; 
for the maxillaries and palatines, regularly, and the pterygoid 
bones, occasionally, send processes downward and inward, 
which meet in the middle line, and shut off from the mouth 
a canal which receives the nasal passages in front, while it 
opens, behind, into the pharynx, by what are now the poste- 
rior 7iares. 

Two ossifications commonly appear near the proximal end 
of Meckel's cartilage, and become bones movablj' 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 
does not seem to be represented in mammals. The remainder 
of Meckel's cartilage usuallj^ 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, 
and the ramus of the mandible thiis formed articulati?s with 
the squamosal bone in mammals, but in other Vertebrata is 



THE OSSEOUS MANDIBLE. 



29 



immovably united with the os articulare. Hence the complete 
ramus of the mandible articulates directly with the skull in 
mammals, but only indirectly, or through the intermediation 
of the quadrate, in other Vertebrata. In birds and reptiles, 



/■rnX' 




Fig. 9. — The head of a fretal Lamb dissected so as to show Meckel's cartilage. M ; tlia 
malleus, m; the incus, i; the tympanic, Ty ; the liyoid, //,' the squamosal, Sq ; 
ptPi-j-goid,Pi; palatine,^;; lachrymal, Z; premaxilla, pmaj ,• nasal sac, if"; Eustachiiji 
tube, Eu. 



the proximal end of the quadrate bone articulates directly 
(with a merely apparent exception in Ophidid), and indepen- 
dently 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 hyomandilular, Avhich repre- 
sents the proximal end of the hyoidean arch (see Fig. 34). 

The ossification of the hyoidean apparatus varies immense- 
ly in detail, but usually gives rise to bony lateral arches, and 
a median portion, bearing much the same relation to them as 
the sternum has to the ribs. When the lateral arches are com- 
j)iete, 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 cohimella auris, or stapes, the innei- end of which, in 
the higner Vertebrata, is attached to the membrane of the 
fenestra ovalis. 

In ordinary fishes, a fold of the integument extends back- 
ward from the second visceral arch over the persistent bra'. 



so 



THE ANATOMY OF VERTEBRATED ANIMALS. 



cliial clefts; within this is developed a series of raylike mem- 
brane bones, termed opercular and branchlostegal, which be 
come closely connected witli the hyoidean arch. A corre- 
sponding process of the skin is developed in the Batraohian 
Tadpole, and grows backward over the branchiae. Its posterior 
edge, at first free, eventually unites with the integum.ent of 
the body, behind the branchial clefts, the union being com- 
pleted 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. 

a 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 lat- 
eral arches, connected by median 
pieces, and, frequently, provided 
with radiating appendages which 
give support to the branchial mu- 
cous membrane. It is only found 
in those Vertebrata which breathe 
by gills — the classes Pisces and 
Amphibia. In the higher Verte- 
brata, the posterior of the two 
pairs of cornua, with which the hy- 
oidean apparatus is generally pro- 
vided, are the only remains of the 
branchial skeleton. 

The skull and face are usually 
symmetrical in reference to a me- 
dian vertical plane. But, in some 
Cetacea, the bones about the re- 
gion of the nose are unequally 
developed, and the skull becomes 
asymmetrical. In the Flatfishes 
{Pleuronectidcts), the skull be- 

Fio.in.-Thoskuiiof a*piaice(«<,te,,a °°"'^/ ^° Completely distorted, that 
rii/niij'h). viewed from above. The the two ej'es lie On One side of 

dotted line a, Z;, is the true mornho- +Vi/i ■Kr^/-^TT ,^1,* I, • 

losical median line; Or. (;,■, Uiepo- ^"® "OGy, WtUCh IS, m SOme CaseS, 

sitionof the two eyes in their orbits; the left, and, in others; +lif> riVVit 

iSA, ethmoid: T'r/ prefrontal; /r! •, t ""' "^ Obliers, Me Tight 

left frontal; j-ri. right f:ontai; Pii, SKic. In Certain of these fishes 

parimi; SO, supra-occipital; Ep.o, the rest of the skull and facia] 

,. , ^ , . ,, . ^o"es, the spine, and even the 

hmbs, partake m this asymmetry. The base of the skull and 




THE CAKPUS AND THE TARSUS. 3i 

its occipital region are comparatively little affected ; but, in the 
interorbital region, the frontal bones and the subjacent carti- 
laginous, or membranous, side- walls of the cranium are thrown 
over to one side ; and, frequently, undergo a flexure, so that 
they become convex toward that side, and concave in the op- 
posite direction. The prefontal bone of the side from which 
the skull is twisted, sends back a great process above the eye 
of that side, which unites with the frontal bone, and thus en- 
closes this eye in a complete bony orbit. It is along this 
fronto-prefrontal bridge that the dorsal fin-rays are continued 
forward, just as if this bridge represented the morphological 
middle of the skull. (Fig. 10.) 

The embryonic PleuroneatidcB have the eyes in their nor- 
mal places, upon opposite sides of tlie 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 hracldum in the fore-limbs, femur in the hind ; the 
middle is antebrachium, or crus ; the distal is tnanus, or pes. 
Each of these divisions has its proper skeleton, composed of 
cartilage and bone. The proximal division, normally, con- 
tains only one bone, os humeri, or humerus, in the bracbium, 
and OS femoris, ov 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 longi- 
tudinal series, except in the Ichthyosauria, where marginal 
bones are added, and some of the digits bifurcate. 

The skeletal elements of the manus and pes are divisible 
into a proximal set, constituting the carpus or tarsus ; and a 
distal set, the digits, of which there are normally five, articu- 
lated with the distal bones of the carpus and tarsus. Each 
digit has a proximal basi-digital {metacarpal or metatarsal) 
bone, upon which follows a linear series of phalanges. It is 
convenient always to count the digits in the same way, com- 
mencing 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, iii, 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 ta,rsus, is 



32 THE ANATOMY OF VERTEBRATED ANIMALS. 

termed the centrale ; on the distal side of this are five car- 
joalia, or tarsalia, which articulate with the several metacar- 
pal or metatarsal bones; while, on its proximal side, are 
three bones — one radlale or tibiale, articulating with the radi- 
us or tibia ; one ulnare or fibtdare, 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, 




Fig. ]1. — The right fore-foot of the Chelonlan CheJydra, and the righthind-foot of the Am- 
phibian Suh'mandra. — U^ ulna; 7?, radius; i'', libula; y, tibia. 

Prcxioiiil carpa! bones: r, radiale; i, intermedium ; w, ulnare; the eentmle is the middle 
unlettered bone. 

Proximal tarsal bones; t, tibiale; ?", intermedium; /, fibulare; c, centrale; 1, 2,8,4,6s 
distal carpalia and tarsalia ; i, li, ui, iv, v, digits. 



commonly, the typical arrangement is disturbed by the sup- 
pression of some of these elements, or their coalescence with 
one another. Thus, in the carpus of man, the radiale, inter- 
medium, and ulnare are represented b}' the scaphoides, lunare, 
and cuneiforme respectively. The pisiform,e is a sesamoid 
bono developed in the tendon of the flexor cafp>i idnaris, 
which has nothing to do with the primitive carpus. The 
centrale is not represented in a distinct shape, having proba 
bly coalesced with one of the other elements of the carpus. 
The fourth and fifth carpalia have coalesced, and form the 
single imciforme. In the tarsus of man, the astragalus repre- 
sents the coalesced tibiale and intermedium ; the calcanexun 
the fibulare. The naviculare is the centrale. Like the cor- 



THE POSITION OF THE LI5IBS. 33 

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

The Positioti of the Limbs. — In their primitive position, 
the limbs are straight, and are directed outward, at right 
angles to the axis of the body ; but, as development proceeds, 
they become bent in such a manner that, in the first place, 
the middle division of each limb is flexed downward and 
toward the middle line, upon the proximal division ; while 
the distal division takes an opposite bend upon the middle 
division. Thus the ventral aspects of the antebraehium and 
cms come to look inwardly, and the dorsal aspects outwardly ; 
while the ventral aspects of the manus and pes look downward 
and their dorsal aspects look upward. When the position of 
the limbs has been no further altered than this, the radius in 
the antebraehium, and the tibia in the crus, are turned for- 
ward, or toward the head ; the ulna and the fibula backward, 
or toward the caudal extremity. On looking at these parts 
with respect to the axis of the limb itself, the radius and the 
tibia SLie pre-axial, 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, ot 
ulnar, or fibular digits, in each limb. The most anterior of the 
digits (i) is called pollex, in the manus ; and haJhix in the pes. 
The second digit (ii) is the index; the third (iii) 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 ordi- 
nary quadrupeds, the brachium is turned backward and the 
thigh forward, 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, in- 
stead of being perpendicular to it. The proper ventral sur- 
face of the brachium looks forward, and that of the thigh 
backward, while the dorsal surface of the latter looks forward. 
The dorsal surface of the antebraehium looks outward and 
backward, that of the leg directly forward. The dorsal surface 
of the manus is external, that of the pes, superior. Thus, 
speaking 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. 



S4 THE ANAT05IY OF VERTEBRATED ANIMAIS. 

In Bats, a line drawn from the acetabulum to the foot la 
also, in the 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 backward ; the proper dorsal surface 
of the thigh looking upward and forward, while the corre- 
sponding surface of the leg looks backward and upward, and 
the ungual phalanges are turned backward. 

The chief modiHoations of the manus and pes arise from 
(lie excess, or defect, in the development of particular digits, 
and from the manner in which the digits are connected with 
one another, and with the carpus or tarsus. In the Ichthyo- 
sauria and Plesiosauria, 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 integument, so as to form 
paddles, in which the several digits have little or no motion 
oa one another. 

The fourth digit of the manus in the Pterosauria, 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 anchylosed together, 
and the digits themselves are enclosed in a common integu- 
mentary sheath ; the third invariably, and the second usually, 
is devoid of a claw. The metacarpal of the poUex is anchy- 
losed 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 (Stis), three {Ji/iinoceros), two (most Huminaiitia), or 
one {Equidoe). 

The Pectoral and Pelvic Arches. — The proximal skeletal 
elements of each pair of limbs [humeri or femora) are sup- 
ported by a primitively cartilaginous, pectoral, or pelvic 
girdle, which lies external to the costal elements of the verte- 
bral skeleton. This girdle may consist of a simple cartilagi- 
nous arc (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, and 
independent of, both ; but it is never united with the verte- 
bras by the intermediation of ribs. At first, it consists of one 



THE PECTORAL ARCH. 



35 



continuous cartilage, on each side of the body, distinguish- 
able only into regions and processes, and affording an articular 
surface to the bones or cartilages of the limb. But ossifica- 
tion usually sets up in the cartilage, in such a way as to give 
rise to a dorsal bone, called the scapula, or shoulder-blade, 
which meets, in the articular, glenoidal cavity for the hu' 
merus, 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 




ec.r 

Tn.cr 



Flo. 12.— Side-view of the pectoral arch and steranro of a Lizard {Iguana tuberculata). — 
Sc, scapula ; 5.SC, supra-scapula ; cr, coracoid ; gl^ glenoidal cavity ; St, sternum ; x.8i, 
xiphisternum ; m.sc, mesoscapula ; p.cr, precoracoid; m.cr, mesocoracoid ; e.et\ epi- 
coracoid ; d, clavicle ; i.c/, 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 epicora- 
coid. 

In the great majority of the Vertebrata above fishes, the 
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 sternum, 
and, becoming anohylosed with the scapula, they appear, in 
adult life, as mere processes of that bone. 

Numerous Vertebrates possess a clavioula, or collar-bone, 
which is connected with the pi'e-axial margin of the scapula 
and coracoid; but takes no part in the formation of the 
glenoid cavity, and is usually, if not always, a membrane 
bone. In many Vertebrata, the inner ends of the clavicles 



36 



THE ANATOMY OF VERTEBKATED ANIMALS. 



are connected with, and supported by, a median membrane 
bone which is closely connected with the ventral face of the 
sternum. This is the interdavicula, freq'jantly called epister- 



fier- 




FlG. 13. — ^VenlTal view of the sternum and pectoral arches of Iguana tub&rtyuXaia. 
letters as in i^g. 12. 



Th» 



The pelvic, like the pectoral, arch at iirst consists of a 
simple continuous cartilage on each side, which, in Vertebrata 
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. 

Tliree separate ossifications usually take place in this car- 
tilage — one in the dorsal, and two in the ventral, moiety. 
Hence, the pelvic arch eventually consists of a dorsal portion, 
called the ilium, and of two ventral elements, \\ie pubis ante- 
riorly, and the- ischium 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 di- 
vided by a ridge into two fossas. The ridge, called the spine 
of the scapula, frequently ends in a prominent process termed 
the acromion, and with this, in Mammalia, the clavicle artic- 
ulates. In like manner, the outer surface of the ilium be- 



THE PELVIC ARCH. 



31 



eomes divided by a ridge which grows out into a great crest 
in Man and other Mammalia, and gives attachment to mus- 
cles and ligaments. 

The ischium corresponds very nearly with the coracoid 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- 
partes ligament, stretches from the ilium to the pubis in many 
Vertebrata and takes its place. (Fig. 14, Pp.) 




;flQ. 14 • 



-Side-view of the left Os Innominatum of Man: /^, ilium; 7a, ischium; Pp, publi 
A^ acetabulum ; JPp, Poupart'B ligament. 



On the other hand, the m,arsupial bones of certain mam- 
mals, which are ossifications of the tendons of the external 
oblique muscles, seem to be unrepresented in the pectoral 
arch ; while there appears to be nothing clearly corresponding 
with a sternum in the pelvic arch, though the precloacal car- 
tilage, or ossicle, of Lizards has much the same relation to the 
isohia 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. 



TJie 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 cartilagi- 



S8 



THE ANATOMY OF VEETEBRATED ANIMALS. 



nous, and even of the bony, constituents of the pectoral iind 
pelvic arches of the latter are traceable in Fishes, the cartila- 
ginous, or ossified, basal and radial supports of the fins them- 
selves cannot be identified, unless in the most general waj, 
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 Elasmohranchii possess three hasal 
cartilages which articulate with the pectoral arch, and are 
called, respectively, from before backward — propterygial, me- 
eopterygial, and metapterygial basalia. With these are artic- 
ulated linear series of radial cartilages, upon which osseous, 
or horny, dermal fin-rays are superimposed. (Fig. 15.) 

Among the Granoid fishes, the fins of Polypterus are, fun- 
damentally, like those of the Elasmohranchii ; but the pro- 
pterygial, mesopterygial, and metapterygial hasalia, are more 
or less ossified, and are succeeded by a series of elongated 
rudialia, which are also, for the most part, ossified. Beyond 




ma IB.— The right pectoral member of the Mookflsh (,5V!mf/«n): h, pronteryelnm - ma 
mesopteiyglum ; mi, metapteryglum. "" ' '» •■ "^ 



THE LIMBS OF FISHES. 39 

these follow some small additional radialia, which remain car- 
tilaginous, and are embraced by the bases of the fin-rays. In 
the other Ganoids the propterygial basale disappears, and 
some of the radialia, pushing themselves between the meso- 
pterygial and metapterygial basaha, articulate directly with 
the pectoral arch. The mesopterygial basale is embraced by, 
and becomes more or less incorporated with, the large ante 
rior 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 pectoral arch, be- 
neath 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 lowermost and hindermost 
answers to the metapterygial basale of the Shark ; the others 
seem to be radialia. {8ee 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, rep- 
resenting a clavicle, with supra-clavicular and post-clavicular 
ossifications, are added. 

In all Elasmobranchs and Ganoids, and in a large propor- 
tion of the Teleosteans, the pelvic fins are situated far back 
on the under side 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 Msoskeleton. — The Exosheleton never at- 
tains, in vertebrated animals, the functional importance which 
it so frequently possesses among the Invertebrata, and it va- 
ries 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 deepei", and 
being thrown off in the superficial, layers ; and a deep vascu- 
lar tissue, the dermis, composed of more or less completely- 



JO THE ANATOMY OF VERTEBRATED ANIMALS. 

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, areas, or processes, of the dermis. "When the 
latter are overlapping folds, the horny epidermic investment 
is called a scale, squama. 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 u, hair, the horny cone simply elongates by continual 
addition of new cells to its base ; but, in a feather, the homy 
cone, which also elongates by addition to its base, splits up, 
for a greater or less distance along the middle line of its undei 
surface, and then spreads out into a flat vane, subdivided into 
barbs, barbules, etc., by a further process of splitting of the 
primary horny cone. 

The epidermis remains soft and delicate in Fishes and 
jimpMbia. In Heptilia it sometimes takes the form of plates, 
which attain a great size in many Ohelonia / sometimes, that 
of overlapping scales, as in Ophidia and many Lacertilia ; 
but, sometimes, it remains soft, as in some Ghelonia and in the 
Chamseleons. Epidermic plates in the form of nails appear 
upon the terminal phalanges of the limbs. 

All A.ves possess feathers. In addition, the beak is partly 
or completely ensheathed in horn, as in some Heptilia. Oorni- 
fied epidermic tubercles or plates are developed on the tarsi 
and toes, the terminal phalanges of which (and sometimes 
those of the wing) have nails. Besides these, some birds pos- 
sess 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. In some 
Cetacea it is almost absent, being reduced to a few hairs, pres- 
ent only in the fcetal state. The Pangolin (Ifanis), on the 
other hand, is almost completely covered with scales, the 
Armadillos with plates, and most terrestrial mammals witli a 
thick coat of hair. The greater part of the mass of the horns 
of Oxen, Sheep, and Antelopes, is due to the epidermic sheath 
which covers the bony core. Where the horny epidermis be- 
comes very thick, as in the hoof of the Horse, and in the horn 
of the Rhinoceros, numerous long papillas of the dermis extend 
into it. These papillae, however, are comparable to the ridgea 
of the bed of the nail, not to the pajpillos of the hairs. 



TUE EXOSKELETON. 



41 



The dermal exosheleton 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 struct- 
ure of bone. It may happen that cartilage is developed in the 
dermis ; and, either in its primary state or ossified, gives riso 
to exoskeletal parts. 




FiQ. 16. — A, outline of a Pike (Kioir), to show the flns: /"jpectoral; TJventral; .4, anal: 
O, caudal; i>, dorsal, fins. Op.^ operculum: P,Op.^ preonerculum ; £r^ branchiostegal 
rays. — B, scales of the dermal exoskeletou of the same fish. 



No dermal exoskeleton (except that of the fin-raj^s) is found 
m the lowest fishes, Amphioxiis and the Marsipobranchii. In 
most Teleostei, the integument is raised up into overlapping 
folds ; and, in these, calcification takes place in lamina, 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 hi 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-^ays. 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 



42 THE ANATOMY OF VERTEBRATED ANIMALS. 

in the dorsal region, or at the extremity of the body, or on the 
ventral aspect, behind tlie anus. Ordinary fin-rays are com- 
posed of a hornlike, or more or less calcified, substance, and 
are simple at the base, but become jointed transversely, and 
split up longitudinally, toward their extremities (Fig. 6). 
Each fin-ray consists of two nearly equal and similar parts, 
which cohere bv their applied faces for the greater part of 
their extent ; biat, at the base of the rays, the halves commonly 
diverge, to embrace, or more or less completely coalesce with, 
cartilaginous or osseous elements of the exoskeleton. 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 vertebrae. 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 CcerAlim 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 Ghdonia; 
and the extinct Labyrinthodonts possessed a very remarkable 
ventral exoskeleton. 

The Ophidia have no dermal exoskeleton. Many Lizards 
have bony dermal plates corresponding in form and size with 
the epidermal scales. All Grocodilia 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 Teleosauria, 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 particularh' described under the head of that order. 

In the Mammalia the development of a dermal exoskeleton 
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 glandu- 
lar and pigmentary organs of the integument may be men- 
tioned. Integumentary glands do not appear to exist in 
Fishes, but they attain an immense development in some of 
the Amphibia, as the Frog. Among Reptilia, Lizards fre- 
quentljr 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 



THE EXOSKELETOJJ. 43 

hairs, or as independent organs, in the form of sweat-glands, 
musk-glands, or mammary glands. 

The color 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 ChamcBleon. 




CHAPTER n. 



THE MUSCLES AND THE VISCBEA A GENEEAl YIEW OF THB 

ORGANIZATION OF THE TEETEBEATA. 

The muscular system of the Vertehrata consists of muscles 
related partly to the exoskeleton, partly to the endoskeletoii, 
and partly to the viscera, and formed both of striated and un- 
striated muscular fibre. The latter is confined to the vessels, 
the viscera, and the integument ; the parts of the endoskele- 
ton being moved upon one another exclusively by striated mus- 
cular 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 theii 
origin, and in their relations to the endoskeleton. The one 
takes its origin in the protovertebrse ; each protovertebra be- 
coming differentiated, as we have seen, into three parts ; a 
spinal ganglion and a segment of the vertebral endoskeleton, 
in the same plane, and a more superficial sheet of muscular 
fibres. These muscular fibres are consequently situated above 
the endoskeleton, or arc episTceletal. Other muscular fibres are 
developed below the endoskeleton, and may be termed hypo- 
sJceletal muscles. The hyposJceletal muscles are separated from 
the episkeletal, not only by the endoskeleton of the trunk (or 
the vertebras and their prolongations, the ribs), but by the 
ventral branches of the spinal nerves. 

As the episkeletal muscles are developed out of the proto- 
yertebrEB, they necessarily, at first, present as many segments 
as there are vertebras, the interspaces between them appearing 
as intermuscular septa. The development of the hj'poskeletal 
muscles has not been worked out, but it appears to take place 
much later than that of the episkeletal set. 



EPISKELETAL AND HYPOSKELETAL MUSCLES. 46 

In the lowest Verteirata — as, for example, in ordinary 
fishes — the chief muscular system of the trunk consists of the 
episkeletal muscles, which form thick lateral masses of longitu- 
dinal fibres, divided by transverse intermuscular septa into 
segments (or Myotonies) corresponding with the vertebrae. 
The lateral muscles meet in the middle line below, and divide, 
in front, into a dorso-lateral mass connected with the skull, 
and a ventro-lateral attached, in part, to the pectoral arch, and, 
in part, continued forward to the skull, to the hyoidean appa- 
ratus, and to the mandible. Posteriorly, 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 represented bj' the 
superior caudal muscles, and by the erector spinai ; which, as 
it splits up, anteriorly, and becomes attached to the vertebrse, 
and to the ribs, and to the skull, acquires the names of spi- 
nalis, semispinalis, longissimus dorsi, sacrohimbalis, it iter- 
transversalis, levatores costarum, complexus, spleiiius, recti 
postici, and recti laterules. 

The ventro-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, extend- 
ing from the pelvis to the sternum — the sterno-hyoidei, be- 
tween 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 svbclavius 
stretching from the first rib to the clavicle ; the scaleni from 
the anterior dorsal ribs to the cervical ribs and transverse 
processes, and the sterno- and cleido-mastoidei from the ster- 
num 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 AmpJiibia exhibit arrange- 
ments which are transitional between those observed in Fishes 
and that which has been described in Man, and which substan- 
tially obtains in all abranchiate yertebrata. 

The muscles of the jaws and of the hyoidean apparatus 
appear to be, in part, episkeletal, and, in part, liyposkeletal, 



A6 THE ANATOMY OF VEKTEBEATED ANIMALS. 

The mandible is depressed by a muscle, the digcistric, arising 
from the skull, and supplied by a branch of the seventh nerve : 
it is raised by a muscular mass, which is separable into mas- 
seter, temporal, and pterygoid muscles, according to its con- 
nection 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 cutane- 
ous muscles, and receive branches from the seventh nerve. 

The hyposkeletal system is formed, partly, of longitudinal 
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 vertebrae 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. Tiie latter are the ohliquus in- 
terims of the abdomen, the fibres of which take a direction 
crossing 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 intercostales interni 
continue the direction of the internal oblique, and the triangu- 
laris sterni that of the transversalis. The diaphragm and the 
levator ani must also be enumerated among 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 Limits. — The muscles of the 
limbs of Fishes are very simple, consisting, on each face of 
the limb, of bundles of fibres, which proceed (usuall3'- in two 
layers) obliquely, from the clavicle and supraolaviole to the 
fin-rays. The pectoral , and pelvic arches themselves are im- 
bedded in the lateral muscles. 

In the Amphibia and all the higher Yertehrata, the muscles 
of the limbs are divisible into — intrinsic, or those which take 
their origin within the anatomical limits of the limb (including 
the pectoral or pelvic arch) ; and extrinsic, 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-Uicial, and a po* 
terior, or post-axial, side. 



THE MUSCLES OF THE LIMBS. 47 

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

JExtrinsio muscles attached to the pectoral and pelvic arches, 
on the dorsal aspect. — 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 vertebrre 
to the scapula and clavicle ; the rhomhoidei, from the spines 
of vertebras to the vertebral edge of the scapula, beneath the 
foregoing. Sometimes there is a tracheloacromialis, from the 
transverse processes of the cervical vertebrae 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 mus- 
cle of the limb ; the peotoralis 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 anguli scapulm • posteriorly, serratus magnus. 

An omohyoid muscle frequently connects the scapula with 
the hyoidean arch. 

The posterior limb does not seem to offer any muscles ex- 
actly homologous with the foregoing. So far, however, as the 
recti abdominis, the obliquus extermis, and the fibres of the 
erector spince, are attached to the pelvic girdle, they cor- 
respond in a general way with the pre-axial, or protractor, mus- 
cles of the pectoral arch ; and the ischio-coccygeal muscles, 
when they are developed, are, in relation to the pelvic arcli, 
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) vertebrae 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 latis- 
simcus dorsi passing from spines of dorsal vertebrse to the 
humerus. On the ventral aspect, the pectoralis major extends 
from the sternum and ribs to the humerus. 

In the hind-limb, the gluiceus maximus, so far as it arises 
from the sacral and coccygeal vertebrae, and is inserted inti i 
the femur, repeats the relations of the latissim,us dorsi. Iii 
the absence of any thing corresponding with the sternum, or 
the ribs, no exact homologue of the peotoralis major can be 
said to exist, though the pectineus comes near it. The psoas 



48 THE ANATOMY OF VEKTEBKATED ANIMALS. 

major, passing from ])osterior dorsal or lumbar vertebrae — tlie 
pt/r{formis from sacral vertebras — the femoro-coccygeus (when 
it exists) from caudal vertebire — to the femur, are all hj^po- 
skeletal muscles, without homologues in the anterior extremity. 
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 hav- 
ing their insertion in the more distal segments. They are 
thus arranged in Man and the higher Manunialia : 

Intrinsic inuadcs proceeding from the pectoral or pelvic 
arches to the humerus or femur, on the dorsal asp)ect. — In the 
fore-limb, the deltoides proceeds frc-m the clavicle and scapula 
to the humerus. This superficial shouldei-muscle continues 
the direction of the fibres of the trapezius ; and, when the 
clavicle is rudimentary, the adjacent portions of the two mus- 
cles coalesce into a cepihalo-humeralis muscle. Beneath the 
deltoid the svvra-spinatus, on the pre-axial side of the spine 
of the scapula ; the infra-sp)inatx(s, 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 vaginal 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 f/liitajus ma.vimv.s, which, 
at first sight, would seem to be the homologue of that muscie. 
The iliacus, proceeding from the inner surface of the crest 
of the ilium to the smaller trochanter, answers to the supra- 
spinatus ; the glutmus tnedius and minimus, which arise from 
the outer surface of the ilium, to the infra-spinatxis and teres. 
In the fore-limb, a muscle, the subscaptdaris, is attached 
to the inner face of the scapula, and is inserted into the hu- 
merus. No muscle exactly corresponding with this appears 
to exist in the hind-limb. 

On the ventral aspect in the fore-limb, the coracohrachialis 
passes from the coracoid to the humerus. In th-e 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 jxctiiieus, and the great ab- 
ductors oi the femur; with the obturator externus, from the 
outer side of the ischiopubic fontanelle, or obturator membrane. 
The gemelli and the qitadratus femoris take their origin fiom 
the ischium. 

No muscle is attached to the proper inner surface of the 
ilium, so that there is no homologue of the subscaptdaris in 



THE MUSCLES OF THE LIMBS. 49 

the himl-linro. On the other hand, a musolc, the obturator 
iiitenius, attached to tlie inner surface of the ischiopubio fon- 
tanelle, and winding round to the femur, has no homologue in 
the upper extremity of the higher Yertehrata, unless it be the 
so-called cora-:obrachialis, which arises from the inner surface 
of the coracoid in many Sauropsida. 

Muscles of the Antehraohiuin and Crus. — On the dorsal 
aspest of the fore-limb, as of the hind-limb, certain muscles 
(trise in part from the arch, and, in part, from the bone of the 
proximal segmeni 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 portion, as supinator 
brevis, into the pre-axial bone (radius) ; whereas, in the hind- 
limb, it is the other waj', 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 mus- 
cles, arising either from the pectoral arch, or from the hume- 
rus, and inserted into the two bones of the forearm. On the 
pre-axial side are two muscles ; one double-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 brachialis 
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 
braohii, 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 
tlie tibia, and replace, without exactly representing, the su- 
pi?iator longus. Corresponding with the brachialis anticus 
is the short head of the biceps femoris, arising from the femur, 
and inserted into the post-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 ob- 
3 



50 TUE ANATOMY OF VERTEBRATED AXIIIAI.S. 

liquely fiom the post-axial condyle of the humerus to the radi- 
us, in the hind-limb, a corresponding muscle, i'm' 'i/uiillt(inis^ 
proceeds from the post-axial condyle of the femur to the tibia. 
The pronator quadnitas, which passes from the ulna to tlie 
radius, has its analogue, in some 3l(trsi(pialia and Reptilia, 
in muscles which extend from the fibula to the tibia. 

The Muscles of the Digits. — The remaining muscles of llie 
two limbs are, primarily, muscles of the digits, and are at- 
tached either to tlie basi-digital (metacarpal or metatarsal) 
bones, or to the phalanges, though they may acquire second- 
ary connections \vith bones of the tarsus or carpus. Tlie 
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 tlie dorsal aspect this digit presents : first, attached to 
the base of its metacarpal bone, the tendon of a distinct mus- 
cle, the extensor carpji ulnaris. Secondly, spreading out over 
the phalanges into an aponeiiiosis, which is principally at- 
tached to the first and second, is a tendon belonging to another 
muscle, the extensor minimi di<jiti. Thirdly, entering the same 
expansion is one tendon of the extensor communis digitorum. 

On the ventral aspect there are : first, attached to the base 
of the metacarpal, the tendon of a distinct muscle, the flexor 
carpi ulnaris ; secondly, ai-ising from the sides and ventral face 
of the metacarpal, and inserted into either side of the base of 
the proximal phalanx, two muscles, the interossei ; thirdly, 
inserted into the sides of the middle phalanx by two slips, a 
tendon of the flexor perforatus ; and fourthl}', passing be- 
tween these two slips, and inserted into the base of the distal 
phalanx, a tendon of the flexor perforans. Thus there are 
special depressors, or flexois, 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 ten- 
dons of the extensor CO mtnunis and extensor mini)ni digit! are 
attached to the middle and the proximal phalanges; and the 
distal phalanx is specially elevated by the tendons of two Ut- 
ile muscles, which, in Man, are usually mere subdivisions of 
the interossei, and pass upward, joining the extensor sheath, 
to be Snally inserted into the distal phalanx. 

The fifth digit of the pes, or little toe, sometimes presents 
the same disposition of muscles, name! 3' : 



THE MUSCLES OF THE LIMBS. 



51 



On the dorsal aspect : first, the peronceus tertlus for the 
metatarsal bone ; secondly, one tendon from the extensor digi- 
torum brevis, but this last is commonly absent in Man ; third- 
ly, one tendon from the extensor digitorum longus. 



'£x^.Z. 



jEV'-i 




Fig. 17. — Part of the middle digit of the maniis of an Orang with the flexors and extensors 
of the phalanges : m<!/?., metacarpal bone ; Pli. 1, Pit. 2, Ph. 3, the three phalanges ; 
-ffa-f. 1, the deep long extensor tendon from the extensor indicis ; Ed:t. 2, the supei-fi- 
cial long extensor tendon from the ext&ntior commnnis ; I. fl., the interosseous short ex- 
tensor ; /./., the interosseous short flexor ; F. pns.., the deep long flexor {perforaiis) ; F* 
pis., the superficial long flexor (perforaius). 



On the ventral aspect : first, the jMronceus brevis, attached 
to the base of the metatarsal ; secondly, two interossei ; 
thirdly, a perforated flexor ; and fourthly, a perforating flexor, 
like those of the manus. The divisions of the interossei, 
wliich send tendons to the extensor sheath on the dorsum of 
the digits of the foot in Man, are hardly distinct from the ven- 
tral divisions of those muscles. 

In addition to the muscles vjrhich have been mentioned, the 
fifth digit has an abductor and an adductor, which may be 
rc^garded as subdivisions of the interossei, 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 lumbricalis 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- 



52 THE ANATOMY OF VERTEBKATED ANIMALS. 

pressed. What are often regarded as muscles special to man, 
such as the extensor proprhis ivdicis and e.rteiisor nunimi 
diglti, are only reuiains of muscles which are more fully de- 
veloped in lower mammals, and send tendons to all four of 
the ulnar digits. 

Only the pollex has an oiyponens* Only the poUex and 
hallux have adductors and abductors. Some of the digits 
luck 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 
i/iferossei) 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 extensors 
of the digits of the pes arise from the femur, while some of 
them arise within the pes itself. The origins of the muscles 
seem to be, as it were, higher up in the fore-limb than iu the 
hind-limb. Nevertheless, several of the muscles correspond 
very closely. Thus, on the dorsal aspect, the exte9isor ossis 
metucarpi pyollicls passes from the post-axial side of the proxi- 
mal 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 entocuneiform and the base of the me- 
tatarsal 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 metaoarpi 
poUicis ; 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 calcaneum. 

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 radiidi,s Ion- 
gus to the base of the second metacarpal ; the extensor carpi 
radialis brevis to the base of the third metacarpal ; the exten- 
sor communis digitoriim to the four ulnar digits ; the extol- 
tor minimi digiti to the fifth digit; the extensor carpi id 

* I have seen an opponens in the hallux rf an Orang. 



THE MUSCLES OF TOE LIMBS. fiS 

naris 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 
peronmus tertius* passing from the dorsal face of the fibula 
to the fifth metatarsal, is the only representative of the exten- 
sor carpi ulnaris. 

On the ventral aspect of the human fore-limb, two deep 
flexors arise from the radius, ulna, and interosseous membrane, 
and run parallel with one another, though disconnected, to 
the digits. These are, on the pre-axial side — the Jlexor poUi- 
cis longus, to the distal phalanx of the pollex ; and the Jlexor 
digitorum perforans, to the distal phalanges of the other 
digits. 

In the hind-limb, two homologous muscles, the flexor hair 
lucis longus and the flexor digit07'um perforans^ arise from 
the tibia and fibula and interosseous membrane, and their ten- 
dons are distributed to the distal phalanges of the digits. 
But, 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 flexor carpi radialis to the base 
of the second metacarpal ; the palniaris 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 plantar is ; 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 plajitaris is a large muscle, the tendon 
of which passes over the end of the calcaneal process en- 
sheathed in the tendo achillis, and divides into slips, which 
become the perforated tendons of more or fewer of the digits. 

* This muscle, which lies altogether on the dorsal face of the hind-limb, 
and which 1 have seen only in Man, should not be confounded, as it often is, 
with one or more muscles, the peroncni itii, iti, et iti digiti, which are very 
often developed in other Mammalia, but arise on the ventral face of the fibula, 
and send their tendons below the external malleolus to the extensor sheuthj 
of the iflli, *)urth and even third digits. 



54 THE ANATOMY OF VEETEBRATED ANIMALS. 

Tlie flexor carpi radialis is also roughly represented by tiio 
tlhialia posticus — a muscle which passes from the tibia and 
interosseous membrane to the entocuneiform, and therefoie 
diflers in insertion, as well as in origin, from its analogue m 
the fore-limb. The/eao?- p>e'i-foratus digitorum of the foot 
takes its origin sometimxes from the calcaneum ; sometimes, in 
part from the calcaneum, and in part from the perforating 
flexor ; or it maybe closely connected with the tendons of the 
plantaris. The pjeronceus brevis represents the ^CTor carpi 
tdnaris by its insertion, but it arises no higher than the fibula, 
and has no sesamoid. 

Tvvo most important muscles yet remain to be considered 
in the leg. The one of these is that which is inserted by the 
tenclo acldllia into the calcaneum, 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 pieronoeus longiis, arising from the fibula, pass- 
ing 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 representa- 
tive in the fore-limb. The gastrocnemius and soleus may pos- 
sibly represent the crural part of tlie 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 adduc- 
tor muscle of the hallux in Man and Apes is the transversalls 
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 
man us. 

Electrical Organs.— Ceitam fishes belonging to the gen- 
era Toipedo (among the JEJlasmobratichii), Oymnotus, Ma- 
lapterunis, and Mormyrua (among the Teleostei), posses 
organs which convert nervous energy into electricity, just aa 
muscles convert the same energy into ordinary motion, and 
therefore may well be mentioned in connection with the nei^ 
vous system. The " electrical organ " is always composed of 
nearly parallel lamellaj of connective tissue, enclosing 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 distributed. The face on which 
the nerves ramify is in all the plates the same, being inferior 
in Torpedo, where the lamelte are disposed parallel to the 



THi; ELECTRICAL ORGANS. 



5S 



npper and under surfaces of the body ; posterior in Oymno- 
tus, and anterior in Malapterunis, tlie laraellse being disposed 
perpendicularly to tlie axis in these two fishes. And this sur- 
face, when the discharge takes place, is always negative to 
the other. 




Fio 18. — The Torpedo, with Us electiical apnsratus displayed. — ^, branchia; ; c. brain * t 
electric organ ; ly, cranium; me, spinal cord; 7t, nerves to the pectoral fliis; n/, iwni 
later (Lies ; np^ brandies of the pneuiuogastric nerves ^oing to the electric organ ■ o, 
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 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 Micephalon. — In all verte- 
brated animals except AmpMoxits, the brain exhibits that 
separation into a, fore-bralii^mid-hrain^z.-aA. hind-brain, which 



5(5 



THE ANATOMY OF VERTEBRATED ANIMALS. 



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 diminished by the 
thickening of their sides and floors. The cavity of the ante- 
rior vesicle is, in tlie adult human brain, represented by the 
so-called third ventride ; that of the middle vesicle, by the 
iter (I. tertio ad qunrtura ventriculum ; that of the posterior 
vesicle, hy the /'(n/rth ■oe/ttz-icle. 

The floor and sides of the posterior vesicle, in fact, thicken 
and become the medulla oblongata/ together with the p07is 
varolii, in those animals which possess the latter structure. 



Fir. 




C9 



RTh 



Fli. 19.— Dlnfframmatic bonzonfcil section of a Vertebrate brain. The followin? lettera 
serve for botb this flgiire .ind Fig. 20: Ml\ Miil-biain. Wliat lies in fiont of this Is the 
fore-brain, and what lies behind, the hind-brain. Z. i.. the lamina terminalis; Olf. the 
olfactory lolies ; 7/m/), the hemispheres ; rii.B,\hc tlialainenceplialon; Pn, the nineal 
pland: Pij. the pituitary bod_v; Fit, the for.amen of Mimm: IS. the corpus striatum; 
7Vt, the optic thalamus ; i.'Q the corpora quadrii:emiua; (.7 '.the crura cerebri; (76,^10 
cerebellum; /* F, the pons varolii; J/^/, the medulla oblong-atn; /, olfactorli; //,opticr 
III, point of exit from the braio of the motores oeulorum \ I\\ of the itathetiei ;' VJ. ot 
the abducentes; V-AVf, orieins of the other ceretiral nerves. 1, oltiictory ventricle* 
2, lateral ventricle ; 3, third ventricle ; 4, fourth ventricle ; -f , iter a tertio ad a-uartuix 
venti-iculum. 



VaE ENCEFUALON. 6^ 

The posterior part of the roof is not converted into nervoua 
matter, liui 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 (or 
myelencephalon) behind, and the cerebellum with the pons 
varolii (which together constitute the metencephalon) in 
front. 

The floor of the middle cerebral vesicle thickens and 
becomes converted into two great bundles of longitudinal 
fibres, the crura cerebri. Its roof, divided into two, or four, 
convexities by a single longitudinal, or a crucial, depression, 
is converted into the " optic lobes," corpora bigernina 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 



M.t. 




Pig. 20. A longitudinal and vertical section of a Vertebrate brain. — Tbe letters as befDra 

The lamina Urminalls la represented by the strong black line between FMajii 3. 

tertio ad quartum ventriculum), are the components of the 
tnid-brain or mesencephalon. 

The anterior cerebral vesicle undergoes much greatci 



58 THE ANATOMY OF VERTEBRATED ANIMALS. 

changes tlian 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 tive 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 thalamencephaloit). 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 structure, and 
become the opitic thalami. Its roof, on the other hand, 
resembles that of the fourth ventricle, in remaining Yevj thin, 
and, indeed, a mere membrane. The pineal gland, or epiphy- 
sis cerebri, is developed in connection with the upper wall of 
the third ventricle ; and, at the sides of its roof, are two ner- 
vous 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 transverse and two 
vertical^the former lying in front of the latter. The trans- 
verse fibres pass on either side into the corpora striata, and 
constitute the anterior commissure which connects those bodies. 
Tlie vertical fibres are the anterior pillars of the fornix, and 
they pass below into the floor of the third ventricle, and 
into the corpora inammillaria, when those structures are de- 
veloped. 

The outer and under wall of each cerebral hemisphere 
thickens and becomes the corpus striatum, a ganglionic struct- 
ure which, from its origin, necessarily abuts against the outer 
and interior part of the opitio thalamus. The line of demar- 
cation between the two corresponds with the lower lip (tmtiia 
semiairaularis) of the aperture of communication (called the 
foramen of Munro) between the third ventricle and the 
cavity of the cerebral hemisphere, which is now termed tlie 
lateral ventricle. In the higher Vertebrata, the upper lip of 
the foramen of Munro thickens, and becomes converted into a 
bundle of longitudinal fibres, ^vhich is continuous, anteriorly, 
with the anterior pillars ot the fornix before mentioned. Pos- 



THE MODIFICATION OF THE BRAIN. 50 

*eriorly, these longitudinal fibres are continued backward and 
downward along the inner wall of the cerebral hemisphere, 
following the junction of the corpora striata and optic thalami, 
and pass into a thickening 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, extending from the floor of the third ven- 
tricle to that of the lateral ventricle, and arching over the fora- 
men of Munro, is produced. 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 gray soft coin- 
niissure • and s. posterior commissure, consisting of transverse 
nerve-fibres, is generally developed between the posterior ends 
of the two thalami. 

In the Mammxalia, a structure, which is absent in other 
Vertehrata, 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 ventr- 
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 ante- 
rior part crosses the interspace between the hemispheres con- 
siderably 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 septum lucidum, with 
its contained fifth ventricle. 

The Modifications of the Srain. — -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 ihigher Mammalia, they extend forward 
over the olfactory lobes, and backward over the optic lobes 
an i cerebellum, so as completely to cover these parts ; and, in 
addition, they are enlarged downward toward the base of the 
brain. The cerebral hemisphere is thus, as it were, bent round 
Its carpus striatum, and it becomes distinguished into regions, 
or lohes, which are not separated by any very sharp lines of 
demarcation. These regions are named the frontal, parietal. 



to THE ANATOMY 01 VERTEBRATED ANIMALS. 

occipital, and temporal lobes — while, on the outer side of tli-j 
corpus striatum, a central lobe (the insula of Reil) lies 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 lay- 
er 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 perios- 
teal membrane which lines the interior of the skull, and is 
itself lined by the parietal layer of the arachnoid, goes by the 
name of the dura inater. 

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 and 22). 

In the Rabbit, the cerebral hemispheres leave the cerebel- 
lum 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 (-4), occipital {JS), and tem- 
poral (C), are only indicated. The olfactory nerves are enor- 
mous, 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 oif, and begins to resemble the unciform gyrus in the 
higher 3Iammalia, of which it is the homologue. The tem- 
poral gyri ( C"), though still very small, begin to enlarge down- 
ward and forward 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 hides the oero- 
bellum when the brain is viewed from above. What in the 
Rabbit was a mere angulation at Sy, in the Pig has become a 
-ong 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 



THE MODIFICATION OF THE BRAIN. 



01 




':3, 21. — Lateral views of the brains of a Rabbit, a Pig-, and a Chimpanzee, drawn of noarlj 
the same abisolute size. The Rabbit's brain is at the top ; the Pig-'s, in the middle, th« 
<.'himpanzee*'s, lowest. — 01^ the olfactory lobe; ^., the frontal lobe; B.^ the occipital 
lobe; C, the temporal lobe; Sy., the Sylvian fissure; /re., the insula; S.Or.^ suiira- 
orbital ; S.F.^ M.F.^ LF.^ superior, middle, and inferior frontal gyi-i ; A.P.^ antero-pari- 
etal ; P.P., postero-parietal gyri ; R^ sulcus of Rolando ; P.Pl^ postero-parietal lobule ; 
O.Pf.^ external perpendicuLir or occipito-temporal sulcus; An^ an^fular cttus; 2, 3, 4^ 
aanectont gyri; A.T., M.T.^ P.T-^ the three temporal, and S.Oc.^ M.Oc, l.Oe., the three 
occipital gyn. 



62 THE ANATOMY OF VEKTEERATED ANIMALS. 

Sylvian fissure, at In^ there is an elevation which answers t& 
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 {substantce perforatice) are completely 
hidden by the temporal gyri ( 6"). 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 complelelj' cover and extend beyond 
the cerebellum, so as to hide it completely from an eye placed 
above. The gyri and sulci have now attained an arrangement 
which is characteristic of all the highest Mammalia. The 
fissure of Rolando (R) divides the antero-parietal gyrus {A.F) 
from the postero-parietal {P.P). These two gyii, with the 
]">ostero-parietal lobule {P.PL), and part of the angular gyrus 
{yin), constitute the Parietal lobe. The frontal lobe, which 
lies 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 lobe, which lies on the roof of the orbit 
(>S. (?r.), presents many small salci and gyri. 

On the inner face of the cerebral hemisphere (Fig. 22) the 
oly sulcus presented by the Rabbit's brain is that deep and 
broad depression (7J) which runs parallel with the posterior 
pillar of the fornix, and gives rise, in the interior of the de- 
scending cornu of the lateral ventricle, to the projection which 
is termed the hippocampus major. In the Pig, this hippocam- 
pal sulcus (-Z7) is much narrower and less conspicuous ; and a 
marginal [IF) and a calossal (C) gyrus are separated by a 
well-marked calloso-marginal sulcus. As in the Rabbit, the 
uncinate gyrus forms the inferior boundary of the hemisphere. 
In the Chimpanzee, the marginal and callosal gyri are still 
better marked. There is a deep internal pe' pendiculnr, or 
occipito-parietal, sulcus {I.}))- The calcarine sulcus (6'ff) 
causes a projection into the floor of the posterior cornu, 
which is the hippjocampms minor ; while the rollateral sukus 
( Coll) gives rise to the eminence of that name in both the 
posterior and descer.ding cornua. The hippocampal sulcus 
(H) is relatively insignificant, and the lower edge of the tem- 
poral lobe is formed by the posterior temporal i:-yrus. 

In the Rabbit, the corpus callosum is relatively small, much 



TUE MOniFICATION OF THE BRAIN. 



liJ 




Fn. 22. — Inner views of the cerebral hemispheres of the Rabbit, Pig', and Chimpacwe^ 
dravpn as before, and placed in the same order. 01., olfectory lobe; Cc, corpus calio- 
sum; A.c. anterior commissure; //., hippocampal sulcus; {7?!., uncinate; J/"., mar- 
ginal; (\ callosal gyri; I.p., internal perpenuicular; Ca., calcarine; Coll., collateral 
sulci; F, fornix. 



inclined upward and backward; and its anterior extremity is 
but slightly bent downward, so that the so-called genu and 
rostrmn are inconspicuous. The Pig's corpus callosum ia 



64 THE ANATOMY OF VERTEBRATED ANIMALS. 

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 Chimpanzee. The Rabbit and the 
Pig have a single corpus niammillare, the Chimpanzee has 
two. The cerebellum 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, 
synmietrical, and large in proportion to the lateral lobes. The 
floeculi, 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 varolii, flattened rec- 
tangular areae, the so-called corpora trapezoidea. 

In the Pig, the cerebellum is relatively smaller, and is par- 
tially covered by the hemispheres ; the lateral lobes are larger 
in proportion to the vermis and the flocouli, and extend over 
the latter. The corpora trapezoidea are smaller. In the Chim- 
panzee, the relatively still smaller cerebellum is completely 
covered ; the vermis is ver^' small in relation to the lateral 
lobes, which cover and hide the insignificant flooculi. There 
are no corpora trapezoidea. 

In 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 con- 
tains, are lined by continuations of the three membranes which 
protect the encephalon. The cord is sub-cylindrical, and con- 
tains a median longitudinal canal, the canalis 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 surrounds the canalis centralis. The cord 
may, in the adult, extend through the whole spinal canal, or it 
rnay come to an end at any point between the caudal extrem- 
ity and the anterior thoracic region. 

The distribution of the two essential constituents of ner- 
vous tissue, ganglionic corpuscles and nerve-fibres, is very defi- 
nite in the spinal cord, ganglionic corpuscles being confined 
to the so-called " gray matter " -ivhich constitutes the isthmus, 
and spreads out into two masses, each of which ends in an an- 
terior (or ventral) and a posterior (or dorsal) horn. Nerve- 



THE MYELON. 



65 




Tig 23.— a diagrammatic view of the Chief Trunks of the Cei-obro-spinal and SyinrathPtfo 
Nervous Systems of Rana esculenia eeen from below (twice the size of nature). — I. Tho 
olfactory nerves. N. The olfactory sac, II. The optic noi-ve. 0. Tho eye. L. op. 
The optic lobes. Ta. Optic tracts passing from the optic lohes to the chiasma, behind 
which lies the pituitary body. 111. OculomntoHvs. IV Patheticus. V The tri- 
geminal, with which the abdueeiu (\ J.), facialis (VII.). and the upper end of the svm- 
pathetic (F.9), are closely connected. Branches of this nervous plexus are F.cf/tho 
nasal and ophthalmic branches of the fifth and the abdncens. V,b,c,d, the palatine, 
maxillary, and mandibular branches of the fifth. FJ «, t!io tympanic branch into which 
the proper facial nerve (VII.) enters, and, with a brancli of the vagus, forms the so- 
caUed facial nerve of the Frog, F. VIII. The auditory nerve. X, with its branches 
X^, X^, X^^ .r*, represents the glossopharyngeal and the vagus. The medulla ()!•■ 
longata {Myelencepkalori) ends, and the medulla spinalis (^Jifj/eloii^ begins, about tlie 
region marked by the letter 3f. 311-10, the spinal nerves. ,1/2, the brachial nerves, 
M 7, 8. 9, the ischiatic plexus, from which proceed the crural (N. c.) and iscliiatic (N. i.) 
serves. iS. The trunk of the sympathetic. KAf. The communicating branches viti 
tho spinal ganglia, tS i-10. The sympathetic; ^anslia. 



66 THE ANATOMY OF VEKTEBRATED ANIMALS. 

fibres also abound in the gray matter ; but the so-calleil " white 
matter," which constitutes the external substance of the cord, 
contains only the fibrous nervous matter, and has no gangli- 
onic corpuscles. 

The spinal nerves arise in opposite pairs from the two 
halves of the cord, and usually correspond in numl^er with the 
vertebrfe through, or between, which they pass out (Fig. 23). 
Each nervo has two roots, one from the dorsal, and one from 
the ventral, region of its half of the cord. Tlie former root 
has a ganglionic enlargement, and only contains sensory 
fibres ; the latter has no ganglion, and exclusively 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- 
cluding 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 con- 
tain, throughout life, a cavity, the olfactory vciUridc, which 
communicates with the lateral ventricle. 

The optic " nerves " [optici) are the second pr/ir of cere- 
bral nerves. In the Lampreys and Hags (Marsipoh'anchii) 
tliese nerves retain their embryonic origin from the thulani- 
encephalon, and each goes to the eye of its own side. In 
other VerteirratK, the nerves cross one another at the base of 
the brain (Teleostei), or are fused together into a chiasma 
[Ganoidei, Ef.asmobrdiiclui, and all the highetYertebraia). 
In the higher Vertebrata, again, the fibres of the optic nerves 
become connected chiefly with the mesencephalon. 

All the other cerel)ral nerves differ from these in arising, 
not as diverticula of any of the cerebral vesicles, but by histo- 
logical differentiation of the primitive brain-case, or lamuice 
dorsnle^ of the skull. 

The third {motores oculorurn) w\^ fourth. [patJtctici) paiis 
of nerves are distributed to the muscles of the eve ; the third 
l;o the majority of these muscles, the fourth to the superior 

• ATnphioxufi appears to ho an exception to tliis, as to most o^her, rules oS 
Vertebrate anatomy. 



THE CEREBRAL NERVES. 07 

oblique muscles. The third pair of nerves issues from the 
crura cerebri, or inferior division of the metencephalon, upon 
the base of the brain ; the fourth pair, from the fore-part of 
the upper division of tlie metencephalon, immediately be- 
hind the optic lobes, upon the superior surface of the brain. 
This region is known as the Valve of Vieussens in the Main- 
nialia. 

All the other cerebral nerves originate in the posterior di- 
vision of the hind-brain — the myelencephalon. Tlie great 
Jifth pair [trigemini) passes out from the sides of the me'.en- 
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 
maxillary, and the inferior maxillary, 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 corre- 
sponds 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 anterior and posterior boundaries, of 
the buccal oleft. Hence the superior maxillary belongs to the 
posterior, or outer, side of the maxillary process, while the in- 
ferior maxillary appertains to the anterior region of the first 
visceral arch. The superior maxillary commonly unites with 
the outer, or lachrymal, division of the ophthalmic ; the in- 
ferior maxillary 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 gan 
glion (the Casserian ganglion), and a ventral motor, non-gan- 
glionated. The fibres of the latter pass almost exclusively 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 maxil- 
lary a third (otic). 

The sixth pair [cibducentes) issues from the inferior surface 
of the brain, at the junction of the myelencephalon with 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 mus- 
cles exist. 

The seventh pair (faciales) supplies the superficial facial 



Q8 THE ANATOMY OF VERTEBEATED ANIMALS. 

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, the 
three motor nerves of the eyeball are completely fused with 
the ophthalmic division of the fifth.* In the Myxinoid fishes 
there are no motor nerves of the eyeball ; but, in the Lamprey, 
the rectus externus and inferior, and the obliqutcs inferior, are 
supplied by the ophthalmic, vs^hile the oculomotor and the pa- 
thetic unite into a common trunk, which gives branches to the 
rectus superior and interims, and ohliquus superior. The ocu- 
lomotor, the pathetic, and the abducens, are more or less con- 
founded with the ophthalmic in the Amphibia • but in Tele- 
ostei, Ganoiclei, Elasmohranchii , and in all the higher Yerte- 
hriita, 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 tri- 
geminal, as in the Frog. In all abranchiate Vertebrata the 
two nerves are quite distinct. 

Whether the nerves are distinct or not, a, palatine, or vidi- 
an, nerve (which, in the higher Vertebrata, is especially con- 
nected 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 contributing to form the 
sphenopcdatine, or Mechelian, ganglion, is distributed to the 
mucous membrane of the roof of the mouth ; and the mandib- 
ular division of the seventh, or chorda tymp>ani, unites with 
the inferior maxillary division of the fifth nerve. 

The eighth, pair [auditorii) is formed by the nerves of the 
orgfan of hearinof. 

The ninth pair {glossophanjii r/ei) 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 {^pneumocja s^trijd or vagi) consists of very 

•I am greatly disposed to tliink that the motor nerves of the eye more 
nearly retain their primary relations \tx Lepidosiren than in any other verte- 
brated animal ; and tliat they are really the motor portions of tlie nerves of 
the orhito-nasal cleft, the third and fourth appertaining to the inner division 
of the ophthalmic, the sixtli to its outer division. 



THE EXITS OF THE CEREBKAL NERVES. G9 

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 Ichthyojysida they give 
off, in addition, long lateral nerves to the integuments of the 
sides of the body. In the higher Vertebrata, these lateral 
nerves are represented only by small branches distributed 
rbiefly to the occipital region. The ninth and tenth pairs are 
both motor and sensorj' in function, and are often so inti- 
mately connected as to form almost one nerve. 

The eleventh pair [accessor ii) 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 pneuniogastrio, 
partly joining it, and partly going to muscles which arise from 
the head and anterior vertebrae, and are inserted into the pec- 
toral arch. 

The spinal accessory exists in no Ichthyopsid vertebrate, 
but is found in all Sauropsida, 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 oftens remains closely 
connected with the first cervical, and may rather be regarded 
as a subdivision of that nerve, than as a proper cerebral 
nerve. 

Thus the nerves arising from the hind-brain, in all the 
higher Yertebrata, fall into three groups : 1st, a sensori-motor, 
pre-auditory, set (3d, 4th, 5th, 6th, 7th) ; 2d, the purely sen- 
sory auditory nerve (8th) ; 3d, the sensori-motor, post-audi- 
tory, set (9th, 10th, 13th). 

The apertures by which several of these nerves leave the 
skull, retain a very constant relation to certain elements of 
( he 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. 

h. The optic nerve constantly passes out behind the cen- 
tre of the orbitosphenoid and in front of that of the alisphe- 
noid. 



70 THE ANATOMY OF TEKTEBRATED ANIMALS. 

c. The third dirision of the trigeminal, or fifth nerve, al- 
ways leaves the skull behind the centre of the alisphenoid and 
in front of the proOtic. 

d. The glossopharyngeal and pneumogastric alvva3'S 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, h, c, d, when surrounded by bone, and 
well defined, are called respectively : a, the olfactory foramen ; 
b, the ojytic foramen ; c, \)i\& foramen ovale ; d, theforameii 
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 enclosing the first visceral cleft. In like man- 
ner, the ninth (glossopharyngeal) nerve is distributed to the 
hinder part of the second arch and to the front part of the 
third, its branches enclosing the second visceral cleft. The 
first branch of the pneumogastric has similar relations to the 
third and fourth arches and to the third cleft ; and, in bran- 
chiate Vertebrafa, the other anterior branches of the pneumo- 
gastric are similarly distributed to the successive branchial 
arches, the two divisions of each branch enclosing 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 repre- 
senting a visceral cleft between the two. The inner and outer 
portions of the first division of the trigeminal are similarly 
related to the inner, or anterior, region of the maxillo-palatine 
process, and the outer side of the trahecula cranii — the orbito 
nasal fissure representing the cleft between the two. 

Considerations of this kind suggest that the trabeculae and 
tiie maxillo-palatine processes may represent pre-oral visceral 
arches, which are bent forward ; and, in the case of the tra- 
beoulce, coalesce with one another. Such an hypothesis would 
enable us to understand the signification of tlie naso-pulatine 



THE SYMPATHETIC NEEVES. 71 

canal of tlie Myxinoid fishes, which would be smiply the iii- 
lerspace, or passage, between the trabeculiu (which must have 
originally existed it ever they were distinct visceral arches) 
not yet filled up ; and the anomalous process of the roof of the 
oral cavitj', wliich extends toward the pituitary body in the 
embryos of the Vertebrata in general, might be regarded as the 
lemains 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, cra- 
nial, visceral arches. 

Supposing that the occipital segment in the brain-case an- 
swers 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 max- 
illo-palatine and trabecular visceral arches. And thus the Of- 
sifications 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 doctiine of its segmentation, 
which is simply a generalization of anatomical facts. 

The Sympathetic. — A Sympathetic Nervous System has 
been observed in all the VertcLrata except Am2}hioxus and 
the Marsipohranchii. It consists, essentially, of two longi- 
tudinal cords, placed one upon each side of the inferior face 
of the cranio-spinal axis. Each cord receives communicating 
fibres from the spinal nerves of its own side, and, when com- 
plete, from all the cranial nerves except those of the special 
senses of hearing, sight, and smell — the Vidian nerves consti- 
tuting the anterior terminations of the sympathetic 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 Marsipobrancliii, the place of the sympathetic ap- 
pears to be taken, to a great extent, by the pneumogastric ; 



'72 THE ANATOMY OF VERTEBRATED ANIMALS. 

and, in 3Tyxine, the two pneutnogastrics unite upon the intes- 
tine, and ibllow 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 
alreadj' 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 integu- 
ment. 

The OlfaHory ^Ipparafus acquires no higher complication 
than this, being either a single sac {Aiiiphio.ras (?) MarsijJO- 
branrhii), or, more commonly, two, the surfaces of which are 
increased by plaiting, or by the development of turhinal carti- 
lages, or bones, from the lateral portions of the ethmoid. 
Upon these, nervous filaments arising from the olfactory 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 raajoritv of fishes, 
they may have only an external aperture, or apertures. 

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

The foramina incisiva, left between the premaxillaries 
and the palatine plates of the maxillaries in 3Iammalia, are 
sometimes closed by the mucous membranes of the nasal and 
oral cavities, and sometimes not. In the latter case they are 
the canals of Stenson, audi place these two cavities in com- 
munication. Glandular diverticula of the mucous membrane, 
supplied with nervous filaments from both the olfactorj' and 
the fifth pair, may open into these canals. Thej' are called, 
after their discoverer, the '■'■organs of Jacolison.'''' 

The Eye is formed by the coalescence of two sets of struct- 
ures, one furnished by involution of the integument, the other 
by an outgrowtii of tlie brain. 

The opening of the integumentary depression which is pri- 
marily 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 metamorphosed into the 
cri/:4<iUi.ne lens ; the cavit3' fills with the aqueous humor. A 
vascular and muscular ingrowth taking place round the cir- 
cumference of the sac, and, dividing its cavity into two seg- 
ments, gives rise to the iris. The integument around the cor 



THE EYE. 73 

nea, growing out into a fold above and below, results in the 
formation of the ej'elids, and the segregation of the integu- 
ment which they enclose, as the soft and vascular conjunctiva. 
The pouch of the conjunctiva very generally communicates, 
oy 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 a proper muscle or muscles. Special 
glands -the lachrymal 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 ori- 
gin. Very early, that part of the anterior cerebral vesicle 
which eventua.ly 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 integu- 
mentary sac. The posterior, or outer, wall of the diverticulum 
then becomes, as it were, thrust in, and forced toward the op- 
posite wall, by an ingrowth of the adjacent connecrtive tissue ; 
so that the primitive cavity of the diverticulum, which, cf 
course, communicates freely with that of the anterior cerebral 
vesicle, is obliterated. The broad end of the diverticulum ac- 
quiring a spheroidal shape, while its pedicle narrows and elon- 
gates, the latter becomes the optic nerve, while the forme r, 
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 ves- 
icle upon itself, gives rise to the retina and the choroid coat: 
the plug, or ingrowth of connective tissue, gelatinizes aiid 
passes into the vitreous humor, the cleft by which it entered 
becoming obliterated. 

Even in the higher 'Vertebrata the optic nerve is, at firs t, 
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 mesencepha- 
lon on that side, and the trunks of the two nerves become in- 
termixed below the third ventricle, in a close and complicated 
manner, to form a chiasma. 

In Amphioxus and Myxine, the eyes are very imperfeclly 
developed, appearing to consist of little more than a rudimen- 
tary lens imbedded in the pigment, which encloses the termi- 
nation of the optic nerve ; and, in Myxine, this rudimentary eye 
is hidden by muscles and integument. It appears doubtful 
4 



74 THE ANATOMY OF VERTEBRA TED ANIMALS. 

wliethei' in these fishes, and in the Lampreys, the ej'e is de- 
vehjped in the same way as in other Vertehrata. 

In all other Vertehrata, the eyes have the typical structure, 
though sometimes, as in the Blind-fish {Amblyo2)sis) and the 
Mole, they have no functional importance. In the Ichthy- 
opsida and Sauropsida, but not in JSIammalia, the sclerotic 
is often partially ossified, the ossification usually forming a 
ring around its anterior moiety. It becomes enormously 
thickened in the CeUicea. 

Except in A.mphtoxus and the Myxinoid fishes, the ej'e- 
ball is moved by six muscles ; of these, four, proceeding from 
the interior of the orbit to the periphery of the eyeball, and 
surrounding tlie optic nerve, are termed superior, inferior, in- 
terna], and external recti. The other two are connected with 
the upper and the lov/er margins of the orbit respectively, and 
pass thence to the outer side of the bulb. These are the supe- 
rior and the inferior ohliqui. In many Reptiles and Mam- 
mals a continuous funnel-shaped sheet of muscle, the muscit- 
lus choanoides, lies within the four recti, and is attached to 
the circumference of the posterior moiety of the ball of the eye. 
It would appear, from the distribution of the nerves, which 
has already been described, that the musculus choanoides, 
tlie external rectus, and the nictitating muscle, constitute 
a group of eye-muscles morphologically distinct from the othei 
three recti, the ohliqui, and the levator palpebroB superioris. 
In many Reptiles, and in the higher Vertehrata, the eyelids 
are closed by circular muscular fibres, constituting an orbicu- 
laris palpelrrarum, and are separated by straight fibres pro- 
ceeding from the back of the orbit, usually to the upper eye- 
lid only, as the levator palpjelnM superioris ; but sometimes to 
both lids, when the lower muscle is a depressor palpehrm infe- 
rioris. 

The Harderian and lachrymal glands are not found in 
fishes ; but the former is met with in the Satrachia , and both 
are of common occurrence in the Sauropsida and Mamnicdia. 

In Zidcertilia, Crocodilia, Aves, and many Fishes, a pecu- 
liar vascular membrane, covered with pigment, like the cho- 
roid, projects from near the entrance of the optic nerve, on the 
outer side of the globe of the eye, info the ^dtreous humor, 
M rid usually becomes connected with the capsule of the lens. 
This is i\\e pecten, or marstipium. 

Tlie Ear. — The first rudiment of the internal ear is an in 
i^ohuion of the integument into a small sac, which is situated 



THE EAR. 



76 



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 (ordi- 
narily) converted into three semicircular canals — the anterior 
and posterior vertical, and the eaternal or horizontal canals 
of the membranous labyrinth. The body of the sac remains, 
lor the most part, as the vestibule ; but a csecal process, which 
eventually becomes shut off from the vestibule, is given oft 
downward and inward, toward 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, Amphioxus, no ear has yet 
been discovered. The Hag [Myxine) has only one, and in the 
Lampreys (Petromyzon) there are only two, semicircular ca- 
nals ; but, in fishes in general, all three are developed, and it 
is a question whether the cochlea is not also represented. 

In fishes, the periotic cartilage and its ossifications enclo.se 
this membranous labyrinth, externally, and present no merely 
membranous gaps, or fenestrcB, toward the first visceral cleft, 
or the space which represents it. 

But in higher Vertebrata {Amphibia, 8auropsida, Mam- 
m.alia), in which the membranous labyrinth is always enclosed 
within a complete bony periotic capsule, the outer wall cf 
this capsule invariably remains unossified over one or two 
small oval areas, which consequently appear like windows wH h 
membranous panes, and are termed ihe 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 
proOtic 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 
i\ie fenestra ovalis, and lies altogether in the opisthotic. It 
forms part of the outer wall of the cavity in which the mem- 
branous cochlea is lodged. 

In the Sauropsida and Mammalia, this membranous coch- 
lea, become flattened and bandlike, and its communication 
with the vestibule obliterated, is lodged in a conical cavity, in 
such a manner as to divide that cavity into two portions, 
called scalce, which only communicate at their apices. The 
base of the one scala, called scala vestibuli, opens into the 



76 THE ANATOMY OF VERTEBRATED ANIMALS. 

cavity which contains the membranous vestibule : that of tlie 
other, saaki tympani, abuts against, and is as it were stopped 
by, the membrane of the fenestra rotunda. The cavity of the 
membranous cochlea stretched between, and helping to divide, 
these two soalce, is called the scala media. 

la Reptiles, Birds, and Ornithodelphous Mammals, the 
cochlea is only slightly bent or twisted upon itself. But, in 
the higher Mammalia, it becomes coiled in a fiat or conical 
spiral of one and a half [Getacm, Esrinaceui) to five {Gdelo- 
genys Paaa) turns. 

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

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

In the majority oiVertebrata of higher organization than 
fishes, the first visceral cleft does not become wholly obliter- 
ated, but its upper part remains as a transversely elongated 
cavity, by means of which the pharynx would be placed in 
communication with the exterior, were it not that the oppo- 
site sides of the canal grow together into a membranous par- 
tition — the niemhrana tympani. So much of the canal as lies 
external to this is 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 tympanum in communi- 
cation with the pharynx. While the outer wall of the tym- 
panum is the tympanic membrane, its inner wall is the periotic 
mass with its fenestroe, ; and, in all Vertebrata below Mam- 
mals, the outer end of the stapes is either free, or, more com- 
monly, is fixed to the tympanic membrane, and thus the latter 
and the membrane of '^e fenestra ovalis become mechanically 
connected. In all these animals the mandible is connected 
with the skull by the intermediation of an as quadratum,. 

But, in the Mammalia, the mandible is articulated directly 
with the squamosal, and the quadratum is converted into one 



THE EAR. 



77 



of the so-called ossicula miditus, and named the malleus. The 
malleus becomes attached to the membrana tympani, hy a 
special process ; while its other extremity, which was continu- 
ous with Meckel's cartilage in the embryo, is converted into 
the processus gracilis, or Folianus, and lies between the tym- 
panic;, 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 upward, 
which passes into the wall of the periotic capsule, just behind 
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-stapedial part is rep- 
resented by cartilage, or ligament, in other Saiiropsida, but 
seems not to ossify. In the Mammalia (B, Fig. 24), the su- 
pra-stapedial part ossifies, becomes the incus, and its proximal 
end is usually articulated by a synovial joint with the malleus 
(= quadratum). A distinct ossification, the os orhiculare, 
usually arises at that part of the hyoidean cartilage in which 
the stapes and the incus unite. That part of the hyoidean 
cartilage which is converted into the styloid process is gen- 
erally connected with the orbieidare by muscular fibres, which 
constitute the stapedius muscle. On the other hand, the pos 




FtG. 24. — Uiaffram of the skeleton of the first and second visceral arches in a Lizard (A) 

Mamma' (B), and an Osseous Fish (C). 
The skeletol of the first viscerfil arch is shaded, that of the second is left nearly unFhaded, 

/. First visceral arch. Mck. Meckel's cartilage. Art, Articulare. Qu. Quadi-atum. 

Mpt. Metapterygoid ; M. Malleus ; p,g.^ Processus pracilis. //. Second vipcerM ir*h. 

//?/. Hyoidean coma. St. II. Stylohyal. S. Stapedius. Stp. Stapes. >i?. l:itp. ^u]>r,v 

fttTijipdial. //J/. Hyouiandibular. The an-ow indicates the first visceral cleft, /'z. ITw 

periotic capsule. Ptg. The pterygoid. 



terror, or short process of the incus, is connected by hga^ient 
with that part of the periotic mass into which the styloid pro- 



78 THE ANATOMY OF VEETEBRATED ANIMALS. 

oess is directly continued, and it is hard to say whether the 
styloid part of the hyoid is continued 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. 

In osseous fishes (C, Fig. 24), which have no fenestra o-\'a- 
lis 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 
its direct connection with the periotio capsule, and becomes 
distinctly ossified, as the rnetapterygoid. In the Sharks, even 
the ascending, rnetapterygoid, part of the quadrate, is lost. 

The quadrate and supra-stapedial portions of the first and 
second visceral arches coalesce in the Chwicera, Dipnoi, and 
ma.nj A.m2)Mbia, into a single cartilaginous plate. 

In the Mammalia, and to some extent in A.ves, osseous 
matter is deposited in the fibrous tissue which surrounds the 
sides and base of the tympanic membrane, and gives rise to a 
special tym^panic bone. In most Mav%m.alia, ossification ex- 
tends 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 de- 
veloped, the mucous membrane is raised into numerous papillte 
of various forms, and is well supplied with filaments from the 
glossopharyngeal nerve. 

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

As special organs of touch in the higher Vertebrata, the 
nervous papillae, containing " tactile corpuscles," and the long 
facial hairs, the papillas of which are well supplied with nerves, 
termed vibrissce, may be mentioned. 

In most, if not all Fishes, the integument of the body and 
cf 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 papillas, vrhich project into the gelati- 
nous contents. These sensory organs are known as the " or- 



THE LIVER AND THE TEETH. 79 

gans of the lateral line" or " mucous canals ; " and they 
were formerly supposed to be the secretory 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, 
oesophagus, 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 cham- 
ber 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 cceca are 
frequently developed from the former. 

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 abdomi- 
nal cavity. Glands appertaining to the lymphatic system 
frequently abound in the mesenteric folds, and a highly-vas- 
cular gland of this system, the spleen, is always (except in 
Amphioxus, Myxine, and the Leptocephalidm) developed in 
close proximity to the stomach. A pancreatic gland very 
generally pours its secretion into the anterior end of the intes- 
tine. 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 ver- 
tebrate animals, which are most characteristic and peculiar, 
are the liver and the teeth. 

The Liver. — In invertebrate animals this organ is always 
ultimately resolvable into caecal 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 proportional 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 in- 
directly, into a receptacle, the gall-bladder. Amphioxus stands 
alone among vertebrated animals, in having a csecal diverticu- 
lum of the intestine for a liver. 

The Teeth. — Teeth, in Mollusoa and Annulosa, are always 



80 TUE ANATOMY OF VERTEBRATED ANIMALS. 

" ecderonic," cuticular, or epithelial structures. In Vertebrata 
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 
Ornithorhynclms, appear to be ecderonic structures, homolo- 
gous 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, characterized by 
the close-set parallel tubuli which radiate through it, branch- 
ing 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 papillee 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 
cither 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, decidu- 
ous, or milk dentition, and a second, or permanent dentition. 
The deciduous dentition, when most completely developed, con- 
sists of incisor, canine, and molar teeth. The incisors are 
distinguished from the rest by the lodgment of the upper set 
in the premaxillsB, and the correspondence of the lower set 
with the upper. Their number and forai vary. The distinc- 
tion 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 formida is a convenient combination 
of letters and figures for making the number and disposition 
of the teeth obvious. Thus, let di, dc, dm, represent, respec- 
tively, 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 teeth of the kind 
symbolized, on each side of each jaw, we shall have the dental 



DENTAL FORMULA. 81 

formula of a given animal. The dental formula of a child 

23 -^ 1 o 2 

over two years of age is thus — di. ^ dc. : — - 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, ani 
developed altogether behind the milk molars, and thus comt- 
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 : 
. 2.2 1—1 2.2 3.3 -. ^, , . 

*-o~o''-i — 1 P'"^- ^m ™- oo—^^ i there bemg two mcisors, 

one canine, two premolars, and three molars on each side 
above and below. It is a rule of very general application 
among the Mamm.alia, that the most anterior molar comes 
into place and use before the deciduous molars are shed. 
Hence, when the hindermost premolar, which immediately 
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 dovm ; and this excess of wear of the first molai 
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 immediately 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 alimen- 
tary canal save the mouth and pharynx — except a 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 vertebrae into the oesophagus. 
And, in the highest Vertebrata, teeth are confined to the pr& 
maxillae, maxillae, and mandible. 

The Circulatory Organs. — The heart of the vertebrate 
embryo is at first a simple tube, the anterior end of which 



82 THE ANATOMY OF VERTEBRATED ANIMAL9. 

passes into a cardiac aortic trunk, while the posterior end ia 
continuous with the great veins which bring back blood from 
the umbilical vesicle — the omphalomeseraic veins. 

The cardiac aorta immediately divides 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 
fello-w, to the hinder part of the body, as a. primitive subverle- 
hral aorta. The two primitive aortse very soon coalesce 
throughout the greater part of their length into one trunk, 
the definitive mbvertehral aorta ; but the aortic arches, sepa- 
rated by the alimentary tract, remain distinct. Additional 
arterial trunks, to the number of four in the higher Verte- 
brata, and more in the lower, are successively developed, 
behind the first, in the other visceral arches, and further con- 
nect the cardiac and subvertebral aortae. 

In the permanently branchiate Vertebrata, the majority of 
these aortic arches persist, giving oif 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 Satrachia (Fig. 35, F) and Gmcilia, 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 Satrachia, 
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 backward ; but the fourth 
pair onl}', 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 " representing the 
remains of the primitive connection of these arches with tlie 



MODIFICATIONS OF THE AORTIC ARCHES. 



83 



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, be- 
come the arteries of the head and upper extremities. 



Mh. mi. J}/-.' En' Bn^ Bn'Bn' Bn" Br.' 

I I I I I I I I L 





Ch. 



iimililililC 




f^e, "js, — A diagram Intended to show the manner in which the aortic arches becomft modi- 
fied in the series of tiie Vertebrata. 

k. A hypottietically perfect series of aortic arches, corresponding with the nine postoral vis- 
ceral arches, of which evidence is to be found in some Shai-ks and Mm's-ipobranchii. 
AC. Cardiac aorta; AI). Dorsal or subvertebral aorta, i-ix the aortic arches corre- 
Bpondlng- with JiJi., the mandibular; Hy,^ the hyoidean, and Br.^ — ^j?r. '^, the seven 
branchial vlscoral arches, i, ii, m, rv, v, vi, ni, the seven itranchial clefts. The firs! 



tJ4 THE ANATOMY OF VERTEBRATED ANIMALS. 

vieeeral cleft is left unnumbered, and one must be added to tne nnmner of each bran* 
chiai cleft to give its number in tlie series of visceral clefts. 

B. Hypothetical diagram of the aortic arches In the Shark Ilepianchun, which has seven 

branchial clefts. Sp. The remains of the fh-st visceral cleft as the spiracle. Branchia? 
are developed on all the arches. 

C. LepidoslrtTi. — The first arch has disappeared as such, and the first ^^sceral cleft is ob- 

literated. Internal branchiae are developed in connection with the second, fifth, sixth, 
and seventh aortic arches; external branehise in connection with the fourth, fifth, and 
sixth. PA. — The pulmonaiy artery. The posterior two visceral clefts are obliterated. 

r A Teleostean Fish. — The first aortic arch and first visceral cleft are obhterated as before. 
The second aortic arcb bears the psendo-branchia {Ps.B.\ whence issues the ophthalmic 
artery, to terminate in the choroid gland {Oh.). The next four arches bear gills. Tho 
.seventh and eighth arches have been observed in the embryo, but not the nintli, 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 glands Ca. G.) which terminates 
it. The fourth pair of aortic arches persist. The fifth and sixth pair lose their connec- 
tions with the subvertebral aortic trunk, and become the roots of the cutaneous and 
pulmonary arteries. The first visceral cleft becomes the tympanum, but ail the others 
are obhterated in the adult. 

The embryonic aorta gives off omphalomeseraic branches 
(Fig. 26, o) to the umbilical vesicle ; and ends, at first, in the 
hyjyogastric arteries (which are distributed to the allantois in 
the abranchiate Vertebrata), and a median caudal continuation. 
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, JDG), which is itself 
formed, upon each side, by the junction of the anterior and 
posterior cardinal veins, which run backward and forward, 
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 umbilical 
vein, or veins (Fig. 26, u), 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 kid- 
neys 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, interrupts 
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 
Bide, with its intestinal part. The latter is thus converted into 
the vena portce (Fig. 26, vp), distributing the blood of the 
Btomaoh and intestines to the liver ; while the former becomes 



THE DEVELOPMENT OF THE VASCULAR SYSTEM. 



8a 



the hepatic vein (vh), carrying the hepatic blood to the in- 
ferior cava, and thence to the heart. 

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. 36, 1}v). 




Fio. 26, — Diagram of the arrangement of tlie principal vessels in a human fo3tus. — IT, th* 
heart ; TA, the aortic trunk or cardiac aorta ; c, the common carotid ; c', the externa] 
carotid ; c", the internal carotid ; fi, subclavian ; -y, vertebral artery ; i, 2, 3, 4, 5, the 
aortic arches — the persistent left aortic arch is hidden. A\ BUbvertebral aorta ; o, om- 
phalomeseraic artery, going to the umbilical vesicle i), with its vitelline duct dv ; o, om- 
phalomeseraic vein \ i)p^ the vena portjB ; L, the liver ; ««, tho hypogastric or umbilical 
arteries, with their placental ramifications, m" «" ; i^, the umbihcal vein ; i>y, the ductus 
venosus ; vK tbe hepatic vein ; cv, the vena cava inferior ; 'ffil, the iliac veins ; az, a vena 
azygos ; vc', a vena cardinalis posterior ; DC^ a ductus Cuvieri ; the anterior cardinal 
vein is seen commencing in the head and running down to the ductus Ouvieri on the 
under side of the numbers 1, 2, 3, 4, 5 ; P, the lungs. 



When the umbilical vesicle and allantois cease to have any 
further import, as at birth, or before, the omphalomeseraic ar- 
teries have become intestinal arteries, and the omphalomeseraic 
vein, the vena portse. The hypogastric arteries are obliter- 
ated, except so much of them as is converted into the common 
iliac arteries. The umbilical vein, or veins, also disappear, oi 
are represented by mere ligaments. 



86 THE ANATOMY OF VERTEBRATED ANIMALS. 

Of the three veins which open into the venous sac — via, 
the inferior cava, and the right and left ductus Cuvieri — all 
may persist, the latter receiving the title of right and left svr 
perior cavcB. Or, as very often happens in the higher Verte- 
brata, the left ductus Cuvieri becomes more or less obliterated ; 
the veins 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 oif anastomosing 
branches, which are converted into the vence azygos ; the an- 
terior cardinal veins become metamorphosed into the external 
jugular veins and venm innominatos. 

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 extremi- 
ties, are called vetim jugulares. 

The caudal veins are either directly continued into the 
cardinal veins, as in Marsipohranchii and Elasmohranchii, 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 abdomi- 
nal walls, may be one or many. In Amphioxus and Myxine 
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 Cuvieri, which are now termed an- 
terior venm cavce. 

The ve7ia cava inferior takes its origin chiefly by the coa- 
lescence of the efferent veins of the kidneys and reproductive 
organs, and does not always receive the whole of the hepatic 
veins — more or fewer of the latter opening independently info 
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 portae in the substance of the kidneys. Tliis 
renal portal system is less developed in Reptilia than in Ainr 
phibia. 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 



THE MODIFICATIONS OF THE VASCULAR SYSTEM. 87 

run along the anterior wall of the abdominal cavity, either as 
two trunks, or united into one. These vence abdominales an- 
teriores are eventually distributed to the liver, along with the 
branches of the proper venm portce. 

In Birds, the sinus venosus is not distinct from the right 
auricle, and there, are two anterior vence cavm. 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 abdominal 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 common 
iliacs. Thus there is no renal portal system in birds. 

In Mammalia, the sinus venosus is not distinct from the 
right auricle. The anterior cavce 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 represented 
only during foetal life, by the umbilical vein or veins. The 
efferent veins of the kidneys open directly into the trunk of 
the inferior vena cava, and the portal vein is composed 
exclusively of radicles proceeding from the chylopoietic 
viscera. 

Many of the veins of AmpMoxus, the portal vein of Myoi- 
ine, dilatations of the caudal vein in the Eel, the vense cavse 
and the iliac and axillary veins of many Amphibia, the veins 
of the wing of Bats, possess a rhythmical contractility, 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 
Dot unite again into larger trunks. These are called retia 
mirabilia. 

Modifications of the Heart. — Great changes go on m the 
structure of the heart, joar« ^)as«M with the modifications of the 



38 THE ANATOMY OF VERTEBRATED ANIMALS. 

rest of the circulatory system, in the development of tho 
highest Vertebrata. The primitively simple tube becomes 
bent upon itself, and divided from before backward into an 
aortic, or ventricular, and a venous, or auricular, portion. A 
median septum then grows inward, dividing 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 efifected in the 
cardiac aorta. The septa are so disposed in the auriculo-ven- 
tricular 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 com- 
municates with the chief aortic trunk, the right with the pul- 
monary artery. Valves are developed at the auriculo-ventric- 
ular 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 
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 Orocodilia, the auricles and ventricles 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 veno- 
sum and a cavum arteriosum. The auricles are completely 
separated (except in some Ghelonid), and the blood of the 
left auricle Hows directly into the cavum arteriosum, 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 arteriosum. 

In all Amphibia, the spongy interior of the ventricle is 
andivided, and the heart is trilooular, though the auricular 
septum is sometimes small and incomplete. In all Pisces, ex- 
cept Lepidosiren, there is no auricular septum. In Aniplil- 



THE MODIFICATIONS OF THE HEART. 89 

C'^.us the heart remains in its primitive state of a simple, con- 
tractile, undivided tube. 

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

The Ganoidei and Elasmobranchii possess, not merely the 
ordinary semilunar valves, at the junction between the ventri- 
cle 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 ves- 
sels 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 ascends. 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 pneumogastric, with which it is supplied, 
must, originally, pass directly to their destination. But, as 
development proceeds, 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 pneiunogastric, 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. 

77ie Sloodr Corpuscles. — Corpuscles are contained in the 
blood of all Vertebrata. In Amphioxus they are all of one 
kind, colorless and nucleated. The genus Leptocephalus, 
among the Teleostd, is said to possess the same peculiarity ; 



eO THE ANATOMY OF VERTEBRATED ANIMALS. 

but, in all other known Vertebi'ata, the blood contains corpus 
cles of two kinds. 

In Ichthyopsida and Sauropsida, both kinds are nucleated ; 
but one set are colorless, and exhibit amaeboid movements, 
while the others are red, and do not display contractility. 
Except in the Marsipobranchii, which have round blood-cor- 
puscles, 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, 
colorless and red, the colorless possessing, and the red being 
devoid of, nuclei. It is but very rarely that a nucleated cor- 
puscle, with a red color especially developed about the nu- 
cleus, 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-colored nucleus. 

The colorless corpuscles of Mamm,alia are spheroidal, and 
exhibit amseboid movements ; the red corpuscles are flattened, 
usually circular, but sometimes oval ( Oam,eUdm) disks, devoid 
of contractility. 

TJie LympJiatic System. — This system of vessels consists, 
chiefly, of one or two principal trunks, the thoracic duct, or 
ducts, which underlie the vertebral column, and communicate, 
anteriorly, with the superior vense cavse, or M'ith 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 Vertehrata, the 
larger branches are like small veins, provided with definite 
coats, and with valves opening toward the larger trunks, while 
their terminal ramifications form a capillary net-work ; but, in 
the lower Vertebrates, the lymphatic channels assume the form 
of large and irregular sinuses, which not unfrequently com- 
pletely surround the great vessels of the blood-system. 

The lymphatics open into other parts of the venous sj-s- 
tem besides the affluents of the superior cava;. In Fishes 
there are, usually, two caudal lymphatic sinuses which open 
into the commencement of the caudal vein. In the Frog, foui 
such sinuses communicate with the veins, two in the coccy- 
geal, and two in the scapular, region. The walls of these si 
nuses are muscular, and contract rhythmically, so that they re- 
ceive the name of Lymithatic hearts. The posterior pair of 
these hearts, or non-jiulsating sinuses corresponding with 
them, are met with in Reptilia and Aves. 



THE RESPIRATORY GROANS. 91 

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 Grocodilia, among Reptilia, that an accumulation 
of such tissue, traversed by lymphatic canals and blood-vessels, 
is apparent, as a Lymphatic gland, in the mesentery. Birds 
possess a few glands in the cervical region ; and, in Mam- 
malia, they are found, not only in the mesentery, but in many 
parts of the body. 

The Spleen is substantially a lymphatic gland. The Thy- 
mus — a glandular mass with an internal cavity, but devoid of 
any duct — which is found in all Vertebrata except Amphioxus, 
appears to belong to the same category.. It is developed in 
the neighborhood 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 abun- 
dantly 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 colorless corpuscles of 
the blood. 

The Respiratory Organs. — ^Vertebrated animals may pos 
sess either hranchicB for breathing the air contained in water, 
or lungs for atmospheric respiration; or they may possess 
both kinds of respiratory organs in combination. 

Except in Amphioxus, the branchim 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 bran- 
chiae of some fishes) even to the mandibular arch. The bran- 
chiae are always supplied with blood by the divisions of the 
cardiac aorta ; and the different trunks which carry the aSrated 
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 Vert^rata, the bran- 



P2 THE ANATOMY OF VERTEBUATED ANIMALS. 

chiaj 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 exter- 
nal plume-like appendages of the neck throughout life. But 
in the adult life of most Fishes, and in the more advanced con- 
dition of the Tadpoles of the higher Amphibia, the branchiae aro 
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 
phar3rnx, with which they remain connected by a shorter or 
longer tube, the trachea, the division of this for each luug 
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 es- 
sential part of the definition of a lung, as many fishes possess 
hollow sacs filled with air; and these sacs are developed, oc- 
casionally, from the ventral, though more commonly from the 
dorsal, wall of the pharynx, oesophagus, or stomach. But 
such air-sacs — even when they remain permanently 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 Vertehrata, 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 condition of the em- 
bryonic lung. In Chelonia and Crocodilia, the lung is com- 
pletely 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 dichotomously into finer and 
finer bronchial tubes, which end in sacculated air-cells. 

* Generally all. hut in some AmpJdhia, siioh as Proteus, part of the blood 
•uppUeJ to Slio lungs enters tlie general cireuliition. 



THE ORGANS OF VOICE. 93 

Blind air-sacs ai'e given off from the surfaces of the lungs 
m the Chainceleonidce, and the principal bronchial tubes ternu- 
nate in large air-sacs in Aves. 

The Larynx, and the Syrhvx. — The trachea is commonly 
kept open by complete, or incomplete, rings of cartilage, and 
I lie uppermost of these undergo special modifications, \\hich 
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 aryt- 
enoid cartilages are movably articulated, and a thyroid car- 
tilage of a V-shape, open behind, is articulated movably with 
its sides. Folds of the mucous membrane, containing elastic 
tissue, termed the vocal cords, stretch from the arytenoid car- 
tilages to the reSntering angle of the thyroid cartilage, and 
between them lies a slit-like passage, the glottis. This is cov- 
ered by a cartilage, the epiglottis, attached to the reentering 
angle of the thyroid, and to the base of the tongue. Folds 
of mucous membrane, extending from the epiglottis to the 
arytenoid cartilages, are the aryepiglottic hgaments. The in- 
ner surfaces of these end below in the false vocal cords, be- 
tween which and the true chordae vocales lie recesses of the 
mucous membrane, the ventricles of the larynx. 

The chief accessory cartilages are the cartilages of San- 
torini, attached to the summits of the arytenoid cartilages, 
and the cartilages of Wrisberg, which lie within the aryepi- 
glottic 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. 

TJie Mechanism of Respiration. — The mechanism by which 
the aerating medium is renewed in these different respiratory 
organs is very various. Among branchiated Vertebraia, A m- 
phioxus stands alone in having ciliated branchial organs, which 
form a net-work very similar to the perforated pharyngeal a 'all 
of the Ascidians. Most Fishes breathe by taking aerated ^^ a- 
ter 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 nostrila 



04 THE ANATOMY OF VERTEBRATED ANIMALS. 

being shut, pumping it, by the elevation of the hyoidean ap- 
paratus and floor of the pharynx, into the lungs. A Frog, there- 
fore, cannot breathe properly if its mouth is kept wide open. 

In most ReiMlia, and in all Aves and Mammalia, the ster- 
num and ribs are capable of moving in such a way as alter- 
nately 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 Heptilia, 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 the fixed 
and little distensible lungs, into the very dilatable and com- 
pressible air-sacs. From these the act of expiration expels it 
back through the principal bronchial passages to the trachea, 
and so out of the body. 

Both in Heptilia (e. g., Ghelonia) 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 Ma- 
titm, 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 in- 
spiration remains far weaker than the sterno-costal inspiration. 

Finally, in the Mamm.alia, there are two equallj'-important 
respiratory pumps, the one sterno-costal, the other diaphrag- 
matic. The diaphragm, though it makes its appearance in 
Sauropsida, 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 toward the abdominal 
cavity, and convex toward the thorax, the result of its con- 
traction, and consequent flattening, necessarily is to increase 
the capacity of the thorax, and thi3^ 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' in- 
dependently of the other. 

The Renal Organs. — The higher Vertebrata are all pro- 
vided with two sets of renal organs, the one existing only dur- 
ing the early foetal state, the other persisting throughout life. 

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



THE REPRODUCTIVE ORGANS. 95 

The WolfBan bodies make their appearance very early, on 
each side of the ventral aspect of the spinal region of the em- 
bryo, as small transversely-disposed tubuli, opening into a duct 
which lies upon their outer side, and enters, posteriorly, into 
the base of the allantois, and thence into the primitive cloaca 
v?ith which that structure is connected. The WolfBan duct is 
one of the first-formed structures in the embryo, and precedes 
the tubuli. 

The Kidneys appear behind the Wolffian bodies, and, ap- 
parently, independently of them ; their ducts, the ureters, arc 
also distinct, but likewise terminate in the pelvic part of the 
allantois. Thus the urinary secretion passes into the allantois, 
and it is that portion of this organ which lies within the abdo- 
men, and becomes shut off from the rest by the constriction 
and obliteration of the cavity of an intermediate part, and its 
conversion into the urachus, that gives rise to the urinary 
bladder. The ultimate secreting tubuli of both the Wolffian 
body and the kidney, are alike remarkable for ending in dila- 
tations which embrace convoluted capillaries — the so-called 
Malpighian tufts. Neither Wolffian bodies nor kidneys have 
been observed in Amphioxus. It is doubtful whether true 
kidneys are developed in Ichthyopsida, or whether the so- 
called kidneys of these animals arc not, rather, persistent Wolf- 
fian 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 ovari- 
um. 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 ^lace that cavity in direct communi- 
cation 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 Ver- 
tebrata, 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 con- 
veyed away by a special apparatus, consisting of the Fallopian 
tubes, which result from the modification of certain embryonic 
structures "called the Mullerian ducts. 

The Miillerian ducts are canals which make their appear- 
ance alongside the ducts of the Wolffian bodies, but, through- 



96 THE ANATOMY OF VERTEBRATED ANIMALS. 

out their whole extent, remain distinct from them. Tlieir 
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, toward their hinder 
openings into the genito-urinary part of the cloaca, they com- 
monly dilate again. In all animals but the didelphous and 
monodelphous Mammalia, the Miillerian ducts undergo no 
further modification of any great morphological importance ; 
but, in the monodelphous Mammalia, they become 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 conflu- 
ence the Miillerian ducts are primarily converted into a single 
vagina with two uteri opening into it ; but, in most of the 
Mo^iodelphia, the two uteri also more or less completely coa- 
lesce, until both Miillerian ducts are represented by a single 
vagina, a single uterus, and two Fallopian tubes. The didel- 
phous 3Iaram,alia have two vaginae which may, or may not, 
coalesce anteriorly for a short extent ; but the two uteri re- 
main perfectly distinct. So that what takes place in them is 
probably, a differentiation of each Miillerian 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 ear- 
lier stages of development in Monodelphia. The Wolffian 
ducts of the female either persist as canals, the so-called ca- 
nals of Gaertner, which open into the vagina, or disappear 
altogether. Remains of the Wolffian bodies constitute the 
parovaria, observable in certain female mammals. 

In the male vertebrate embryo, the testis, or essential re- 
productive 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 3Iarsipo- 
branchii, this tissue appears to pass directly into spermatozoa ; 
but, in most Vertebrata, it acquires a saccular or tubular struct- 
ure, and from the epithelium of the sacs, or tubuli, the sperma- 
tozoa are developed. At first, the testis is as completely de^ 
void of any excretory canal as the ovary ; but, in the higlier 
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 
rest abort. 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 



THE REPRODUCTIVE ORGANS. 



97 



diverticulum of the vas deferens, near its posterior end, which 
serves as a receptacle for the semen. 



■W.d M 




Pia. 27. — ^Dia^am exhibiting the relations of the female (the left-hand flffure, 9) and of the 
male (the right-hand figure, i ) reproductive organs to the general plan (the middle fig- 
m-e) of these organs in the higher Vertebrccta, 

CI, the cloaca ; R, the rectum ; Bl, the urinary bladder ; U, the ureter ; K, the kid- 
ney ; TTh, the urethra ; (?, the genital gland, ovary, or testis ; W, the Wolffian body ; 
Wd, the Wolffian duct; M, the Mtiilerian duct; Pst, prostate gland; Gp, Cowpor'a 
gland ; Cajp, the corpus spongiosum ; (7c, the corpus cavernosum. 

In the female, V, the vagina; Ut, uterus; Fp, the Fallopian tube; Gt, Gaertner'fl 
duct ; Pjo, the parovarium ; A, the anus ; Cc, C.s/>, the cUtoris. In the male. Cap, Oo, 
the penis; K, the uterus masculinus; Fs, vesicula seminalis ; F^f, the vas deferens. 



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 bet\A!'een the two. But' the anal, genital, and uri- 
nary apertures are found thus related only among certain 
groups of fishes, such as the Teleostei. In all other Vertebrata 
there is either a cloaca, or common chamber, into which the 
rectum, genital, and urinary organs open ; or, the anus is a 
5 



98 THE ANATOMY OF VERTEBRATEU ANIMALS 

distinct posterior and superior aperture, and the opening of a 
genito-urinary sinus, common to the urinary and reiiroduclive 
organs, lies in front of it, separated by a more or less consid' 
erable perincEum. 

These conditions of adult Vertebi-afa repeat the states 
tlirough wliich 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 Mullerian ducts, in front, and llie 
rectum behind. But, as development advances, the rectal di- 
vision of the cloaca becomes shut off from the other, and opens 
by a separate aperture — the definitive aims, which thus ap- 
pears to be distinct, morphologically, from the anus of an osse 
ous fish. For a time, the anterior, or genito-urinary part of 
the cloaca, is, to a certain extent, distinct from the rectal di- 
vision, though the two have a common termination ; and this 
condition is repeated in Aves, and in ornithodelphous Many- 
malia, 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 jwo«- 
tate. It thus 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 protrudes 
from the cloaca ; and, while the corpus spongiosum terminates 
the anterior end of it, as the (/lands, the corpora cavernosa at- 
tach themselves, posteriorly, to the ischia. The under, or pos- 
terior, surface of the penis is, at first, simply grooved ; by de- 
grees 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 
frequently dilated into the so-called bulbus iirethrae, glands, 
called Goicper''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 coa 



MODIFICATIONS OF THE REPRODUCTIVE ORGANS. 99 

dition of a process of the ventral wall of the cloaca, grooved 
on one face. In ornithodelpbous mammals the penial urethra 
is complete, but open behind, and distinct from the genito- 
urinary sinus. - In the Didelphiu the penial urethra and gen- 
ito-urinary sinus are united into one tube, but the corpora 
cavernosa are not directly attached to the ischium. 

Certain Meptilia possess a pair of eversible copulatory or- 
gans situated in integumentary sacs, one on each side of the 
cloaca, but it does not appear in what manner these penes 
are morphologically related to those of the higher Vertebrata, 

In the female sex, the homologue of a penis frequently 
makes its appearance as a clitoris, but rarely passes be3'ond the 
stage of a grooved process with corpora cavernosa and corpus 
spongiosum — the former attached to the ischium, and the lat- 
ter developing a glans. But, in some few mammals (e. g., the 
LemuridcB), the clitoris is traversed by a urethral canal. 

In no vertebrated animal do the ovaries normally leave the 
abdominal cavity, though they commonly forsake- their primi- 
tive 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 peritonaeum, 
descend temporarily or permanently into a pouch of the integ- 
ument — the scrotum. In their com'se they become invested 
with looped muscular fibres, which constitute the cremaster. 
The cremaster retracts the testis into the abdominal cavity, or 
toward 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 sus- 
pended by a narrow neck in front of the root of the penis. 

In most mammals the penis is enclosed in a sheath of in- 
tegument, the preputiwn ; 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 scro- 
tal, the la^ia minora the preputial, part of the male organ of 
copulation. 

Organs not directly connected with reproduction, but in 
various modes accessory to it, are met with in many Ferfo- 
Jyrata. Among these may be reckoned the integumentary 
pouches, in which the young are sheltered during their devel- 
opment in the male Pipefish {Syngnathus), in some female 
Amphibia {N'otodelphys, Plpa), and Marsupialia ; together 
with the mammary glands of the Mammalia. 



CHAPTER ni. 

THE IBOVINCES OF THE VERTEBHATA THE CLASS PISCES. 

The Vertebrata are divisible into three primary groups or 
provinces : the Ichthyopsida, the Saurqpsida, and the Mam- 
malia. 

I. — The Ichthyopsida 

1. Have the epidermic exoskeleton either absent, or very 
slightly 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 vertebrae 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 parasphenoid. 
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 un- 
ossified or very imperfectly ossified. 

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

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

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



TEE SAUROPSIDA. 101 

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

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

10. There is no thoracic diaphragm. 

11. The urinary organs are permanent Wolffian bodies. 
13. The cerebral hemispheres may be absent, and are 

nev^er united by a corpus callosum. 

13. The embryo has no amnion, and, at most, a rudimen- 
tary allantois. 

14. There are no mammary glands. 

II. — The Sauropsida 

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

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

3. The skull has a completely ossified occipital segment, 
and a large basisphenoid. No separate parasphenoid exists 
in the adult. The proOtic is always ossified, and either 
remains distinct from the epiotic and opisthotic throughout 
life, or unites with them only after they have anchylosed with 
adjacent bones. 

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

5. The mandible is always present, and each ramus con- 
sists of an articular ossification, as well as of several mem- 
brane bones. The articular ossification is connected with the 
skull by a quadrate bone. The apparent " ankle-joint" is situ- 
ated, not between the tibia and the astragalus, as in all Mam- 
malia, but between the proximal and the distal divisions of 
the tarsus. 

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 branchiae, 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 



102 THE ANATOMY OF YERTEBRATED ANIMALS. 

11. The Wolffian bodies are replaced, functionally, by per- 
manent 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, whicb presents a uterine dilata- 
t ion in the lower part ot 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 
vi tell us of the egg. 

IG. There are no mammary glands. 

III. — The Mammalia 

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

2. The vertebras are ossified, and (except in the ornitho- 
delphici) their centra have terminal epiphyses. 

3. All the segments of the brain-case are completely ossi- 
fied. No distinct parasphenoid exists in the adult. TheproStic 
ossifies, and unites with the epiotic and opisthotic 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, 
and the supra-stapedial element of the hyoidean arch, are con- 
verted into a malleus and an incus, so that, with the stapes, 
there are, at fewest, three ossicula audiMs. 

6. The alimentary canal may, or may not, terminate 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 brancliia3, 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 hy a corpus cal- 
losum. 

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



THE CLASS PISCES. 103 

14. The embryo has an amnion and allantois. 

15. Mammary glands supply the young with nourishment. 

The Ichthyopsida. — Class I. — Pisces. 

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 characteristic and diag- 
nostic of them. But they are the only vertebrated 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 Yertebrata. 

The presence of the peculiar integmentary organs con- 
stituting what is known as the system of mucous canals and 
the organs of the lateral line {supra, p. 79 ), is highly charac- 
teristic of Fishes, though these organs cannot be said to exist 
m the entire class. 

The class Pisces is divisible into the following primary groups : 
A. The notoohord extends to the anterior end of the body. There are no 
skull, brain, auditory, or renal organs, such as exist in the higher Yerte- 
brata. The heart is a simple tube, and the liver is saccular. (Lepio- 
CAKDiA. Haeokel.) 

I. — Pharyngobranchii. 
B The notoohord ends behind the pituitary fossa. A skull, brain, auditory, 
and renal organs are developed. The heart is divided into auricular and 
ventricular chambers. The liver has the ordinary structure. (Paciiy- 
CARDIA. Hck.) 

a. The nasal sac is single, and has a median external aperture. Neither 

mandibles nor limb arches are developed. (Monorhina, Hck.) 

II. — Marsipobranchii. 

b. There are two nasal sacs with separate apertures. Mandibles and 

limb arches are developed. {Amphirhina. Hck.) 

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. 

III. — ElasmobranchU. 
p. Membrane bones are developed in relation with the skull. 

1. The optic nerves fosm 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. 

Y.—Teleostei. 

b. The nasal passages communicate with the oral cavity. Tlier* 

are lungs, and the heart has two auricles. 
VI. — Dipnou 



lot 



THE ANATOMY OF VERTEBRATED ANIMALS. 



I. The PHAETNUOBEAircHn. — ^This order contains but one 
species of fish, the remarkable Lancelet, or Amphioxus lanceo- 
latus, -which lives in sand, at moderate depths in the sea, in 
many parts of *he world. It is a small, semitransparent crea- 
ture, pointed at both ends, as its name implies, and possessing 
no limbs, nor any liard epidermic or dermal covering. 

The dorsal and caudal regions of the body present a low 
median fold of integument, which is the sole representative of 
the system of the median fins of other fishes. The mouth 
(Fig. 28, A, a) is a proportionally large oval aperture, which 
lies behind, as well as below, the anterior termination of the 
body, and has its long axis directed longitudinally. Its mar- 
gins are produced into delicate ciliated tentacles, supported by 
semi-cartilaginous filaments, which are attached to a hoop of the 
same texture placed around the margins of the mouth (Fig. 
29,/", 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 




PLC, 2S. — AmpJiioxv^ lanceolaUis.~a, mouth; 6, pharyngobranchial chamber; c, anus; 
d, liver ; «, abdominal pore. — B, tlie head enlarged ; a, the notochord ; ft, the represent- 
atives of neural spines, or fin-rays; c, the jointed oi-al ring ; rf, the filamentary append- 
ages of the mouth; *?, the eihated lobes of the pharj'nx ; /, 17, part of the branchial sac 
\ the spinal cord. 

clefts, and richly ciliated, so that it resembles the pharynx of 
an Ascidian (Fig- 28, B, /, g). Tliis great pharynx is con 
nected with a simple gastric cavity which passes intr i. 



THE PHARYNGOBRANCni. 



105 



straight intestine, ending in the anal aperture, which is situ- 
ated at the root of the tail at a little to the left of the me- 
dian line (Fig. 28, A, c). The mucous membrane of the in- 
testine is ciliated. 

An aperture called the abdominal pore (Fig. 38, A, e), 
placed in front of the anus, leads into a relatively spacious 
cavity, which is continued forward, on each side of the 
pharynx, to near the oral aperture. The water which is con- 
stantly propelled into the pharynx by its ciha, 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 
ntestine, the apex of which is turned forward. 




fin . 29.— Anterior end of the body of Am/pMomis.—Oh, notochord; My, myeloo, or apini«l 
chord ; a, position of olfactory (?) sac ; S, optic nerve ; c, fifth (?) pair ; (L, spinal ceives : 
e, representatives cf neural spines, or fln-rays;/ g, oral skeleton. The lighter ana 
darker shading represents the muscular segments and their interspaces. 

The existence of distinct kidneys is doubtful ; and the re- 
pi )ductive 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 
in the earliest embryonic stage only, in other Yertebrata. 
The blood brought back from the body and from the ali- 



106 THE ANATOMY OF VEETEBRATED ANIMALS. 

raentary canal eaters a pulsatile cardiac trunk, which rung 
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, therefore, 
are so many branchial arteries. Contractile dilatations 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 
aerated blood from the branchial bars, into a great longi- 
tudinal 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 that a 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 repre- 
sents the hepatic vein, and is continued into the cardiac trunk 
at the base of the branchial sac. The corpuscles of the blood 
are all colorless 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 terminates, at 
each extremity, in a point (Fig. 28). The investment 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, or ribs. A longitudinal series of 
small semi-cartilaginous rod-like bodies, which lie above the 
neural canal, represent either neural spines or fin-rays (Fig. 
38, B, b). Neither is there a trace of any distinct skull, jaws, 
or hyoidean apparatus ; 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 part of the 
cephalic region (Fig. 39, a), ought to be considered as an olfac- 
tory org'an. 

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. 26, b, c). 

According to M. Kovvalewsky,* who has recently studied 

* "Memoirca de rAcailemie Imperiale dea Sciences de St. Petersburg," 
1867 



THE PHAEYNGOBRANCHII. 107 

the development of Amphioxus, the vitellus undergoes com- 
plete segmentation, and is converted into a hollovv 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 re- 
ducing the primitive cavity to nothing, but giving rise to a 
secondary cavity, surrounded by a double membrane. The 
operation is, in substance, just the same as that by which a 
double nightcap is made fit to receive the head. The blasto- 
derm 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 becomes the anus. 
M. Kowalewsky points out the resemblance, 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 lamincB dorsales, which unite in the charac- 
teristically vertebrate fashion ; and the notochord appears 
between and below them, and very early extends forward be- 
yond 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 disk 
formed by this coalescence. The branchial apertures arise by a 
similar process which takes place behind the mouth ; and they 
are, at first, completely 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 
coalesce on the ventral side, leaving only the abdominal pore 
open. One cannot but be struck with the resemblance of these 
folds to the processes of integument which grow over the bran- 
chiae of the amphibian larva ; and, in like manner, enclose a cavi- 
ty 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 
branchiae and alimentary canal ; and in the extension of the 
notochord forward to the anterior end of the body — ■Amphi' 
(xntx differs from every other vertebrated animal. Hence 
Prof. Haeokel has proposed to divide the Vertebrata into 
tvro primary groups — the Leptocardia, containing Amphi' 



108 



THE ANATOMY OF VERTEBRATED ANIMALS. 



oxiiS ; and the Pachycardia, comprising all other Verieorata. 
The great peculiarities in the development of Amphioxus, 
and the many analogies with invertebrate animals, particu- 
larly the Asoidians, which it presents, lend much support to 
this proposition. 

No fossil form allied to Amphioxus is known. 

II. The MAKSiPOBKANCHn. — 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 cartilages, 
and there is a distinct skull presenting cartilage at least in its 
base, and retaining many of the characters of the foetal cra- 
nium of the higher Vertebrata. The notochord terminates in 
a point in the base of this cartilaginous skull behind the pitui- 
tary body ; and the skull is not movable upon the spinal col- 




f\Q. 80. — A, the skull of a Lamprey, viewed from the side ; B, from above : — a, the ethmovo 
merine plate; 6, the olfactory capsule ; c, the auditory capsule ; tf, the neural arches of 
the spinal column; s, the paLitopteiygoid portion ; /, probably, the metapterygoid. or 
Buperior quadrate, portion, and g, the inferior quadrate portion, of the subocular arch ; A, 
Btylohyal process; i, ling:ual cartilage; A-, inferior, Hateral. prolongation of the craiiisi 
cartilage; 1, 2, 8, accessory labial cartilages; m, branchial skeleton. The spaces OD 
either side oJ 1 are closed by niembrane. 



THE MARSIPOBRANCHII. 109 

nmn. There are no jaws ; but the palatopterygoid, the quad- 
rate, the hyomandibular, and the hyoidean apparatus of higher 
Vertebrata, are imperfectly represented (Fig. 30,/", g, h). In 
some genera a basket-like cartilaginous apparatus strengthens 
the walls of the oral cavity ; while, in others, such a framework 
supports the gill-sacs. 

The Marsipohranchii possess neither the pectoral nor the 
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 cartilages. 
The alimentary canal is simple and straight, and the liver is 
not sac-like, but resembles that organ ia other Vertebrata. 

The heart has the usual piscine structure, consisting of a 
single auricle preceded by a venous sinus, a single ventricle, 
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, dis- 
tributes its branches to the respiratory organs. These consist 
of aatero-posteriorly flattened sacs, which communicate directly 
or indirectly, on the inner side, with the pharynx, and, exter- 
nally, with the surrounding medium. 

In the Lamprey there are seven sacs, upon each side, which 
open externally by as many distinct apertures. Internally, 
they communicate with a long canal, which lies beneath the 
oesophagus and is closed behind, while anteriorly it communi- 
cates freely with the cavity of the mouth (Fig. 33, Pr). 

The kidneys are well developed, and have the ordinary ver- 
tebrate 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 high- 
er Vertebrata — that is to say, a fore-brain, mid-brain, and hind- 
brain. The fore-brain is further divided into rhinencephala, 
Bolid prosencephalic lobes, and a thalamencephalon ; the hind- 
brain, into metencephalon and myelencephalon (Fig. 31). 

The auditory organ is simpler than in other fishes, possess- 
ing only two semicircular canals and a sacculated vestibule iii 
the Lamprey. In Myxine the whole organ is represented by 
a single circular membranous tube, without further distinction 
into canals and vestibule. 

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



no THE ANATOMY OF VERTEBRATED ANIMALS. 

a sac placed in the middle line of the head, and having a sin- 
gle, median, external aperture. In all other Vertebrata there 
are two nasal sacs. In the Lampreys, the nasal sac terminates 




PiQ . 81. — Side and upper tIcwb of the brain of Petromyzon Jtv/daUUe, and an upper and 
inner view of tlie membranous labyrinth of P. Tnarinus. The following letters refer to 
the flgnres of the brain : I., the olfactory nerves, narrow anterior prolongations of the 
rhinencephalon (A) ; B, the prosencephalon ; C, the thalamencephalon ; D, the mesen- 
cephalon ; E, the medulla oblongata ; F, the fourth ventricle ; e, the narrow band which 
Is all that represents the cerebellum ; G, the spinal cord ; II., the optic ; III., the oculo- 
motorius ; lY., the patheticus ; V., the trigeminal ; VI., the abducens ; VII., the facial, and 
the auditory; VIII., the glosso-pharyngeal 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: k, the auditory nerve; n, the vestibule; c, the two semi- 
circular canals, which correspond mtb the anterior and posterior vertical canals of other 
Ynftebrata ; iZ, their union and conamon opening into the vestibule ; 6, the ampullro. 



blindly belovr and behind, but in the Hags (Myxine), it opens 
>nto the pharynx. In no other fishes, except Ziepidosiren^ does 
the olfactory apparatus communicate with the cavity of the 
mouth. 

The reproductive organs of the llarsipohranchii are solid 
plates suspended beneath the spinal column, and Ihey have no 



THE ELASMOBRANCHII. Ill 

ducts, but shed their contents into the abdomen, whence they 
pass out by an abdominal pore. In the early stages of their 
development the Lampreys present some singular resemblances 




Fte r^-X —Vertical anil longitudinal section of the anterior part of the body of a Lamprey 
vP.uVomy^ora TnaHnus): ^, the cranium with its conliained brain; a, section of the 
ed%e of the cartili«ge marked a, in Fig. 30 ; Olf, entrance into the olfactory chamber, 
whiiih is proIongeQ into the caacal pouch, o ; P\ the pharynx; Pr, the branchial chan- 
nel, with the inner apertures of the branchial sacs ; M^ the cavity of the mouth, with its 
horny teeth ; 2, the cartilage which supports the tongize ; 8, the oral ring. 

to the Amphibia. They also undergo a metamorphosis, the 
young Petromyzon being so unlike the parent, that it was, un- 
til lately, regarded as a distinct genus — Ammocoetes. But 
the young Lampreys never possess external branchial filaments 
or spiracula. 

The Marsipohranchii are inhabitants of both fresh and salt 
water. The Myxinoids are remarkable for their parasitic hab- 
its — the Hag boring its way into the bodies of other fishes, 
such as the Cod. No fossil Marsipohranchii are 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 favorable circumstances. 

in. The Elasmobeanchii. — This order contains the Sharks, 
the Rays, and the Ghimmra. 

The integument may be naked, and it never possesses scales 
like those of ordinary fishes ; but, very commonly, it is devel- 
oped into papillae, which become calcified, and give rise to 
toothlike structures : these, when they are very small and close- 
Bet, 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, iohthyodorulites. All 
these constitute what has been called a ^ plaooid exosledeton j " 



112 THE ANATOMY OF VERTEBEATED ANIMALS. 

and, iQ minute structure, they precisely resemble teeth, as has 
been already explained. The protruded surfaces of the dermal 
defences are frequently ornamented with an elegant sculptur- 
ing, which ceases upon that part of the defence which is im- 
bedded 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 Marsipohranchii, or having mere osseous rings devel- 
oped in its walls, to complete vertebrae, with deep conical an- 
terior and posterior concavities in their centra, and having the 
primitive cartilage more or less completely replaced by concen- 
tric, or radiating, lamelte of bone. In the Rays, indeed, the 
ossification goes so far as to convert the anterior part of the 
vertebral column into one continuous bony mass. 

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

The terminal part of the notochord is never enclosed with- 
in a continuous bony sheath, or urostyle. The extremity 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. Elasmobranclis with tails of 
this conformation are truly heterocercal, while those in which 
the fin-rays of the tail are equally divided by the spinal col 
umn, or nearly so, are diphy cereal (p. 21). The Monkfish 
(Squatina) and many other Elasmobranchii are more diphy- 
cercal 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 movable 
upon the spinal column, it articulates therewith by two con- 
dyles. 

In its general form and structure, the cartilaginous skull 
of an Elasmobranoh corresponds with the skull of the verte- 
brate foetus 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 embryonic situ- 
ation upon the under-surface of the skull. 

Neither premaxillce nor maxillae are present, the "jaws " 



THE ELASMOBRANCHIl. 



113 



of an Elasmobratich 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 
be represented, as in the Ghimmra (Fig. 33), by the anterior 
portion {S, 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 sus- 
pensoriura ; or there may be, on each side, a cartilaginous bar 
movably 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. 

In the latter case, which is that met with in the Sharks 
and Rays (Figs. 34 and 35), a single cartilaginous rod (g) is 
movably articulated with the skull, in the region of the peri- 
otic capsule, upon each side ; and, by its opposite extremity, 
is connected by ligamentous fibres both with the palato- 
quadrate (A) and with the mandibular or Meckelian cartilage 
{^Mn). This cartilaginous suspensorium represents the liyo« 




Fig. 83. — Vertical section of the skull of CMm,os/ra nwnstrosr.^ without the labial and nasdl 
cartilage s: j4, the basi-occipital regrion; P, the pituitary fossa ; JVa, partition between 
the olmctory sacs ; JS, alveolus for the anterior upper-jaw tooth ; 0, D, the rejrion of the 
trianf^lar cartilage which answers to the hyomandibular and quadrate ; D, B, that 
which answers to the quadrate, pterygoid, and palatina ; Jfft, the mandible ; / Or, the 
interorbital septum ; asc and psc^ the anterior and posterior semicircular canals ; I., II., 
v., VIII., exits of the olfcetory, optic, fifth and eighth pairs of nerves. 

mandibular and the symplectic bones of the Teleostei, and 
gives attachment to the hyoidean apparatus (-Hy). The lat- 



114 THE ANATOMY OF VERTEBRATED ANIMALS. 

ter consists of a lateral arch upon each side, united with its 
fellow, and with the branchial arches, by the intermediation 
of medial basal elements below ; and it is succeeded by a 
variable number of similar arches, which support the branchial 
apparatus. 

From the hyoidean and from the branchial arches carti- 
laginous filaments pass directly outward, and support the walla 
of the branchial sacs. Superficial cartilages, which lie par- 
allel with the branchial arches, are sometimes superimposed 
upon these. There are no opercular bones, though cartilagin- 
ous 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 
Chimoera, 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 and 
35, i, k, I.) 

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 Vertebrata. 
The pectoral fins, the structure of which has already been de- 
scribed, are always the larger, and sometimes attain an enor- 
mous size relatively to the body. 

In these fishes, teeth are developed only upon the mucous 
membrane which covers the palato-quadrate cartUage 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 
have 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. 
The Rays usually have somewhat obtusely-pointed teeth, but 
in lltjliobates, the middle teeth have transversely-elongated, 



THE ELASMOBRANCIIII. 



115 




and the lateral ones hexagonal, flat crowns, and the various 
teeth are fitted closely by their edges into a pavement. In 



116 THE ANATOMY OF VERTEBRATBD ANIMALS. 

Aetobatis only tlie middle transversely elongated teeth remain. 
In the Sharks and Rays the teeth are developed from papillfe, 
or ridges, situated at the bottom of a deep fold within the mu- 
cous 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 successive rows, 
from the bottom of the groove. No such successive develop- 
ment takes place in the Chimwra. 

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

The intestine is short, and usually commences by a dilata« 
tion separated from the stomach by a pyloric valve. This 
duodenal segment of the intestine is usually known as the 
JBursa Mitiana. 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 intes- 
tines 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 
( Garcharias, 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 re- 
productive organs. The peritoneal cavity communicates with 
that of the pericardium in front, and, behind, opens 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 con- 
tain 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 
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. 



THE ELAFMOBRANCHII. 



117 



In a good many Elasmohranchii there is a spiracle, or 
ai)erture leading into the cavity of the mouth, on the upper 
Bide of the head, in front of the suspensorium. From this 
aperture (which, according to the observations of Prof. Wy- 




FiG. 86. — The aortic bulb of a Shark (LanvncC)^ laid open lo show the three rove of valves, 
», w, w, and the thick muscular wall, m. 

man, is the remains of the first visceral cleft of the embryo), 
as well as from the proper branchial clefts, long branchial fila- 
ments protrude, in the foetal state. These disappear in the 
adult, the respiratory organs of which are flattened pouches, 
with traversely-plaited walls, from five to seven in number. 
They open by external clefts upon the sides (Sharks and Chi- 
mcera), 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 
liyoidean arch. Between the posterior wall of the first, and 
the anterior wall of the second sac, and between the adjacent 
walls of the other sacs, a branchial arch with its radiating car- 
tilages is interposed. Hence the hyoidean arch supports one 
series of branchial plates or laminae; while the succeeding 
))ranchial arches, except the last, bear two series, separated by 
a septum, consisting of the adjacent 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 aerated by the water which is taken in at 
the mouth and forced through the pharyngeal apertures, put- 
ward. 



118 



THE ANATOMY OF VERTEBRATED ANIMALS. 



The kidneys of the Elasmohranclui do not extend so far 
forward as those of most other fishes. The ureters generally 
become dilated near their 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 resti/ormia) are singularly folded (Fig. 37, A., 
a) ; and moderate-sized optic lobes, which are quite distinct 
from the conspicuous thalamencephalon, or vesicle of the third 




ri«. 87.— The brain of the Skate (iSo^o iaiis). A. From above ; B. A portion of the tbd- 
tral aspect enlarged ; s, the olfactory bulbs ; a, the cerebral hemispheres which are milted 
In the middle line ; b, the thalamencephalon ; c, the mesenccptialon ; <?, the cerebellum • 
a a, the plaited bands formed by the corpora restiformia ; L, II., IV., V., the cerebral 
nerves or the corresponding pah's; f, the medulla oblongata : w, a blood-vessel. In R ; 
ch, the chiasma of the optic nerves; h, the pituitary body; mand v. vessels connected 
with It; *, the saceua vaeouloaua; p, the pyramids of the medulla oblongata. 



THE ELASMOBRANCHII. l]g 

ventricle. The third ventricle itself is a relatively wide and 
short cavity, which sends a prolongation forward, 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, more properly, to be 
considered as the thickened termination of the primitive en- 
cepbalon, in which the lamina terminalis and the hemispheres 
are hardly differentiated. The large olfactory lobes are usually 
prolonged into pedicle?, which dilate into great ganglionic 
masses where thev come into contact with the olfactory sacs 
(Fig. 37, A., s). The latter always open upon the under-sur- 
face of the head. A cleft, which extends from each nasal aper- 
ture to the margin of the gape, is the remains of the embryonic 
separation between the naso-frontal process and the maxillo- 
palatine process, and represents the naso-palatine passage of 
the higher yertebrata. The optic nerves fuse into a complete 
chiasma (Fig. 37, £., ch), as in the higher Vertebrata. In 
some Sharks, the eye is provided with a third eyelid or nictitat- 
ing membrane, moved by a single muscle, or hy 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 articulates with the ex- 
tremity of a cartilaginous stem proceeding from the bottom of 
the orbit. 

Except in Chimcera, the labyrinth is completely enclosed 
in cartilage. In the Raj's, the anterior and posterior " serai- 
circular " canals are circular, and open by distinct narrow ducts 
into the vestibular sac. In the other JE lasmobranchii they are 
arranged in the ordinary 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 verte- 
brate 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 Vertdirata. The vas def- 
erens of each side opens into the dilated part of the ureter. 
Attached to the ventral fins of the male are peculiar append- 
ages, 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 
are true FaUopian tubes, which communicate freely with the 
abdominal cavity at their proximal ends. Distally, they dilate 
into uterine chambers, which unite and open into the cloaca. 



120 THE ANATOMY OF VEUTEBRATED ANIMALS. 

The eggs are very large, and comparatively few. 

The Dogfishes, the Rays, and the Chinimra, are oviparous, 
and lay eggs, enclosed in hard, leathery cases ; the others are 
viviparous, and, in certain species of Musteliis (icevis) and Car- 
charias, 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, provided 
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 functionally replaced by 
internal gills as development advances. 

The Elasmohranchii are divided into two groups, the Holo- 
cephali and the Plagiostomi. 

In the Solocephali, the palato-quadrate and suspensorial 
cartilages are united with one another and with the skull into 
a continuous cartilaginous plate ; the branchial clefts are cov- 
ered 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 sub-order con- 
tains the living Ghimaera and Gallorhynchus, 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 limestones. 

In the Plagiostomi, the palato-quadrate and suspensorial 
cartilages are distinct from one another, and are movable upon 
the skuU. The branchial clefts are not covered bj- any oper- 
cular membrane. The teeth are usually numerous. 

The Plagiostomi are again subdivided into the Sharks 
(Selachii or Squali), with the branchial apertures at the sides 
of the body, the anterior ends of the pectoral fins not connected 
with the skull by cartilages, and the skull with a median facet 
for the first vertebra ; and the Rays (Pajce), 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 Plagiostom,i occur in the Mesozoic 
rocks. In the Palasozoio epoch, dermal defences and teeth of 
Elasm^ohranchii abound in the Permian and Carboniferous 



THE GANOIDEI. 12] 

formations, and are met with in the Upper Silurian rocks. 
Bat, except in the case of Pleuracanthus (a Selachian), it is 
impossible to be certain to what special divisions they belong. 

IV. The Ganoidei. — In former periods of the world's his- 
tory, 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, Ao- 
cipe?iser, Scapirhynahus, and 8patularia, which are either par- 
tially 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 organization, but agree in 
the following characters, some of which they possess in com- 
mon with the Elasmobranehii, and others with the Teleostei, 
Thus: 

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

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

c. There is a well-developed spiral valve in' the intestine, 
as in the Elasmohranchii, 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 sao, which extends beyond 
them, as in the Elasmohranchii ; 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 permanently 
open pneumatic duct with the oesophagus, as in many Teleostei. 

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

The ventral fins are always abdominal in position. The 
tail is diphycercal, or heterocercal, and the terminal portion 
of the notochord is not ossified. The cavity of the abdomen 
is placed in communication with the exterior by abdominal 
pores. Finally, the ducts of the reproductive organs communi- 
cate with those of the permanent urinary apparatus, which is, 
in part, an Elasmobranch, in part, an Amphibian, character. 

The exoskeleton presents the most extreme variations in 
the Ganoidei. Spatularia is naked ; Acaipenser and Scapi- 
rhynahus develop numerous dermal plates composed of true 
bone ; Amia is covered with overlapping cycloid scales ; Lepi- 
dosteus and Polypterus have solid, rhomboidal, enamelled scales, 
6 



122 



TEE ANATOMY OF VERTEBRATED ANIMALS. 



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




Fig. 3S. — The brain of Lepidoatens seTniradJatus. A. From above; 5. From below./ 
the medulla oblongata ; d, the cei-eboUum ; c, the optic lobes of the mesenceiiha!<in . {/^ 
the cerebral hemispheres ; h, the pituitary b^dy ; i, the lobi inferiores. t7/i, the chlad- 
ma ; I., olfactory ; II., optic nerves. 



The endoskeleton is not less diversely modified; and it la 
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 sheatb of which mere cartilaginous rudiments of the 
arches of vertebrae appear. The ribs, when present, are par- 
tially ossified. Polypterus and Amia have fully ossified ver- 
tebrae, the centra of which are amphicoelous. Lepidosteus alsc 
has fully-ossified vertebrie ; but their centra are opisthocce- 
lous, having a convexity in front and a concavity behind, as in 
some Amphibia. 

More or fewer of the anterior vertebrae, or their cartilagi- 
nous representatives, are united witb one another, and with 
the posterior part of the skull. And the cranium may consist 
principally of cartilage, membrane bones being superadded ; 
or the primordial cartilage maybe largely superseded bj' bone, 
as in the Teleostei. 

Spatularia^ Scapiirhynchus, and Accipenser, have skulls of 
the former description. The cranium is one mass of cartilage, 
continuous behind with the coalesced anterior spinal cartilages, 
so as to be immovably 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 



THE GANOIDEl. 



123 



beak, wbich, in Spatularia, is very long, flattened, and spatu- 
late. In the perichondium of the base of the skull, median 
bones, answering to the vomer and to the parasphenoid of 
Teieostean fishes, are developed ; and, in that of its roof, ossi- 
fications, which represent the parietals, frontals, and other 
membrane bones of the Teleostei, appear. 

The framework of the jaws in Spatularia is verj' similar 
to that in the jElasmobranchii. There is a partly cartilagi- 
nous, and partly ossified, suspensorial cartilage {A, JB, Fig. 39), 
which gives attachment below, directly, to the hyoidean arch 
(Sy), and, indirectly, to the jaws. The latter consist of a 



All /« 




Fig. 89.— Side-view of the skull of /SpaiM^oWo, with the beak cut away, and the autenor 
(asc\ and posterior ( psc), semicircular canals exposed : Au, auditory chamber ; Or, 
the orbit with the eye ; N, the nasal sac ; Hy, the hyoidean apparatus ; Br, the repre- 
sentatives of Jhe branchiostegal rays ; Op, operculum ; Mn, mandibk ; A, B, suspenso- 
rium; D, palflto-quadrato cartilage; E, maxilla. 

palato-quadrate cartilage {D) united by ligament with its fel- 
low, and with the prefrontal region of the skull at F. ; and 
presenting, at its posterior end, a convex articular head to the 
cartilage of the mandible, or Meckelian cartilage, Mn. It is 
obvious that A, JB, corresponds with the hyomandibular, or 
suspensorial, cartilage in the Sharks and Rays ; D, with the 
palato-quadrate cartilage, 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 vis- 
ceral arch; while a membrane bone {E) representing the 
maxilla, and another {Mn,) the dentary, of the lower jaw ia 
Teleostei, are developed in connection with the palato-o;aadrate 
and mandibular cartilages. 



124 



THE ANATOMY OF VERTEBRATED ANIMALS. 



In the Sturgeon (Fig. 40), the membrane bones of the roof 
ol the skull are more numerous and distinct than in Spatularia, 
and large dermal bones (I K, JL) are united with them, to 




Fig. 40. — The cartilaginous skull of a Sturgeon, with the cranial bones. The foiiner is 
shadud, and supiiosed to be seen through the latter, which are left unshade.l : a. ridge 
formed by the spinous processes of the anterior vertebrse ; 6, ^, lateral wingliitt: pro- 
cesses; e, rostrum; Au^ position of the auditory organ; iVtz, position of the nasal sacs; 
Or, that of orbit. The membrane bones of the upper surface are : A, the analogue o* 
the suiira-occipital; B, £, of the eiiiotics; E, of the ethmoid; O, G, of the postfrontals ; 
//, //, of the prefrontals ; C, C, the parietals ; D, If, are the frontals, and E, J''', the squa. 
mosals ; A', the anterior dermal scute ; /, /, and X, Z, dermal ossifications connecting th« 
p'^ctoral arch with the skull. 

form the great cephalic shield. The suspensorium (/, ^, h, 
Fig. 41) is divided into two portions, to the lower of which 
(at A) the proper hj'oid is attached ; and the palato-quadrate 




g^<3. 41, — Side-view of the cartilaginous cranium of Accipenser : a, rostrum; b, nasal 
chamber ; Or, orbit ; c, auditory region ; d, coalesced anterior vertebrae ; e, ribs ; /, g, A, 
Buspeusorium ; k, palato-majtillary apparatus ; Ifn, mandible. 



cartilages, with their subsidiary ossifications, 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 proOtic ossifications of the primordial cartilage, 
to which others may be added. The vomers are double, as in 
the Amphibia (? Polypterus). The apparatus of the jaws lias 
become modified in accordance with the Teleostean type of 



THE GANOIDEI. 125 

structure. The suspensorium consists of two ossifications 
united by a cartilaginous intermediate portion. The upper — 
broad, and movably 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 prefrontal region of the skull ; be- 
hind it, lie representatives of the pterygoid, the metapterygoid, 
the ectopterygoid ; and, most posteriorly, of the quadrate 
bone. The last furnishes a condyle to the articular element 
of the mandible. The symplectic is either loosely connected 
with the quadrate, as in Lepido&Uus. or more closely united 
with it, as in the other genera. 

In Lepidosteus and Amia, a f.trcng and long membrane 
bone, the preopercidum^ 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 man- 
dibular cartilage ossifies, and becomes a distinct articidare. A 
dentary element is added on the outer, and a splenicd one 
upon the inner side of the cartilage ; and in Lepidosteus, an- 
gidar, supra-angular, and coronary elements are added, so 
that the components of the mandible are as numerous as in 
reptiles. Lepidosteus and Amia have branchiostegal rays, 
but Polypterus has none — at any rate, of the ordinary kind. 
A single jM^M/ar plate is developed between the rami of the 
mandible in Amia, and there are two such plates in Polypterus, 
which may possibly represent branchiostegal rays. 

In A(:cip>enser, Spatularia, and Amia, the pectoral arch 
presents two constituents : one, internal and cartilaginous, 
answers to the cartilaginous pectoral arch of the JElasmo- 
branchii, and to the scapula and coracoid of the higher Ver- 
tehrata ; the other, external, consists of membrane bones rep- 
resenting the clavicular, supra-clavicular, and post-clavicular 
bones of the Teleostei. In Lepidosteus one centre of ossifica- 
tion appears in the cartilage ; in Polypterus, two. The upper 
represents the scapula, and the lower the coracoid. 

It has been already stated (p. 38) that Polypterus comes 
nearest to the Elasmobranchii 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 disk formed by the skeleton of the fin ; and the 
scaly integument is continued to the bases of the fin-rays, 



126 



THE ANATOMY OF VERTEBRATED ANIMALS. 



which thus seem to fringe a lobe of the integument. Hence 
the fin is said to be lobate. In the other genera, only two of 
the basal cartilages are present, and some of the radialia 
come into contact with the shoulder-girdle between then». 
In addition, the anterior dermal iin-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 Ganoidei are intermediate between the 
Eldismohrancldi and the Teleostei. 

In certain Ganoids, as Lepidosteus, jiccipenser, 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 fulcra. 

In Accipenser and Polypterus, 
spiracula, or openings which com- 
municate with the mouth, lie on the 
top of the head, in front of the sus- 
pensorium, as in many Elasmo- 
branchs. 

Lepidosteus, Accipensa; and Sea- 
inrhynchus, have branchiae attached 
to the hyoidean arch, as in the JElus- 
mobranchii. They are now called 
opercular gills. 

In Folypterus the air-bladder is 
double and sacculated, and the pneu- 
matic duct opens upon the ventral 
aspect of the cesophagus. The air- 
bladder thus becomes exceedingly 
''■like a lung; but its vessels are in 
communication with those of the ad- 
jacent parts of the body — not with 
the heart, as in a true lung. 

In Lepidosteus, the ducts of the 




-The female reproductive male and female reproductive organs 
a of A^ia ?«'.'"^--^^'..«5 are continuous with those bodies, 



Fio. .J3.- 
organa i 
tbe open ends of the „ 

ducts; hi oviducts; c, d the and each duct opens into the dilated 

nght and left divisions of tlie , ^ .^^ .^ t i i ^ 

lu-inarj- bladder; e, e, the open- Ureter OI its SIQC. in the other Ga- 

tS-:',XZXToX't. '^oids the proximal ends of the geni- 
dominal pores; A, the urogenital tal ducts, in both sexes. Open widely 
"''" *■ into the abdominal cavity. In Fo- 

lypterus the united ureters open into 
the cavity of the confluent oviducts, while, in the other Ga- 
noids, the oviducts open into the dilated ureters. (Fig. 42.) 



THE GANOIDEI. 



127 



When the fossil, as well as the existing Ganoidei, are 
taken into account, they form a large order, divisible into the 
following sub-orders : 1 Aniiadce, 3. Lepidosteidae, 3. Grosso- 
pterygidce, 4. C/iondrosteidce, all of which have living repre- 
sentatives ; while the other three — viz., 5. Gephalaspidce, 6. 
Placodermi, and 7. Acanthodidm — have been extinct since 
the Palceozoic epoch, and are only ranged among the Ganoids 
provisionally, inasmuch as we have no knowledge of their in- 
ternal anatomy. 

1. The Amiadce 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, preoperoulum, single median jugular plate, 
branchiostegal rays, non-lobate paired fins, and heterocercal 
tail, diagnose the sub-order. 

2. The Lepiidosteidce have rhomboidal enamelled scales, a 
preoperoulum, branchiostegal rays, non-lobate paired fins, and 
heterocercal tail. These are represented in the rivers of 
North America at the present ^ay, and in tertiary formations, 
by Lepidosteus ; in the Mesozoic rocks, by a great variety of 
genera — Lepidotus, CEchmodus, Dapedius, etc. ; and, in the 
Palaeozoic epoch, by Paleonisaus in the Carboniferous, and 
probably by Gheirolepis, in the Devonian, formation. 

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




Fia. 48.— Restoration of EoloptycMvA 



rhomboid. The dorsal fins are either two in number, or, if 
single, verv long, or multifid. The pectoral fins, and usually 
the ventrals, are lobate ; they are sometimes rounded^ as in 
Polypterus — sometimes greatly elongated and almost filiform, 
as in IToloptychius (Fig. 43). There are no branchiostegal 
rays, but twj principal, and sometimes many smaller lateral, 



128 THE ANATOMY OF VERTEBRATED ANIMALS. 

jugular plates. The tail may be either dipliyceroal or hetero 
cereal. 

The only living representatives of this sub-order are Polyp- 
terns and Calamoichthys, vs^hich inhabit the rivers of North 
Africa. Neither of these are known to occur in the fossil state. 
The only family of the sub-order at present known among 
Mesozoic fossils is that of the Gailacanthini, a remarkable 
group of fishes with a persistent notocbord, rudimentary ribs, 
an air-bladder with ossified walls, and a single interspinous 
bone for each of the two dorsal fins. The Ccdacanthini also 
occur in the Carboniferous formation ; and the great majority 
of the Grossopteryijldm are found in this and the Devonian 
formations ( Osteolcjns, Diploi^erus, Glyptolcemus, MegalicJi- 
thys, IloJojityrldus, Rhizodus, Dipterus, Phci7ieropleuro7i, etc.). 
3Iegalichthys, Diptenis, and probably a few other of these 
fishes, have partially ossified vertebral centra ; the rest pos- 
sessed a persistent notochord. It is by the Grossopterygidm 
that the Ganoids are especially connected with the Dipnoi, 
and, through them, with the Amphibia. 

4. The Ghondrosteidce are either naked, or have derma! 
plates of bone in the place of scales. Neither the pectoral nor 
the ventral fins are lobate. The branchiostegal rays are 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 {Aceipenser) — which inhabit the northern 
rivers of Europe, Asia, and America, occasionally migrating 
to the sea — Spatularia, Aud Scapirhynchus (found in the rivers 
of North America), are the recent members of this group, 
which is represented, in the older Mesozoic rocks, by Ghon- 
drosteus. 

5. The GephalaspidoB are remarkable fishes, probably allied 
to the Cho7idrosteida3, which occur only in the Lower Devo- 
nian and the Upper Silurian rocks, and are some of 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 backward prolongation usually bears a 
spine, in Gephalaspis ; 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 imknown. 
Notwithstanding the excellent preservation of many of the 
specimens of these fishes, they have, as yet, yielded no evi- 
dence of jaws or teeth. Should jaws be absent, the Gepho 



THE GANOIDEI. 129 

laspidm would approach the Marsipobranchii more nearly than 
any of the other amphirhine fishes do. 

6. The JPlacodermi, comprising the genera Coecosteus, 
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 encased in great bony 
plates, which, like those of the skull, are ornamented with 
dots of enamel. The caudal region was covered with small 
scales in Pterichthys, while in Coccostevs it appears to have 
been naked. The pectoral member of Pterichthys is exceed- 
ingly long, covered with suturally-united bony plates, and 
united with the thoracic plates by a regular joint. In Coccos- 
teits the pectoral member seems to have had the ordinary con- 
struction. The bones of the head and thorax of Goccosteus 
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. 

t. The A-canthodidcB, on the other hand, seem to have con- 
nected the Ganoidei with the Elasmohranchii. 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 Elasmohranchii^ 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. 

The Pycnodontidce, which are commonly grouped among 
the Ganoids, are fishes with much-compressed bodies, like the 
John Dory or the Filefishes, covered with large rhomboidal en- 
amelled scales, from which bony ridges projected internally, 
and were imbedded in the integument. The notochord is per- 
sistent, but the neural arches and the ribs are ossified. The 
proximal ends of the ribs, imbedded in the sheath of the noto- 
chord, 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 sutures, giving rise to spurious 
vertebrse. The skull is high and narrow, as in JBalistea ; the 
preraaxillas are small, and there are no teeth in the maxillae, 
but several longitudinal series of crushing teeth (the vomer 
and parasphenoid ?) 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 
Pycnodonts have no vertical successors. The pectoral fins are 
small, the ventral, obsolete. The Pycnodonts are all extinct, 



130 THE ANATOMY OF VERTEBRATED ANIMALS. 

but existed, formerly, for a very 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 JSlasmobranchii^ 
with which they constitute the oldest Vertebrata Fauna ; they 
al>ound in the Devonian formation, and constitute, with the 
Jt! lasmobranchii, the whole of the Palaeozoic Fish Fauna. 
We are in ignorance of the true affinities of Tharsis and 
Thrissops, and of the Soplopleuridm ; 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 Cretaceous series. 

V. The Teleostei. — The osseous fishes are occasionally de- 
void of any exoskeleton. Sometimes they present scattered 
dermal plates of true bone ; or, as in the Trunkfishes ( Ostra- 
cio?i), the body may be encased in a complete cuirass, which is 
calcified, but has not the structure of bone. Again, as in the 
Filefishes [JBalistes), the skin may be beset with innumerable 
small spines, somewhat like those which form the shagreen of 
tlie Elasmobranchs in appearance, though they differ from them 
in structure. But, usually, the exoskeleton of the Teleosteans 
takes the form of overlapping scales, which rarely exhibit the la- 
cunae 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 cen- 
tra, and the primordial cartilage of the skull is more or less 
replaced by bone. The centra of the vertebrae are usually bi- 
concave, each face presenting a deep conical hollow. In cer- 
tain Eels [Symbrcmchus), the centra of most of the vertebrae 
are flat in front and concave behind, the most anterior pos- 
sessing a convexity in front. In many Siluroid fishes a cer- 
tain number of the anterior vertebrae are anohylosed together, 
and with the skull, into one mass, as in the Ganoids. 

The vertebrae are distinguishable only into those of the 
trunk and those of the tail. The latter are provided with com- 
plete 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-abdominal viscera. The ver- 



THE TELEOSTEI. 131 

fcebrae are commonly united by zygapophyses, or oblique pro- 
cesses, placed above the centra ; in addition to which, the 
lower margins of the centra are, not unfrequently, united bv 
additional articular processes. Transverse processes common- 
ly exist, but the ribs are articulated with the bodies of the 
vertebrae, or with the bases of the transverse processes, not 
with their extremities. 

When a dorsal fin exists in the trunk, its rays are articu- 
lated with, and supported by, elongated and pointed bones — 
the ijiterspinous hones, which are developed around preexist- 
ing cartilages, and lie between, and are connected with, the 
spines of the vertebrae. The fin-rays maj' be entire and com- 
pletely ossified, or they may be transversely jointed and lon- 
gitudinally 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, page 19), 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 characteristically Teleostean 
structure of the tail-fin has been termed homocercal — a name 
which may be retained, though it originated in a misconcep- 
tion of the relation of this structure to the heterocercal con- 
dition. 

In no Teleostean fish is the bent-up termination of the 
notochord replaced by vertebrae. Sometimes, as in the Sal- 
mon (Fig. 6, page 20), it becomes ensheathed in cartilage, and 
persists throughout life. But, more usually, its sheath be- 
comes calcified, and the urostyle thus formed coalesces with 
the dorsal edge of the upper part of the wedge-shaped hypural 
bone, formed by the anchylosis 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 ver- 



132 



THE ANATOMY OF VERTEBRATED ANIMALS. 



tebrse, and bear the fin-rays of the anal, and, in part, of the 
caudal fin. 

The 2'eleostei differ very much in the extent to which the 
primordial cranium persists throughout life. Sometimes, as 
in the Pike (Figs. 44 and 45), it grows with the growth of ilie 




e^msmsa. 



I.O'r. AS. JiS Flirt. 



FiQ. 44. — The cartilagiDous cranium of the Hke (Esox lucius), vrith its intriosic fssifica- 
tions; viewed, A, from above ; B, frombeloTv; C, from the left side : i\^, -^, nasatfosaee; 
/. Or, Interorbital septum ; a, groove for the median ridge of the parasphenoid ; &, canal 
for the orbital muscles. Sq., wrongly so marked, is the Pterotic. Y. and VIII. mark 
the exits of the fifth and pneumogastric nerves ; 8, 8, small ossifications of the rostrum. 

fish, and only becomes partially ossified ; in other cases it al- 
most disappears. A basi-occipital {J5. 0.), ex-ocoipital (E. 0.), 
and supra-occipital {S. 0.) bone are developed in it, and form a 
complete occipital segment. The proper basi-sphenoid {£S) 
bone is always a very small, and usually somewhat Y-shaped, 
bone. The alisphenoids (AS.) sometimes are and sometimes 
are not developed. The presphenoidal 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 



THE TELEOSTEI. 

f&rtns an interorbital septum (Z Or.). 
the cranial cavity is consequently re- 
duced to a comparatively narrow pas- 
sage above the septum (Vig. 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 diminish- 
ing forward. The ethmoidal cartilage 
usually remains unossified, but Rome- 
times, as in the Pike, ossification may 
take place in it. (Fig. 44, 3, 3.) The 
antorbital, or lateral ethmoidal, pro- 
cesses of the primordial cranium os- 
sify, and give rise to the prefrontal 
bones (I'rf.). The postorbital pro- 
cesses also ossify as postfrontals (Ptf.). 
The upper and posterior part of the 
primordial cranium exhibits five pro- 
cesses — one postero-median, two pos- 
tero-lateral, and two postero-external. 
The postero-median ossifies as part of 
the supra-occipital (S. 0.). The pos- 
tero-lateral ossifies as part of the epi- 
otic {^p. 0.), which lies upon the sum- 
mit 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 tUe higher Vertebrata. 
Not unfrequently, as in the Cod, for 
example, the opisthotio (Op.O.) is a 
distinct bone, and enters into the for- 
mation of the postero-external process. 
The proOtio ( JV. 0.) is always a well- 
developed bone, and occupies its regu- 
lar place, in front of the anterior ver- 
tical 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 numer- 



133 



The anterior moiety of 




Fig. 45.— Lon^tudinal and ver- 
tical section of a fresli Pifco^a 
Blcul]. — ThecTiteurfaceof oar- 
tikge is dotted. For S. V. 0... 
and P.V.G., read a.8.c., an- 
terior, and p.8.c,^ posterior 
semicircular canal ; x, tlw 
parasphenoid ; y, the basi 
spbenoid ; Fo, the voioer 
P., the pituitary fossa. 



134 



THE ANATOMY OF VERTEBRA TED ANIMALS. 



ous membrane bones. These are, on the roof of the 
skull— 

1. The parietal bones (I'a.), which sometimes meet in a 
sagittal suture, as in most of the higher Vertebrata, but are 
very generally separated by the junction of the Jrontals with 
the supra-occipital. 

2. The large frontals (-Z'r.), which may or may not unite 
into one. 

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




Fio. 46. — Side and upper viewa of the skull cf a Pike {Esox luciuB\ without the facial or 
eupra-orbital bones : ?/, the basisphenoid; is, the alispheuoid; a, the articular fecet for 
the hyomandibular bone. 



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

A supra-orbital bone (& Or.) is the only membrane bone 
attached to the sides of the brain-case. Two premaxillary 
bones [Pmx.) are attached, sometimes closely, sometimes 
loosely, to the anterior extremity of the cranium ; and behind 
these are the maxillse (Jfo.), 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 maxillae take little 
or no share in the formation of the gape, which is boimded 
above by the backwardly-extended premaxillfe. 

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



THE TELEOSTEI. 



13G 



Amia, The honiologiie of the suspensorium of the Elasmo- 
branchil is articulated with a surface furnished to it bj the 
postfrontal, pterotic, and proOtio bones. Usually it moves 




ill- An SijPrO/\ -Bra 

f IQ. 47.— Side-Tiew of the skull of a Pike (Esox lualua) : Prf, prefrontal ; IT. 3f., hyoman- 
dibular bone; Op, operculum; S.Op., suboperculum ; LOp, interoperculum; Pr, Op, 
preoperoulum ; Brg, branchiostegal rays; Sy, symplectlo; Mt, metapterygoid ; pL 
palato-pterygoid arch; ^«, quadrate bone; Ar, articular; An, angular; i>, dentarv: 
S.Or, suborbital bone. . > = . . i < 

freely upon that surface, but, in the Plectognathi, it may be 
fixed. It ossifies so as to give rise to tw^o bones : an upper 
broad hyomandibular {H.M.), with which the operculum artic- 




Art 



Pig. 48.— Palato-quadrate areh, with the hyomandibular and symplectic of the Pike, viewed 
from the inner side ; the articular piece i^Art), of the lower jaw, and Meckera cartilage 
{Mck.) of the Pike ; seen from the inner side : «, the cartilage interposed between the 
hyomandibular {S.M.\ and the symplectic i^S]/-) ; &, that which serves as a pedicle to 
the pterygo-palatine arch ; c, process of the hyomandibular with which the operculum 
ai-tieulates ; d, head of the hyomandibular which articulates with the skulL 



ulateS; and a lower styliform symplectic {Sy.), which fits into 
a groove on the inner and posterior surafce 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 {PL) in front, and 



136 THE ANATOMY OF VERTEBRATED ANIMALS. 

the quadrate {Qu.) behind and below. Besides these there 
may be three others: an external, ectopterygoid {Ecpt.), an 
internal, entopterygoid {Ept.), and a metapterygoid (Mpt.). 
The last envelops the upper and posterior portion of the 
primitive quadrate cartilage ; and, fixing- itself against the 
hyomandibular, contributes to the firmness of the union already 
effected by the symplectic. 

Meckel's cartilage (MbJc.) 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 
(-Z?.) membrane bone are commonlj' added (Fig. 47). 

The hyoidean arch is usually composed of two large oornua 
— connected with the cartilaginous interval between the hyo- 
mandibular and the symplectic by a stylohyal ossification, and 
abutting, in the middle line below, upon one or more median 
pieces, the anterior of which {entoglossal) supports the tongue, 
while the posterior (urohyal) extends back to join the median 
elements of the branchial apparatus. The cornua themselves 
are usually ossified into four pieces : an upper (epihyaV) and a 
lower {ceratohyal) large ossification, and two small ones (basi- 
hyals) 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 no bran- 
chial filaments, but commonly support teeth, and are called 
hypopharyiigeal bones. In certain osseous fishes, thence 
called Pharyyigognathi, they anchylose together into one bone. 
The anterior four pair are composed of several joints, and the 
ujapermost articulations of more or fewer of them usually 
expand, bear teeth, and form the epipharyngeal bones. Sun- 
dry important membrane bones are connected with the man- 
dibular and hyoidean arches. 'Y\\q preoperculum, (P. Op.), oper- 
culum (Op.), and branchiostegal rays, {Br.), already met with 
among the Gfanoidei, are the most constant of these. Beneath 
the operculum, lies a suboperculum {S. Op.), and below this 
an interoperculum {I. Op.), which is connected 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 
tigamentous, as in the Siluroids. 

The branchiostegal rays are attached partly to the inner, 
ind 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. 



THE TELEOSTEI. 



137 



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 Murmnophis, 
The ventral fins are frequentlj' situated in their normal posi- 
tion beneath the posterior part of the trunk ; but in consider- 
able groups of these fishes they are immediately behind the 
pectoral fins {thoracic), or even in front of them [jugular). 
In the asymmetrical Pleuronectidoe 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 ( GL), which meets its fellow in the middle line, and 
is usually joined to it by ligament, but sometimes, as in the 




Fio 49. — ^The bones of the pectoral arch and fore-limb o f the Pike {Esox Iticius) : A, a 
semi-diagrammatic view of these bones, to show their relative natural position. The 
clavicle ((7/) is supposed to be transparent. S.cl, supra-claWcula; p.cl, post-clavicula 
c, d, the posterior and anterior ends of the outer margin of the scapulo-coracoid.— B, th« 
sciipiilo-coracoid and limb separate and on a larger scale ; iScp, scapula; Or, coracoid 
a, basal cartilages ; 6, fin-rays ; c, corresponds with c in the foregoing figure. 



138 THE ANATOMY OF VERTEBRATED ANIMALS. 

Siluroids, by sutural union. By its inner surface it gives 
attachment to the coraco-scapular — and sometimes above 
them, to a styliform bone whicli extends back among the 
lateral muscles — the post-davicula (p.cl.). 

Attached to the dorsal end of the clavicle, there is usually 
a second much smaller bone, the siq^ra-dav/cnla ()S.cl.), and 
this is very generally connected with the skull by a superficial 
membrane bone, the post-temporal^ which, in front, becomes 
forked, and attaches itself by one prong to the epiotic bone, 
by the other to the pterotio, 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 ossified, cartilages, which are placed 
side by side and articulate 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 enclosed 
by the base of the anterior fin-ray, and eifects that articulation 
with the shoulder-girdle which is so remarkable in many SUu- 
roid fishes. The posterior cartilage, or bone, is the metaptery- 
gial basale, and the intermediate three are radialia (p. 39). 

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 toward the base, 
but this folding never goes so far as in the Ganoids. The dif- 
ferent kinds and modes of arrangement of the teeth may be 
classified as follows : 

1. Isolated, more or less pointed teeth, developed from 
papillas of the mucous membrane, which do not become en- 
closed in sacs — frequently anchylosed 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, ■\^'hioh become imbedded in sockets, and 
are replaced vertically. 

Such teeth are seen in the premaxillse of Sargus, where 
they curiously simulate the form of human incisors ; and, im- 
Jjcdded 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 
K'ear away in front, and are replaced by new teeth developed 
behind the others. Tliis structure is seen in the coalesced 
hypopharyngeal bones of the Parrotfish [Scarits). 



THE TELEOSTEI. 139 

4. Beak-like compound teeth, attached to the pi-emaxillaa 
«!id dentary bones of the mandible. 

These are of two kinds. In the Parrotfisli {Scm'us) the 
beak is formed by the union of numerous separately-developed 
teeth into one mass. But in the Gymnodonts (Tetrodon and 
Dio'Jon) the beak is produced by the coalescence of broad 
calcified horizontal lamellije 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, Gyprlnoids, 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 bj' the presence of 
more or less numerous caecal diverticula, the pyloric cceca. 
The small intestine has no spiral valve, though the mucous 
membrane may be raised into large transverse folds. The rec- 
tum 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-Madder underlies the ver- 
tebral column, and is connected by an open pneumatic duct 
vrith the dorsal wall of the oesophagus, or even with the stom- 
ach, as in the Herring. In other Teleostei, the air-bladder oc- 
cupies 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 Slennii, the Pleuronectidce or Flatfishes, 
the Sand-eel (Ammodytes), the Zioricarini, and Symhranchii, 
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 di- 
verticula ; or retia mirabilia may be developed in its walls. 
Sometimes the air-bladder is brought into direct relation with 
the membranous labyrinth, as in Myripristis and Sparus, and 
the Herring, Shad, and Anchovy — ^prolongations of the one or- 
gan being separated from the other only by a membranous 
fenestra in the wall of the skull. In the Sihiroidel, Gypri- 
noidei, and Charaeini, and in the Gymnotini, the anterior 
end of the air-bladder is connected with the membranous vesti- 
bule by the intermediation of a series of bones attached to the 
vertebral column, some of which are movable. 

The vessels of the air-bladder are derived from, and empty 



140 THE AXAT05IY OF VERTEBRATED ANIMALS. 

themselves into, those of the adjacent parts of the body, in 
which respect, and in the dorsal position of the oesophageal 
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 aortoe, which is not rhyth- 
mically contractile. 

The cardiac aorta divides into trunks to form the branchial 
arteries, which run upon the outer, or convex, side of the bran- 
chial arches, and are distributed to the branchial filaments. 
The blood is collected thence into a branchial vein, which also 
lies on the convex side of the arch ; and, increasing toward 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 
backward and meet in the trunk of the dorsal aorta under the 
spinal column. 

The anterior branchial vein gives off, at its dorsal termina- 
tion, a considerable carotid trunk, which passes forward under 
the base of the skull ; and this is united with its fellow by a 
transverse branch — so that a complete arterial circle, the cir- 
culus cephalicus, is formed beneath the base of the skull. Be- 
low, the anterior branchial vein gives off the hyoidean artery, 
which ascends along the hyoidean arch, and very generally 
terminates by one Ijranch in the cephalic circle, and b}- another 
enters a rete mirabUe, which lies in the inner side of the hyo- 
mandibular bone, and sometimes has the form of a gill. This 
is the pseudohranchia. The branches of the rete mirahile 
unite again into the ophthalmic artery, which pierces the scle- 
rotic, 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 considerable 
spaces of integument separate their rounded outer apertures. 

In the ordinary Elasmohranchii, the branchial pouches are 
more flattened from before backward, and their outer apertures 
are more slit-like. The integumentary spaces between the 
slits aie correspondingly narrower, and the adjacent walls of 
successive pouches are more closely approximated, so that they 
art divided only by scpia ; but the vascular plaits of the sup 



THE TELEOSTEI. 141 

face of the respiratory mucous membrane do not reach the 
outer edges of these septa. 

In Chiinmra, the free edges of the septa are exceedingly 
narrow, and the apices of the branchial processes extend out- 
ward to them. 

In the Sturgeon, the septum is not more than three-fourths 
a» long as the branchial processes, the apices of which are 
oonsequently free. 

The process of reduction is carried still further in the lele- 
Ostei — 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 cartilaginous 
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, Cydopterun, Zeus, etc.), the 
number is reduced to seven ; the fourth branchial arch having 
only one series, the anterior. In this case, the gill-cleft, which 
should lie between this arch and the fifth, is closed. Some- 
times there are only six series of branchial processes, the fourth 
arch being devoid of any (e. g., Lophius, Diodon). In Hal- 
thma the number is reduced to five, only the anterior series of 
the third arch being developed; and in Amphipnous cuchia 
only the second branchial arch possesses branchial filaments, 
the first, third, and fourth, being devoid of them. 

Many Teleostean fishes possess accessory respiratory or- 
gans. These may take the form of arborescent appendages to 
the upper ends of some of the branchial arches, as in Clarias, 
Seterobranchus, and Seterotis ; or, as in the Climbing Perch 
(^Anabas) and its allies, the epipharyngeal bones may enlarge 
and acquire a labyrinthic honeycombed structure, and support 
a large surface of vascular mucous membrane ; or, as in the Clu- 
peoid {Lutodeira chanos), an accessory gill may be developed 
in a curved csecal prolongation of the branchial cavity. Final- 
ly, in iSaccoh'anchits 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 branchise, 
while they return it into the dorsal aorta. 

All these fishes (except Lutodeira) are remarkable for their 
pow^er of sustaining life out of the water. Manj' inhabit the 
marshes of hot countries, which become more or less desic- 
cated in tlie dry season. 



I +2 



THE ANATOMY OF VERTEBIIATED ANHFALS. 



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 a urinary 
bladder which opens behind the rectum. 

The brain in the Teleostei has sol- 
id cerebral hemispheres, and, when 
viewed from above, the thalaraen- 
coplialon is hidden by the approxima- 
tion to the hemispheres of the large 
and hollow optic lobes of the mesen- 
cephalon, which has a pair of inferior 
enlargements, lohi inferiores. There 
is a peculiarity about the structure. of 
the optic lobes, which has given rise 
to much diversity of interpretation of 
tlie parts of the brain in osseous fish- 
es. 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 forward into a deep fold 
which lies above the crura cerebri, 
and divides the iter a tertio ad quar- 
tum 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 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. 

The optic nerves simply cross one another, and form no 
chiasma. The cerebellum is usually large. 

The cephalic part of the sympathetic nerve is present, as 
in the higher Vertebrata. 

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 Ken- 
tucky {Amblt/opsis spelceus). A fibrous band often passes 
from the back of the orbit to the sclerotic, and represents tiie 
cartilaginous pedicle of the Elasmobranchs. There is no nic 




Fig. 50 — Brain of tlie Pike, view- 
ed from above : ^, tlie olfactory 
nerves or lobes, and beneath 
tbem the optic nerves ; £, the 
cerebral hemispheres; C, the 
optic lobes ; J}, the cerebellum. 



THE TELEOSTEI. 143 

titating membrane, but immovable external eyelids may be 
developed. The choroidal gland, mentioned above, surrounds 
the optic nerve between the sclerotic and the choroid. Very 
generally , a. faloiform process of the latter membrane traverses 
the retina and vitreous humor to the crystalline lens. This 
represents the pecten of higher Veftebrata. As in other fishes, 
the lens is spheroidal, and the cornea flat. The sacculus of the 
auditory organ contains 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 semicircular 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 backward into ducts 
which open beside, or behind, the urinary aperture. 

Some few Teleostei are ovoviviparous (e. g., Zoarces vi- 
viparus), the eggs being retained in the interior of the ovary, 
and hatched there. In the male 8yngnathus, and other Lo- 
phohranchii, integumentary folds of the abdomen grow down 
and form a pouch, into which the eggs are received, and iu 
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 Teleostei is not yet in a thoroughly 
satisfactory state, and the following arrangement must be re- 
garded as provisional : 

1. The Physostomi. — This group contains the Siluroidei, 
the Gyprinoidei, the Characini, the Gyprinodontes, the Sal- 
monidoB, the Scopelini, the Esoeini, the Monnyri, the Galax- 
ice, the Glupeidce, the Seteropygii, the Muraenoidei, Sym- 
branchii, 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 po- 
sition. The fin-rays (except in the pectoral and dorsal fins of 
sundry Siluroidei) are all soft and jointed. The inferior pha- 
ryngeal bones are always distinct. 

In all other Teleostean fishes the air-bladder is either ab- 
sent, or devoid of an open pneumatic duct. Hence they are 
termed, collectively, Physoclisti by Haeckel. 

3. The Anaeanthini. — The body has cycloid or ctenoid 



144 THE ANATOMY OF VEKTEBRATED ANIMALS. 

scales, or is naked. The ventral fins, if present, are jugular in 
position. The fin-rays are all articulated. The inferior pharj'n- 
geal bones are distinct. ( Ophidini, Gadoidei, Pleuronectklce. ) 

The Pleuronectidm are ihe most aberrant of all Teleostean 
fishes, on account of the disturbance in the bilateral symmetry 
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 
distmct inferior pharyngeal bones. The Percoidei, Cata- 
phracti, Sparoidei, Scicenoidei, Labyriiithici, Mugiloidei, iVb- 
tacanthini, Scomberoidei, Squamipennes, Tcenioidei, Gobioi- 
dei, Plennioidei, Pediculati, Theuthyes, and Fistulares, be- 
long to this great group. 

4. The Pharyngognathi is the name given by MuUer to a 
somewhat artificial assemblage of fishes, the only common 
characters of which are the anchylosis of the inferior pharyn- 
geal bones and the closed pneumatic duct. They have either 
c}'c"loid 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, Pomacentridm, Chro- 
m idcB ; or articulated, as in the Scomberesoces. 

The two remaining groups are very peculiar ; but I con- 
fe.ss I do not see upon what ground they can be regarded as 
of ordinal value. 

5. The ZiophobrancMi. — The body is covered with bony 
plates. The ventral fins are almost always absent. The infe- 
rior pharyngeal bones are distinct. The branchial processes 
have a clavate form, being larger at the free than at the at- 
tached ends, and are in this respect unlike those of any other 
fishes. {PegasidoB, Syngnathidce.) 

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 pre- 
maxillse and, usually, the hyomandibular, are immovably united 
with the skull — a character of rare occurrence among other 
fishes. ( Gymnodontidm, Ostraciontidm, Palistidw.) 

The greater number of Teleostei are marine. No Anacan- 
tliini, Plectognathi, or ZjophobrancJiii, and only one family of 
Pharyngognathi (the Chromid(B), 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, fresh-water fish. 

If the JjeptolepidcB {Thrissops, Zeptolepis, Tharsis) are 



THE DIPNOI. 



145 



Ganoids, the Teleostei are not known before the Cretaceous 
epocli, when both Physostomi and Acanthopteri make their 
appearance, under forms, some of which (e. g., Beryx) arc 
generically identical with fish living at the present day. 

VI. The Dipnoi.— 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 Atn- 
phibia. 

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 extremities, and with a 
caudal fin. 




Pig. 51.— Tbo Mudfish (J^^pidosiren). 
C Or ? 




M/n 



Fifl, 52. — Skull ot Lepido siren annectens: A, the uarieto-frontal bone ; .S, the supra-orbi- 
tal ; C, the nasal ; D, the palato-pteryg:oid ; ^, tne vomerine leetn ; ^, (3., the ex-occlpl 
tal ; Mn, the mandible ; Jfy, the hyoid ; Br, the branchiostegal rays ; Op, the opei-cular 
plate : a), the parasphenoid ; y, the pharyngo-brancMal ; Or, the orbit ; Au, the auditcry 
chamber ; 27\ the nasal sac 

7 



M6 THE ANATOMY OF VERTEBRATED ANIMALS. 

The spinal column consists of a thick notochord, invested 
by a cartilaginous sheath, \vithout any osseous or cartilagi- 
nous 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. 

Fin-rays support the median fin. The skull, the palato- 
quadrate, and suspensorial apparatus, form, as in CMrrKxra, 
one continuous cartilaginous mass, into the base of which the 
notochord penetrates, terminating in a point behind the pitu- 
itary fossa. 

No cartilage bone is developed in the place of the basi-occi- 
pital, 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 
(a;) underlies the base of the skull. Upon its roof a great single 
bone (^), answering to the parietals and frontals, extends 
from the occipital to the ethmoidal regions. In front of this 
are two nasal bones { C). There is no alisphenoid, but the 
fronto-parietal and parasphenoid send processes toward one 




Fib. 58. — Lon^tudinal and vertical section of the skull of L&pidosiren, The cartilage U 
dotted ; the membranous and bony constituents are shaded with lines. A^ £, C, -D, S, 
Hijy as in the preceding figure ; c, ?■, the parasphenoid; P, iS^, cartila^ons presphenoi- 
dal region ; cft, notochord ; Aii^ situation of auditory chamber ; 1, 3, first and second 
vertebrffi; /Z, 7"., 77//., exits of optic, trigeminal, and vagus nerves; a, quadi-ato- 
mandlbuiar articulation. 

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 through- 
out. In front of the exit of the optic nerves, however, it is 
longitudinally divided by a membranous septum. 

The ethmovomerine cartilage is continued to the anterior 
extremity of the skull. It bears teeth, but no distinct vomer, 

A great palato-pterygoid osseous arch {V) extends from 
the middle line along the upper and the under surface of the 



1UM DIPNOI. 147 

palato-quadrate arch on each side to near the articular surface 
of the mandible. In the middle of the roof of the mouth, di- 
vergent, 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 J^l 

The mandible presents dentary plates corresponding with 
those of the palate, and biting between the latter. The hj'oi- 
dean arch is attached to the posterior and lower edge of the 
Buspensorium — which bears a bony ray representing an oper- 
culum — while the hyoidean arch itself carries a single bran- 
chiostegal ray {Jir, Fig. 53). 

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 coraoo-scapular cartilages of other 
fishes. 

The filiform fin is supported by a many-jointed cartilagi- 
nous rod, articulated proximally with the coraco-scapular. 
Upon this are disposed fine fin-rays like those of the Elasmo- 
branchs, 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 aerated in the lungs is re- 
turned. In addition to lungs, Zepidosiren possesses both in- 
ternal and external gills, but the latter are rudimentary in the 
adult. 

The diflFerent species seem to differ in the manner in which 
the primitive aortic arches are metamorphosed ; but it may be 
said, generally, that the first has disappeared ; the second sup- 
plies 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 branchise ; while the seventh is 
connected only with an internal branchia. The pulmonary 



148 THE ANATOMY OF VERTEBRATED ANIMALS. 

artery seems originally to have been given off from an eighth 
aortic arch. 

It is a remarkable circumstance that, while the Dipnoi pre- 
sent, 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 
Uiose of any other fishes. 



CHAPTER IV. 



THE CLASS AMPHIBIA. 




The Ichthtopsida. — Class 11. — Amphibia. 

The only clearly diagnostic characters of this class as com- 
pared with Fishes are the following : 

1. A/mphihia have no fin-rays. 

3. 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 ( Ccecilia, JSphippifer). In the 
extinct Labyrinthodonta, the dermal armor 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. 

i. The suspensorial apparatus of the mandible is continu- 
ous with the skull, which has two occipital condyles, and no 
completely ossified basi-occipital. 

5. There are no sternal ribs. 

The Amphibia are divisible into the following groups : 
A. A distinct and often long tail ; the vertebrae ampliicoelous or opis. 
thocoelous ; the proximal elements of the tarsus not elongated. 
A. Two or four limbs ; no scutes or scales. 

I. SaurobcUrachia or Urodela. 
a. External branchiEc or gill-clefts persistent, or disappearinjj 
only in advanced age ; no eyelids ; vertebrae ampbiccelous ; 
uarpus and tarsus cartilaginous. 



150 THE ANATOMY OF VERTEBRATED ANIMALS. 

1. Proteiika. 
b. No branchisB or branchial clefts in the adult ; eyelids present; 
carpus and tarsus more or less ossified ; vertebrte coinn?only 
opisthocoelous. 

2. Salamandridea, 
B. Limb? absent, o r all four present. Three large pectoral osseous 
plates and an armor of small scutes on the ventral suTfiic<" 
of tlie body ; vertebrae amphiccelous ; walls of the teeth more 
or less folded. 

n. Lahyrinthodonta, 
B. Tail obsolete in the adult. 

A. Limbs absent; numerous minute dermal scutes imbedded in 
the integument of the serpentiform body. 

III. G^mnophiona. 
£. 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 \K 

IV. Batrachia or Anura. 

The inlegntnent in most Amphibia is soft and moist, as in 
the Frog, where numerous glands open upon its surface. The 
Gymnojyhiona are exceptional, among existing Amphihin^ 
in possessing small, rounded, flexible scales, like the cycloid 
scales of fishes, imbedded within the wrinkled integument. 

In certain Batrachia ( Geratophrys dorsata, Ephippifer 
cmrantiaous), flat dermal bony plates are developed in the 
dorsal integument, and become united with some of the sub- 
jacent vertebrtB. Many of the extinct Labyrinthodonta, and 
probably the whole of the members of that group, possessed 
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 rhomboidal. The 
lateral ones are somewhat triangular, and unite with the 
anterolateral margins of the median plate by one side, sending 
a process upward and backward from their outer angles. 
The outer surfases 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 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, Micropjholis. I have not met 
with dermal ossicles in this position in otlier Labyrinthodonts. 



THE AMPHIBIA. 151 

But in Archegosaurus, Pholidogaster, Urocordylus, Kerater- 
peton, Ophiderpeton, Ichthyerpeton, the integument between 
the thoracic plates and the pelvis presents regularly-disposed 
rows of small elongated ossicles, which, for the most part, 
converge from without, forward and inward, toward the mid- 
dle 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 vertebrae 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 vertebra are completely ossified biconcave disks, 
very like the centra of the vertebrae of Ichthyosaurus. 

In the existing JProteidea, and in the Oymnophiona, the 
vertebral centra are amphicoelous. In the Salamandridea 
they are opisthoccelous. In Plp>a and Bombinator they are 
also opisthoccelous, but in other Batrachia they are, for the 
most part, procoelous, 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 modified 
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 capitu- 
lar and a tubercular process. 

In the Gymnophiona, the Saurobatrachia, and the Laby- 
rinthodonta, the number of the vertebrse in the trunk is con- 
siderable, and the members of the two latter groups have long 
tails. But in the Batrachia, the total number of vertebrae 
does not exceed eleven, of which eight belong to the presacral 
region, one to the sacrum, and two (modified vertebrse) to the 
coccygeal region. The transverse processes of some of the 
presacral vertebras 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 termina- 
tion of the notochord, and corresponding with the urostyle of 



152 



THE ANATOMY OF VERTEBRATED ANIMALS. 



the Teleostei ; and of two neural arches, which lie over its 
anterior end, and become anchylosed 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 Amphibian. 
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 
aie present in other Labyrinth odonts. 

No Amphibian possesses a complete basi-occipital, supra- 
occipital, basisphenoid, alisphenoid, or presphenoid cartilage 
bone. In existing Amphibia, a proOtic ossification appears 
to be verj' constant. The constant existence of distinct opis- 
thotio and epiotic elements is doubtful. 

The Frog's skull is characterized by the development of a 
very singular cartilage-bone, called by Cuvier the " os en 
oeinture," or girdle-bone. This is an ossification which invades 
the whole circumference of the cranium in the presphenoidal 
and ethmoidal regions, and eventually assumes somewhat the 
form of a dice-box, with one-half of its cavity divided by a 
longitudinal partition. The latter, corresponding 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 to the ethmoid, the anterior half 




Fid 54.- 



-The cai-tila^ous cranium of Rana effculenta. A, from above; B, frfjm below; 

2/, the " OS en ceinture,^^ or ^dJe-bone. 



of the girdle-bone to the prefrontals, or part of them, and the 
posterior half of the girdle-bone to the orbitosphenoids of 



THE AMPHIBIAN SKULL. 



163 



other Vertebrata. Turbinal ossifications are developed in the 
cartilage bounding the nasal capsules in some Amphibia. 



Viiix 



Prmr 




Fie. S5. — Skull of Itwnu esauienta. A^ from above; B, from below ; G. from tbe left Bide 
03, pai-asphenold ; y, gtrdle-bone; Z, *be " temporo-mastoid.'' 



The membrane bones of the Amphibian skull are : 1. Front- 
als and parietals, which, in the £atrachia, may be fused to- 
gether into one bone. 2. Nasals are generally present. 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 skuU from the 
occipital to the ethmoidal region, as in Teleostei and Ganoidei. 

5. A membrane bone {Z), called " temporo-mastoid " by Du- 
g^s, lies on the outer side of the suspensorium, 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 preopercu- 
lum of fishes, and to the tjrmpanic of the higher Vertebrata. 

Two premaxillse are always developed. The maxillae are 
asually present, and may be connected, as in most Batrachia, 
by quadrato-jugal ossifications with the outer side of the end 
of the suspensorium, in whi6h an ossification representing tho 



154 THE ANATOMY OF YERTEBRATED ANIMALS. 

quadrate bone is often developed. But the quadrato-jugals 
(and even the maxillae) 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 Batrachia. The 
suspensorium, which is inclined downward and forward in the 
lower Urodela, passes almost directly downward, or a little 
backward, in the higher, and in the Batrachia slopes greatly 
backward ; and it undergoes the same modifications in direc- 
tion, 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 ele- 
ment, but the distal moiety is ossified in some Batrachia. 
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. Dis- 
tally, they are connected with a broad lamellar body, from the 
posterior margin of which two processes which embrace the 
'arynx are usually given off. In the perennibranchiate Pro- 
teidea, the hyoidean arches are united by narrow median en- 
toglossal and urohyal pieces, as in Fishes. 

In the Batrachia, the branchial arches disappear in the 
adult ; but in the Qymnophiona 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 Salaniandridea, there are, primitively, 
four branchial arches, but of these, portions of only the two 
anterior remain in the adult. Four are developed in the 
Gascilia, and three of these are permanent. 

Some peculiarities exhibited by the skulls of the Crymno- 
phiona, and by the Labyrinthodonta, are worthy of especial 
notice. 

In the former, e. g., in Ichthyophis glutinosa, the skull is 
covered b}' a complete bony roof, formed, mainly, by the ex- 
oocipitals, parietals, frontals, prefrontals, nasals, and ascending 
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 



THE LIMBS OF AMPHIBIA. 



15a 



answer to the bone (z) of the Frog, and to its quadrato-jiigal. 
Between the nostril and the maxilla, the nasal bone and the 
premaxi la, there is a bone which seems to be an ossification 
of the cartilaginous ala nasi. Another bone nearlj' encircles 
the orbit, and, as a supra- and postorbital bone, has no ana- 
logue among existing Amphibia. The palatine bones sur- 
round the posterior and 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 A7n- 
phibia. 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. 




s.i-. 



Fin. .56. — Side and upper views of tlie skull of Tr&matom'ii/rug. The sculpture of the cra- 
nial 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 characterized by the 
development of distinct pointed epiotics, like those of fishes, 
and of paired ossifications, which take the place of the supra- 
occipital, as in many Qanoidei. In many Labj'rinthodonts 
the articular element of the lower jaw is completely ossified. 

Archegosaurus possessed branchial arches when young, 



156 THE ANATOMY OF VEETEBRATED ANIMALS. 

and there can be little doubt that the other Labyrinthodonta 
resenabled it in this respect. 

The limbs and their arches are completely absent in the 
Gy innophiona, and, apparently, in the extinct Ophiderpeton 
of the Carboniferous formation. In all otber 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 ex- 
panded 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, pre- 
coraooidal, or pubic part, and a posterior, coracoidal, or ischial 
part. 

• In the TTrodela 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 devel- 
oped. In Siredon, the Derotremata, and Salamandridea, the 
ooracoids 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 Satraclda, the coraco-scapular cartilages are some- 
times, as in the common Frog, firmly united in the middle 
line, and send forward a median process, which becomes ossi- 
fied, and is the omosternvm (Fig. 57, o.st.). Behind^ the cora- 
coids articulate with a well-developed sternum {st.). Distinct 
ossifications arising on either side of the glenoidal cavity rep- 
resent the scapula (.sc.) and the coracoid («'.), and the upper 
moiety of the scapula may be distinctly ossified as a supra- 
scapula (s.sc). The coracoid is divided by a large membra- 
nous space ov fontanelle into a proper coracoid {cr.), which lies 
behind the fontanelle ; a persistently cartilaginous epicoracoid 
(fi.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 ex- 
tremity of the sacral rib. An iliac ossification is always devel- 
oped ; an ischial, in all but Proteus. The pubis does not ap- 
pear to be regularly represented by a distinct ossification. In 
the Satrachia the applied flat faces of the expanded ventral 
divisions of the pelvic arch coalesce into a disk. 



THE LIMBS OF AMPHIBIA. 



157 



In the genus Amphiuma, 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 limbs 




x.st 



Pis. 57. — The sternum and pectoral arches of a Frog, seen from above. The left supra* 
scapula is removed : flc, scapula ; s.sc, supra-scapula ; ^.«c., preacapular process ; cr., 
coracoid ; d-or., epicoracoid ; cr.f., coracoid fontanelle. The bar which bounds this Id 
front is the precoracoid, and bears the clavicle: o.si.y omosternum; si., sternum; x.Bt^ 
xiphistcraum. 

are tridactyle, the posterior didaotyle. Menohranchus has 
tetradactyle feet, while in the other TTrodela the anterior limbs 
are tetradactyle, the posterior pentadactyle. The Satrachia 
have four digits, with or without a rudiment of another, in the 
fore-limb, and five in the hind-limb. In the perennibranchiate 
TTrodela, the cartilages of the carpus and tarsus, which, except 
in Proteus, present little deviation from the typical number 
and arrangement (Fig. 11, p. 33), remain unossified ; in the 
other TTrodela, and in the JBatrachia, they are for the most 
part ossified. 

In the Satrachia, 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 
caloaneum and an astragalus, while the distal series is reduced. 
The limbs of the Labyrinthodonts were feeble in compari- 



158 THE ANATOMY OF VERTEBRATED ANIMALS. 

son with the size of the body. In the genera Archegosaurus^ 
Keraterpeton, Vrocordylus, Lepterpeton, each foot possessed 
five digits, and the carpus and tarsus were unossified. 

The Amjjhibia usually possess teeth on the vomers, pre- 
maxillae, maxilte, 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 
aiTangement which is very characteristic of the group. In 
the larvae of the HutracJtia, and in Siren, the premaxillae 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 ; Menohranchus and 
Siredon have pterygoid teeth. Many of the Labyrinthodonts 
possess palatine teeth. In some Gymnophiona the mandible 
has a double row of teeth, and there is an approximation to 
this structure in the Labyrinthodonts. 

The teeth usually become anchylosed with the adjacent 
bones. In existing Amphihia their structure is simple, but 
in the Labyrinthodonts, the parietes of the teeth, at a certain 
distance below the summit, become longitudinall}^ 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 Labyrinthodonts, again, two of 
the anterior mandibular teeth take on the form of long tusks, 
which are received into fossae, 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 Satrachia, the tongue, 
which is usually long, and fixed by its anterior end to the sym- 
pli3'sis of the mandible, can be rapidly protruded and used as 
an organ of prehension. No distinct salivary glands have 
been observed 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 larvae (which are vegetable-feeders) than in the 
adults. A gall-bladder is always present. 

The heart presents two auricles, a single ventricle and a 



THE CIRCULATION OF THE FROG. 159 

lulbus 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, Menohran- 
chus, and Siren, the septum of the auricles is less complete 
than in the 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 cham- 
ber with well-defined parietes. The walls of the long bulbus 
arteriosus contain striated muscular fibres, and are rhythmi- 
cally contractile. Valves are sometimes placed at each end 
of it, and it may be imperfectlj' divided into two cavities by 
an incomplete longitudinal partition. It terminates, 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 ar- 
teries, 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 inter- 
rupted, 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. 83) ; the hindermost pair (n.) gives off the 
pulmonary arteries, the three next (v., iv., ni.) supply the ex- 
ternal branchise ; 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 oblit- 
erated, and remains as a mere ductus Botalli. The fourth 
trunk gives off the pulmonary artery; some twigs for the 
oesophagus, and a few cardiac branches, next arise from it; 



160 THE ANATOliy OF VERTEBRATED ANIMALS. 

and it thea unites with the second and third to form the root 
of the dorsal aorta. The basal moiety of the first trunk en- 
larges at its extremity, close to the angle of the mandible, into 
a spongy organ, the carotid gland, from which the carotid ar- 
tery, 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 in- 
complete longitudinal septum into two passages ; and, at its 
extremity, divides into two trunks, each of which is parti- 
tioned internally into three passages. The middle, or systemic, 
passage passes directly into a trunk, which unites with its fel- 
low beneath the spinal column into the dorsal aorta. The an- 
terior, or carotid, passage ends, as in Salamandra, in a ca- 
rotid 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, especially toward their junction ; 
as the left gives off, just before this point, a large coeliaco- 
mesenteric artery to the abdominal 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 mechanical arrangements by which this is brought about 
have been beautifully analyzed by Brlicke, 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, communicates with the ven- 
tricular opening of the aortic bulb ; secondly, that the aortic 
bulb is imperfectly divided by a longitudinal septum, the 
upper left edge of which is attached, 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 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, pre- 
sents a mechanical obstacle to the flow of the blood through 
it ; fifthly, that there is a valvular fold open toward the heartj 



THE RESPIRATORY ORGANS OF AMPHIBIA. 161 

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 ilow through the bulb, it will gradually 




Fia. 88.— The Aiolotl (Strtdan). 

force the 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 ventric- 
ular cavity which lies nearest the opening of the bulb ; and, 
when the ventricle contracts, the blood first driven into the 
bulb is whoUy 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. 
But, as the pulmonary vessels fill, the pressure on the two 
sides of the septum becomes equalized, and the systemic pas- 
sages, which offer the next least resistance, fill with blood, 
which is now mixed, as it comes from the middle of the ven- 
tricle. Next, the septum, being driven over to the left side, 
prevents any more blood from going into the pulmo-cutane- 
ous 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 
jn the carotid passages. Hence the latter fill, and send arteri- 
alized blood to the head. 

The organs of respiration of the Amphibia, in the adult 



102 THE ANATOMY OF VERTEBRATED ANIMALS. 

state, are either external branchise, combined with lungs, a3 
in the perennibranchiate Urodela ; or lungs only, as in the 
other Urodela, the Batraehia, the Gymnophiona, and, prob- 
ably, the majority of the Lahyrinthodonta. 

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 integu- 
ment, 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 fila- 
ments. 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 Hatrachia 
and Gymnophiona, are devoid of both external gills and gill- 
clells, in tlie adult state. 

In all the Amphibia, a glottis, placed on 
the ventral wall of the oesophag-us, opens into a 
sliort laryngo-tracheal chamber 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 Gymno- 
phiona). The walls of the pulmonary sacs 
'are more or less sacculated. In most Am- 
phibia the lungs are equal in size ; but in the 
snake-like Gymnophiona, the right is much 
smaller than the left. In Proteus, the pul- 
monary blood is not all returned to the heart, 
some of it entering the veins of the trunk. 
Aerial respiration is effected, in the Amphibia, 
by pumping the air from the oral cavity into 
-The brain of the luiis's. To this end the mouth is kept 

Jiana CHCulenta, i.i. t ,,-,... ^ 

from, above, magni- Shut, and mgress and egress to the air is given 
toe'itat^epMOTt'by the nasal passages, which always open 
or olfactory lobes, immediately behind the vomers, at the anterior 
tory' nerves; /fo., P'i-rt of the roofof the mouth. These passages 
the cerebral hemi- being opcu, and the hyoidcan apparatus de- 
ihaianiencepiiaion pressed, the air fills the cavity of the mouth. 
^land, p'l: l^^t, '^'^® external nostrils are then shut, and, the 
optic lobes; c, cere- hyoidean apparatus being raised, the air is 
fou "til ventricle; forccd, through the open glottis, into the lungs, 
Mo^ medulla i.bion- ^\ Amphibia posscss a urinary bladder, 




THE RESPIRATORY ORGANS OF AMPHIBIA. 163 

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. 

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 indistinctly 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 verj' small, and covered by the integument, 
in Proteus, the Gymnophiona, and the genus Pipa. The . 
perennibranchiate and derotreme Urodela have no eyelids ; 
but most Satrachia have not only a well-developed upper 
eyelid, but a nictitating membrane, moved by special muscles. 

All Amphibia possess a fenestra ovalis with a cartilagi- 
nous, or osseous, columelliform stapes, the expanded proximal 
end of which is fixed to the membrane of the fenestra. In 
many Patrachia, if not in all, there is a fenestra rotunda, 
though the presence of a distinct cochlea has not been ascer- 
tained. The Zfrodela, the Oym,nophiona, and the Pelobatidea, 
among the Batraohia, have no tympanic cavity, nor mem- 
brane. In the other Batrachia there are tympanic cavities 
communicating freely with the throat. Each is closed exter- 
nally by a tympanic membrane, with which the outer extremity 
of the stem of the stapes is connected. In the Afflossa, 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 Elasmo- 
hranchii, the proximal end of the oviduct is open, and com- 
municates with the peritoneal cavity. The male has no penis, 
unless a papillary elevation of the wall of the cloaca may rep- 
resent such an organ. The testes of the male Amphibia are 
composed of tubules, and vasa efferentia convey the contents 
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-urinary 
duet, 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 margin of the kidneys 



164 THE ANATOMY OF VERTEBRATED ANIMALS. 

into the genito-urinary duct. In the JSatrachia there is like- 
wise a genito-urinary duct, and the vasa efferentia run to the 
inner edge of the kidney and enter it. In Bombinator igneua 
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 efferentia 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 
seminalis, 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 MuUerian ducts of the 
higher Veriebrata. 

In most Amphibia the ova are impregnated and hatched 
outside the body, but internal impregnation and incubation 
occur in some of the Urodela. In I*ipa 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 
branchial aperture, and, in the Sairachia, 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 the oesophagus. The nasal sacs are at first 
mere caecal involutions of the integument, but nasal passages 
communicating with the mouth are soon formed, and boiJi 
aiirial and aquatic respiration are completely established. 



THE DEVELOPMENT OF AMPHIBIA. 



165 



In the Batrachia, as development proceeds, the external 
branchiae disappear, and are succeeded, fuuctionally, by short 
branchial filaments developed upon the whole length of each 
of the branchial arches, of which there are four. 







Fig. 60. — A. B., Tadpoles with external branchlee : «, nasal sacs : a, eye; o, ear; k &, braU' 

cMffl ; m, mouth ; «, horny jaws ; s, suckers ; £?,' opercular fold, 
0., a more advanced Frog's larva : y, the rudiment of tne hind-limb ; k s, the single branchial 

aperture. The figure has not been reversed, so that this aperture appears ""to he on the 

nght side Instead of the left. 

Before the development of the lungs the heart has only 
a single auricle; afterward, 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 JSatrachia 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 anasto- 
moses dilate ; the direct communication between the afferent 
and efferent trunks of the second pair of internal branchias ia 
reSstablished ; and they become the permanent arches of the 



166 THE ANATOMY OF VERTEBRATED ANIMALS. 

aorta. The anterior branchiee 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 
branchiae are converted into the stem of the cutaneous artery, 
and the afferent trunk of the fourth pair of branchiae into that 
of the pulmonary artery. The diagram (Fig. 25, p. 83) 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 
soiled up into a close spire, like a watch-spring, in the ab- 
domen, but its length becomes relatively less as age advances. 
At the same time, the diet changes from vegetable to animal 
— the young tadpole being chiefly herbivorous, the adult, 
insectivorous. 

In the TTrodela the tail persists, and develops complete 
vertebrae ; but, in the Satrcichia, 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 be- 
comes converted into the urostyle, which eventually anchyloses 
with the two hindermost neural arches. 



CHAPTER V. 

TDE CLASSIFICATION AND THE OSTEOLOGY OF THE EEPTILIA. 

The province Sauropsida is divisible into the two classes, 
Meptilia and Aves. 

All Reptilia, so far as their organization is known to us, 
are distinguished from A.ves by the following characters : 

1. The exoskeleton is composed of horny plates (scales), 
or bony plates (scutes), never of feathers. 

3. The centra of the vertebrae may be amphicoelous, pro- 
coelous, opisthocoelous, or may have nearly flat articular faces ; 
but these faces are spheroidal or oval, and are never cylin 
droidal, even in the cervical region.* 

3. When reptiles possess a sacrum, the sacral vertebrs 
have large expanded ribs, with the ends of which the ilia 
articulate. 

4. The sternum is rhomboidal ; and, when many ribs are 
connected with it, the hindermost of these are attached to a 
single, or double, median backward prolongation (except, per- 
haps, in the Pterosauria). The sternum may be converted 
into cartilage-bone, but (with the possible exception of the 
Pterosauria) 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. 

7. In all existing reptiles, the ilia are prolonged farther 
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 dovraward and forward, and, like the 

* The articular fsMses of the vertetrse of some JPleromwria are very much 
eloDgated trausvereely. 



168 THE ANATOMY OF VERTEBRATED ANIMALS. 

ischia, meet in a ventral symphysis. In the extinct Dino 
sauria, the pelvis exhibits forms transitional between the rep- 
tilian and the ornithic arrangement. 

8. The digits of the pes are not fevi'er than three ; and the 
metatarsal bones are not anchylosed 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 : 

1. The exoskeleton consists of feathers. Ossifications of 
the dermis are rare, and never take the form of scutes. 

3. In all recent birds, the centra of the cervical vertebrae, 
at least, have subcylindrical articular faces. If, as in some 
birds, the faces of the centra of the other vertebree are sphe- 
roidal, they are opisthocoelous, which is the rarest arrange- 
ment among reptiles. 

3. The proper sacral vertebras 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 pro- 
longation, all the ribs being attached to its sides. The carti- 
laginous sternum is replaced, in the adult, by membrane-bone, 
and ossifies from two, to five or more, centres, 

5. When an interclaviole 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 acetab- 
ulum, the inner wall of which is membranous. The pubes 
and ischia are directed backward, 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 anchyloses with the latter bone. In this 
character, Birds differ from all existing Reptiles. The fool 



THE DIVISIONS OF THE REI'TILiA., 100 

contains not more than lour digits. The first metatarsal is, 
almost always, free, shorter than the rest, and incomplete 
above. The other three are anohj'losed 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 immovable 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 
Rrterial trunk, the pulmonic, is given off from the right ven- 
tricle. 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 exist- 
ing birds the extremities of the chief pulmonary passages 
terminate in air-sacs. There is a rudiment of this structure 
in the Chamseleons, and the extinct Pterodactyles very prob- 
ably possessed such sxcs. 

11. The corpora bigemina are thrown down to the sides 
and base of the brain. 

The Reptilia. — This class is divisible, by well-defined char- 
acters, into the following groups : 

A. The dorsal vertebrse (which, like all the other vertebra, are devoid of 
transverse processes) are not movable upon one another, nor are the ribs 
movable upon the vertebrte {Pleurospondi/lia). Most of the dorsal vertebrae 
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 sym- 
metrical, 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 vertebrae (which have either complete, or rudimentary, 
transverse processes) are movable upon one another, and the ribs upon 
Ihem. There is no plastron. 

a. The dorsal vertebrae have transverse processes, which are either 
entire, or only very imperfectly divided into terminal facets (Erpe- 
to^pondt/lia). 
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. 
h. The transverse processes are short, and sometimes rudimentary; 
the limbs present or absent ; when they are fully developed, the 
digits are free, and there is a well-developed sternum with sternal 
ribs. 
8 



I -JO THE ANATOMY OF VERTEB RATED ANIMALS. 

a. A pectoral arch and urinary bladder. 

III. — LacertiUa. 

b. No pectoral arch, and no urinary bladder. 

IV. — Ophidia. 
i>. JThe dorsal vertebrre bave double tubercles in the place of traisvcrse 
processes {Ferospondi/lia). The limbs are paddle-like. 

V. — Icldhyosauria. 
c. The anterior dorsal vertebrae have elongated and divided transverse 
processes, the tubercular being longer than the caoitular division 
i^SuchoHpondylla). 

a. With only two vertebrae in the sacrum. 

VI. — Crocodilia. 

b. With more than two vertebras in the sacrum. 

a. The manus without a prolonged ulnar digit 

1. The hind-limb saurian. 

VII. — Dicynodontia. 

2. The hind-limb ornithic. 

VIII. — Ornithoscelida. 

b. The manus having an extremely prolonged ulnar digit. 

IX. — Plerosaiiria. 

I sliall describe the exoskeletal, endoskeletal, and dental 
systems of the chief groups of the Septilia, under the several 
heads here enumerated, and I shall then give an 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. 

1. 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 tj^pe, in some respects. 

A homy epidermic exoskeleton is absent in the soft Tor- 
toises ( Trionyx), the bodies of vs^hich are covered by a soft 
integument ; but, in the other Chelonia, the epidermis is modi- 
fied into horny plates, vchich constitute the so-called " Tor- 
toise-shell," and have in general a very definite arrangement. 
The dorsal surface of the body presents three series of central 
plates, of vrhich 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 



THE CUELONIA. 171 

on each side, marginal. The ventral shield sometimes pre- 
sents 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 correspond with the 
bony dermal ossifications. In addition to these principal 
plates, smaller scale-like patches of horny epidermis are de- 
veloped on other parts of the body, and on the limbs. 

The dermal ossifications may best be described in connec- 
tion with the endoskeleton. 

The presacral vertebrse are few in number. In the Green 
Turtle ( Chelone midas) there are eight cervical, and ten dor- 
sal, in front of the sacrum, which is composed of two vertebrse. 
In all the cervical vertebrae the neurocentral sutures persist; 
there are no transverse processes, or ribs, and the spines are 
low or obsolete. The first vertebra, or atlas, i& a ringlike 
bone, composed of three pieces, one basal and twj superolat- 
eral. The second is a true axis vertebra, the central part of 
the centrum of the atlas ossifying apart, as an odontoid bone, 
(i.nd attaching itself to the front face of the centrum of the sec- 
md vertebra. 

The other cervical vertebrae are remarkable for the singu- 
(ar variety in the disposition of their articular cups and balls. 




Fig. 61. — ^The Alligator Terrapene {OMlydra Serpmtma). 

Thus the third is opisthocoelous ; the fourth, biconvex ; 
the fifth, procoelous ; the sixth, also procoelous, but the pos- 
terior face is nearly flat, and very broad ; in the seventh, belli 
the anterior and the posterior faces are very broad and flat- 
tened, the posterior being the more convex. The eighth cer- 
vical vertebra is procoelous, and differs from the rest by the 
expansion of its neural spine, and by the arching backward 
of its postzygapophyses over the convex prezygapophyses of 



172 



THE ANATOMY OF VERTEBRATED ANIMALS. 



blie first dorsal vertebra, upon which the former play back- 
ward and forward. 

All the cervical vertebrae are very freely movable upon 
one another, and confer great flexibility on the neck. In 
strildng contrast with this aiTangement, the ten following 
vertebrae have flattened faces, firmly united by cartilage. If 
any one of these vertebrae, from the second to the ninth, be 
examined, it will be found that the elongated centrum is only 
looseiy 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, but a rib is articulated 
between the centrum and the neural arch. At a short dis- 
tance from its attachment, this rib passes into a broad plate 
of bons, which extends upward to unite suturally with the 
neural plate ; and, in front and behind, becomes similarly con- 
nected with preceding and succeeding costal plates. The rib 
may be traced along the under-surfaoe of the costal plate, be- 
yond the outer margin of which it protrudes ; and its free ex- 
tremity 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 diflfers from the others in many 
respects. The anterior face of its centrum is concave, and 
looks downward and forward, while its prezygapoph3'ses are 

-y 




Pia. 652. — Transverse -seetinn of the skeleton of CJichne midas in tlie dorsal reg:ion: C^, 
centrum: F, cxpindftl neural plate; (7, costal plate ; 72, rib; .37", marginal plate ; P, lal^ 
eral element of the plastron 



much prolonged, in order to articulate with the convex poste- 
rior face of the centrum and prolonged postzygapophyses of 
the last cervical vertebra. The spinous process of this verte- 
bra does not pass into the bony nuchal plate of the carapace, 
which lies above it (Fig. 63, Nu), 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 thia 



THE CARAPACE OF THE CHELONIA. 173 

rertebra is shorter, from before backward, than its centrum j 
and the neural arch of the second dorsal vertebra extends for- 
ward and overlaps the centrum of the first, for the space thus 
left unoccupied. The rib of the second vertebra is also carried 
forward, and articulates 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 ver- 
tebras 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 cos- 
tal plate. 

The union of the neural and costal plates of the eight dor- 




riG. 68. — Dorsal view of the carapace of C?iel<mf> midas : Ku^ nuchal plate ; J/", marginal 
plates; i2, ribs; 1-8, neural plates ; (7, 1-C.8, costal plates; Py, pygal plates. 

sal vertebrae, 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 dor- 
sal vertebree contribute nothing to the carapace, 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 
serrated suture, lies a large nuchal plate (Fig. 63, Nu), which 



174 THE ANATOMY OF VERTEIBRATED ANIMALS. 

forms the anterior median boundary' of the carapace. This 
nuchal plate sends down from its under-surface a median pro- 
cess, which is joined by ligament with the expanded neural 
spine of the eighth cervical vertebra. Behind the eighth neu- 
ral plate, three other median pygal plates (Fig. 63, Py) suc- 
ceed one another. The anterior two of these are united by 
sutures with the eighth neural and costals, and with one an- 
other ; but the third is connected externally only with the 
marginal plates. All three are perfectly distinct from the sub- 
jacent vertebrae. , 

The sides of the carapace are completed, between the 
nuchal and pygal plates, by eleven marginal plates (Fig. 6.3, 
M) on each side. Eight of these receive the ends of the ribs 
of the second to the ninth dorsal vertebrae, in the way already 
described. 

There is no doubt that the nuchal, the pygal, and the mar- 
ginal plates of the carapace are membrane-bones, developed 
in the integument, quite independently of either the vertebrae 
or the ribs. But it appears that the neural plates and the 
costal plates exist, as expansions of the cartilages of the Tieu- 
ral spines and ribs of the primitive vertebrae, before ossifica- 
tion 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 rela- 
tion 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, be- 
hind, the umbilicus of the foetus. The latter, at least, there- 
fore belong to the abdomen, and the plastron is a thoracico- 
abdominal structure. 

In the turtle the plastron consists of nine pieces — one me- 
dian 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 {ourth, xiphiplastron* The entoplastro7i 

* Believing the pliistron to nnswer to tlie sternum of other Verteiraia^ 
anatomists have termed these elements of the plastron eniodernvm^ epiiifT' 
num, hyosiernum^ hypostern-um^ iiud xiphibhrn-um. 



THE PLASTRON OF THE CHELONIA . 



175 



and the two ^iplasira correspond with the median and lateral 
thoracic plates of the Labyrinthodont A/mphibia, and very 
probably answer to the interclavicle and clavicles of other 
Vertebrata. 




Fig. 64 — The plastron of the Green Turtle {Chflaw miiUzs): Ld^ intercIaTide ; cZ, da^- 
cies; ^.p^ hyoplastzon ; ^.j)., hypophstron ; J^., xiphiplastzon. 

The sacrum consists of two vertebrae. The expanded 
sacral ribs are not anchylosed with the centra and arches of 
their vertebrae. 

The tail is flexible, and consists of procoeloua vertebras. 







fte. 65. — ^External view of a section of the anditoryrc^Q of the skuH in aTnrlle (<7AcZ(wm 
mida«)'. f. o-. fenestra ovaliB:/. r., fbn^tra rotonda; esa, asc, psc^ external, anterioi^ 
ind jmBterifH* semicircuUu: capaU. 



£76 



THE ANATOMY OF ■VERTEBRATED ANIMALS. 



The anterior caudal vertebrse have no transverse processes, 
but possess ribs which may not become anchylosed 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 Ghelonia all the bones, except the 
mandible and the hyoidean arch, are immovably united to- 
gether. 

In the occipital segment of the adult, the supra-occipital 
is united with the epiotic, but the ex-occipital usually remains 
perfectly distinct from the opisthotic. The basisphenoid is 
large and distinct. The alisphenoidal region remains unossi- 
fied ; but the large parietals send down a prolongation on 
each side, which plays the part of an alisphenoid. Neither 
the presphenoid nor the orbitosphenoids are represented by 




Tia. 66. — Lonffitudinal sections of the skull of the Turtle. The upper fig:ure represents the 
entire skull witli the outline of tlie brain in ftiiit ; the lower gives a tarffer view of the 
iimer face of the bones of the p-^torior moiety of the skull. 



THE CHELONUN K.ULL, 



177 



Pmse 



bone, but there are large frontals. In the peri otic capsule the 
large proOtic and the opisthotic (Cuvier's occipitale externe) 
remain distinct bones, but the epiotic unites with the supra- 
occipital. 

The naso-ethmoidal cartilage largely persists ; but it be- 
comes covered above and at the sides by a large bone, which 
meets with its fellow in the middle line, and occupies the po- 
sition of the lachrymal, prefrontal, and nasal. The premaxilla^ 
are small, and usually united together. There is a single 
vomer, produced downward into a median internasal plate, 
which expands below, and joins the palatine plate of the 
palatine bone. 

Above the posterior and upper part of the orbit lies a post- 
frontal, and, behind this, a squamosal is placed at the sides of 
the periotic capsule, and above the large quadrate bone. The 
postfrontal and spuamosal occupy the 
upper part of the temporal region of 
the skull. Below these, a quadrato- 
jugal and a jugal connect the quad- 
rate bone with the large maxilla. 

In some genera, as Chelone and 
Chelydra, the skull possesses a sort 
of false roof, formed by the expan- 
sion of a median ridge, developed 
from the parietal bones, into a broad 
plate, which becomes suturally united 
with the postfrontals 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 Plesiosauria and Croco- 
dilia. They unite only with the up- 
per part of the quadrate bone, as in 
the latter reptiles. 

The palatines are firmly united Ko- 67.— The left half of the nn 

..1 .. ^ . ■ 1 1 1 • J 1 •i_-\ derside of the skull of a Turtle; 

With the pterygoids, behind, and with m\ posterior nares. 
the vomer above and in front. They 

are prolonged downward, and develop a short palatine plate, 
which unites with the produced and expanded lower edge of 
the vomer, to bound the posterior nares. (Fig. 67, Fb, i^T'.) 




BS 



so 



178 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 coimection 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 b 3 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 skele- 
ton, the anomaly does not really exist on the ventral side. 
And, as to the dorsal side, the pectoral and pelvic arches of 
the fcetal 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 re- 
mains distinct. The free ends of the coracoid and precoracoid 
are usually connected together by a fibro-cartilaginous 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 tfrodela — 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 
are very large) and the ischia meet respectively in a long 
symphj'sis ; 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 Ghelys, Ghelodina, and some other 
genera, the ilia unite by synchondrosis, or anchylosis, with the 
last costal plate, and the pubis and ischium with the xiphister- 
nal 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 interme- 
dium, and of •a.Jibulare or calcaneum. In Chelyclra there is a 



THE DIVISIONS OF THE CUELONIA. 179 

centrale. In CJielone, J^inys, Testudo, and Trionyx the centraU 
is united with the astragalus ; and in Emys, the calcaneum 
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 Ghelonia are divisible into the Testudinea, the Mmy- 
dea, 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 de- 
veloped. 

The Land Tortoises belong to this division. The carapace 
is usually very convex, and sometimes (as in the genus Pyxis) 
the anterior part of the plastron is movable, and can be shut 
up like a lid. In Ginyxis, the hinder part of the carapace is 
similarlj' mobile. 

3. 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 homy plates of the carapace 
and plastron are well developed. 

These are the River and Marsh Tortoises. They are further 
divisible into two groups, in the one of which, the Terrapenes, 
the pelvis is free, the neck bends in a vertical plane, and the 
head, is almost completely hidden by the carapace when re- 
tracted (Emys, Gistudo, Ghelydra). In Gistudo,Ginostenum, 
and Staurotypus, the hinder part of the plastron is mobile. 
In the other division, the Ghelodines, the pelvis is fixed to the 
carapace and plastron, the neck bends sideways, and the 
head cannot be completely retracted under the carapace 
(Chelys, Ghdodina.) 

3. In the Trionychoidea (Mud or Soft Tortoises), the jaws 
have an external cutaneous lip ; the nasal organ is prolonged 
into a kind of snout, and the head is covered by a soft skin 
without any visible tympanic membrane. The limbs are flat- 
tened, somewhat fiulike, and pentadactyle ; but only three 
digits have nails. The integument develops no horny plates, 



180 THE ANATOMY OF VERTEBRATED ANIMALS, 

but is quite soft. Tlie costal plates are shorter than in other 
Chelonia, and the marginal ossicles are either rudimentary or 
absent. 

The genera Gymnopus, Cryptopus, and Cydoderma, con- 
stitute this division ; the}- 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 immovably 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, intermediate 
between the Euereta and the Trionychoidea, but present no 
approximation to any other order of Reptilia. 

II. The Plesiosaueia. — In some of the Plesiosauria, the 
head, not more than one-twelfth or one-thirteenth of the length 
of the bodv, is mounted upon a neck as long, in 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 comparatively short tail. The 
integument was certainly devoid of any scutes ; and was, prob- 
ablj', smooth and possessed no scales. 

The cervical vertebrae maj' 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 connection 
existed it cannot now be traced, it becomes difficult to dis- 
tinguish between cervical and dorsal vertebrse, and one is 
obliged to have recourse to some method of separating the 
two, diifering from that already adopted. Now, in these 
animals, the neurooentral suture persists for a considerable 
period, if not throughout life ; and the surfaces for the articu- 
lation of the cervical ribs, which are at first altogether below 
the neurocentral sutures, gradually 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 
witl , some facts to be mentioned by-and-by in the structure of 
the Crocodilia, to take the last of the vertebrae in which the 



THE PLESIOSAURIA. 181 

costjtl articular surface is cut by the neurocentral suture, as 
the last of the cervical series. 

The two anterior cervical vertebrae, as thus defined, con- 
stitute the atlas and axis, and are frequently anchylosed to- 
gether. The centre of the other cervical vertebrae have slightly 
concave anterior and posterior surfaces ; well-developed neural 
arches ; anterior and posterior oblique processes, or zyga« 
pophyses, of the ordinary character ; and stout, but somewhat 
short, spinous processes. The centrum presents, upon each 
side, an oval rugose pit, sometimes more or less divided 
iiito 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 corresponding facets, but is 
otherwise undivided. The rib is continued backward into a 
short and straight body, and the angle, or the part at which 
the neck and the body of the rib join, is produced forward, so 
that the cervical ribs of the JPlesiosauria 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 outward, as 
transverse processes, developed from the arches of the verte- 
bras. (Fig. 68, C.) 

In the anterior dorsal vertebrae, these transverse processes 
rapidly acquire their full length ; and they are continued un- 
der this form, descending somewhat lower upon the arches of 
the vertebrae toward the sacrum, to the end of the dorsal re- 
gion. The neural spines acquire greater length, the zyga- 
pophyses are well developed, and the articular surfaces of the 
centra retain the form which they possessed in the cervical 
region. There are usually between twenty and twenty-five 
dorsal vertebrse. The sacral vertebrae are two, and resemble 
the others, except that the sacral ribs are large and broad for 
the attachment of the ilium. The caudal vertebra, usually 
between thirty and forty in number, becqme, 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 spines and ar- 
ticular processes, with ribs which become anchylosed to the 
bodies of the vertebrEe, only late in life. Well-developed 
chevron-bones are attached between the ventral margins of 
successive centra of the caudal vertebrae. 

As has been mentioned, there appear to be no sternal ribs, 



182 THE ANATOMY OF VERTEBRATED ANIMALS. 




-SB 




Fro. 68. — Diagram showing: the structure of the most important parts of tlie skeleton of 
Ple-iiosaurvs. — A, the skull: J\^a, nasal aperture. — B, the left fore-limb : 77, humerus; 
U, ulua: B. radius; r. i. u., radiale, intermedium, and ulnare, in the proximal row of 
carpal bones; 1, 2, 8, distal carpal bones; iJ/c, raeticarpus; P/t, phalanges. — C, a dors^ 
verlebra vnih ribs (Ii.\ and ventral ossifications v V.o). — D, the left hind-limb : ^, femur; 
T, tibia; F. fibula; t. i.f., tibiale, intermedium, and fibulare, in tlie proximal row of tar- 
sal bones ; 1, 2, 8, distal tarsal bones ; Mt, metatarsus ; PA, phal. nges. — E, the pectoral 
arch; •^■r, scapula; Co, coracoid; a, clavicles and interclavicle (?).— F, the pelvic arcli; 
/'&, pubis ; A ilium ; js, ischium. 



but there is a well-developed system of ossifications of the 
wall of the abdomen, arranged in transverse rows from before 
backward ; each row consists of a median bone, slightly bent 
upon itself, thick in the middle, and thin at each end — and of 
six other bones, three on each side, which are elongated and 



THE PLESIOSAURIA. 183 

pointed at each end, and so disposed that their pointed ends 
overlap one another. (Fig. 68, C.) 

In some JPlesiosauria, 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 skull is 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 fossse, being wide. The occipital con- 
dyle 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 parietals 
send off comparatively short processes backward, which be- 
come connected with the large squamosals. The latter unite 
with the postfrontals, which separate the orbits from the tem- 
poral fossa, and the orbit is completed behind by the junction 
of the postfrontal with the jugal. The jugal bone is continued 
backward 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 circumstance in which the skull of Plesiosaurus 
diifers from that of most Iteptilia 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 outward and backward to 
the quadrate bone. On each side of the middle line of this 
region of the skull, is seen an ovoidal fossa or depression. 
The pterygoids are continued forward, and are united exter- 
nally with transverse bones, and more anteriorly with flattened 
palatine bones. When the fore-part of the under-surface of the 
skull is exposed, two other fossae are visible, one on each side 
of the middle line, bounded behind by the palatine bones, and 
separated by what appear to be the vomers. I conceive that 
these are the true posterior nares, and that the posterior aper- 
tures are simply spaces left between the pterygoid bones and 
the basis cranii. 

At the sides of the base of the skuU, specimens of Plesio- 
saurus occasionally exhibit two styliform bones, which lie 
parallel with the axis of the skull ; these may be parts of the 



184 THE ANATOMY OF VERTEBRATED ANIMALS. 

hyoidean apparatus. No trace of anj' sclerotic ring has been 
found. 

The teetli of the Plesiosauria are sharp-pointed, curved, 
and the outer surfaces of their crowns striated. Each tooth 
is lodged in a distinct alveolus, with which, as in the Groco- 
diUa, it does not become anchylosed. 

The pectoral arch (Fig. 68J E) is one of the most remark- 
able parts of the organization of the Plesiosauria. It consists, 
in the first place, of two very large coracoids, the long axes 
of which are parallel with one another, while their inner 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 circumstance which 
results from the manner in which the coracoids are received 
into grooves in the anterolateral edges of the rhomboidal part 
of the sternum. Hence it would appear that the Plesiosauria, 
like the Ghelonia, did not possess any thing corresponding to 
thia 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 scapulce are unlike the corresponding organs in any 
other reptile. The glenoidal end, stout and strong, is con 
tinued horizontally forward and inward, as a bony prism, with 
a somevvhat concave inner edge, and flat inferior surface. The 
outer surface, rising 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 bone which bears this surface is 
produced upward and backward, 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 pregleuoidal process of the scapula, which extends 
forward and inward as a free bony bar in many Lacertilia — 
for example. Iguana. 

In well-preserved specimens, a broad hoop of substance 
(Fig. 68, E, 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 backward in the middle line, to the junction of the 
two coracoids. This corresponds very nearly in form and 
position to the epicoracoidal ossifications of the Lacertilia, 
combined with the clavicles and interclavicles; but I have 
never been able to detect any distinct clavicular, or intercla- 



THE PLESIOSAURIA. 185 

viciilar, elements in any Plesiosaurus, though they appear to 
have been well developed in Noihosaurus. 

The humerus is a stout bone — prismatic, and with a rounded 
head at its proximal end, flatten^ and broad distaUy. (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, being convex posteriorly, 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, com- 
posed 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 correspond- 
ence with the size of the hind-limb, which is usually longer 
than the fore-limb. (Fig. 68, F and D.) The ilium is a 
vertically elongated bone, narrower below than above, where 
it becomes connected with the sacral ribs. Inferiorly, 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 feriiur 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 fofe-Umb, as to need no special 
description. 

There can be little doubt that all the bones of the limbs 
were, like those of the Getacea, 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 confined 
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-Triassio, in age. 

The Post-Triassic group contains the genera Plesiosaurus 
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 

* It may be a question whether the fourth distal hone in the carpus and 
tarsus (Fig. 68, B and D) belongs to carpus and tarsus, or to metacarpus and 
metatarsus ; or whether it is formed by the confluence of elements belonging 
to both recions. 



186 THE ANATOMY OF VERTEBRATED ANIMALS. 

of the vertebrae. In tlie species which have beeu named 
Pliosaurus, the vertebrae are wide in proportion to their 
length, and deeply excavated in front and behind. Pliosaurus 
attained gigantic dimensions, paddles of some individuals 
reaching a length of not less than six feet. 

The Triassic genera, Nothoaaunis, Simosaurus, Pisto 
saurus (for a knowledge of the organization of which we are 
chiefly indebted to the labors of Hermann von Meyer), appear 
to have differed from Plesiosaurus principally in the following 
respects : 

The connection of the neural arches with the centra of the 
vertebr» seems to have been looser. The supra-temporal 
fossse 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 Plesiosaurus, but apparently lacks the poste- 
rior fossffi ; while there is no doubt whatsoever that the true 
posterior nares are situated far forward, in the position as- 
signed to them in Plesiosaurus. 

The pectoral arch of Noihosaurus, again, presents a very 
interesting deviation from the Plesiosaurian type. The cora- 
coids, 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 scapulae have a horizontal 
prolongation, not quite so long as in Plesiosaurus, with an up- 
standing proper scapular part of corresponding 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, consisting 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 con- 
stituents of this bony bar correspond with the interclavicles 
and clavicles of Lacertilia and Ichthyosauria. 

in. The Lacbettlia. — Some few Lacertilia, like the Cha- 
mseleons and the Ampliisbmiim, are covered by a soft integu- 
ment; but, in the majority, there is an epidermic exoskeleton 
composed of homy plates, tubercles, or spines, or overlapping 
scales. In some forms (e. g., Scincus, Cyclodus) the dermi 
beneath the horny scales is ossified, and the body has a com- 
plete armor 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 numbei 



THE LACERTILIA. 187 

of vertebrse ; and, except in the AmphisbmncB and some few 
other Lizards, the tail is long. Those Lizards which possess 
hind-limbs have a sacrum, into which not more than three 
vertebrae, and rarely more than two, enter. The presacral 
vertebrae 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 vertebrae are devoid of ribs, they 
become lumbar. Not more than nine vertebrae 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 cylindroidal. 
A separate ossification is sometimes formed on the under-sur- 
face of the spinal column at the junction of each pair of ver- 
tebrae. Such a separate ossification, or sub-vertebral wedge- 
bone, is commonly developed beneath and between the odon- 
toid bone and the body of the second vertebra. 

The centra of the vertebra are either proooelous, or amphi- 
coelous ; the former being by far the more common condition 
in existing Lacertilia, all of which, except the Geckos and 
Sphenodon, have procoelous vertebrae. The cups and balls 
are usually ellipsoidal, the long axis of the ellipsoid being 
transverse. In the G-eokos, the centra of the vertebrae 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 vertebrse of existing Lacertilia are not anchy- 
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 vertebrae, and 
not in the intervals between adjacent vertebrae. In many 
Lacertilia [Lacertm, Iguanm, Geckos) the caudal vertebrae 
have a very singular structure, the middle of each being trav- 
ersed 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 the tail, that 



188 THE ANATOMY OF VERTEBRATED ANIMALS 

appendage is pretty certain to part at one of these weuk 
points. 

The arches of the vertebrse of the Lacertilia are articulated 
together by the ordinary oblique processes, or zygapophyses. 
In the Iguance. 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 {zygantrum). 
These LacertUian vertebrae thus nearly approach the vertebias 
of the Ophidia. 

The transverse processes of the vertebrae are very short, 
and are, at most, divided into two indistinct facets, with which 
corresponding facets on the proximal ends of the ribs articu- 
late. 

Ribs may be developed in all the cervical vertebrae except 
the atlas, and they usually increase iu length toward the dor- 
sal region, where more or fewer of them become connected 
with the sternum. The dorsal moiety of the primitive carti- 
lage of the rib becomes ossified, and the primitive cartilage- 
bone is finally replaced by membrane-bone. The ventjal moi- 
ety 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 ster- 
num, when fully formed, consists of a rhomboidal anterior por- 
tion, from the posterior angle of which a single, or double, 
backward prolongation is continued into the wall of the abdo- 
men. 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 com- 
plete hoops across the wall of the abdomen (Geckos, Chamag- 
leons, Scincoids). 

The Flying Lizard (Draco volans) is remarkable for the 
elongation of many of its posterior ribs, which are continued 
into, and support, the parachute-like expression of the integu- 
ment by which it is enabled to perform its flights. 

The skull of the jLacertilia resembles that of the Chelonia 
in the development of an interorbital septum (except in the 
AmpMsboBnce), and in the absence of alisphenoids, or of any 
complete ossification of the presphenoidal or orbito-sphenoidal 
regions. The premaxillae and maxillas 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 



THE LACEETILIA. 



189 



roof of the skull in the course of the sagittal suture, or between 
tJie parietals and the frontals. 




Fig. 69. — The skull of Oi/elodus, entire and longitudiQally bisected. 



In the principal group of the Iiacertilia, a column-like 
membrane-bone, called the columella (but which is not to be, 
by any means, confounded with the stapes, to which the same 
name is qfteu applied in Reptiles), extends from the parietal 
to the pterygoid on each side, in close contact with the mem- 
branous or cartilaginous wall of the skull. Hence they have 
been called '•'■ Kionocrania" or " column skulls." This coliir 
mella (Fig. 69, Co) appears to correspond with a small inde- 
pendent ossification, which is connected with the descending 
process of the parietal and with the pterygoid, in some Che 
Ionia. 

In the great majority of the Lacertilia (as in the Chelonia), 
the side-walls of the skuU, in the region of the ear, are pro- 
duced into two broad and long parotic processes, into the com- 
position of which the opisthotic, ex-occipital, and prootic 
bones enter. Each quadrate bone is articulated with the outer 



190 THE ANATOMY OF VERTEBUATED ANIMALS. 

end ot" one of these processes (in which a small separate ^tero- 
tia ossification sometimes appears), and is usually movable. 
The parietal bones do not unite suturally with the occipital 
segment of the skull, or with the prootic bones, but are con- 
nected with them only by fibrous tissue. And as the presphe^ 
noidal region remains unossified, or incompletely ossified, it 
follows that the fronto-parietal portion of the skull is, in most 
Lizards, slightl}' movable upon the oocipito-sphenoidal part. 

Each parietal bone is prolonged backward into a process 
which articulates with the upper part of the parotic prolonga- 
tion of the skull ; and to the outer side of the posterior ex- 
tremity 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 
Spheiiodon, among recant 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 presents 
a number of distinct fossae in the dry state. A supra-temporal 
fossa lies between the parietal, the post-frontal, and the squa- 
mosal, on the upper face of the skull ; a post-temporal, between 
the parietal, the occipital, and the parotic apophysis on the 
posterior face ; a lateral-temporal, between the squamosal and 
post-frontal above, the jugal and quadrate 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 ptery- 
goid. The posterior ends of the pterygoids are usually con- 
nected 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,'transverse 
bone (Fig. 70, Tr) usually passes, to unite the palatine and 
pterygoid with the maxilla. 

The anterior ends of the palatines unite with the maxillae 
and the vomers ; but, in existing LaceHilia, they do not meet 
one another, or come into contact with the basisphenoid or 
presphenoid in the middle line. The palatine apertures 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 tow 



THE LACERTILIA. 



101 



PmiB 



ard one another in the middle line, and so form a posterioi 
nasal passage, partially separated from the oral cavity. 

The two rami of the lower jaw are 
usually, though not invariably, firmly con- 
nected 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" tongue ; 
and, usually, of two long cornua on each 
side of this. The cephalic ends of the an- 
terior comua may be perfectly 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 devel- 
oped ; or only one pair (either the ante- 
rior or the posterior) may be present ; 
or they may be entirely absent. When 
present, they may be mere styliform rudi- 
ments, or may possess any number of 'bo\ 
digits from two to five. Even when the 
limbs are altogether ^.bsent, the pectoral 
arch remains, though the pelvic arch kg. to. 
seems to vanish. When the pectoral arch 
is complete, it consists of a suprascapula, 
scapula, coracoid (with precoracoid and epicoracoid elements), 
and two clavicles, united by an interclavicle, which lies in a 
groove of the sternum. (Figs. 12 and 13, pp. 35 and 36.) 

The coracoids articulate with grooves in the anterolateral 
edges of the sternum, and usually more or less cross and over- 
lap one another, in front. 

In the genus JAalis, 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 no ribs, nor, though it lies between the 
coracoids, does it articulate with them. Each ooraco-scapulax 
arch is a continuous cartilage, narrow in the middle, but ex- 
panded 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 cora- 




Under-view of th« 
skull of Oydodus: N-, 
posterior nafial aperture. 



192 THE ANATOMY OF VERTEBRATED ANIMALS. 

coid 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 cartilage merely presents scattered 
granular calcification. Along the front edge of each 6oraco- 
scapular arch, and closely connected with its ossified part, is a 
long curved clavicle, entirely composed of membrane-bone, 
and united with its fellow in the ventral median line, by liga- 
mentous fibres. There is no interclavicle. The pectoral arch 
in other snake-like Lizards, such as the Blind-Worm [Angids) 
and the Sheltopusik (J'seudopus), is in much the same con- 
dition as in Lialis. 

When the hind-limbs are well developed, there is a com- 
plete pelvis. The ilia are movably articulated with the fibre- 
cartilages which cover the ends of the sacral ribs. The pubes 
and the ischia meet in median symphyses, and the anterior mar- 
gin of the pubis usually, as in the Chelonia, gives off a strong 
curved process. In many Lacertilia a partially-ossified or car- 
tilaginous rod {os cloacoe) is continued back from the sym- 
physis of the ischia, and supports the front wall of the cloaca. 

In most JLacertilia 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 poUex 
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 
foiirth, the fifth being smaller than the rest, and divergent in 
direction. Two large bones, very closely united, or complete- 
ly fixed together, represent the calcaneum and the astragalus, 
and are articulated, in a manner which allows of very little 
motion, with the tibia and fibula. In 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 calcaneum 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 astragalus 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 perhaps contain a tarsal element, and repre- 
sent not only the fifth metatarsal, but the corresponding distal tarsale. 



THE LACERTILU. 1G3 

The LacertiUa all possess teeth, which may be confined 
to the preraaxilliB, maxillo3, 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 blade-like, with serrated edges 
( L/uana) ; or with broad, crushing, and spheroidal crowns 
( G'jdodus). As a general rule, the teeth become anohylosed 
i<j 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 he 2^lsuro- 
dont ; 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 Laeertilia are divisible into numerous groups, the leading distinctive 
characters of which are exhibited in the following table : 

I. — The pterygoid and quadrate bones united. 
A. A columella and an interorbital septum in the sliull. 
Kionocraiiia (Stannius). 

a. Amphicoelous vertebraj (K. Amphiccdia). 

a. Dentition acrodont or pleurodont. 

1. Ascalaboia. 

2. Rhynrhocephala. 

3. Homceosauria* 

b. Dentition thecodont (?). 

4. Proloro^auria.* 

b. Proocelous vertebrae ( IC. proccdia). 

a. Not more than nine cervical vertebrae. 

a. The nasal bone, single. 

5. Platynoia. 

b. The nasal bones, two. 

1. The integument of the head not 

covered with epidermic plates. 

6. Munota, 

2. The integument of the head covered 

with epidermic plates. 
Y. Laceriina. 

8. Chalddea. 

9. Scincoidea. 

b. More than nine cervical vertebriB. 

10. DoHchosauria.'* 

11. Mosa-iauria, 
a No columella ; no interorbital septum. 

12. Amphisbwnoida. 

II. — The pterygoid and quadrate bones disunited. 

13. Cliamcdeonida, 

* The columella has not been observed in these groups, 
9 



194 THE ANATOMY OF VEETEBRATED ANIMALS. 

1. The Ascalahota. — The Geckos, which constituie this 
group, are Lizards of small size, which inhabit the hotter parts 
of botli the Old and the New Worlds, and have always attract- 
ed attention by their habit of running with exceeding swift- 
ness 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 integu- 
ment 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 vertebrae are amphiccelous. 

Neither the upper nor the lower temporal arcades are ossi- 
fied, the post-frontal being connected with the squamosal, and 
the maxilla with the quadrate, by ligament. 

The jugal is rudimentary, and the squamosal very small. 

There are no eyelids, but the integument 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 Satteria, or 
Rhynchocephalus). The vertebrae are biconcave. Some of 
the ribs have recurrent " uncinate " processes, as in Birds and 
Crocodiles. The sternal and vertebral ribs are connected by 
an articulation, and there is a very peculiar system of abdomi- 
nal ribs. The infra-temporal arcade is completely osseous in 
this, but in no other recent, lizard. The quadrate bone is im- 
movably iixed, not merely by anchylosis with the squamosal, 
quadrato-jugal, and pterygoid, but by the ossification of the 
strong membrane, which, in Lizards in general, extends be- 
tween the quadrate, the pterygoid, and the skull, and bounds 
the front walls of the tympanum. The dentary pieces of the 
mandible are not suturally united. The premaxillEe are not 
anchylosed together, and, as in some other Lizards (e. g., Tlro- 
masth'), liave a beak-like form, the large premaxillary teeth 
becoming completely fused with the bony substance of the 
premaxilliB. 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 longitudinal 
groove which lies between the maxillary and the palatine 
teeth. By mutual attrition, the three series of teeth wear one 



THE rue TOROSAURIA. 195 

another down to the bone in such a waj, 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, Mhynchosaurus and 
Syperodapedon, appear to have been very closely allied to 
Sphenodon. 

3. The Somceosauria. — The remains of Lizards of small 
size, and agreeing in the most important points of their osteol- 
ogy with the ordinary Lacertilia, but having amphiccelous ver- 
tebriB, have been found in the older Mesozoic rocks, from the 
Solenhofen slates to the Trias inclusively. They cannot be 
identified with either the Mhynchocephala, or the Ascalabota, 
and may be provisionally grouped as Somceosauria. The 
genera Somoeosaurus, Saphceosaunts, 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 mod- 
em representatives of this group are known. 

The Thuringian Lizard (^Protorosaurus) 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 moderate 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, vertebrae, 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 
vertebrae. In all these vertebrae 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 vertebrae are very short, antero-posteri- 
orly flattened, plates, and the strong ribs are articulated n ith 
them by undivided heads. The sternum has not been pre- 
served. In the abdominal region of some specimens, numerous 
short and filiform bones appear to represent, and correspond 
with, the abdominal ribs of Plesiosauria and Crocodilia. 

The spinous processes of the caudal vertebras, up to nea/ 



196 THE ANATOMY OF VERTEBRATED ANIMALS. 

the middle of the tail, have the ordinary structure ; but bej'ond 
this point they bifurcate, so that each vertebra seems to have two 
spinous processes, a peculiarity uiiknovcn in other Lacertilia. 

The large chevron-bones are articulated between the bod- 
ies of the caudal vertebrae, as in the Crocodilia, but also as in 
some Lacertilia, such as the Geckos. The skull is preserved 
in one specimen onlj"-, 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 implanted 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 limb 
bears five digits. The manus contains certainly eight, possi- 
bly nine, carpal bones, five of which correspond with the meta- 
carpals. The number of phalanges is exactly the same as in 
most existing Lacertilia (3, 3, 4, 5, 3). In the pes, again, the 
number of the phalanges is characteristically Lacertilian (3, 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 connect- 
ed together than in existing Lacertilia, and there v^ere, 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 ar- 
rangement similar to this is met with only in the Ascalabota. 

5-9. The great majority of existing Lacertilia belong to 
the proooelous I^ionocrania, with not more than nine cervical 
vertebree, 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 Seloderma, 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 fossfe. In the Chalcidea and Scincoidea, 
in which the body sometimes becomes elongated and snake- 
like, and the limbs rudiinentary, the supra- and infra-temporal 
arcades are apt to be ligamentous, and the post-frontals and 
squamosals small. 

10. TJie Dolichosauria. — A very singular Lacertilian found 
in the Chalk, and resembling an eel in form and size, has been 



THE MOSASA0RIA. I97 

described by Prof. Owen under the name of Dolichosanrus. 
It possesses an exceedingly elongated bodj', but is provided 
with limbs and with a distinct sacrum, consisting of two ver- 
tebrae. Its most remarkable peculiarity, however, lies in the 
number of its cervical vertebrae, which were not fewer than 
seveuteen. 

11. The Mosasauria. — The cretaceous rocks of Europe 
and America have yielded another remarkable long-bodied 
marine Lacertilian, which attained a great size. This is the 
genus Mosasaimis, remains of which were first obtained from 
the Chalk near Maostricht. 

Eighty-seven vertebrce 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 vertebrae 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 vertebree are concave in front and 
convex behind ; but the concavities and convexities are less 
marked in the posterior, than in the anterior, vertebrte. Tiie 
atlas and axis are not well preserved in this series of vertebras, 
but the nine following all have inferior spinous processes, 
which become shorter in the posterior vertebrce, and, in the 
last two, are represented only by a pair of low elevations. 
They have short transverse processes, each terminated by a 
simple costal facet. It is probable that these are cervical 
verlebrte. In the dorsal vertebrae, 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, vertebrae. There are no inferior processes. All the 
vertebrae which have been mentioned hitherto have the circum- 
ference of the centrum rounded, and are articulated to one 
another by zygapophj'ses. But a series of eleven, which fol- 
low them, have no zygapophyses, and the centra assume a 
more or less triangular prismatic form. The transverse pro- 
cesses of these are long, thin, and bent a little downward and 
backward. These seem to have been lumbar vertebrae. No 
sacrum has been discovered, but there are numerous caudal 
vertebrae 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 
vertebrae the bodies are cylindrical, the transverse processes 
are obsolete, and the chevron-bones, anchylosed to the under- 
sides of the centra, are long, inclined backward, and overlap 



108 THE ANATOMY OF VERTEBRATED ANIMALS. 

one another. And, in the hindermost caudals, the spinoiib 
proyesses and the chevron-bones disappear. 

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 apei-- 
tures, and the fusion of the nasals into a narrow bone. But 
sharp recurved teeth are anchylosed by their bases, not only 
to the premaxillary, maxillar}', and dentary bones, but also to 
the pter3'goid bones ; and these pterygoid bones are unlike 
those of other Lacertilia, not only in form, but because they 
articulate together in the middle line for a considerable dis- 
tance behind the posterior nasal aperture. 

12. The Amphisbcenoida. — These lizards have completely 
snake-like bodies ; one genus of the group ( Chirotes) has a 
pair 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 arese arranged in transverse rows. The 
tail is exceedingly short, so that the vent is close to the end 
of the body. 

The numerous procoelous vertebrfe have less elliptical 
articular faces than those of the typical XacertUia. There is 
no sacrum, and all the precaudal vertebrae, 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 vertebrae. The vertebrae have no zygantrum nor zygo- 
sphene. Amj^liisbcena has no sternum. Chirotes has a ster- 
num, but it is not united with the ribs. 

The skull, unlike that of JOacertilia in general, develops no 
interorbital sejitum. In this respect, and in the complete 
closure of its anterolateral walls by bone, it resembles the 
Ophidian cranium. There is no columella. Post-frontals are 
absent, and the squamosal is very small. The quadrate bone 
is small, and inclined not only downward, but forward, in a 
manner unknown in other Xacertilia. The two rami of the 
mandible are firmly united by suture. 

In AiirphhJia;na the premaxilla3 bear two rows of teeth, 
one behind the other, and one tooth lies upon the symphysis 
of the premaxillse. 

13. The Chamfeleonida. — The Cliamaeleons are distin- 
guished from the Kionocra.nia not only by the negative 



THE OHAM^LEONIDA. 199 

character of the absence of the columella, which they share 
with the preceding group, but by a number of very important 
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 modi- 
fied feet. The digits are arranged in bundles of two and three, 
the manus having the pollex, the index, and the medius, syn- 
dactylous and turned inward ; while, in the foot, it is the 
hallux and index only which are thus united and turned in- 
ward, the three other toes being similarly connected together 
bj"- integument as far as the ungual phalanges, and directed 
outward. To these characters may be added the remarkable 
tongue, capable of protrusion and retraction with almost light- 
ning rapidity. 

The vertebrae of the Chamseleons are similar in their char- 
acters to those of the proooelous Kionocrania. The sacrum 
is composed of only two vertebrae. Only a few of the anterior 
ribs are united with the sternum. A large number 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 Ghamce- 
leonida depart most completely from the ordinary Lacertilian 
type. The parietal bone is not movable upon the occipital, 
the supra-occipital sending up a median ridge, which unites 
with the base of a corresponding crest or process extending 
backward for a considerable distance from the middle line of 
the parietal bone. The summit of this sagittal crest is joined 
by two curved prolongations of the squamosal, the three 
giving the occipital region of the Ohamaeleon 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 the anterior nasal apertures. These apertures, in fact, 
are situated upon the sides of the fore-part of the skull, and are 
separated from the nasal bones, in part, by a membrane which 
stretches outward from the nasal bones ; and external to this 
by a prolongation forward of the prefrontal bone, which unites 
with the maxilla, and in some specimens of Chamfeleons is 
prolonged forward 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 quadrate 
bone itself is not, as in most other Laoertilia, movable upon 
the sides of the skull, but is firmly anchylosed with the bonea 



200 THE ANATOMY OF VERTEBRA TED ANIMALS. 

which lie adjacent to its upper end. The pterygoid bones 
are produced downward ; and, by a very exceptional peculiar- 
ity, do not articulate with the quadrate bones, but are con- 
nected 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 por- 
tion of the hyoid is represented by a long median cylindrical 
entoglossal bone, and its posterior 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 inter- 
clavicle 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 Chamae- 
leons differ very much from the ordinary Lacertilia. There is 
no OS cloac<e. 

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 constit- 
uents of the digits. Besides these, there is an ossicle repre- 
senting 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 articulating 
with the five proximal bones of the digits. In both manus 
and pes the number of the phalanges, counting from the pre- 
axial to the postaxial side, is 2, 3, 4, 4, 3. 

IV. The Ophidia. — This order of Reptiles has been divided 
as follows : 

A. The palatine bones widely separated, and their long axes longitudi- 

nal ; a transverse bone ; the pterygoids united with the quadrate 
bones. 

a. None of the maxillary teeth grooved or canaliculated. 

1. Aglt/phodontia. 

b. Some of the posterior maxillary teeth grooved. 

2. Opis/hoffli/^ihia. 

t. Grooved anterior maxillary teeth succeeded by solid teeth. 

3. Proierorjlyphia, 

d. Maxillary teeth few, canaliculated, and fanglike. 

4. '%/ri/f>r////phia. 

B. The palatine bones -neet, 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. TijphlopidiB. 



THE OPHIDIA. 



201 



All the Snakes possess a scaly epidermic investment, which 
it. usually shed in one piece, and reproduced at definite inter- 
vals. As a general rule these scales are flat, and overlap one 
another ; but sometimes, as in Acroohordus, they become 
more tubercle-like, and do not overlap. In the Rattlesnakes 
( Grotalus) the body is terminated by several loosely-conjoined 
rings of liorny 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 vertebrje 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 precaudal re- 
gions, as there is no sacrum, nor any distinction between cer- 
vical, dorsal, and lumbar vertebrae. The atlas and the odon- 
toid 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 




tv3. 71. — Anterior and posterior views of the dorsal vertebra of a Python : s. «., zygosphenaj 
e. a., zygantrum; p. s., prezzgapophysea ; pt. e.^ postgygapophyses ; t,p,^ bransvense 
jtroccsses. 

the arch above the neural canal is produced into a strong 
wedge-shaped zygosphene, which fits into a corresponding 
zygantrum of the next preceding vertebra ; and, on the pos- 
terior surface of the arch, there is a zygantrum for the zygo- 
Ephene of the next preceding vertebra. (Fig. 71.) 



202 THE ANATOMY OF VHRTEBUATED ANIMALS. 

The transverse processes :ini short and tuborrle-like, and 
the heads of tlio ribs which articulate with them are simple. 
Each rib usually <j;ivos olf a short upward process at a little 
distance from its lii>ad ; it is curved, usually hollow, and ter- 
minates, inferiorly, in a cartili\nc which is always free, no 
trace of a sternum (wistinn;. Strong descending processes are 
given off from the undersides of many of the presacral verte- 
br:B. In the caudal region, elongated transveree processes 
take the place of the ribs. Chevron-bones, like those of the 
Ld.certUla, do not exist, but the caudal vertebrae possess bifur- 
cated 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 sep- 
tum, are wanting; the floor of the cranium being nearly flat, 
and the vertical height of its cavity diminishing gradually 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 cav- 
ity are as well ossified as those of its posterior moiety, and the 
bones which constitute the brain-case are firmly united to- 
gether. 

3. On the other hand, the nasal segment is less complete- 
ly ossified, and may be movable. The prcmaxilliB are usually 
represented by a single small bone, which very rarely bears 
teeth. It is connected with the maxilla? only by fibrous tissue. 

4. The palatine bones never unite directly with the vomer, 
or with the base of {\\o skull, but they an; usually eonncct.ed 
with the maxilho by transverse bones; and, by the pterygoids, 
wJtb the mobile (jiiadiate bones. Hence the connection of the 
palatd-maxillary apparatus with the other bones of the skull ia 
always less close in Ophidia than in Lacertilia, and some- 
times 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. 

G. The hyoidean apparatus is very rudimentary, consisting 
only of a pair of cartilaginous filaments, which are united to- 
gether in front, and lie parallel with one another beneath the 
trachea. They have no connection with the skull. 

These are the most apparent differences between the 



THE OPniDIA, 



203 



Ophidian and the Lacertilian skull. But there are others, of 
a less obvious but more remarkable character, bj which the 
skulls of the Ophidian depart not only from that of the Liz- 
ard, but from that of other Vertebrata. Thus the basi-sphe- 
noid passes in front of the sella turcica, into a great rostrum, 
which extends forward to the ethmoidal region, and probably 
results from a parasphenoidal ossification. Li many adult 




ftll3C 



fiG. 72.-— The skull of a Python, viewed from the left side, and in longitudinal section; Oji» 
stapes ; 7Z, turbinal bone. 



Ophidia two cartilaginous rods he in grooves on the upper 
face of this rostrum, and pass behind into the basisphenoid, 
while in front they are continued into the cartilaginous ethmoi- 
dal septum. These rods are the trabeculcB cranii of the foetus, 
which do not become united in Snakes, as they do in all the 
other abranchiate l^crtebrata. The roof and side-walls of the 
Ophidian skull are completed in front of the occipital segment, 
by two pairs of bones, which appear to be parietals and front- 
als. The " frontal " bones not only completely wall in the 
sides of the frontal region, but extend inward below, and meet 
in the middle line, above the basisphenoidal rostrum and the 
persistent trabeculse. The " parietals " unite suturally with 
the basisphenoid. These relations are not usual in true front- 
als or parietals (though the latter unite with the basisphenoid 
in C/icloiiia, and the frontals unite in the middle line of the 
floor of the skull in some Mammals) ; and as there are only 



204 THE ANATOMY OF VERTEBRATED ANIMALS. 

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 represent orbitosphenoids + frontals, and 
alisphenoids + parietals ; or whether they represent over- 
grown frontals and parietals only ; or whether, lastly, they are 
tlie result of an excessive development of the orbitosphenoids 
and alisphenoids, true frontals and parietals being absent. 
According to Rathke's elaborate investigation into the de^•el- 
opinent of the skull in Coluber natrix, the two bones on each 
side are formed from single centres of ossification, which ap- 
pear in patches of " cartilage," which are situated, at first, in 
the superolateral regions of the skull, in the place normally 
occupied by orbitosphenoids and ahsphenoids, and that these 
grow up and meet in the middle line. In this case the bones 
in question are orbitosphenoids 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 reexamined. 

The Ophidia usually possess well-developed post-frontals, 
and they have large membrane-bones in front of the orbit, 
which lie upon the cartilaginous nasal chambers, and are or- 
dinarily regarded as lachrymals. Large nasals lie upon the 
upper surface of the nasal capsule between the lachrymals ; 
and, forming the floor of the front part of the nasal chamber, 
on each side, is a large concavo-convex bone {Tl, Fig. 72), 
which extends from the ethmoidal septum to the maxilla, pro- 
tects the nasal gland, and is commonly termed a turbinal, 
though, if it be a memljrane-bone, it does not truly correspond 
with the turbinals of the higher Vertebrata. The squamosals 
are usually well developed. There is no jugal, or quadrato- 
jugal. 

Though the general conformation of the skull in the Opihid- 
ia is that which has now been described, it presents remark- 
able modifications in diiferent 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. Each is con- 
nected by a transverse bone with the maxilla, which Hes at the 
side of the oral cavity ; and the pterygoids diverge posteriorly 
toward the quadrate bones, with which they are connected by 
ligaments. 



THE OPHIDIA. 



205 



Fmx 



But, in the remarkable group of the Ty2)hlopid(B, the slen- 
der palatine bones meet upon the base of the skull in the mid- 
dle line, and are directed transversely, in such a manner as 
to bound the posterior nasal apertures behind, as in the Satra- 
chia. There is no transverse bone. The pterygoids lie par- 
allel with one another under the base of the skull, and are not 
eonueoted with the quadrate bones. The maxillse are short 
plates of bone which are connected with the outer extremities 
of the palatine bones, and are directed obliquely toward the 
middle line of the oral cavity, into which their rfree 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 (Jrotalus [Solenoglyphia). 

Thus, Python (Figs. 73 and 73) has well-marked premaxillsB, 
large maxillary bones, palatine bones 
which are firmly united with the ptery- 
goids, and transverse bones which bind 
the noiaxillaries and palato-pterygoid 
bars into one solid framework. 

The maxillaries give attachment to 
a long series of recurved teeth, which ^° 
are not very unequal in size. And Py- 
thon (like Tortrix, but unlike all other 
Ophidia) possesses teeth in the premax- 
ill». 

The squamosal bones are very long, 
and adhere to the skull, upon which 
they are slightly movable, 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, ggl 
The rami of the mandible are loosely 
connected by an elastic symphysial liga- 
ment. Thus, not only can these rami 
be widely separated from one another, 
but the squamosal and quadrate bones 
constitute a kind of jointed levfer, the 
straightening of which permits of the 
separation of the mandibles from the 




Fig. 78. — Under-7iew of ti * 
left half of the sknll and 4- 
clal bones oi Python. 



206 



THE ANATOMY OF VERTEBRATED ANIMALS. 



base of the skull. And all these arrangements, taken together, 
allow of that immense distention of the throat which is requi- 
site for the passage of the large and undivided prey of the 
serpent. 

In Tortrioi, this mechanism does not exist, the short quad- 
rate bone being directly articulated with the skull, while the 
squamosal, like the post-frontal, is rudimentary. The maxillar3' 
bones are also almost fixed to the skull. 

In the Rattlesnakes ( Crotalus, Fig. 74), the premaxillae 
ai'e very small and toothless. The maxillary bone has no 
longer the form of an elongated bar, but is short, subcylindri- 
cal, and hollow ; its cavity lodges the fossa formed by the in- 
tegument in front of the eye, which is so conspicuous in these, 
and sundry other, poisonous Snakes. The upper and inner 
part of the maxilla articulates with a pulley-like surface fur- 
nished to it by the lachrymal, so that the maxilla plays freely 
backward and forward 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 
hinge-like joint with the anterior end of the transverse bone, 
which has the form of an extremely elongated and flattened 
bar connected posteriorly with the pterygoid. 



JVa J^a. 




T u. 74.— A, the skull of Crotalus, vlewert from the left side; B, a trfflisrerse seetlon takra 
9t the pomt. B, in Fi^. A, showing 7; the persistent cartilagiDous ti-aheculffi. The max- 
illa is supposed to be transparent, and the anterior half of the palatine bone is seen 
through it. 



THE OPHIDIA. 207 

The latter is long and stout, and, as usual, is united, be- 
nind, with the distal end of the quadrate bone. In front of, 
and internal to, its union with the transverse it is prolonged 
forward, and becomes united, by a movable joint, with the 
short palatine bone, which is flattened from side to side, 
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 downward and backward. 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 channelled poison- 
fangs are attached, to look backward. 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, pull- 
ing up the angle of the mandible, at the same time thrusts 
the distal end of the quadrate bone forward. 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 lachry- 
mal joint, the hinder edge of the maxillary being thrust down- 
ward and forward. In virtue of this rotation of the maxillary, 
through about a quarter of a circle, the dentigerous Tace of the 
maxilla looks downward, and even a little forward, instead of 
backward, 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 poisou- 
gland, the poison is injected into the wound through the canal 
of the fang; and, this being withdrawn, the mouth is shut, all 
the previous movements are reversed, and the parts return to 
their first position. 

No Ophidian possesses any trace of anterior extremities, 
but the TyphlopidcB, the Pythons, Boas, and Tortrices, have 
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 be- 
come anchylosed to the bones hy which they are supported. 



208 THE ANATOMY OF VERTEBRATED ANIMALS. 

They may be developed in the premaxillaries, maxillaries, 
palatuies, pterygoids, and the dentary piece of the mandible, 
but their presence in the premaxillaries is exceptional. In 
JJtopeltis and some other genera, there are no palatine teeth; 
and in the egg-eating African snake, Rachiodon, 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 vertebrae are long, and tipped, at their apices, with a 
dense enamel-like substance. These project through the 
dorsal wall of the oesophagus into its cavity, and the eggs, 
which are swallowed whole, are thus broken in a position in 
which all their contents must necessarily 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, bj"- 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 IcHTHTOSAUEiA.— 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 oif 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 Ichthyosaurus may 
have been provided with a sort of fin-like expansion of the 
integument. This fish-like body was propelled, like that of 
the Hesiosaurus, by four paddles ; but the anterior paddles 
were placed close behind the head, and were, generally, very 
much larger than the posterior ones. 



Pig. 7S.— a restnriitiou oi Jehthyosaunii. The existence of the caudal fin is doubtftll 



THE lOHTHYOSAUKIA. 



209 



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 con- 
nected with the sternum, to the posterior end of the bodj- ; 
and there is no sacrum. The caudal region, however, is dia 




Fig. 76. — Different parts of the skeleton of lehthyosaurit^i intermediuHy drawn to the sama 
scale. A, the skull; B, the fore-limb: JT^ humerus; Ji^ radius; JT^ ulna; ?'. i. u., radi- 
ale, intermedium, ulnare; Cp^ carpalia; 1, 2, 3, 4, 5, digits : m.n «i.«. radial and ulnar 
marfiinal ossicles. — C, a dorsal vei-tebra, with the ribs {R) and ventral ossiiicntiong 
iV.O). — D. the hind-limb: F^ femur; T, tibia; Fb^ fibula; t^ «,/, tibiale. intermedium, 
flbubire ; T». tarsalia ; Mt, metatnrsalia ; P\ phalanges ; m, i&, tibial marginal ossicloa 
— E, the pectoral arch, seen Iron- the ventral siiit ; F, the same aspect of the pehic arch. 



210 THE ANATOMY OF VERTEBRATED ANIMALS. 

tinguished by the chevron-bones which are attached beneath 
its vertebrfB. The vertebrae of Ichthyosauria in general have 
certain characters by which they differ from those of all other 
Vei'tebrata. (Fig. 76, C.) Not only are the centra flattened 
disks, very much broader and higher than they are long, and 
deeply biconcave (circumstances in which they resemble the 
vertebrte of some Labyrinthodonts and Fishes), but the only 
transverse processes they possess are tubercules, developed 
iVom 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 vertebras, by mere 
synriondroses. The neural arches themselves are forked 
bones, with only rudiments of zygayjophyses, 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 eleva- 
tions, or articular surfaces, which are at first situated in the 
upper half of the lateral surface. Toward the posterior half 
of the dorsal region they descend, and, gradually approaching 
one another, coalesce into one in the caudal vertebra;. The 
form of the proximal ends of the ribs corresponds with the 
arrangement of these tubercles ; for, where they are separate, 
the proximal end of the rib 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 also undivided. 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 vertebrae 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 concave face of the centrum of the atlas, serves to com' 
plete the cup for the occipital condyle. 

The skull of Ichthi/osaurus (Fig. 76, A) is remarkable for 
the great elongation and tapering form of the snout, the huge 
orbits, the great supra-temporal fossae, and the closinsr over of 
the infra-temporal fossa; by plates of bone. Again, the two 
rami of tlie mandible are united in a symphysis, which, for 
length, is comparable to that observed in the modern Gaviala 
and in the ancient Teleosauria. The basi-occipital bone fur- 



THE ICHTHYOSAUKIA. 211 

nishes the round articular condyle to the first vertebra, and 
becomes very stout and thick in front. It appears to have 
been anchylosed neither with the basisphenoid 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 basi- 
sphenoid, a deep and stout bone, is produced in front into a 
long and slender parasphenoidal rostrum. There do not ap- 
pear to have been any ossified alisphenoids. The parietals re- 
main separate throughout life ; and, in some species, not 
merely present a great parietal foramen close to the coronal 
suture, but are completely divided by a median fissure. Ossi- 
fied presphenoids and orbitosphenoids appear to have been 
altogether absent, and the frontal bones are relatively small. 
The proStic bones are, as usual, situated in front of the ex-oo- 
cipitals, 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 proC5tic. 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 Ohelonia. 

In the naso-premaxillary segment, the nasal bones, con- 
tinuing the direction of the frontals, attain considerable size, 
but the premaxillffi make up by far the greater part of the 
snout. The maxillsB are reduced, as in birds, to comparatively 
small and slender rod-like 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 premaxUlary bones. 

On each side of the frontal there is a large prefrontal, 
which passes back above to meet the post-frontal, and thus 
bound the orbit. Below, the maxilla is connected with a 
jugal. From the post-frontal to the jugal, the posterior mar- 
gin of the orbit is constituted by a distinct, curved, postorbi- 
tal bone (Fig. 76, A, Pi. O). 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 post- 
orbital, the post-frontal 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 Heptilia. The squamosal bone is 
very large and stout, and forms the postero-external angle of 



212 THE ANATOMY OF VERTEBRATED ANIMALS. 

the skull. From this point it sends a process forward to meet 
the post-frontal, inward to unite with the parietal, and down- 
ward 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 forward. Behind, and separated by an inter- 
val traversed by the rostrum of the basisphenoid bone, the 
very large pterygoids commence, by slender and pointed ends, 
which lie on the inner side of the palatine bones at the level 
of the posterior nares. They then widen, and passing back- 
ward with a slight outward curvature, on each side of the 
sphenoidal rostrum, end in three processes— one which con- 
nects itself with the basisphenoid, another passes outward and 
backward to the quadrate, while the third runs upward to the 
squamosal bone. 

The lower jaw is composed of two rami, which unite, 
anteriorly, in a very long symphysis. Each ramus is com- 
posed of the normal six pieces, the splenial being remarkably 
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 vol Lacer- 
tilia, 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 Plesiosaurus j so that, in this genus also, the rhom- 
boidal part of the sternum appears to have been absent or 
revy small. 

But there is a very distinct T-shaped interclavicle (Z Gl.), 
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 clav- 
icles (CL), the outer extremities of which abut against, and 
are no less closely connected with, the upper part of the an- 
terior edge of each scapula. This arrangement of the clav- 
icles and interclavicle presents interesting conditions intei^ 
mediate between those observed in JVothcsaurus, on the one 
hand, and those coram.on in the JLacertiUa, 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 



THE IGIITHYOSAURIA. 213 

end of the liumerus presents two facets, which articulate with 
a couple of short flattened polygonal bones, which represent 
the radius and the ulna {Ji, V). To these succeed two rows 
of smaller polygonal ossicles in the place of a carpus : three, 
representing the radiale, intermedium, and ulnure (r. i. u.), 
lie in the proximal row, and three or four carpalia {G2).) in 
I he distal row. With the distal carpal bones are connected, 
by means of the metacarpal ossicles (Mc.), longitudinal series 
of very numerous polygonal bones, adapted together by their 
edges, and becoming gradually smaller toward the distal ex- 
tremity 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.ii., in.r.). There 
is thus formed a paddle, which is unlike either that of a Ce- 
tacean, or that of a JPlesiosaurus, or that of a Turtle — depart- 
ing more than any of these structures from the ordinary form 
of vertebrate limb. 

There is no trace of any sternum behind the pectoral arch, 
but the abdominal walls were strengthened by a number of 
transverse arcuated bones, similar to those observed in the 
Plesiosauria, though not so strong. Each 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, F:a) 

The pelvis (Fig. 76, F) is not connected by bone with the 
vertebral column. It consists of an ilium (J'7.), an ischium 
{Is,), and -a pubis {Pb.), uniting together to form an acetabu- 
lum, while the pubis and ischium of each side meet in the mid- 
dle line. The ischium is a narrow and almost rod like bone, the 
pubis is somewhat broader, especiallj- at its symphysial end. 

The hind-limb (Fig. 76, D) has substantially the same 
structure as the fore-limb, but is always smaller, and generally 
of much less size. 

The only other bony structure appertaining to Ichthyosaii- 
nis that need be noticed, is a circle of plates developed in the 
eclerotic of the enormous eye, which is frequently met with in 
a very perfect state of preservation. 

* I leave open the question wliether these series of marginal ossicles ara 
remains of the digits of a poljclactyle manus, such as exists in the Elasmo- 
branch fishes. 



214 THE ANATOMT OF VERTEBRATED ANIMALS. 

It is possible that the Ichthyosauria occur in the Trias" 
tbej 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. inter- 
medius, communis, etc.) ; and such as have longer snouts, long 
paddles, and three carpalia {I. longirostris, tenuirostris, pla- 
tyodo7i). 

VI. The Ceocodilia. — Crocodiles, the highest living -Rep- 
tilia, "are Lacertilian in form, with long tails and four well-de- 
veloped limbs, the anterior pair being the shorter, and pos- 
sessing 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 fore-foot, 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 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 exist- 
ing genera are marine, though many ancient Crocodilia inhab- 
ited the sea. 

The dermal armor is composed of scutes covered by epi- 
dermic scales of corresponding form. When the armor is 
complete — as in Oaiman 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 taU. The scutes of the same row are 
united suturally ; those of each row overlap their successors, 
which present smooth facets to receive their under-surfaces. 
In existing Crocodilia, in the extinct Crocodilus SastingsioB, 
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 it) 



THE CKOCODILIA. 216 

all crocodiles, and those upon the neck sometimes form dis- 
tinct " nuchal " and " cervical " groups, distinct from the dor- 
sal shield. The dorsal scutes do not always overlap, and the 
ventral scutes are absent, or incompletely ossified, in most ex- 
isting Grocodilia. 

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- 
tebrae is twenty-four; that of the sacral, two, in all the recent 
forms, and probably in the extinct genera also. The number 
of the caudal vertebra varies, but is not less than thirty-five. 
The number of the cervical, dorsal, and lumbar vertebrae varies ; 
but there are usually nine of the first, eleven or twelve of the 
second, and four, or three, of the third description. 

lu existing Grocodilia all the vertebra, except the atlas 
and axis, the two sacrals, and the first caudal, are procoelous. 
The majority of the pre-cretaceous Grocodilia have the corre- 
sponding vertebrae amphicoelous, the concavities of the centra 
being very shallow. One genus, Streptospondylus, which is 
perhaps Crocodilian, has the anterior vertebrae opisthocoelous. 
It is characteristic of the Grocodilia, that the centra of the 
vertebrae are united by fibro-cartilages, and that the neurocen- 
tral 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 Ghelonia. A large odontoid 
bone is closely united to, but not anchylosed 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 odontoidum and to the second 
vertebra, by distinct capitular and tubercular processes. The 
other cervical vertebra all possess ribs with distinct and long 
capitula and tubercula — the latter attached above the neuro- 
central suture to the neural arch, the former to the centrum 
below the neurocentral 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 vertebrae 
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 



210 THE AXATOMY OF VERTEBRATED ANIMALS. 

are attached are raised into tubercles ; and, by degrees, these 
become elongated into distinct capitular and tubeicular pro- 
cesses, between which, in the third to the ninth vertebrffi, the 
neurocentral suture passes. But in the tenth and in the elev- 
enth vertebrte, the capitular process, which lies nearer the 
neurocentral suture in the posterior than in the anterior cervi- 
cal vertebrae, rises upon the body of the vertebra to the level 
of the neurocentral suture, by which it is traversed, and tlio 
tubercular process becomes longer than it. (See Fig. 5, p. 19.) 
The terminal cartilage is united with the sternum by a sternal 
rib, -which may become 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 cervical vertebra, while 
the outer end of the process articulates with the tuberculum 
of the rib, and represents the tubercular process. The neuro- 
central suture, in this and the succeeding dorsal vertebrte, 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 distinct centres of ossification.* 

In the succeeding dorsal vertebrae the " step " of the trans- 
verse process gradually moves outward, until at length it be- 
comes confounded with the tubercular facet, and a correspond- 
ing 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 vertebrae have long transverse processes which 
arise from the neural arches, i. e., above the neurocentral su- 
ture. 

The centra of the two sacral vertebrse have their applied 
and firmly-united faces flat, their free faces concave ; conse- 
quently, the first has the anterior face concave and the poste- 
rior flat, while the second has the anterior surface fiat and the 
posterior concave. Each sacral vertebra has a strong rib ex- 
panded at its distal end ; and wedged in at its proximal end, 



ffenous, 

the' dorsal vertebrio of the Grocodilia have no parapophyses. 



THE CROCODILIA. 217 

between rough sutural surfaces furnislied by the neural arch 
above and the centrum below. 

The first caudal vertebra is biconvex, but all tlie others are 
procoelous ; 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 anchylosed in that position. Chevron- 
bones are attached to the posterior edges of the centra of the 
vertebrae, except that of the first, and those of the posterior 
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 GrouodiUa, being sometimes narrow, 
sometimes broad and flattened. An elongated plate of carti- 
lage, 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 cartilagi- 
nous part of the vertebral rib. (Fig. 5, P.u.) 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 con- 
tinued 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-bones, which 
are termed " abdominal ribs ; " though it must be recollected 
that they are quite distinct from true ribs, and rather corre- 
spond with the dermal ossicles of the Labyrintfiodonta. Each 
series is composed of four elongated and more or less curved 
ossicles, pointed at each end, and so disposed that inner ends 
of the inner pair meet at an angle, open backward in the 
middle line, while their outer ends overlap the inner ends of 
the outer pair. The most 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 
and orbitosphenoidal regions remain cartilaginous, or very 
incompletely ossified, 
10 



218 TUE ANATOMY OF VERTEBRATED ANIMALa 




FN 



Fig. 77.— Longitudinal and vertical section of the hinder part of the skuli of a Crocodile; 
£hi^ Eustachian tube : P N^ posterior nares ; P, pituitary fossa. 

2. All the bones of the skull (except the mandible, stapes, 
and hyoid) are firmly united by sutures, which -persist through- 
out life. 

3. There are large parotic processes. Both the upper and 
the lower temporal arcades are completely ossified, and formed 
by post-frontal, squamosal, jugal, and quadrato-jugal bones; 
Bupra-temporal, lateral- temporal, and post-temporal fossae are 
formed, as in the Lacertilia, though their relative sizes are 
\rery diiferent. 

4. The maxillary and the palatine bones develop palatine 
plates, which unite suturally in the middle line, and separate 
the nasal passages from the cavity of the mouth, as in Main- 
malia ; and in aU existing Crocodiles, but not in Teleosavrm 
or Selodon, 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. 



THE CROCODILIA. 219 

6. There are larger alisphenoids, but the orbitosphenoids 
are absent or radimentary. 

7. There is no parietal foramen. 

8. The quadrate bone is very large, and fixed immovably 
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 surface 
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 mandi- 
ble plays. 

10. The tympanic cavity is completel}' bounded by bone. 
The proOtic and opisthotic (which is united with the ex-oc- 
cipital) form its inner walls, the quadrate its outer wall, the 
squamosal and post-frontal its roof, and the quadrate, the basi- 
ocoipital, 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 basioccipital, and divides between those bones into a 
right and left lateral canal. Each lateral canal subdivides 
into an anterior branch, which traverses the basisphenoid, and 
a posterior, which 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 apertures on the 
inner side, while the quadrate bone narrows them on the outer. 

In adult Grocodilia, 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, whence the 
air passes through a membranous tube into the hollow ar- 
ticular piece of the mandible. The hyoidean apparatus is 
greatly simplified, consisting only of a broad plate of cartilage, 
which may become partially ossified, anJof two ossified 
cornua which are not directly conn^r* a with the skull. A 
minute styliform cartilage, which livs in close proximity with 



220 THE ANATOMY OF VERTBBRATED ANIMALS. 

the portio dura, on the upper part of the posterior face of the 
quadrate bone, represents the stylohyal, or proximal end of 
the hyoidean arch. 

The pectoral arch has no clavicle, and the coracoid has no 
distinct epicoraooidal element, nor any fontanelle. The carpus 
consists proximally of two elongated and somewhat hour-glass- 
shaped bones, articulated respectively with the radius and the 
ulna. The radial is the larger, and is partially articulated 
with the ulna. Behind these, and directed transversely, lies 
another curved 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 ulnar proximal carpal and 
the second, third, fourth, and iifth metacarpals, the last three 
of which it supports altogether. On the radial side, a disk 
of cartilage, which never becomes completely ossified, is con- 
nected by ligament with the lenticulare, and is interposed 
between the radial proximal bone and the head of the meta- 
carpal of the poUex. From the ulnar side of the head of this 
bone a cartilaginous ligamentous band proceeds, over the head 
of the secoad 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 ventral symphysis, 
and, with the ilium, forms almost the whole of the acetabulum. 

The pubcs take hardly any share in the formation of the 
latter cavity in the adult. Their axes are directed forward 
and inward, and they coalesce in the middle line ; but as the 
inner, or median, moietj^ 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 verte- 
brate in which ijuoh a process is developed (Fig. 78, C. Ca.). 

Two rounded c>'«tal tarsal bones, of which the fibular is 
much the larger, lie •^.'^ween the calcaneum and the third, 
fourth, and rudimentaiy ti.''t-li, metatarsals. A thin plate of 



THK CROCODILIA. 221 

cartilage is interposed between the distal end of the astragalo- 
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. 

In the Grocodilia the teeth are confined to the premaxillfe, 
maxillae, 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 predeces- 
sor. 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 Grocodilia 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 occur in 
strata of Triassic age, and abound, under forms which differ 
but little from some of those which now exist, in the Mesozoio 
sind Cainozoic formations. 

They may be divided into the following groups : 

A. With procoelous presacral vertebras, 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 
forward. The mandibular symphysis not extending beyond 
the fifth tooth, and the splenial element not entering into it. 
The cervical scutes distinct from the tergal. 

1. AlUgatoridce. 

Alligator. Caiman, Jacare. 

b. The head longer. The teeth unequal. The first mandibular 

tooth biting mto a fossa ; the fourth, into a groove, at the 
Bide of the upper jaw. The premaxillo-maxiUary suture 
straight or convex backward. The mandibular symphysis 
not extending beyond the eighth tooth, and not involvmg 
the splenial elements. The cervical scutes sometimes dis- 
tinct from the tergal, sometimes united with them. 

2. Crocodilida. 

Crocodilus. Mecistops. 



222 THE ANATOMY OF VERTEBRATED ANIMALS. 

b. The nasals are excluded from the external nasal aperture. The head 
very long; the teeth subequal. Both the first and the fourth 
mandibular teeth bite into grooves in the margin of the upper ja«-. 
The premaxillo-maxillary suture acutely angulated backward. The 
mandibular symphysis extends to at least the fourteenth tooth, and 
the splenials enter into it. The cervical and tergal scutes foiTu a 
continuous series. 

3. Oavialidce. 

Rhynchosuchus. Gavialis. 
B. With the- presacral vertebrae amphiccelons (the anterior vertebra! 
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. 7'eleosauridce. 

Tcleosaurus, Go7iiopholis. 

Streptospondylus. Stagonolepis. Galesaurus (?). 

b. With the external nares on the upper part of the base of the snout 

near the orbits. 

6. Belodontid(e. 
Belodon. 

There is a large number of extinct Heptilia which resemble 
the Crocodilla in the characters of their pre-sacral vertebrsB, 
but differ from them, and resemble JLacertilia (Jhelonia, or 
Birds, in other respects. 

These are the Dicynodontia, the Ornithoscelida, and the 
Pterosauria. 

VII. The DiCTisroDONTiA. — Dicynodon and Oudenodon 
are lacertiform animals, sometimes of large size, with crocodil- 
ian vertebrae, four or five of which are anchjlosed 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. Never- 
theless, 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 clav- 
icle. 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 obturator foramen. The limb-bones are lacer- 
tihan in character. 

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. 



THE DICTNODONTIA. 



223 




Fio , 78. — Tlie pelvis and htnd-limb of, A., Drom^us ; B., an omlthoscelid reptile, such af 
Iffitcmodon^ or RypsilopkocLon ; and C, a Crocodile. Ttie'blrd's limb is in its natural 
position, as is tliat of the Omithoscelid, though the metatarsus of the latter may not, in 
nature, hare been so much raised. The Crocodile's limb is purposely represented in an 
unnatural position. In nature, the femur would be turned out nearly at right angles t^ 
the middle rertical plane of the body, and the metatarsus would be horizontal The Tetters 
are the same throughout. 7?, ilium ; /s, ischium ; Pb, pubis ; a, anterior process, b^ 
posterior process, of the ilium ; TV", inner trochanter of the femur ; T^ tibia ; J*, fibula ; 
.4.5, astragalus; Cte, calcaneum. /., /Z, ///, IV.^ the digits. 



Vni, The Oknithoscelida. — The very remarkable extinct 
reptiles which constitute this group, present a large series of 
modifications intermediate in structure between existing Rep 
lilia and At^es. 



224 THE ANATOMY OF VERTEBRATED ANIMALS. 

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 Grocodilia. 

In the bird (Fig. 78, A.), the ilium is greatly prolonged iu 
front of the acetabulum, and the roof of the acetabular cavity 
is a wide arch, the inner wall of that cavity remaining mem- 
branous. The anterior pier of the arch, or pree-acetabular pro- 
cess, extends farther downward than the posterior pier, or 
post-acetabular process. 

But, in all the Omithoscelida, 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 pro- 
cess downward (Fig. 78, B.). 

3. The ischium, in the reptile (Fig. 78, C), is a moderately 
elongated bone, which becomes connected with the pubis in 
the acetabulum, and extends downward, inward, and somewhat 
backward, to unite with its fellow in a median ventral sym-- 
physis. The obturator space is not interrupted by any for- 
ward process of the outer and anterior half of the ischium. 

In all birds (Fig. 78, A.), the ischium is elongated and in- 
clined backward, the backward direction being least marked 
in Apteryx^ and most in Rhea. The ischia never come to- 
gether 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 generally sends off a pro- 
cess which unites with the pubis, thus dividing the obturator 
space. 

In all the Omithoscelida (Fig. 78, B.), in which I have 
been able to identify the bone {Thecodontosaurus, Terato- 
smirus, Megalosaurus, Iguanodon, Stenopelyx, Madrosaurus, 
Ilypsilophodon), the ischium is greatly elongated. In Iguaii' 
odon it has the obturator process characteristic of the same 
bone in Birds ; and I imagine that the same process is seen in 
Gompsognathus. In Sypsilophodon there can be no mistake 
about the matter, and the remarkable slenderness and prolon- 
gation of the ischium give it a wonderfully ornithic character. 



THE ORNITHOSCELIDA. 225 

In Iguanodon the slenderness and prolongation are even car- 
ried beyond what are to be seen in Birds. I am disposed to 
think, however, that, as was certainly the case in Eypsilopho- 
don, the ischia united in a median ventral symphysis in all the 
Ornithoscelida. 

3. In all reptiles the pubis is inclined forward, as well as 
downward, toward 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 Gompsognathus are, unfortunately, obscured 
by the femora. They seem to have been very slender ; and to 
have been directed forward and downward, like those of Liz- 
ards. Some lizards, in fact, have pubes which, if the animal were 
fossilized in the same position as Gompsognathus, would be very 
similar in form and direction. Hypsilophodon, however, affords 
unequivocal evidences of a further step toward the bird. The 
pubes are not only as slender and elongated as in the most 
typical bird, but they are directed downward and backward 
parallel with the ischia, thus leaving only a very narrow and 
elongated obturator foramen, which is divided by the obtura- 
tor process. 

It remains to be seen how far the hypsilophodont modi- 
fication extended among the Ornithoscelida. The remains of 
Gompsognathus and of Stenopelyx tend to show 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 forward, or forward and inward; and the 
other backward, or backward and outward. And when the 
posterior edges of the two condyles of the proximal end of the 
tibia rest on a flat surface which looks forward, the long axis 
of the distal end is either nearly parallel with that surface, or 
is inclined obliquely from in front and without, backward and 
inward. 

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 



226 THE ANATOMY OF VERTEBRATED ANIMALS. 

downward, nor does it send a process upward 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 forward and 
outward 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 
re,st upon a flat surface, the one flat face of the distal end of 
the bone looks outward as well as forward, and the other in- 
ward as well as backward. Further, the long axis of the dis- 
tal end is inclined, at an angle of 45° to the flat surface, from 
within and in front, backward and outward, thus exactly re- 
versing 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 ascending 
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 concave 
proximal, and a convex, pulley-like, distal, surface. A process 
ascends from ils front margin in the groove on the front face 
of the tibia. This process is comparatively short, and perfo- 
rated by two canals for the tibialis anticus and extensor com- 
munis, in the Fowl ; while in the Ostrich and Emeu it is ex- 
tremely long and not so perforated. 

6. The astragalus becomes anchylosed with the tibia 
(though it remains distinct for a long time in the Ostrich and 
Itliea, and in some breeds of fowls). 

In the Ornlthoscelida : 

1. There is a great cnemial crest and a ridge for the fibula. 
3. 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 
pioximal, 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, Megalosaurus^ and 



THE ORMTIIOSCELIDA. 227 

many other genera ; but it seems to have become anchylosed 
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 know^n terrestrial animals. They oc- 
cur throughout the whole range of the Mesozoic formations, 
being represented by Thecodontosaurus, Paloeosaurus, Tera- 
tosaurus, Platmosaurus, and other genera in the Trias ; by 
Seelidosaurus in the Lias ; by Megalosaurus, Poikilopleuron, 
Euskelosaurus, Hylceosaurus, Polacanthus, Acanthopholis, 
Iguanodon, Sadrosaurus, Trachodon, and Laelaps in the 
middle and upper Mesozoic strata. 

There is no evidence that Megalosaurus, or Iguanodon, 
possessed any dermal armor ; but several genera (e. g., Seeli- 
dosaurus, Hylceosaurus, and Acanthopholis) had osseous 
dermal scutes, sometimes produced into prodigious spines. 

The faces of the centra of the vertebriB are slightly am- 
phicoelous, or nearly jSat ; but those of the anterior dorsal and 
cervical regions seem, in some cases, to have been opisthocce- 
lous. The sacrum seems to have consisted of at fewest four 
vertebra, which in some {Seelidosaurus) are crocodOian, in 
others {Megalosaurus) take on a somewhat ornithic character. 
The caudal region had many and long vertebrae, between 
which the chevron-bones are attached. The rami of the chev- 
ron-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 rea- 
son to think that the sternum was broad and expanded. Ab- 
dominal dermal ribs are developed in some species, if not 
in all. 

The structure of the skull seems to have been intermediate, 
in many respects, between the crocodilian and the lacertilian 
types. In Iguanodon and Sypsilophodon, the extremities of 
the premaxillse appear to have been edentulous 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 Megalosaurus, to the broad grinders, wearing 
down by mutual attrition, of Iguanodon. Their mode of im- 
plantation varies, but they are not anchylosed to the jaws. 

The scapula is vertically elongated, narrow, and devoid of 
any acromial process ; the coracoid rounded and without fon- 
tanelles or processes. 



228 THE ANATOMY OF VERTEBKATED ANIMALS. 

No Ornithosoelidan 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 
iimer 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 Oompsognatha. The type of the latter 
division is the wonderful little extinct reptile, Compsogna- 
ihus, which differs from the Dinosauria in the great length 
of the centra of the cervical vertebrae, 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 astragalus appears to 
have been anchylosed with the tibia, as in birds. A single 
specimen only of this reptile has been obtained, in the Solen 
hofen slates. 

IX. The Pteeosaueia. — The iiying Reptiles, which belong 
to this group, and are commonly known as Pterodactyls, are, 
and long have been, extinct, their remains occurring only in 
Mesozoic rooks, 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 expan- 
sion of the integument, like the patagium of a Bat (Fig. 79). 

The vertebral column is distinctly divided into cervical, 
dorsal, sacral, and caudal regions, the cervical vertebras being, 
as in Birds, the stoutest of all. The atlas and axis are anchy- 
losed together, at least in the cretaceous species. The other 
cervical vertebrae, apparently not more than six or seven in 
number, have low, or obsolete, spinous processes ; and, like 
the vertebrae of the rest of the spine, are proccelous, and 
have the neuro-central suture obliterated. The existence of 
cervical ribs is doubtful. From fourteen to sixteen vertebras 
intervene between the cervical and the sacral regions ; and 
not more than one or two of the hindermost of them, if any 



TliK PTEROSAURiA. 



229 



Rre devoid of ribs. The number of vertebra auchylosed 
together to form the sacrum, is not fewer than three, nor more 
than six. 




Pjg. 79.— The nearly entire skeleton of Pterodaeiylua apeotabiUs (Von Meyer), as showi 
by tlie two halves of a split block of lithographic slate, o, the left pre-pubio bone 
on the right side this bone is not shown, and the ilinm is exposed. 



The tail is very short in Pterodaetylus, and, in this genus, 
all the vertebrae are movable upon one another ; but in Mham- 
phorhynchus, it is extremely long, and the vertebrae are 
immovably fixed by what appear to be ossified ligamentous 
fibres. 

The vertebral ribs are slender, and the anterior ones, at 
any rate, have distinct capitula and tubercula. There are 



•30 THE ANATOMY OF VERTEBRATED ANIMALS. 

ossified sternal ribs, and splint-like abdominal ribs. Tlie 
sternum is broad, and, unlike that of other Ite})tilia, is very 
completely ossified, and bears a strong median ciest on the 
anterior part of its ventral surface. No median posterior pro- 
longation has been observed in connection with it. 

The brain-case is more rounded and bird-like than in the 
other Reptilia, and, in 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 
anchylosed very early ; the orbits are very large, and the ex- 
ternal nares are situated close to them. The premaxilte are 
very large, the maxillae slender, and the dentary pieces of the 
mandible are fused together into one bony mass, without any 
trace of a symphysial suture. 

The resemblance to birds is still further increased, in some 
species, by the presence of wide lachrymo-nasal fossae between 
the orbits and the nasal cavities, and by the prolongation of 
the extremities of the premaxillse and of the symphysial part 
of the mandible into sharp, beak-like processes, which appear 
to have been covered with homy sheaths. But the reptilian 
type is kept up by the presence of a distinct post-frontal, which 
unites with the squamosal and thus gives rise to a supra- 
temporal fossa. The post-frontal and the jugal unite behind 
the orbit, in LacertUian 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 8auropsida^ but are extremely similar 
to the same parts in birds, and indeed to the shoulder-girdle 
of the less reptilian Carinatm. 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 cylin- 
droidal, concave from above downward, convex from side to 
side. The coracoid, elongated and comparatively narrow, is 
devoid of fontanelle, epicoracoid, or procoracoid. 

No trace of any clavicle has been discovered. 

The humerus has a great deltoid ridge or process. Tlie 
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. An- 
other styliform bone attached to the carpus does not appear 
to have belonged to the metacarpal series. The radial meta- 
carpal bears two phalanges ; the second, three ; the third, four, 
BO that these represent the poUex and the succeeding digits 



THE PTEROSAURIA. 231 

of the Lizard's manus. The terminal phalanx of each of these 
digits is strong and curved, 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 correspondingly 
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 ; 
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 exag- 
geration of the pre-pubic process of Lacertilia and Ghelonia. 
Or it may be (though I do not think this very probable) that 
the broad flat plates correspond almost altogether to the ischia, 
and thit the spatulate ossifications are the pubes ; in which 
case the structure of the pelvis would be a sort of extreme ex- 
aggeration of that observed in the Grocodilia. 

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 further 
elucidation. In some Pterosauria there seem to be only four 
digits, with, perhaps, a rudiment of a fifth, in the pes ; but 
others, such as Jthamphorhynchus Gemmingi, have five digits 
in the foot. Where there are only four, each digit is termi- 
nated by a curved and pointed ungual phalanx, and the num- 
ber 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 Pterosauria have thin walls, enclos- 
ing a large cavity, which appears to have contained air, as in 
many birds ; and pneumatic foramina are visible on the sides 
of the vertebrae. 

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 Solenhofen. 

They are thus grouped into genera : 



232 THE ANATOMY OF VERTEBRATED ANIMALS. 

A. With two jointa in the ulnar digit of the manus. 

B. With four joints in the ulnar digit. 

a. The jawa strong, pointed, and toothed to their anterior ex- 

tremities. The tail very short. The metacarpus usually 
longer than half the length of the antebrachium. 
Pkrodaciyliis, 

b. The extremities of the jaws produced into toothless beaks, 

probably ensheathed in horn. The tail very long. The meta- 
carpus shorter than half the length of the antebrachium. 

a. All the mandibular teeth similar. 

Ehamphorhynchus. 

b. The posterior teeth for the most part very short. Tho 

anterior long. 

Dimorphodon. 

I am much inclined to suspect that the fossil upon which 
the genus Ornithopterus has been founded, appertains to a true 
Bird. 



CHAPTER VL 

THE CLASSIFICATION AND THE OSTEOLOGY OF BIRDS. 

The class Aves. — Though this class contains a great 
number of specific forms, 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 Ghelonia, do. Hence the char- 
acters 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 anchylosed together. The tail longer than the 

body. 

I. — Sauruk^. 
1. Arch<eopierygid(e. 

B. The metacarpals anchylosed together. The tail considerably shortei 

ihan the body. 

». The sternum devoid of a keel. 

II. — Eatit^. 

a. The wing with a rudimentary, or very short, humerus and 

with not more than one ungual phalanx, 
u. A hallux. 

2. Apierygidce (The Kiws). 
p. No hallux. 

3. Dinornithidce (The Miias). 

4. Casuaridce (The Cassowaries). 

b. The wing with a long humerus and with two ungual 

phalanges. 

a. The ischia uniting immediately beneath the sacrum, 
and the pubes free. 

5. Rheidm (The American Ostriches). 

/3. The ischia free and the pubes uniting in a ventral 
symphysis. 

6. Strulhionidce (The Ostriches). 
B. The sternum provided with a keel.* 



' The keel is rudimentary in the singular Parrot Strigopi, 



234 THE ANATOMT OF VERTEBRATED ANIMALS. 

Ill, — Carinat^e. 
a. The vomer broad behind, and interposing between the 
pterygoids, the palatines, and the basispheuoidal rostrum 
(DromceognatJice.) 

I. Tinamomorphw (The Tinatnous). 

b The vomer narrow behind ; the pterygoids and palatines 
articulating largely with the basisphenoidal rostrum. 

a. The maxillo-palatines free.* 
i. The vomer pointed in front. 
(Schizoffnaihce.) 

8. Charadriomorphce (The Plovers). 

9. Cecomorphce (The Gulls). 

10. Spheniscomorphas (The Penguins). 

II. Geranomorphm (The Cranes). 

1 2. Tumicimarphm (The Hemipods). 

13. AUctoromorpJice (The Fowls). 

14. Pteroclomorphie (The Sand-grouse), 

15. Peristeromorphm (The Pigeons). 

16. Seteromorphm (The Hoazin). 
ii. The vomer truncated in front. 

{JEgilhocin athm. ) 
IT. Coracomorphw (The Passerines). * 

18. Cypselomorphai (The Swifts). 

19. Celeomorphai (The Woodpeckers). 
(3. The Maxillo-palatines united. 

{Desmognathce.) 

20. Aetomorpha (The Birds of Prey). 

21. PsiiiacomorphcB (The Parrots). 

22. Coccygoniorpha (The Cuckoos, Kuig- 

fishers, Trogons). 

23. Chenomorphcc (The Anserine Birds). 

24. Amphimorphce (The Flamingoes). 

25. Fdargomorpha (The Storks). 

26. DysporomorphoE (The Cormorants), t 



• "With the exception of Dicltolophus and some species of Crax. 
t The subjoined Table, whioli shows with which of the above groups the 
old orders of Birds correspond, may be useful to the student : 

/. — ACCIPITKES 1 

or >-.... —AetoinorplKB. 

Kaptores ) 

77. — SoANSOREs = Psittacomorphm, CoecygomorpJus (in part). 

'■^ rASSERES I ^1 Qoracomorplice, Vypselommphce, Celeomoi-~ 
INS°ESS0RE9 \ ' ' ' ' \ phc^, CoooygomoTpli,^ (in part). 

I y, — GalliNjE (with Columbje) = Alectoromoiphm, Perideromorphoi, Pterodo' 

moiphoi, Turnieimorphm. 

V. — CcESORES =Ratitce. 

r/. — GRALLiB = Chi-irndriofnorphce^ Geranomorplice^ A-mphi- 

morp/toi, Pelarg&morphcR. 

ypi. — FiLMiPEnES , , . ■ =Cecnmorphce, SphtniKcoworphm, Chenomor- 

photy Dysporomotphcn, 



THE FEATHERS OF BIRDS. 235 

The exoskeleton of Birds consists almost entirely of epi- 
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 pennce, 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 : A main stem (soapus) forming the axis 
of the feather, and divided into a proximal hollow cylinder, 
partly imbedded in a sac of the derm, called the calamus, or 
quill ; and a distal vexillum, 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 processes, the barbs. 
The calamus has an inferior aperture {umbilicus inferior), into 
which the vascular pulp penetrates ; and a superior aperture 
{umbilicus 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 upward and downward, 
when the vexillum of the feather is horizontal. The inter- 
stices 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 inter- 
lock 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 close to the superior umbilicus. The aftershaft is 
generally much smaller than the chief vexillum ; but in some 
birds, as the GasuaridoB, 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 pennae, in having the barbs 
soft and free from one another, when they constitute penno- 
plumoB, or plumuloB (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 
Jilopluma. 

The contour feathers are distributed evenly over the body 
only in a few birds, as the Ratitoe, the Penguins, and some 
others. Generally, the pennse are arranged in definitely cir- 



206 THE ANATOMY OF VERTEBRATED ANIMALS. 

cumscribed patches or bands, between which the integument 
is either bare, or covered only with down. These series of 
contour feathers are termed ^feryto, and their interspaces, 
aj^teria. 

In some birds, such as the Herons, plumulee of a peculiar 
kind, the summits of which break off into a fine dust, or pow- 
der, -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 excre- 
tion 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 highlj'-vascular and sometimes 
erectile processes (combs, wattles). 

The spinal column of birds contains numerous and well- 
ossified vertebrae, a considerable number of which (more than 
six) are anohylosed together to form a sacrum. Of the verte- 
br£e which enter into the composition of this complex bone, 
however, not more than from three to five can be regarded as 
the homologues of the sacral vertebrae of a Crocodilian or 
Laoertilian reptile. The rest are borrowed, in front, from the 
lumbar and dorsal regions ; behind, from the tail. The cervi- 
cal region of the spine is always long, and its vertebrae, which 
are never fewer than eight, and may be as many as twenty- 
three, are, for the most part, large in 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 aper- 
ture into two — an upper, for the spinal cord, and a lower for the 
odontoid process of the axis vertebra. The os odontoideum 
is always anchjdosed with the second vertebra, and constitutes 
a peg-like odontoid process. 

The spines of the succeeding cervical vertebrfe are often 
obsolete, and are never very prominent in the middle region 
of the neck. The anterior faces of their elongated vertebral 
centra are oylindroidal, slightly excavated from above down- 
ward, and convex from side to side ; while the posterior faces 



THE VERTEBRJC IN BIRDS. 237 

are convex from above dovpnward, and concave from side to 
Bide. Hence, in vertical section, the centra appear proccelous ; 
in horizontal section, opisthocoelous ; and this structure is ex- 
ceedingly characteristic of birds. The under surfaces of the 
centra frequently give off median inferior processes. In the 
RntitOB, it is obvious that the cervical vertebrae have short 
transverse processes and ribs, disposed very much as in the 
Crocodilia. For, in young birds, the anterior end of the lat- 
eral face of each vertebra bears two small processes, an upper 
and a lower ; and the expanded head of a styliform rib is ar- 
ticulated with these by two facets which represent the capitu- 
lum and the tuberculum. With age, the cervical ribs may 
become completely anchylosed ; 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 sympathetic nerve. The cervical 
ribs and transverse processes are similarly disposed in very 
young Carinatoe; but in these birds their form frequently be- 
comes much modified in the adult ; and they develop pro- 
longations, which extend downward and inward, 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 cervi- 
cal vertebrae become elongated and freely movable in the 
Carinatce, as in the JRatitw. 

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 con- 
nected by a true articulation with the margin of the sternum. 

The number of the dorsal vertebrae (reckoning under tnat 
head all the vertebrae, after the first dorsal, which possess dis- 
tinct ribs, whether they be fixed or free) varies. The centra 
of the dorsal vertebra 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 Pen- 
guins. In this case, the convex face is anterior, the conca\ e, 
posterior. They may, or may not, develop inferior median pro- 
cesses. They usually possess well-marked spinous processes. 
Sometimes they are slightly movable upon one another ; some- 
times they become anchylosed together into a solid mass. 

It is characteristic of the dorsal vertebrae of Birds that the 
posterior, no less than the anterior, vertebrae present a facet, 
or small process, on the body, or the lower part of the arch, 



238 THE ANATOMY OF VERTEBKATED ANIMAl-S. 

of the vertebra for the capitulum of the rib, while the tipper 
part of the neural arch gives off a more elongated transverse 
process for the tuberculum. Thus the transverse processes of 
ail the dorsal vertebrae of a bird resemble those of the two an- 
terior dorsals of a crocodile, and no part of the vertebral col- 
umn of a bird presents transverse processes with a step for 
head of the rib, like those of the great majority of the vertebrae 
of Grocodllia, Dlnosauria, Dicynodontia, and Pterosauria. 

The discrimination of the proper lumbar, saoral, and ante- 
rior caudal vertebrae, in the anchylosed mass which constitutes 
the so-called " sacrum " of a bird, is a matter of considerable 




^7/ 

Pio. 80. — The "Sacram" of a Chick, dl^ dorso-lumbar ; «., sacral ; c, caudal vertebne. 

difl&oulty. The genei'al arrangement is as follows : The most 
anterior lumbar vertebra has a broad transverse process, which 
corresponds in form and position with the tubercular trans- 
verse process of the last dorsal. In the succeeding lumbar 
vertebrse this process extends downward ; and, in the hinder- 
most, 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 vertebra 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 fora- 
mina in front of and behind this vertebra enter into the lum- 
bar plexus, which gives origin to the crural and obturatoi 
nerves, and not into the saoral plexus, which is the product of 
the nerves which issue from the intervertebral foramina of the 
proper sacral vertebras in other Vertebrata. Behind the last 
lumbar vertebra follow, at most, five vertebras, which have no 
ribs, but their arches give off horizontal, lamellar, transverse 
processes, which unite with the ilia. The nerves which issue 
from the intervertebral foramina of these vertebrae unite to 

* It would be more proper to say that oaaifioation extends into it from the 
centrum as well as from tne neural arch. The process, like other processes, 
eiists before the centrum is differentiated from the arch by ossifioation. 



THE VERTEBRA IN BIRDS. 239 

form the sacral plexus, •whence the great sciatic nerve is given 
off; and I take them to be the homologues of the sacral ver- 
tebra of Heptilia. The deep fossaa between the centra of these 
vertebrae, their transverse processes, and the ilia, are occupied 
by the middle lobes of the kidneys. 

If these be the true sacral vertebrae, it follows that their 
Buocessors are anterior caudal. They have expanded upper 
transverse processes, like the proper sacral vertebr£e ; but, in 
addition, three or four of the most anterior of these vertebrae 
possess ribs vi^hich, like the proper sacral ribs of reptiles, are 
suturally united, or anchylosed, proximally, with both the 
neural arches and the centra of their vertebrae, while, distally, 
they expand and abut against the ilium. The anchylosed 
caudal vertebrae may be distinguished as urosacral. The 
caudal vertebrae which succeed these may be numerous and all 
distinct from one another, as in Archceopteryx and Rhea ; but, 
more generally, only the anterior caudal verlebriE are distinct 
and movable, the rest being anchylosed into a plough-share 
shaped bone, or pygostyle, which supports the tail-feathers 
and the uropygial gland, and sometimes, as in the Wood- 
peckers and many other birds, expands below into a broad 
polygonal disk. 

The centra of the movable presacral vertebrae of Birds 
are connected together by fibro-cartilaginous rings, which 
extend from the circumference of one to that of the next. 
Each ring is continued inward into a disk with free anterior 
and posterior faces — the meniscus. The meniscus thins tow- 
ard 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 communicate 
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 
vertebrae. 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- 
tion of the notochord. As JSger * has shown, it is the homo- 
logue of the odontoid ligament in the cranio-spinal articula- 
tion ; and of the pulpy central part of the intervertebral fibro- 
cartilages in Mammalia. 

*"Da3 Wirbeliorpergelenk der Vogel." Sitzungsteriohte der WieEel 
Akademle, 1858. 



240 THE ANATOMY OF VERTEBRATED ANIMALS. 

All the vertebral ribs in the dorsal region, except, perhaps, 
the very last free ribs, have wideh'-separated capitula and 
tubercula. More or fewer have "well-ossified uncinate processes 
attached to their posterior margins, as in the Crocodlliu. 
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.* It begins to ossify' by, at 
fewest, two centres, one on each side, as in the Hatiice. In 
the Garinatm 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 ossification (r. to rn. x. in Fig. 81) is termed 
the lophosteon, the antero-lateral piece which articulates with 
the ribs, pleurosteon [pi. o.), and the posterolateral bifurcated 
piece, metosieon. 

Though the sternum, in most birds, seems to differ very 
much in form from that of the MeptUia, it is rhomboidal in 
the Gasicaridce, 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 con- 
vexity of its ventral surface. But in other birds, and notably 
in many CarinatCB, 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 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 somanj* divis- 
ions of the xiphoid process of the sternum in Mammalia^ and 
hence are called middle, internal, and external xiphoid pro- 
cesses. Sometimes, a median process, rostrum or manubrium 
(r., Fig. 81), is developed from the anterior angle of the ster- 
num, and its antero-lateral angles are frequently produced into 
costal processes (c p., Fig. 81), which may bear the articular 
surfaces for more or fewer of the ribs. The two last-named 
structures are very distinct in the Coracomorplim, or Passerine 
Birds. 

* These statements respcctincr tlio vertebral column, ribs, and sternum, 
like those furtlier on toucnino; the skull, do not apply to Ayckaofteryx, in 
which ail these parts are unknown or imperfectly known. 



THE STERNUM IN BIRDS. 



941 



The extent to which the keel of the lophostcon is devel- 
oped in the carinate birds varies very much. In Strigops it 
is ruiliinentary ; in birds of powerful flight, as vvc41 as in those 
which use their wings for swimming, it is exceedingly large. 




Fig 81. — Front and side views of the sternum of a Fowl, r., rostrum, or manubrium: c.p^ 
costal process; pi. o., pleurosteon (the line from the letter goes to the point of junc- 
tion between the pleurosteon and the metosteon) ; m. aj., the middle xiphoid process ; 
ca., the carina or keel. 

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 Pteronauria. 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 fossas, 
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 3Ix. in 
11 



242 



THE ANATOMY OF VERTEBKATED ANIMALS. 



Fig. 82), there is a laohrymo-nasal fossa, or interval unoccupied 
by bone, between the nasal, lachrymal, and maxillary bones, 
such as exists in some Teleosawia, JDinosauria, and Ptero- 
saur ia. 

The posterior nares lie 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 Eustachian tubes generally traverse the basisphenoid, 
and ha\'e a common aperture upon the middle of the under 
sui-face of the skull. 






F "3 S2 — ^T.aTeral, upper, and under views of the skull of a common Fowl {Phasianus gal 
lu^Y vixp., the niaxlllo-palatine process. <2^. , the quadrate bone. The dotted lint 
Acctdentaily stops at the angular process of the mandible. 



The bones of the brain-case, and most of those of the face, 
rery early become ancbylosed together into an indistinguish- 



THK SKULL IN BIRDS. 243 

able whole in most birds, but tbe sutures remain distinguisli- 
able longer in the Ghenomorphce and SpheniscomorphcB ; and 
especially in the jRatitae. 

All the constituents of the occipital and parietal segments 
of the skull are represented by distinct bones, but 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 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 sur- 
face of the skull, between the nasal and the frontal bones ; and 
the internasal septum, in front of the ethmoid, may present 
very various degrees of ossification. Very frequently, the in- 
terspace 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 Par- 
rots, and some other birds, this joint is converted into a true 



M/i 




SO 



^To. 83. — A longitudinal and vertical section of the posterior half of the skull of an Ostrich 
P., the pituitary fossa; o«c., ^sc, anterior and posterior vertical semicircular canals oi 

t.hfl CRT. 



articulation, and the range of motion of the upper beak be- 
comes very extensive. 

The periotic capsule is completely ossified, and, as in other 



244 THE ANATOMY OF VERTEBRATED ANIMALS. 

S twopsida, the epiotic and the opisthotic are anohjlosed 
with the occipital segment before they unite with the prootic. 
In the primordial skull of the bird the olfactory organs are 
surrounded by cartilaginous capsules, the lateral walls of which 
send in turhinal processes of very various degrees of complex- 
ity. When the posterior wall of this capsule is ossified, the 
boue thus formed represents the prefrontal, or lateral mass of 
the ethmoid, of the mammal. It is largely developed in the 
Apteryx, in the CasuaridcB, and many other birds, but is ab- 
sent in the Struthio?iidw / and, in other birds, is often repre- 
sented by a mere bar of bone standing out from the ethmoidal 
ossification. 

Tlie 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 be- 
comes undistinguishably fused with the prefrontal. Some- 
times, on the contrary, as in the Parrots, it acquires a large 
size, and sends a process backward beneath the orbit, which 
may join with a post-orbital process of the frontal, and so cir- 
cumscribe the orbital cavity. Opisthoconius exhibits the pe- 
culiarity of the complete anchylosis 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 be- 
low the orbit, parallel with the jugal arch. A post-orbitf 1 
process may be developed from the frontal, or from the ali- 
sphenoid ; and, in the latter case, may be separately ossified. 

The squamosal is closely applied to the skull, and is, usual- 
ly, anchylosed with the other bones. It often sends a process 
downward 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 premaxillas are modified in a manner which finds a 
partial parallel only among the JReptilia. They are tri-radiate 
bones of great size, whicli, usually, give off three processes ; 
AW ascending process to the frontal ; a palatine process, along 
tiie middle of the palate, to the palatine bones ; and an exter- 
nal, or maxillary process, vrhich forms the greater part of the 
margin of the beak, and unites with the maxilla. The two bones 
are very early represented by one continuous ossification. 



THE SKULL IN BIKDS. 245 

The vomers vary more than almost any other bones of the 
skull. They underlie and embrace the inferior edge of the 
ethmo-piesphenoidal region of the basis cranii, and, in all 
birda in which they are distinctly developed, except the Os- 
trich, 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 Coracomorphoe, and seem to be 
always separate in the Woodpeckers. The coalesced vomers 
constitute a very large and broad bone in most HaiitCB, and in 
the TinamomorphoB ; a narrow elongated bone pointed in 
front in SchisognathoB ; a broad bone deeply cleft behind, and 
abruptly truncated in front, in Coracomorphce. In most Des- 
mogtiathm the vomer is small ; and, sometimes, it appears to 
be obsolete. 

The maxillse of birds are usually slender, rod-like bones, 
articulating by squamous suture, in front, with the premaxillae, 
and, behind, with the equally slender jugals. In the great 
majority of birds the maxilla sends inward a maxillo-palatine 
process (Fig. 83, mxjx), which, sometimes, is mere thin lamel- 
la of bone, sometimes, becomes swollen and spongy. In the 
Ratitm and the Desmognathce (Fi^. 84), the maxillo-palatine 
processes unite with the vomer, or with one another, and foim 




Jl/U 



Tlfl. S4. — The tinder surface of tlie cranium of the S^firetan' bird (^Gypogernvii^). ns an ex- 
ample of tlicDosmoiniathousaiTrangement. J/JT^., maxillo-palatine process ; Bpt, bbsl 
ptciygjid piocOBSca. 



246 THE ANATOMY OF VERTEBRATED ANIMALS. 

a complete bony roof across the palate. In the SchizognathcB 
(Fig. 82), and JEgithognathoi, 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 
liinder extremity of which presents, on its inner side, an artic- 
ular 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 (i. e., on the ven- 
tral side of) the maxillo-palatines and unite with the premax- 
illse, sometimes by a squamous suture, sometimes by anchy- 
losis, rarely, as in the Parrots, by a flexible joint. Posteriorlv, 
they always unite with the pterygoids. In most birds, the 
palatines converge, posteriorly, toward the basi-sphenoidaJ 
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 Ratitm, or in the Tinamous, 
among the Carinatm. In these (with the exception of 
Strut/do), the palatines are, as it were, borne off from the ros- 
trum by the divergent ends of the great vomer, and the dispo- 
sition of the parts is more lacertilian 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 be- 
come articulated with the basi-sphenoidal rostrum. In all em- 
bryonic birds, in all the Ratita?, and in many Carinatce, such 
as the Tinamomorphoi, Charadriomorphw, Alectoromorplue, 
Peristeromorj^hw, Glienoinorphcv, longer or shorter processes 
extend from the basi-sphenoid, and present terminal articular 
facets to corresponding facets upon the inner sides of the 
pterygoids. These are hasi-pterygoid processes, similar to 
those which occur in Lacertilia and some Ophidia. 

The quadrate bone is almost always movable upon the 
skull, articulating with the prootic, alisphenoid, and squamo- 
sal, 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 movement of the distal 
end of the quadrate, such as must take place when the mandi- 
ble is depressed by the digastric muscle, causes the maxillo- 
jugal bar to thrust the premaxilla upward and forward ; the 
palatine and pterygoid bones, at the same time, sliding for- 
ward upon the rostrum of the basisphenoid. Thus it comes 



THK PECTORAL ARCH IN BIRDS. 



247 



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 mandible consists primitively of six pieces, as in other 
Sauropsida, 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 Grocodilia ; 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 movable. The angle of the mandible may 
be truncated or produced backward into a long curved pro- 
cess, as in Fowls (Fig. 83), 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 periotio region of the skull, 
and commonly remain quite free. In some of the Wood- 
peckers, however, the long posterior cornua are immensely 
elongated, and curved upward and backward over 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. 

The pectoral arch presents a long, narrow, and recurved 
scapula (<So. Fig. 84^), without any suprascapula ; and a cora- 
coid (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 ; otherwise, the 
shoulder-girdle is unlike that of any of the Reptilia, except the 
Pterosauria. The coracoid is usually completely ossified, and 




Pia. 84J —The rlgM scapula (*.) and coracoM (f,'n.) of a Fowl: (it, the plono'.dal cavity 
/, the right clavicle, or right half of the fiireulum ; hp^ the hyijocleidiuiu. 



248 THE ANATOMY OF VERTEBRATED ANIMALS. 

presents no fontanelle. There is no distinct epicoracoid. The 
two bones take nearly equal shares in the formation of the 
glenoidal cavitj-, and usually remain unanchylosed and distinct 
in this region. 

In the Matitce 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 completely 
anchylosed. But, in all the Garinatm, the long axis of the 
scapula forms an acute, or only slightly obtuse angle ( Ocydro- 
mus, Didus) with that of the coracoid. A small bone, the 
scapula accessoria, is developed on the outer side of the shoul- 
der-joint in most Coracomorphce and Celeomor^jJicn. 

In the CarinatGB, 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 cora- 
coid is in like manner divided into two portions ; 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 Rcititce there is no dis- 
tinct 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 Par- 
rots. In the Emeu, and in sundry Garinatm (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 anchylosed together, and with the repre- 
sentative of the interclavicle, in the middle line, into a single 
bone, the furculwn, the strength of which bears a pretty close 
relation to the exertion required of the wings in ilight, or in 
natation. In the passerine birds the scapular end of the clav- 
icle is usually expanded, and ossifies separately, as an epiclei- 
diuin. A median process [hypocleidiwin) is frequently devel- 
oped 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 anchylosed with the manubrial part of the ster- 
num, on the one hand, and with the coracoids on the other. 
Anchylosis of the furculum with the coracoids has also been 
observed in Didus. 



THE f ORE-LIMB IN BIRDS. 249 

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 or- 
dinary reptile ; and this change is of a character similar to, 
but in some respects greater than, that which the arm of a man 
presents, when compared with the fore-limb of a quadrupedal 
mammal. The humerus lies parallel with the axis of the body, 
its proper ventral surface looking outward. The forearm is in 
a position midway between pronation and supination, and the 
manus is bent back upon the ulnar side of the forearm, in a 
position, not of flexion, but of abduction. 

In ordinary birds, the proximal end of the humerus is ex- 
panded, and its articular head transversely elongated ; its ven- 
tral face is convex, and provided with a strong preaxial ridge, 
ivhich gives attachment to the pectoral muscle. The proper 
dorsal face is concave from side to side, especially toward the 
postaxial margin, where the pneumatic aperture occurs in those 
birds which have the humerus hollow. The distal end is ex- 
panded, and the articular surface for the radius is a convex 
facet, directed obliquely inward, on its ventral face. In this 
respect the bird's humerus exaggerates a feature of that of the 
Lizards. 

In the MatitoB these peculiarities are very feebly, or not at 
all, marked, the humerus being a slender, cylindrical, slightly- 
curved, bone. In the Casuaridce, Dinornithidoe, and Aptery- 
gidw, the fore-limb is extraordinarily reduced, and may become 
rudimentary. In the Penguins and, to a less degree, in the 
great Auk, the humerus becomes flattened from side to side ; 
the proximal end is singularly modified, and, at the narrow 
distal end, the articular surface for the radius lies completely 
in front of, and rather above, that for the ulna. 

The ulna, which often presents a series of tubercles, indi- 
cating the attachment of the secondary quill-feathers, is usu- 
ally a stronger, and a longer, bone than the radius. There are 
only two carpal bones, one radial and one ulnar. 

In the Apterygidce and in the Casuaridm, 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 StruthionidoB and JRheidce, and in all Carinatm, there 
are three digits in the manus, which answer to the poUex and 
the second and third digits of the pentadactyle fore-limb ; and 
the metacarpal bones of these digits are anchylosed together. 
As a 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 



250 



THE ANATOMY OF VERTEBRATED ANIMALS. 



interspace between 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 en- 
sheathed in a horny claw. The second digit 
has three phalanges, and the terminal pha- 
lanx is similarly provided with a claw in sun- 
dry birds. In the ostrich, both the pollex 
and the second 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 con- 
trast in two groups of birds, which are alike 
remarkable for their powers of flight. These 
are the Swifts and Humming-birds, in which 
the humerus 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 free 
phalanges, and its metacarpal bone seems to 
be anchylosed with that of the second digit. 
The third metacarpal is slender and straight. 
The bones of the manus are singularly elon- 
gated and flattened.- 

The pelvis of a bird (Fig. 86), is remark- 
able for the great elongation, both anteriorly 
and posteriorly, of the iliac bones (-11.), 
which unite with the whole length of the 
ed^as of the sacrum ( Sm.) and even extend 
forward over the posterior ribs of the dor- 
sal region. Below, each iliac bone forms a 
wide arch over the upper part of the acetab- 

g'L";™ctaenfl|lr'ed. ^^^^ i^'^-), t^s Centre of which is always 
closed by fibrous tissue, so that, in the dry 
skeleton, the bottom of the acetabulum is perforated 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 broad- 
ens toward its hinder end, extends back, nearly parallel with 
the hinder part of the ilium, and is united with it by ossifica- 
tion, posteriorly. The iliosciatic interval is thus converted into 
a foramen. The pubis {Pb.) enters, by its dorsal or aeetabulai 




Fio. 85.— The radius (r); 
ulna (m) ; radial and 
uloar carpal booes (r', 
u') ; with the throe di- 
gits (i., ii., iii,)' of the 
rii^ht fore-limb of a 
Fowl. The terminal 
phalanf^es of both the 
first aad the second di 



THE PELVIS IN BIRDS. 



251 



end, into the formation of the acetabulum, and then passes 
backward and downward as a comparatively slender, curved, 
bone, nearly parallel with the ischium. It is united with its 




Fig. 86.— a, lateral; and B, dursal, Tiew of the pelvis of a Fowl. *S^., sacrum ; 77., iUuih 
/s., ischium; P&., pubis ; .4m., acetabulum. 

fellow only by fibrous tissue. Neither the ischia, nor the pubes, 
unite directly with the sacrum. Very few birds present any 
important deviation from this structure of the pelvis. In it- 
nanvus, Casuarius, Dromceus, Apteryx, Dinornis, the ischium 
is not united with the backward extension of the ilium by bone. 
In Hhea, the ischia unite with one another beneath the verte- 
bral column, and the vertebrae in this region are very slender 
and imperfectly ossified. In Struthio, alone, among birds, do 



252 



THE ANATOMY OF VERTEBRATED ANIMALS. 



the pubes unite in a median ventral symphysis. Another, not 
less remarkable circumstance, in the ostrich, is, that the 31st 
to the 35tli vertebrae inclusively (counting from the atlas) de- 
velop five lateral tuberosities. The three middle tuberosities 
are large, and abut against the pubis and the ischium. In 
these vertebras, as in the dorsal vertebra of Ghelonia, the neu- 
ral arch of each vertebra shifts forward, so that half its base 
articulates with the centrum of the next vertebra in front ; and 
the tuberosities in question are outgrowths, partly of the neu- 
ral arch, partly of the juxtaposed vertebral centra, between 
which it is wedged. Hence, in young ostriches, the face of 
each tuberositj' 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 Igiianodon and other Ornithosce- 
lida. The shaft is relatively short and 
thick, and the two terminal condyles are 
large and elongated antero-posteriorly. 
A prominent ridge, which plays be- 
tween 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 JLacertilia, 
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 alwaj^s imper- 
fect, 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 tihio-tarsus, is a highly-char- 
acteristic bone. Its proximal end is 
expanded and produced anteriorly, into 
a great cnemial process (which may be 
F 0. 87.— The right tibia and variously Subdivided) as in Dinosauria. 
^ew^K fxt:Li\te™5 The distal end is terminated by a well- 
marked, pulley -like, articular surface 
which is inclined somewhat forward as 
well as downward. Not unfrequently 
there is an oblique bar of bone on the anterior face, just above 
the pulley, beneath which the long extensor tendons pass. 




new. T., tibia; P., flhula; 
C^., cremijil process; As^ 
astragalus. 



THE HIND-LIMB IN BIRDS. 



253 



The extremity of the cnemial process in Struthio and JRhea 
is ossified as an epiphysis ; and, in young birds, the whole of 
the distal articular end of the bone is separated from the rest 
by a suture, and also appears to be an epiphysis. But it is, 
in fact, as Prof. Gegenbaur has proved, the proximal division 
of the tarsus (apparently representing only the astragalus of 
the other Vertebrata), which exists in the embryo as a separate 
cartilage, and, as it ossifies, anchyloses with the tibia. The 
so-called tibia of a bird is therefore, properly speaking, a tibio- 
tarsus (see p. 226, Fig. 87, A, and Fig. 88). 

In all birds, even in Archceopteryx, tlie fifth digit of the 
pes remains undeveloped; and the second, third, and fourth 
metatarsals are anchylosed 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 re- 
main separate, and offer convex articular surfaces to the proxi- 
mal phalanges of the digits. 





Fio. 88 —The distal end of the 
left tibia (T*.) vrtth the 
astragalus (^s.) detached, 
of a young Fowl. Viewed 
from in front, and from the 
onter side. 



Fig. 89. — The right tarso-metatarsus 
of a Fowl, consisting of three 
digits, ii., iii., iv., anchylosed with 
one another, and with the osseous 
core of the spur. A., front aspect ; 
B., inner aspect. 



In the Penguins, large apertures lie between the several 
metatarsals of the adult tarso-metatarsus ; and, in other birds, 
more or less considerable passages persist between the middle 
and the lateral metatarsals proximaUy, and the middle and the 



254 TUE ANATOMY OF VERTEBRATED ANIMALS. 

outer, distally. In most birds, the middle metatarsal does not 
remain parallel with the others, but its proximal end inclines 
a little backward, and its distal end a little forward. 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, in most birds, the posterior face of the proximiil 
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-tarsus 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 in- 
complete above, and is united by ligament to the inner, or the 
jjosterior, surface of the tarso-metatarsus. In the Frigate-bird 
{Phaethon) and in Steatornis, the hallucal metatarsal is re- 
markably long. The genus Phaethon stands alone, so far as 
I know, in having the hallucal metatarsal anchylosed with the 
others. 

In many of the Alectoromorj^hoe, a spur (calcar), consisting 
of a bony core ensheatlied in horn, is developed on the inner 
side of the metatarsus, and becomes anchylosed with the meta- 
tarsal of the second digit. In a few birds, similar spurs [Fala- 
medea), or osseous excrescences (Pezojyhaps), are developed 
in relation with the metacarpus. 

The normal number of the pedal phalanges in birds is (as 
in ordinary Lacertilia) 2, 3, 4, 5, reckoning from the hallux to 
the fourth digit. Among the few birds which constitute ex- 
ceptions to the rule are the Swifts, in which the third and 
fourth toe have only three phalanges each (3, 3, 3, 3), and the 
Goatsuckers and the Sand-grouse, in which the fourth toe 
only has the number thus reduced (2, 3, 4, 3). 

Many birds have only three toes, by suppression of the 
hallux. In the Ostrich, not only the hallux, but the phalanges 
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 phalanges 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 backward, and the other tliree digits forward. But 
in many Aetomorphce (especially the Owls), the outer toe can 



THE FOOT IN BIRDS. 255 

be turned outward, or even backward, at will. And in the 
Parrots, Toucans, Cuckoos, Woodpeckers, and other so-called 
" scansorial " birds, the outer toe is permanently reversed. 
Under these circumstances the distal end of the outer meta- 
tarsal 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 yrhich is turned back- 
ward. Lastly, in the Swifts, the DysporomorphcB and the 
Spheniscomorphm, the hallux is directed more or less forward, 
so that all four toes are turned to the front. 

As a general rule, the osseous tissue of birds is remarkably 
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 neighborhood. Such air- 
cavities are always found in the skull, in connection 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, Penguins, 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 skele- 
ton, 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 beneath 
the integument. 



CHAPTER Vn. 



THE MtrSOLES AND THE VISCEEA OF THE SAUEOPSIDA. 

The most important deviations from the ordinary arrange- 
ment of the muscular system occur, as might be expected, in 
the Ophidia^ in the Chelonia, and in Aves. In the iirst-men- 
tioned group, the numerous muscles of the limbs are, of course, 
absent, and the mobility of the vertebrae, ribs, and jaws, is ac- 
companied by a corresponding differentiation of the muscles 
of those parts. The episkeletal muscles form a continuous 
series (divisible 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 outward 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 a rectus abdominis. This muscle is contin- 
ued forward to the hyoidean apparatus, and thence to the 
mandible. 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 
che 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 correspond 
with the transversus abdominis commence in the tail by trans- 
versely-directed bundles of fibres, which arise from the roots 
of the caudal ribs (transverse processes), and meet in a median 



MUSCLES OF THE SAUEOPSIDA. 257 

aponeurosis. In the trunk, similar bundles arise from tlie 
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 recti are 
very weak, but muscles answering to the pyramidales extend 
from the pubes to the inner surface of the plastron. A mus- 
cular expansion analogous to a diaphragm may be attached to 
the bodies and ribs of the third and fourth dorsal vertebrae, 
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 vertebrae and to the procoracoid. There is also a 
single retractor of the pectoral arch, apparently representing 
a serratus magnMS, and passing from the first costal plate to 
the scapula. The pectoralis major arises from the inner sur- 
face of the plastron. The representative of the latissimus dor- 
si arises from the inner side of the first costal plate. 

The cutaneous muscles of birds are well developed, and 
form broad 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 patagium, a fold of in- 
tegument which extends between the trunk and the brachi- 
um behind, and between the brachium and ante-brachium in 
front. In correspondence with the slight mobility of the dor- 
sal vertebrae, the episkeletal and hjrposkeletal 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 ab- 
dominal muscles are usually small, and the internal oblique 
may .be absent. A diaphragm, consisting of bundles of mus- 
cular fibres, which pass from the ribs to the aponeurosis cover- 
ing the ventral face of the lungs, is developed in all birds, but 
attains the greatest degree of completeness in the JRatitce, and 
especially in Apteryx. 

The muscles of the limbs are remarkably modified by the 
excessive development of some of those found in other Verte- 
bi'ata, and the suppression of others. 

Thus in all birds possessing the power of flight, the pec- 
toralis 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. 



258 THE ANATOMY OF VERTEBRATED ANIMALS. 

The elevation of the wing is chiefly effected by the juecVo- 
ralis tertius, which arises beneatli 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 pecul- 
iar 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 unit- 
ing with ihe flexor digltoriim perforatiis. The result of this 
arrangement is, that the toes are flexed whenever the leg is 
bent upon the thigh, and, consequentljf, the roosting bird is 
held fast upon his perch by the weight of his own body. 

In all the Sauropsida the cerebro-spinal axis is angulated 
at the junction of the spinal cord with the medulla oblongata, 
the latter being bent down toward the ventral side of tlie 
body. The region in \\'hich the nerves of the anterior and 
posterior 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 lat- 
ter, they diverge and give rise to the sinus rhomboidcdts, 
which is a sort of repetition of the fourth ventricle, the dilated 
central canal of the spinal cord being covered merely l)v a 
thin membrane consisting chiefly of the ependyma and arach- 
noid. 

The brain (Fig. 90) fills the cavity of the skull in the 
iiigher Sauropsida, and presents a well-developed cerebellum ; 
a mesencephalon divided above into two optic lobes ; and 
relatively large prosenccphalic hemispheres, which attain a 
considerable size in Crocodilia, and jives, but never conceal 
the optic lobes. In Crocodilia the cerebellum presents a dis- 
tinct vermis, with transverse fissures. In birds the latter are 
more distinct, and the lateral appendages of the cerebellum, 
or flocculi, become well defined, and are lodged, as in many 
of the lower MammaJla, in cavities of the side walls of the 
skull, arched over by the anterior vertical semicircular 
canal. 

There is t\o 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 con 
tain ventricles. In Ileptilia, the optic lobes usually lie close 
together upon the dorsal side of the mesencephalon, liut in 
Aves (Fig. 90 B, D) they are thrown down to the sides of the 



NEUROLOGY OF THE SiUROrSIDA. 



259 




Py- 



flQ, 90. — A, C, the brain of a Lizard (_P6a'm7n08avrus BwiffalenMsX and B, D, of n liinl 
{MeleagHs giilloxiaro^ the Turkey), drawn a3 if tliey were of equal lengths. A, B, 
viewed from above ; 0, D, from the left side. (9?/'., Olfactory lobes ; Prt., Pineal er'aiJiI ; 
//m/>., cerebral hemispheres; .J/&., optic lobes of the mid-brain; (76., cerebellum ; M, 
O^ medulb oblont^ata ; ii.^ in., m., second, fourth, and sixth pans of cerebral nerves ; 
Py., pituitary body. 



base of the brain, and are connected over the aqumductiis 
Sylvii by a broad commissural band. 

Each prosencephalic lobe contains a lateral ventricle (con- 
tinuous through the foramen of Munro with the third ven- 
tricle), which is little more than a fissure between the very 
thin inner wall of the lobe and its thick outer part, which con- 
tains the corpus striatum. The corpora striata are united by 
an anterior commissure, which is not of large size. The thin- 
ning of the inner wall of the lobes, from the margin of the 
foramen of Munro backward, wliich gives rise to the fissure 
of Bichat in the Mammalia, extends for a very short distance 
in the Sauropsida, even in birds. 

The olfactory lobes are usually elongated, and contain ventri- 
cles continuous with those of the prosencephalic hemispheres. 

In all Sauropsida the motor nerves of the tongue pass 
through a foramen in the exoccipital 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 Ichthyopsida are absent, 

but the pneumogastric gives a recurrent branch to the larynx. 

The third, fourth, and sixth nerves arise quite independently 

of the fifth. 



200 



THE ANATOMT OF VERTEBRATED ANIMALS. 



The sympatlietic is well developed, except in the Ophidia, 
where it is not distinct from the spinal nerves, in the greater 
part of the trunk. 




««y 



Fxfl. 91. — The brains of a Lizard {Psammosnwnis Benpalenfns) and of a bird {3feteaffns 

gallopavo), in longitudinal and vertical section. Tlie upper iigure represents the liz- 
ard's brain ; the lower (taken, like Fig. 90, B, D, from Carus's " Erlauterunga-Tafeln '') 
that of the bird. 

The letters as in the preceding figure, except L. t, lamina terminaUs, or anterior wall 
of the tliird ventricle ; f. M., foramen of Munro ; a., anterior commissure ; Th. E., thala- 
moncephalon : «., soft commissure ; p., posterior commissure ; is., indicates the exact point 
of exit of the fourth pair from that part of the brain which answers to the value of Vioussens, 



The Ojohidia, many Sauria, 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 ex- 
tinct Ichihyosaurla, attains very great absolute and relative 
dimensions. 



THE EYE -MUSCLES IN SAUROPSIDA. 2G1 

In the Ophidia and some Lacertllia (tlie Amphishoenoidea, 
Boiiie Scincoidea, all Ascalobota), the integument is continued 
over the eye, and becomes transparent. These reptiles are 
commonly said to possess no eyelids ; but it must be remarked 
that tliis is not true of them in the 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 Vertehrata, and 
is separated from the eyeball by a chamber lined by conjunc- 
tiva, 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, CrocodUia, and Aves, possess 
a nictitating membrane moved by special muscles, which pre- 
sent 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 pre- 
sphenoidal region of the inner wall of the orbit, passes back- 
ward through the sheath, and then forward to be attached to 
the nictitating membrane. When the muscle contracts it 
necessarilj' pulls the latter over the eye. A Harderian gland 
is always developed, and a lachrymal gland very generally, 
though not always. 

In the Chelonia, muscular fibres (forming the so-called 
pyramidalis muscle) arise from the inner side of the eyeball, 
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 pyramidalis muscle 
talcing 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 to- 
gether the first and the second, is that seen in birds. A juy- 
ramidalis muscle arising from the inner and under surface of 
(he eyeball, soon ends in a tendon which sweeps round the 
upper and outer surfaces of the sclerotic to the nictitating 
membrane, as in the crocodiles. But there is also a bursalis 
muscle, which however arises, not, as in lizards, from the wall 
of the orbit, but from the upper surface of the sclerotic itself, 
whence it passes backward and ends in a fibrous slieath which 
encloses the tendon of the pyramidalis. The contraction of 



262 THE ANATOUy OF VERTEBRATED ANIMALS. 

this muscle necessarily tends to draw the tendon of the^y- 
ramidalis away from the optic nerve. A tubercle is some- 
times developed from the sclerotic above the entrance of the 
optic nerve, and prevents the tendon of the jiyramidalis from 
shifting forward and inward. 

The eyeball is always moved by iour recti and two obliqui. 
The superior oblique does not pass over a pulley. The Ghe- 
lonia and most Lacertllla have a more or less completely de- 
veloped retractor, or.choanoid, muscle. 

A ring formed of bony plates is developed in the fore-part 
of the sclerotic in Ziaoertilia, Ghelonia, Ichthyosauria, Dl- 
cynodontia, Pterosauria, and Aves, but not in Ophidia, Plesi- 
osauria, or Crocodllia. 

The iris and the tensor choroidel contain striated muscu- 
lar fibres. 

A pecten is very generally developed. It attains a large 
size, and becomes much plaited, in most Aves. 

Only Crocodllia and ^yes possess a rudiment of an exter- 
nal ear. 

The OpJiidia and the AinpMsboenoidea have no tympanic 
cavity. In some Ghelonia, in Sphenodon, and in the Chamrc- 
leons, the tympanic membrane is covered by the integument, 
but a tympanic cavity exists. In Ziacertilia, the tympanic 
cavities communicate by wide openings with the pharynx ; 
but in Ghelonia, Grocodilia, and Aves, the communicating 
passages, reduced in size, become Eustachian tubes. In the 
Ghelonia, these curve backward, downward, and inward, 
round the quadrate bones, and open separately on the roof of 
the mouth. In the Grocodilia there are, ;is has been described 
above (p. 319), three Eustachian tubes — one median and two 
lateral. In Aves, there is but one Eustachian aperture, an- 
swering to the median of the Grocodilia; and, as in the latter 
group, each Eustachian tube usually traverses the osseous 
base of the skull, to join with its fellow in the common aper- 
ture. 

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 tym- 
panic cavity. 

All Sauropsida possess a fenestra rotunda, as well as a 
fenestra ovaUs, and all have a cochlea, which is never coiled 
spirally, and is more rudimentary in the Ghelonia than in 
other groups. Three semicircular canals, an anterior and 



THE ALIMENTARY CANAL IN SAtJROPSIDA. 263 

poslerior verticnl, and an external liorizontal, are connected 
with the membranous vestibule. In Aves, the anterior vertical 
canal is very large in proportion to the others, and the adja- 
cent crura of the two vertical canals overlap before they unite 
with one another. 

Labial and buccal glands are developed in some Sauropsida, 
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 attain an immense size in the Wood- 
pecker. The tongue varies greatly, being sometimes obsolete, 
as in the Crocodile and some birds (e. g., the Pelicans), some- 
times horny and even spinose, sometimes fleshy. In the 
snakes, and some lizards, the tongue is forked, and capable 
of retraction into a basal sheath. In the Chamseleons, it is 
clubbed at its extremity, and can be retracted or protruded by 
the invagination or inversion of its hoUovr stem. 

The alimentary canal of the Sauropsida is generally divided 
into an oesophagus, 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 peritonaeum. 

The stomach is usually a simple dilatation of the alimen- 
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 approximated. 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 thickening of the 
muscular tunic of the stomach attains its maximum in the 
graminivorous birds ; and it is accompanied by the develops 
ment 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 oesophagus, 
which is usually dilated, and forms a proventriculus, connected 



264 THE ANATOMY OF YERTEBKATED ANIMALS. 

by a narrow neck with the above-mentioned muscular stomach 
or gizzard (gigerium). 

Some Ophidia have a caecum at the junction of the small 
intestine with the large ; and two such CEeca, which sometimes 
attain a large size, are very generally developed in Aves. In 
this class also, the small intestine, not unfrequently, presents 
a CEecal appendage, the remains of the vitelline duct. The 
duodenum of Birds constantly makes a loop, within v?hich the 
pancreas lies, as in Mammalia. 

The liver in the Sauropsida 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 Sursa 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 Ghelonia, Lacertilia, and Ophid- 
ia ,• the second, that in the Crocodilia ; and the third, that 
in Aves. 

1. In the Chelonia, Lacertilia, and Ophidia, there are 
two auricles. Generally, a distinct sinus venosus, with con- 
tractile V7alls, and communicating by a valvular aperture with 
the auricle, receives the blood from the venoe cavm, 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 aper- 
ture, and constituting a rudiment of a second valve. The 
ventricle contains only one cavity, but that cavity is im- 
perfectly divided into two or three chambers, by septa devel- 
oped from its muscular walls. 

In the Turtle (Fig. 92), a partly muscular, and partly carti- 
laginous, septum extends from the front wall of the ventricular 
cavity toward its right-hand end. It imperfectly divides the 
common ventricular cavity into a right small, and a left large 
moiety. The latter of these receives the blood from the auri- 
cles. In consequence of the elongated form of the ventricular 
cavity, and the projection into it of the large auriculo-ven- 
tricular valves, especially of that of the right side, this left and 
larger moiety of the common ventricle is virtually divided into 



THE HEART IN SAUROPSIDA. 



265 



kwo, 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 arteriosum • 
the right receives the venous blood from the right auricle, and 
is the cavum venosum. 

No arterial trunk arises from the cavum arteriosum, but 
two arterial trunks arise from the right-hand end of the cavum 
vetiosum / these are the two aortic arches. One of these 
passes to the left and the other to the right side, and thev 

A. 





'^r, 92.— Tlie Heart of a Turtle {Qlielone midas). — -4, a drawing from nature: the ventraJ 
face of the ventricle being laid open. B, a diagram explanatory of the arrangement of 
the cavities and vessels. 2i. A., L. ^., right and left auricles, w, a;, arrows placed In 
the auriculo-ventricular apertures to indicate the course of the blood at the auricular 
systole. ?j, the right, and 1)^, the left median auriculo-ventricular valves. C. ?).. cafinm 
verbOHum. C. p., cavwm- pulmonale, a, the incomplete septum which divides the 
cavum pulmonale from the rest of the cavity of the ventricle. P. A,, pulmonary artery. 
E, Ao.^ Z. Ao.^ right and left aortic, s, arrow showing the course of the blootl in thfl 
left aorta; t, in the right aorta; s, in the pulmonary artery; ?/, between the camtvi 
venosum and camtm pulmonale ; £C,in the left, and w,ia the right auricalo-ventriculju 
aperture. 

12 



266 THE ANATOMY OF VEKTEBRATED ANIMALS. 

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 right 
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 arises 
from the cawm m'terlosutn, the red blood can be driven out 
of the latter, during the systole, only into the cavum venosum. 

The right, comparatively small, moiety of the ventricle 
is separated from the cavum venosum by the already-men- 
tioned septum, which is attached between the origin of the 
left aortic arch and that of the pulmonary artery, its free edge 
looking toward the dorsal face of the heart. Thus the pul- 
monary arterj' arises from what is, virtually, a separate sub- 
division of the ventricle, or a cavum pulmonale. 

When the systole of the ventricle takes place, the practical 
result of these arrangements is, that the pulmonary artery, 
and the aortic arches, at first, receive wholly venous blood 
from the cavum, venosum and cavum pulmonale. But as the 
arterial blood of the cavum, arteriosum is driven into the 
cavum venosMm, 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 arterialized blood. The left arch receives a larger pro- 
portion 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 arterialized blood ; consequently none of this 
reaches the lungs. 

2. In the Crocodilia, the cavum, venosum and the cavum, 
arteriosmn are converted into perfectly distinct right and left 
ventricles. The right ventricle gives off the pulmonary artery, 
and, in addition, an aortic arch ^\-hich 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 cur- 
rents communicate only outside the heart, not within it as In 
the foregoing groups. 



THE LAKYNX IN SAUKOPSIDA. 267 

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 membranous 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 Groco- 
dilia / 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 Iiacertilia, 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 Heptilia, 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 Heptilia, 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. 

All the Sauropsida possess a larynx, a trachea, and one 
or two lungs. The bronchi do not divide dichotomously, as 
tliey do in Mammalia. 

In Ghelonia and Grocodilia the larynx consists of a cir- 
cular 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 Laeertilia have, for the most part, a similar larynx, 
but the circular cartilage is often interrupted by round, or 



268 THE ANATOMY OF VERTEBKATED ANIMALS. 

elongated, membranous fontanelles. In the Chameleons, tlie 
mucous membrane of the larynx between the circular cartilage 
and the first ring of the trachea protrudes in the form of an 
air-sac. 

In the AmpMsboenoidea, and in the Ophidla, the skeleton 
of the larynx consists of two lateral longitudinal bands of 
cartilage, united by from four to sixteen transverse bands. In 
other words, the structure which answers to the circular carti- 
lage is greatly elongated, and has many transversely-elon- 
gated fontanelles. There is a single arytenoid cartilage, 
which is sometimes represented by a process of the anterior 
dorsal margin of the circular cartilage. An epiglottis is rarely 
present. 

In 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 in the syrinx, or lower larynx, which may be developed 
in three positions : 1. At the bottom of the trachea, from tlie 
trachea alone. 2. At the junction of the trachea and bionchi, 
and out of both. 3. In the bronchi alone. The syrinx may 
be altogether absent, as in the Ratitm and the GathartidoB, or 
American vultures. 

The commonest form of syrinx is the second mentioned 
above, or tlie hroncho-tracheal syrinx. It is to be met with in 
all our common song-birds, but is also completely developed in 
many birds, such as the crows, which have no song. In its 
commonest condition this form of syrinx presents the following 
characters : The hindermost rings of the trachea coalesce, and 
form a peculiarly-shaped chamber, the tympanum. Immedi- 
ately 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, toward 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 
Ulterior a cartilaginous 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 bron- 
chus of its side ; which, in this part of its extent, is membra- 
nous and elastic, and receives the name of the membrana tym- 
ipaniformis interna. 

The bronchial " rings " opposite this are necessarily in 



THE RESPIRATORY ORGANS IN SAUROPSIDA. 269 

complete internally, and have llie form of arches embracing 
the outer moiety of the bnjnchus. The second and third of 
these bronchial arcs are freely movable, 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 membrana semiluna- 
ris. 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 tra- 
cheal 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 possessed by birds in general, and are 
usually two pair, passing from the trachea to the furcula and to 
the sternum. Some birds possessing a bronoho-tracheal syrinx 
such as has been described, &s'ihe Alectromorphw, Ghenomorphce 
and Dysporomorphm, 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 
arcs, below. The majority of the Goraconiorphoe, have five or 
six pairs of intrinsic syringeal muscles, which pass from the 
trachna and its tympanum to the movable bronchial arcs. The 
Parrots have no septum, and only three pairs of intrinsic 
musel es. 

T^ie tracheal syrinx occurs only in some American Cora- 
comophce. 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 ligamentous band. 
Thes' rings are excessively delicate, so that this part of the 
trach';a is in great part membranous. 

T<ie hronchial syrinx occurs only in Steatornis, and Gro- 
tophaga. 

I'l the genus Ginyxis, among the Ghelonia, and in some 
species of Grocodilus (C acMiws, e. g.), the trachea is bent 
upon itself. Similar flexures attain an extraordinary develop- 
ment in many birds, and may lie outside the thorax under the 
integument ( Tetrao urogallus, some species of Grax and Pe- 
7ielope) ; 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 furcula 
(the Guinea-fowl). In the Eraeu some of the "rings of the 
trachea are incomplete in front, and bound tlie aperture of an 
air-sac which lies in front of the trachea. Some birds {Apte- 
nodytes Procellaria) have the trachea divided by a longitu- 



270 THE ANATOMY OF VERTEBKATED ANIMALS. 

dinal septum, as in Sjihargis among the Chelonia. The tra- 
cheal tympanum is greatly enlarged in Gephalopterus, 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 being generally the larger. 

" In the OpMdia, the bronchus opens at once into the lung ; 
and the latter is an elongated sac, the walls of -which are pro- 
duced 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 un- 
equal in size, and the left is usually the smaller. Very fre- 
quently, 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 OpMdia, 
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 manv Chamre- 
leons, and in some Geckos, the posterior half of each lung is 
produced into narrow diverticula, which lie among the abdomi- 
nal 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 La- 
certilian. 

The Chelonia have similar lungs ; but while, in the fore- 
going groups, the two lungs are free and invested on all sides 
by the peritonaeum, in this they are fixed against the inner 
periosteum of the carapace, and are covered by peritonajum on 
their ventral face only. This resemblance to the arrange- 
ment of the lungs in birds is increased by the presence of a 
muscular diaphragm, the fibres of which spread over the ven- 
tral faces of the lungs. 

In Aves the lungs are firmly fixed on each side of the ver- 
tebral column, the dorsal surface of each lung being moulded 
to the superjacent vertebrce 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 aponeu- 
rosis upon the ventral surface of the lungs. 

Each bronchus enters its lung nearer the centre than the 
anterior edge ; and, immediately losing its cartilaginous oi 



THE AIR-SACS IN BIRDS. 271 

bony rings, .dilates, and then traverses the lung, gradually 
narrowing, to the posterior edge of that viscus, where it ter- 
minates by opening into the posterior air-sac, which generally 
lies in the abdomen. From the inner side of the bronchus, ca- 
nals are given off, one near its distal end, and others near its 
entrance into the lung, which pass directly to the ventral sur- 
face of the lung, and tliere open into other air-sacs. Of these 
there are four. Two, the anterior and ih& posterior thoracic, 
lit! 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 inter- 
nal and inferior, the interclavicular. This last unites into one 
cavity with its fellow of the opposite 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 surface, 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 tertiary canals ; and thus the whole substance of 
the lung becomes interpenetrated by tubuli, the walls of the 
finest of which are minutely sacculated. The different sys- 
tems of tubuli are placed in communication by perforations in 
their avails. 

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 exten- 
sively ramified system of air-passages, which may extend 
through a great many of the bones, and even give off subcu- 
taneous sacs. Thus the interclavicular air-sac generally 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 vertebral canal of each side, which 
supply the bodies of the cervical vertebras, and communicate 
with elongated air-chambers in the spinal canal itself. When 
the dorsal vertebrfe are pneumatic, they communicate with 
the system of the cervical air-sacs. The abdominal air-sacs 
send prolongations above the kidneys to the sacral vertebrae 
and to the femora, whence these bones, when they are pneu- 
matic, receive their air 



272 THE ANATOMY OF VERTEBRATED ANIMALS. 

The pulmonary air-saos and their prolongations do nol 
communicate with the air-cavities of the skull, which receive 
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 Sauropsida, the ureters open directly into the cloaca, 
which is provided with a urinary bladder in the Lacertilia 
and the Chelonia, but not in other Meptilia, nor in Aves. 

Organs of copulation present themselves under three 
forms : 

1. In the Chelonia, the Crocodilia, and the Ostrich, a sim- 
ple solid penis, grooved upon its posterior aspect, is attached 
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 Rheiclm, Gasuaridae, Aptery- 
gidre, Tbiamomorphce ; Penelope, and Grax, among the Alec- 
toromorphce / 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 tne cloaca. The integument is pro- 
longed inward, on each side, into a blind sac, ^vhich lies upon 
the inferior caudal muscles. The inner 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 
a,perture of the vas deferens. The wall of the blind sac con- 
tains erectile tissue, and it can be erected or retracted by ap- 
propriate muscles. 




CHAPTER Vm. 

rilE CLASSIFICATION AJSD OEGANIZATION OF THE MAMMALIA, 

The class Mammalia is divisible into the following groups : 

A. There are large and distinct coraeoid 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 a 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. — Oenithodelphia. 

1. Monoiremata. 

B. The coraeoid bones are mere processes of the scapula in the adult, and 
lo not articulate with the sternum. 

The ureters open into the bladder ; the genital ducts, into a ure- 
thra 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. 

n. DiDELPHIA. 

2. MarsupiaKa. 

B. The embryo has an allantoic placenta. The vagina is single. 

III. — ^MONODBIPHIA.* 

a. Median incisor teeth are never developed in either jaw. 

3. Edentata. 

b. Median incisor teeth are almost always developed in one or 

both jaws. 



■* The manner in which the MonoielpMa are here subdivided must be re- 
^rded as merely provisional. 



2-74 THE ANATOMY OF VERTEBRATED ANIMALS. 

i. The uteru3 develops no decidua {Non-dedduata). 

4. JJiigidata. 

6. Toxodontia (?).* 

6. Sirevia (?).* 

Y. Ceiacea. 
a. The uterus develops a decidua [Deciduaia). 
u. The placenta is zonary. 

8. Hyracoidea. 

9. Prohoscidea. 

10. Oaryiivora. 

$. The placenta is discoldal. 

11. Rodeniia, 

12. Insedivora. 

13. Cheiroptera. 

14. Primates. 

L The Okmithodblphia are those Mammals which approach 
nearer to the Sauropsida, although separated from them by all 
the essential characters of the Mammalia which have already 
been defined. 

The two genera Echidna and Ornithorhynchus, which con- 
stitute this division, agree with one another, and differ from 
all other Mammals, in the combination of the following char- 
acters : 

In the spinal column, the centra of the vertebrae are devoid 
of epiphyses. The os odo7itoideum, or so-called "odontoid 
process " of the second cervical vertebra remains for a long 
time, if not throughout life, unanchylosed 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 Sauropsidan 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 central por- 
tion 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 ossi- 
fied for a considerable distance ; and these ossifications appear 
b the dry skeleton as bones, which are articulated with the 

* The plaeentaticn of the Toxodontia and Sirenia is unknown. 



THE ORNITHODELPHIA. 275 

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, inasmuch as they have noth- 
ing to do with the marsupium, or pouch, in which the young 
are sheltered in most of the Didelphia. 

In the upper view of the brain the cerebellum is left com- 
pletely uncovered by the cerebral hemispheres. The latter 
are connected by only a very small corpus callosum. The an- 
terior commissure, unlike that of any of the &auropsida, at- 
tains a very great size, and the hippocampal sulcus is pro- 
longed forward 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 Sauropsicla 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 Mammalia, and in these 
only, the ureters do not open into the urinary bladder. Tlie 
testes remain in the abdomen throughout life. The penis is 
attached to the front wall of the cloaca, and is not united 
directly with the ischia. It is traversed by a urethral canal, 
which opens into the cloaca posteriorly, but is not directly con- 
nected with either the seminal or the urinary passages. It is 
probable that, during copulation, the posterior aperture of the 
penial urethra is applied to the anterior aperture of the xao- 
geuital 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 Sauropsida. 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 3. small area of the integument which is not 
raised up into a teat, so that, in the strict etymological sense 
of the word, these animals are not Mam/malia. The mam- 
mary gland is compressed by the panniculus carnosus, and not 
by any prolongation of the crem,aster. 

There is no sufficient evidence of the nature of the foetal 



J 76 THE ANATOMY OF VERTEBRATED ANIMALS. 

appendages ; but the embryo is born in an imperfect condition, 
and may be provided with a knob or caruncle upon the pre- 
maxillse, such as is found in the Sauropsida. 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, Echidita, 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 pro- 
truded. 

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 inflected. 
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 heart is provided with 
two superior cavse. In Echidna the right auriculo-ventricle 
valve is membranous, but, in Orniihorhynchus, it is more or 
less fleshy. 

The hemispheres of the brain are abundantly convoluted 
in Echidna, but are smooth in Ornithorhynchus. The ovaries 
are of equal size in Echidna; but, in Ornithorhynchus, the 
right is much smaller than the left, as in Birds. As has al- 
ready been stated. Echidna is entirely devoid of teeth, while 
Ornithorhynchus has four large horny teeth. 

n. The DiDELPHiA. — In the Didelphia, the " odontoid 
process " early becomes completely anchylosed 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 epicora- 
coid, such as exists in the Ornithodelphia. There is no T- 
shaped interclavicle, but the clavicles, which are always pres- 
ent (except in PerameUs) articulate with the manubrium of 
the sternum, in the same way as in ordinary Mammalia. 
The floors of the acetabula are completely ossified, and consc' 



THE DIDELPHIA. 277 

quen Jy are imperforate in the dry skeleton. The cochlea i3 
coiled upon itself. 

There is a shallow cloaca, the sphincter muscle being com- 
mon 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 
>\ hich traverses the penis, form one continuous canal, which 
opens outward only at the extremity of the penis. 

Ill the female, the vaginal is perfectly distinct from the 
urinary passage. The mouths of the Fallopian tubes are fim- 
briated, and the ova are not larger than those of the Mono- 
delphia. 

The mammary glands are provided with long teats. 

In all the preceding characters the Didelphia agree with 
the Moyiodelphia, and differ from the Ornithodelphia. 

But they agree with the Ornithodelphia, and differ from 
the Monodelphla in possessing either bones or cartilages, at- 
tached to the |)ubes, 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 commissure. The 
hippocampal sulcus is prolonged forward over the corpus cal- 
losum. 

The crura of the corpus cavernosum of the penis are not 
fixed to the ischium. 

The embryo does not become connected with the parent 
by villi developed from the allantois, and it is born in a very 
imperfect condition. 

Certain characters are peculiar to the Didelphia. Thus, 
the testes of the male pass into a scrotum, which is suspended 
in front of the penis. In the female, the cremaster muscle is 
largely developed, and spreads over the surface of the mam- 
mary gland, whicb 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 marsu- 
pial pouch, which is a sort of bag, formed by a fold of the in- 
(egument 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 forward or backward. The mammary glanda 
ie in the dorsal wall of this pouch, into which the teats project 



278 THE ANATOMY OF VERTEBRATED ANIMALS. 

There is no direct comraunication between the female gen- 
erative Orleans 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 rnarsupmm, and each be- 
comes 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 cre- 
master 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 Ce- 
tacea; and thus respiration goes on freely, while the milk 
passes, on each side of the laryngeal cone, into the oesophagus. 

It very commonly happens among the Didelphia that the 
two long vaginse are bent upon themselves, their proximal 
ends becoming applied together and dilated, and these dilated 
portions not unfrequently communicate. Another very gen- 
eral peculiarity of the Didelphia is the inflection of the lower 
margin of the angle of the mandible inward into a strong hori- 
zontal process. In the genus Tarsipes, 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 man- 
dible. 

Many of the cranial sutures, especially in the occipital 
region, persist throughout life; and the squamosal, the united 
poriotic ossifications, and the tympanic bones remain distinct 
from one another. 

The jaws are always provided with true teeth ; and, usual- 
ly, these teeth are readily distinguished into incisors, canines, 
false molars, and true molars. The canines, however, are ab 
sent in some genera, either in both jaws or in the mandible. 
There are usually four true molar teeth, and, as Prof. 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 Phascolonnjs has an 



THE DIDELPHIA. 279 

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 vertebras is almost 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 
Chmiopus the outer digits become rudimentary. 

The fibula is always complete at its distal end. In some 
oasoT it becomes anchylosed with the tibia, while in the 
Wombat (^Phascolomys), the Phalangers [Phaluiicfistida;), 
and the Opossums (Didelphice), it is not only free, but is ca- 
pable of a rotatory movement upon the tibia, similar to the 
movement of pronation and supination of the radius upon the 
ulna in Man. The rotation of the fibula toward the ventral 
side of the tibia is efi'ected by a muscle which, in great meas- 
ure, occupies the place of the interosseous ligament, and is 
analogous to the pronator quadratus in the fore-limb. This 
muscle is antagonized 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 especiall}' carnivorous Marsupials — the Didel- 
phidce, of America, and the Dasyuridm, of the Australian 
province — the second and third digits of the pes are not 
united together by the integument. In the Didelphidoe, the 
hallux is nailless, but large and opposable, so as to convert 
the pee into a prehensile organ like that of many Primates; 
in the Dasyuridm, on the other hand, the liallux is rudimen- 
tary or absent. In all the other marsupials, the second and 
third digits of the pes are syndactyle, or united together by in- 
tegument. In the Wombat, the fourth toe is bound together 
with the other two, and the small hallux is devoid of a nail. 
In the Phalangers, only the second and third toes are syn- 
dactyle, and they are slender, compared with the other digits, 
while the hallux is well developed and opposable. In the 
Peramelidoe (Bandicoots) and Macropodidoe (Kangaroos), the 
metatarsus is much elongated, and the second and third digits 
united and slender, while the fourth toe is very large. The 
hallux is reduced to its metatarsal bone in the Peramelidoe^ 
and the fifth digit is small or rudimentary. In the Kangaroos, 
the hallux disappears altogether, but the fifth digit remains 
well developed, though not so large as the fourth. 



J80 THE ANATOMY OF VERTEBRATED ANIMALS. 

There is a great range of variation in the characters of tb*} 
brain. The carnivorous Marsupials {Didelphys, Basyurus, 
Thylacinus) exhibit the lowest type of cerebral structure, the 
olfactory lobes being very large and completely exposed, 
while the cerebral hemispheres are comparatively 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, Phascolomys). 
In the Kangaroos, it becomes immensely elongated, with 
longitudinal muscular bands and transverse sacculations, so that 
it resembles the human colon. The cfflcum, which is large in 
the Kangaroos, but absent in the Dasyuridoe, is provided, in 
the Wombat, with a vermiform appendix like that of Man. 

The liver always possesses a gall-bladder. There are two 
veniB cavm superiores, and they receive the vence 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 vesiculae seminales, and the glans penis is 
bifurcated in many species. The marsupial pouch is absent in 
some Opossums and Dasyuridce. When it is present, its 
mouth is usually directed forward, but in Thylacinus and in 
some JPeramelidce it looks backward. In Thylacinus also the 
" marsupial bones " remain cartilaginous. The condition of 
the foetus is known only in the Kangaroos, and further observa- 
tions on the embryology of the Didelphia are much needed. 
The foetus is said to possess a large umbilical sac, the vessels 
of which extend on to the plaited chorion ; and a small allan- 
tois ; and to be devoid of a thymus gland. 

The DideljMa are at present confined to the Australian 
and the Austro-Columbian provinces, some few species stretch- 
ing beyond the borders of the latter into the northern parts of 
North America. The Didelphidm alone are found in Austro- 
Columbia, all the other groups being Australian. 

Gigantic, Kangaroo-like, or Phalangistic, forms {N'otothe' 
rium, Diprotodon, Thylacoleo), have been found in post-ter- 
tiary deposits and oaves in Australia. In Europe, Diddphidce 
occur in Eocene strata ; Itidelphidm, Dasyuridm, and Macro- 
podidm {Phascolotherium, Amphitherium^ Plagiaulax), in 
middle Mesozoic rocks ; and Macropodidm (?) (Microlestes) in 
the Trias. 



THE MONODELPHIA. 281 

m. The MoNODELPHiA. — 111 the Monodelphia, the os 
odontoideum very soon becomes anchylosed with the second 
cervical vertebra, of which it appears merely as the odontoid 
process ; and the cervical ribs early become inseparably united 
with their vertebras. The coracoid is reduced to a mere pro- 
cess 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 cora- 
coid, with the sternum, and not with any interclavicle. The 
acetabula are imperforate. The pelvis is devoid of marsupial 
bones ; though, in some Garnivora, 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 Edentata very closely approaching those of the 
Didelphia in respect of the corpus callosum and anterior com- 
missure; while, as regards the hemispheres themselves, they 
may either be so small as to allow the cerebellum to be com- 
pletely exposed on the dorsal aspect, or so large as com- 
pletely to cover it and project beyond it. The external sur- 
face 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 throi;ghout life, or may 
pass into a scrotal pouch. But, when this scrotum forms a 
distinct sac, it lies at the sides of, or beliind, the penis, and 
not in front of it. The cystic urethra is always continuous 
with that part of the urethra which travel ses the penis. 

The ova are small, and the mouths of the Fallopian tubes 
are fimbriated. The vagina is a single tulie, which may, how- 
ever, be partially divided by a longitudinal partition. The 
eremaster 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 and deciduata. 

In the non-deciduala tlie foetal villi of the placenta are, al 



282 THE ANATOMY OF VERTEBRATED ANIMALS. 

birth, simply withdrawn from the uterine fosste, 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 pla- 
centa. 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 foetus ; and, at 
birth, this decidual and maternal part of the placenta is thrown 
off along with the foetus, the mucous membrane of the uterus 
of the parent being regenerated during, and after, each preg- 
nancy. 

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 placentation 
of which is unknown. The other is the ill-defined and hetero- 
geneous assemblage called Edentata. Some of the members 
of this group certainly possess deciduate placentEe, while, in 
others, it appears questionable whether the decidua is, or is 
not, developed. And, as this group, the Ii!dentat<t, 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 EDE^TATA, or Brtjta.- — In these Mammals the teeth 
are by no means always wantirg, 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 in* 
cisors 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 Arma- 
dillos. The ungual phalanges of the digits support long and 
strong claws. 

There are mammas upon the thorax, and sometimes, in ad- 
dition, on the integument of the abdomen ; or, in the inguinal 
region. 

The brain varies greatl}', its hemispheres being sometimes 
quite smooth, with a very small corpus callosum and large an- 
terior commissure ; while, in other cases, the corpus callosum 
is much larger, and convolutions appear upon the surface of 
the brain. 

The Edentata are divided into the Phytophaga, or vege- 
table-feeders, and the Entoniophuga, or insect-eating forms. 



THE EDENTATA PHYTOPHi^GA. 283 

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 medul- 
lary 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 anchylose and form one. The 
ischia become united with the anterior caudal vertebree, and 
these anchylose 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, resting 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 confined to 
the great forests of South America, where they lead a purely 
arboreal life, suspended by their strong, hooklike, 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 be- 
ing longer than the posterior pair. In both the fore-and the 
hind-limbs the internal and the external digits are rudimen- 
tary, but the hind-foot always has the three middle toes com- 
pletely developed ; while, in the fore-foot, it sometimes hap- 
pens that only two remain. The ungual phalanges are very 
long and hooked. 

The zygomatic arch is incomplete posteriorly, not being 
united by bone with the squamosal. The cervical vertebrae 
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, vertebrte in the neck. 

The pelvis is exceedingly spacious, and the acetabula are 
directed backward as well as outward. The femur is devoid 
of a ligamentum, teres. The distal end of the fibula sends in- 
ward a process which fits into a fossa situated upon the outer 
surface of the astragalus, giving rise to that kind of peg-and- 
Bocket ankle-joint which is peculiar to these animals. 

A good deal of confusion prevails respecting the structure 
of the ankle-joint in the Sloths. Ouvier (" Ossemens fossiles," 
L viii., p. 143) writes of the Ai, or three-toed Sloth : 



284 THE ANATOMY OF VERTEBRATED ANIMALS. 

" In the greater number of animals, the principal articu- 
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 ex- 
tremity of the fibula penetrates, like a pivot. {See PI. 308, 
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 arrangement is that the fool 
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 bj' spreading out the leg so as to make it almost hori- 
zontal." 

Meckle f has already justly remonstrated against Cuvier'a 
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 fol- 
lows Meckel, but Rapp (" Edentaten," p. 46) adopts Cuvier's 
statement in its fulness : " Extension and flexion of the foot 
caimot take place, but only abduction and adductior,." How- 
ever, 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 : first, in abduction and adduction ; a move- 
ment in azimuth, when the leg is vertical; secondly, in flexion 
and extension ; a more extensive movement in altitude, un 
der the same circumstances ; and, thirdly, 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- 
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 inward and upward, while the other looks outward and 
upward. The former, convex from before backward, as well 
as from side to side, is by no means a mere rim, though it is 

* Cuvier's words are : " II en r^sulto encore que le plan, le corps du pied^ 
est presque vertical quaTid la jambe Test." 

f " System der vergleichenden Anatomie," 2te Theil., 2te Abtheilung, 
p. 467. 



THE ANKLE-JOINT OF THE SLOTHS. 285 

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 re- 
ceived a correspondingly conical process of the distal end of 
the fibula, which is directed from above and without, down- 
ward and inward — not verticallj-, therefore, but very oblique- 
ly. Hence, even if the pivot fitted its socket quite accurately, 
there would still be abundant opportunity for flexion and ex- 
tension, though the movement of the pes would be obliquely 
inward, as well as upward, in the former case ; and obliquely 
outward, as well as downward, 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 ex- 
ternal 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 calcaneum, cu- 
boides, naviculare, the three cuneiformia, the three complete 
and the three rudimentary metatarsals, and the three basal 
phalanges of digits ii., Hi., and «"«., are anchylosed together 
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 mov- 
able upon one another are : 1. The distal phalanges, which 
have a movement of extension and flexion through 180° upon 
the middle phalanges. 3. 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 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, however, 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 efiicient antagonists ; so that their tonic contraction 
must pull the navicular metatarsal tuberosity, into which they 
are inserted, as far upward as it will go, causing the tarso-pha- 
langeal synostosis to rotate upon the astragalus, and thus 
obliging the sole of the foot to look inward. 

In the two-toed Sloth, or Unau ( Cholmpus), the general 
structure of the ankle-joint is the same, but the fossa of the 



286 THE ANATOMY OF VERTEBRATED ANIMALS. 

astragalus looks almost directly outward, and the pivot of the 
fibula is more nearly horizontal, when the leg is vertical. The 
tibial facet of the astragalus looks directly upward. Hence, 
the movement of the pes is more exclusively one of flexion 
and extension than in the Ai. No anchylosis 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 calcane< 
um is twisted round under the astragalus, in such a mannei 
tliat its proper external face becomes inferior, while the articu- 
lar surface for the cuboid is not only below, but is partiall}' 
internal to, the navicular facet of the astragalus. As a 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 vertical. 

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 contrary, it 
results, in the Unau, from the manner in which the calcaneum 
and naviculare articulate with the astragalus ; and, in the Ai, 
from the action of the muscles on the tarso-phalangeal synos- 
tosis. Neither in the Ai, nor the Unau, is there any thing to 
interfere with free flexion and extension of the pes. 

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, like 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 artic- 
ular surfaces of the dorsal vertebrae 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 devoid of any fossa upon its outer 
\ surface. But another kind of peg-and-socket ankle-joint is 
produced by the interlocking of the surfaces of the tibia and 
of the astragalus. 

The great extinct animals. Megatherium., 3Iylodon, Mega- 
lonyx, etc., the remains of which have been found almost wholly 
in later tertiary deposits of America, belong to this group. 



THE EDENTATA ENTOMOPHAGA. 287 

2. The Entomophaga. — In this group of Edentata the 
zygoma sends down no process from its lateral region, al- 
though, 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 TubuUdentata, and 
d. the Iioricata. 

a. The group of the Mutica contains the genera Myrme- 
cophaga and Oyclothurus, 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- 
maxilliB 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 
bullae, 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 pro- 
longed, 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, coroncid process, and angle 
of the jaw, being obsolete. The articular surface of the con- 
dyle is flat. The hyoid is placed far back beneath the posterioi 
cervical vertebrse, and is connected with the skull only by 
muscles. The thyroid and the cricoid cartilages are ossified. 
The dorso-lumbar vertebrae are complicated by the presence 
of accessory articular processes. Well-developed clavicles are 
present in the climbing Cyclothurus 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 
edo-e, 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 hyoid by the ordinary hyo-glossus mus- 
cles ; but long muscles, which are attached to the sternum 
(sternoglossi), retract it, while it is protracted by the genio- 
glossi and stylo-hyoidei. 



288 THE ANATOMY OF VERTEBRATED ANIMALS. 

Immense submaxillary glands extend back over the thorax, 
and cover the tongue with a viscid secretion, when it is thrust- 
into the nests of the ants, upon which the Myrmecophaga 
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 muscular as to be comparable to 
a gizzard. The brain presents numerous convolutions, and 
has a large corpus callosura. 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 Myrmecophaga dklactyla. 

h. The group of the Squamata contains the single genu? 
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 elon- 
gated and extend backward beyond the bullate tympanic 
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 in communication 
with the other and extind 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. 

c. The Tubuiidentata are also represented only bj' a single 
genus, Orycterop>us, 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 m-ainly 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 pentadaotyle. 



THE EDENTATA LORICATA. 289 

The skull has a complete zygoma and well-developed pre- 
inaxillas. 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 pro- 
portions in the Sauropsida. The mandible has an ascending 
ramus. The clavicules 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 j.*, but the small anterior ones 
fall out, reducing them to ~^. The hindermost, and the small 
anterior ones, are simple cylinders, but the middle teeth pre- 
sent 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 cascum. 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 ossi- 
fications, 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 
armor of one of these animals presents five distinct shields, 
the edges of which permit of a certain amount of motion be- 
tween 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 tree and movable segments, 
covers the posterior dorsal and lumbar region, as the thoraco- 
abdominal shield; and the fifth, tYie pelvic, is attached by its 
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 premaxillee 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 

13 



200 THE ANATOMY OF VEETEBRATED ANIMALS. 

the ground evenly, and indeed the hind-limbs are usually 
plantigrade, or nearly so ; but, in the singular genus Tol]/- 
peutes, the fore- foot is supported upon the extremities of tlie 
long nails. The pollex is always present in the fore-foot, but 
the fifth digit sometimes becomes rudimentary. There are 
always five toes in the hind-foot. 

In the genus JSiiphractes, each premaxilla contains a single 
tooth, which, consequently, is an incisor. 

This group contains two divisions, the Dasypodidm and 
the QlyptodontidcB ; both are South American, but the former 
is chiefly composed of living animals, while the latter only 
contains an extinct genus.. 

The DasypodidoB 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, thir- 
teen, transverse movable zones of scutes. 

In the skull, the ends of the nasal bones project beyond 
the level of the premaxilte, so that the nasal aperture looks 
more or less downward. The premaxillas have a considerable 
size, and articulate largely with the nasals. The anterior part 
of the jugal arch offers, at most, a rudimentary downward pro- 
longation. The mandibular symphysis has but a moderate 
length, and the posterior alveoli of the mandibles do not ex- 
tend 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. 

The odontoid A'ertebra is anchylosed with a greater or 
smaller number of its successors. The cervical vertebrae 
which follow these have peculiar accessory articular surfaces ; 
and the hinder dorsal and the lumbar vertebras are also pro- 
vided with accessory articular facets and processes. A number 
of the anterior caudal vertebrae are always anchylosed with one 
another, and with the true sacrals, to form the long sacrum ; 
and the transverse processes of some of these caudal vertebra3 
abut against the inner surfaces of the ischia, and become an- 
chylosed therewith. 

The first rib is broad and flattened, and the anterior piece 
of the sternum is expanded. The succeeding vertebral ribs 
arc 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- 



THE EDENTATA LOEICATA. 291 

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 Glyptodontidoe contains the single 
genus Gly2?todon, 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 Y^ertebrata. 

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 mar- 
gin of scutes with raised conical surfaces. 

The nasal bones are short and broad, and their free ends 
do not project so far as the preraaxilte ; whence the anterior 
nasal aperture looks slightly upward as well as forward. The 
premaxillae, however, are very small bones, and, if they unite 
with the nasals at all, do so for a very short distance. The an- 
terior portion of the jugal arch gives oil a great downward pro- 
cess. The mandibular symphysis is very long, and the posterior 
alveoli of the mandible are situated upon the inner face of the 
very high perpendicular part of the ramus. The teeth are 
trilobed, two deep grooves excavating their inner and their 
outer surfaces. And, as the crowns of those of each jaw arc 
placed opposite each other, they are worn flat. 

The last cervical and the anterior dorsal vertebras are 
anchylosed together into a single " tri-vertebral " bone which 
moves by a hinge-joint upon the third dorsal. This and the 
succeeding dorso-lumbar vertebriE are immovably united, and, 
for the most part, anchylosed, 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 columnar. 

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-condj'loid 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 phalangea 
are comparatively short and truncated. 



292 THE ANATOMY OF VEETEBRATED ANIMALS. 

The Non-dbciduatb Mamjialia. — I. Ungulata. — A large 
number of the non-deciduate Mammalia are oonveniently com- 
prehended 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 a<ioumulated 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. 

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 ung aligra'le. Some few, however, rest the weight of 
the body upon the under surfaces of the phalanges, or are 
digitignid:': The metacarpal and metatarsal bones are elon- 
gated, and take a vertical, or much inclined position. 

In the female, the mammae are either few in number, when 
they are inguinal in position ; or numerous, when they are dis- 
posed in two rows along the abdomen. 

The intestiie is very generally provided with a caecum 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 clown with the increase of our 
knowledge of fossil forms. 

1. In the Perissodactyla, the number of the dorso-lumbar 
vertebrae 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 astr.igalus are very unequal; the less articulating with 
the cuboid bone. 

* Or at least very nearly so. 



THE PERISSODACTYLA. 



2Q3 



In the skull, the tympanic bone is small ; and, as in sun- 
dry other Mammals, the root of the pterj'goid 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 cascum exceedingly 
large. 

The teats are inguinal, or situated in the groin. When 
the head is provided with horny appendages, they are entire 
ly epidermal and devoid of a bony core ; and they are placed 
in the middle line of the skull. 



mfh 




i%f 



Fio. 93.— A, Front aspect of the left tarsus of a Horse.— 1. Calcanenm. 2. Astnigalus. B. 

Naviculare. 4. Ectocuneiform. 5. Caboides. 
B, Posterior aspect of the left metatarsus of a Horse.— 1. The metatarsal of the third dlfflt 

2, 3. The metatarsals of the rudimentaiy digits. 

The Perissodactyla consist of the existing families Equid(B^ 
Rhinoeerotidm, and Tapiridm, and of the extinct Falmoih& 
rldce and Macrauchenidce. 



294 THE ANATOMY OF VERTEBRATED ANIMALS. 




Pig. 94.— a, rijrM fore-foot of a Horse.— 1. Radius. 2. Groove In the front fa«e of the radl- 
UB. 3. Scaphuifles. 4. Lunare. 5. CuDeilbrme. 6. Pisiforme. 7. Magnum, 8. Un» 

ciforme. 9. Meticarpale, Hi. 10. Metacarpale, iv. 11. Sesamoid bones in the liga- 
ments at the back of the motacarpo-phalangeal artlcnlation. 12. Proximal phfilanx (fet- 
ter-bone). 13. Widdle phalanx (coronarj^). 15. Distal phalanx (coffin-bone). 14. Sesa- 
moid bono in the tendon of i\\Q Jiexar per f oralis (called " navicular " by Veterina- 
rian a). 
tf, left h'ud-foot of a ITnrse.— 1. Tibia. 2. Calcaneum. S. Astragahis. 4. Cuboid. 5. Na- 
vicular, or scaphoid. I'l Eeloeuneiform. T. Metatarsals sti. S. Metatai-sale, in. 9, 11, 
12. Phalanges. 10, 14. i^e^.uuoids. 



THE PERISSODACTTLA. 295 

a. The Equidce, or Horses and Asses, have one toe on 
each foot — the third — much longer and larger than the rest. 
The latter are represented only by their metacarpal or meta- 
tarsal bones, the inner and outer toes being absent, or repre- 
sented by mere ossicles (as rudiments of their metacarpals or 
metatarsals) in all existing JEquidce. But, in the extinct Sip- 
2?arion, the second and fourth digits were complete, though 
small and like dew-claws ; while the miocene Atic/iitherium, 
which most nearly approaches the Palmotheridm, has the lat- 
eral toes much larger, and taking their share in supporting 
the weight of the body. 

The dental formula is i. |^' c. \^^ p.m. ~ m. 3-4^. 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 bicrescen- 
tic in transverse section ; and two inner ridges, which are 
curved more or less inward and backward, and correspond re- 
spectively with the anterior and the posterior crescents of the 
outer wall. The valleys may be more or less completely filled 
up with cement, which also coats the tooth. The incisors are 
similar in form in each jaw, and in Equus and Hlpparion their 
crowns present a wide and deep median cavitj', formed by a 
fold of the enamel. 

These are the distinctive characters of the JEquidce. It 
may be useful to add some special details respecting the anat- 
omy of the Horse as a familiar example of the perissodactyle 
group. 

The Horse has seven cervical vertebrae, twenty-four dorso- 
lumbar (eighteen or nineteen of which are dorsal), five sacral, 
and about seventeen caudal vertebrse. The atlas has very 




Fia. 95.— A cerrlcal vertetra of a Horse.— 1. The rudimentary spine. 2, 3. Tie pre- and 
posi^zygapopLyses. 5. The convex anterior face of the centrum. 9. Its concave pos- 
terior face. 6, T. The transverse processes and rudimentary ribs. 



290 



THE ANATOJTY OF TERTEBRATED ANIMALS. 



wide lateral processes, the faces of which look obliquely down- 
ward and forward, and upward and backward. The centra 
of the other cervical vertebra are much elongated, strongly 
convex in front, and correspondingly concave behind. The 
neural spines are obsolete in all but the seventh. Tlie liga- 
'iiicntwn nuchce is a great sheet of elastic tissue, which extends 
from the spines of the anterior dorsal vertebrje to the occiput, 
iind is fixed, below, into the neural arches of the cervical ver> 
tebra;. 

In the dorsal region, the opisthocoelous character of the 
centra of the vertebrse gradually diminishes, though the ante- 




THE IIOESE. 29V 

rior face of the centrum of the last lumbar is still distinctly 
convex. The spines of these vertebras increase in length to 
the fourth or fifth. The spine of the sixteenth is vertical, 
those in front inclining backward, and those behind a little 
forward. 

In none of these vertebrae do the prezygapophyses bend 
round the postzygapophyses of the vertebra in front, as is 
often the case in the Artiodactyla. The transverse processes 
of the penultimate, and of the last, lumbar vertebras present 
concave facets upon their posterior margins, which articulate 
with convex facets developed upon the anterior margins of 
the last lumbar and first sacral vertebrse respectively. 

In the skull, the plane of the supra-occipital is inclined 
upward and forward, and gives rise to the middle part of a 
transverse ridge which is continued at the sides into the squa- 
mosal. The ridges which limit the origins of the temporal 
muscles above, unite in the middle line posteriorly, and thus 
produce a low sagittal crest. The orbit is bounded behind by 
the united post-orbital 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 prsenasal bone. The posterior margin of the palate is 
opposite the penultimate molar tooth. TTie glenoidal surface 
is transversely elongated and convex from before backward. 

The tympanic bulla is not very large, and is rugose inferi- 
orly. It is not anchylosed with the surrounding bones. The 
post-tympanic process of the squamosal does not approach 
the post-glenoidal 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-oc- 
cipital. 

The rami of the mandible are anchylosed at the symphysis. 
The perpendicular part of each ramus is long, the condyle 
transverse and convex from before backward, 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 preeminent 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 
Tentral surface and sides, and thus produces a hoof. 



298 



THE ANATOMY OF YEETEBRATED ANIJIALS. 



The animal is supported by these greatly-developecl nails, 
aad hence is said to be unguligrade. The long axis of its 
phalanges are greatly inclined to the surface upon which it 
stands, while those of the metacarpals and metatarsals are per- 
pendicular 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." Tbo 




Fl6. !)7 --Longitudinal median section of the foot of a Ilorso. — 13, 14, 18. The three pha* 
Lmg^s. 16. The navicular sesamoid. 5. The flexor perforatus. C. Tho flexor perforaiUt 
19. Th.« hoof. 



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 forearm is fixed in the prone position. The arm 
and thigh are closely applied to the sides of the body and en- 
closed in the common integument, so as to be capable of very 
little proper motion. At the same time, the axis of the hu- 
merus is inclined obliquely backward and downward, at right 
angles with the long axis of the scapula ; and that of the 
femur obliquely forward and downward at right angles with 
Lhat of the os innominatum ; and the long axes of both these 



THE HORSE. 



299 



bones make a great angle with those of the forearm and leg 
respectively. Each 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 
scapulae. 

The scapula is long and narrow ; 
the low spine has no acromion ; the 
coracoid process is small, and there is 
iio clavicle. 

The head of the humerus looks 
backward, and the distal articular sur- 
face of the bone is completely gingly- 
moid. The two bones of the antibra- 
chium are anchylosed ; the shaft of the 
ulna becomes exceedingly slender, and 
its small distal end is distinguishable 
only with difficulty. The articular sur- 
face for the carpal bones is, therefore, ' 
almost wholly furnished by the radius. 
There are seven carpal bones, the tra- 
pezium being obsolete. A line pro- 
longing the axis of the third metacar- 
pal and that of the os magnum does 
not pass through that of the lunar e, 
but corresponds more nearly with the 
junction between scaphoides and 
lunare. 

The pollex and the fifth digit are Fig. 98.— Front view of the right 

suppressed, or represented only by mi- S' °\'l^Z\':"6t 
nute nodules of bone, and the only phsides. 4. pisiforme. 5. un- 
complete digit is the third ; the sec- 
ond and the fourth being represented 
only by the splint-like metacarpal bones. The third meta- 
carpal, which is somewhat flattened from before backward, is 
nearly symmetrical in itself. Careful observation, however, 
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 sesamoid 
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. 




ciforme. C. Magnum. 7. Ti-a- 



300 THE ANATOMY OF VERTEBRATED ANIMALS. 

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. 




Fto. 99. — The OBsa innominata of a Tlorse viewed from the left side and behind.— 1. The 
crest of the ilium. 2. The surface by which it articulates with the sacrum. 4. The 
acetabulum. 6. The ischium. 

The femur has a lar^'c third trochanter (°, Fig. 100), into 
which the glutceus tiiaxunus is inserted. Its head presents a 
deep pit for the round ligament, and there is a peculiar and 
very characteristic fossa ('") on the inner and posterior face of 
the distal moiety of the bone. 

The proximal end of the fibula is reduced to a mere rudi- 
ment ; its shaft is not represented by bone ; and its distal end 
is anchylosed with the tibia, and has the appearance of being 
an external malleolar process of that bone. The distal end 
of the tibia presents two deep, obliquely-directed concavities, 
which correspond with the convexities of the astragalus. 

There are six or seven tarsal bones, according as the ento- 
and meso-cuneiform bones remain distinct or become anchy- 
losed. The astragalus (Fig. 93 A, 94 B) is extremely charac- 
teristic. It presents two convex ridges separated by a deep 
fossa, and directed obliquely from behind and within, forward 
and outward, to the tibia ; and it has a nearly flat distal face, 



THE MUSCLES OF THE HORSE. 



301 



not borne upon any distinct neck, whicli articulates almost 
wholly with the naviculare, presenting only a very small facet 
to the cuboid. 

The naviculare and the ecto-cunei- 
forra are peculiarly broad and flattened 
in form (Fig. 93 A, 94 B). 

The metatarsus and digits repeat the 
arrangements of the fore-limb ; but the 
principal metatarsal is more slender in 
its proportions, and is flattened from 
side to side rather than from before back- 
ward (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 soapulce (which really form one 
muscle), together with a sterno-soapur 
laris, form the great sling already men- 
tioned, 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 ex- 
tensors, are well developed. The supra- ' 
and infraspinatus are large. There is 
a great cephalo-humeralis, answering to 
the clavicular 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 mus- 
cles are very large, as are the flexors and extensors of the 
antibrachium. 

The supinators and pronators are wanting ; but there ia 
a distict extensor ininimi digiti, the tendon of which unites 
with that of the extensor communis. Radial and ulnar ex- 




Fro. 100.— A, Left femur of a 
Horse, posterior vr-mt. — 

I. Head. 2. Great tio- 
chanter. 3. Thii-d tio- 
chanter. 4. Lesser tro- 
chanter. 5. Pit for round 
ligament. 10. Fossa. 

II. Condyles. 



302 THE ANATOMY OF VEETEBRATED ANIMALS. 

tensors of the carpus are also present. 'Y\i.e, flexor ■perforatu& 
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 intorossei of the third digit are represented only by 
the ligaments which connect the greater sesamoid bones with 
the metacarpal, and in which a few muscular fibres are some- 
times found. There are said to be two others, one for each 
lateral metacarpal, and a lumhricalis. 

In the hind-limb, the femoral muscles are in the Horse 
the same as in Man, but enormously developed. There is 
no tibialis anticus, peronceus longris, 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 ex- 
tensor brevis. 

The flexor hallucis smA. 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 
lylantaris, which passes over a pulley furnished by the cal- 
caneum. 

The deciduous or milk dentition of the Horse has the fol- 
lowing formula : d.i. 1^^ d.c. J^ d.m. \~^. It is complete at birth, 
with the exception of the outer incisors, which appear before 
the foal is nine months old. The incisors have the same struct- 
ure as in the adult. The canines and first deciduous 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 backward, two con- 
cave surfaces separated by a vertical ridge. From the anterior 
end, and from the middle, of this outer wall, two laminae of 
the crown pass inward and backward, so as to be convex in- 
ward and concave outward, and thus to include two spaces 
between themselves and the outer wall. From the inner sur- 
face of the hinder part of each of these crescentic laminse a 
vertical pillar is developed, and the inner surface of the pillar 
is grooved vertically. The outer wall, the laminje, and the 
pillars, are all formed of dentine and enamel, thickly coated 
with cement. The attrition which takes place during mastica- 
tion 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 



THE TEETH OF THE HOUSE. 303 

eacb, 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 other, and with 
their concavities turned outward which arise from the wear 
of the wall; internal to these, of two other crescents, partly 
transverse in direction, and connected by their anterior ends 
with the wall, which arise from the wear of the laminse ; 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 re- 
sulting pattern are quite different. The outer wall presents 
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, necessarily, two 
crescents, the concavities of which are turned inward. A 
vertical pillar, longitudinally grooved on its inner face, is de- 
veloped 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 ap- 
pears in connection with the inner face of the posterior end 
of the outer wall. 

Thus the grinding surface of the upper molars may be rep- 
resented 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 outward ; the lower concave 
inward; and by this arrangement, together with the unequal 
wear of the dentine, enamel, and cement, a permanently un- 
even triturating surface is secured. 

As is the general rule among Mammals, the first permanent 
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 maintained for a long time, and 
furnishes a very useful means of distinguishing the last pre- 
molar from the first molar in the adult, when, as in the Horse, 
the premolars and molars are very similar. 

The first deciduous molar usually falls out when the first 
premolar appears, and is not replaced ; but it is occasionally 
retained. AH the other milk-teeth have successors, and there 



501 THE ANATOMY OF YERTEBRATED ANIMALS. 

are three permanent molars. Consequently the dental formula 
of the adult Horse is 

.3-3 1—1 3-3 3'3 .„ 

«• VI c. '[^zfpm- 3^3 m. 5T-3 = 40. 

The permanent canines are the last teeth to be fully de- 
veloped, and, in the mare, they do not often make their appear- 
ance. 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 diccstema, 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 produced. 
As the incisors wear down, the mark changes its form in con- 
sequence 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 indica- 
tion of age. The structure and patterns of the grinding sur- 
faces of the permanent molars are essentially the same as those 
of the milk-molars ; but the enamel becomes more or less 
jDlaited ; 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 succeeds it. 

Tiie 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 distin- 
guished by the dense epithelium which lines the inner surface 
of the former. 

The CcBoum is enormous, having fully twice the volume of 
the stomach. There is no gall-bladder. A cartilage is de- 
veloped in the septum of the heart. There is no 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 ex 
tremities, 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 



THE VISCERA OF THE HORSE. 305 

presents corpora trapezoidea. The flocculi do not project at 
the sides of the cerebellum, and the vermis and lobes of the 
cerebellum are unsymmetrically convoluted. The cerebral 
hemispheres are elongated and suboylindrical, 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 protuberance) and the region which answers 
to the insula are not hidden by the overlapping of the con- 
volutions in the lateral aspect of the brain. The Sylvian fis- 
sure is indicated. The corpus callosum is large, and the an- 
terior commissure 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 unguinal canal re- 
mains permanently open. 

The prostate is single. Cowper's glands are present, and 
there is a large uterus masculinus. The large penis is shel- 
tered 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 foetus 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. 

The existing Equidae, are naturally restricted to Europe, 
Asia, and Africa ; and are distinguished into the Horses, 
which have homy 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-lirabs. 

Fossil remains oi EquidoR sx& abundant in the later ter- 
tiary deposits of Europe, Asia, and the Americas ; but tlie 
group is not known to be represented earlier than the miocene, 
or later eocene, epoch. 

The EquidoB are among the very few groups of Mammalia, 
the geological history of which is sufficiently well known, to 
j)rove that the existing forms have resulted from the gradual 
modification of very different ancestral types. The skeleton 
of the older pliocene and newer miocene Mippnrion very 
closely resembles that of an Ass, or a moderate-sized Horse. 
There is a curious depression on the face in front of the orbit, 



306 THE ANATOMY OF "VERTEBRATED ANIMALS. 

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 through- 
out its whole length although firmly anchylosed with the 
radius. The distal end of the fibula is so completely anchy- 
losed with the tibia, that, as in the Horse, it is difficult to 
discern any trace of the primitive 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 
tho tooth becomes a detached pillar. The smaller plications 
of the enamel are also more numerous, close-set, and compli- 
cated. On the outer face of the lower milk-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 proportion 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 Sipparion, and is 
less closely united with the radius. T]je 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, however, the middle of the 
shaft seems to have been incompletely ossified. Not only are 
there three toes in each foot, as in Ilipparion, 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 
AnrJi.itlicrlum is just such a step bej'ond the Mipparion, as 
the Hippurion 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, 



HIPPAKION AND ANCHITHERIUM. 307 

and their crowns lack tbe peculiar pit which characterizea 
those of JEquus and Bipparlon. The first grinder is propor- 
tionately 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 enlargements of the 
ridges, while in the lower jaw these pillars have almost disap- 
peared. 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 Equidae. 

In all those respects in which Anchitherium daparts from 
the modern Equine type, it approaches that of the extinct 
PaloBOtheria / and this is so much the case that Cuvier con- 
sidered the remains of the Anohitherium with which he was 
acquainted to be those of a species of Palceotherium. 

b. In the Rhinocerotidce the second, third, and fourth toes 
are nearly equally developed in both the fore- and the hind- 
feet. 

The dental formula is i. ^ or i. —^ c. ^^p.m. i^ ni. |,|. 

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 diBFer greatly in form from 
those which are situated in the lower jaw ; and, in some spe- 
cies, 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 be converted into a jointed 
armor ; 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 agglomer- 
ation of a great number of hair-like shafts. 

The distal phalanges of the tridactyle feet of the Rhinoce- 
ros 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 dorso-lumbar vertebra; are twenty-two or twenty-three, 
of which twenty are dorsal. There are four sacral and twen- 
ty-two caudal. The cervical vertebras, as in the Horse, are 
strongly opisthocoelous, and the transverse processes of the 



308 THE ANATOMY OF VERTEBRATED ANIMALS. 

last lumbar articulate witli 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 which 
the orbit and temporal fossa form one cavity. The nasals are 
immense, and are separated from the premaxillse by a wide 
extent of the maxilla on each side. The premaxillse are rela- 
tively small and reduced to little more than their palatine por- 
tions. 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-tym- 
panic or the paramastoid. It unites vnth the post-tympanic 
to form a kind of false auditory meatus, in the absence of any 
proper ossified canal of that kind. The periotio and the tym- 
panic bones are anchylosed, the tympanic being a mere irreg- 
ular hoop of bone. The 2:>ars niastoidea is completely hidden 
by the junction of the short post-tj'mpanic with the long par 
amastoid. 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 coronoid 
process ascends slightly above the condyle. In a vertical and 
longitudinal section of the skull, the form of the cerebral cav- 
ity 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 anchylosed. 

The carpus has the eight ordinary bones. In the manus 
the digits ii., iii., iv.,are complete, and a bony tubercle articu- 
lated with the outer facet of the cuneiforme represents 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 tro- 
chanter. The tibia and the fibula are complete, and 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. 



THE RHINOCEROT. 309 

In some s-peoies. oi Hhinoceros there are |^ incisors in tlie 
milk detention, and ^—^ or {^ incisors in the permanent denti- 
tion. 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 laminoe of the upper 
molars take a much more transverse direction ; the laminas 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 laminsB. 

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 
csecum 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, vesiculas 
seminales, and Cowper's glands, are present. The long penis 
has a mushroom-shaped glans, and the animal is retromingent. 
The cornua uteri are proportionately longer than in the mare. 
The teats are two and inguinal in position. The characters 
of the fcetal 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, inhabited Europe 
and Asia during the cold of the glacial epoch., R. incisiviis 
had four digits in the manus, and larger incisor teeth than any 



310 THE ANATOMY OF VERTEBRATED ANIMALS. 

existing species. H. hexaprotodon had more numerous iiKjis- 
ors than any other species. 

c. In the Tapiridce there are four toes on the front-foot, 
though the ulnar digit does not reach the ground. The bind- 
foot has three toes. 

The dental formula is i. ^-rj c. j-[ p.m. —^ ra. j-rj. 

The molar teeth each present two 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 dorso-lumbar 
vertebrae, of which nineteen or twenty are usually dorsal. 
The centra of these vertebrae, 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 vertebra. The skull is partly Rhinocerotio, 
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 paramastolds, 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 Rhino- 
cerotio. 

Thus the tympanic is quite rudimentary; the post-glenoid- 
al process is larger than in the Horse ; the orbit is not sepa- 
rated from the temporal fossa ; the nasals are widely sepa- 
rated from the premaxillae ; the premaxilla3 are very small, and 
are early anchylosed. 

Tlie 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- backward with a convex edge in 
a remarkable 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 one another. 
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 manifested by the fact 
that the third is longest, and symmetrical in itself, while the 
others are asymmetrical. The femur has a strong third tro- 
chanter ; the fibula is complete ; the astragalus more Rhino- 
cerotio than Equine. There is no trace of a hallux, but the 



THE TAPIEID^. 311 

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 approximated to the incisors 
than in the Horse, especially in the lower jaw, and, conse- 
quently, the diastema is verj' 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 slightly-marked concavities (in the maxillary teeth) 
or convexities (in the mandibular teeth) on its outer face. 
From this two ridge-like laminae run inward and a little back- 
ward across the crown of the tooth. The valleys are broad 
and shallow, and the coat of cement very thin. The molar 
tooth of the Tapir thus represents the plan of structure com- 
mon to the Ferissodactyle in its simplest form. Deepen the 
valleys, increase the curvature of the wall and lamina, 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 an- 
terior moiety of the crown is incompletely developed. In the 
anterior lower premolar the anterior basal process, which ex- 
ists in all the molars, is excessively developed, so that the 
crown of the tooth assumes the bicrescentic pattern of the 
Rhinoceros's lower grinder. This probably indicates the man- 
ner 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 pjdorio 
orifices being closely approximated. The caecum is proportion- 
ally 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 antei-ior, 
and the aorta divides into an anterior and a posterior trunk. 
There is no third bronchus. No distinct scrotum is present 
There are vesiculfe 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 of Tapir at present living 



312 THE ANATOMY OF VEETEBKATED ANIMALS. 

in South America and one in Southwest China, Malacca, and 
Sumatra. The genus Taplrus has been found fossil in Europe 
in rocks of miocene age. The closely-allied extinct genera 
Lophiodon (and Coryphodonf) carry the Tapir idai back 
through the eocene epoch. 

d. The Pakmtlieridce. — 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, Pala? other id ium, resembles the 
Tapir in most respects, but has only three digits in the manus 
as well as in the pes. The dental formula, however, is 

i. -1^ c. r-r p.in. ^rA m.^^- 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 Macrauolienidx.. — The genus Macrauchenia is also 
an extinct form, which occurs in later tertiary or quaternary 
deposits in South America. 

The feet are tridactyle, and the dental formula is 

i. |4f c. |4^ p.in- -j-rj ni. ~ The teeth are disposed in a nearly 

continuous series. The crowns of the incisors present a deep 
fossa, as in the Equidm. The molars are in part Equine, in 
part Rhinocerotic in character. The skull is, on the whole. 
Equine, but the nasal bones are very short and Tapiroid. The 
vertebras of the long nock are extraordinarily similar to those 
of the Gamelidcp, and especially of the Llamas. 

3. The Artiodactyla. — The number of the dorso-lumbar 
vertebrae 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 astragalus 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 s]3henoid 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 SUIDjE. 313 

The stomach is more or less complex. The caecum, though 
well developed, is smaller than in the Perissodactyla. 

The mammae are inguinal or abdominal. When horns are 
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 Ifon-Ruminantia 
and the Ruminantia. 

A. The No7i-Ruminantia usually have more than one pair 
of incisors in the upper jaw. The molar teeth have either a 
niammillate, a transversely-ridged, or a rhinocerotic pattern. 
In only one genus, Dicotyles, are any of the metacarpal or 
metatarsal bones anchylosed together. They are devoid of 
horns, and the stomach has rarely more than two divisions. 

The Nbn-Ruminantia are divisible into three families : 
The SuidoB,t}ie SlppopotamidcB, a,nd the Anoplotheridm ; but 
more or fewer of the members of this last group may have 
ruminated. 

a. The Suidae have the skin of moderate thickness and 
hairy ; the limbs slender, and the third and fourth toes con- 
siderably 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 trans- 
versely-ridged grinding surface. 

In the genus Sus, the dental formula is i. ^ e. ^^- p.m. 

r4 ^- 3^- 

^y way of contrast with the Horse, I add some more de- 
tailed statements regarding the anatomy of the Pig as a com- 
mon and very good example of an Artiodactyla. The Pig has 
seven cervical vertebrae, nineteen* dorso-lumbar, of which 
fourteen are dorsal, four sacral, and twenty to twenty-three 
caudal. The atlas has wide oblique alae, as in the Horse. 
The centra of the other cervical vertebrae are short, with 
nearly flat articular surfaces, and this flatness is retained in 
the dorso-lumbar region. The cervical and dorsal vertebrae 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 backward ; beyond it they slope forward, if at all. 

In the ninth dorsal vertebra the postzygapophysis presents 
Bn articular surface on its dorsal side, and the prezygapophysis 
of the tenth vertebra bends round so as to overlap this surface. 
This character is continued in the succeeding vertebrae as far 

• Exoeptioually, the namtier may be increased to twenty-tV70. 
14 



Hi THE ANATOMY OF VERTEBRATED ANIMALS. 

as the first sacral. The transverse processes of the penulti- 
mate and last lumbar vertebra are tolerably long, but they are 
inclined forward as well as outward, and do not articulate 
with one another, or with the first sacral. 

In the skull the supraoccipital is inclined upward and foi^ 
ward into a great transverse crest, to which the parietals con- 
tribute but little. The parietals are early anchylosed. 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 
lachrj-mal is very large, and its two canals open on the face. 
The nasals are very long, and the premaxillae unite with them 
for a great distance. There is a prsenasal bone, or ossification 
of the cartilaginous septum of tVie nose. The bony palate ex- 
tends back beyond the level of the last molar. The base oi 
the external pterygoid process is not perforated. The surface 
for the articulation of the lower jaw is transversely elongated, 
convex from before backward, and bounded behind and inter- 
nally bj' a post-glenoidal ridge. 

The tympanic bulla is very large, and the exceedingly long 
bony meatus curves upward and outward, between the squamo- 
sal and the mastoid, with both of which it is anchylosed, to 
the root of the zj'goma, where its aperture looks almost directly 
upward. 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'ex- 
tending behind and below the mastoid. 

The rami of the mandible are completely anchylosed at the 
sj'mphysis. There is a long perpendicular portion of the 
ramus. The condyle is transversely elongated and. 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 anchylosed to- 
gether in the prone position. The distal end of the ulna 
ft] ticulates 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 metacarpal 



TUE OSTEOLOGY OF THE PIG. 3I5 

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. 
Each 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 cal- 
caneum. There are the usual seven tarsal bones. 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 sub- 
cylindrical 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 miinus. 

The fore-part of the body is supported upon the anterior 
extremities by a muscular sling composed of the serratus, leva- 
tor anguli scapulm, and sternoscajmlaris, much as in the Horse, 
with which the Pig exhibits a general correspondence in its 
myology. The muscles which move the digits, however, have 
undergone less modification. Each digit of the manus, for 
example, has its proper extensors, and there is an extensor ossia 
metacarpi pollicis which ends on the basal phalanx of the 
second digit. A }}rotiator teres is inserted into the lower half 
of the radius. The flexor perforatKS has onh' 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 interos- 
seus muscle on the radial side of the third digit, and another 
on the ulnar side of the fourth ; but the interossei of the inter- 
space 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 goMrocnemius ; and, en- 
closed 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 calcaneum as over a pullej', 
enters the sole, and finally divides into the two perforated 
tendons of the third and fourth digits. Tlie inner and outer 
digits, of the pes, like those of the manus, have no perforated 
tendons. 

A large and fleshy _;?ea;or hallucis longus arises from the 



S16 THE ANAT05IY OF VERTEBHATED ANIMALS. 

fibula and the interosseous ligament, and its broad tendon 
passes into the sole and coalesces with the tendon of the 
smaller j?ea;o;- longus dlgitorum. 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 
antious, 

A very complicated muscle represents the extensor longus 
digitorum and the perouceus 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 eotocuneiform. 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 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 2^6roncBus longus is present, and its tendon is inserted 
into the entocuneiform and the second metatarsal. There is 
no pero7iceusbrev is. Aperonceusiti et 5ti digiti smseB iiom 
the upper part of the fibula, behind the peronoBus 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 com- 
plete at the third month after birth) is d.i. |^, d.o. J^ d.m. —^ 

The outer upper incisors are directed obliquely outward 
and backward. 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 man- 
'iible 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 



THE DENTITION OF THE PIG. 317 

year, at which time the first deciduous molar, which is not 
replaced, falls out. Hence the formula of the permanent denti- 

i- • . a-S - 1—1 8*8 ij.8 Ar\ 

tion IS ^. 5T-3 c- ,-zi p.m. jr-, m. 3-, = 40. 

The permanent incisors in the upper jaw have short, broad, 
vertically-disposed crowns, and lie in a longitudinal series, tlie 
external being separated by an interval from the others. Tho 
elongated inferior incisors lie side by side, are greatly inclined 
forward and upward, and are grooved upon their upper or 
inner faces. The strong, angulated crowns of the canines are 
bent upward and outward 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 longitudinal 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 cascum, in 
which is a spiral fold of the mucous membrane ; and, at the 
entrance of the oesophagus, the epithelial lining is folded so 
as to form a sort of valve. Folds of the mucous membrane, 
between which there lies a groove, extend from the cardia 
toward the pylorus, and foreshadow the more developed struct- 
ure observable in Ruminants. 

The cfficum has not above one-sixth the capacity of the 
stomach, and the ilium projects into it, so as to form a very 
efficient iUocsecal valve. The liver is provided with a gall- 
bladder. The heart is devoid of a Eustachian valve, and 
sometimes, but not always, possesses a septal ossification. 

There is only one anterior cava. The aorta gives oif an in- 
nominata, whence the right subclavian and the two carotids 
arise, and a left subclavian. This is an arrangement midway 
between that observed in the Horse and that in Man. 

The trachea, before it divides, gives ofi' 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, 



318 THE ANATOMY OF VERTEBKATED ANIMALS. 

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 is lobed. There is a large 
uterus masculinus and well-developed vesiculas seminales. 
The ducts of Cowper's glands open into a csecal cavity con- 
tained in the muscular bulb. Tlie testes descend into a scro- 
tum. 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 umbilical vesicle at the same 
time assume a spindle-shape. 

The allantois soon becomes divided into an internal epithe- 
lial and an external vascular layer ; the latter becoming united 
with the chorion, through the extremities of which the allan- 
tois eventually passes. The villi are very numerous, minute, 
and spread over the whole surface of the ovum. 

The Suidce exhibit great variations in their dentition and 
in the structure of the stomach. 

In Porcus (the Babyrussa) the dental formula is i. ^^ c. jf, 

p.m.m. '-J^ ; the canines are enormously elongated and recurved, 

and the pharynx is provided with peculiar air-sacs. 

The stomach is divided into three chambers, and the groove 
leading from the oesophagus toward the pylorus is more dis- 
tinctly marked than in the 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 tuberculated 
than in &us. 

The stomach is divided into three sacs, and is provided 
with an oesophageal groove as in the preceding genus. 

The middle metatarsals and metacarpals coalesce into a 
cannon-bone, and the fifth digit of the pes is represented only 
by its metatarsal. 

In Phacochcerus (the Wart-hog) the upper incisors are 
reduced to one pair, and the hindermost molars, which are the 
only ones which are not shed in the old animal, are of great 
size, and possess a complicated, tuberculated structure. 

The Suidce are represented by one genus or another in ali 



THE HIPP0P0TAMIDJ3. 319 

the great distributional provinces except the Austrahan* and 
Novo-Zelanian. Porcus is peculiar to part of the Malay Ar- 
chipelago, Dicotyles to South America, and Phacochcerus 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. 

h. The Sippopotamidce are represented at present only by 
the genera Mippopotamus and Ghmropus. These animals 
have a huge head, a heavy body, covered with a thick integu- 
ment, 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. 

The dental formula of the adult Sippopotamus is i. ^ 

c. |4^ p.m. |J| m. ^, while Chaeropus 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 
downward in the upper jaw, upward in the lower. Their mu- 
tual attrition wears the anterior face of the extremity of the 
upper, and the posterior face of that of the lower, flat. 

The milk dentition consist of d.i. °~ d.c. \^, d.m. ^1 The 

•i ' 3 1 ' 1 4.4 

last lower deciduous molat is trilobed, and the first deciduous 
molar persists a long time, and seems not to be replaced. 

The stomach is divided into three or four compartments, 
and there is no caecum. 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 centra are slightly convex in 
front, and concave behind, in the cervical region, but not else- 
where. The prezygapophyses overlap the postzygapophyses 
in the posterior dorso-Iumbar vetebrfs. On the other hand, the 
transverse processes of the last lumbar vertebras articulate 
with those of the preceding and succeeding vertebrae, 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 premaxillae unite for a great extent. The 

• The Papuan pig may have been introduced from the weatward. 



320 THE ANATOMY OF VERTEBRATED ANIMALS. 

osseous palate is long ; the large tympanic bone is anchylosed 
with the approximated post-gienoidal and post-tympanic pro- 
cesses. 

The mandible is extremely massive, and has a backwardly 
produced angle. 

The scapula has a short acromion. The radius and ulna 
are complete and anchylosed, 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 Hippopotamidcn are at present confined to Africa; 
but a species abounded in the rivers of Europe in the later 
tertiary times. 

Merycopotamus of the miocene Fauna of the Sewalik 
Hills appears to have been a Hippopotamid, with upper molars 
having a quadri-crescentic, ruminant-like pattern, and lower 
molars bi-crescentic and rhinocerotic in character. 

In the SuidoB and Sippopotamidm, 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, Parens, and Phacochoerus ; and 
the great complexity of the stomach in Dicotyles and Hippo- 
potamus ; as they are so many approximations toward the 
structure of the Ruminant Artiodactyla. And the transition 
from the non-Ruminant to the Ruminant groups, or rather the 
common stem of both, is furnished by the Anoplotherida. 

c. The family 'of the Anoplotheridm exclusively contains 
extinct Marairials belonging to the eocene and miocene epochs. 
They are most conspicuousl}' 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 pre- 
ceding genera, but form an uninterrupted and even series, as 
in Man. 

The dental formula of the adult Anoplotheriwn is i. y\ 

-J p.m. — in. — , supposing that the first premolar is really 



i-i 



such, and not a persistent milk-molar. 

The upper and lower molars have the general structure of 
those of the Rhinoceros ; but the lamina? of the upper are Lent 
more backward 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 
2'ragulidce in structure, but the orbit is incomplete behind 



THE ANOPLOTHERID^. 



321 



The rest of the skeleton partly resembles that of the Pigs, 
and partly that of the Ruminants.* 

In Xiphodon and Gainotherium, which are ordinarily com- 
prised among the AnoplotheridcB (though, in all probability, 
they are true Ruminants of the Traguline group), the orbit ia 




* Ir Anoplotherium semndatwimi the digit ii. is developed in each foot, 
ttoagh not nearly so long as m., which is nearly symmetrical in itself. Then 
is an approach to the same structure in the manus of Gainotherium. 



322 THE ANATOMY OF VERTEBRATED ANIMALS. 

complete, and both upper and lower molars put on the Rumi- 
nant characteristics. In dentition, Gainotherhim 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 AHiodactyla that it is highly probable they may 
have possessed the faculty of rumination in a more or less per- 
fect degree. 

B. The Huminantia. — In the commonly-recognized mem- 
bers of this division of the Artiodactyla there is never 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 gen- 
erally inclined forward and closely approximated to the inci- 
sors, which they usually resemble in form. It consequently 
happens that they are often reckoned as incisors, and Rumi- 
aants are said to possess eight cutting teeth in the lower jaw. 

With one exception [Ryoeinosckus), the metacarpal and 
metatarsal bones of the third and fourth digits early become 
anchylosed 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 papillfe. 
This chamber is the Rumen, or Paunch. It communicates, 
by a wide aperture, with a much smaller chamber, which coi> 
stitutes the second subdivision of the cardiac moiety. This is 
called the Reticulum, or JSbneycomb 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, enclose a multitude of hexagonal-sided cells. The reticu- 



THE RUMINANT STOMACH. 



323 



lum commuaicates by a narrow aperture with the first sub- 
division of the pyloric moiety, which is somewhat more elon- 
gated in form. The mucous membrane of this subdivision ia 
produced into a vast number of longitudinal folds of various 
heights, but the majority of them are sufficiently large to ex- 




FlG. 102. — A, the Btomach of a Sheep. B, that of a Musk-deer {7'ragulus). ce., ffisi 
/in., runien ; lief., reticulum ; /*«., psalterium ; A., Al/,^ abomasoiQ ; Itu. 
denum ; Fy,^ pylorus 



tend almost completely across the cavity of the chamber; 
they thus reduce that cavity to a series of narrow radiating 
clefts interposed between the lamellse. When this portion of 
the stomach is slit open, longitudinally, the lamellse fall apart 
like the leaves of a book, whence it has received the fanciful 
name of the Psalterium from anatomists, while butchers give 
it that of Manyplies. The fourth segment of the stomach, or 
second subdivision of the pyloric moiety, is termed the Abo- 



524 THE ANATOMY OF VERTEBKATED ANIMALS. 

masum, or Mennet stomach. This portion is comparatively 
slender and elonguted, 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 reticu- 
lum and the abomasum ; nothing but very finely-divided, or 
semi-fluid matter, being capable of traversing the interstices 
of its lamellse. 

The gastric aperture of the oesophagus is situated at the 
junction of the paunch and the reticulum ; the margins of its 
opening are raised into muscular folds, and are produced, 
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 oesophagus to the psalte- 
rium. 

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- 
maxill*. The bunches of grass are then hastily swallowed, 
accompanied by abundant saliva. After grazing until its ap- 
petite 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 some- 
thing 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 stomach, and is re- 
turned, 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 second stroke, and all 
those which follow it until the bolus is sufiiciently masticated, 
take place from right to left, or in the opposite direction to 
that of the first. While the mastication is going on, fi-esh 
quantities of saliva are poured into the mouth, and, when the 
grass is thoroughly ground up, the semifluid product is passed 
back into the pharynx and swallowed once more. These 
actions are repeated until the greater portion of the grass 
which has been cropped is pulpified. 



THE ACT or RUMINATION. 323 

The precise nature of the operation, the external features 
li 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 in- 
terference 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 
backward and forward, from the one into the other, by peris- 
taltic 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 oesophageal 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 re- 
turned into the mouth. More probably, a sudden and simul- 
taneous contraction of the diaphragm and of the abdominal 
muscles compresses the contents of the rumen and reticulum, 
and drives the sodden fodder against the cardiac aperture of 
the stomach. This opens, and then the cardiac end of the 
oesophagus, 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 oesophagus, 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 narrowness 
of that aperture, and in part by the fine grating formed by the 
edges of the psalterial lamina. But when the semifluid 
matter, returned after mastication, once more reaches the 
cardia, it is compelled to pass toward the psalterial end of the 
reticulum (even apart from the guidance afforded by the lips 
of the oesophageal groove) on account of the direction of the 



326 THE ANATOMY OF VERTEBRATED ANIMALS. * 

oesophagus 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 re- 
ticulum reaches the psalterium ; and, in consequence of the fine 
state of division of its solids, readily traverses the interspaces 
of the lamellae of that organ, and passes into the fourth 
stomach, there to be submitted to the action of the gastric 
juico and to undergo the digestion of the protein compounds, 
which have remained unaffected by the previous mastication 
and insalivation. 

The Ruininantia are divided into three groups : a. the 
TragulidcB, b. the Cotylophora, and c. the Gamelidce. 

a. The TraguUdoB 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 diiferent 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 Anoplotheridue. Thus, 
the second and fifth digits are complete in both fore- and hind- 
feet, and the metacarpals and metatarsals of the third and 
fourth digits unite very late, or, as in one genus, Hyoemoschus, 
not at all. The canines are well developed in both jaws, and 
the premolar teeth are sharp and cutting. 

The oesophagus opens at the junction of the rumen with 
the reticulum, the communication between the two being very 
wide (Fig. 102 B). The epithelium of the rumen is papillate, 
and there are two oesophageal folds, as in ordinary Ruminants, 
but the psalterium is represented only by a very short and 
narrow tube, the lining 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 remark- 
ably minute in the Tragulidce, not exceeding ±^^(,1, of an inch 
in diameter. They have oirculai contours. 

The placenta is very nearly diffuse, the foetal villi being 
scattered over the chorion in bands, not collected into cotyle- 
dons. 

As further remarkable peculiarities of this group may be 
mentioned the anchylosis of the malleolar bone with the tibia, 



THE COTYLOPHOEA. 327 

and tlie tendency to ossification in the pelvic ligaments and 
of the aponeurosis of the, muscles of the back, in adult males. 
Finally, the navicular, cuboid, and ectocuneiform bones in the 
tarsus are all anchylosed together. If, as is probable, XipJio- 
don is one of the Tragulidoe, the group has existed since the 
eocene epoch. 

b. The Cotylophora are, like the preceding group, unguli- 
grade, but the outer metacarpals and metatarsals are incom- 
plete at their proximal ends, and the middle ones are early 
imchylosed into a cannon-bone. The malleolar bone is always 
distinct. The navicular and the cuboid bones of the tarsus are 
anchylosed 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. 

The blood-corpuscles are circular, and may have a diametei" 
of as little as -g-j^j-j- of an inch. 

The foetal villi are gathered together into bunches or co- 
tyledons, vrhich may present either a convex or a concave face 
toward the uterus. They are received into persistent eleva- 
tions of the mucous membrane of the uterus, the surfaces of 
which present a reverse curvature. 

All the Gotylophora 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 integ- 
ument 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 unfrequently called Gavi- 
comia (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 homy sheath 
is annually shed and replaced by a newly-formed one. 

Of the second kind of horn, or that which acquires no homy 
sheath, there are also two kinds. In the Girafi"e, the horn- 
oores are attached over the coronal suture, at the junction of 
the frontal and parietal bones, with which they are not anchy- 
losed ; 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 Reindeer. The 



328 THE ANATOMY OF VERTEBRATED ANIMALS. 

horns attain their full size very rapidly, and tben a circular 
ridge, which makes its appearance at a short distance from tiie 
root of the horn and is called the " hnrr" 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 heani 
now gradually languishes, its integument dies and peels off, and 
the dead 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 vchich the development of bony matter 
into Deer-horn takes place is wonderful, horns weighing sev- 
enty-two 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 farther than the miocene epoch. 

c. The Camelidos 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 integumentary cushions 
form a sole to the foot; while the nails are flattened and can 
hardly be called hoofs. 

The arches of the cervical vertebrae, and not their trans- 
verse processes, are perforated by the canal of the vertebral 
artery ; a character which the camels share with the Macrau- 
chenidcB. 

The metacarpals are separated by a deep cleft, and the 
distal phalanges of the digits are nearly symmetrical in them- 
selves. The distal facets of the astragalus are more unequal 
than in the other JRwninantia, and the navicular and cuboid 
bones are not anchylosed together. 

The premaxillse 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 
CEsophagus 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 narrow 
mouths, are developed. These, the so-called "water-cells^^ 



THE TOXODONTIA. 829 

Berve to strain off from the contents of the paunch, and to 
retain in store, a considerable quantity of water. 'I'he reticu- 
lum is sharply defined from the rumen, and communicates with 
it by a comparatively small aperture. The oesophageal groove 
is bounded by only one ridge, which lies upon its left side. 
The psalterium is reduced to a mere tubular passage, without 
laminae; 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 
caecum is short and simple. By a remarkable exception 
among the Mammalia, the red blood-corpuscles are elliptical. 
The foetal villi are scattered evenly over the chorion, so that 
the placenta is diffuse. 

While the Tragulidm connect the typical Ruminants with 
the non-ruminant Artiodaotyles, the Gamelidoe, on the other 
hand, link them with Macrauchenia and the Perissodactyles. 

The Gamelidoe 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 ToxoDONTiA. — 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 upward and forward. There are supraorbital pro- 
longations. 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 ure six incisors. In 
the mandible there are canines in the middle of the interval 
between the incisors and the grinders. In the upper jaw of 
the adult, only indications of the former existence of alveoli 
for canines remain. The grinding teeth are seven on each side 
above, and six on each side below. They are greatly bowed 
(whence the name of the genus), so as to be convex outward 
and concave inward. They grow from persistent pulps, and 
the enamel is absent upon their inner faces. 

The centra of the cervical vertebrae have flattened articular 
faces. The dorso-lumbar vertebrae 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 io 



330 THE ANATOMY OF VERTEBKATED ANIMALS. 

Tapirus. 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 corresponding bone 
in the Elephants. 

It is a curious comment upon the pretension to reconstruct 
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 Toxo- 
don, no one ventures to predict the characters of its feet, still 
less to say any thing 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 tj'pe of a new order. 

III. The SiRENiA. — 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-limbs, while the integument of the caudal 
end of the body is produced into a flattened horizontal fin. 
No dorsal fin is ever present. The demarcation between the 
head and neck is but obscurely marked, and the fore-limbs 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, Avhich 
are perfectly distinct from one another, are situated consider- 
ably above its termination. There is a well-developed third 
eyelid, the pinna of the ear is absent, and the mammae are 
thoracic ; a circumstance which has probably not a little con- 
tributed to the origination of the myths respecting the exist- 
ence of mermaids. 

The Sirenia were formerly united with the Whales and 
Porpoises as Getacea lierhivora. But their organization dif- 
fers from that of the true Cetaceans in almost every particular, 
while they are closeh' allied with the Utigulata. 

The cervical vertebrae are reduced to six in one genus — 
Manatus. The bodies of these vertebrae are always com- 
pressed from before backward, but they are never all an- 
chylosed together (it is rare for any of them to be thus 
united), and the second has a distinct odontoid process. The 
dorsal vertebrae have broad and depressed spines, and may be 
as many as seventeen or eighteen in number, while there are 



THE SIRENIA. 33] 

not more than three lumbar vertebrae ; and the hindermost of 
these even is probably to be regarded as sacral. There are 
twenty or more caudal vertebrse, the terminal ones being not 
polygonal, but depressed, with w^ell-developed processes. 

The zygapophyses of successive vertebrae articulate to- 
gether in the dorsal region; but, in the lumbar and caudal re- 
gions, the postzygapophyses disappear and the prezygapo- 
pbyses 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 sub- 
vertebral chevron-bones are placed beneath the interarticular 
cartilages of the caudal vertebra. The heads of the ribs 
articulate with the centra of all the vertebrse. The bodies of 
the ribs are very thick, rounded, and have a remarkably dense 
and laminated structure. 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 
cranial cavity is worthy of notice, as it strongly contrasts with 
the form of the brain-case in the Cetacea. The supraoccipital 
is very large and slopes upward and forward 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 nre prolonged into broad supraorbital processes. 
The nasal bones are abortive, and, in the dry skull, the external 
nares are very wide, and look upward. The tympanic bone is 
a thick hoop, anchylosed with the periotic bones, and readily 
comes away from the skull with them. The zygoma is 
enormously stout. The premaxillas 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 poUex is rudimentary, and 
the other digits have no more than three phalanges each. 

The pelvis is rudimentarj', the bones which represent the 
ossa innominata being connected by their proximal ends with 
the transverse processes of the last of the precaudal vertebrae. 
They are disposed vertically to the axis of the body. No 
trace of the hind-limbs has been observed in any of the exist 
in<T Siren ia. 



332 THE ANATOMY OF VERTEBRATED ANIMALS. 

Tlie premaxillary region of the palate, and the correspond- 
ing surface of the mandible, are coated with mammillated and 
rugose horny plates formed of hardened epithelium ; and, in 
the extinct genus jRhytina, these plates were the only masti-, 
eating organs, as there were no teeth. In Salicore (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 male has 
two tusk-like incisors which project from their sockets in the 
premaxill* ; while, in the female, the tusks remain concealed 
in their alveoli. 

In the foetal state, both Salicore and Manatus have in- 
cisors in the mandible as well as in the premaxiliae. 

The stomach is divided into two portions by a median con- 
striction, and its cardiac end is provided with a peculiar gland. 
Its plyoric end, in some species, gives off two caeca. 




Fig. 103. — Dorsal view of tbc heart of a Dugong {UaUcors), its cjivities beinj? laid open. — R 
v.. right VL-ntricIe; L. v., left ventricle. V, c. s. ft,, left superior vena cava. V. c. s. d.. 
right su]ierior vona cava. V. c. i., vena cava inferior. F. o. r.. the inner end of a csecai 
diverticulum of the right auricls, into which a style is introduced, and which represents 
the foramen ovale. , the auricular septum. 

There is a casoum at the junction of the large and small in- 
testine. Salivary glands are well developed. The apical pop> 
tion of the septum ventriculorum is deeply cleft, so that the 
ventricles are separated from one another through about half 
their extent. 

There are two superior cavae and a Eustachian valve. Ex- 



THE CETACEA. 333 

tensive 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 diaphragm takes a 
very unusual course, extending very obliquely from before 
backward, and causing the upper 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 cham- 
ber, while the broad heart lies in its anterior and sternal portion. 

The arytenoid cartilages are not prolonged as in the Ceta- 
cea. 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 humerus, 
and the sub-caudal muscles extend forward as far as the pos- 
terior lumbar vertebrae. The chief muscles of the antibrachium 
and manus are present. 

The male Sirenia possess vesiculsB seminales. The uterus 
is two-horned. 

There are two living genera of Sirenia — the Dugong 
(JTftlicore), 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, Mhytina, which had a coriaceous integu- 
ment almost devoid of hair, and possessed no teeth, abounded 
in Behring's Straits less than a century ago. It is now alto- 
gether extinct. 

The Miocene genus, Salitherium, 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 gradu- 
ally into that of the body. A horizontally-flattened caudal 
fin is always present ; and, very generally, the dorsal integu- 
ment is produced into a median, laterally-compressed dorsal 
fin. The body is incased in a thick smooth integument, be- 
neath 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 
division into brachium, antibrachium, 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 iioae 



S34 THE AXATOMY OF VERTEBUATED ANIMALS. 

opsas externally, are always situated at the top of the hi;ad, 
and far removed from the extremity of the snout. There is 
no third eyelid, and the very small auditory apertures are to- 
tally 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 vertebrae are 
flat, and the epiphyses usually remain distinct for a long time. 

The spinal column, as a whole, is remarkable for the short- 
ness of its cervical, and the length of its lumbar region, there 
being sometimes a greater number of lumbar than of dorsal 
vertebrae. There is no sacrum. The caudal vertebrae are only 
distinguishable from the posterior lumbo-sacral vertebrae by 
their chevron-bones. The second vertebra of the neck is de- 
void of any odontoid process ; and it very commonlj' happens 
that more or fewer of the cervical vertebrae, the bodies of 
which are often so short as to be mere disks, are anchylosed 
together, either by their arches, or by their centra, or by both. 
The centra of all the succeeding vertebrce are large in propor- 
tion to their arches, and the inter-vertebral fibro-cartilages are 
exceedingly thick, so as to confer great flexibility and elasti- 
city on the spine. The arches of the hinder dorsal vertebrae, 
and of those of the lumbar and caudal regions, are not articu- 
lated together by zygapophyses. The centra of the posterior 
caudal vertebras 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 
vertebrae, and not with their bodies. 

The skull is even more remarkably modified than the ver- 
tebral column. The brain-case itself has a spheroidal form ; 
while the jaws are greatly prolonged, the principal enlarge- 
ment of the upper jaw taking place in the region which lies in 
front of the nasal aperture. The basis cranii, as a whole, is 
ramarkably broad, and its upper surface concave from before 
backward, 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 Mamm,alia ,' the 
Bupraoccipital, with an interparietal bone, being interposed be- 
tween them, and extending forward so as to unite with the 
frontals. Each frontal bone is produced outward into a great 
bony plate which covers the orbit. The squamosal bone sends 
a very large and stout zygomatic process forward to meet this 
supra-orbital prolongation of the frontal. The proper jugal 



THE OETACEA. 335 

bone, on the other hand, which bounds the orbit below, is ex- 
ceedingly slender. The very large maxilla extends backward 
and outward in contact with the frontal, or even overlapping 
the greater part of its surface ; and it stretches forward to 
very near the anterior end of the snout, so that almost the 
whole of the gape is bounded by the maxilla. 

The premaxillae, on the other hand, though very long, inas- 
much as thej' occupy the whole length of the jaw in the mid- 
dle 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 verti- 
cal, in consequence, for the most part, of the rudimentary con- 
dition 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 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, it is a low ridge situated close to the ante- 
rior edge of the bone ; but it commonly terminates in a long 
acromion process,, and, sometimes, there is a conspicuous, 
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 
iinperfectly ossified. When the carpal bones are complete, 
they are polygonal and imbedded in a fibrous tissue ; not 
united by articulations 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, thereforcj probably .-epre- 



336 THE ANATOMY OF VERTEBRATED ANIMALS. 

sent the ischia. They are elongated, convex upward and con- 
cave downward, and are connected with the vertebral column 
only by fibrous tissue. In some few Cetacea (Salwnoidea) 
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 Mam- 
malia, move the antibrachium 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 verj' greatly, but they are almost alwavs nearly 
uniform in character. There appear to be no salivary glands. 
The stomach is complicated, being divided into, 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 relia mi- 
rabiUa, 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 pro- 
duced, 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 alwaj's remain in the abdomen, and there are 
no vesiculae seminales. The penis is devoid of a bone. The 
uterus of the female is deeply divided into two horns, and the 
villi of the foetus are scattered over its chorion, as in other 
mammals with a diffuse placentation. 

The Cetacea are divisible into three groups : the JSalce- 
noidea, the Delphi?ioidea, and the Phocodontia.* 

* For further information fespectingtlie characters of the recent Cetacea, I 
refer the reader to Prof. l''lo%¥ei's'a very valuable memoir "On the Osteology 
of Inia and J-ontoporia,^' published in the "Transactions of the Zoological 
Society for 1867." 



THE BALJiNOIDEA. 



337 



a. In the BaZmnoidea 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 spiracles. These 
are not connected with any saccular dilatations of the nasal 
passages, situated between the skull and the integument. 

In the spinal column, no rib has a complete neck and capi- 
tulum, the heads of even the most anterior ribs being united 




EQ 



Sta. IM.— Lateral and snperlor views of the skull of a foetal Whale (Salcma AusfraHt)j— 
Thejugal bones are absent, and the ^ure does not sufficiently Indicate the outward 
oarratnre of the ramus of the mandible (Mn.). 

1.5 



338 



THE ANATOMY OF VEETEBRATED ANIMALS. 



with the bodies of the vertebrae only by ligament. The chief 
connection of all the ribs, therefore, and the only connection 
of most of them, is with the transverse processes of the verte- 
br£e. The short and broad sternum unites only with the iirst 
rib, and the union is direct, so that there are no sternoiujstal 
libs. 




Fig. 105. — "Ear-booes" of the adult Balama Avstraivt. — Seen from within In the npi:ei 
figure; fi-om without in the lowor. Ev-., Eustachian canal; Au.^ oxtemal 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, JVu., 
though short, are longer, and more like those of ordinary 
mammals, than is the case in other Cetacea. The maxilla, 
Mic., extends outward in front of the great supraorbital process 
of the frontal, ^., but it does not cover the frontal bone. 
There is a distinct lachrymal. Each ramus of the mandible, 
Mil., is convex outward and concave inward ; 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 upward 



THE BAL^NOIDBA. 839 

and concave inferioily. The two rami of the mandible are 
connected only by ligament at the symphysis. 

Minute teeth are developed in foetal Haloenidce, but are 
very soon lost, and their place taken by the so-called Whale- 
bone, or Baleen plates. Each of these is triang-ular, with a 
thick, smooth outer edge, somewhat concave from above down- 
ward, which, in the natural position of the plates, is nearly 
vertical, and is covered by the great lower lip. The upper 
edge of the plate, also slightly concave, is attached to a trans- 
verse elevation of the gum covering the palate. Vascular 
papillee extend from this ridge into cavities of corresponding 
dimensions, which lie, parallel with one another, in the baleen 
plate. The third side of the triangular baleen plate, somewhat 
convex and sloping from the middle line above, downward and 
outward, 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 plate:^, which are longest in the middle 
of each series, and shortest at each end, enclose a cavity, the 
bottom of which is occupied by the large and fleshy tongue. 
By raising the tongue, whatever solid matters are enclosed in 
the mouth can be forced back into the pharynx and swallowed ; 
while the water in which thej' 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 con- 
stantly 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 JSaloenoidea, e.g., Jial(^na rostrata, the 
cricoid cartilage and the rings of the trachea are incomplete 
in front, and a large air-sac is developed in the cricothyroid 
space. The JBalcenoidea possess olfactory nerves and a dis- 
tinct, though small, olfactory apparatus. The sclerotic coat 
of the eyeball is enormously thick, and the optic nerve is sur- 
rounded by a rete-mirdbile. The tympanic membrane is con- 
nected 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 antibrachium and manus are not 
altogether absent. 

The right Whale [Bdlmna), and the Fin-fishes [MeffO- 
pt^a, BaloBnoptera, etc.), belong to this division. 



340 THE ANATOMY OF VERTEBRATE!) ANIMALS. 

I). In the Delphinoidea the nasal chambers open by only 
a single spiracle on the top of the head; and saccular dilata- 
tions 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 integument 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 vertebrae, as 
in other Mammalia. The elongated sternum is, almost al- 
ways, composed of several pieces arranged in a longitudinal 
series ; and cartilaginous, or ossified, sternal ribs are present 
in greater or smaller number. The nasal bones, which are 
very short, and have their upper surfaces tubercle-like, are 
more or less asymmetrically developed, as are also the max- 
illse ; so that the facial part of the skull appears distorted. 
The maxillse are expanded behind, and cover the orbital pro- 
cess of the frontal bone wholly or partially. 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 outward, 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-premax- 
illary part of the skull. 

Teeth always exist after birth, and are never replaced by 
baleen plates. They are usually numerous, but sometimes few 
and deciduous. Occasionally, only one or two teeth persist, 
and these, as in the Narwhal, may take the form of immense- 
ly-elongated tusks. 

To this division belong the Physeteridw Platanistidae and 
DelphinidcB. 

The Physeteridce possess functional teeth only in the low- 
er jaw. The asymmetry of the skull is strongly pronounced ; 
and, in the adult, the maxillary and frontal bones are pro- 
duced, so as to form a sort of basin upon the upper and ante- 
rior surface of the skull. The pterygoids meet in the middle 
line below, and the mandibular symphysis is sometimes ex- 
tremely long. 

The areater number of the cervical vertebrae are anchy- 
losed. The hinder ribs lose their tubercular, but retain their 
kiapitular articulation with the vertebras. The costal carti- 
lages are not ossified. The pectoral limbs are small, and a 
dorsal fin is usually present. 

The proper Sperm Whales {Physeterinw) have an enor- 
mous head, with a quadrate truncated snout, at the anterior 



THE DELPHINOIDEA. 



841 



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. Am- 
bergris is a sort of bezoar, found in the alimentary canal of tho 
Cachalot, and seemingly derived from the fatty matter con- 




S^G. 106. TTpper (A), under (B), and lateral (C) views of the skull of a fretjil Cachalot 

iVhysete^). — The nasal hones arc not n'presented in the upper view, and the hinder ead 
of the jugal Is displaced from its natural connectiou with the squamosal in (C), 



342 THE ANATOMY OF VERTEBRATED ANIMALS. 

tained in the CepluiJopodn on -svhicli the Cetacean feeds. In 
the other group of the Physeteridir, — the Ziphiinm or lihyn- 
choceti — to which the Bottlenosed Whale {Hyperoodon) be- 
longs, there are only one or two pairs of fullj'-formed teeth in 
the mandible. Some recent and many fossil (middle and later 
tertiary) genera of the Cetaceans are remarkable for the elon- 
L^ated rostrum formed by the solid ossification and anchj-losis 
of the ethmoid, premaxilte, and maxillse. 

The Platanistid m are fluviatile or estuarine Cetacea, 
which occur in the Ganges and in the rivers of South America. 
The cervical vertebrse are not anchylosed, and the costal car- 
tilages are not ossified. The tubercula and capitula of the 
ribs blend together posteriorly. The symphysis of the man- 
dibles is extremely long and the jaws are narrow. Numerous 
teeth with compressed fangs are found in both jaws. The 
eyes are small, and in Platan ista they are rudimentary. 

In the Depldnidoe 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 vertebrfe are generally anchj'lcsed 
together. The posterior ribs lose their capitula and become 
articulated only with the transverse processes of the vertebrae. 
The costal cartilages are well ossified. The symphysis of the 
mandible does not exceed one third of the rami in length, and 
the frontal and maxillary bones are not especially produced 
upward at their edges. 

As the common Porpoise (PhocCBna 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 pe- 
culiarities. 

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 downward and forward. The eyes are small 
end 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 be- 
liind the eye, and is so minute as to be discovered with diffi- 
culty. The genital aperture is placed a long way in front of 



THE SKELETON OF THE PORPOISE. 343 

tlie anus in the male ; while, in the female, the interval, in 
which the fossse 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 Getacea. 

In the spongy texture of all the bones, the absence of me- 
dullary cavities in those of the limbs, and in the long per- 
sistent separability of the epiphyses of the centra of the verte- 
brae, the Porpoise resembles other Getacea ; as it does in the 
shortness of the cervical, and the length of the lumbar, region 
of the spinal column. 

The seven cervical vertebrae are all anchylosed together, and 
the atlas, which is very large in proportion to the rest, over- 
laps them above and at the sides. The centra of the hinder 
oervicals are so short and broad that they are mere plates of 
bone. There are twentj^-eight dorso-lumbar vertebra, of which 
fifteen are dorsal. In all but the most anterior of these 
vertebra, the zygapophyses are abortive ; and long accessory 
processes, developed from the front-part of the neural arches, 
loosely embrace the spine of the vertebrae in front. This ar- 
rangement, 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, 
vertebra are very long. There are five pairs of true ribs. The 
sternebrae anchylose into an elongated sternum. The anterior 
caudal vertebrae 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 
concave contour of the base of the skull ; the extreme shallow- 
ness of the sella turcica ; the presence of an ossified tentorium; 
and the broad imperforate anterior wall, in the place of the 
(sribriform plate of the ethmoid, are striking features. The 
synchondrosis between the basi- and presphenoid is persistent. 
On the base of the skull the basi-occipital gives ofi" great pro- 
cesses outward and downward, to form, together with a para- 
niastoid prolongation of the exocoipital, and the squamosal, a 
chamber in which the anchylosed tympanic and periotic bones 
are contained. The ex- and supra-occipitals, together with the 
interparietals, form the whole back wall and middle of the 



344 THE ANATOMY OF VERTEBRATED ANIMALS. 

roof of the cranium, separating tlie parietals completely, and 
the frontals largely, and reaching the nasal bones. 

The basi-sphenoid is anchylosed with the small and almost 
horizontal alisphenoids, and there are no sphenoidal pterygoid 
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 completely anchylosed to- 
gether, where they form the front wall of the brain-case. Pos- 
teriorly and above, they diverge to receive the interparietal. 
The supra-orbital processes are extremely large, and are 
directed forward and outward, not backward and outward, 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 upward, and are con- 
vex toward one another and to the middle line. Correspond- 
ing 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 premaxillse are anchylosed with the inner 
margins of the maxillse, and contribute only a very small por- 
tion 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 ex- 
cavated 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 uncovered in conse- 
quence of the small size, tubercular form, and backward posi- 
tion of the nasal bones. The squamosal is relatively small, but 
has the characteristically cetacean, large, zygomatic process ; 
this extends forward 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 
anchylosed with the no less heavy and thick, scroll-shaped 
tympanic. Tlie 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. 



THE SKELETON OF THE PORPOISE, 345 

When the tympano-periotio 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 ansvrer to the optic and sphenorbital foramina. The 
posterior pair take the place of the oval, posterior lacerated, 
and jugular foramina, and the precondyloid 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. 

In the natural position the fore-limbs stand out from the 
body with their flat surfaces looking upward and downward ; 
the upper surface being directed a little backward, and the 
lower a little forward. The tuberosity of the short humerus 
is directed forward. The carpus contains six or seven ossifica- 
tions. 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 upward, and their smaller ends for- 
ward, within an inch of the centra of the vertebras, 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 cavemosum of its side. 

The cutaneous muscle is very largely developed, and lies 
between two layers of blubber, the thick surperficial one sepa- 
rating it from the skin, and the thin deep layer from the subja- 
cent 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 hu- 
merus, which act as powerful adductors, abductors, protractors, 
and retractors of the fin. There is no trapezius, and the rep- 
resentative of the latissimus dorsi is very small. A strong 
occipito-humeralis, from the paramastoid to the tuberosity of 
the humerus, seems to represent the cleido-mastoid and clavicu- 
lar deltoid. A costo-humeralis extends from the sternum to the 
inner tuberosity of the humerus. A small coraco-hrachialis ex- 
tends 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 attachment of 
the third and fourth ribs, and is inserted into the ulna. The tri- 



346 XHE ANATOMY OF VERTEBRATED ANIMALS. 

cejys extensor is represented by tendinous fibres in which niiiscle 
cannot always be detected, which extend frora the posterior face 
of the humerus to the ulna. The other muscles of the forearm 
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 forward, 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 ^.poneurosis 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 
vertebrae, as far as the ninth lumbar. A strong fibrous apo- 
neurosis is continued back over the subvertebral muscles to the 
pelvic bones. Between these bones and the ends of the trans- 
verse processes of the twenty-eighth and twenty-ninth verte- 
brte (counting from the first dorsal) the aponeurosis 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 peritonseum. 

The teeth are small and numerous, and their crowns are 
obtuse and constricted. The passage of the pharynx is di- 
vided in the middle, the soft palate being prolonged into a mus- 
cular funnel, the opening of which closely fits the constricted 
neck of the long cone into which the epiglottis and the aryte- 
noid cartilages are produced. Thus the arrangement which is 
transitory in the Marsupial is permanent in the Cetacean. 

The stomach is divided into three sacs. The first is large, 
conical, and lined by a coarse white epithelial coat. The gul- 
let opens directly into it. The second stomach communicates 
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 mem- 
brane is quite smooth. A small, circular, pyloric aperture 



THE HEART OF THE PORPOISE. 347 

places this in communication with the dilated commencement 
of the duodenum, which has sometimes been regarded as a 
fourth stomach. Its lining membrane presents longitudinal 
ragBd continuous with those of the duodenum itself. The con- 
joined pancreatic and biliarj' ducts open just beyond the di- 
lated part of the duodenum. There is no coecum, or demar- 
cation between the large and small intestines. The bUobed 
liver has no gall-bladder. 

In the heart the fossa ovalis is distinct, but there is neither 
Eustachian nor Thebesian valve. The vena cava 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 ori- 
gins. The arteries have a great tendency to break up into 
plexuses. Thus the internal carotids form great net-works 
which communicate with vertebral plexuses, extending through- 
out 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. Th<; veins form 
plexuses corresponding to, and mixed up with, those of the 
arteries ; and a very large venous plexus lies on the subverte- 
bral 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 cor- 
responding facial region of the skull, on the contrary, is very 
concave. The interval between the two is occupied, in part, 
by fibrous and fatty tissue ; and, in part, by a singularly sac- 
culated 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 frorn 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 
rharaber. Each nasal passage, after it ceases to be surrounded 
bv bone, sends off two diverticida, one forward and one back- 
vvard. The anterior, which lies between the anterior valve 
and the premaxilia, is a simple sac, lined with a thin, black, 



348 THE ANATOMY OF VERTEBRATED ANIMALS. 

smooth membrane. The posterior diverticulum lies between 
the posterior valve and the ethmoid and nasal bones. It is 
incompletely divided by a sort of shelf, is prolonged forward, 
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 maxillae to its anterior lip. Their ac- 
tion 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 together 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 pulled 
downward and forward, its surface becoming somewhat de- 
pressed, and its fi-ee 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 Getacea come up to breathe, the expired vapor 
suddenly condenses into a cloud ; and, if expiration commencea 
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 " spouting " of Whales, which does not arise, as it is 
commonly said to do, from the straining off of the sea-water 
swallowed 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 summit 
into a knob. The muscular soft palate embraces the neck of 
this knob so closely that it cannot be withdravfn 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, after 
its prey. The point at which the extra bronchus to the 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 thdn 



THE PHOCODONTIA. 349 

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 hemi- 
spheres 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 pos- 
terior cornu has been observed, in the lateral ventricle. The 
corpus callosum is small, relatively to the size of the hemi- 
spheres, and the anterior commissure is almost obsolete. The 
medulla oblongata has corpora trapezoidea. The olfactory 
nerves are wanting — a circumstance which agrees with the 
entire absence of ethmoidal turbinals. The eye has a thick 
sclerotic, and there is a choanoid muscle ; no nictitating mem- 
brane 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 ossification. 

The Eustachian tube passes through the notch in the ptery- 
goid and opens into the nasal passage on the inner side of that 
notch. Close to its commencement it communicates, by an 
oval aperture, with a remarkable air-chamber, which extends 
backward between the periotic mass and the basis cranii, and 
forward 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 is devoid of a bone, and, ordinarily, is bent up 
in the long preputial sheath. 

c. The Phocodontia are represented only by Zeuglodon, 
Squalodon, and other large extinct cetaceans of the tertiary 
epoch. These remarkable fossil forms constitute connecting 
links between the Geta,cea and the aquatic Garnivora. The 
cervical vertebrse are distinct and unanohylosed, nearly re- 
sembling those of the Rhynooceti. The caudal vertebrse 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 



350 THE ANATOMY OF VERTEBRATED ANIMALS. 

cetacean. The zygomatic processes of the squamosal 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 the 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 diifers from all the other Cetacea in the circum- 
stance that some of its teeth have vertical successors. 

The Deciduatb M ammat. ta. — These may be subdivided, 
according to the form of the placenta, into two groups : the 
Zonaria and the Discoidea. In the former the placenta sur- 
rounds 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 disk, which is sometimes more or less lobed. 

Tlie mammalia which possess a zonary placentation are the 
Gctrnivora, the Prohoscidea, and the Syracoidea. 

Each of these divisions is very closely related to one of the 
foregoing. Thus the Carnivora approach the Cetacea; the 
Proboscidea, the Sirenia ; and the Syracoidea, the tingiir 
lata. 

The ZoNAEiA. 1. The Caenivoea. — In this order the 
head, relatively to the body, is of moderate or small size ; and 
hair is abundant. 

The cervical vertebras are free and unanchylosed, and their 
centra are elongated. The odontoid process of the second is 
well developed. The dorso-lumbar vertebrae are almost always 
twenty in number, rarely twenty-one or nineteen. The num- 
ber of dorsal and lumbar vertebra, respectively, varies be- 
tween sixteen dorsal and four lumbar, and thirteen dorsal and 
seven lumbar. The dorso-lumbar vertebriB are always articu- 
lated together by their zygapophyses, and there is a com- 
plete sacrum. 

The sternebras 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 



THE CARNIVORA. 351 

coronoid process, and the long axis of the articular surface 
wliich 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 
lietween the acromion and the sternum. The scapula has a 
distinct spine, and a large supra-spinous fossa. 

Neither the hallux nor the pollex is opposable. The car- 
pal and tarsal bones have the ordinary number and arrange- 
ment ; 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 
crowns are covered with enamel. There are aKvays 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 cfficum, 
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 convolutions sur- 
rounding the Sylvian fissure. But, in the aquatic Carnivora, 
the gyri are much more numerous and complicated ; the cere- 
bral hemispheres are much broader and longer in proportion 
to the length of the brain ; and they may even exhibit a rudi- 
ment of the posterior cornu. In all these respects they ap- 
proach the Cetacea. 

The inferior tiu-binal bones are always large and have a 
complicated form. 

There are no vesiculse seminales, and an os perns is very 
generally present. The ovary is enclosed in a peritoneal s?c. 

The Carnivora are divisible into the IHnnipedia, or aquatic 
Carnivores ; and the Ftssipedia, which are mainly terrestrial 
and cursorial. 

a. In the Flssipedia the incisors are, with one exception 

(Mhhydris. the Sea-otter, with i. \^^, six in number in each jaw- 



352 



THE ANATOMY OF VERTEBRATED ANIMALS. 



The hind-limbs have the position usual in mammals, and 
the tail is free to its root. The pinna of the ear is fully de- 
veloped. 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. Tha 
phalanx which supports the claw has a similar form, and a 



THE ANATOMY OF THE DOG. 353 

plate of bone rises from its base as a short sheath. An elastic 
ligament connects the base of the ungual phalanx with the 
middle phalanx, so that, when ihe flexor profundus 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 integumentarj' sheath. 

The olfactory lobes are usually large and the cerebral hemi- 
spheres elongated. 

As the Dog {Canis /amiliaris) 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- 
tebra, of which thirteen are dorsal and seven lumbar, three 
sacral, and eighteen to twenty-two caudal vertrebrse. The 
atlas has broad and rounded alae, the anterior margins of 
which are deeply excavated near the roots. The posterior 
edge of the spinous process of the axis vertebra is almost per- 
pendicular and very thick. 

Nine pairs of ribs are usually connected by sterno-costal 
cartilages vdth the sternum, which is composed of eight lat- 
erally-compressed stemebrae. Only two of the three anchy- 
losed sacral vertebrae 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 backward. The sagittal and lambdoidal crests are 
greatly developed and meet in a prominent occipital spine ; 
the zygomata are very wide and arched outward ; 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 supra-angular process 
projects outward from the ascending portion of the ramus, 
and takes the place of the proper angle. The articular 
condyle is much elongated transverselj', narrow and convex 
from before backward ; and the pre- and post-glenoidal pro- 
cesses of the squamosal are produced downvrard so as to 
convert the joint into a complete ginglymus and to restrict 
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 tym- 
panum is bounded below by a convex osseous wall, which is 
termed the bulla. It opens externally by the short external 



354 THE ANATOMY OF VERTEBRATED ANIMALS. 

meatus, at the inner end of which is a circular elevation for 
the attachment of the tympanic membrane. 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 
huDa 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 in- 
ternally, the periotic region of the bulla presents a canal, 
through which the internal carotid artery passes. The pos- 
terior opening of the carotid canal looks into the foramen 
lacerurn 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 lacerurn posteritis. A large 
foramen behind the glenoidal cavity transmits a vein from the 
interior of the skull. In the nasal cavity, the ethmoidal ti;rbi- 
nals are very large ; the superior turbinals are prolonged into 
the great frontal sinus, and the inferior turbinals unite, in the 
middle line, \\'ith the septum. 

The clavicles of the Dog are always rudimentarj', 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 oth'^r digits. When the Dog 
stands, the metacarpal bones of these digits are nearly verti- 
cal; the basal phalanges are horizontal; the middle and the 
distal phalanges are inclined in the form of a V with the apex 
(the articulation between the two) downward. The claws 
are, consequently, raised from the ground, the foot resting 
partly on a thick integumentary pad, which lies beneath the 
basal phalanges; and, partly, on the under surfaces of the 
joints between the middle and the distal phalanges. The dis- 
tal phalanges are kept bent upon the middle ones by elastic 
ligaments, which pass from one to the other, and which an- 
tagonize the action of the long flexors. The Dog, therefore, 
possesses the mechanism for the retraction of the claws, but 
its action is not sufficient to protect them from wear. Fahellm^ 
or sesamoid bones developed in the tendons of the (in^trocne 
inius, lie behind the condyles of the femur. The fibula is thin 



THE MYOLOGY OF THE DOG. 355 

End closely applied to, but not anchylosed 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 developed. 

In the myology of the Dog the insertion of the tendon of 
the external oblique muscle of the abdomen presents some in- 
teresting peculiarities. The outer and posterior fibres of this 
muscle end in a fascia which is partly continued over the 
thigh as fascia lata, and partly forms an arch (Poupart's liga- 
ment) 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 peotineus 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 
muscle ; and, in the absence of a complete clavicle, the outer 
fibres of the latter and those of the anterior part of the del- 
toid are conlinuous. In this way a muscle which has been 
called levator humeri lyroprius is formed. The omohyoid and 
the subolavius are absent. There is a trachelo-acromialis and 
a dorso-epitrochlearis. The supinator longus is absent, but 
there is a pronator quadratus. The extensor cominunis digi- 
torum mawds divides into four tendons, in which sesamoid 
bones are developed over the articulations between the first 
and second phalanges. The extensor primi intemodii pollicis 
is absent. The extensor secundi intemodii is one muscle witli 
the extensor indicis. The extensor minimi digiti sends ten- 
dons to the third, fourth, and fifth digits. All these deep ex- 
tensors have sesamoid bones over the metacarpo-phalangeal 
articulations. The palmaris longus appears to be absent; 
but all the other flexors of the raanus, even the palmaris hre- 
vis, are represented. The tendons of the flexor pollicis longus 
aud flexor digitorum, perforans are united. The divisions 
which the common tendon sends to the five digits develop 
sesamoid bones, just before their insertions into the bases of 
the distal phalanges. The fifth digit has its abductor, flexor 



356 THE ANATOMY OF VERTEBRATED ANIMALS. 

brevis, and opponens ; the poUex, an abductor, adductor, flexor 
brevis, and, perhaps, an opponens. The second, third, and 
fourth digits have each a pair of flexores breves, which repre- 
sent the interossei, and are inserted into the bases of the prox- 
imal phalanges, a relatively large sesamoid being developed 
in each. Each 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 flsxor brevis digitorum 
pedis. The tendons of the fl£xor hallucis longus and flexor 
perforans unite into a common tendon, which subdivides into 
slips for the digits. 

The dental formula of the Dog is i. j-i-j c. ^j p. m. \^^ 

in. j4^=4:3. The two upper inner incisors, on each side, have 

distinctly trilobed crowns — the lateral cusps of the crown 
arising from outgrowths of the cingulum at its base. The 
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 fore- 
going ; but, firstly, the posterior lobe is relatively much larger, 
and pointed, so as to form an obvious second cusp ; and, sec- 
ondly, a strong process of the crown projects inward from its 
anterior end, and is supported by a distinct fang — so that this 
premolar is three-fanged. It is termed a carnassial, or secto- 
rial, tooth, as it bites like a scissors-blade against a corre- 
sponding tooth in the mandible. The preceding teeth have 
cutting crowns ; but those of the molars are broad and crush- 
ing. 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 ante- 
rior. 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 pos- 
terior edge of which is trilobed, as in the upper premolars; 



THK DENTITION OF THE DOG. 367 

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, which bites against the 
inner side of the upper fourth premolar, 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 cusp. The two posterior cusps are very much 
lower than 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 
premolar, and the lower the anterior molar. The milk denti- 
tion of the Dog is d.i. |^ d.c. J^ 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, dentition. 
The middle deciduous molar in both jaws resembles the hinder- 
most premolar of the adult dentition, and the hindermost, the 
tirst molar of the adult. The so-called " first premolar " of the 
adult, and the anterior molars, appear before any of the decid- 
uous molars are shed. 

The caecum 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 subclavian. 

In the brain, the olivary bodies are inconspicuous, the 
corpora trapezoidea large, and the corpora mammillaria dis- 
tinctly double. The olfactory lobes are very large, and ex- 
pand posteriorly on the sides of the brain into a broad mass 
continuous with the gyrus uncinatus, or hippocampal lobule. 
The cerebral hemispheres extend for a considerable distance 
over the cerebellum, in the upper view, and overlap it later- 
ally. 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-mar- 
ginal 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 



358 THE ANATOMY OF VERTEBRATED ANIMALS. 

immediately bounds the Sylvian fissure, one which runs along 
the upper margin of the hemisphere, and one between these 
two. The corpus callosum is long, and the anterior commis- 
sure well developed. 

There is a museulus 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 prom- 
ontory, and its tendon passes directly outward to the mal- 
leus. 

The male is devoid of Cowper's glands. The penis has a 
bone, and the glands 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 Procyonidm depart, on the one hand, and the 
Cats, Civets, and Hyeenas on the other. The former grou)) 
[Arctoidea) have the cavity of the bulla tympani 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 lacerurn 
jyosticuni. The intestinal canal is devoid of a cseouva. The 
large penis has a bone which is not grooved ; there are nc 
Cowper's glands, and the prostate 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 
par-occipital is closely applied to the posterior wall of the bulla. 
The mastoid process is often obsolete. The condyloid foramen 
opens into a fossa common to it and the foramen lacerum 
posticum. All have a short cascum. The penis is small, ar.d 
lits bone small, irregular, or absent. They have Cowper's 
'glands and a well-developed prostate. 

The Gynoidea are all digitigrade, and resemble the Dog 
in their dentition. The Arctoidea are plantigrade, while the 

* See Prof. Flower's important memoir on tlie Glassifleation of the Gar 
nivora in the Proceedings of the Zoological Society for 1869. 



THE PINNIPEDIA. 359 

Ailuroidea are for the most part digitigrade, but may be plan- 
tigrade. 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 
tectorial teeth lose their marked characters, and the molars 
have flat and tuberculated crowns. The anterior premolars 
fall out as age advances. It is a remarkable circumstance that 
the teeth of frugivorous and carnivorous Bears exhibit no such 
differences as would lead to a suspicion 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 i. |^ c. -Ej p.m. |^ 
m. J-f-J = 30. The canines are very long and sharp. The pre- 
molars are like the Dogs', except that they are sharper, and 
that the hindermost (the sectorial tooth) has hardly any in- 
ternal 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 deepl^'-bifnrcated 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 digitigrade, 
and the apparatus for the retraction of the ungual phalanges 
is so well developed that the claws are completely retracted 
within sheaths of the integument, when the animal does not 
desire to use them. To this end the 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 naila 
are sometimes reduced in number, or even altogether abortive. 
The inner and the outer digits of the pes are very large. The 
incisors vary in number and lose their cutting form. The pre- 



860 THE ANATOMY OF VERTEBRATED ANIMALS. 

molar and molar teeth are similar in character, 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 Carmvora ; 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 cerebral 
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 Otaridce, the 
2'richechidce, and the Phocidce. 

1. The Otaridce, or Eared 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 supporting 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 tympaid, 
the perforation of the alisphenoid by a canal, and the presence 
of a crest on the inner surface of the parietals, is extremely 
ursine. 

2. The Trichechidae, or Walruses, are devoid of external 
ears, but resemble the Otaridoe 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 develop- 
ment of the superior canines. The Walruses resemble the 
Bears in another point, namely, in the presence of a supple- 
mentary bronchus ; the right bronchus, before it reaches the 
lung, dividing into two trunks, a large and a small. The thy- 
roid 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 rudimentary 
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 



THE PHOCID^. . 361 

jaw. In the mandible there are no incisors, but a single short 
canine is followed by three, similar, simple teeth, and by one 
ctlier, which is caducous. 

The dental formula is therefore i. ^ c. ^^ p. m. ni. ^ 

3. The I'hocidoB, 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 mai-ked, though shorter in proportion than 
that of the Eared-seals. The nasal apertures are slit-like and 
can be closed at will, the eyes large and brilliant, and the 
auditory apertures small and devoid of a pinna. The limbs 
are large, and their distal longer than their proximal divis- 
ions. The fore-limb is buried beyond the elbow in the com- 
mon 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 backward 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 a Cetacean. The Seal has twenty 
dorso-lumbar vertebrse, of which five are lumbar. There are 
four sacral vertebras, but only one of these unites with the ilia. 
Eleven vertebrae enter into the formation of the short tail. 
There are ten true ribs and nine sternebrse, the manubrium 
being prolonged forward into a long cartilaginous 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 downward 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 hori 
16 



362 THE ANATOMY OF VERTEBEATED ANIMALS. 

zontal, and the synchondrosis between the basisphenoid and 
presphenoid persists. In all these respects the Seal's skull is 
Btrikinglj' 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 ossi- 
fied into one mass with it. The two ethmoidal turbinals (or 
the superior and middle) are small and flattened, and the lat- 
ter anchyloses 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 anchylosed with the periotic and tympanic. 
The latter is massive and shell-shaped, somewhat as in the 
Cetacea, but it has rather diiferent relations to the auditory 
meatus. The periotic is very large, and its tumid pars mas- 
toidea 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 premaxillse are very small, but 
these bones extend far up the sides of the anterior nares. 
The maxillae 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 articu- 
lates with the cuneiform bone, as well as with the unciform. 

The ilium is short, and the long pubis and ischium are 
greatly inclined backward, so that the long diameter of the os 
innominatum makes only an acute angle with the spine. The 
femur is much shorter than the humerus. The tibia and fibula 
are anchylosed, and more than twice as long as the femur. 
The pes is longer than the tibia. The astragalus has a pecul- 
iar, roof-shaped, tibial surface, and sends a process backward 
which contributes to the formation 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 peetoralis tnajor is very large, and 
■rises 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, flexor brevis, and oppo- 



THE PHOCID^. 363 

nens 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 iu 
effecting the locomotion of tlie Seal. The pectineus is very 
small, and the other adductors are inserted, not into the femvir, 
but into the tibia. The glutmus maximics is inserted into the 
whole length of the femur. The semi-membranosus and semi- 
tendlnosus are replaced by a caudo-tiMalis, which arises from 
the anterior caudal vertebras and is inserted into the tibia, 
some of its tendinous fibres extending to the plantar aspect 
of the hallux. The poplitmus and gastrocnemius are strong, 
but there is no solasus. The tendon of the plantaris passes 
over tiie calcaneum and ends on the plantar fascia of the per- 
forated tendon of the fourth digit. The other perforated ten- 
dons seem to arise from the fascia attached to the calcaneum. 

The dental formula is i. ^ c. ^ m.p.m. ^-^ — 34. 

The grinding teeth have triangular crowns with notched 
edges, and at most two fangs. 

The milk-teeth are shed during foetal 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 hindermost of 
these last will be a true molar. 

The tongue is bifid at the extremity. The oesophagus, 
verj- wide and dilatable, passes without any very well-marked 
line of demarcation into the stomach, which is a great pyri- 
form 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 with a csecum. 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 vence hepaticce of 
the several lobules open. After traversing 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, sui> 
ported bv a loop of the cutaneous muscle. There is a large 
OS penis, which presents a groove for the urethra inferiorly. 
Tlie prostate is small, and there are no vesicute nor Cowper's 
glands. The testes lie just outside the inguinal canal. Tlie 



36-1 



THE ANATOMY OF VERTEBRATED ANIMALS. 



anus 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. 

11. The Probosaidea. — These are massive animals, walking 
upon the extremities of the five toes, with which each foot i3 
provided, and upon a great tegumentary cushion which uuitoa 
these, and forms a flat sole behind them. 




Tlie nose is prolonged into a flexible proboscis, which is at 
once a strong, and a delicate, organ of prehension. The hairy 
covering is scanty in the recent species ; but there were abun- 



THE PROBOSCIDEA. 36ib 

3aiit long hair, and an undercoat of wool, in at least one 
extinct Proboscidean, the Mammoth {Elephas primigenms), 
which ranged over Northern Europe and Asia during the gla- 
cial epoch. The pinna of the ear is large and flat. The testes 
of the male remain in the abdomen, and the mammse of the 
female are placed between the fore-limbs. 

The dorso-lumbar vertebras 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 vertebra, followed by a comparatively short tail. The 
centra of the vertebrae are far more flattened, from before 
backward, 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 cav- 
ities in the diploe. The interspace between the inner and the 
outer tables of the skull is often, in an old elephant, consider- 
ably 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 pari- 
etals are much narrower at the sagittal suture than elsewhere. 
The premaxillae are very large, and the nasal bones short, the 
nasal passages being nearl}' 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 anchylosed 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 Pro- 
boscidea present many curious approximations. There are 
no clavicles. In the antebrachium, the radius is permanently 
fixed (though not anchylosed) in the prone position, crossing 
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 acetabu- 
lum, 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 hiiid-leg ; the flexion of which, 
at this point, when the animal walks, gives an elephant a gait 



306 THE ANATOMY OF VERTEBRATED ANIMALS. 

which is strikingly different from that of other quadruped* 
The tibia is relatively short. The fibula is distinct and com- 
plete, 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 com- 
posed of dentine and cement, with or -without a longitudinal 
belt of enamel, and, in the recent Elephants, 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 unworn, are always ridged, the ridges very 
often being made up of distinct tubercles. The intervals be- 
tween 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 bv the attrition of those which are opposed to them. 

The stomach is simple and elongated, and there is a very 
wide coscum. The trilobed liver has no gall-bladder. The 
heart has two anterior cavse. 

The cerebellum is left uncovered by the cerebral hemi- 
spheres ; -which, in the existing Elephants, are large, and have 
greatly-convoluted surfaces. 

The male reproductive organs exhibit two very large ve- 
siculse 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 mandible, in 
addition to the large ones in the premaxillie. And in some of 
these animals, as in certain other extinct Elephants, the an- 
terior grinding teeth had vertical successors. The Miocene 
genus, Dinotherhim, possessed two large, downwardly-direct- 
ed 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 
Africa, where they are represented by t-wo very distinct forms. 



THE HYKACOIDEA. 367 

to -which the names oiLoxodon (E. Africanus) and JHuelephas 
{JE. 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 Hyrax, which is the 
sole member of this group, was referred by Pallas to the Ro- 
dents ; and by Cuvier, who demonstrated that it could not be a 
Rodent, it was placed among the Ungulata, in the immediate 
neighborhood of Bhinooeros, without any better evidence than 
that afforded by the characters of the molar teeth. Prof. 
Brandt, of St. Petersburg, in an elaborate memoir just pub- 
lished, arrives at the conclusion that it is a " gliriform Ungu- 
late," 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 be- 
tween the ZTngulata, on the one hand, and Hodentia and In- 
sectivora, on the other. 

The small, Rabbit-like, animals comprised in the genus 
Syrax 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 biud-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 pen- 
dulous penis, but no scrotum ; and there are four inguinal and 
two axillary teats. 

There are from twenty-nine to thirty-one dorso-lumbar 
vertebrae, which is the greatest number known in any terres- 
trial mammal. Twenty-one or twenty-two of these are dorsal. 
No mammal, except Gholoepus, the two-toed Sloth, possesses 
so large a number of dorsal vertebrae 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. Part of the articular 
facet for the mandible is formed by the jugal, which extends 
i'orward until it comes into contact with the lachrymal bone. 
The base of the external pterygoid process is perforated by a 
canal, as in Ferissodactyla and Lemuridce. There are large 
pre- and post-tympanic processes, and the post-tympanic is 
much shorter than the par-occipital process. The premaxillaa 
are large, and unite extensively with the nasal bones ; the 



368 THE ANATOMY OF VERTEBRATED ANIMALS. 

perpendicular ramus of the mandible is very wide, and some- 
what 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 
Pmssodactyla. There are no clavicles, but the coracoid pro- 
cess 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 Ro- 
dents. The tibia and fibula are complete. The extremity of 
the inner malleolus articulates with a slielf-like process of the 
astragalus, the distal face of which bone has no facet for the 
cuboid. The digits i. and v. are not represented even by rudi- 
ments. The terminal phalanx of ii. is longitudinally cleft. 

The dentition of the adult is i. jr^ c. 5T0 jo.wi. ^-rj, and 

m. jT-j. The outer upper incisors are very small, and soon 

fall out ; the inner, which are very large, curved, and have a 
thick coat of enamel on their anterior faces, continue to gro^v 
throughout life, as in Rodents. The lower incisors have 
crowns denticulated at the edges, like those of Galeopithecus 
and some Bats. They bite upon a callous pad which lies be- 
hind 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, part of the Eustachian 
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 oiF the cardiac from the pyloric 
division of the stomach. The cardiac portion is lined by a 
dense epithelium. The intestine is provided with three cseca 
— one in the ordinar}' 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 ilammals general!}', but 
near the fundus, as in some few Rodents. 

The male has vesiculce semi?iales, prostatic and Cowperian 
glands. The uterus is two horned, and the vulva and anus are 
surrounded by a common fold of integument. 

In the foetus the yelk-sac and the vitello-intestinal duct 
early disappear. The amnion is not vascular. The allantoia 



THE KODENTIA. 3C9 

spreads over the interior of the chorion, and gives rise to the 
broad zone-like placenta, which is composed of both maternal 
and foetal parts. The maternal vessels pass straight through 
the thickness of the placenta tovrard its foetal surface, on 
which they anastomose, forming meshes, through which the 
vessels of the foetus pass toward the uterine surface of the 
placenta. 

The species of the genus Syrax are found only in Syria 
and Africa. No fossil Hyracoidea are known. 

The DiscoiDEA. — The Mammalia with discoidal placentae 
are the Modentia, the Cheiroptera, the Insectivora, and the 
Primates. 

1. The RoDBNTiA. — 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. 

With the exception of one group of Rodents, there are only 
two teeth in the premaxillee ; and these have the same char- 
acters 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 hinder- 
most has displaced a milk-tooth ; but, where the grinding- 
teeth are fewer than three, or only three, none of them dis- 
place 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 be- 
fore backward. 

With the exception of one group, the Dormice {MyoxinoB), 
all Rodents have a large cacum. 

The cerebral hemispheres leave the cerebellum largely 
uncovered, when the brain is viewed from above. They are 



370 THE ANATOMY OF VEETEBRATED ANIMAIiS. 

either smooth externally, or very moderately convoluted. 
The coq3us callosum is well developed. 

With the exceptions noted, the foregoing characters are 
universal among the Uodentia. There are other peculiarities 
which are generally present, and, when they exist, are very 
characteristic, though they are not universal. 

Thus the dorso-lurabar vertebrae are usually nineteen in 
number. There is a large interparietal ossification. The 
jugal bone is comparatively short, and occupies only the mid- 
dle 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 backward 
over the infra-spinous fossa. There is a ninth bone in the car- 
pus 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-sea- 
son. Vesiculce serainales and prostatic glands are present. 
In the female the uterus is, in many genera, completely di- 
vided 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 dor- 
sal region of the body are very much enlarged, acquire a pe- 
culiar structure, and formed the so-called " quills." Some of 
the Porcupines have prehensile tails. 

In Cavia and Uijdrochoerus 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 D'lpus^ the Jerboa, the long metatarsals 
become anchylosed together into a cannon-bone. 

In the Porcupines, the suborbital foramen is enormous, 
and an anterior fasciculus of the masseter muscle arises fi'om 
the maxilla, and traverses the foramen to its insertion. 

The Hamster ( Cricetus) has great cheek-pouches, provided 
with special retractor muscles connected with the spines of 
two lumbar vertebnr. 

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 glandular mass. The 
cardiac end of the oesophagus of the Dormouse is glandular 



THE ANATOMY OF THE RABBIT. 371 

and dilated like the prove nficuhis of a bird. And, in Arvicola, 
the stomach becomes deeply constricted, and a groove leads 
from, the oesophagus toward 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 Rodetitia are 
more numerous than those of any other mammalian order; 
aud 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 integument be- 
tween 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 Sathyeryus ; 
or aquatic, like the Water-vole — their structural differences 
are comparatively insignificant, and the subdivision of the 
order into large groups is proportionately difficult. 

Brandt has divided the Rodents according to their cranial 
characters into Soiuromorpha, Myomorpha, Systricomorpha, 
and Lagomorpha ; or, Squirrels, Rats, Porcupines, 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 pinnae 
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 vertebrae, of which twelve 
are dorsal. Of the four sacral vertebrae only the first unites 
with the ilia. The dorsal vertebrae have well-developed spinous 
and transverse processes. At about the eighth, a mammillary 
^locess, or metapophy sis, becomes obvious ; and in the succeed' 



S72 THE ANATOMY OF VERTEBRATED ANIMALS. 

ing vertebras this increases in length and strength, till in 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 
vertebrte. Accessory processes, or (mapophyses, are observa- 
ble in the last dorsal and four or five anterior lumbar vertebrae. 
The transverse processes of the lumbar vertebrae are exceed- 
ingly long, and that of the first lumbar is bifurcated at its ex- 
tremit}'. 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 longis- 
simus 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 related 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 vertebrae ; these give attach- 
ment to the crura of the diaphragm. 

The tubercles of the second to the eighth ribs inclusively 
are prolonged into spiniform processes, which give attachment 
to the tendons of the longissinnis dorsi. There are five ster- 
nebras and a 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 com- 
pressed 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 anchylosed 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 bj' the post-tympanic hook of the squamosal on 
the outside. The tympanic is prolonged upward and outward 
into a tubular meatus. The glenoid cavity is elongated from 
before backward. 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, oi 
incisive foramina are enormous ; and partly in consequence of 



THE MYOLOGY OF THE RABBIT. 373 

tliis, 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 pronation. 

The femur has a small third trochanter. The tibia and 
fibula are anchylosed. The internal cuneiform bone is want- 
ing, and the plantar surface of the navioulare 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 navioulare. This may represent a rudiment 
of the hallux with the en to-cuneiform. 

In the myology of the Rabbit the vast size of the flexors 
and extensors of the back has already been noted. The mus- 
cles moving the fore- and especially the hind-limbs, and the 
masseter, are not less remarkable for their dimensions. In the 
fore-limb, the supinator longus is absent. The extensor indicts 
and secundi internodii poUiois ioim one muscle. The extensor 
minimi digiti goes to the fourth and fifth digits. 'Yhe flexor 
perforans and the flexor pollicis longus unite in a common 
tendon which divides into five slips, one for each digit. There 
are three lurabricales from the radial sides of the tendons for 
the third, fourth, and fifth digits. 1\\eflsxor sublimis, ov per- 
floratus, for digits ii., Hi., and iv., arises from the inner con- 
dyle as usual ; but that for the fifth digit springs from the 
pisiform bone — thus simulating the ordinary arrangement of 
the perforated flexor in the pes. There is no pronator quad- 
ralus y but the palmaris longus is distinct, and its slender ten- 
don expands into the palmar aponeurosis. Each digit, except 
the pollex, has a pair oiflsxores 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 A.chillis, 
which passes over the end of the calcaneum, being connected 
with this and the tendo Achillis by a strong fascia laterally, 
but being otherwise separated from it by a sjmovial sac. In 
he sole of the foot it divides into four tendons, which be- 
come the perforated tendons of the four digits. The flexof 
perforans and flexor hallucis are fused into one muscle, the 



374 THE ANATOMY OF VEETEBEATED ANIMALS. 

tendon of which divides in the sole into the four perforating 
tendons. There are three lumbrioales, and four pair of inter- 
ossei [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 pop- 
litasus, becomes tendinous about the middle of the leg, passes 
behind the inner malleolus, and runs along the inner and dor- 
sal aspect of the second metatarsal to be inserted into the ex- 
tensor tendons. It seems to stand in the same relation to the 
second digit as the peroruxus qidnti, on the opposite side of 
the pes, to the fifth digit. The peronmus longus is inserted 
into the base of the second metatarsal : & peronmus hrevis, p. 
quarti, and^. 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. 60, and Figs. 21 and 22). 
There is a single large corpus maminillare. Of the corpora 
quadrigemina, the nates are larger than the testes. There 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 cresoentic aperture leads into the 
lachrymal canal. The large lachrymal gland lies above and 
external to the eyeball, and there is a well-developed Harde- 
rian gland on its lower and inner side. 

The dental formula is i. -j^j- c. ^ p.m. jr^ fn. jr^ =: 28. 

The lower, and the inner upper, incisors are very large and 
long ; thej 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 inci- 
sors from the first premolar above and below. The grindiug- 
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 pre- 
senting some differences. The young Rabbit has three inci- 
3oi's 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 cseoum. Spe- 
cial glands pour their secretions at the side of the anus. 

The pancreas is very large, and its duct enters the intea 



THE INSECTIVOEA. 375 

tine nearly a foot from the pylorus, and far distant from the 
biliary duct. 

There are two anterior cav£e; and the external jugular 
7ein 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 tinciv 
into the vagina. 

The distribution of the Rodentia is almost world-wide, 
Madagascar being the only considerable island in which indi- 
genous Rodents are unknown. The Austro-Columbian prov- 
ince 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 Insectivoka. — It is exceedingly diflficult to give 
an absolute definition of this group of Mammals. But all the 
Inseotivora possess more than two incisors in the mandible ; 
and their molar teeth, which are always coated with enamel, 
have tuberculated crowns, and form roots. 

The fore-limbs have the structure usual among ungui- 
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 toward the Rodentia, the Tupayw toward the 
Lemurs; while the Moles, on the one hand, and the Galeo 
pithed on the other, are aberrant modifications. Relations of 
a more general character' connect them with the Garnivora 
and the Ungulata. 



J76 THE ANATOMY OF VERTEBRATED ANIMALS. 

The Hedgehog [Erinaceus JEuropceus) is pentadactyle and 
plantigrade. It has a long flexible snout. The eyes are 
small; the pinna3 of the ears are rounded, and the integument 
lining the concha is produced into a transverse, shelf-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 converted into strong fluted spines. There are 
tvrenty-one dorso-lumbar vertebrae (of which fifteen are dor- 
sal, and six lumbar), three or four sacral, and twelve to four- 
teen caudal. Accessory processes, or metapophyses, are de- 
veloped on several of the dorso-lurabar vertebrae. The sterne- 
brsB 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 perpendicular 
occipital face of the cranium, and looks backward. 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 fora- 
men lies upon the face. There are unossified spaces in the 
bony palate, and the posterior margins of the palate are thick- 
ened, as in the Lemurs. The large and bullate tympanic bone 
does not anohylose 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 anchylosed at the symphysis. The supra-scapular fossa is 
wider than the infra-scapular. The spine is strong, and the 
acromion bifurcates, sending a prolongation backward. The 
clavicles are long and convex forward. The humerus has an 
intercondyloid foramen ; but there is no foramen above the 
inner condyle, and this circumstance is unusual among the 
Tnsectivora. The bones of the antibrachium are fixed in thg 
prone position. There is an os centrale in the carpus, so that 
it has nine bones. The scaphoid and lunare are anchylosed, 
as in the Oarnivora, and the pisiform bone is much elongated. 
The poUex and the fifth digit are the shortest. 



THE MYOLOGY OF THE HEDGEHOG. 377 

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 trochanter. The distal 
ends of the tibia and fibula are anchylosed 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 pannieuli, encircles the body latr 
erally. 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 orbicular muscle pass into one an- 
other 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 dimensions 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 toward the centre of the ventral 
side of the body, and forcibly enfolding the trunk and limbs 
within the bag thus formed. It is, in fac t, the chief agent in 
coiling the body up, and keeping it so ceiled. 

Numerous muscular bundles take a 1 adiating direction on 
the dorsal aspect of the body, and antagonize the orbicularis : 
1. A pair of slender occipito-frontales arise from the occipital 
crest, and are inserted into the integument 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 orbicu- 
laris. 3. A pair of broader cervico-orbioulares arise from 
Ihe fascia of the neck, and pass to the dorsal part of the an- 
terior fourth of the orbicularis. 4. Slender dorso-orbiculures 
arise close to the hinder ends of the trcqjezii and spread out 
above the foregoing. 5. Two stout muscles, coccygeo-orbicu' 



378 THE ANATOMY OF VERTEBEATED ANIMALS. 

lares, arise from the middle caudal vertebrae, and, after re- 
ceiving fibres from the ventral region, end in the dorsal mar- 
gins of the orbicularis. 6. Tvi^o muscles attached to the 
pinnae of the ears (auriculo-orbiculares) pass backward 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 outward and forward to the sides of the lower jaw and 
the integument of the face and ears. Muscular slips fi-om 
these are sent up over each shoulder to the orbicularis. 2. A 
humero-abdominalis arises from each humerus beneath the in- 
sertion of the pectoralis major, and, passing backward 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 regions to the coccy- 
geo-orbicndaris ; the internal fibres pass to the prepuce, and 
over the middle line of the abdomen, in front of it. 3. A hu- 
mero-dorsalis arises from the humerus close to the foregoing, 
and, passing upward and backward through the axilla, spreads 
out in the mid-dorsal integument and the orbicularis. 

The contraction of all these muscles must tend to bring 
togther the edges of the integumentary bag, and to tuck the 
head, tail, and limbs into it. 

In the myology of the limbs the following points are note- 
worthy : The supinator longus, pronator teres, and palmaris 
longus, are absent. The palmaris brevis is present. A single 
muscle takes the place of the extensor secundi intern odii polli- 
cis and extensor indicia, and sends a third tendon to the m.id- 
dle digit. The extensor minimi digiti supplies the other two 
digits. The flexor perforans and flexor pollicis longus are rep- 
resented by five distinct muscular heads, each with a tendon 
of its own ; but all the tendons unite in the middle of the fore- 
arm, and the common tendon again subdivides into only four 
slips, the poUex receiving no tendon. There are no Imnbrica- 
les. The pollex has only a rudimentary _7?ea;c»r brevis and au 
abductor. The other digits have each two interossei, ot flex- 
ores breves, inserted into the raetacarpo-phalangeal sesamoids. 

In the leg, the solsus has only a fibular head, and iheflexoT 
brevis digitorum arises wholly from the calcaneum. 'Yhxi flexor 
hallucis and flexor pierforans have a common tendon, which, 
In the sole, divides into five tendons, one for each digit. 
There are no lumbricales, nor flexor accessorivK. The tibialis 
posticus seems to be represented by twc small muscular bel- 



THE BRAIN OF THE HEDGEHOG. 379 

.ies, 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 mus- 
cle goes to the tibial and plantar surface of the hallucal meta- 
tarsal, while the latter is inserted into the ento-cuneiform 
bone. The interossei pedis are represented by a pair oi flex- 
ores 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 

J 1 • . 3 ■ 3 0—0 4 — i 8 • 3 o /> 

formula is t. ^, c. ^p.m. ^, m. 3T3 = 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 Anthropomorpha^ 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 cusps are remarkably 
sharp and pointed, and the outer surface of the postero-ex- 
ternal 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 tbe 
anterior ridge is a basal prolongation of the tooth, on to which 
a curved ridge is continued inward and forward from the an- 
terior principal ridge, giving rise to an imperfect crescent with 
its convexity outward. 

According to Rousseau there are twenty-four milk-teeth, 

i. 4-7! d.m. j4y» which fall out seven weeks after birth. 

The brain of the Hedgehog is remarkable for its low or- 
ganization. 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 
marks the 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 man- 
ner, to the temporal lobe. The inner face of the hemisphere 
E resents neither convolution nor sulcus, except behind and 
elow, where a very broad depression follows the contour of 
the fissure of Biohat and the fornix, and represents the dentate 
Bulcus. Above, this sulcus ends behind the posterior margin 



380 THE ANATOMY OF VERTEBRATED ANIMALS. 

of the corpus callosum. The latter is remarkably short, and 
directed obliquely backward and upward. 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. 

In a transverse section, the corpus callosum is seen to be 
verv thin, and to curve upward and outward into the roof of 
the' ventricular cavity. The inner walls of the lateral ven- 
tricles, which answer to the septum lucidum, are thick, while 
tlie fornix is comparatively thin and slender. The anterior com- 
missure is very stout. In this circumstance, 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 calcarine fissure, and the lateral ven- 
tricle extends forward 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 trans- 
versely elongated. The cerebellum has a large vermis and 
small lateral lobes ; Hhe flocculi are prominent and are lodged 
in fossffi 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 rugae. The intestine is about six 
times as long as the body, and presents no distinction into 
small and large ; nor is there any caecum. The liver is 
divided by deep fissures into six lobes; a cential 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 
sarotid is remarkable. When it reaches the base of the skull 
it enters the tympanum and there divides into two branches, 
of vchich one traverses the stapes, and, passing forward in a 
groove of the roof of the tympanum, enters the skull and gives 



THE SPLANCHNOLOGY OF THE HEDGEHOG. 381 

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 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 foiu:-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 diaphragm. 

The testes of the male do not leave the cavity of the 
abdomen, but they descend as far as the inner side of the in- 
guinal ring, to which they are connected by a short guber- 
naculum and cremaster. The vasa deferentia descend 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 sperma- 
tozoa, and are usually regarded as vesiculse seminales. The 
middle pair (the so-called " prostatic 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 differentiated into prostatic and bulbous 
urethra. 

The ovaries are enclosed in wide-mouthed peritoneal sacs, 
and a ligamentous band, the diaphragmatic ligament, extends 
from the ovary to the posterior surface of the diaphragm. 
The comua uteri are large and long. There are five pair of 
teats; the anterior pair being axillary and the posterior 
InguinaL The other three pair are equidistant, and lie along 
the ventral surface, internal to the edge of the orbicularis panr 
niculi. 



382 THE ANATOMY OF VEETEBRATED ANIMAIS. 

Like the Rodentia, the Inseotivora have a great diversity 
of habit; some Galeo^jitheci flitting through the air after the 
fashion of the flying Squirrels ; some arboreal, as the Tupaym ; 
some terrestrial and cursorial, like the majority of the order. 
A few are swimmers ; and some, like the fflole, are the most 
completely fossorial of Mammals. 

The most aberrant form of the Insectivora is the genus 
Oaleopithecus, 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 integument, 
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 expan- 
sion, the G-aleopitheous is enabled to make floating leaps, 
from tree to tree, through great distances. When at rest, 
the Galeopitheoi suspend themselves by their fore- and hind- 
feet, the body and the head hanging downward ; 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. The 
lachrymal foramen is in 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 
restrjcts the movement of the mandible to the vertical plane. 
A longitudinal section of the skull shows a large olfactory 
chamber projecting beyond that for the cerebral lobes, and twc 
longitudinal ridges, upon the inner face of the latter, prove thai 
ihese lobes must have possessed corresponding sulci. The 
tentorial plane is nearly vertical and the floccular fossae are 
very deep. 

The ulna is very slender infe.riorly, where it becomes anchy- 
losed to the distal end of the radius, which bears the carpus. 
When the ilia are horizontal, tlie acetabula look a little up- 
ward and backward as well as outward. The fibula is com- 
plete. As in the Sloths and most Pn?7iates, the navicular and 



GALEOPlTnECirS. 383 

cuboid readily rotate upon the astragalus and calcaneum, so 
that the planta pedis is habitually turned inward. 

The dental formula is i. ^75 c. j^ p.m. m. j^ = 34. 

The outer incisor, in the upper jaw, has two roots, a 
peculiarity 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 longitu- 
dinal 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 sac- 
culated cfficum is as long as the stomach, and its capacity 
must be greater than that of the latter organ. 

Galeopitheeus 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 
JPrimates. 

Galeopitheeus 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 acetab- 
ula, such as is seen in its extreme development in the Bats ; 
in the imperfect condition of the ulnse ; and in the pectoral 
position of the teats and the pendent penis. Both of these 
last, however, it must be recollected, are also Primatic charac- 
ters. Finally, the somewhat similarly pectinated lower incisor 
teeth are found in the Cheiropteran genera, Diphylla and 
Desmodus. 

But Galeopitheeus 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 caecum. 

On the other hand, the peculiarities of the skull and brain 
are mainly insectivorous, as is the two-fanged canine ; and 1 
see no reason for dissenting from Prof. Peters's view that Gal- 
eopitheeus belongs neither to the Primates, nor to the Chei- 
roptera, but tha,t it is an aberrant Insectivore. 

With respect to other Insectivora, it is worthy of note, 
that MacrosceJAdes has the radius and the ulna ancbylosed. 
The TupayoB possess a large caecum. Chrysochloris has pec- 
toral mammary glands ; Gentetes and the Moles have tte penis 
pendent. 



384 THE ANATOMY OF VEnTEBRATED AXDIALS. 

The TupaycB are soft-furred, long-tailed, tree-loving ani- 
mals, with complete bony orbits and a large cacum, and are 
those Insectivora whici 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 anchylosed, and the pubic bones do not 
meet in tlie symphj'sis. 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 anchylosed with 
the jaws. There is no caecum, and peculiar musk-glands are 
sometimes developed at the sides of the body. 

The Moles ( Talpince) 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 ihe carpus. 
The palmar surface of the broad manus is turned outward and 
backward. 




FiQ. 199.— The skeleton of a Flylug-Fo.'! (Pterop}ia). 

The manubrium of the sternum is very broad, and its ven- 
tral surface gives rise to a strong median crest. The scapula 
is as long as the humerus and the radius together. It is tri- 
quetral and possesses an acromial process, but no distinct cor 



THE CHEIROPTERA. 385 

racoid. The clavicle, which is verv strong, is perforated by a 
great foramen, and at the middle of its posterior margin sends 
off a truncated reentering process. Proximally, it furnishes 
an articular surface for the humerus. In the carpus there is a 
distinct centrale, and a large accessory C-shaped bone lies on 
its radial side. The pubes are separate 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. 

III. The Cheieopteea. — The Cheiroptera may be regard- 
ed 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 patagium, or expansion of 
the integument, uniting the fore-limbs with the body, and ex- 
tended, 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 upward and backward, in such a manner that 
its extensor face looks forward, and its flexor face backward. 
In consequence of this the knee looks upward and backward, 
and the toes are turned backward and slightly outward. Un- 
der 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, while the pollex, with its 
claw, is extended forward. In this position the animal shuffles 
along, with considerable rapidity; hauling itself forward by 
the claws on the polHces, and shoving itself along, by extend- 
ing the hind-limbs. 

The favorite attitude of a Bat, when at rest, however, is 
that of suspension by the claws of one or both legs, with the 
head downward and the patagium folded over it like a cloak, 
llie most active movement of the Bat is effected by flight, the 
fore-limbs being extended, and the patagium, which they sup- 
port, playing the part of the feathers of a bird's wing. 

The cervical vertebrae are remarkably large in proportion 
17 



386 THE ANATOMY OF VERTEBRATED ANIMALS. 

to the others, but, as in the rest of the vertebral column, the 
spinous 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 forward and to 
describe almost the quarter of a circle. As a consequence, the 
ftxis of the sacrum is at right angles to that of the anterior 
thoracic vertebrse. 

In the skull, the orbit is not divided by bone from the 
temporal fossa, and the premaxillie are relatively small, and 
sometimes altogether rudimentary. 

The clavicles are remarkably long and strong, and the 
broad scapula has a strong spine. The ulnoe are imperfect 
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. 

Tlie pelvis is very narrow and elongated, and the pubic 
bones are widely separated at the symphysis, as in some Jn- 
sectivora. The anterior caudal vertebras and the ischia are 
frequently united. The axes of the acetabula are directed 
toward the dorsal side of the body as well as outward ; 
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 bj' ligament, and there 
is an elongated bone, or cartilage, attached to the inner side 
of the ankle-joint which lies in and supports the patagium, 
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 cfECum. 

The heart is provided with two superior cavfe, a right and 
left ; and the smooth cerebral hemispheres leave the cerebel- 
lum completely exposed. 

The testes are abdominal throughout life, or may descend 
into the perinaeum, but there is no true scrotum. The penis 
is pendent. There are vesiculce seminales. The form of the 
uterus varies, being sometimes rounded and sometimes two- 
homed. 

The Bats are ordinarily divided into the Fncgivora and 
the Insectivora. 

a. The Frugivora live, as their name implies, exclusively 



THE CHEIROPTERA, 387 

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. 

The incisors do not exceed ^j. 

The pyloric portion of the stomach is immensely elongated. 

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 color, they are known as " Flying-Foxes " (Pteropus, 
Sarpy ia, etc.). 

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 an3' 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 |J-j or ?^, but their number may 
be much reduced. 

The integument of the nose is developed into an append- 
age 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 
Hbematophilma has been formed) are the most completely 
blood-sucking of all the Bats in their habits. They have a 
pair of enormous, sharp-pointed, upper incisors, while the four 
lower incisors are small and pectinated. I'he canines are very 
large and sharp, and the molars, which are reduced to two 
above and three below, on each side, have their crowns con- 
verted into sharp longitudinally disposed ridges, like the; 
edges of scissors. In Desmodus, the very narrow oesophagus 
leads into a stomach which would be of extremely small di- 
mensions, 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 



388 THE ANATOMY OF VERTEBRATED ANIMALS. 

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 
ly Orbignyi : 

" The Vampire Bat is often the cause of much trouble by 
bitino- the horses on their withers. The injury is generally 
not so much owing to the loss of blood as to the inflammation 
which the pressure of the saddle afterward produces. The 
whole circumstance has lately been doubted in England. I 
was therefore fortunate in being present when one was act- 
ually caught on a horse's back. We were bivouacking late 
one evening near Coquimbo, in Chili, when my servant, noti- 
cing that the horses were very restless, went to see what was 
the matter, and, fancying he could distinguish sometliing, sud- 
denly 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 distinguished, from being slightly swollen 
and bloody. The third day afterward we rode the horse with- 
out any ill eflFects." 

IV. The Primates.— The Primates have two pectoral 
mammae, and, rarely, additional ones upon the abdomen. In- 
cisor and molar teeth are always present, and, with one excep- 
tion, 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 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 exten- 
sive 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 Lemuridm, b, the 
Siniiadm, and c, the Anthropidm. 

a. The first of these divisions, the Lemuridm, is more 
widely separated, anatomically, from the other two, than these 
are from one another,f and it contains some forms which 
very closely approximate to the Insectivora, while others are 
nearly affined to the Rodentia. 

* "Voyage of the Beagle," Mammalia, p. 2. 

■f On tlie strength of these difl'erences M. Gratiolet relegated the Lemurs to 
the Insectieorn,; and Mr. Mivart, in his valuable paper ''On the Axial Skele- 
ton in the Primates," publislied in the Proceedings of the Zoological Society 
for 1855, divides the Primates into two sub-orders, Lemnroidea and Anthro- 
poidea. 



THE LEMURIDjE. 389 

All the JLemuriddB 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 patclies upon the integument covering 
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 its 
nail. 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 axis ; 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 face, outside the front margin of the or- 
bit. The frontal and the jugal bones are united behind the or- 
bit, 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 
communication. 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 vertebrae 
composing it, in some cases, being as many as nine. There 
are nine bones in the carpus. The ilia are narrow and elon- 
gated, and the ischia are not everted. In most Lemurs, the 
tarsal bones resemble those of the other Primates ; but, in 
Otolicniis and Tarsius, they have undergone a modification, a 
parallel towhich is not to be found among Mammals, but must 
be sought among the Batrachia. When the distance between 
the heel and the digits is great in other Mammalia, the elon- 
gation affects the matatarsal bones and not the tarsus ; but, in 
these Lemurs, the calcaneum and the naviculare 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 



390 THE ANATOMY OF VERTEBRATED ANIMALS. 

si^e, and is often denticulated, or comblike, at its free end. 
The stomach is simple, with the cardiac and pyloric apertures 
ajiproximated. The ca3cum is long, and has no vermiform 
appendage. 

In many Lemurs {Stenops, JSTycticehus, Perodicticus, Arcto- 
celnis, Taivh's) 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 uncovered. 
The gyri and sulci are scanty, or absent, upon the outer sur- 
face of the hemispheres, but the internal face exhibits the cal- 
carine sulcus. The large olfactory lobes project forward be- 
vond the cerebral hemispheres. 

The pendent penis of the male commonly contains a bone ; 
tlie testes are lodged in a more or less complete scrotum ; and 
vesiculffi seminales are generally present. 

In the female, the uterus has two long comua, and the 
urethra traverses the clitoris. Sometimes there are one or 
two pairs of teats on the abdomen, in addition to the ordinary 
pectoral pair. 

The LemuridcB are distinguishable into two families, the 
Lemurini and the Chelromyini. 

In the Lemurini, the pollex is large, opposable, and almost 
always has a broad, flat nail. 

The usual dental formula is i. -jr-j c py^.m. m. jtj, or j^^. 

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 compressed, 
long and proclivous, and the canines, which resemble them in 
form and direction, are closely appHed to the outer incisors. 
When six grinders are present, the anterior three are premo- 
lars. The anterior premolars, and sometimes all of them, have 
triangular and sharp-pointed crowns ; the first premolar of the 
lower jaw, in fact, resembles a canine, but its true nature is 
shown bv its biting behind the upper canine, not in front of it. 

Very generally the crowns of the upper molars are quad- 
ricuspidate, and an oblique ridge passes from the antero-ex- 
ternal to the postero-internal cusp, as in the highest Primates ', 
while, in tlie lower jaw, there are either two transverse ridges, 



THE SIMIADiE. 391 

»r longitudinal crescents. The cusps of the molars are usually 
much produced, as in the Insectivora. 

In the Gheiromyini, the pollex is not truly opposable, and 
its naU 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 atfy 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 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 Modentia. No canines 
are developed, and there are four grinders with simple crowns 
on each side above and below. 

The formula of the milk dentition is d.i. ^r-j d.c. J^ d.m. j4|. 

The JLemuridcB are confined to Eastern Asia, Madagascar, 
and South Africa ; Madagascar presenting the greatest num- 
ber and diversity of genera and species. 

b. In the great group of the Simiadm, which contains the 
Apes and Monkeys, the attitude is sometimes habitually quad- 
rupedal, the axis of the body being horizontal ; but, in a few 
species, the trunk is habitually held in a more inclined posi- 
tion, and the animals readily assume the erect attitude. 

The Simiadce are sometimes terrestrial in habit, and good 
runners, but they are always excellent climbers, and, in some 
oases, they are necessitated by their organization to be almost 
as thoroughly arboreal as the Sloths. 

The hallux is 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 oth- 
ers, 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 

* Among the Lemuridce, the outer and upper incisors of Nijcticebus and 
Tardus soon fall out. Ziehanotm and Tarsim have only one pair of incisors 
in the mandible. 



S92 THE .VN'ATOMY OF VERTEBRATED ANIMAT-S. 

brain. The absolute capacity of the cranium is less than forty 
cubic inches ; and, if there is any difference in the length and 
abundance of the hair which covers the body, it is longest on 
the back. The uterus is undivided, and the clitoris is not 
perforated by the urethra. The teats are only two in number, 
and they are pectoral. 

The Siiniadw are divisible into three families — the Arcio- 
pitheclni, the Flatyrrhini, and the Catarrhiiii. 

1. The Arctopitheoini, or Marmosets, are small, thickly 
furred, long-tailed, habitually quadrupedal. Squirrel-like ani- 
mals, 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 PlatyrrhinL 




THE ARCTOPITHECINI. 393 

The fore-liinbs are shorter than the hind-hmbs. The pol- 
.ex is not opposable, nor susceptible of extensive abduction 
from the other digits, which it resembles in being provided 
with a sharp, curved claw. The manus, consequently, is a 
mere paw, and the term " hand " is not applicable to it. 
The hallux of the foot is very small, and is provided with a 
flat nail. The nails of all the other digits of the pes are fal- 
cate. The plantar surface is very long, and the digits are very 
short. It follows from these facts that the term " quadrumar 
nous " is not appUoable, in any sense, to the Marmosets. 

The skull is remarkable for the smooth and rounded sur- 
face and relatively large size of the brain-case. Although the 
orbits are large, the brow ridges are inconspicuous, and the 
occipital region of the skull projects so far backward that the 
occipital foramen may lie completely upon the under surface 
of the skull, toward the junction of its middle and posterior 
thirds ; and have its plane almost horizontal, when the face 
looks forward. 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 usually nineteen dorso-lumbar vertebra, and the 
transverse processes of the atlas are somewhat broad and flat- 
tened. 

The dental formula is i. j— j c. ^^ p.m. 3T3 »i. 2T5 = 33. Thus 

the number of the teeth is the same as in man and the Catar- 
rhini ; but in the number of the premolars and molars the 
Arctopithecini differ from both the Gatarrhini and the Platyr- 
rhini, having one premolar more than the former and one true 
molar fewer than the latter. In Sapale, the lower incisors 
are proclivous ; and the canines are approximate to them, and 
similarly inclined, as in the Lemurs. 

Although the manus is a paw and the pollex is not oppos- 
able, 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 ihe flexor pr<yfunf 
dus 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 SimiadoB. The extensor seoundi internodii pollicia 
is united with the extensor indicia, and the extensor minimi 
digiti gives oflF slips to the third, fourth, and fifth digits, so that 



S94 THE ANATOIIY OF VERTEBRATED ANIMALS. 

there is a complete set of deep extensors. The four dorsal and 
three pahnar iiiterossei are not distinctly subdivided, but they 
send slips to the extensor tendons. 

There are four 7>s/-0rt,cei .■ p. longus,p. hrevis,p. quarti, and 
p. quiiiti digiti. Tlie flexor brevis dlgitorum 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 aoaessorius furnishes almost 
the whole of the long flexor tendons of the hallux, the flexor 
lo7igus digitorum supplying the perforating tendons of the 
second and fifth digits; while the_^fia;or hallucis longus gives 
off the corresponding tendons of the third and fourth digits. 
The interossei, in the pes, appear to be represented only by 
the pairs of muscles which act as short flexors of the basal 
phalanges, and these lie altogether 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 completely 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 hemispheres are al- 
most smooth, but the Sylvian fissure is well marked, and there 
is a trace of that of Rolando. On the inner face of each hemi- 
sphere, the calcarine fissure is deep and gives rise to a well- 
marked hippocampus mi?ior within the posterior comu of the 
lateral ventricle. The corpus callosum has about a third the 
length of the hemispheres. The septum 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 [Ateles), 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 modified, 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 Monke3^ In most, the fore-limbs are shorter than 
the hind-limbs, but the reverse is the case in the Spider Men 



THE PLATYRRHINI. 395 

Keys. The pollex differs less from the other digits than it 
does in the Gatarrhitii. 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 extensive movements in abduction and adduc- 
tion. 

The number of the dorso-lumbar vertebras varies from 
ieventeen to twenty-two, the greatest number being pos- 
sessed hy Nyctipithecus^ which has 33 (14 + 8 or 15+7). In 
those forms which have prehensile tails the terminal caudal 
vertebrae are flattened from above downward. The articular 
surface of the head of the humerus looks more backward than 
inward ; and, not unfrequently, there is a foramen above the 
inner condyle. The carpus contains nine bones. The pollex 
is generally complete, but, in Ateles, it is reduced to a small 
metacarpal (to which, usually, a single minute nodular phalanx 
is articulated), and is completely hidden beneath the integu- 
ment. The pelvis is, generally, elongated, and the anterior 
ramus of the pubis lies at right angles with the long axis of 
the narrow ilium. The tuberosities of the ischia are everted, 
but not rugose. In Aieles, the pelvis is broader, and the pubis 
forms a more open angle with the ilium. The calcaneal pro- 
cess 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 auditoiy meatus is 
not ossified, the tympanic bone retaining its foetal, 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 surface of the periotic bone 
there is a fossa overarched by the anterior vertical semicircular 
canal, in which the flocculus rests. In Ateles the greater part 
of the tentorium is ossified. In other respects, the skull pre- 
sents 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 facia] 
angle. The roof of the brain-case is depressed ; the plane of 
the occipital foramen is almost perpendicular to the basi-cra- 
nial axis; and that of the tentorium is very much inclined. 



396 TUE ANATOMY OF VERTEBRATED ANIMALS. 

The occipital condyles are, consequently, situated at the pos- 
terior end of the basis cratiii, 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 tentorium is hori- 
zontal, 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 cerebral cavity. The pre- 
maxillo-maxillarj' suture disappears early in Cebus. 

The formula of the adult dentition is i. ^ c. — n.m. — 

2 • 2 1 — 1 -r 3-3 

in. ^=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 perma- 
nent canines usually make their appearance before the last 
molar. 

The stomach is simple, the caecum 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 developed 
from the posterior wall of the windpipe between the cricoid 
cartilage and tlie first ring of the trachea. A very remarkable 
modification of the hyoid and larjnx takes place in Mycetes. 
The cornua of the hyoid are rudimentary, but its body is con- 
verted 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 carti- 
lages of Wrisberg and Santorini are replaced by a fibrous mass, 
which is united posteriorly with its fellow of the opposite side, 
[n addition to the hyoidean air-sac the ventricles of the larynx 
are dilated and prolonged upward, 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 Ateles, all its characteristic muscles {abductor, ad- 
ductor, flexor brevis, and opponens) are present, except the 
long flexor. 

In Nyctipithecus the pedal interossei are flexores breves, 
and lie on the plantar surfaces of the metatarsal bones, as in 
the Marmosets ; but both the adductor hallucis and the tranS' 
versus pedis are well developed. 



THE CYNOMORPHA. 397 

The biairi varies remarkably in dilTerent Platrjrrhini. In 
Chnjsothrlx, the cerebral hemispheres project beyond the 
cerebellum to a greater relative extent than in any other Mam- 
mal, 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 Ceius, 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 Gatar- 
rhini ; but, in Pithecia, Chrysothrix, and Nyctipithecios, the 
external sulci gradually disappear, until the brain is almost as 
smooth as in the Marmosets. On the inner faces of the hemi- 
spheres, however, the internal perpendicular, the calloso-mar- 
ginal, the calcarine, and the collateral sulci remain, while, in 
the interior of the hemispheres, the posterior comu 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 ossification, 
as in the Marmosets. The upper ends of the pyramids are 
separated by corpora trapezoidea from the pons Varolii. 

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 be- 
hind, the penis. The female Ateles has a long clitoris, which 
depends from the vagina. 

The Plaiyrrhini occur only in the Austro-Columbian prov- 
ince, and are known in the fossil state only in certain caves 
of that region. 

3. The Gatarrhini. — The Simiadm 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 ; in the 

dental formula i. 1^' O- frj pm. ^ »*• ^rl and in being in- 
habitants of the Old World. They fall into two very distinct 
groups, the Gynomorpha and the Anthropom,orpha. 

a. The Gynomorpha are distinguished from the other 
group by being essentially quadrupedal, and usually provided 
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 



308 THE ANATOMY OF VERTEBRATED ANIMALS. 

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 colored. 

The dorso-lumbar region of the spinal column is concave 
toward the ventral aspect, and the lumbo-sacral angle is very 
large. The atlas has narrow transverse processes. The or- 
dinary number of dorso-lumbar vertebrae is nineteen, of which 
twelve, or thirteen, are dorsal; and seven, or six, lumbar. 
The middle cervical vertebrse have short spines, which are not 
bifurcated at their extremities. In the posterior dorsal and 
anterior lumbar vertebrae, the mammillary and accessory pro- 
cesses may be enlarged and interlock. The long transverse 
processes of the lumbar vertebrse bend forward. The sacrum 
usually contains only three anchylosed vertebrae. The caudal 
vertebrae vary in number, from three in Inuus (where they 
form little more than a coccyx), to as many as thirty-one. In 
the anterior part of the tail the vertebrae 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 sternebrEe which 
follow it are compressed and constricted. 

The skull presents a considerable range of variation. In 
the Semnopitheci and Colobi, the frontal region is rounded, 
the facial angle is comparatively large, and the ascending por- 
tion of the ramus of the mandible is high. In the Macaci and 
Cynocephali, on the other hand, the supra-orbital ridges be- 
come so much enlarged as to hide the forehead ; and the hori- 
zontal portion of the ramus of the mandible is much larger 
than the ascending portion, in accordance with the great pro- 
duction of the upper jaw, and the consequent low facial angle. 
In many of the Cynocephali, longitudinal osseous ridges are 
developed upon the maxillse, and greatly increase the brutish- 
ness of their aspect. Sagittal and lambdoidal crests may ap- 
pear along the lines of the corresponding sutures. There is 
no distinct 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 squamo- 
sals with the frontals. The brain-case is flattened and elon- 
gated, and the convex roofs of the orbits project into it, and 
greatly diminish the capacity of its frontal portion. The olfac- 
torj' fosssB 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 OSTEOLOGY OF THE CYNOMORFHA. 399 

tlie ethmoid, and thus narrow the entrance to the olfactory 
fossje. The basicranial axis is shorter than the cerebral cavil}', 
but is still proportionally long. The occipital foramen lies in 
the posterior sixth of the base of the skull, and it looks ob- 
liquely backward and downward. The premaxillo-niaxillary 
suture never disappears until long after the second dentition 
as complete, and may persist throughout life. The palate is 
long and narrow. The nasal bones are fiat, and early anchy- 
losc 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 di- 
rected upward and inward, but upward and backward ; the 
bicipital groove hes on the inner side; and the shaft of the 
bone is so bent that it is convex forward. In all these char- 
acters the fore-limb shows its relation to the function of sup- 
port. The radius exhibits modiiications which have the same 
signification. Its proximal head is transversely elongated, 
and lies somewhat in advance of the ulna, articulating more 
largely with the humerus than in the higher Apes. The neck 
of the radius (between the head and the bicipital tuberositv) 
fits more closely to the ulna, and hence the movements of pro- 
nation 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 ouneiforme, it furnishes an articular face for 
the ulna. The distal articular surface of the trapezium is 
saddle-shaped, and the poUex is usually complete, though 
short relatively to the other digits. In Colohus it is rudi- 
mentary. 

The pelvis is long and narrovi^. The ilia are narrow bones 
with much-excavated posterior and outer faces. Their crests 
generally lie opposite the transverse processes of the penulti- 
mate 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. 
Tlie symphysis pubis is very long, and the subpubic arch cor- 
respondingly reduced. The posterior ends of the ischia are 
everted, broad, and rough, for the attachment of the callous 
pads of integument. The femur has a round ligament. The 
tarsus has not more than one-third the length of the fcot. 



too THE ANATOM'X OF VERTEBKATED ANIMALS. 

The calcaneal process is flattened from side to side, and has a 
pulley-like excavation upon its posterior extremity. The 
tibial facet of the astragalus is inclined slightly inward, as 
well as upward, and its outer edge is raised. The distal di- 
vision of the tarsus, consisting of the cuboid and navicular, 
with the cuneiform bones, is capable of a considerable amount 
of rotatory motion upon the astragalus and the calcaneum. 
The ento-ouneiform bone is large, and has a transversely-con- 
vex 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 " tailless " 
genus, Jnuus, proper caudal muscles are present. In the limbs 
there is a levator clavioulce which passes from the transverse 
process of the atlas to the acromion ; a dorso-epitrochlearis, 
consisting of a muscular bundle detached from the latissimiis 
dorsi near its insertion, and passing to the distal and inner 
end of the humerus, or even farther down ; a scansorius, from 
the ventral edge of the ilium to the great trochanter, which 
sometimes becomes confounded with the glutoeus minimus ; a 
special abductor ossis metacarpi quinti ; and a peronmus 
quinti digiti, arising from the fibula, between the peronmus 
longus and brevis, passing behind the external malleolus, and 
sending its tendon to the extensor sheath of the fifth digit. 

The extensor primi internodii pollicis and the peronceus 
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 
digitorwn 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 
tratisversus pedis is usually fully developed, but has only two 
heads of origin from the distal ends of the second and third 
metatarsals. The interossei pedis are just visible on the dor- 
sal aspect of the foot, but none are, properly speaking, dorsal. 
None of them are penniform 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 proximal phalanges, and give off no distinct ten- 
Jons to the extensor sheaths. Additional muscles may ariao 



THE DENTITION OF THE OyNOMORPHA. 401 

over the proximal ends of the metatarsal bones, and pass to 
the three fibular digits. 

The interossei manus 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 
6ubdi\'ision v^hich is seen in the Anthropomorpha, 

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 extensor indicis one to 
the third digit. The extensor ossis metacarpi piollicis gives a 
distinct slip to the trapezium, and thus precisely corresponds 
■with the tibialis anticus, which has two tendons, one for the 
en to-cuneiform, and one for the metatarsal of the hallux. The 
flexor digitorum profundus and flexor longus pollicis are rep- 
resented by one muscle, a slip from the ulnar side of the ten- 
don of vchich usually goes to the pollex. 

The tendons of the flexor perforans digitorum and flexor 
hdllucis unite to form the deep flexor tendons of the pedal 
digits in very variable proportions. The flexor acccssorius 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 as cissors-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. Sometimes 
there is " heel " behind the posterior ridge of the last lower 
molar. 

The formula of the milk dentition is d.i. ^ d.c. t.J d.m. 

^ = 20 ; and the anterior milk molar resembles the perma- 
nent 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 
Irom the first premolar below. 

The Cynomorpha very generally possess cheet-pouchea, 
which serve as pockets for the temporary stowage of food. 
The stomach is usually simple, with a globular cardiac ex- 
tremity and an elongated pyloric portion ; but, in Semnopithe- 
cus and Colobus, the stomach is divided into three compart- 
ments, the middle of which is sacculated. A groove with 



102 THE ANATOMY OF VERTEBEATED ANIMALS. 

raised edges leads from the cardiac end of the gullet to the 
middle compartment. 

The cfficum, 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 axillae, in 
some Semnopitheci and Cynocephali. The right lung is usu- 
ally four-lobed, the left two-lobed. 

The kidney has only a single papilla. 

The ppsterior lobes of the cerebrum project beyond the 
cerebellum in all the Gynomorpha; they are shortest in the 
Semnopitheci, and longest in the Cynocephali. The principal 
sulci 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 ventricle 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 haemorrhage, and comparable to 
menstruation. The placenta is often bilobed. 

b. The Anthropomorpha differ from the Cynomorpha in 
the following characters: They are especially arboreal ani- 
mals, which habitually assume a semi-erect posture, support- 
ing the weight of the fore-part of the body upon the ends of 
the fingers, or, more usually, upon the knuckles. There is no 
tail. The thigh and the leg are, respectively, shorter than 
the arm and the fore-arm. The dorso-lumbar vertebriE are 
seventeen or eighteen in number, and their spines are not in- 
clined toward a common point. They develop no interlocking 
mammillary and accessory processes. The sacrum contains 
more than three anchylosed vertebras. The thorax is rather 
broad than laterally compressed, and the sternum is flattened 
from before backward, and wide. The axis of the head of the 
humerus is directed more inward than backward, and the up- 



THE ANTHKOPOMOKPHA. 403 

per part of the shaft is not bent as in the Gynomorpha. 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 tlie 
outer lower incisors are larger than the others. The crowns 
of the upper and lower molars have the same patterns as those 
of iMan. 

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 Gynomorpha. The plantaris does not pass over a pulley 
furnished by the calcaneal process, as in the Gynomorpha ; 
and the flexor brevis has an origin from that process. The 
peronoBUS quinti digiti has not been observed. 

There are three well-marked genera of Anthropomorpha — ■ 
ITylobates, 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 ; Hylo- 
hates, the Gibbons, of which there are several species, is found 
over a considerable area of Eastern Asia and the islands of the 
Malay Archipelago. The Ghimpanzee 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 Gynomorpha. They possess ischial cal- 
losities, and the nails of the pollux and hallux, only, are 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 arras. Nev- 
ertheless, 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 antibrachium considerably longer than 
the brachium. The Gibbons do not exceed three feet in 
heio"ht; 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 stat- 
ure of more than four feet and a half, the arms are very long, 



404 THE ANATOMY OF VERTEBRATED ANIMALS. 

their span, when outstretch ed, being nearly double the height 
of the animal. The brachiura and the antibrachium are equal 
in length. The long and narrow pes is longer than the equal- 
ly 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, ia 
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 poUex and the hallux are both short, the latter remaik- 
ablj' so ; and the hallux is not uncommonly devoid of a nail. 
The palmar and plantar aspects of the digits are naturally con- 
cave, 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 antibrachium 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 ground, 
and the Chimpanzee easily stands or runs erect. But his fa- 
vorite attitude is leaning forward and supporting himself on 
the knuckles of the manus. Both the hallux and the poUex 
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 antibrachium. 
The pes is longer than the manus, and both are much 
broader than in the other A?ithropomorpha. In consequence 
of this circumstance and of the greater development of the 
heel, the erect posture is easily maintained, but the ordinary 
attitude is the same as that assumed hj the Chimpanzee. The 
hallux and the pollex have well-developed 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 dorso-lumbar 
vetebrae form a curve, which is nearly as much concave for- 
ward as in a new-bom child. In the Chimpanzee the spinal 
column begins to exhibit the curvatures which are character- 
istic of the adult human subject; and these are still more 
marked in the Gorilla. 

Tlie spinous process of the second cervical vertebra is 



THE ANTHROPOMORPHA. 405 

bifurcated in the Chimpanzee, but this human character does 
not appear in the others. 

In the Gibbons there are usually eighteen dorso-lumbar 
vertebriE ; 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 Gib- 
bons may possess fourteen pairs of ribs. The thorax is wide, 
and the sternum broad and flat. In the Orang it may ossify 
fiom a double longitudinal series of centres, as sometimes hap- 
pens in Man. 

In the Gibbons the transverse processes of the last lumbar 
vertebra are not exceptionally broad, and do not unite with 
the iha. But in both the Chimpanzee and Gorilla they are 
wide, and become more or less closely connected with the ilia. 
The last lumbar vertebra may become anchylosed with the 
sacrum in the Gorilla. All these conditions of the last lum- 
bar vertebra are occasionally met with in Man. 

The sacrum is broad, and contains not fewer than five 
anchylosed vertebrce, 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 vertebrae. In the skull, 
the proper form of the brain-case is always more or less dis- 
guised 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 othei 
Apes, but the sagittal and lambdoidal crests are strong. In 
the old male Gorilla the sagittal and lambdoidal crests, and 
the supraorbital ridges, are alike enormous. The frontal si- 
nuses 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 Chimpanzee. 

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 upward and outward. The oc- 
cipital foramen is situated in the posterior third of the base 
of the skull, and looks obliquely backward and downward. 



i06 THE ANATOMY OF VERTEBRATED ANIMALS. 

The frontals meet in the base of the skull over the ethmo- 
prespheuoidal suture in the Gibbons and in the Grorilla, 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 alisphenoid from the parietal, as happens, excep- 
tionally, in Man. The nasal bones are flat and early anohylosed 
together, in the Gibbons, Orangs, and Chimpanzees. In the 
Gorilla the nasal bones are distinctly convex from side to side, 
and rise above the level of the face. None of these Apes have a 
spina nasalis anterior ; and, only in the Siamang, is there a 
rudiment 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 os- 
sified 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 ex- 
cavated posteriorly. 

The scapula of the Orang is most like that of Man, espe- 
cially in the proportion of the supra- and infra-spinous fossas, 
in the proportional length of the anterior and the posterior 
borders, and in the angle made by the spine with the verte- 
bral 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- 
ward and inward, 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 Hylobates the articular 
surface presented by the trapezium for the pollex is almost 



TUE FOOT IN THE ANTHROPOMORPHA. 407 

globular. It is evenly convex in the Chimpanzee ; but, in tlie 
Gorilla, it has the characteristically human saddle shape. The 
pollex is longest and strongest in proportion in Bylohates ; 
its length in proportion to that of the manus being in S. syiir- 
dactylus as three to seven. In the Gorilla, the pollex has 
rather more than one-third the length of the manus ; in the 
Orang and Chimpanzee it has about one-third the length of 
the manus. 

The pelvis differs but little from that of the Gynomorplia 
in Hylobates. In the other genera the pelvis is still elongated. 
The antero-posterior diameter of the brim of the pelvis great- 
ly 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 forward in the Chimpanzee 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 meas- 
urement 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 ligament, and differs 
in this respect from the same bone in the other Anthropomor- 
pha. 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 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 Chim- 
panzee, the phalanges, taken together, are longer than the 



408 THE ANATOMY OF VERTEBRATED ANIMALS. 

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 astrag- 
alus the articular surface for the tibia is broadest in the Goril- 
la ; but, in this Ape, as in the others, it is inclined a little in- 
ward when the foot is in its natural position ; and the surface 
for the external malleolus is oblique, and looks upward as well 
as outward. 

It is a mistake, however, to suppose that the disposition 
of these surfaces has any thing to do with the more or less 
marked tendency of the plantar surface to turn inward, and 
of the outer edge of the pes to be directed downward, 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 astragalus and the calca- 
neum on the other ; the consequence of which is, that the dis- 
tal portion of the pes, with the first-mentioned bone, being 
pulled by the tibialis anticus, easily rotates round its own 
axis, upon the surface presented by the astragalus and calca- 
neum. This ready inversion of the sole must as much facili- 
tate climbing, as it must interfere with the steadiness of the 
foot in walking. 

The distal surface of the ento-cuneiform is much inclined 
inward in all the Anthropomorpha^ and is convex from side to 
side, or subcylindrical. The metatarsal bone of the hallux pre- 
sents a corresponding articular concavity to this surface, and 
has a great range of motion in adduction and abduction. Thfj 
inward inclination of the articular facet of the ento-cuneiform, 
and its consequent separation from the facet upon the mcso- 
cuneiform for the second digit, is 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 vari- 
eties in the human subject. These are the levator claviculce, 
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 extensor primi 
internodii pollicis\ and ihe peronceus tertitts. The former of 

* Not actually described in the Gorilla, and absent in some Cbimpanzees. 

t The former muscle is said to be present by several anatomists in tha 
Chimpanzee and other Apes ; but what they have taken for it is the metacar- 
pal division of the extemw oesis metacarpi. 



THE MYOLOGY OF THE ANTHROPOMOEPHA. 409 

tliese is sometimes, and the latter frequently, wanting in the 
human subject. 

The flexor accessorius appears to be regularly absent in 
Hylohates 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 solcetcs has 
only a fibular head, and takes no origin from the tibia. The 
flexor brevis digitorum pedis never arises altogether from the 
oalcaneum, 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 sec- 
ond 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 fibu- 
lar interosseous muscle of the second digit. Hence, of the so- 
called dorsal ititerossei (or interossei 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 manus. 
The flexor polliois 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 
Hylohates, 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 Chimpanzee, 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 com- 
mon tendon which divides into two, one for the pollex and 
the other for the index. In Hylohates, the short head of the 
hiceps brachii arises from the pectoralis major, and the ad- 
ductor hallucis and transversus 2:>edis form but one muscle. 

The flexor longus hallucis takes an origin from the ex- 
ternal condyle of the femur in the Orang ; and the pectoralis 
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 subdivided, 
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 
18 



410 THE ANATOMY OF VERTEBRATED ANIMALS. 

the metacarpal bone of the poUex. 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 halluois. 

In the Gibbons and in the Orang, there is a complete set 
of deep extensors for the four ulnar digits, the tendons of the 
evtensor indicis and extensor minimi digiti subdividing to 
s apply the third and fourth digits. 

In the Gorilla and Chimpanzee each of these muscles have 
but a single tendon, as is the usual arrangement in Man. 

The interossei of the hand are each divided into two mus- 
cles with distinct tendons — & flexor brevis primi internodii and 
an extensor brevis tertii internodii. The division is less obvi- 
ous in the Orang than in the other Anthropomorpha. 

In Hylobates, the tendon of the fl^exor 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 suppHes the second and the 
fifth digits, and the flexor 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 con- 
nected with that of ^% 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 a long tendon into the pre- 
axial side of the ungual phalanx of the second digit ; it may 
be termed " abductor tertii internodii seaundi 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 

• It must be borne in mind that tbese statements respecting the myology 
of the Anthropomo'rpha are based upon my own dissections Csometimes sup- 
plemented by those of Duvemoy and other anatomists) of particular speci- 
mens. KndlesB varieties will no doubt be met with by those who carry meii 
inquiries further. 



THE BRAIN IN THE ANTHKOPOMORPHA. 411 

oerebrum, -which, in this anthropomorphous Ape, do not ovei> 
lap 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 downward and 
inward, in correspondence with the projection of the upwardly 
convex roofs of the orbits into the cranial cavity. The pos- 
terior cornu of the lateral ventricle is always well developed, 
and contains a prominent hippocampus minor and eminentia 
collateralis. An occipito-temporal or "external perpendicu- 
lar" 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. 31 and 33). The fissure of Sylvius is less in- 
clined backward, and that of Rolando is placed more forward 
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 sur- 
face. The first remains folded upon itself, and gives rise to 
the characteristically simian occipito-temporal or external per- 
pendicular 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 precom- 
missural fibres are well developed. The vermis is small in 
proportion to the lateral lobes of the cerebellum, and the floc- 
culi are relatively small, and lie below the latter. 

The whole cerebellum is larger in proportion to the cere- 
bral hemispheres; the latter being to the former, as 8^ to 1 in 
Man, but as 5f to 1 in the Chimpanzee.* The nerves are 
larger in proportion to the brain than in Man. There arc 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. The premolars 

• It must be reooUeoted ttat the brains of young anthropomorphous 
Apes, only, have been examined. Perhaps this has to do with the absence of 
mineral deposits in the pineal gland of the Apes. 



412 THE ANATOMY OF VEETEBRATED ANIMALS. 

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-iaternal cusp ; and those of the middle molar, below, 
have five cusps, -as in Man. The crown of the anterior premo- 
lar in the lower jaw is pointed, and has a long, sharp, ob- 
lique 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 circumvallate papillae of the tongue are 
arranged in a V, as in Man. In the Chimpanzee they are dis- 
posed like a T, with the top turned forward. The Chimpanzee 
and the Siamang have a 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 car- 
diac and more tubular pyloric portion. An appendix vermi- 
formis is found in the OEeoum 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 speci- 
mens the left carotid comes off from the innominata, and only 
the subclavian of the left side arises directly from the aorta. 
In Sylobates, the latter arrangement appears to obtain. 

The kidney has only a single papilla in Sylobates and 
Pithecus. 

Only one species of Sylobates, namely, the Siamang, is 
known to possess a laryngeal sac. This is globular, and com- 
municates by two apertures, situated in the thyro-hyoid mem- 
brane, with the larynx. In the Orang, Chimpanzee, and Go- 
rilla, 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 axillaa, 
and sometimes open into one another in the middle line. 

In the adult male Chimpanzee the penis is small and slen- 
der, and terminates in a narrow and elongated glans. The 
testes are very large, and the communication between the 
tunica vaginalis and the peritonreum 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 
closerl on the other. An os penis is developed in the males. 
The females have the clitoris large, and the uterus, which 



RELATIONS OF ANTHROPOMORPHA TO MAN. 413 

is undivided into cornua, resembles that of tlie human subject. 
The placenta of a Chimpanzee foetus, 11^ inches long, was sim- 
ple, rounded, 3^ 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 exceedingly 
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 C'y 
nopithecini. 

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 Gorilla 
and the Chimpanzee do. 

The Chimpanzee approaches Man most closely in the char- 
acter 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. 

c. The AnthropidcB are represented by the single genus 
and species, Man, and they are distinguished from the 
Simiadoe, 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 cal- 
caneal process is long, and expanded posteriorly. The hallux 



414 THE ANATOMY OP VERTEBRATED ANIMALS. 

has half the length of the foot, and is nferly as long as the 
second digit ; and its mobility in adduction and abduction ia 
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 axillae, 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 forward, and the vertebro-sacral angula* 
tion is slight ; but, in the adult, the spinal column is concave 
forward in the thoracic, and convex forward in the lumbar 
region, mainly in consequence of the disposition of the elastic 
ligaments which connect the faces and the arches of the ver- 
tebrse. There is a stronglj'-marked vertebro-sacral angulation. 
Normally, there are twelve dorsal, five lumbar, five sacral, and 
four coccygeal vertebriB, 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 bifurcated. 
The breadth of the sacrum is greater than its length. In the 
skull, the occipital condj'les lie within the middle fifth of the 
base, and the occipital foramen looks downward, and either a 
little forward or but slightly backward. Neither sagittal nor 
lambdoidal crests are developed, but the mastoid processes 
are distinct, and generally conspicuous. The supraorbital 
ridges are never so largely developed as in some of the Aiv 
thropomorpha. 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 hne 
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 only human skull in which I have heen able to find no trace of the 
existence of the anterior nasal spine, is that of an Australian, wliich, some 
years ago, I presented to the Museum of the Royal College of Surgeons. 



THE ANTHROPID^. 415 

The post-glenoidal process of the squamosal is small, while 
khe 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 bonea 
{ossa plana) are nearly parallel with one another. 

The symphysis of the lower jaw has a mental prominence. 
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 nasal suture usually persists, and the direction of the 
fronto-nasal suture is nearly transverse. 

The cranio-faoial 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 upward 
and outward, as they are in the Anthropoinorpha. The cri- 
briform plate is long and wide, and the crista 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 con- 
cavity, and their crests an S-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 Anthropoinorpha this angle is much more open. 

The tuberosities of the ischia are hardly everted. The 
symphysis pubis is comparatively short, and the sub-pubic arch 
well marked. The width of the whole pelvis, from one iliao 
crest to the other, is greater than its height, which is the re- 
verse 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 occasionally obtains. 
The female pelvis is more spacious, and has a wider sub-pubic 
arch than the male. 

The proximal articular surface of the astragalus looka 
almost directly upward, and hardly at all inward, when the 

* See p. 420 for the explanation of this term. 



416 'rilE ANATOMY OF TERTEBIIATED ANIMALS. 

■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 inferiorly, but produced into 
two tuberosities on which the heel rests. The form and dis- 
position 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 downward. 
The comparatively slight mobility of the metatarsal bone of 
the hallux arises partly from this circumstance, partly from 
the fact that the proximal articular surfaces of the four outer 
metatarsal bones are not perpendicular to the axis of those 
bones, but are obliquely truncated, from the tibial side, back- 
ward, to the fibular side. Hence the four outer metatarsal 
bones, instead of diverging widely from the hallux as they 
would do if their axis 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 pre- 
hensile 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 be- 
neath the metatarso-phalangeal articulations, from the hallux 
to the fifth digit. 

In the infant, the sole naturally turns inward, 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 extensor primi internodi ]}ol- 
licis and the jyeronceus tertius. 

The only pecuharities in the origin of muscles v/hich ordi- 
narily obtain in Man, and have not yet been found in the Apes, 
are — the complete separation of the flexor poUicis longus ironi 
xhe flexor digitorumperforans ; the presence of a tibial, as well 
as of a fibular, origin of the soleus ; the origin of all four heads 
oi the flexor hrev if: dif/itoruin p>edis from the calcaneum; the 
origin of the fibula interosseus of the second digit of the pes 
from the middle metatarsal, on the dorsal side of the tibial 



THE BRAIN OF MAN. 417 

interosseus of the middle digit. The result of the last-men- 
tioned arrangement is that the second digit of the pes has 
two " dorsal " interossei, like the third digit of the manus. In 
the Apes the interossei of the second digit are generally ar- 
ranged in the same way in both manus and pes. 

The tendons of the flexor hallucis longiis ^nd flexor digi- 
torum perforans are usually more closely connected in the 
sole of the foot in Man, than in the Anthropomorplia. But 
it is to be noted that all the apparently distinctive peculiari- 
ties of the myology of the Anthropomorpha are to be met 
with, occasionally, as varieties in Man. 

Ill 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 exca- 
vation of the orbital face of the frontal lobe ; and the larger 
size of the cerebral hemispheres, as compared with the cere- 
bellum and the cerebral nerves. 

There is no diastema, though the summits of the canines 
project, slightly, bej'ond 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 
and sharp. 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 
gians), and its glans has a different shape from that of any of 
the Anthropomorpha. The vulva looks downward and for- 
ward, 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 foetus 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 arrns and legs are of about 
the same length, and are shorter than the spine. The forearm 
is about as long as the upper arm, and the leg as the thigh. 
The manus and pes are very similar in size and form ; and 
neither poUex, nor hallux, are so different from the other digits 
as at later periods. In a foetus rather more than five inches 
high, the head occupies a , fourth 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 forearm 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 



418 THE ANATOMY OF VERTEBRATED ANIMALS. 

In a foetus 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 fcstus 
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 
forearm 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 ges- 
tation, after the embryo has attained more than two inches in 
length ; the arms grow proportionally quicker than the body 
and legs, in tlie middle of gestation, when the proportions 
most nearly resemble those of the Anthropomorpha. In the 
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 continued. 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 outstretched arms is equal to the height in average Eu- 
ropeans. 

Sexual differences, independent of the genitalia, are per- 
ceptible at birth ; and the female infant is, as a rule, slightly 
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 fe- 
male is nearer the umbilicus than in the male. The hips are 
wider in proportion to the shoulders, 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 variation in their 
anatomical characteristics. The color of the skin varies from 
a very pale reddish brown — of the so-caUed " white " races — 



THE RANGE OF VARIATION IN ANTHROPID^. 419 

through all shades of yellow and red brovvns, 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 be- 
comes greatly developed over the lips, chin, and sides of the 
face, on the thorax, abdomen, and pubes, in the axilte, 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 forearm slope toward the elbow, and 
those of the leg and thigh away from the knee, as in the A.n- 
thropomorpTia. 

Enormous accumulations of fat take place upon the but- 
tocks of the Bosjesmen, especially in the females ; and the 
nymphse of these and some other Negroid tribes become great- 
ly elongated. 

It appears in some of the lower races, e. g., Negroes and 
Australians, the forearm and hand, and the foot and leg, are 
often longer in proportion than in Europeans. From not 
wearing shoes, the hallux is much more movable 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 vertebrae sometimes 
cease, more or less completely, to be bifiu-cated in the lower 
races. Thirteen pair of ribs are sometimes present, and occa- 
sionally there is a sixth lumbar vertebra. There may be one 
more sacral vertebra than the normal number ; and a modifi- 
cation of the last lumbar, so that it resembles a sacral verte- 
bra, 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, espe- 
cially in the tendency to equality of the transverse and antero- 
posterior diameters of the brim, and the narrowness of the in- 
tersciatic diameter, than in the higher races. This is particu- 
larly 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 com" 



420 THE ANATOMY OF VERTEBRATED ANIMALS. 

moner among the Bushwomen of South Africa than else- 
where. 

But it is in the skull that the different races of mankind 
present the most striking osteological differences. The pro- 
■s.ortions of the antero-posterior and the transverse dimensions 
of the brain-case vary extremely. Taking the antero-posterior 
diameter as 100, the transverse diameter varies from 98, or 99, 
to 62. The number which thus expresses the proportion of 
the transverse to the longitudinal diameter of the brain-case 
is called the cephalic index. Those people who possess crania 
with a cephalic index of 80 and above are called hracliy' 
cephali ; those with a lower index are dolichocephali. The 
brain-case also varies greatly in its relative height. The pro- 
portion of the length of the cerebral chamber to the basicranial 
axis (as 100) may rise 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 backward or forward 
upon this axis. The position and the aspect of the occipi- 
tal foramen vary considerably, as does the plane of that part 
of the squama occipitis which lies above the superior semicir- 
cular ridge. The supra-ciliary ridges vary greatly in their 
development, 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 premaxilla to the 
anterior extremity of the basicranial axis, may be taken to 
represent the facial axis, 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 orihog- 
nathous. 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 ver- 
tical, tends toward orthognathism ; 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 lowei 
races, notably the Australians. 



THE ULOTRIOHI AND THE LEIOTRIcni, 421 

The mental' prominenoe 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 forward, in the lower. 

The diflferent races of mankind are divisible into two 
primary divisions ; the Ulotrichi, with crisp or woolly hair, 
nnd the Leiotrichi, with smooth hair. 

a. The color 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 Negroes 
and Bushmen of ultra-Saharal Africa, and the Negritos of the 
Malay peninsula and archipelago, and of the Papuan Islands, 
are the members of this Negroid stock. 

b. The lieiotrichi 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. 

3. The Mongoloid group, with, for the most part, yellow- 
ish-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, Esqui- 
maux, and American races. 

3. The X^anthoohroic 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, Scandinavians, and 
the fair Celtic-speaking people are the chief representatives 
of this division ; but they extend into North Africa and West- 
em 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 Melano- 



422 THE ANATOMY OF VERTEBRATED ANIMALS. 

chroi are not a distinct group, but result from the mixture of 
Australioids and Xanthochroi. 

Fossil remains of Men or implements of human manufac- 
ture have hitherto been found only in late Tertiary (Quater- 
nary) deposits, and in caves, mingled with the remains of ani- 
mals which lived during the glacial epoch. 



INDEX. 



fcootPEN3ER, cartilaginous cranium oi^ 124. 

Sdr-sacs in birds, 271. 

Alimentary canal, 79. 

Alligator terrapene, 171. 

A.mia, caudal extremity of, 20. 

calva, reproductive organs ot 1 26. 

Ajnphibia, general characteristics, 149. 

■ development, 164, 

groups, 149, 

heart, 169. 

limbs, 156. 

muscles, 45. 

reproductive organs, 163. 

respiratory organs, 161. 

teeth, 158. 

Amphisbcenoida, 198. 

Antle-joint of sloths, 288. 

Anoplotheridffl, 320. 

Antibrachium, muscles o^ 49. 

Anthropidse. See Man. 

Anthropomorpha, general characteristics oi, 
402. 

comparison o^ with man, 413. 

divisions, 403. 

A.ortic arches. See Arches, aortic. 

Apes. See Simiadae. 

Arch, pectoral, 34. 

pelvic, 36. 

pectoral and peMc, of chelonia, 1T8. 

pectoral and pelvic, of plesiosauria, 184, 

185. 

Arches, aortic, 83, 84. 

number o^ belonging to skull, 71. 

pectoral, and sternum, of a frog, 157. 

Arches, visceraL skeletons o^ 77. 

Arctopithecini (marmosets), general charac- 
teristics o^ 392. 

brain, 894. 

limb^ 898. 

muscles, 398. 

skull, 893. 

teeth, 893. 

vertebrae, 393. 

Axmadillos, general characteristics o^ 290. 

Artiodactyia, non-ruminantia, 313. 

— ^ raminantia, 321. 

Ascalabota, 194. 

Australians, peculiaritleB of^ 495. 

Ares. See Birds. 

hx<i\QVL{^redon\ 161. 

— — aortio uvh olj 84, 



BiL^aroiDEA, general characteristics of, 837 

Baleen plates, or whalebone, 339. 

Bats. See Cheiroptera. 

Birds, general characteristics of, 168. 

air-sacs of, 271. 

brain of Meleagris gcUlopa/oo. 259. 

—' classification, 238, 

digits, 250, 254. 

ear. 262. 

heart, 267, 

larynx and syrinx, 367. 

limbs, 249, 252. 

lungs, 270. 

muscular system, 257. 

^— organs of copulation, 272. 

pectoral arch, 247. 

pelvis, 251. 

sacrum of a chick, 238. 

— skull, 241. 

spur, 254. 

sternum, 240, 241. 

vertebrae, 236. 

See alao FowL 
Bears, teeth o^ 859. 
Blood, circulation o^ in frog, 160 

corpuscles, 89. 

Bloodsucking bats, 38T. 
Bones of cetacea, 885. 

cynomorpha, 898. 

delphinoidea, 840. 

elephant, 865. 

the fece, 27. 

fishes, 29, 79. 

galeopithecus, 882. 

hedgehog, 876. 

pig, 315. 

rhinoceros, 308. 

the skull, 25, 26. 

See also Os, Ossa. 
Bosjesmen, fat of; 419. 
Bram of anthropopiorpha, 411, 

camivora, 85l. 

chimpanzee, 60-65. 

cynomorpha, 402. 

^visions o£ 55, 

dog, 857. 

frog, 163. 

hedgehog, 379. 

horizontal section, 56. 

lemuridae, 890. 

longitudinal and vortical sectton pl 



424 



INDEX. 



Brain of man. 417. 
• marmoset, 394. 

modifications of, 59. 

pig:, 60-65. 

pike, 142. 

platyrrhini, 897. 

■ porpoises, 849. 

. rabbit, 60-G5 874. 

Brain-case. See bkull. 

Uruta, or Edentata. See Edentata. 



Ga :niLOT, skull of, 341. 

Oainozoic Jbrmation, crocodiles in, 221. 

Oamelidffi or tylopoda, 828 

Canal, alimentary, 79. 

spinal, and cord, 64. 

Canals of Stenson, 72. 

Carnivora, general characteristics of, 350. 

classification, 358. 

divisions, 851. 

Carpus, skeletal elements of, 31. 
Catarrhine monkey, skeleton of, 892. 
Catarrbini, characteristics of, 398. 
Cats, teeth of, 359. 

Caudal extremities of polypterus, amia, and 
salmo, 20. 

vertebra, 21. 

Cerebral nerves, 66. 

Cetacea, general characteristics, 334. 

gTOiips, 336. 

Characters, distinctive, of vertebrata, 7. 
Chalk, ichthyosauria in, 214. 

lizards found in, 196, 199. 

Chama?lonida, 198. 

Cheii'Optera, general characteristics of, 385. 

digits, 84. 

position of limbs of bats, 88. 

Chelone midas, carapace ol^ 173. 

section of skeleton of, 172. 

Chelonia, general charactei-istics, 170. 

divisions, 179. 

heart, 264. 

lungs, 2T0. 

musculai" system, 257. 

organs of copulation, 278. 

pectoral and pelvic arches, 178. 

plastron, 174. 

skull, 176-178. 

Chelydra, fore-foot of, 83. 

Chimiera monstrosa, section of skull, 112, 113. 
Chimpanzee, 404. 

brain of, 60-66. 

Circulatory organs, 81. 
Cochlea, development of, 75, 77. 
Comparison of man mth anthropomorpha, 

418. 
Corpuscles, blood, 89. 

lymph, 91. 

Corpus callosum in mammalia, 59. 
Cotylophora, 827. 
Cranial nerves, 69. 

system, 21. 

Cranio-facial angle, 415, 420. 

Crocodile, segment of endoskeleton in tho- 
racic region of, 19. 
Crocodilia, 214. 

- deiToal armor, 214. 

ear. 262. 



Crocodilia, groups, 221. 

heai-t, 266. 

lungs, 270. 

pelvis and hind-limb, 222. 

reproductive organs, 273. 

— - skull, 218. 

teeth, 221. 

vertebrEP, 215. 

Cinis, muscles of, 49. 

Cutaneous muscle of hedgehog, 877. 

porpoise, 345. 



* D. 

Dreb, boms of, 827. 
Delpbinoidea, characteristics of, 340, 
Dental formulffi. See Teeth. 
Dentition. See Teeih. 
Development of amphibia, 163. 

cochlea, 75-77. 

^SS, 9. 

fowl, stages o^ 11, 18, 16, 23. 

■ lamb, 20. 

Bkuil of fishes, 24. 

vascular system, 83-87. 

vertebrata, 9. 

DiAGRAJvis : 

Accipenser, skull, 124 

Alligator terrapene, 171. 

Amia, caudal extremity, 20. 

Amia calva, reproductive organs, 126. 

Amphioxus lanceolatus, 104, 105. 

Aortic arches, 88. 

Axolotl, 161. 

Bu^ and lizard, brain, 258, 269. 

Cachalot, skuU, 341. 

Catarrhine monkey, 392. 

Chelone, skeleton, shell, 172, 173. 

Chelydra, foot, 83. 

Chimaera, skull, 118. 

Chimpanzee, brain, 61, 63. 

Crocodile, anterior thoracic region, IS 

• pelvis and hind-limb, 223. 

skull, 218. 

Cyclodus (Jaeertilia), skulL, 189, 190. 

gromasus, pelvis, and hind-limb, 223. 
ugong, heart, 332. 
Elephant, skeleton, 364. 
Fish, visceral arch, 77. 
Fcetus, human, principal vessels. S5. 
Fowl, development, 11, 13, 16, 23. 

fore-limb, 250. 

leg, 258, 254. 

pelvis, 251. 

• sacium of chick, 288. 

scapula and coracoid, 247. 

skull, 242. 

spur, 254. 

sternum, 241. 

Flying fox, skeleton, 885. 
Frog, nervous system, 65. 

skull and bram, 152, 153, 162. 

■ sternum and pectoral arch, 15T. 

Holoptychus, 127. 
Homo, pregnant uterus, 9. 
Horse, carpus, 299. 
cervical vertebrae, 295. 

femur, 301. 

foot, 204, 293. 

ossa innominata. 300. 



INDEX. 



425 



Dl A.G RAK.»^C07ltilVUed. 

Horse, skeleton, 296. 

tarsus, 298. 

Ichthyosam-us, 208, 209. 

Iguanodon, pelvis and hind-limb, 228. 

Lamb, fcetal, head, 29. 

Lamprey, skull and brain, 108, 110, 111. 

Lepidosteua, 122. 

Uon, skoletoii, 852. 

Lizards, pectoral arch and sternum, 85, 86. 

visceral arch, 77. 

Mammal, visceral arch, 77. 

Monkfish (jiquaUna), pectoral member, 

"skull, 115. 

Mudfish, skuU, 145, 140. 

Orang, digit, 51. 

Os innominatum of man, 8fi, 

Ostrich, skull, 243. 

Ox, skeleton, 321. 

Pig, brain, 61, 63. 

Pike, brain, l42. 

outline, 41. 

pectoral arch and fore-limb, 137. 

skuU, 182-135. 

Plaice, skull, 30. 
Plesiosaurus, skeleton, 182. 
Polyptenis, caudal extremity, 20. 
Pterodactylus, skeleton, 229. 
Python, dorsal vertebrEe, 201. 

skull, 208, 205. 

Eabbit, brain, 61, 63. 

Rattlesnake, skull, 206. 

Eeproductive organs in higher vertebra- 

ta, 97. 
Salamander, foot, 82. 
Balmo, caudal extremity, 20. 
Secretary-bird, skull, 245. 
Shark, aortic bulb, 108. 
Sheep, stomach, 32S. 
Skate, brain, 118. 
Spatularia, skull, 123. 
Sturgeon, skull, 124. 
Tadpoles, 165. 
Torpedo, 55. 

Trematosaurus, skull, 155. 
Turtle, heart, 265. 
plastron, 175. 

skull. 175-177. 

Vertebrate brain sections, 56, 57. 
Whale, skull, 337, 838. 

Dicynodontia, 222. 

Didelphia, characteristics oi^ 276. 

peculiarities of, 277. 

stomach o^ 280. 

Digits of anthropomoi-pha, 406, 408. 

bat, 34, 385, 887. 

birds, 254. 

cynomorpha, 401. 

dog, 854. 

lacertilia, 196. 

lemuridse, 889. 

man, 31, 418. 

marsupialla, 279. 

muscles of, 50. 

rabbit, 871. 

seal and turtle, 34, 862. 

Dinotherium, 866. 
Dipnoi, 145. 
Dog-, anatomy of, 358. 
— - digits, ^54. 



Dolichosauria. 1 96. 

Dromasus, pelvis and hind-limb, 228. 

Dugong, heart of, 882. 

B. 

Eab, 74. 

bones of whale, 838. 

in sauropslda, 262. 

See Hearing, organs of. 

Edentata entomophaga, groups and chsrao. 
teristics of, 287. 

extinct, 286. 

loricata, 269. 

mutica, 287. 

phytophaga, characteristics of, 282. 

squamata, 288. 

teeth of, 282, 286. 

tubulidentata, 288. 

Egg, development of, 9. 

Elasmobranchii, 111. 

Electrical organs, 54, 55. 

Elephant, skeleton of, 864. 
See Proboscidea. 

Embryo of vertebrata, development of, 10. 

Encephalon, 55. 

Endoskeleton, segment o^ in thoracic region 
of a crocodile, 19. 

of vertebrata, 14, 

Entomophaga, 287. 

Eocene strata, didelphidae In, 280. 

extinct mammals of, 820. 

fossils of equidffi in, 805, 806. 

fossil rodents of, 875. 

Episkeletal muscles, 44. 

Equidae, fossil, 305. 

(horses and assos) general characteris- 
tics of, 295. 
See Horse. 

Exoskeleton, 89. 

in birds, fishes, repKles, and mammala, 

40-43, 168, 285. 

of reptilla. 167. 

Eye-muscles of sauropsida, 259. 

structiu'e of; 72. 

Face, bones of. 27. 

of man, 414. 420. 

Facial muscles, 07. 

Feathers, 385. 

Femur of the horse, 801. 

Fins of fishes. ■■■i9. 40. 

Fishes, electrical organs of, 54. 

groups in class, 108. 

Smbs, 87. 

muscu lar system, 45. 

raylike bo'ies, 29, 

skeleton of visceral arches of opsmjiie 

fish, 78. 

SkuU, 24, 80. 

Fissipedia, jjeneral characteristics of, 3M. 
Flatfishes { j'leiiTonecUdre), 80. 
Flying-fox. skeleton ot, 385. 
Foetal appendages of vertebrata, 12. 
Foetus, human, arrangement of principal vea 

sels in, 85. 
Foot of anthropomorpha, 407, 410. 

horse, 29o, 298. 

maji, 415. 



426 



INDEX. 



FosbUs in chalk, 197, 198, 214. 

eocene strata, 280, 305, 806, 820, 875. 

lias, 180, 214. 

—— human, 421. 

mesozoic formation, 185, 187, 195, 221, 

227, 228, 280. 

miocene formation, 806, 807, 809, 812, 

820, 328, 829. 

permian formation, 195. 

—— post-triassic formation, 185. 

triassic formation, 195, 214, 221, 222, 261. 

Fowl, stages of development o^ 12. 17, 21, 23. 

polyis, 250. 

scapula and coracoid, 247. 

skull, 242. 

sternum, 241. 

tibia and fibula, 252, 253. 

Frog, aortic arch o^ 84. 

brain, 162. 

cerebro-spinal and sympathetic nervous 

system, 65. 
circulation of blood, 160. 

larva, 165. 

skull, 152, 153. 

sternum and pectoral arches, 156. 

G. 

Galeopttheous, general characteristics o^ 

382. 
Ganoidei, existing and fossil, 127. 

genera o^ 121. 

Gibbons, 403. 

Glyptodon, peculiar character of, 291. 

GorUla, 404. 

Growth in man, laws of^ 418. 

H. 

Hags {ma/rsipohraThchii\ optic nerves o^ 65. 
Hand of anthropomorpha, 403, 410. 
Head and trunk, muscular system of, 44. 

of sperm-whale, 840. 

Hearing, organs of, cases, 26. 

in cetacea, 349. 

Heart of amphibia, 158. 

bat, 386. 

birds, 267. 

crocodiles, 266. 

■ modifications oi, 87. 

porpoise, 346. 

■ sauropsidai, 264. 

teleostet 140. 

turtle, 265. 

Hedgehog, 375. 

Hippopotamidffl, general characteristics of, 

ITomoBOsauria, 195. 

Uorns of deer, etc., 327. 

llorse, p-enerai characteristics of, 293. 

cervical vertebra, 295. 

femur, 301. 

fore-foot and hind-foot, 294, 298. 

limbs, 297. 

muscles, 301. 

ossa innominata, 300. 

skeleton, 296. 

skull, 297. 

teeth, 295, 802. 

viscera. 804. 



Hyposkeletal muscles, 44. 
Hyracoidea, characteristics of^ 36T. 

I. 

IcnriTYOPSiBA, characteristics of, 100. 
Ichthyosauria, 208. 

pectoral arch, 212. 

pelvis, 214. 

skeleton, 209. 

skull, 210. 

vertebrsE;, 210. 

Impregnation of vertebrata, 9. 
Insectivora, characteristics of, 875. 

J. 

Jacobbon, organs ot, 72. 



K. 



KiONOCEA:!nA, 196. 



Laoebtilta, 186. 

groups, 193. 

organs of copulation, 272. 

skull, 188. 

Lamb, development of; 28. 
Lamprey, optic nerves of^ 66. 67. 

sections of skull, 103, ill. 

skull, 24. 

teeth, 79. 

Larva of frog, 164. 

Larynx, 93. 

platyrrhini, 396. 

sauropsida, 267. 

Leiotrichi, 421. 

Lemuridffi, general characteristics o:^ 884 

brain, 890. 

Ijmbs, 889. 

organs of reproduction, 890. 

skull, 389. 

teeth, 890, 391. 

Lepldosiren, aortic arch of^ 84. 
Lepidosteus semiradiatus, brain o^ 121. 
Lias, chelonia in, 180. 

- ichthyosauria in, 214. 
Limbs of ampliibia, 156. 
birds, 249. 

carnivora, 351. 

fishes, 87. 

galeopithecus, 882. 

hedgehog, 879. 

horse, 297. 

hyrax, 368. 

^— lemuridse, 889. 

man, 413. 

marmoset, 898. 

muscular system of^ 46, 

pig, 315. 

porpoise, 365. 

position o^ 83. 

seal, 361. 

vertebrated animals, 31. 

Lion, skeleton of, 35a. 
Liver, 79. 

in sauropsida, 264. 

Lizard, brain of; 259, 260. 
I pectoral arch and sternum, 85, 8Sb 



INDEX. 



42'J 



Lizard, skeleton of visceral arches, 77. 
Lymphatic System, 90. 
Lymph-corpuscles. 91. 



M. 

Maobatjoeibnidje, 812. 

Mammalia, general characteristics of; 102. 

classification, 278. 

deciduate, 850. 

dental formulae, 81 . 

development of heart, 89. 

skeleton ot visceral arches of mammate, 

77. 

teeth, 803. 

Man, arrangement of principal vessels in hu- 
man foetus, 85. 

general characteristics of; 418. 

comparison of anthropomorpha vnth, 

digits o^ 81. 

divisions of— 

Leiotrichi, 421. 
TTloti-ichi, 421. 

fossil, 421. 

laws of growth in, 418. 

muscles of digits, 50-54. 

■ — - muscles of limbs, 46. 

OS innominatum, 86. 

position of limbs, 88. 

" races " of; 418. 

— — section of pregnant uterus of a decidu- 
ate placental mammal, 10. 

sexual differences, 418. 

teeth, 81. 

Marmosets. See AretopitheclnL 

Marsipobranchii, 108. 

Marsupialia, digits of; 279. 

Mastodon, 866. 

Mesozoic formation, crocodiles in, 221. 

didelphidie, etc., itx, 280. 

lizards in, 194. 

omithoscelida in, 237. 

plesiosauria confined to, 186. 

pterosauria in, 228, 

Miocene epoch, cotylophora o^ 328. 

extinct mammals, 820. 

fossil camehdBe, 829. 

fossil equidse, 806, 807. 

fossil hippopotamidae, 820. 

fossil rmnoceros, 810. 

fossU tapirs, 312. 

genus of sirenia, 883. 

Modifications of the brain, 69. 

ofthe heart, 88. 

of reproductive organs, 98. 

Moles (talpincE), 384. 

Monkeys. See BimiadEe. 

Monkfish (squatmay, pectoral member o^ 
88. 

sections of skull, 114. 

Monodelphia, characteristics o^ 281. 

Mosasauria, 197. 

Mudfish, 146. 

Muscles of amphibia, 46. 

. antibrachlum, 48. 

anthropomorpha, 408. 

■ cms, 48. 

-^— CTOomorpha, 400, 

. the digits, 50. 



Muscles of dog, 855. 

eye in sauropsida, 259. 

— fishes, 46. 

hedgehog, 377-379. 

horse, 801. 

' the limbs, 47. 

man, 416. 

marmoset 394. 

ophidia, 256. 

pig, 816. 

platyrrhini, 896. 

rabbit, 878. 

seal, 362. 

system o^ in ophidia, eheloola, And 

aves, 266. 
—^ trunk and head, 44. 
Musk-deer, stomach of; 323. 
Myelon, 65. 
Myxine, 109. 

N. 

Negboes, peculiarities of; 419. 
Nerves, cerebral, 66. 

ofthe eye, 73-75. 

sauropsida, 258. 

spinal, 65. 

sympathetic, 71. 

Nervous system of frog, 66. 
Non-ruminating animals, 813. 



Olpactoby apparatus, 72. 

nerves, 66. 

Ophidia, groups of; 200. 

fbssil, 208. 

muscular system, 266. 

organs of copulation, 272. 

skull, 202. 

teeth, 208. 

vertebrae, 200. 

Optic nerves, 66, 73, 74. 
Orangs, 408. 

middle digit oi; 50. 

Organs, circulatory, 81, 

of hearing, 74. 

renal, 94. 

reproductive. See Beproductire Or* 

gans. 

respiratory, 91. See also Eesplratioa. 

of sight, 72. 

of taste, 78. 

of touch, 78. 

of voice, 9S. 

Omithodelphia, characteristics of, 274. 

Omithoscelida, 223. 

transitional character of skeleton ot 

224. 
Os innominatum of man, 86. 
Ossa innominata ofthe horse, 800. 
Ossification of fkcial apparatus, 27. 

skull, ,24. 

vertebrse, 17. 

Ostrich, reproductive organs ot 272, 

skull, 243. 

Otaridse (eared-seals), 360. 
Ox, skeleton of; 321. 



428 



INDEX. 



Pai-.eotiierid.e, 812. 
Palate of cctui-ea. 83G. 
Pectoral arch, 84. 
■ in birds, '^47. 

chelonia, 178. 

ci-ocodiles, 219. 

and foro-llDib of pike, 133. 

of plesiosauiia, li>4. 

Pectoral fins, 89. 

member of monkflsb (squatina\ 38. 

Polvic arcb, 36. 

of cliolonia, 178. 

of nlesiosaurla, 185. 

Pelvis ol antbropomorplia, 407. 

bat, 83G. 

birds, 251. 

CL'tiicea, 335. 

crofutUles. 220. 

cyiiomorpha, 400. 

hedgehog, 877. 

man, 415; lower races of man, 419. 

ofplatyrrhini, 395. 

porptiiso, 345. 

pterosauria, 230. 

sirenia, 331. 

Permian formation, lizards of, 195. 

Perissodactyla, 292. 

Phnryngobranchii, 104. 

Phouidie, gcDL^ral characteristics of, 861. 

Phocodontia, 849. 

Pliytopliaga, '.iS2. 

Pig, anatomy of. 818. 

brain, 00, 65. 

diijitai muscles, 53. 

Pike, brain o£, 142. 
■ fljis, 41. 

pectoral ai-cb and foro-limb, 137. 

skull, 132-135. 

Pinnipedia, characteristics o^ 859. 

gl'OUpS, oOlK 

Hsccs. See Fishes. 

" I'lacoid exoskeleton," 111. 

Plaice, skull of, 80. 

Plastron of the chelonia, 174. 

Platyrrhlnl, c'-'uernl cluiracteriBtics of, 394. 

Plesiosauria, ISO, 185. 

pi'lvk; arch of, 135. 

skeleton, 181. 

— — extinct, confined to Mesozoic rocks, 185. 
PleurouecLidie (flatfishes), 30. 
Polypteixs, caudal extremity of. 20. 
Porpoise, general ciiaractcristics of, 842. 

heart. 34G. 

muscles, 846. 

pelvis, 845. 

respiratory apparatus, 847. 

skull, 843. 

stomach, 346. 

teeth, 810. 

■ vertebno, 843. 

Post-Triasslc group of plesiosauria, 185. 
Poupart's ligament^ 87. 
Priiiwtes, char.ictoristlcs of, 888. 

■ divisions of, ysu. 

Proboscidea, gonorai characteristics of, 8C4. 

bones. SCO. 

fossil, 868. 

ruprodnrtive or^'aus, 866. 

. — skull, 8t4. 



Proboscidea. Btoaiach o^ :"i05. 

teeth. 866. 

vertebroj, 8&1. 

Protorosauria, I'.T). 
ProtovL'rtebrffi, 1*"'- 
Psaltcriuni of ruminants. 821. 
Pterodactylus, skeleton of. 2'.i9 
Pterosauna, 2-lS. 

groups of, 281. 

skull, 229. 

verU-lirie, 2':9. 

Python, dorsal vertebra of^ 201. 

skuU, 203, 205. 

K, 

Rabbit, anntomv of, !^T1. 
. brain, 60-65, 374, 

digital muscles, 53. 

hmbs, 373, 374. 

muscles, 37:^. 

reproductive organs, 374. 

skull, 872. 

teeth, 374. 

vortebrte. 371. 

viscera, 374. 

Races of man, 418. 

liana esculenta, cerebro-spinal and sympa 

thetic nervous system of, 05. 
Rattlesnake, skull of. 206. 
Rays, pectoral arch of, 34. 

. skull, 24. 

Renal organs, 94. 
Reproductive organs, 95. 

of amia calva, 126. 

aninhlbia, 163. 

antliro|iomorpha, 418. 

bat., Syil. 

birds, 2T2. 

dog, 853. 

bi'clg.'hog, 381. 

lemuridic, S!)0. 

mail, 415, 417. 

moililicalions of, 97. 

o^ti'ich, 272. 

Itorpiiise, 849. 

sauropsida, 273. 

Reptilia, characteristics of, 105. 

groups, 169. 

Respiration, mechanism of, 93. 
organs of, 91. 

in amphibia, 161. 

porpoises, 348. 

sauropsida, 269. 

teleostei. 140. 

Rbinoccros, general characteristics of, SOT. 

bones, 303. 

fossil, 809. 

reproductive organs, 809. 

skin, 31)7. 

skull, 807. 

tet-th, 807, 809. 

vertebrse, 807. 

viscera, 809. 

Khynchocephala, 194. 

Rodeiilia, genfral charactei-istlcs oC B69. 

- bniin, 370 

- di'.nts, 371. 

rcproiliictivo organs, 8T1. 

U-vih .369, 370. 

\ertcbi-a:, 370. 



INDEX. 



41!9 



RuinlnatlDg' animals. 822. 

act of feeding", &i4. 

act of raminatioa, 325. 

ffi-oups of; 826. 



!:*A,LAMANDRA, hind-foot of, 38. 

Salmo, caudal extremity of, 20. 

Sicrum of birds, 238. 

8im-opsid.a, general characteristics of, 101. 

lilimentarv canal o^ 262. 

bi-ain, 258, 259. 

■ ear, 262. 

eye-muscles, 259. 

heart, three forms of^ 264 

laiyux, 26T. 

- — liver, 264. 

niusdes and viscera, 256. 

nerves, 258. 

reproductive organs, 272. 

respu-atory organs, 269. 

stomach, 264. 

tongue of, 262. 

Soala. See OtariJae, Phocidse, Pinnipedia. 

Secretary-bird, skull of, 246. 

Seusoiy organs, 72. 

8exu.ll differences in man, 418. 

Sharks, aortic arch of; 89. 

aortic bulb, 116. 

pectoral arch, 34, 

skull, 24. 

Sheep, stomach o:^ 323. 
Shrews {sorices), 384. 

Simiadre, general characteristics o^ 391. 
- — - divisions of, 392. 

skull, 391. 

— - teeth, 891. 

Sirenia. characteristics o^ 830. 
Skate, brain of, 118. 
Skeleton, amphibian, 151, 152. 

. of anthropomorpha, 404. 

catarrhine monkey, 392. 

chelone midas, section of, 172. 

elephant, 864. 

llying-fox, :3S4. 

. fossil equidie, 805, 306. 

horse, 296. 

icLhyosauria, 209. 

limbs. 31. 

lion, 352, 

oExaitiJOScelida, transitional character of, 

OS. 321. 

pleslosauras, 183. 

porpoise, 343. 

pterodactylus, 229. 

the skull, 23. 

'.'iscei-al arches of lizard, mammal, and 

tish. 73. 

See also Endosfceleton, Exoskeleton. 
Skull of accipenser, 124. 
amphibian, 153. 

of anthropomorpha, 405. 

arches belonging to, 71. 

of bat, 886. 

bii-ds. 241. 

carnivora. S50. 

'— common fowl, 343. 
. oetacea, 834. 



Skull of chelonia, 176, 177. 

cranial system, 22. 

crocodile, 218. 

cynomorpha, 397. 

dog, 853. 

elephant, 865. 

fishes, 81. 

foital cachalot, 841, 

f\-og, 152, 153. 

hedgehog, 876. 

horse, 297. 

lacertiUa, 1S9, 190. 

lemuridfe, 3S9. 

man, 414, differences in, 420, 

marmoset, 393. 

modifications of, 24. 

nmdfish, 145, 146. 

nerves of, 66-71. 

ophidia, 202. 

ornithosceUda, 227. 

ostrich, 243. 

osseons brain-case, 24, 25. 

pig, 814. 

pike, 182-135. 

plaice, 80. 

platyrrhini, 395. 

plesiosanria, 188. 

■ porpoise, 343. 

■ pterosauria, 230. 

rabbit, 872. 

rattiesnake (<irotalus), 206. 

rhinoceros, 307. 

seal, 363. 

— — ■ secretary-bird, 240. 

sirenia, 880. 

spatularia, 128. 

sturgeon, 124. 

trematosaurus, 123. 

typical segment o^ 25. 

walrus, 860. 

whale, 827, 823. 

Sloths, characteristics o^ 238 
ankle-joint, 283. 

Umbs, 233. 

pelvis, 283. 

• tongue. '2S6. 

— vertebrae, 2S3, 
Snakes. See Ophidia. 
Sorices (shrews), 384. 
Spatularia, skull o^ 123. 
Spinal canal and cord, 65. 

system, 17. 

Spleen, 91. 

Spouting, mechanism of; In cetacea, 843. 

Spurofbh-ds, 254. 

Squatina (monkflsh), pectonu member ot K) 

sections of skull, 115. 

Stenson, canals of, 72. 
Sternum in bhxis, 240, 241, 

of frog, 157. 

of lizai-d, 35, 36. 

Stomach, 79. 

of camels, etc., 828. 

carnivora, 351. 

musk-deer, 823. 

porpoise, 846. 

ruminating animals, 323. 838. 

sauropsida, 264. 

sheop. 323. 

teleostel, 139. 

Sturgeon, skull o^ 31. 124. 



430 



INDEX. 



buldro, 812. 

variation? in, 818. 

Sympathetic nerves, 71. 

SjTinx, 98. 

of birds. 268, 



Tadpoles, 165, 166. 

Tapirs, characteristicB of, 810. 

Tarsus, skeletal elements of, 31. 

Taste, organ of; 78. 

Teeth, 79. 

of amphibia, 158. 

— — anthropomorpha, 411. 

bat, 886, 887. 

carnlvora, 850. 

cats, 859. 

■ ■ cetacea, 885. 

crocodiles, 221. 

cynomoipha, 401. 

delphlnoidea, 840. 

didelphla, 278. 

dog, 856, 859. 

edentata, 282, 286. 

edentata tubulldentata, 288. 

elephant, 865. 

extinct mammids, 820. 

fishes, 114, 188. 

galeopithecus, 888. 

hedgehog, 879. 

hippopotainus, 819. 

horse, 295, 802. 

hyrax, 868. 

lacertilia, 198. 

lemiiridBB, 390. 

■ macrauchenidse, 812. 

man, 417, 420. 

marmoset, 892. 

opbidia, 208. 

ornithoscellda, 227. 

palflBotheridfe, 812. 

pig, 816. 

[jlatyrrhinl, 896. 

porpoise, 846. 

rabbit, 874. 

rhinoceros, 807. 

i-otlentia, 869. 

seal, 863. 

sirenia, 882. 

suidffi, 813, 818. 

tiipirs, 810. 

toxodontia, 829 

wab-us, 860. 

whale, or whalebone, 839. 

Teleostei, 180. 

aortic arch of, 84. 

Tertiary I'pocb, extinct cetaceans of, 850. 

late, fossil man in, 421 

Thymus, 91. 

Tungue of amphibia, 158. 

sauropslda, 263. 

sloths, 237. 

Torpedo, electrical apparatus of, 55. 

Tortoises, 170. 

Touch, organs of, 78. 

Toxodontia, extinct, characteristics ol^ 829, 

Tragulidoa, 826. 

Transition of skeleton of ornithoscellda, 224. 

Trematosa nrua, skull of, 155. 



Triassic formation, crocodiles oi; 221. 

extinct lizards, 195. 

dicynodontio, 224. 

Ichthyosauiia, 218. 

macropodidDB, etc., 280. 

Triassic groups of plesiosaurla, 185. 
Trichechida) (wah-usea), 860. 
Trigeminal nerves, 63, 70. 

lYunk and head, muscular system o( M 
Turkey, brain o^ 259. 
Turtles, 170. 

heart, 264, 265. 

plastron, 174. 

skull, 176. 177. 

Tylopoda or cameUdse, 828. 



ULOTKiom, 421. 

Ungulftta, characteristics oi^ 292. 



Vampiee bat, 888. 

Vascular system, 83-87. 

Veins, 83. 

Ventral flns, 89. 

Vertebne of anthropomorpha, 40\ 

bat, 885. 

bbds, 2S6. 

caudal, 19. 

of carnlvora, 850. 

cetacea, 384. 

crocodiles, 214. 

cynomorpho, 398. 

dog, 853. 

hedgehog, 876. 

horse, 295. 

. hyrax, 867. 

'chthyosaurla, 208. 

- - '-fccertilia, 387. 

— — *emurida3, 889. 

man, 414 ; lower races o^ 420. 

marmoset, 398. 

■ ornithoscellda, 227. 

ossification of, 17. 

of pig, 813. 

platyrrhine, 894. 

porpoise, 843. 

proboscidea, 864. 

pterosauria, 229. 

rabbit, 871. 

rhinoceros, 807. 

rodentia, 870. 

seal, 860. 

sh-enia, 880. 

snakes, 201. 

tapirs, 801. 

• • whales, 836. 

Vertobrata, distinctive charaotere o( 1 

development, 9. 

foetal appendages, 12. 

impregnation, 9. 

Umhs, 31. 

provinces or groups, 100. 

VertcDHite endoskeleton, 14. 

exoskeleton, 39. 

Vesicles of the brain, 55. 
Viscera of nnthropomorpha, 413. 

f'.innfilklm. 354.. 



camelidffl, 824. 
cynomorpha, 401. 



INDEX. 



431 



Viscera of elephant, 866. 

hedgehog, 880. 

horse, 8G4. 

hyrax, 868. 

lemuridffl, 889. 

pig, 818. 

platyrrhinl, 896, 89T. 

rabbit, 814. 

rodentia. 8T0. 

seaL 863. 

tapirs, 811. 

Vtscenu arohes and deits, 14. 



I Visceral arches, skeletons ot Tl. 
I Voice ot birds, 268. 

organs oi^ 93. 

W. 

■WHALEBOlfB, 839 

Whale, ear-bones of, 888. 

8kuUof,888. 

skull of foetal, 887. 

sperm, head oi; 840. 



THE END.