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THE LIBRARY

THE UNIVERSITY

OF CALIFORNIA

PRESENTED BY

PROF. CHARLES A. KOFOID AND

MRS. PRUDENCE W. KOFOID

Dunglisori }s American Medical Library.

THE

STUDENT'S COMPENDIUM

COMPARATIVE ANATOMY.

BY P. EYERS,

LICENTIATE OF THE ROYAL COLLEGE OF SURGEONS IN IRELAND, &C.

Sparsa coegi."— Ovid.

PHILADELPHIA :

PRINTED AND PUBLISHED BY A. WALDIE, 40 CARPENTER ST.

1839.

PHILIP CRAMPTON, M. D., F. R. S.

SURGEON GENERAL TO THE FORCES IN IRELAND,

<fcc. Sec. Sec.

AS AN INADEQUATE, BUT SINCERE TESTIMONY OF RESPECT,

DISTINGUISHED SCIENTIFIC ATTAINMENTS,

AND

DESERVED PROFESSIONAL EMINENCE,

THIS VOLUME

IS INSCRIBED,

HIS GRATEFUL AND OBLIGED FRIEND,

THE AUTHOR.

y&w

PREFACE.

In the compilation of these pages no originality is claimed, but
the labours of modern authors have been freely appealed to, and
it is trusted, on every occasion, with due respect. A list of the
several authors consulted has been added at the end of the book.

I have to acknowledge several obligations to my friend Dr.
Houston of this city, whose scientific acquirements and connec-
tion with the Museum of the College, have well qualified him for
the many auxiliary favours he has conferred on me.

P. E.

Dublin, 33 Aungier Street,
September, 1838.

COMPENDIUM

COMPARATIVE ANATOMY.

CHAPTER I.

PRELIMINARY OBSERVATIONS.

When we turn our attention to the busy theatre of animal life,
we are at once attracted by scenes of wonder and delight. The
works of nature appear unbounded in extent, variety, and riches.
Wherever the eye is cast, from the icy regions of the pole to the
scorching sands of the line, it beholds life displayed in forms as
endless as they are enchanting.

Every region and every element is the abode of numerous animals,
and is admirably suited to their peculiar living habits and instincts ;
the vastness of their number may be estimated from the declaration
of the celebrated Ehrenberg, that a single cubic line which is less
than a drop of fluid contains 500,000,000 monads.

But however varied and delightful the occupations of the zoolo-
gist may be, his information is still defective, and he perceives that
the interior machinery of life is hidden from his observation, and its
springs concealed by clouds which nothing but the light of dissec-
tions can dispel.

When once engaged in this captivating department of his inves-
tigations, he begins to observe the beautifully progressive develop-
ment of organisation, varied and modified in obedience to certain
laws ; he will often behold the same animal, according to the parti-
cular epoch of its existence, undergoing metamorphosis, appearing
under different characters, and playing very different parts on the
stage of life.

Having entered a little more fully into the details of comparative
anatomy, he will often observe an organ which has attained a high
degree of development, and whose functions are perfectly under-
stood in one animal ; diminutive, rudimentary, and apparently use-
less in another. Hence it must be obvious, that he who aspires to a
perfect knowledge of human structure and function, must extend
his researches to an examination of the animal kingdom in general ;
and accordingly great advantage will be found in a previous ac-
quaintance with some one or more of the most approved classifica-
tions in natural history.

Every classification hitherto proposed has in some particular or
other its imperfections ; but it matters little what scale we adopt.

8 EVERS'S COMPARATIVE ANATOMY.

or whether we make use of several, provided that our object of con-
veying or acquiring a knowledge of the comparative structure of
animal bodies be attained. This must be my excuse for appearing
in some places to have followed the arrangement of Cuvier, and in
others, that of Dr. Grant, both having their excellences, and their
authors holding the highest place as authorities on the subject.

Cuvier's and Grant's classifications are therefore subjoined, ac-
companied by familiar illustrations of each, to lead the student at
one glance to the objects which each subdivision embraces. The
examples appended to Grant's classification have been added by
myself, whilst those of Cuvier have been taken from Dr. Houston's
Descriptive Catalogue of the Preparations in the Museum of the
Royal College of Surgeons in Ireland, with a few additional exam-
ples from Roget's Bridgewater Treatise.

It might appear an omission not to make some allusion to the
arrangement of the animal kingdom adopted by the immortal Lin-
neeus, but the researches of later zoologists have proved it so defec-
tive, that it is not followed by any writer or teacher of the present
day, and needs therefore but a cursory allusion. Suffice it to state
that he divided the whole animal kingdom into six classes, Mam-
malia, Aves, Reptilia, Pisces, Insecta, Vermes, founding his classi-
fication mainly on the peculiarities afforded by the respiratory and
sanguineous systems.

OUTLINE OF CUVIER'S CLASSIFICATION OF ANIMALS.

FOUR GREAT DIVISIONS.

1. Vertebrata. 3. Articulata.

2. Mollusca. 4. Radiata.

VERTEBRATA.

Characters. — Internal skeleton — brain and spinal marrow in separate cavi-
ties— red blood and muscular heart — mouth with horizontal jaws — five
organs of sense — never more than four limbs — separate sexes.

MOLLUSCA.

Ch. — No skeleton — muscles all attached to external skin — nervous system
situated in the visceral cavity and composed of separate masses joined by
nervous filaments — taste, sight, or as in one instance, hearing, the only senses
— organs of circulation, respiration, and digestion very perfect.

ARTICULATA.

Ch. — No skeleton — two long nervous chords with ganglia at intervals —
have usually taste and sight — divided in jointed rings, soft or hard, to inside
of which muscles attached — sometimes lateral limbs, sometimes none — jaws
when present alwavs lateral.

CLASSIFICATION.

RADIATA.

Ch. — Organs of movement and sense disposed circularly around a centre,
not symmetrically as in the preceding — no visible nerves — no organs of sense
or circulation — respiration by the outward integument — intestines often a
simple bag— sometimes the animal is but a homogeneous pulp without aper-
ture or cavity.

I. YERTEBRATA.

Class 1. MAMMALIA.
Order 1. Bimana - - Examples, Man.

2. q,cadrumana

3. Cheirotera -

4. Insectivora -

5. Plantigrada -

6. DlGITIGRADA -

7. Amphibia - -

8. Marsdpialia -

9. Edentata - -

10. Rodentia - -

11. ruminantia -

12. Pachydermata

13. Cetacea

Cl. 2. AVES.

Orel

Exam.

Orel

Orel.

1. Accipitres

2. Passeres - -

3. ScANSORES - -

4. GALLIN2B - -

5. Grallje - -

6. Palmipedes -

Cl. 3. REPTILIA.

1. Chelonia - Exam.

2. Sauria - - -

3. Ophidia - -

4. Batrachia -

Cl. 4. PISCES.
1. Chondropterygii Exam.

Monkey, ape, lemur.

Bat, colugo.

Hedge-hog, shrew, mole.

Bear, badger, glutton.

Dog, lion, cat, marten, weasel, otter,

Seal, walrus.

Opossum, kangaroo, wombat.

Sloth, armadillo, ant-eater.

Beaver, rat, squirrel, porcupine, hare,

Camel, deer, giraffe, sheep, ox.

Elephant, hog, rhinoceros, tapir, horse,

Dolphin, whale.

Vulture, eagle, owl, hawk.
Thrush, swallow, lark, crow, sparrow.
Woodpecker, cuckoo, toucan, parrot.
Peacock, pheasant, grouse, pigeon.
Plover, stork, snipe, ibis, flamingo.
Auk, grebe, gull, pelican, swan, duck.

Tortoise, turtle, emys.

Crocodile, lizard, gecko, chameleon.

Serpents, boa, viper.

Frog, salamander, newt, proteus, siren,

2. Malacopterygii

3. LoPHOBRANCHII

4. Pleclognatiii

5. Acanthopterygii

Head crowned with tenta-
cula which serve as feet

Progression by fins placed
near the head.

Head free progression on
the belly.

Without distinct head.

:■

Lamprey, shark, ray, sturgeon.
Salmon, herring, cod, sole, eel.

Pike-fish, pegasus.

Sun-fish, trunk-fish.

Perch, mackerel, sword-fish.

II. MOLLUSCA.
Cl

I. Cephalopoda Exam. Cuttle-fish, cala-
mary, nautilus.

2. Pteropoda

3. Gasteropoda

4. Acephala

Clio, hyaloea.

Slug, snail, lim-
pet.

Oyster, muscle,
ascidia.

EVERS S COMPARATIVE ANATOMY.

Two long arms at the mouth
for seizing objects.

Arms very numerous, arti-
culated, horny.

5. Brachiopoda Exam. Lingula, tereba-

tula.

6. Cirrhopoda Barnacle, triton.

III. ARTIOULATA.
CI. 1. ANNELIDA.

Ord. 1. Tubicola - - -

2. Dorsibranchia -

3. Abranchia - -

- Exam.

Serpula, sabella, amphitrite.
Nereis, aphrodite, lob-worm.
Earth-worm, leech, nais, hair-worm.

Cl. 2. CRUSTACEA.

Ord. 1. Malacostraca - - Exam.

2. Decapoda - - -

3. Stomopoda - - -

4. Amphipoda - - - i

5. LiEMODIPODA - -

6. ISOPODA - - - - , .

7. Entomostrata - -

Cl. 3. ARACHNIDA.
Ord. 1. Pulmonalia - - - Exam.

2. Trachealia

Cl. 4. INSECTA.

Ord. 1. Aptera - -

2. Coleoptera -

3. Ortiioptera

4. Hemiptora -

5. Neuroptera

6. Hymenoptera

7. Lepidoptera

8. Rhipiptera -

9. Diptera - -

Exam.

Lobster, crab, prawn.

Squill, phyllosoma.

Grammarus, sand-hopper.

Cyamus.

Wood-louse.

Monoculus.

Spider, tarantula, scorpion.
Phalangium, mite.

Centipede, podura.
Beetle, glow-worm.
Grass-hopper, locust.
Fire-fly, aphis.
Dragon-fly, ephemera.
Bee, wasp, ant.
Butter-fly, moth.
Xenos, stylops.
Gnat, house-fly.

IV. RADIATA vel Zoophyta.

ClaSS 1. ECHINODERMATA

2. Entozoa - -

3. acalephje - -

4. Polypi -

5. Infusoria - -

Exam. Star-fish, sea-urchin.

! Fluke, hydatid, tape-worm.

Actinia, medusa.

Hydra, coral, madrepore, pennatula.

Brachionus, vibrio, proteus, monas.

GRANT'S DIVISION OF THE ANIMAL KINGDOM.

Division. Class.

f 1. POLYASTRICA

I. CYCLO-NEURAl I £°RIFE*A " "

-RAD.ATA 1 4:I0orEP„T- I
I 5. Echinodermata

Exam. Monad, madrepore.

— Sponges.

Polypes, corals.

Medusa, actinia.

Star-fish, sea-urchin.

SKELETON IN THE INVERTEBRATA.

Division.

II. DIPLO-NEURA
vel ARTICULA-
TA.

III. CYCLO-GAN-
GLIATA vel
MOLLUSCA.

IV. SPINI-CERE-
BRATA vel
VERTEBRATA.

Class.
f 6. Entozoa -

7.
8.
9.
10.
11.
12.
113.
fl4.
115.
{jft.
117.

Lis.
f19.

I 20.
<2l.

| 22.
123.

Rotifera -

ClRRHOPODA
ANiNELIDA -

Myriapoda
Insecta - -
Arachnida
Crustacea
Tdnicata -
conchifera
Gasteropoda
Pteropoda
Cephalopoda
Pisces - -
Amphibia -
Reptilia -
Aves - -
Mammalia

Exam. Intestinal worms, hyda-
tids.

Patella.

Barnacle, triton.

Earth-worm, leech,

Scolopendra.

Bee, butter-fly.

Spider, scorpion.

Lobster, crab.

Ascidia intestinalis.

Muscle, oyster.

Slug, snail.

■ Clio, hvalosa.

Cuttle-fish.

Salmon, shark, eel.

Frog, toad, proteus.

Tortoise, lizard, serpent.

1 Eagle, heron, duck.

Man, kangaroo, whale.

Many other arrangements of the animal kingdom have been pro-
posed by different zoologists; some, as Linneeus, founding their basis
of classification on the vascular and respiratory systems, and others on
the peculiarities afforded by the generative organs. Aristotle divided
all animals into those with, and those without red blood; and
Lamark into the apathic, the sensitive, and the intelligent.

CHAPTER II.

SKELETON IN THE INVERTEBRATA.

General observations. — The skeleton gives figure, strength, and
solidity to the entire frame ; it serves as a basis of support to the
soft parts, forms levers of locomotion, and encloses cavities to pro-
tect and defend the most delicate and important organs. Its use,
however, being chiefly of a mechanical nature, it will be found to
vary much, according to the respective wants, habits, and instincts
of animals. In all the operations of nature we find that there is a
rigid economy observed ; the means employed are such only as
are required, and always the most simple by which the intended
purposes can be accomplished. Hence we shall not be surprised to
meet with infinitely varied modifications of skeleton throughout
the widely extended range of the animal world. The chemical
composition of this solid frame-work presents some variety. For
instance, silica is found in the lowest forms of the radiata ; carbo-
nate of lime in the molluscous animals; carbonate and phosphate of
lime in the articulata ; and phosphate of lime in the organised skele-
tons of the vetebrata. This frame-work is sometimes placed external
to the soft parts, and in others it is internal to them. In no instance
do we meet with a bony skeleton except in animals possessed of

a regularly formed brain ; and here it is obvious to those who un-
derstand the difference between the growth of shell and bone that
the former would be unfit for the purpose, since there is no provi-
sion made for the enlargement of the original cavity.

Radiata, Cuvier ; Cyclo-neura, Grant. — In this acrite or
lowest division of the animal kingdom the skeleton generally holds
an internal situation, and is composed either of one large mass or
several smaller pieces symmetrically disposed, composed of silicious
or calcareous spicula. In many of the polygastrics the organ of
support consists in a condensation of the common integument en-
veloping the body — occasionally in the form. of an elastic vagini-
form sheath into which the animal can retreat on the approach of
danger, (fee, as seen in the vaginicola innata. Among the pori-
phera, skeletons are met with of a horny, silicious, or calcareous
structure, variously modified. In none does nature seem to have
amused herself more in the construction of skeletons than among the
zoophytes. Here they are met with internal or external, soft, horny,
or calcareous ; branched, globular, or filiform ; free or fixed. The
astenas and others of the echinodermata present us with skeletons
in the form of external crusts or shells, disposed after the manner
of plates, and composed of carbonate, with a trace of phosphate
of lime.

Articidata, Cuvier; Diplo-nerose Animals, Grant. — The bo-
dies of these animals are generally long, cylindrical, and divided
transversely into segments. Their skeletons are generally thin,
light, and situate externally, chiefly composed of phosphate of lime,
though occasionally of carbonate, as in the cirrhopoda and Crusta-
cea. The entozoa owe their peculiar stiffness and rigidity to the
tough, strong, and transparent covering enveloping their entire
body. In some of the inferior orders of them, as in the acanthoce-
phalous species, their retractile proboscis and part of their bodies
are set with dense, sharp spines, which enable them to move with
freedom and precision through the fleshy media in contact with
them. The rotifera are closely allied to the entozoa in their ex-
terior coverings. In the former, however, this texture possesses a
greater degree of firmness, from the attachment of numerous mus-
cles to it. There are no earthy deposits in any part of the body of
these animals. The cirrhopoda, like the mollusca, are usually
enclosed in shells, dense, thin, laminated, and composed of carbo-
nate of lime. These testaceous coverings are best developed in the
balani. and least in the anatiferse. The reverse order of develop-
ment obtains with respect to their extremities.

The amielida, or red-blooded worms, lead us a step higher in
the development of skeleton; for, although the halithea, the leech,
the nais, &c, possess a flexible membraneous covering, many others,
as the serpulas, are shielded by adventitious, solid, calcareous tubes.
The common earth-worm is provided with four pairs of sharp
spines, or setas, for the purpose of progression. The skeleton of
insects is for the greater part composed of a thin, epidermic layer,

SKELETON IN THE INVERTEBRATA. l3

and a thick internal one resembling the woody fibres of plants, but
of an animal nature, termed chitine and coccine, blended with por-
tions of phosphate of lime, magnesia and iron. These animals
also present distinct legs and wings.

In the arachnida we meet with a more consolidated form of
skeleton; generally more than three pairs of legs : and, at the sides
of their head, a pair of sharp-pointed piercing" instruments, suited
to their retired, cunning, and carnivorous habits. These animals
throw off periodically their exterior coverings, like the larvae of
insects; and, like the Crustacea, they are capable of reproducing
their members when destroyed. The Crustacea affords us by far
the most solid form of skeleton met with in any of the articulata.
In the decapods it contains half its weight of carbonate of lime,
and a considerable proportion of phosphate, with traces of iron,
soda, and magnesia, all of which are secreted from the true skin.
These animals have generally five pairs of legs, two strong mandi-
bles, two pairs of slender maxillae, and two pairs of antennae. The
solid crust forming the skeleton of Crustacea is cast off periodically.
This is accomplished by the animal first detaching the cutis and
muscles from the inner surface of the old shell; "then secreting
from the surface of the cutis a new layer of epidermis ; next a layer
of colouring matter; and, within this, the calcareous materials of
the new shell.

Mollusca, Cuvier ; Cyclo-gangliated animals, Grant. The
shells of these animals are formed of carbonate of lime, without
the phosphate, and are remarkable for their want of symmetry on
the two sides of the body, and their inconstancy in animals of simi-
lar structure. In the tunicata we meet with an exterior cartilagi-
nous skeleton, in some instances thick and opaque, as in the ascidia
— in others more delicate and transparent, as in the cynthia papil-
lata. The shells of the conchifera usually consist of two movable
pieces placed on the exterior of the body, connected by ligament
and muscle. All these animals, however, are not bivalved ; some,
as the pholades, have additional pieces at the hinge of the valve,
constituting the multivalves. They have a muscular foot, and a
pair of tentacula. The gasterpoda possess hollow, unilocular, co-
nical shells. Many of them have no shell, as the tritonia and
doris; some have a thin calcareous lamina within the skin of the
back, as the aplysia; whilst others have only a partial covering of
shell as the testacella. In the cephalopodous mollusca we recog-
nise the transition from the external unorganised shells of the in-
vertebrated tribes to the internal organised bones of the vertebrata.
The shells are sometimes external, as in the nautilus, and some-
times internal, as in the sepia. In this complicated class of ani-
mals we find a near approach to the cartilaginous fishes in the pre-
sence of cranium, spinal column, &c, in a mdimental form.

RECAPITULATION.

1. All animals are included under the heads vertebrata and in-
vertebrata.

2. Great advantage to be derived from a knowledge of arrange-
ment and classification.

3. The osseous system is neither the most important nor the
most uniformly existing.

4. Skeleton exists in every class of animals, but modified accord-
ing to each class.

5. Skeleton generally internal in the radiata, and external in the
articulata, subject to exceptions.

6. Skeleton remarkable for inconstancy and want of symmetry
in the mollusca.

7. Basis of skeleton — silica in the lowest radiata, carbonate and
phosphate of lime in the articulata, and carbonate of lime chiefly in
the mollusca.

8. No bony skeleton where regularly formed brain does not
exist.

CHAPTER III.

VERTEBRATA.

General observations. — It will appear hereafter that the principal
part of the nervous system consists in a single central mass extended
along the back, and composed of a series of distinct portions, each
of which, like the cerebral ganglion of one of the sepiae, is indicated
by its giving off one or more pairs of nerves. To coincide with such
a disposition, the chief portion of the skeleton is formed by a series
of osseous rings, which being mutually articulated and collectively
forming a closed cavity, compose a series of spinal vertebra? consti-
tuting the spinal column — the distinctive character of this division
of the animal sphere. The vertebral column, which is the first
rudiment of skeleton observed in the human embryo, is also the
primary and most essential portion of it in the higher classes of ani-
mals generally, and in many cases alone composes nearly the whole
of the skeleton.

Another characteristic of the skeleton in this department of ani-
mals is, that it is placed internal to the soft parts, and is not exuviable
in a mass, as it was in most of the invertebrate classes. Here
the phosphate of lime is the predominant ingredient, and its propor-
tion increases as we ascend through the vertebrated classes.

The appearance of the skeleton is greatly varied by the situation
of the ribs ; for instance, in fish and aquatic mammalia the thorax is
placed near the anterior part of the column, to allow of the mobility

VERTEBRATA. 15

of the posterior portion for the purposes of swimming. In birds,
where the neck is used as a prehensile oro-an, the thoracic portion of
the column is situate near its posterior extremity. Whilst in quad-
rupeds aud reptiles balanced on two pairs of extremities, the solid
portion of their trunk is placed near the middle of their column.

PISCES.

The bones of fishes closely resemble those of the higher grades
of organisation in their embryotic state, not only in their soft carti-
laginous character, but also in the isolated condition of their several
centres of ossification, especially in the complicated bones of the
head. The bones of the cartilaginous tribes are composed of water,
gelatine, and the sulphate, subcarbonate and chloruret of soda;
whilst the more dense bones of the osseous fishes are indurated and
strengthened by the more insoluble phosphates. As the human
embryo originally consists almost exclusively of the vertebral
column, so also in fishes we find that the spine, and the head, which
is only an increased development of it, constitute the most impor-
tant parts of the skeleton.

Spine. — The vertebrae in this class are very numerous, and may
be divided into the abdominal and caudal. The bodies of the verte-
bras are the elements first developed ; they are the most important, and
form almost the entire of the skeleton in the lowest species of cartila-
ginous fishes. They are concave on both surfaces ; consequently
enclose large spaces, filled with a thin gelatinous fluid ; and in many
of the cartilaginous species, the inter- vertebral substances communi-
cate and form a continuous elastic chord passing through the entire
column as in the lamprey. The spinous processes of the abdominal
vertebras are very long superiorly, and assist, by their shanks, to
form the spinal canal ; whilst the caudal vertebrae are distinguished
by having long spinal processes both above and below. Between
the roots of the inferior spinous processes there is enclosed a simi-
lar canal, but larger for the passage of the great systemic artery.

The vertebral column in fishes is constructed in such a manner
as to give considerable perpendicular extent to the trunk, and thus
favour their horizontal mode of progression. The number of ver-
tebra varies greatly; thus in the carp we find 41, in the burbot 57,
in the eel 115. and in the shark as many as 207. In the osseous
fishes, the ribs form an upper and a lower range ; the latter are
better developed and more uniform in their existence than the former.
The number of ribs is generally determined by that of the abdo-
minal vertebrae. In some, however, as the chaetodon, scomber, &c,
the caudal vertebrae are furnished with ribs. These bones articulate
with one vertebra only, as a consequence of which they enjoy but
little motion, and are but slightly subservient to respiration. In the
shark they are cartilaginous ; in the carp they are long and firm ;
in the eel short and slender ; and in many genera, as the raia, fis-
tularia, &c., they are almost wholly absent. The sternum, when

16 EVERS'S COMPARATIVE ANATOMY.

present, consists, as described by Meckel, of a variable number of
V-shaped pieces, pointed downwards and overlapping each other.
This rudimentary bone is best seen in the herring and the dory.

Head. — To the researches of Oken, Meckel, Cams, Blainville,
&c, we are indebted for the important fact that the cranium, is
nothing more than a highly developed portion of the vertebral
column. The composition of the cranium in the cartilaginous
fishes is very simple; in many, as in the skate, consisting chiefly of
one large piece. In the osseous tribes, on the contrary, the com-
ponent parts are very numerous — amounting to 80 in the head of
the perch. The bodies of the vertebras continue forward in a straight
line with the spine along the base of the scull, forming the basilar
part of the occipital, the body of the sphenoid, and the ethmoid
bones. In the bony fishes the cranium is remarkable for being thin,
diaphanous, elastic and having its elements united by squamous
sutures, which favours the extension of the period of growth of each
part. The cavity of the cranium is occupied chiefly by the cellular
tissue of the arachnoid coat; the brain occupying but a small por-
tion of the base of the skull.

The bones of the face present but few peculiarities. The inter-
maxillary bone consists of three triangular pieces inserted between
the vomer, the palate, the nasal, and the superior maxillary bones.
The central piece is generally cartilaginous. In connection with
the upper jaw, we have to notice the os quadratum ; this is composed
of several pieces, which closely resemble the ascending process of
the lower jaw in man. The three portions of which it is mainly
composed are articulated, one to the inferior maxilla and palate
bone, the second to the temporal bone, while the third consists of a
thin round plate, and is called os discoideum. Behind the lower
jaw, and connected to the os quadratum, is the operculum. This
is a plate of bone usually composed of four pieces, which have been
considered analogous to the bones of the tympanum, on account of
the absence of this cavity from the ears of fishes ; others have
regarded it as a portion of the lower jaw. Be this as it may we find
the operculum covering the respiratory apparatus in the same man-
ner as the shells of bivalves cover the subjacent gills.

The os hyoides reaches a high degree of development here, as in
all water breathing vertebrata ; it consists of a body or lingual bone,
and five pieces on either side of it: it is suspended from the tem-
poral bones ; and it is, by its free antero-posterior motions that res-
piration is effected in fishes, and in amphibia, as will be shown
hereafter. It forms an arch, having the lower jaw above it, and the
scapular and coracoid bones below. Its sides support the four pairs
of branchial arches, and externally it has attached to it the opercular
membrane.

Extremities. — In fishes fins supply the place of extremities ; the
anterior corresponding to the arms, and the posterior to the legs.
They are named according to the parts they are attached to, as
dorsal, pectoral, ventral, caudal, and anal fins. The anterior or

VERTEBRATA. 17

pectoral fins are larger and more uniform in their existence than
the posterior; they also commence their development at an earlier
period; in all of which they resemble the embryo of the higher
classes. The ventral fins are wanting in the apodes, as well a*s in
several species of other orders ; whilst the pectoral fins are generally
present.

The anterior fins are generally joined to the back of the skull by-
means of an osseous belt, formed behind by the scapula, and in front
by the coracoid bones. A humerus, generally long and angular, is
attached to these above, and to the radius and'ulna below. To these
succeed the carpal bones, and the member is terminated by long
and numerous phalanges. The posterior members, or ventral fins,
have no connection to the spine, but are suspended from the rib-like
iliac bones, and placed on the lower part of the trunk, at a variable
distance between the head and anus. The presence of a sacrum
in this class would be injurious to the free motion required in
swimming. In the abdominal fishes the pelvic bones are uncon-
nected to the skeleton : and in the apodal families they are wholly
absent. The long phalanges of the feet are attached directly to the
pelvic bones, there being rarely a trace of intermediate bones
developed.

The want of symmetry observed in the skeletons of many fishes
forms a singular peculiarity in this class. In the pleuronectes, for
instance, one side is turned upwards, instead of the back ; both
eyes are placed on the same side; the cranial vertebra- seem
twisted in their long axis ; and the lower part of the head is imper-
fectly developed. The bones, especially the intermaxillary, are
much larger on the side opposite to that on which the eyes are
placed.

RECAPITULATION.

1. The bones of fishes resemble the embryotic condition of the
osseous system in the higher classes of animals.

2. The spine is the most important part of their skeleton.

3. The spinal column enjoys very (ree motion, chiefly in the
lateral direction.

4. The construction of the head is as simple in the cartilaginous
as it is complex in the osseous fishes.

5. The os hyoicles is greatly developed to support the branchial
apparatus.

6. The anterior fins are larger, earlier developed, and more uni-
form in their existence than the posterior.

7. The pelvic bones and posterior fins are absent from the ske-
letons of many cartilaginous fishes.

8. Want of symmetry is a striking peculiarity in the skeletons
of many fishes.

' * evers 2

18 EVERS'S COMPARATIVE ANATOMY.

AMPHIBIA.

In the Batrachia the ribs are almost wholly absent ; it is only
in the rana pipa and the salamanders that small cartilaginous
appendages are found attached to the transverse processes of some
of the vertebrae. In these animals the spine consists of dorsal,
sacral, and caudal portions — the distinction being marked by the
connection of one of the vertebras to the ilium on each side. The
salamander has fourteen dorsal, one sacral, and twenty-seven cau-
dal vertebrae ; in the common frog there are only nine vertebrae ;
and in the rana pipa but eight; whilst the siren has forty-three in
the trunk, and about forty-five in the tail ; from the second to the
eighth inclusive have rudimentary ribs attached to them. The
bodies of the vertebrae are concave on their surfaces; so that, when
in apposition, they give rise to the existence of an intervertebral
oval cavity filled by a gelatinous mass.

When we consider the habits, food, and mode of progression, of
the frog — that its movements, which are chiefly on land, are both
active and extensive, as well for the purpose of seizing its prey as
of escaping from danger — it becomes obvious why its spine should
be short and firmly anchylosed — how the presence of a tail would
be worse than useless, and why a necessity exists for a full deve-
lopment of the posterior extremities. The absence of ribs will
hereafter be accounted for by an interesting peculiarity in the func-
tion of respiration.

Cranium. — The elements composing this cavity are remarkable
for remaining permanently ununited, a state of things which is
strikingly imitated during the progress of the development of these
parts in the higher orders of animals. The maxillary, intermaxil-
lary, tympanic, and jugal bones are greatly expanded, in the
transverse direction, giving the face a flattened appearance. The
lower jaw consists of three pieces on each side.

Of all parts of the osseous system of this class, there is none so
interesting as the os hyoides, on account of the changes to which
it is subjected during the transit of the amphibia from the pisciform
to the reptile state. The branchiae are external, supported by car-
tilaginous arches connected with os hyoides. As the age of
the tadpole increases, the branchiae disappear, the lungs become
developed, and the os hyoides grows, from a small rhomboidal
point, to the large size and peculiar from which it presents in the
full-grown frog.

Anterior extremity. — The shoulder of a frog consists of scapula,
clavicle, and coracoid bone, all of which unite to form the glenoid
cavity. The humerus is short and thick, having a round head
above, received by the glenoid cavity, and also a spherical extremity
below, to articulate with the bones of the fore-arm, which consists
of radius and ulna so united that a faint line indicates their former
separation. The carpal bones are six ; the metacarpal, four. The

VERTEBRATA. 19

middle and index fingers have each two phalanges, the others
three.

The posterior extremity, for reasons before assigned, reaches a
high degree of development. The cotyloid cavity is constituted by the
ilium, ischium, and pubis. The femur is long and cylindrical. The
tibia and fibula are consolidated into one bone, and joined inferiorly
to two bones representing astragalus and os calcis. Between these
and the long metatarsal bones are placed four small, irregular
bones. Of the rive toes, the internal is best developed, and sus-
tains three long, slender phalanges.

The structure and form of the salamander, proteus, and siren,
are well contrasted with those of the froo\ In the former animals,
the spinal column attains a high state of development : the extre-
mities are reduced to a rudi mental type. The bones of the fore-
arm and leg, instead of being anchylosed as in the frog, maintain
a permanent state of separation. The toes, which are four in
number, are but slightly developed. The whole economy of the
frog is admirably organised for rapid terrestrial progression, while
that of the other animals is designed to favour their movements
through a watery element.

Who can fail to observe the extreme wisdom manifested in the
metamorphosis of these animals? In the early part of their exist-
ence, and while they enjoy an aquatic mode of life, their organi-
sation is in due accordance ; at first their members are scarcely
perceptible, whilst their tail is of great length, and continues so in
those destined to continue their watery habitation ; but in the frog,
(fee, which are to breathe by lungs, the tail is gradually removed
by absorption, and the extremities, particularly the posterior, un-
dergo a rapid evolution.

REPTILIA.

Chelonia.—These reptiles present a tolerably perfect form of ske-
leton. Their spine consists of eight cervical, fourteen dorsal, three
sacral, and from twenty to thirty caudal vertebrae. There are
eight pairs of immovable ribs, united to each other by sutures, and
attached between the bodies of the vertebrae. By the union of the
ribs with each other, and with the spinous processes of the dorsal
vertebras, they form the upper shield or carapace. The nine pieces
of the sternum which are movable in the turtle, form the lower
shield or plastron. This unyielding frame-work is well suited to
resist pressure, as well as to favour their muscular movements on
land, whilst the mobility of the several elements of the sternum in
the aquatic species is applicable to their extensive respiration in that
dense element.

The bones of the head are firmly united by sutures. The occi-
pital condyle presents three facets, formed by the basilar and the
two condyloid portions. The inter-maxillary bones are narrow,
but present a large palatine surface. The bones of the ear are

20 EVERS'S COMPARATIVE ANATOMY.

anchylosed, and the body and cornua of the os hyoides are fully
developed.

In the anterior extremity, which is attached to the inner side of
the chest, we distinguish scapula and clavicle united by suture ;
humerus twisted, with a large articular condyle; radius and ulna
short, strong, and expanded inferiorly, fixed in a state of pronation;
carpal bones, sometimes as many as ten, arranged in three rows;
five short metacarpal bones; and the phalanges, two for the thumb
and last finger, and three for each of the others.

The ilia are long and cylindrical in the land tortoise ; the pubis
and ischium broad and flat. The femur presents indications of
trochanters, as in man ; its head is large, and joins the shaft at a
right angle. There is no round ligament in the hip, though rudi-
ments of semilunar cartilages connected to crucial ligaments in the
knee. The tibia and fibula are separate. The metacarpal bones
are five, and the number and arrangement of the phalanges the
same as observed in the phalanges of the fingers, with the exception
of the outer toe, which is generally rudimentary. In the aquatic
chelonia, the bones of the extremities are longer, straighter, and
more slender than in the land species.

Ophidia. — The skeleton in serpents consists of little more than a
vertebral column, possessing such a degree of mobility as enables
them to creep with speed along the surface, to swim through the
waters, to spring into the air, to climb trees, and to combat with and
conquer their prey. Extremities are here wholly absent, and the
spinal column and ribs constitute the sole organs of progressive
motion. For this reason the spine is characterised by immense
strength and great mobility. The vertebrae are more numerous
in this than in any other class of animals, being 49 in the anguis
fragilis, or blind worm ; 201 in the crotalus horrid us, or rattle-snake ;
and 316 in the coluber natrix. The bodies of the vertebrae have
ball and socket articulations, so disposed as to admit of free lateral,
but limited antero-posterior motion. The ribs of serpents are tubu-
lar, narrow and compressed from before backwards. Their head
presents a broad, arched, concave surface, to articulate with the
rounded, prominent, transverse processes of the vertebra?, whilst
their ventral extremity tapers to end in a thin, flexible cartilage.
The ribs extend from the atlas to the anus, and are 32 pairs in the
blind worm, 175 in the rattle-snake, and 204 in the coluber natrix.
They are all of the false kind, there being no rudiment of sternum,
except in the ophisaurus and blind worm alone, in which also faint
traces of shoulder and pelvis may be discerned.

The head resembles the preceding order (or that of the chelonia)
in the small size of the cranium, whilst the multiplicity and detached
condition of its bones ally it to the fishy tribes. This loose state of
the component elements of the head is necessary in serpents, for,
being deprived of organs of prehension, they are compelled to swallow
their prey entire. As a consequence of the looseness of the other
bones, the two parietals are anchylosed along the median line, to

VERTEBRATA. 21

protect the brain during the exposure of these animals to the
trampling of quadrupeds, &c, whilst concealed in their natural
haunts. Their teeth are small, conical, and sharp ; they are placed
in the two maxillary, the intermaxillary, and the palate bones.

Sauria. — In this order we meet with a more perfect development
of skeleton than in the last, as they possess a sternum, a scapular
and pelvic apparatus, together with atlantal and sacral extremities.
The lacerta iguana presents 5 cervical, 11 dorsal, 9 lumbar, 2
sacral, and 72 caudal vertebrae ; the crocodile of the Nile 7 cervical,
12 dorsal, 5 lumbar, 2 sacral, and 34 caudal — articulated by ball
and socket. There are false ribs behind and before the true ones.
In the chameleon there are 17 pairs ; in the crocodile 12. The
sternum is prolonged posteriorly as far as the pubis, and has attached
to it five pairs of cartilaginous arches, for the purpose of supporting
the abdomen.

The head is extended forwards in a line with the spine, as in the
other inferior vertebrata ; like these, also, its component elements
are loosely connected. As in serpents, the basilar condyle is elon-
gated transversely, and the parietal bones anchylosed. The lower
jaw consists of six pieces on each side ; and here, as in serpents,
the prehensile teeth are attached by broad base to the surface of the
jaw, and the new teeth rise by the side of the old, and not in their
interior as in the crocodile.

Anterior extremity. — The scapula is broad, thin, and curved.
The acromion is a distinct bone, and the clavicles are anchylosed
in form of a cross, on the front of the sternum. The humerus is
expanded at its extremities, and the same form as in man ; the ulna
is without an olecranon, stronger than the radius, and separated from
it below. There are from four to nine bones in the carpus, five
in the metacarpus; and the phalanges are, two for the thumb,
three for the second and last fingers, and four for each of the
others.

Posterior extremity. — The three portions of the os innominatum
contribute to the formation of the cotyloid cavity. The ossa pubis
and ischii form a lengthened symphisis in front; and the spine of
the iliac bones is extended backwards along each side of the sacrum.
From the front of the pubic bone a process passes up towards the
sternum as in the marsupiales. The head of the femur is com-
pressed and directed forwards ; the great trochanter is also flat and
turned towards the tibia. The patella is small ; the tibia short,
thick, and curved ; the fibula slender in the centre, expanded at its
extremities, and apart from the tibia. In the crocodile there are five
bones in the tarsus, four in the metatarsus, and the toes are so
arranged that the most internal sustains two phalanges, the second
three, and the third and fourth, four each.

In the skeletons of the nilotic crocodiles, alligators, and other
reptiles destined to swim by the lateral movements of a muscular
tail and long webbed feet, their long bones are filled with a thin
oily marrow, and the bones of the head firmly united.

RECAPITULATION. — Amphibia.

1. In amphibia rudiments of ribs only are met with.

2. Vertebrae range from eight in the rana pipa to eighty-nine in
the siren.

3. In the frog, the extremities, especially the posterior, are fully
developed ; the tail is absorbed.

4. Salamander, proteus, and siren, may be well contrasted with
the frog ; in the former the spinal column attains and maintains a
high degree of development, whilst their members are reduced to a
mere rndimental type.

5. The bones of the cranium remain loosely united through life.

6. The os hyoides undergoes remarkable changes during the
metamorphosis of the animal from the pisciform to the reptile
state.

recapitulation. — Reptilia.

1. The vertebrae and ribs are more numerous" than in any other
class of animals.

2. The chelonia differ from the sauria in having immovable ribs,
and from the ophidia in having arms and legs.

3. The bones of the head generally maintain a permanent state
of separation, except the parietals which are firmly auchylosed.

AVES.

As in this department of my subject I avail myself of much of the
valuable matter contained in the article, Aves, in the Cyclopaedia of
Anatomy and Physiology, by that clear, accurate, and scientific
writer, Mr. Owen, it becomes necessary to state that he divides the
class into the following orders : —

1. Raptores, birds of prey, or raveners ; 2. Insessores, perchers ;
3. Scansores, climbers ; 4. Rasores, scratchers ; 5. Cursores,
coursers; 6. Grallatores, waders ; and 7. Natatores, swimmers.

Positive characters of the class. — Animal, vertebrated, oviparous,
biped: anterior extremities organised for flight; integument plu-
mose ; blood red and warm ; respiration and circulation double ;
lungs fixed and perforated.

Negative characters. — No auricles, teeth, lips, epiglottis, dia-
phragm, fornix, corpus callosum, or scrotum.

The bones of birds are remarkable for being permeated by atmo-
spheric air, for their compact and laminated texture, their white
colour, and their fragility, owing to a preponderance of phosphate of
lime.

The vertebrae are the first bones observed in the development of
the osseous system of birds, and of all parts of this system, they
present the fewest variations. The spine here consists of cervical,
dorsal, sacral and caudal portions. The first and last are the most

VERTEBRATA. 23

movable, and in many species of the dorsal and caudal portions
admit of no motion at all. This fixity facilitates the flight of the
bird, whilst the length and mobility of the cervical portion of the
spine compensate, in some degree, for the unfitness of the anterior
members to the purposes of prehension, &c.

The cervical portion of the spine is generally composed of a greater
number of vertebrae than any of the other divisions ; they are not
fewer than nine, as observed in the sparrow, nor more than twenty-
three, as in the swan.

The bodies lock into each other, and are so disposed as to allow
the superior and inferior ones to move forwards, and the middle
backwards. The transverse processes are long, and have rudi-
mentary ribs connected to them ; these are particularly well deve-
loped in rapacious birds, and hence the great breadth of their necks.
The atlas is a simple ring, generally articulated to the occipital
tubercle by a single facet; but the penguin and ostrich have two
other facets continuous with the central one. From the dentata
down, a movable inter-articular cartilage is found, as in the joint of
the lower jaw of the mammalia.

The dorsal vertebrae range from six in the bull-finch to eleven as
seen in the swan. The bodies of these vertebrae are short and
compressed laterally, except in the ostrich. The transverse pro-
cesses are greatly developed. The anterior cartilaginous surface is
convex in the vertical direction, concave in the transverse, and
connected by fibrous capsules and synovial membranes. Most
birds have the middle and lower vertebrae anchylosed ; even the
transverse and spinous processes of the superior are anchylosed in
those birds requiring great fixation of the trunk ; while in those that
cannot fly, as the penguins, they are all movable.

The sacral vertebrae are firmly anchylosed with one another,
and with the ilia laterally; consequently it is difficult to determine
their real number ; it is not, however, greater than nineteen, as
seen in the emeu and cassowary, nor less ihan eight, as observed in
the hoopoe. The bodies of these vertebrae are broad, but shallow,
and the canal greatly enlarged, to correspond to the size of the
chord, which here supplies nerves to the posterior extremities.
When it is considered that the head, posterior members, viscera, &c,
are suspended in flight from this central portion of the trunk, the
necessity for the mechanism consolidating these vertebrae will be
readily appreciated.

The coccygeal vertebrae are generally movable, and from five
to nine in number. With the exception of the last, they are broad,
short, and perforated for the spinal marrow. The last has no pro-
cesses ; it is compressed laterally, and terminates above and below
in a sharp edge ; it supports the coccygeal oil-gland, and affords a
firm basis to the tail feathers, or retrices of Linnaeus. These bones
possess ligamentous connections, except the sixth and seventh which
re provided with a capsule and synovial fluid.

EVERS'S COMPARATIVE ANATOMY.

TABLE OF THE VERTEBRAE IN BIRDS.

ORDER RAPTORES

VBRTEBR.K.

ORDER RASORES.

VERTEBRAE

Species.

Derv.

Dor.

Sac.

Cau.

Species .

Cerv.

Dor.

Sac.

Cau.

Vulture,

Crested Curas-

Eagle,

sow,

Sparrow-hawk,

ORDER CCRSORES

Kite,

Ostrich,

' 18

Hawk-owl,

Cassowary,

ORDER INSESSORES.

Emeu,

Fly-catcher,

ORDER GRALLATORES.

Blackbird,

Heron,

Crow,

Crane,

Magpie,

Spoonbill,

Jay,

Avoset,

Starling,

Plover,

Bull-finch,

Woodcock,

Sparrow,
Goldfinch,

Curlew,

Oyster-catcher,

Lark,

Coot,

Redbreast,

Flamingo,

Swallow,

ORDER NATATORIS.

Humming-bird,

Pelican,

Kingfisher,

Cormorant,

ORDER "CANSORES.

Gull,

Woodpecker,

Catarrhactes,

Parrot,

Swan,

ORDER RASORES.

Goose,

Pigeon,

Duck,

Peacock,

Sheldrake,

Pheasant,

Mergancer,

Turkey,

Grebe,

Skull. — It has been already shown that the bones composing the
skull of the crocodile, and other cold blooded vertebrata, were not
consolidated till a late period of life, giving rise to some difficulty
in tracing a correspondence between their bones and those of a
higher order. A still greater difficulty is experienced in determining
the component parts of the head in birds ; for in them the bones of
the skull are anchylosed, and every trace of suture effaced at an
early epoch ; therefore, in order to accomplish their perfect separa-
tion, it must be undertaken at an early period of their existence.

In the majority of birds, the head is articulated to the spine, by
means of a single hemispherical tubercle on the basilar process of
the occipital bone ; but in the penguin and ostrich, the condyloid
portions contribute to its formation, and the articulation is such as
to admit of very great freedom of motion.

The occipital bone is originally composed of four pieces, basilar,
spinous and two condyloid. The temporal consists of the petrous,
squamous, and tympanic portions ; the last is movably articulated
to the inferior part of the squamous portion, and is sometimes called
osquadratum. The alae majores of the sphenoid bone remain a
long time separate, and are called interarticular, or omoid bones.
The remaining bones of the skull present no remarkable peculiarities

VERTEBRATA.

save that they are all early and firmly anchylosed, with the excep-
tion of the tympanic bone.

The bones of the face correspond in number and position to those
of the mammalia, especially the order rodentia. They are movably
connected with the bones of the cranium, and remain separate to a
much later period. The upper mandible is chiefly characterised by
the presence of the intermaxillary bone. This consists of three
processes, a central, and two lateral ; the former passes up between
the superior maxillary bones, and becomes joined to the nasal and
ethmoid ; this union is ligamentous in the parrot, and those birds
that apply the upper mandible to the purposes of climbing. The
two lateral processes of the inter-maxillary bone, extend upwards
and backwards external to the superior maxillary bones, to which
they are firmly united.

There are few more ingenious or beautiful pieces of mechanism
than that by which the mouth of a bird is opened. The tympanic
bone as before observed, never anchyloses with the other elements
of the temporal; on the contrary, it articulates with the zygomatic
portion of the latter bone, by two transverse condyles above ; below
it articulates by a broad surface with the upper and back part of the
lower jaw, while in front and near its lower extremity, it has
applied to it the long, slender malar bone which reaches to the
superior maxilla. When the tympanic bone is drawn forwards,
either by the action of the pterygoid muscles attached to it, or by
the depression of the lower jaw, the malar bone is advanced against
the superior mandible, which is elevated at the same moment that
the lower one is depressed. The moment the pressure ceases to
exist below, the elasticity of the union of the intermaxillary bone
with the cranium restores the upper mandible to its situation.

The inferior maxilla originally consists of six pieces on each
side, named anterior dental, two condyloid, angular, supra-angular,
and opercular. As this bone, together with the upper jaw, forms
the chief organ of prehension in birds, it is but natural to expect
that it shall present numerous modifications, indicative of the food
and habits of each species.

There is more uniformity observed in the skulls of birds than in
any other class of the vertebras department. It generally presents
the form of a five sided pyramid, the base represented by the occiput,
and the apex by the bill. In the Raptores it is short, broad, and
deep ; nearly spherical in the Warblers ; flattened, and of great
breadth, in the Scansores ; narrow, and slightly raised in theRaso-
rial birds ; and remarkable for its great length in the Waders.

Thorax. — The extent and energy of the respiratory function of
birds, are clearly indicated by the peculiar and perfect condition of
this part of their osseous system. The ribs, as in the mammalia,
are arranged into true and false, with this difference, that the false
ribs are placed both above and below the true ones. There is
some, though not very great variety in the number of ribs presented
by this class : for instance, in the Insessores we meet with seven or

eight pairs ; and in the willock, of the order Natatores, twelve
pairs; the average number is eight or nine pairs. The true ribs
are joined to the sternum by straight osseous portions, called ster-
nal ribs, instead of by elastic cartilages, and are movably connected
at each end. It is highly interesting to observe the mode of articula-
tion of the vertebral extremity of the ribs. In such as require
fixity of the chest, for the purposes of flight, the rib is articulated
to the side of the vertebra, having no connection to the inter-arti-
cular cartilage; but in the ostrich, and others of the cursores,
where the dorsal vertebras preserve their mobility, the heads of the
ribs are attached to the intervertebral spaces.

There is another interesting fact connected with the ribs, in
birds of powerful flight ; it consists in a number of small osseous
plates being detached from the posterior margin of each true rib,
and passing backwards and upwards to be connected to the suc-
ceeding rib, by means of strong, oblique, fibrous ligaments. In
the ostrich, rhea, emeu, and cassowary, these bony splints present a
mere rudimentary type.

Sternum. — The modifications presented by this bone, strictly
conform to the functions which the anterior extremities are designed
to execute. Hence, in the cursorial birds which do not fly, it is met
with in the form of a simple square plate of bone like a shield, while in
those birds that possess great powers of flight, it extends over the
whole of the lower aspect of the thorax and abdomen, even to the
pubic bones, and in order to afford sufficient space for the attach-
ment of the pectoral muscles, it is armed with a huge crest, extend-
ing the whole length of its lower surface. This crest, or keel, is
uniformly developed in proportion to the size of the pectoral mus-
cles, and hence declares the power of the anterior extremities. The
sternum is sloped obliquely on each side of its anterior extremity,
for the reception of the clavicle, and in the centre is connected
with the fork-bone, either directly or by means of ligaments; the
true ribs are attached to it on each side. The sternum of the crane
has within it a large cavity, containing several convolutions of the
trachea. This condition is repeated in the wild swan; but in the
tame swan, and some of the grallae, as the ciconia and gallinae, it
is but very feebly developed.

On the internal surface of the sternum, chiefly along the mesial
line, several apertures may be observed, for the passage of air into
the bone.

Anterior extremity. -—Here, as in the mammalia, the extremity
consists of shoulder, arm, fore-arm. and hand. In the first, we
recognise a scapula, a coracoid bone, and a clavicle.

The scapula is generally a long, narrow bone, increasing in
thickness as it approaches the shoulder joint, where it expands in
the transverse direction, to form the posterior half of the glenoid
cavity ; here also it articulates with the coracoid bone and clavicle.
The direction of the scapula is longitudinal. In birds with active

VERTEBRATA. 27

powers of flight, it reaches to the last rib. while in the emeu it covers
only two. This bone is broad and flat in the penguins.

The coracoid. or posterior clavicle, is a strong bone, broad in-
feriorly. where it is received in a transverse groove in the sternum ;
it extends upwards, outwards, and forwards", to articulate with the
scapula and clavicle. The glenoid cavity thus resulting from the
union of this bone with the scapula, is often unequal to^the recep-
tion of the head of the humerus ; hence, in the raptores and inses-
sores, a small but distinct bone extends between the coracoid and
scapula, over the superior part of the cavity,|which it here completes.
It was discovered by Nitzsch, who called it the capsular bone.

The clavicles are subject to considerable variety. In the ground
parrots of Australia, for instance, they present only a rudimentary
type, while in the psittacus mitratus, &c, they are wholly absent;
they are feebly developed in the emeu, rhea, and cassowary. When
these bones are enchylosed together at their sternal extremities, as
they ordinarily are, they constitute a single bone, named furculum.
In the ostrich they do not come in contact inferiorly, although they
reach the sternum ; and in the toucans, they neither come "in con-
tact below, nor reach the sternum. It is remarkable that in the
ostrich they are anchylosed above with the coracoid and scapula,
whilst almost in every other species they either continue separate,
or are movably jointed superiorly.

The humerus attains its greatest length in the albatross, and is
shortest in the struthious birds and penguins, whilst in the swifts
and humming birds it is characterised by its thickness, strength,
and the development of its muscular processes. In the cursores it
is short and attenuated, resembling the corresponding part in the
paddle of the turtle. Its head is oblong transversely, and enlarged
by two lateral crests, under one of which are to be found the air
passages leading into the bone. The lower extremity of the hu-
merus is formed after the manner of a hinge, consisting of an in-
ternal spherical portion to articulate with the ulna, and an external
oblong portion for the radius.

The radius and ulna are straight and slender bones, enlarged at
their extremities, and placed one in front of the other, so as scarcely
to admit of any pronation or supination. In the penguins the bones
of the fore-arm are flattened, and articulated with the anterior edge,
and not the extremity of the humerus.

The carpus is composed of two bones only, and so wedged in
between the metacarpus and fore-arm, as to limit the motionsof the
hand to adduction and abduction.

The metacarpus is chiefly formed of two bones, a small ulnar
one, which supports a single phalanx, and a large radial one, which
sustains two phalanges. A small rudimental bone is usually an-
chylosed to the outer side of the proximal extremity of the radial
metacarpal bone.

Lower extremity. — The pelvic bones, like those of the shoulder,
are three in number: the ilium represents the scapula, the ishium

28 EVERS'S COMPARATIVE ANATOMY.

the clavicle, and the pubis the coracoid bone. Unlike the shoulder,
however, these bones are always anchylosed into one piece on
either side, and with one exception, never join in the mesial line ;
this single exception is afforded by the ostrich, in which the pubic
bones complete the pelvic circle by anchylosing" at their inferior
extremities. The vulture cinereus, and some acquatic birds, form
the nearest approach to this last condition. In them the pubic
bones are often surmounted by a cartilaginous appendix at their
anterior extremity.

The ilium is the only bone of the pelvis that comes in contact
with the spine ; it is elongated in form, narrow in the centre, and
expanded at its extremities. This bone is anchylosed with the
sacrum, the ischium, and the spinous and transverse processes of
one or two dorsal vertebras.

The ischium lies parallel with the ilium; it is a small oblong
bone, not presenting any peculiarity.

The pubis unites with the ischium in a two fold manner in the
humming bird and some others, so as to form two foramina obtura-
toria, while in others, as the stork, it is only united to it at the coty-
loid foramen. This cavity is always incomplete at its internal part,
where it is closed by some fibrous bands.

The femur is short, and slightly convex anteriorly; its head is
hemispherical, and joined to the shaft at a right angle, without
the intervention of a neck. There is but one trochanter; it is of
a large size, continuous with the external part of the shaft, and gene-
rally rises above the level of the head. The lower extremity of
this bone presents two condyles, the inner one for the tibia, the
outer one, which is longer and larger, rests on the tibia and fibula;
it is convex from behind forwards, and terminates in a groove in
both these directions.

The tibia is the principal bone of the leg, the fibula ending in a
point inferiorly, and achylosed to the tibia for a considerable extent.
The lower extremity of the tibia forms a transverse trochlea, above
which there is a deep groove or foramen, to transmit the tendon of
the extensor digitorum communis. The upper and anterior part of
the tibia gives rise to a long pointed process, which ascends in the
shape of an olecranon in front of the joint, being also anterior to
the patella.

The tarsus can only be recognised as a distinct segment of the
foot, when examined at an early period of the bird's existence ;
then only can be found a distinct astragalus of a flattened oval form,
convex superiorly, and concave below, where it meets the three
bones of the metatarsus partially separated. A rudiment of os calcis
may also be found in the extensor tendons. In the penguins, the
three metatarsal bones are only anchylosed at their extremities ;
but in other birds, faint grooves alone indicate their existence.
The remote extremity of the metatarsus presents three convex facets
to articulate with the toes. These last are subject to great variety
as to number, being reduced to two in the ostrich, and increased to

VERTEBRATA. 29

five in the gallinaceae. The phalanges bear no proportion to the
size or number of the toes, being found to vary from one up to five.

RECAPITULATION.

1. There is more uniformity observed in the skeleton of birds,
than in any other of the vertebrated classes.

2. The bones are white, thin, and brittle; in early life, filled
with a thin serous oil, which is subsequently removed to be replaced
by atmospheric air, especially in those of the high-flying kind.

3. The bones are early and rapidly ossified, particularly those of
the head, thorax, and pelvis. This ossification also affects the ten-
dons of the muscles of the leg, sclerotic tunic of the eye, inferior
larynx, and the rings of the trachea.

4. Arms adapted solely for flight ; legs for support.

5. Head and neck long, for the purposes of prehension.

6. The dorsal and sacral portions of the spine the most fixed.

7. Cervical vertebras more numerous than in the mammalia;
occasionally, three times the number.

MAMMALIA.

The number of vertebrae contained in the spine, is very variable ;
but the human type is by far the most generally predominant. In
the cetaceae there is no distinction between lumbar, sacral, and
caudal vertebras ; and in the porpesse, there are sixty-six posterior
to the dorsal : these mammalia, however, have no pelvis. The
cervical vertebrae are uniformly seven throughout this class, not-
withstanding Cuvier imagined lie had found a solitary exception in
the neck of the ai, bradypus tridactylus; but it has been well as-
certained since, that what he conceived to be the two last cervical
vertebrae of this animal, have two rudimental ribs attached to them.
When we are reminded of the localities and habits of the sloth,
hanging from the branches of trees, and passing from bough to
bough, aided by the current winds, it becomes obvious why such a
provision should exist, of modifying the two superior dorsal verte-
brae, and of consigning to them the offices of cervical, rather than
infringe on a law which at present seems without an exception.

The dorsal vertebrae range from twenty-three, as seen in the
unau, bradypus didactylus, to twelve, as presented by man, mice,
bats, rabbits, hares, and several apes. In the megatherium there
are sixteen, in the horse eighteen, and in the elephant twenty.
The lumbar vertebrae are generally seven; they vary, however,
there being two in the two-toed ant-eater, and nine in the lori. The
sacral vertebrae are seven in the mole ; in the vampyre bat, opossum,
and some apes, there is but a single sacral vertebra, the usual
number being three. The caudal vertebrae are four in man and
the ourang-outang; forty in the two-toed ant-eater; and in the
vampire bat they are altogether absent.

30 EVERS'S COMPARATIVE ANATOMY.

In most animals, it has been said, that the head and neck together
equal in length the fore-feet, except where the latter are used as
hands, as in the apes and rodentia. The neck attains its greatest
length in the genus cameius, and is shortest in the order cetacea,
owing to the consolidation of the vertebrae. According to the
statement of Gore, the number of cervical vertebras in certain of
the cetacea, as the balaena, manatee, and dugong, amounts only to
six. In the rodentia, and most long necked animals, the spinous
processes are almost wanting. The atlas, in the carnivora, rumi-
nantia, solipida, pachydermata, <fec, is distinguished by its length,
and by its large aliform transverse processes. The free motion and
beautiful arch observed in the necks of some horses, camels, &c, is
explained by the bodies of the cervical vertebras having a perfect
articular head on their upper surface, and a corresponding depres-
sion on their lower, similar to what we observe in the necks of
serpents, with this difference, that the surfaces are reversed. The
ruminantia, rhinoceros, elephant, &c, are remarkable for the great
length of the spinous processes of the dorsal vertebrae. Bats have
scarcely any spinous processes; and, with the exception of the
second dorsal, they are short in the rodentia. In the lumbar ver-
tebrae, the form of the transverse processes is very variable — almost
absent in bats, very strong in the ruminantia, rodentia, and carni-
vora. The megatherium possesses long spinous processes. In the
sloth, the length, breadth, and consolidation of the sacral vertebrae
remind us of the sacrum of birds. The few first only of the caudal
vertebrae in mammalia contain a prolongation of the vertebral canal.
Animals with long movable tails, as the two-toed ant-eater, have
oblong triangular processes on the under surface of the caudal
vertebrae, as in the crocodile. The connection of the vertebrae is
almost always by means of interarticular cartilage, as in man, and
consists of concentric rings, most evident in the whale. In the
pig and rabbit the interarticular cavities are filled with an albu-
minous fluid, as in fishes.

Ribs. — Man has seven true and five false ribs ; the balaena
whale, one true and eleven false ; in the unau, or two-toed
sloth, there are twenty-three pairs, of which eleven are false ; in
the horse eighteen, and eight of them false; in wolves, cats, and
some apes, there are thirteen pairs, four of which are false; in the
guinea pig, armadillo, and porpoise, there are thirteen, of which
seven are false ; in the manatee, of sixteen pairs, but two are true;
in the dugong but three out of eighteen ; and in the ornithorhynchus
but six out of seventeen. The breadth of the ribs is greater in the
ruminantia, pachydemata, in the manatee, and especially in the
two-toed ant-eater, than in other mammalia. The connection of
the ribs with the sternum is in general effected by cartilage; but in
the cetacea, ant-eaters, dasypus, bradypus man is, ornithorhynchus,
echidna, and frequently in bats, the union is completely bony.

Sternum. — This bone, though essentially the same as in the
human subject, is somewhat modified in form by the shape of the

VERTEBRATA. 31

chest. In ungulated animals, where there are no clavicles, the
sternum- is compressed laterally, and projects in the centre like a
ship's keel. The superior piece of the sternum is very considera-
ble in the mole, where it forms a distinct bone. It is proportionably
small in the bat, seal, horse, rhinoceros. In the cetacea it is
short and large, being composed of five pieces in the dugong, and
three in the dolphin, the porposse, and the platanist. In the bat
and ornithorhynchns, the upper part of the sternum is T-shaped,
the transverse process being for the articulation of the clavicle.

The figure of the thorax in most apes, bats, and the greater
number of the rodentia, and, in fact, of the class mammalia, having
clavicles, agrees with that of the human subject. In ungulated
animals, on the contrary, where there are no clavicles, the thorax
is laterally compressed and elongated.

The whole arrangement of the thorax proclaims man to be
destined to move in the erect attitude: he is the only animal in
which its transverse exceeds the antero-posterior diameter; even in
the chimpanse, which approaches nearest to him, the latter exceeds
the former measurement, reminding us of the form of this cavity
in the very young subject. Its great lateral width and inconsider-
able depth from sternum to spine, throw the arms apart, and in-
crease their sphere of motion. The reverse characters, together
with the absence of clavicles in quadrupeds, allow the fore legs to
approximate, to fall perpendicularly under the front of the body,
and support it with ease and security.

Head. — We shall cease to wonder at the striking" differences
observed in the construction of this part of the skeleton, when we
consider that it forms the receptacle for the brain, most of the ex-
ternal senses, the masticatory apparatus, &c. Man combines by
far the largest cranium with the smallest face; and animals deviate
from these relations in proportion as they increase in stupidity and
ferocity. In man, the area of the section of the cranium is nearly
four times as large as that of the face; three times as large
in the ourang-outang; twice as large in the sapajous; and they
are nearly equal in the baboons and carnivora. In the hare
and marmot, the face exceeds the cranium by one third; in the
porcupine and ruminants, by one half. The face is three times
as large as the cranium in the hippopotamus, and four times
as large in the horse.

The superior maxillary bones of the human subject are united
to each other, and contain all the upper teeth ; in some other
mammalia, however, they are separated by a coniform bone, which
contains the incisor teeth, and hence named os insicivum; but it
exists where there are no incisor teeth, as in the kerotophara, the
elephant, and the two-toed rhinoceros of Africa, and even where
there are no teeth at all, as in the ant-eater and some of the ceta-
ceans, for which reason Blumenbach calls it os intermaxillare. In
some it is a single bone, in others double; it is absent from the
chimpanse, though present in the ourang-outang. The former of

these animals possesses supercilliary ridges, which are wanting in
the ourang.

The head of the ourang, viewed in front, is pear-shaped, expand-
ing from the chin upwards, the cranium being much the larger
end. The frontal sinuses are very large in the dog, wolf, porcu-
pine, sloth, sheep, bull, pig, horse, and especially in the elephant;
they are small in bats, rats, squirrels, ant-eaters, the hippopotamus,
rhinoceros, &c. In cats, martens, and bears, the parietal bones
give off from their inner and posterior edge a process of bone
which projects into the cavity of the skull, and forms a perfect
bony tentorium cerebelli. In the dog and horse, similar processes
arise from the petrous portion of the temporal bones.

The lower jaw is subject to many varieties in the mammalia.
In the whale it resembles two enormous ribs, united at the point,
without any trace of ascending rami or coronoid processes. The
articular head here, as well as in the porpoise, is directed back-
wards, and is attached to the skull by means of strong cellular
tissue, filled with oil.

In the hare, rabbit, and guinea-pig, of the order rodentia, the
coronoid process is very small; in others, as squirrels and rats, it
is pretty large. The condyloid, or articular process, is compressed
latterally, directed from behind forwards, and larger in front than
behind.

In the carnivora, the articular head is directed transversely, and
so closely adapted to the glenoid cavity of the temporal bone that
the jaw retains its situation after the destruction of the ligaments.
This is well seen in the marten and sea-otter. In the ruminants
the condyle is very flat, to admit of the lateral motion necessary
during the process of rumination. In the carnivora, rodentia, and
ruminantia, the two halves of the lower jaw are never firmly
united — in this particular affording us an instance of the perma-
nence of a condition in other mammalia, which in man is peculiar
to the earliest periods of life.

Swine have two small bones placed at the aterior openings of
the nares for the support of the snout. In fine, it is to be remarked
that the crania of all the quadrumana, together with the other
mammalia, are distinguished by the comparative size, great'length
and projection of the jaws.

Anterior extremity. — This extremity in the lower animals cor-
responds to the superior of the human subject, and contains all
the elements of it. modified according to the habits of the animal.
Sometimes connected to the trunk by means of muscle only, as in
the cetacea, pachydermata, ruminantia, and solipe a; in other in-
stances by ligament and muscle, as seen in the insectivora.

Clavicle. — The importance of this bone, in the motions of the
upper or anterior extremity, may be well estimated by the fact of
its being present in those animals only whose habits of life require
free and varied motions of the shoulder. Thus in the quadrumana
it is strong and curved, as in the human subject. The bat, hedge-

VERTEBRATA. 33

hog, and mole, among the insectivora, afford examples of clavicle
in its highest degree of development. It is very perfect in the
rodentia, as the squirrel, beaver, rabbit, rat, &c. Among the eden-
tata, those animals only whose habits are fossorial possess clavicle,
as the ant-eater, the dasypus, and the gigantic megatherium ; in
the last named animal it presents the peculiarity of being articulated
with the first rib instead of the sternum.

Where the anterior extremity is employed merely for the purpose
of progression, we find no clavicle, as in the pachydermata, rumi-
nant ia, cetacea, and solipeda. In the carnivora. where there is a
slight increase in the range of motion of the anterior extremities,
the clavicle exists in a rudimental form, and its development is in
proportion to the motion enjoyed ; hence it is small and short in
the cat, the bear, and the dog ; in those animals it has no attachment
to the sternum or scapula, but lies loose among the muscles.

Scapula. — This bone forms an essential element of the thoracic
extremity, and exists wherever the latter is fully developed, but
greatly modified, according to the uses to winch the extremity is
applied. The cetacea, in general, have a large scapula of a trian-
gular form; the pachydermata, ruminantia, and solipeda, have a
long narrow scapula placed perpendicularly on the anterior and
lateral part of the chest. In the carnivora and rodentia, where
strength and freedom of motion are required, the scapulas are placed
obliquely over the ribs; and it is interesting to observe how the
obliquity of the glenoid cavity varies with the motions required.
This fact has not escaped the observation of the horse-jockey, who
is well aware that the upright shoulder is the mark of a stumbling
horse.

Humerus. — When the fore-arm and hand are used for seizing
objects, as in apes, many rodentia and carnivora, or for flying, as
in the bat, the humerus is formed essentially in accordance with
the human type. On the contrary, when the anterior part of the
member is but slightly developed, as in the cetacea, the bone is
short and thick; and in the whalebone whale, it is nearly as broad
as it is long. In the mole it is short, thick, and strong; its tuber-
osities greatly developed, and its upper extremity presents two arti-
culating surfaces, one for the scapula, and the other for the clavicle.
This large size of the bone prevails in all the other fossorial ani-
mals, as the mighty megatherium, the pangolins, beavers, ant-eaters,
and monotremata. The humerus of the lion is remarkable for
being perforated by the brachial artery and nerve, in order to avoid
being crushed by the huge and powerful mass of muscles exhibited
in this part of the economy of the king of beasts.

Fore-arm. — The radius and ulna are very short in the cetaceans,
and in most of them consolidated too-ether at both extremities. In
the cheiroptera they are long, slender, and firmly united, to accord
with their mode of progression by flight; in some the olecranon is
wholly absent, and in others, as the vampyre, it exists in the form
of a patella. The ruminants and solipeds have these bones con-
7 — ff cvers 3

solidafed into one. The rodentia, many carnivora, pachydermata,
insectivora, and edentata, the bones are distinct throughout, but
admit of no motion. The sloth, however, among the edentata,
enjoys great freedom of pronation and supination ; here the bones
are long, arched, and widely separated in the centre.

Carpus. — The bones composing this part of the extremity are
usually disposed in two rows, as in man. though the number almost
invariably differs from that model. The following is Cuvier's
statement of their number: — In man and the elephant. 8; in apes,
the hare, and the mole, 9: in the solipeda, carnivora and several
rodentia, 7 ; in the ruminantia from 6 to 7 ; in the edentata, 6; and
in cetacea from 4 to 7. In apes, carnivora, and several of the un-
gulata, the pisciform bone is very large, and by affording attachment
to the flexor muscles of the hand, performs the office of os calcis
in the foot. The simise, in general, have nine bones in the carpus —
another distinction between their hand and that of man. In the
most anthropo-morphous of them, the chimpanse and the ourang-
outang, the ninth is a sesamoid bone in the tendon of the abductor
pollicis longus.

The metacarpal bones in the whale are five in number and
flattened in the form of phalanges. These last are, two in the
thumb, three in the little finger, four in the index and ring fingers,
and five in the middle, collectively forming a short but strong
paddle. The shovel-shaped hand of the mole consists of five fingers,
each having a metacarpal bone and three phalanges. In the
bat the thumb is short, and not included within the flying membrane,
The metacarpal bones are long, slender, and cylindrical : the distal
phalanx is hooked, and sustains a nail by which the animal suspends
itself. The simias have these parts constructed as in man, except
the thumb, which is small, and extends only to the metacarpopha-
langeal articulation. In bears and badgers the five fingers are of
equal length, and parallel to each other. In the endentata several
of the fingers disappear; for instance in the two-toed ant-eater, the
thumb, index, and little fingers, are merely rudimentary; the
middle finger, however, is proportionally developed.

Among the ungulata the hand is still more diversified ; the ele-
phant, for example has five fingers all united into one mass within
the skin. The pig almost wants the thumb; he, however, has four
perfect fingers, but walks only on two. The ruminantia have but
two fingers, each metacarpal bone supporting three phalanges. In
the solipeda there is but a single finger; for instance, in the horse
the carpus corresponds to the knee ; the metacarpal bones are con-
solidated into one, cannon bone, behind which there are two small,
splint bones, commencing broad at the knee, and terminating in a
pointed manner behind the lower third of the cannon bone. Here
we meet with three phalanges, the first called pastern, the second
coronet, and the third coffin bone.

Pelvis. — It has been truly asserted that in the human skeleton
alone, a true pelvis is to be found. This arises from the form and

VERTEBRATA. 35

manner of connection of the bones entering into the formation of
this cavity. The chimpanse and elephant afford ns the nearest
approach to the human formation, even here the ilia are narrow
and elongated ; and the sacrum and coccyx are flat, contracted, and
continued in a direct line with the spine. Next in the order of
development may be ranked the rhinoceros, the ox, the horse, the
carnivora and the rodentia. In ant-eaters, moles, and shrews, the
symphysis pubis remains open; and in the two latter genera the
pelvis is so small that the pelvic viscera are placed without it. The
megatherium and sloth, however, have pelvis of large dimensions.
Some of the edentata, as the dasypus, have the ilia joined to the
sacrum. In others, as the sloth and some of the ant-eaters, the
ischium is connected with the sacrum, forming an ischiatic foramen,
instead of a notch. The cetacea present but slight rudiments of a
pelvis in the form of two small bones united to each other and to
one of the vertebrae by cartilage. Finally the marsupial animals
present a small, elongated pelvis, especially remarkable for the pre-
sence of two particular bones not found in any other mammiferous
animal even in a rudimental state, and named 0.95a marcip'ialia.
These bones are attached, but not articulated, to the anterior part
of the pubis, near the symphysis; each is about three inches long
in the kangaroo, flat, with anterior thin, and a posterior thick
edge. The bone is triangular in form, the broad end being at the
pubis, while the narrow has attached to it the abdominal muscles.
The use of these bones is to support the marsupium, or abdo-
minal pouch, in which the mammary apparatus is lodged, and the
young animal nurtured.

The posterior or abdominal extremity is altogether absent in
the cetacea. In the other mammalia inhabiting the sea, the seal,
for instance, the several elements of the posterior extremity, even
the toe-nails, are distinctly recognisable, but consolidated by a
membranous web into a kind of caudal fin.

The femur in the lower mammalia is short and straight ; the
neck is either absent or but little developed, the head being placed
vertically over the shaft. The trochanters and linea aspera are
badly marked. This bone is shorter than the tibia, the converse to
what obtains in man. In the megatherium its thickness equals
half its length. The trochlea is a deeper and the transverse
diameter of the condyles less than in man.

The patella is usually present in the mammalia; best developed
in the pachyderms, solipeds, and monotrems; least so in the carni-
vora and quadrumana; and wholly absent in the marsupiata and
cheiroptera.

Tibia and Fibula. — Throughout the mammalia these bones
coincide pretty nearly with those of the fore-arm. As in man, the
tibia forms the chief bone of the leg. The fibula is analogous to
the ulna, and is found only in a rudimentary state in the solipeds
and ruminants, as the latter bone was in these animals. In the
solipeds, the fibula is applied to nearly the upper half of the outer
surface of the tibia, being pretty large above, and ending in a fine

36 EVERS'S COMPARATIVE ANATOMY.

point below. Ruminants, on the contrary have the fibula better
developed inferiorly where it forms the external malleolus and ex-
tends but a short way up the leg. Pachyderms, and all the ungili-
Gulata, possess a fibula well developed ; and in sloths its lower
extremity ends in a conical point, which enters a corresponding
cavity in the astragalus. In the rodentia, and insectivora, particu-
larly the mole, the tibia and fibula are united through their inferior
half. Carnivora have these bones fully developed and detached:
this is well seen in the phocidee and felina?. In the dog they are
united posteriorly.

Tarsus. — The bones composing this part of the foot for the
greater part resemble those of man. The cheiroptera present a
remarkable peculiarity in the formation of a long slender bone,
extending from the back of the os calcis half way to the tail, and
enclosed within the flying membrane. Cuvier and Meckel supposed
it to be a portion of the os calcis, whilst Daubeton conceived it to
be a distinct bone. On the inner side of the tarsus of the mole, a
sickle-like process of bone is found, similar to that observed on the
carpus. The metatarsus and toes in ruminants and solipeds are
disposed pretty nearly as in the anterior extremities. The rodentia
and carnivora have usually five toes, the great one being often
shortened, or as in cats, dogs, and hares, altogether absent. The
quadrumana and marsupiales have the great toe separated from the
rest, bearing the same relation to the foot as the thumb to the hand.

Although the disproportion in the respective size and length of
the upper and lower extremities of the human subject, indicate the
different functions they are designed to execute, yet they present
many similarities throughout their divisions, the construction of
their articulations, and the number and form of their bones. The
arm, fore-arm, and hand, lor instance, resemble the thigh, leg, and
foot; the os innominatum may be compared to the scapula; the
hip, knee, and ankle, to the shoulder, elbow, and wrist: and the
carpus, metacarpus, and fingers, to the tarsus, metatarsus, and toes.
Contrast. — A line falling perpendicularly from the shoulder in the
erect attitude, would pass behind the hip. The upper extremities
diverge below, whilst the inferior converge. The deep acetabulum,
and the strong tight capsule of the hip, may be well contrasted
with the shallow glenoid cavity, and weak, loose capsule of the
shoulder. The lower extremities are as long as the head and
trunk together, being only equaled in this respect by the kangaroo
and jerboa.

The great length of the shaft and neck of the femur, its perpen-
dicularity with the spine, and the depth of its internal condyle, are
characters peculiar to man : in the fore-arm every thing conspires
to procure freedom of motion; in the leg, strength and security are
the objects aimed at. The hand is articulated on a line with the
fore-arm, and enjoys free and varied motions; the leg joins the
foot at a right angle, and moves chiefly in the angular direction;
the entire surface of the tarsus, metatarsus, and toes, rests on the
ground : the two latter circumstances are exclusively confined to

VERTEBRATA. 37

the human subject. The parts composing the hand and foot are
disposed inversely as regards their development and importance.
The solid part of the hand is small, weak, and but slightly deve-
loped ; that of the foot is large, firm, and ossified at an earlier
period of life. The fingers are long, slender, and mobile; the toes
are short, thick, and enjoy only a limited share of motion. But the
distinguishing characteristic of the human hand is due to the
strength, situation, and development of the thumb, which is oppos-
able to the fingers, and rendered useful in the thousand offices
which it has been designed to execute.

Man is distinguished from all other animals by the great size of
the cranium over that of the face. One method of expressing
these relative proportions, is by the course of the facial line, and
the number of degrees in the facial angle. A line drawn from the
greatest prominence of the forehead to that of the upper maxillary
bone, in the erect attitude, describes the direction of the face, and
is called the facial line ; a second line, perfectly horizontal, drawn
backwards from beneath the basis of the nostrils, forms with the
other what is termed the facial angle, and gives the measure of
the relative prominence of the jaws and forehead. In the adult
human subject the facial angle varies from 65° to 85°; in children
it reaches 90°; a sufficient proof of its inadequacy as a standard
for the measurement of intellect. The situation of the foramen
magnum, and occipital condyles, being but little posterior to the
centre of gravity, are also distinctive characters of man. Aline
drawn forwards parallel to the plane of the foramen magnum, will
come out just under the orbits. In the ourang-outang this line
would pass below the level of the lower jaw, and in most other
animals the foraman magnum is placed on the back of the head,
its plane being nearly vertical. The great weight of the human
head, the absence of ligamentum nuchas, and of the rete mirabile,
or some analogous provision for moderating the influx of blood to
the brain, coupled with other facts hereafter to be mentioned, in-
contestably prove that man was intended for the erect attitude, and
that he is quite unfit to move on all-fours, as some modern authors
would have it.

Nature has clad in defensive mail the armed rhinoceros, provided
the lion and the ti^er with weapons of defence, clothed the sheep
in wool, and the bear in fur; every animal she has bountifully
provided in all that was necessary for its subsistence, and adapted
to its destined mode of existence. Man alone she has abandoned,
weak, naked, and defenceless, unarmed in the midst of dangers,
and uncovered to the winds of heaven. But she has bestowed on
him gifts far more than equivalent to all that was denied: she has
given him an illimitable capacity for improvement; she has endowed
him with terrestrial ubiquity, or a capability of inhabiting every part
of the known world: and above all, she has conferred on him in-
tellect and inventive genius, which have raised him to a measure-
less superiority over the rest of created beings. By means of these
endowments he has made most animals subservient to his purposes,

and obedient to his commands ; and such as their native ferocity-
renders incapable of utility, or dangerous to Ii is repose, he has
banished to the "howling wilderness." In fine, the surface of the
earth attests his industry and intelligence, and nature herself is
delighted to obey him.

Recapitulation. — Characters Peculiar to Man.

Biped ; bimanous ; erect attitude ; great proportion in the size
of the cranium over that of the face; development of brain ; direc-
tion of facial line; articulation of the head with the spine; rational;
endowed with speech ; prominent chin, and teeth of peculiar cha-
racters; absence of ligamentum nuchas and intermaxillary bone:
great transverse measurement of the chest; curved spine, sacrum,
and coccyx; large pelvis; short arms; long, powerful thumb, pos-
sessing separate flexors ; length and direction of the neck of the
femur ; depth of internal condyle ; the whole flat of the foot resting
on the ground, and the leg joining it at a right angle. Man is also
remarkable for the smoothness of his skin, and the slowness of his
growth.

The following are Camper's measurements of an ourang-outang,
compared with those of man :

MAN.

OURANG

Whole length of the

body

from vertex to heel

71 inches.

Less than 30 ii

ic\

Superior extremity.

32 "

24|

Inferior do.

39 "

Humerus,

13 "

Ulna,

91 "

Hand,

8* "

Thumb,

4i "

Middle finger,

41 M

Femur,

20 "

Tibia,

16| "

Foot,

10i "

Middle toe,

2\ "

FOSSIL BONES OF ANIMALS.

It is the undivided opinion of geologists, that there has been a
regular succession of deposits in the earth, and that the remains of
different animals (many of them long since extinct) are to be found
in the several strata. In the deeper strata, the remains of animals
low in the scale of organisation are to be met with ; in higher
strata, oviparous animals of large size and complex structure are
discovered; above these are found mammalia; and still nearer to
the surface, the bones of the megatherium, mastodon, rhinoceros,
elephant, &c. ; and it is now the prevalent opinion that man was
created last of all.

LIGAMENTS. 39

Some bones are found with their animal ingredients remaining
others are fossilised. The phosphate of lime loses its phosphoric
acid, and the earth remains incorruptible, while the soft animal
matter decomposes and dissipates. The bone in this condition
may become fossilised ; silicious earth, or lime combined with iron,
may pass, by infiltration, into the interstices of the original earthy
matter, and in this state it is permanent as the solid rock.

There is preserved in the Royal Museum of Madrid, a skeleton
of the enormous megatherium of Cuvier. It is supposed that the
animal was seven feet in height; for its femur is three times the
diameter, and its pelvis twice the breadth of that of an elephant.

CHAPTER IV.

LIGAMENTS.

In the lowest grades of animal beings, cartilages, synovial mem-
branes, capsular or accessary ligaments, scarcely exist at the joints.
We here rind the movable points formed of a tough connecting
material, which, by its elasticity, admits of the limited motions
required.

No ligamentary apparatus appears in the soft, gelatinous animal-
cules ; but the silicious and calcareous spicula of the poripherous
radiata are supported by a tough, elastic species of cellular tissue.
The plates composing the shells of the echinida are united by
sutures, and the enarthroidal joints of the spine by capsules, and
often by a ligamentum teres, as in the cidaris. In the larger Crus-
tacea and coleopterous insects portions of the skeleton are locked
into each other, where they move securely, but to a limited extent,
in the angular direction without ligaments. The shells of the con-
chifera are united by their locking teeth, and by a strong, tough
ligament, which, by its elasticity, constantly tends to the separation
of the bivalves.

In the soft, flexible skeletons of the cartilaginous fishes, the liga-
ments are few, and confined to the organs for mastication and pro-
gressive motion. But in the osseous fishes the ligaments of the
spine are white, fibrous, dense, and highly elastic ; and here, for the
first time, we meet the contiguous ends of bones incrusted with car-
tilage. In the amphibia, and in the reptiles, the bodies of the vertebrae
are united by enarthroses, furnished with strong fibrous capsules and
synovial secretion. Here we have external fibrous bands, inter-
spinous ligaments, and occasionally loose cartilages in the joints.
The capsular ligaments of birds are thin and strong : their cartilages
of incrustation are also thin, but their joints are freely supplied
with synovia and their hip joint furnished with a strong ligamen-
tum teres.

40 EVERS's COMPARATIVE ANATOMY.

In the mammalia, thick fibro-cartilages appear interposed between
the bodies of the vertebras, and in the carnassier and climbing
mammalia, the articular processes are furnished with well developed
synovial capsules. The tails of many quadrupeds enjoy full motion
from their coccygeal vertebras being united by synovial capsules.
The anterior and posterior common ligaments of the spine are
powerfully strong and highly elastic along the pliant columns of
the cetacea. In the large and heavy-headed herbivorous quadru-
peds, the ligamentous nuchas is of great size and strength, extending
from the occipital protuberance along the cervical and dorsal spines,
and in many instances, to the coccygeal and iliac spines. The
light-headed, and active muscular carnassier have this ligament
short and small, and in the quadrumana and many of the rodentia
scarcely a trace of it is to be found. The inter-articular cartilage
of the lower jaw is met with, in this, but not in the preceding classes,
the ligamentum teres is found in most of this class, but is said to be
absent from the ourangs, the elephant, the rhinoceros, the hippopo-
tamus, the kangaroo, the sloths, and the monotremata. The two
toes of those ruminants, whose habits oblige them to make rapid
and bounding movements, are secured by strong transverse liga-
ments passing between their phalanges.

CHAPTER Y.

ON THE MUSCULAR SYSTEM IN THE INVERTEBRATA.

General observations. — In the higher orders of animals, there is
a close relation, and a perfect mutual dependence between the
osseous and the muscular systems; so much so, indeed, that the
arrangement of one may be at once inferred by any one who pos-
sesses a sufficient acquaintance with the other. It is by means of
this system that animals are enabled to move from place to place, to
seize, masticate, and swallow their aliment, to circulate their fluids,
to expel their excretions, to produce various sounds, and to accom-
plish an infinitude of other purposes. A system ordained to execute
so many offices cannot fail to present some interesting peculiarities
in the animal kingdom. In obedience to a law, often alluded to,
we find that the muscles of the highest classes of red-blooded ani-
mals, during their development, pass through the soft, colourless,
and gelatinous condition of those of the lowest species before they
attain the characters peculiar to them in their highest state of
development.

Radlata. — No muscular fibres have been hitherto found in the
polygastric animalcules. Their rapid motions through the fluids
which they inhabit appear to be accomplished by means of the vibra-
tions of minute cilia (which are analogous to the villi on the mucous
surface of a small intestine) growing from the outer surface of their

MUSCULAR SYSTEM OF THE INVERTEBRATA. 41

bodies ; the cilia which in these animalcules, serve the double pur-
pose of locomotive and respiratory organs, have been observed in
every class of animals, even the mammalia.

In the zoophytes, the soft, fleshy mass, which we have seen
secrete the solid matter of the skeleton, possesses distinct, but lan-
guid irritability: no part of these animals is, however, so irritable
and contractile as their prehensile sacs or polypi. It is not till we
arrive at the stellerida and asterias that distinct muscular fibres
have been satisfactorily demonstrated ; and in the echinida strong
adductor and abductor muscles are seen attached to, and moving the
jaws of several species.

Articulata. — Seeing that these animals possess an extensive sur-
face for respiration, and a highly developed nervous system, we are
prepared to meet with considerable muscular energy. Accordingly,
in the nematoid entozoa, strong muscular fibres are seen taking
different directions: the rotiferous or wheel-animals, are also re-
markable for the development of the muscular apparatus provided
for the movements of their jaws, and long vibratile cilia. The
common earth worm has distinct muscles appropriated to the move-
ments of its conical pointed feet, and its anus is well furnished with
levator and sphincter muscles. The insects and the air-breathing
arachnida possess a well marked muscular system ; but of all the
branchiated invertebrata, the Crustacea possess the largest proportion
of muscle ; this they require for the purpose of swimming, escaping
from danger, &c. Although these animals are provided with ex-
ternal organs of mastication, the interior of their stomach is set
with numerous teeth, and its exterior provided with a suitable
arrangement of muscle.

Mollusca. — The muscular system presents much greater variety
of form in this than in the articulate class. The tunicata possess
a distinct muscular coat within their cartilaginous covering, by
which they act on their entire body, and empty their thoracic
cavity; the orifice of which, as well as the anus, is provided with
sphinctorial muscles. The foot of the conchifera, by which they
swim, creep, burrow, or attach themselves, is hollow, and composed
almost entirely of muscular fibres, taking different directions. This
foot occasionally admits the water into its interior, and is absent
from the oyster and others where the shell is permanently fixed.
In the gasteropoda, the foot is the largest muscle in the body, and
in trachelipodous gasteropods or those residing in turbinated shells,
its fibres are traceable up to the neck, and backwards to be attached
to the shell. The predaceous gasteropods possess a powerful mus-
cular proboscis provided with a fleshy tongue, armed with sharp
conical teeth, as seen in the common whelk, (buccinum undatum.)
In the chephalopoda and pteropoda, muscular fins are attached to
the side of the trunk for progressive motion. And in the naked
cephalopods, a thin panniculus carnosus with interlacing fibres, is
spread all over the body, beneath the coloured skin of the mantle.
The octopus is destitute of any lateral fins, but is provided with a

muscular membrane extended between the bases of its feet, by
which it is enabled to swim ; but what is curious about it is, that
it swims backwards by impelling the water forwards.

CHAPTER VI.

ON THE MUSCULAR SYSTEM IN THE VERTEBRATA.
PISCES.

In all the vertebrata the soft parts are uniformly placed external
to the hard resisting textures : in them the muscles of animal life
are generally of a red colour, and connected to bone by at least one
extremity, through means of tendinous or fibrous structure. In
fishes, the muscular fibres are soft, gelatinous, and colourless as in
the in vertebrata, and the embryos of the higher vertebrated classes.
In the salmon, however, they are of a higher red, especially about
the head ; and in the lamprey they are blackish gray. The
arrangement of the muscles in the osseous fishes is such, that a
large mass extends from head to tail on each side, divided by fibrous
bands into numerous strata. The active movements of fishes are
not subject to much variety ; their ascent or descent is effected
by the compression or expansion of the air-bladder, and by their
pectoral fins, whilst they are impelled forwards by the lateral motion
of the tail opposed by the resistance of the water. When the
swimming bladder is absent, as in the sole genus, or very small, as
in the cobitis fossilis, the animal either remains at the bottom, or
swims on one side by the vertical motions of the tail. The remora,
lump-sucker, and others are provided with a muscular disk in the
form of a sucker, by which they adhere to other fish or bodies
moving through the water: so powerful is the muscular tail of the
salmon, that, aided by the great elasticity of its spine, it is able to
mount over cataracts fifteen feet high. The shark is especially
remarkable for speed, so much so, that according to a calculation of
Sir E. Home, it would, if not compelled to rest, swim over the cir-
cumference of the globe in thirty weeks.

AMPHIBIA.

The proteus, siren, and the tadpoles of the higher anurous spe-
cies, are moved through the water by the same kind of lateral
motion of the spine and tail as in fishes. The oreat lateral mus-
cles that accomplish these motions are still pale, bloodless, and
feeble, and their connecting cellular tissue is soft, scanty, and
colourless; the muscles are slightly connected to the skin, and pre-
sent but little appearance of tendinous structure. So far the mus-
cular system closely resembles that of fishes, but in the adult state

MUSCULAR SYSTEM IN THE VERTEBRATA. 43

of the anurous species, it presents characters very remote from them,
arising from their great extent of respiration, and their inhabiting a
rarer medium. The oblique caudal muscles in the tadpole of the
tailless tribe, become absorbed with the vertebras to which they are
attached, as the animal assumes its permanent form ; but its change
of habits is still provided for by the great development of the
muscles of the posterior extremity, in fact they closely resemble
those of the human leg; and hence the act of swimming in man
is an accurate imitation of that of the frog. In this animal, the
extensors are much stronger than the flexors of the leg, and those
of the arm are but feebly developed.

REPTILIA.

The rarity of the medium through which the air-breathing rep-
tiles move, at once declares an increased development of muscular
energy in this class. In the progressive motion of serpents, their
vertebral column forms several S-shaped lateral curves; is shortened,
and again stretched forwards, whilst the posterior part of the body
is fixed: this rapidly performed constitutes a leap or dart. The ribs
being free at their distal extremities, admit of extensive motion, and
are furnished with large intercostal muscles of various lengths,
some passing from rib to rib, and others over one or more to have
distant insertions. These muscles have small shining tendinous
bands, by which a great number can be attached to a small space,
and thus admit of great variety in the movements of the ribs,
which are not only subservient to respiration, but to progressive
motion in these animals. The muscles of the head are strong, and
in the rattle-snake and others, a portion of the temporal extends
forwards like a buccinator, to embrace the poison gland and force
its secretion into the perforated fang.

The saurian reptiles possess members sometimes organised for
progression on the surface, sometimes for climbing, sometimes for
swimming, and occasionally for flying ; hence their muscles are
more numerous and complicated than in serpents. A rudiment of
diaphragm may be perceived in the dragons and geckos ; and in the
prehensile tongue of the chameleon there resides a beautiful muscu-
lar apparatus ordained to govern its stealthy movements in obtaining
his food, and as Sir C. Bell aptly describes it, he lies more still than
the dead leaf, his skin is like the bark of the tree, and takes the hue
of surrounding objects. Whilst other animals have excitement
conforming to their rapid motions, the shriveled face of the cha-
meleon hardly indicates life ; the eyelids are scarcely parted ; he
protrudes his tongue with a motion so imperceptible towards the
insect, that it is touched and caught more certainly than by the
most lively action. In the chelonia, the muscles of the extremities
together with those of the shoulders and pelvis are well marked,
whilst those of the jaws, lips, and chest are almost wholly absent.

44 EVERS'S COMPARATIVE ANATOMY.

AVES.

A greater degree of uniformity pervades the muscular system of
this than any other of the vertehrated classes, yet it will be found to
present many peculiarities. From the rarity of the element they
inhabit, as well as from their rapid and long continued movements
through it, their muscles require a considerable degree of vital
energy, hence they are red, vascular, dense, and irritable in the
high flying and rapacious tribes, although pale, soft, and feeble in
those of heavier and slower habits. The fleshy portions of the
muscles are short and thick, whilst the tendons are long, slender,
dense, and often ossified ; their trunk being almost fixed, the
muscles of the dorsal and lumbar regions are feeble and indistinct,
those of the neck, on the contrary, are well developed in accordance
with the perfect and varied motions of this part of the spine. The
muscles of the abdomen are week and feeble, and the diaphragm so
imperfect in the centre as to allow the heart to come in contact
with the liver as in reptiles. Of all the muscles, none reach so
great a degree of development as those of the anterior extremity,
especially those attached to the humerus. Birds possess three pec-
toral muscles, an anterior, middle, and posterior: they are all
attached to the sternum and the proximal extremity of the humerus.
In birds of flight, the great pectoral often equals in weight all the
other muscles of the body combined. The latissimus dorsi and
deltoid are feebly developed, whilst the psoEe, obturator externus,
and quadratus lumborum, are wholly absent. The muscles of the
lower extremity are remarkable for their long, slender tendons, and
especially for the beauty and perfection of the mechanism by which
they support the bird when asleep on roost, without any muscular
action. This is accomplished by the gracilis, which, arising from
the pubis, descends along the inner side of the thigh, and ends in a
strong tendon, which passes in front of the knee-joint, and subse-
quently over the projection of the heel to terminate by attaching
itself to the outer origin of the flexor digitorum perforatus. From
this disposition it results, that the more the joints are bent, the
firmer the twig on which the bird rests, is grasped, and the heavier
it sleeps, the more secure it is. Every one is familiar with the
fact of birds generally sleeping on one leg, this is for the purpose
of throwing the entire weight of their body on it, and so grasping
the firmer, and in order to increase the effect by adding to the
weight of the body, some birds are in the habit of never going to
roost without grasping a stone, or some ponderous body in the
other foot.

Flight, which is the most chracteristic mode of progression in
birds, is effected by the animal springing into the air ; or, where the
legs are so short, and the wings so Ions: that it cannot jump high
enough to gain the requisite space for the expansion of the wing,
it throws itself from some elevated point. The humerus is next

MUSCULAR SYSTEM OF THE VERTEBRATA. 45

raised, and the fore-arm extended, a considerable extent of sur-
face thereby gained ; the entire member being then forcibly
depressed, the resistance which it receives from the air, effects the
elevation of the bird; velocity of flight depends upon the rapidity
with which these strokes succeed each other. The eider-duck is
supposed to fly 90 miles an hour; the hawk 150, and everyone
has heard of the falcon belonging to Henry IV. king of France,
flying in one day from Fontainbleau to Malta, a distance of 1350
miles.

MAMMALIA.

Some of the animals composing this class are destined to move
like fishes through a watery element, some to fly through the air
like the feathered tribes, some to climb treess, some to dig and
burrow in the earth, and others to walk upon its surface. Habits
so diversified bespeak corresponding diversities of muscular arrange-
ment. Many approximations to the human type present themselves
on the one hand, and indisputable recurrences of simpler forms on
the other. The fleshy portions of the muscles are generally large
and plump, proportioned to the size of the body, or the massive
bones of the skeleton. The respiration being here less extensive,
and the circulation more slow, than in birds, the temperature is
lower, the muscular fibre less dense, and the tendons less prone to
undergo ossific changes.

The arrangement of the muscles in the cetacea nearly coincides
with that in fishes, the latter moving horizontally, the former chiefly
in a verticle direction. The muscles of the ribs, spine, pharynx,
os hyoides, and exterior naresa are well developed, those of the pelvis
and posterior extremities disappear with those parts, and the muscles
of the anterior extremities are curtailed and simplified, least so,
however, in the phytophagous cetacea. The large herbivorous
quadrupeds require strong muscles to move their massive and
heavy trunks, and the active and predatory habits of the carnivora
demand a still greater development of this system. In theruminan-
tia, pachydermata, and those animals without clavicles, the anterior
extremities are placed under the trunk, which is suspended between
their long vertical scapulas by the great serrati muscles, in many
instances prodigiously developed. The buffalo, the bull, and others
of the ruminants, with many of the pachyderms, have the muscles
of the neck large and powerful to move their heavy heads, which
are often armed with large teeth, tusks, a proboscis, or huge horns.
The external muscles of the ear are greatly developed in many of
the herbivorous quadrupeds, and the muscles of the nose in the
hog tribe.

The panniculus carnosus. which is thin, and finely spread over
the trunks of the pachydermata, is strong and fleshy in the soft
skinned ruminantia, where it is attached to the humerus and to the
femur. In the mammalia covered with spines, as the echidnia, the

hedge-hog, and the porcupine, and those covered with scales, as the
rnanis and the armadillo, this muscle is important in erecting or
moving these epidemic organs, and in coiling or uncoiling the body.
In the mole, and those animals that dig the earth, the flexors of the
arm, the pectoralis major, the latissimus dorsi, and the teres major,
are of vast size. In the rodentia, the muscles are pale, and those of
the jaws of great magnitude. The marsnpiata have the panniculus
carnosus extended over the pouch in such a manner as to support
the young abortive-like fretus, and force the mammary secretion
into its mouth. The arrangement of the muscles approaches nearer
to the human type in the quadrumana than in any others of the
mammalia. In them the flexor muscles are strongly developed on
all their extremities. The thumbs, have no long separate flexors,
but receive tendons from the flexors of other fingers. r^ne P^an~
taris muscle, which is very fleshy in monkeys, instead of termina-
ting, as it does in man, by insertion in the os calcis, passes over that
bone to be connected with the planter fascia and flexor perforatum.
In other quadrupeds it passes over the os calcis to the sole of the
foot, and supplies the place of the flexor digitorum brevis. The
glutaeus maximus, which is the largest muscle of the human body,
is small and feeble in the simise and other animals, its chief use being
to support the trunk upon the lower extremity, and thus assist in
maintaining the erect attitude, and not, as the pious Spigelius
imagined, to form a soft cushion for the body to rest on during
divine cogitation.

Finally, the extensors of the knee, the flexors of the toes, and the
other muscles forming the calf of the leg. are relatively larger in the
human subject than in any other animal.

RECAPITULATION.

1. Muscular fibres have been satisfactorily shown to exist in the
higher species of the radiata.

2. Muscle is found all through the articulate and molluscous
classes, but better and more uniformly developed in the former.

3. The soft parts are uniformly placed external to the hard, in
the vertebrated classes.

4. The muscles in fishes are generally soft and pale, as in the
lower classes.

5. In the amphibia, the muscles present different characters in
the tadpole and adult state.

6. Great variety in the reptiles, chiefly referable to their diversi-
fied habits.

7. The muscular system in birds is characterised by great
uniformity throughout the class.

8. The muscles of the aquatic mammalia resemble those of
fishes.

9. Serrati magni greatly developed in the quadrupeds not pos-
sessing clavicles.

NERVOUS SYSTEM IN THE INVERTEBRATA. 47

10. Panniculus carnosus best marked in the echidna, the hedge-
hog, the porcupine, the manis, the tatu, the marsupiata, and The
thin-skinned ruminants ; less so in the pachydermata, and absent
from some, as the hog. It is found in monkeys, but not in the
chimpanse.

11. Lattismus dorsi, teres major, &c, are very powerful in the
mole and ant-eaters.

12. The plantaris, which is rudimental in man, is large in mon-
keys and some quadrupeds.

13. Man is characterised by the magnitude of his buttocks, thio-hs,
and calves.

CHAPTER VII.

ON THE NERVOUS SYSTEM IN THE INVERTEBRATA.

This system, when perfectly developed, consists of an internal or
central, and an external or circumferential portion ; to the latter
belong the nerves and ganglions ; to the former, the spinal cord, the
medulla oblongata, the cerebellum, and the cerebrum. The nervous
system presides over the movements of our muscles and the sensi-
bility of our bodies; by it we are connected with surrounding
objects, and an injury inflicted on any part of the body, at once
declares the extent of its distribution, as well as the close relation
that subsists between its several parts.

The nervous system has been detected in every division, although
not in every class, of the animal kingdom : it commences its develop-
ment at the circumference, and grows towards the centre, and its
forms corresponds pretty closely with that of the body of the animal.

The nervous matter is extremely soft in the inferior grades of
animals, as well as in the embryo of the higher classes ; and its
colour presents some variety, being bright red in the helix stagnalis •
blackish red in the aplysias ; and bright yellow in the common fresh
water muscle. The nerves are composed of tubes filled with minute
globules. The brain is also composed of globules, eight times
smaller than those of the blood, larger and more numerous in the
medullary, than in the cineritious substance, and in the former dis-
posed in lines which gave it its fibrous character.

Cyclo-neura, Grant. — In the two first classes of this division,
the polygastrica and the porifera, no nervous filaments have been
detected, yet, from their active movements, their sensibility to the
impression of light, and their consciousness of each others approach,
it is but reasonable to infer the existence of a nervous system in
them, though from its transparency or some other cause, it cannot
be demonstrated. Both nerves and ganglions are found to exist in
the three remaining classes of the radiata. Distinct nervous fila-
ments surround the muscular foot of the actinia; and in the

48 EVERS'S COMPARATIVE ANATOMY.

acaiephae and echinodermata, fine nervous filaments and small
white, ganglions surround the entrance of the alimentary canal.

Dlplo-neura, Grant.— In this great division, the nervous
system, presents the same extended form as the body, placed on the
ventral surface of the alimentary canal, and except in the higher
classes, not enclosed in an osseous sheath. Among the higher
forms of the entozoa, as the ascaris, two fine nervous filaments
extend along the median line of the abdomen, separating to embrace
the oesophagus, and the vulva of the female. In the notommata
clavulata of the rotifera, we find nine pairs of ganglions disposed
along the course of the lateral columns. Scarcely a trace of ner-
vous system can be perceived in the simple forms of the annelida.
In the nereids, however, and many others of this class, the sympa-
thetics become quite distinct ; and numerous nerves are seen to pass
off in the lateral direction. The common leech, which presents
about eighty rings in the trunk of its body, has five and twenty
ganglia placed along: the abdomen, approximated at the two extre-
mities of the column. In the most inferior of the diversified class
of the crustaceans, the nervous system presents itself in the form of
two slender abdominal filaments, in imitation of what we have seen
in the preceding classes, and by a gradual development from the
peripheral to the central parts, it arrives at that concentration of
nervous ganglia around the oesophagus, which connects the highest
of the articulate with the molluscous classes.

' Cyclo-gangliata.— The greater number of the mollsuca being
aquatic, their nerves present the same pale and soft characters
observed in the other aquatic invertebrates ; hence the difficulty of
indicating their particular distributions. Here as in the radiata, the
same tendency to accumulate nerves around the entrance to the
alimentary canal prevails, but in this case more generally accom-
panied with ganglia. In the lowest classes of the division, as the
tunicata and conchifera, the nervous chords are placed beneath the
alimentary canal ; in the two next classes gasteropoda and ptero-
poda, they are more in the vicinity of the stomach ; arid in the ce-
phalopoda, which is the last and highest of the division, the nervous
ganglia attain a more elevated position, they cease to embrace the
oesophagus; and a distinct brain, as in the vertebrata, with nume-
rous symmetrical ganglia along the abdomen take, their place.

CHAPTER VIII.

NERVOUS SYSTEM IN THE VERTEBRATA.

PISCES. ^

We no longer find the nervous system perforated by the alimen-
tary tract. On, the contrary, in all the succeeding classes, it

NERVOUS SYSTEM IN THE VERTEBRATA. 49

occupies a dorsal situation, and is protected by an osseous sheath.
In the lowest orders of fishes, as the lamprey, and the gastrobranchus,
we perceive a repetition of the two nervous columns extending
along the back as observed in the worm. This simple condition
resembles the embryo state of this system in the highest grades of
the vertebrata, previous to the development of their extremities.
With kw exceptions the spinal chord extends the whole length of
the vertebral column ; whence, from the great number of vertebrae,
it attains a very remarkable length. In some, however, as the
lophius piscatorius, it is stated to be very short, forming a kind of
Cauda equina as in man. It usually terminates in a single thread,
presenting several enlargements throughout its tract, which corres-
pond very accurately with the number, magnitude, and situation of
the extremities. For instance, when the anterior members are very
large, as in rays and flying-fishes, the anterior enlargements are
proportionally developed ; and where a large caudal fin is to be
supplied, the chord presents a sensible enlargement posteriorly
where the nerves join it. The spinal marrow, here, as in the
human foetus, usually contains a canal of considerable size, and is
distinguished by an anterior, a posterior, and two lateral grooves.
From the latter, the nerves arise by two roots, the posterior or sen-
sitive root having a ganglion on it, receives the anterior root im-
mediately external to the canal.

The brain m fishes does not fill the cavity of the cranium, a
considerable portion of it being occupied by the soft cellular tissue
of the arachnoid. The medulla oblongata is of great length, lobed,
and deeply grooved above by the calamus scriptorius.

Tn most fishes, the optic lobes are larger than the hemispheres,
they are hollow and communicate freely with each other and with
the fourth ventricle. The earlier they are examined the larger they
are found to be ; their development is proportionate to that of the
optic nerves and eyes, and inversely to that of the cerebrum and
cerebellum. The cerebral hemispheres are small in the osseous,
apodal, and cyclostome fishes, and in the plagiostome species they are
larger than the optic tubercles. In the osseous fishes they resemble
the embryo condition of the human brain in being destitute of ven-
tricles, and having no convolutions on the surface. In sharks and
rays the hemispheres attain a large size, present irregularities on
the surface, and ventricles in their interior. In front of the hemi-
spheres are placed the olfactory tubercles, elongated transversely, and
exceeding in magnitude the hemispheres themselves; subject, how-
ever, to considerable variations, regarding form, size, and situation.

The cerebellum is scarcely to be recognised in many of the
cyclostome fishes. When present it appears as a transverse band,
rising vertically in the osseous fishes, and forming a small vermiform
median lobe, slightly laminated in the plagiostome fishes. In sharks
and rays not only does this median lobe attain considerable magni-
tude, but small hemispheres are developed laterally, corresponding
in size to that of the carpora restiformia. The pineal gland is found
8 — e evers 4

in all fishes, lodged between the hemispheres and optic tubercles,
but so small in the osseous tribes that its existence has been ques-
tioned. These several lobes are covered with a layer of cineritious
substance, and closely invested by a delicate layer of pia mater;
outside of which is the soft, gelatinous, cellular arachnoid tunic, and
all are surrounded by an envelope of dura mater.

Nerves. — The olfactory nerves are white and fibrous ; they are
very large in the rays and sharks, and in many instances form a
ganglion before their termination ; as may be seen in the carp.
The optic nerves are developed in proportion to the size of the optic
tubercles and eyes ; hence they are large in the carp, and slender in
the eel. In the osseous fishes they generally cross without any in-
termingling of fibres; in the plagiostome fishes their fibres are
blended at the commissure as in the mammalia; and in the skate,
the right nerve goes through a fissure in the left. The third, fourth,
and sixth nerves are developed in proportion to the size of the
muscles they supply. The fifth nerve presents a greater size, and
gives off more branches in this class than in any other of the verte-
brata. The ophthalmic, superior, and inferior maxillary are dis-
tributed to the face, palate and lower jaw. In the rays, and many-
other fishes, it sends a branch to the ear, and in the torpedo, to the
electrical organs. These latter are composed of a series of mem-
branous cells occupied by a gelatino-albuminous substance, per-
forming the office of a Leyden jar or electrical battery. They lie
in the torpedo on the upper surface of the lateral fin. In the elec-
tric eel, on the posterior part of the abdomen ; and in the silurus
electricus they are situate between the muscles and skin over the
entire body. In the last named fish the nerves appear to be derived
from the pneumo gastric. Both portions of the seventh pair are
small and distributed without any peculiarity. The pneumo-gas-
tric arises from the side of the medulla oblongata, behind the fifth
pair ; it forms a large ganglion below its origin, from which
branches proceed to the branchiae, the oesophagus, the stomach, and
rudimentary lungs. This nerve gives off also a branch to the
tongue analogous to the glossopharyngeal, and one to the lateral
part of the body analogous to the spinal accessary, both of which
are rudimental in fish. The ninth pair is wholly absent and its
place supplied by a branch from the fifth. The distribution of the
spinal nerves is very simple, and their development is always pro-
portioned to the size of the fins ; the sympathetic is very slender,
and its ganglions small in fishes. It is most developed in the pla-
giostome chondropterygii, and least so in the cyclostome species ; it
receives filaments from the spinal nerves, and its meshes accompany
the arterial trunks in their distribution on the digestive, respiratory,
and generative organs.

AMPHIBIA.

The condition of the brain, the medulla oblongata, and the spinal
chord are nearly the same in the perennibranchiate amphibia, and

NERVOUS SYSTEM IN THE VERTEBRATA. 51

in the larva state of those which undergo metamorphosis, as are
observed in the osseous fishes. The lobed form of the medulla
oblongata, the small cerebellum, the optic thalami, with the ventri-
cles, and the diminutive extent of the hemispheres, all evince a
degree of perfection not much above that noticed in fishes. The
spinal chord is prolonged, small and tapering into numerous coc-
cygeal vertebrae, and without sensible enlargements where the
nerves are to come off to supply the future members. The meta-
morphosis of the caducibranchiate species, from the pisciform to
the reptile state, develope an interesting series of phenomena. The
hemispheres become enlarged, the cerebellum, which was scarcely
visible, increases in size across the median line ; as the limbs begin
to appear, the spinal marow exhibits corresponding developments,
but dwindles posteriorly as the coccygeal vertebrae disappear. So
rapid are these changes in the nervous system of the frog, that we
can appreciate them from day to day. The sympathetic system is
more distinct in this class than in that of fishes.

REPTILIA.

In this class the cerebral hemispheres exceed in size the optic
lobes, and contain a distinct ventricle. The cerebellum is remark-
ably small ; and, in the sauria and chelonia, the spinal marrow
presents an obvious enlargement, opposite the attachment of each
nerve. The medulla oblongata is broad ; the nerves are large,
compared with the cerebral centres, but present no peculiarity of
distribution. The plexuses of the sympathetic are here more
closely connected with the arterial trunks, than in the preceding
classes.

AVES.

The brain and spinal chord are in this class developed with more
uniformity and perfection than in the cold-blooded reptilia ; and
bear a remarkable correspondence with the perfection of muscular
energy which they possess. In a pigeon weighing 3360 grains,
without the feathers, the brain weighed 37, and the spinal chord 11
grains=48.

The spinal chord extends from the foramen magnum to the
coccygeal vertebrae, where it is greatly reduced in size, and expends
itself in distributing a few nerves through the lateral foramina. The
length of the chord is considerable, compared with the size of the
brain ; its shape is cylindrical ; its anterior and posterior grooves
are very distinct, as well as a minute canal extending through its
whole length, arising from the union of the two halves of the
chord: the dilatation of this canal in the pelvic region, is called
"rhomboidal sinus." The spinal chord is chiefly composed of
white matter, but contains a small quantity of gray, internally.
Two enlargements occur on the chord, bearing a relative size to
the development and powers of the extremities: in general the
posterior enlargement is the greater, especially when the business

of progression devolves on the posterior members, as in strnthious
birds. The form of the chord is not altered in the alar enlarge-
ment, but simply increased by an accession of gray and white
substances; — the lower one, on the contrary, not only receives
additional matter, but the pillars separate, so that the fluid in the
sinus is merely covered by pia mater.

The brain of the bird differs from that of the reptile in the
greater size of the cerebrum, and the more complex structure of
the cerebellum; it differs from the brain of a mammal in the
smaller size of the cerebellum, and the rudimentary state of the
fornix; and it differs from the brain of every other vertebrate class
in the inferior position of the optic lobes. The cerebral hemispheres
are generally of a convex condiform shape, with the apex directed
forwards; they are disunited through their whole extent, being
only joined by a round anterior commissure; they are destitute of
convolutions, and have a small ventricle in their interior. The
olfactory tubercles are greatly reduced in size, and retain their
tubular communication with the cerebral ventricles. The optic
lobes are small ; gray on the surface, white internally, and contain
each a small ventricle ; they are connected by transverse medul-
lary bands on which the pineal gland rests, with its peduncles
directed forwards over the optic thalami. These last bodies are
covered by the cerebral hemispheres, united by a commissura
mollis, and destitute of transverse sulci. The medulla oblongata
is large and wide; its components are marked on the surface, but
it is without tuber annulare. The cerebellum presents a median
vermiform lobe, and rudimentary hemispheres, sulcated trans-
versely, with a faintly-marked arbor vitae in the interior. The
membranes investing the brain differ but little from those of the
mammalia.

Nerves. — The nerves in this class present but few striking pecu-
liarities, being distributed nearly as they are in man. The olfactory
arise from the front of the hemispheres, pass forwards through
distinct osseous canals in the cribriform plate, and are distributed
in a radiated manner on the superior spongy bone. The large
optic nerves arise from the optic tubercles, and form a perfect
decussation in front of the infundibulum ; where, as in the iguana,
an incision displays a mutual intermixture of the fibres. The
remaining cerebral nerves are distributed pretty nearly as in mam-
malia; the portio dura is, however, small in accordance with the
insensibility of the superficial parts of the face. The spinal nerves
correspond in number to the vertebrae ; they arise by two roots, the
posterior having a large ganglion on it. The sympathetic, which
is well developed, communicates through the anterior lacerated
opening with the fifth and sixth nerves. From the third cervical
vertebra to the thorax, it is contained in the canal in the transverse
processes, in company with the vertebral artery. It form a series
of ganglions, from the base of the skull to the end of the coccyx ;
and communicates, in its course, with every neighbouring nerve.

NERVOUS SYSTEM IN THE VERTEBRATA. 53

MAMMALIA.

In this class the increased development of the nervous system is
marked by the size and length of the spinal chord ; the magnitude
of the cerebrum and cerebellum, and the number of their gray
deposits and commissures, as well as by the number and arrange-
ment of the ganglions, together with the extent and systematic dis-
tribution of the great sympathetic.

The spinal chord is larger in proportion to the size of the body,
but smaller when compared with the brain, in this than in any of
the preceding classes; its internal canal has almost ceased to exist,
and its lateral portions are more intimately united. It is shortest
in man, quadrumana, and the tailless cheiroptera, and longest in
the cetacea, where, as in apodal fishes, tadpoles, serpents, and the
human embryo, it presents no posterior enlargements. In the long-
tailed quadrupeds it extends to the sacrum; the posterior groove is
generally shallow, though sometimes of considerable depth, as in
cheiroptera and rodentia. The medulla oblongata is small : the
corpora pyramidalia decussate very distinctly: the olivary bodies
are small, and generally contain a corpus dentatum in their interior,
and the transverse fibres of the pons or great cerebellic commissure
are well seen.

Brain. — In the class mammalia, the cineritious matter bears a
small proportion to the white substance. The convolutions are
very superficial in the cetacea, edentata, ruminantia, and pachyder-
mata, and wholly absent in the rodentia, and monotremata, as in
birds; whilst they are deep in man, monkeys, and carnivorous ani-
mals. The optic lobes, without cavities, are smallest in man,
quadrumana, and carnivora, larger in the herbivora, and largest of
all in rodentia and edentata. A contrary ratio obtains respecting
the development of the cerebral hemispheres, and the olfactory
tubercles. The anterior and inferior cornua of the lateral ventri-
cles, as well as the several commissures, are always present in this
class. The posterior lobe of the brain, and the posterior cornua of
the lateral ventricle, first appear in the quadrumana ; the former
has no convolutions.

The vast superiority of man over all other animals in mental
faculties, led physiologists at a very early period to seek for corres-
ponding differences in the brains of man and animals. They
compared the weight of the brain with that of the body, and their
researches led them to conclude that man had the largest brain in
proportion to his body. Since the time of Aristotle till within a
late period this opinion has been received : but more modern inves-
tigations have proved that the proportion of the brain to the body
in some birds exceeds that of man, and that several of the quadru-
mana and some rodentia equal him in this respect. The illustrious
Soemmering proposed another mode of comparison, that of the
ratio which the mass of the brain bears to that of the nerves arising
from it, and in this point of view man is decidedly pre-eminent.

The brain of man far exceeds in size that of the simiaa compared
with the nerves proceeding from it, and in these latter and in the
seal it is larger in proportion than in other animals, while it is
smallest in the glires, marsnpialia, cheiroptera, and edentata. The
largest brain which Soemmering has found in a horse weighed
1 lb. 4oz., and in an adult man was 2 lb. 5£oz. : yet the nerves arising
from the former were ten times larger than those of the latter.
Coeteris paribus^ small animals have a larger brain in proportion
to their size, than large ones, and in cold-blooded animals its di-
mensions are very small, compared with those of a higher tempe-
rature. The following table shows the relative weight of the brain
to that of the body in several of the vertebrate classes of animals: —

Fishes. — Silurus glanis, one-1 887th ; dog-fish, one-1344th ; shark,
one-2496th ; carp, one-560th.

Reptiles. — Turtle, one-5688th; colubar natrix, one-792d ; frog,
(amphibious,) one-172d.

Birds. — Goose, one-360th ; duck, one-257th ; eagle one-260th ;
falcon, one-102d ; sparrow, one-25th ; canary-bird, one-14th.

Cetacea. — Porpoise, one-93d; dolphin, one-102d, one-60th, one-
36th, one-25th.

Solipeda. — Ass, one-254th ; horse, one-700th; one-400th.

Ruminantia. — Ox, one-S60th; stag, one-290th; sheep, one-192d;
calf, one-2l9tb.

Pachydermata. — Wild boar, one-672d ; domestic, one-512th ;
elephant, one-500th.

Rodentia. — Beaver, one-290th ; hare, one-228th ; rabbit, one-
152d; rat, one-76th; mouse, one-43d; field-mouse, one-3 1st.

Carnivora. — Dog, one-305th, one-47th ; fox, one-205th ; wolf,
one-230th; cat, one-156th, one-82d ; ferret, one-138th.

Plantigrada. — Hedge-hog, one- 1 68th; bear, one-265th; mole,
one-36th.

Cheiroptera. — Bat, one-96th.

Le?nurs. — Vari, one-84th; mococo, one-61st.

Baboons. — Magot, one 105th; great baboon, one-104th ; macaque,
one-85th.

Apes. — Mangabey, one-48th; the monk ape. one-44lh ; malbrouk,
one-24th.

Sapajous. — (American apes) Coa'ita, one-41st; Sai, one-25th ;
Saimiri, one-22d.

Onranfr-outangs. — The gibbon, one-48th; chimpanse, 26 inches
in height, 11 oz. 7dr.

Child of six years, one-22d; adult man, one-35th.

The Cerebellum is smaller in proportion to the cerebrum in
man, the saimiri, and the ox, than in any others of the mammalia.
In the human subject and in ourangs only, is it covered by the
posterior lobes of the brain. The superior vermiform process and
the hemispheres of the cerebellum are developed in every class
in the inverse ratio of each other. In the saimiri ape, the cerebel-
lum is to the cerebrum as 1 to 14 ; in man and the ox, 1 to 9 ; in

NERVOUS SYSTEM IN THE VERTEBRATA. 55

the monk ape and the dog, 1 to 8 ; in the magot, papio, and wild
boar, 1 to 7 ; in the sai and hare, 1 to 6 ; in the mole, 1 to 4 ; in
the rat and beaver, 1 to 3 ; and in the mouse, 1 to 2.

Nerves. — The olfactory nerves are largest in the ruminantia,
pachydermata, and carnivora, smaller in the cheiroptera and qua-
drumana, and discoverable with difficulty in many of the cetacea.
In the squirrel, rabbit, hare, and other large-eyed nocturnal quadru-
peds, the optic nerves are very large; they are small in rats, mice,
bats, hedge-hogs, and subterranean moles, and in the sorex arraneus,
mus typhlus, muscapensis. and others, they are said to be altogether
wanting. They unite before the infundibulum, and form a partial
decussation of their fibres. The third, fourth, and sixth nerves are
distributed as in man, and are very small in subterranean animals.
Of all the cerebral nerves, none reaches so great a degree of deve-
lopment as the fifth pair, in the inferior classes of animals and in
the foetal state of the human subject: it is also of enormous size in
most aquatic birds. Its branches are freely and extensively distri-
buted in those animals with proboscis, long muzzles, large lips, and
broad bills, as the cetacea, ruminantia. pachydermata, carnivora,
and ornithorhynchi, and also in those possessing horns, spines,
bristles, and whiskers. This nerve is supposed to preside over the
peculiar instinctive actions so remarkable in those grades of ani-
mals which indicate an inferior degree of mental endowment, and
this opinion receives strength from the fact of its great size in the
very early periods of human existence, when we know the actions
are purely instinctive. The remaining cerebral, the spinal, and the
sympathetic nerves are distributed so much after the human type
as to merit no particular remarks.

In most mammalia the arteries of the brain form a complicated
net-work around the petuitary body at the base of the cranium
named rete mirabile, obviously designed to impede the flow of
blood to the brain, in those animals with pendent heads. The
veins occasionally run in osseous canals in order to avoid pressure;
this is well seen in the cribriform plate of the mole's skull, and in
the bony falx cerebri of the porpoise. A bony falx cerebri is also
found in the ornithorhynehus, an animal which abounds in in-
stances of anomalous structure. Animals which possess a bony
tentorium are of far more common occurrence: it is well developed
in most species of the cat and bear kind; it is not so well marked
in the dog, seal, horse, and wombat, and it is merely rudimentary
in the pig, the rabbit, and the mouse.

It has been generally supposed that these structures exist in such
animals only as jump far, and that they served the purpose of pro-
tecting the respective portions of the cerebrum and cerebellum from
undue pressure during these active movements, but this opinion is
rendered quite untenable from the fact of their absence in many
animals notable for jumping, as the wild goat, (fee, and their pre-
sence in those animals alike remarkable for their slow and easy
movements, as the bear. It is more probable they exist for the

56 EVERS's COMPARATIVE ANATOMY.

purpose of obviating the concussion which would arise from the
strong exertions in biting; for such exertions are made by all the
animals which possess them, even by the horse in his wild state.

RECAPITULATION.

1. A nervous system exists in every class of animals, though not
in all the animals of each class.

2. In the invertebrate classes it has a peculiar tendency to accu-
mulate around the oesophagus.

3. In all the vertebrata its principal parts are protected by osseous
sheaths.

4. The spinal marrow is tubular in the human embryo, and most
of the lower vertebrata.

5. This system undergoes remarkable changes in the amphibia,
during their metamorphosis.

6. It is highly developed, and with great uniformity in birds.

7. The chord presents enlargements corresponding in size to the
members most used.

8. The spinal chord bears a large ratio to the size of the body in
most mammalia.

9. Man's superiority is due to his mental faculties.

10. The brain is larger in proportion to the size of the nerves
connected with it in man than in any other animal.

11. The fifth cerebral, or the nerve of instinct, is very large in
most mammalia, and in the foetal state of the human subject.

CHAPTER IX.

ORGANS OF SENSE.

General observations. — The organs of sense are those instru-
ments which are placed upon the distal extremities of certain cere-
brospinal sensitive nerves, whose office being to establish a relation
between the internal sentient principle and the external objects of
surrounding nature, are necessarily placed in connection with the
external surface of animals, and generally in the neighbourhood of
the entrance of the alimentary canal. They are more numerous,
more varied, and more perfect in the higher than in the lower tribes
of animals, but they are more developed in the active insects and
others of the articulata, than in the slow and torpid mollusca, and
they attain their greatest degree of perfection in the vertebrata where
the most complicated and delicate forms of organisation are con-
signed to their careful watch.

Vision. — Organs of vision have been figured and minutely de-

ORGANS OF SENSE. 57

scribed in many of the polygastric animalcules ; they vary in number
from one in the polygastrics, up to eight in the acalepha. In the
rotifera, optic nerves and ganglia are quite visible, and in the aca-
lepha a lenticular body is superadded. Visual organs are met with
in almost every class of the diplo-neurose division ; in some there
is but a single eye, in others they are more numerous, and placed
apart on different aspects of the head. The medicinal leech pos-
sesses ten prominent eyes disposed transversely, and the neiris nun-
tia has two large pairs placed on the upper part of the head, and
nearly a hundred smaller ones grouped around the mouth. Many
of the higher insects present in their optical apparatus all the essen-
tial ingredients found in the highest forms of the organ. The eyes
of the crustaceans, are generally compound like those of insects, and
in many instances are moved by distinct muscles, and covered in
front by a transparent layer of epidermis. In the Crustacea, as in
insects, the optic nerves enlarge into a ganglion in the globe of the
compound eye, from which small filaments radiate to the several
lenses of the component eyes.

Organs of vision are less required, and consequently less deve-
loped in the torpid mollusca than in the active articulata ; they
never form groups of simple eyes like the myriapods, nor compound
organs like the insects and Crustacea. In the acephalous mollusca
they are simple, separate and numerous as in worms, but in the
higher forms of gasteropods, pteropods, and so on, they are more
complicated, and but two in number, disposed on the sides of the
head as in the vertebrata ; and in these possessing opaque coverings,
as the inhabitants of bivalve shells, they are altogether wanting. In
those, however, which enjoy rapid motion, as the pectem maximus,
they are upwards of fifty in number, each being about a quarter of
a line in diameter. The eyes of these animals are generally flat-
tened in front, they possess a rudiment of membrana nicitans; the
iris and the lids are usually motionless, yet in the general plan of
their formation they form a near approach to the condition of these
organs in the higher vertebrated classes.

In all the vertebrata the eyes are two in number, and with the
exception of a few species, are symmetrically disposed on the sides
of the head ; the differences they present being chiefly referable to
the density of the media in which the various animals reside. From
the density of the watery element through which fish move, their
eyes are generally of considerable size, except in the worm-shaped
fishes, as the eel and the lamprey. Sometimes they are directed
backwards or upwards as in the star-gazer : less frequently they are
placed on one side, as in the sole. The eye is spherical posteriorly,
and flattened in front. The conjunctiva is continued across in front
of the cornea, and admits of easy separation from it in the eel and
many other species. The eyelids are merely rudimentary and the
lachrymal gland is wholly absent. The sclerotic tunic is thick,
deuse, laminated, elastic, and occasionally ossified anteriorly. The
choroid is divisible into three layers, the internal or tunica Ruys-

chiaria, the middle or the membrana vasculosa Halleri, and the
external with its shining pearly lustre passes in front of the iris
and produces the gold and silver colours so much admired. The
cornea is remarkable for its flatness, the iris for its immobility, and
the crystalline lens for its density, magnitude, and sphericity. The
aqueous humour is scanty, the ciliary processes are rarely deve-
loped, and the yellow spot of Soemmerring is altogether wanting.
Between the layers of the choroid, and embracing the optic nerve, a
reddish mass of a horse-shoe shape is found in most fishes named
choroid gland, which, according to some, secretes the colouring
matter ; according to others it is a sort of rete mirabile, and others
again look upon it as an enlargement of the optic nerve, whilst the
prevailing opinion at present seems to be, that it is a muscle
destined to modify in some way the reflection of the rays of light.
From the inner layer of the choroid another body, campanula
Halleri, passes forwards towards the lens, somewhat analogous to
the marsupium of birds. The pupil in fishes is large and round,
and the eye is moved by four recti and two obliqui muscles.

The eyes of the amphibia are very large, and like those of
fishes contain a small quantity of aqueous humour, and are flat in
front. They enjoy great latitude of motion and are provided with
palpebrae and a membrana nictitans; the superior lid is small and
scarcely movable; the inferior large and very movable. The
opaque integument veils the front of the eye in the proteus ; in
most other characters the eyes resemble those of fishes.

The reptilia present us with characters of eyes well suited to
the rare medium they inhabit, such as convexity of cornea from
abundance of humours, and a compressed state of the lens. .Like
the amphibia, they are furnished with three lids, but unlike them
and fish, they are provided with lachrymal apparatus; they ap-
proximate the succeeding classes in many respects, as having ciliary
processes, a movable iris, generally a vertical pupil, a dark pecten
prolonged from the choroid into the vitreous humour, and osseous
plates around the anterior margin of the sclerotic. In the chame-
leon only a small portion of the eye is to be seen through a narrow
vertical slit between the margins of the lids, which conceal a large
membrana nictitans.

We cannot fail to observe how the remarkable peculiarities pre-
sented by the organs of vision in birds, coincide with the vigour of
their respiratory, circulatory, and locomotive systems. In all the
other vertebrate classes we meet with instances, where the eyes, if
not absent, are at least rudimentary, but in this class they are
remarkable not only for their uniform existence but for their great
size and perfect development. From the convexity of the anterior
segment of the eyes and their lateral location, birds command an
extensive sphere of vision, and in many of the high-flying rapa-
cious kind, the orofan is prolonged in front into a tubular form, but
in aquatic birds the anterior half is more flattened. The sclerotic
is thin, flexible, and elastic posteriorly ; it is divisible into three

ORGANS OF SENSE. 59

layers, between the middle and outer of which, from 15 to 17 osse-
ous quadrangular plates are placed anteriorly, a repetition of what
we have seen in reptiles and fishes; these scales overlap each other,
they are connected by the sclerotic, and are capable of a limited
degree of motion. The cornea is dense, and possesses a consider-
able degree of convexity, as well from the abundant humours as
from the pressure of the surrounding muscles ; and, according to
the discovery of Crampton, it is capable of varying its convexity
by the action of a muscular sphincter attached to the posterior
layer at its circumference. The choroid is the same as in mam-
malia: the iris is remarkable for the freedom of its motions which,
in some instances, seem voluntary: the pupil is generally circular,
but elongated transversely in the goose and dove, and vertically
oval in the owl. The chief peculiarity in the eye of birds consists
in the marsupium nigrum or pecten plicatum ; this wedge-shaped
body, which in appearance simulates choroid, is composed princi-
pally of vessels, and extends from the entrance of the optic nerve
through the vitreous humour towards the lens which it sometimes
reaches, and gets an attachment to. Petit supposed that this sub-
stance rendered objects in front of the eye more distinct by absorb-
ing the lateral rays of light: Home, that by its muscularity it
retracted the lens; but this is impossible when it does not reach it.

Owen considers it an erectile organ, destined to push forward
the lens either directly or through the medium of the vitreous hu-
mour; others look upon it as a gland for secreting the vitreous
humour, and many are of opinion that it is placed there for the
purpose of absorbing the super-abundant rays of light during the
exposure of the eye to the blazing sun when soaring aloft.

The aqueous and vitreous humours present no peculiarities ;
the lens is flat in high-flying birds of prey, and more convex in
the aquatic species ; it is not here as in the other classes an achro-
matic lens, in consequence of the absence of central nucleus. The
globe of the eye is moved by four recti and two oblique muscles.
The lower lid is the more movable in birds and is provided with a
distinct depressor muscle. The third eyelid, or membrana nicti-
tarts is a conjunctival fold connected with the inner angle of the
eye and capable of being moved across the organ by a peculiar
pair of muscles. One of these, from its shape, is named quadratics ;
it arises from the upper and back part of the sclerotic; its fibris
descend in a convergent manner towards the optic nerve, a little
above which they terminate in a free semilunar aponeurotic margin,
containing a canal. The second muscle called pyramidalis arises
from the inferior internal and posterior part of the sclerotic, its
fibres pass converging to the upper surface of the optic nerve, where
it forms a slender tendon, which passes though the canal in the
quadratus; it then passes from the outer to the lower surface of the
sclerotic, conducted in a cellular sheath till it gains the free margin
of the membrana nictitans, into which it is inserted.

By the simultaneous action of this pair of muscles the membrane

60 EVERS'S COMPARATIVE ANATOMY.

is rapidly and forcibly drawn downwards and outwards over the
front of the eye, and is restored to its former situation by its own
elasticity. The lachrymal gland is situated at the external angle
of the eye, and at the internal angle there is another gland named
Harderian, from its discoverer, but is nothing more than a con-
geries of mucous follicles to compensate for the absence of meibo-
mian glands. There is a third gland in or near the orbit, called
nasal, its secretion being wholly destined for the nose.

In the mammalia the organs of vision are Constructed in perfect
accordance with the media the animals move in ; they are usually
placed laterally, but in the nocturnal quadrupeds they are directed
forwards as much as in man, and in the quadrumana even more
so. The eyes are of a large size in ruminantia, rodentia and many
pachydermata; and they are small in moles, shrews, whales, and
in most cheiroptera. In the mus typhlus the eye is covered by
hairy conjunctiva ; and in the mole of Libanus, it is so small as to
be almost invisible. The form of the eye is generally spherical,
but in the cetacea flattened anteriorly as in fish, and in bats it
approaches to that of birds. In the cetacea the aqueous and vitre-
ous humours are less abundant than in terrestrial quadrupeds, the
cornea is flat, the lens is large, dense, and round, and the sclerotic is
an inch thick posteriorly in a whale, with an eye the size of an
orange; the lids are imperfectly developed, the lachrymal apparatus
is absent, and the superior oblique muscle of the eye is destitute of
a pully ; but the smallness of the eye in this order of mammalia,
compared wi th that of fish, bespeaks a higher development of internal
perceptive organs.

In the carnivora the cornea is prominent, the pupil vertically
oval, the thick choroid without pigmentum nigum posteriorly, and
a blue or green tapetum glitters in the bottom of the eye. The
cornea covers half the eye in the rat and porcupine, and is elongated
transversely in the marmot, and generally in ruminants. The
tapetum also exists in the ruminantia, solipeda, pachydermata, and
cetacea. In the dog, wolf, and badger it is white, bordered by blue.
The iris is subject to numerous varieties as regards its colour,
structure, and the shape of the pupil: the latter is of a circular
form in the rodentia, bats, and simise ; transversely oval in the ru-
minantia, solipeda and cetacea ; in these instances the oval form
does not seem to pervade the entire thickness of the iris, but only
its external layer. The retina in carnivora, and many rodentia, as
in some birds, is confined to the posterior half of the eye: in the
former on account of the breadth of the corpus ciliare ; in the
latter on account of the width of the iris.

In the mammalia the eyelids are formed generally as they are in
man, the superior b«ing the larger and more movable, and the
membrana nictitans exist in the entire class, with the exception of
man, apes, and the cetacea. The ornithorhynchus histrix has but
a single circular lid. In addition to the lachrymal gland, which is

ORGANS OF SENSE. 61

found in all mammalia, except the cetacea, the glandula Harden
exists in the carnivora, ruminantia, pachydermata, and some roden-
tia. Instead of puncta lachrymalia, the hare and rabbit have a slit
opening into the nasal duct ; the eye is moved by four recti and
two oblique muscles, and in many of the genus felis the superior
oblique is perforated by the rectus superior : the inferior oblique
has the same relation to the inferior rectus in the tiger, though not
in the lion. All the muscles of the eye are said to be wanting in
those animals in which the organ is in a rudimentary state.

Hearing. — When we consider the many services arising from
this sense, such as indicating the approach of danger, conducting
predaceous animals to their prey, the bringing together the two sexes,
(fee, we should expect to find, as we really do, an organ of hearing
in almost every division of the animal kingdom. In the radiated
division of animals no distinct acoustic organs have been detected ;
it is probable, however, that the undulations produced by the per-
cussion of outward bodies in the media in which these low creatures
reside, produce some impression, though feeble it may be, upon the
general surface of their bodies. It is not till we ascend in the scale
as high as the active air breathing insects of the articulata that we
meet with special organs appropriated to this sense ; and here they
consist of auditory nerve, vestibule, and two rudimentary semicir-
cular canals. In many of the inferior torpid mollusca there do not
seem to be any particular organs devoted to the perception of sound,
but in the higher cephalopods which approach the nearest to fish
in their general characters, the organs of hearing present a similar
degree of complexity.

Fishes, like the cephalopodous mollusca, receive their acoustic
impression by undulations through the dense medium surrounding
them, and in the lowest cartilaginous species, as the lamprey, the
organ consists of a simple vestibule, and three membranous semi-
circular canals, separated from the cavity of the skull merely by
dura mater. In the bony fishes the vestibule and semicircular
canals are highly developed, fenestra ovalis appears, and by and by
a rudimentary cochlea and tympanum without air are seen ; in the
cavity of the vestibule two or three small bodies are found, soft and
pulpy in the cartilaginous fishes, but of a stony hardness in the
osseous kind, and composed of carbonate of lime.

In the aquatic amphibia and in the tadpole state of the reptiliform
species, the organ of hearing possesses a near affinity to that of
fishes ; it consists of the vestibular cavity containing its cretaceous
bodies, the membranous semicircular canals, and fenestra ovalis
closed by stapes, all contained in a cavity of the temporal bone, and
covered externally by the common integument. But in the adult
state of the frog and salamander the apparatus is more complicated,
the semicircular canals are lodged in the temporal bone ; the tym-
panum is closed by membrana tympani, contains three ossicula
united, and communicates with the fauces by a Eustachian tube.

The reptiles present a higher development of acoustic organs ; in

serpents, however, they closoly resemble the caduci-branchiate am-
phibia, and by their vestibular saculus, containing solid cretaceous
bodies, they resemble the osseous fishes. The cavity of the tym-
panum is larger in the saurian than in the ophidian reptiles. As
we ascend to the higher orders, we meet with a cochlea, which is
the last part of the internal ear that attains perfection, slightly cnrved
and divided into a scala tympani and scala vestibuli.

In birds the organ of hearing resembles that of the crocodile ;
there is no cartilaginous external ear, and but a rudimentary concha,
which, however, is compensated for, especially in rapacious birds,
by a peculiar arrangement of feathers around the external meatus,
which in general they can erect at will so as to catch distant sounds,
and by that means either flee from danger, or pursue their prey
through dark and gloomy places. The external ear of owls is fur-
nished with a crescentic fold of integument in the form of a valve.
The oval tympanum, surrounded by bone, communicates with the
air-cells of the cranium by three large openings, and with the
fauces by two short wide Eustachian tubes which open by a single
orifice in the swan at the back of the posterior nares. There is but
one bone in the tympanum analogous to the stapes, with processes
rudimentary of the malleus and incus, and moved by a single tensor
muscle, which comes from the occiput and increases the convexity
of the membrana tympani by drawing it outwards. The cochlea,
though more developed than in reptiles, has not yet reached perfec-
tion, and the other parts of the internal ear present no remarkable
peculiarities different from the inferior grades of the next class.

In the mnmmalia, generally, the organ of hearing is distinguished
by the development of a true cochlea ; by an increased number of
auditory hones ; by the formation of external canal, and by the
addition of an external movable ear. We will meet, however, with
evident, though gradual, transitions from the simple state of organ
already seen in the inferior classes, up to man, where it has attained
its most complex and perfect condition. The concha is very small
in otarite, beavers, and otters, and wholly absent in the cetacea,
seals, walruses, the mole, the manis, and the ornithorhynchus. The
aquatic shrew and other mammalia which frequently go into the
water, form an approach to the crocodlile in having the external
auditory opening furnished with a valve. This external orifice in
the dolphin is merely large enough to admit a pin, and from it a
long narrow winding passage leads to the tympanum through the
fat which lies under the skin. As we ascend through the mam-
malia, residing more exclusively on the land, the concha acquires
greater size, and by the development of cartilage and powerful
muscles it becomes to enjoy very free and varied motions. It is
large, movable, and directed backwards in the ruminantia, pachy-
dermata, cheiroptera; and especially in the timid and feeble rodentia ;
and in the carnivora it is small and inclined forwards.

The cavity of the tympanum communicates with the mastoid cells,
contains four movable ossicula and three distinct muscles ; it is

ORGANS OF SENSE. 63

closed by a raembrana tympani, which is concave externally, except
in the whale. In the ornithorhynchus, which in so many points of
view constitutes the connecting link between reptiles and the higher
classes of animals, the external passage is long and singularly tor-
tuous, the ossicula auditus anchylosed, the cochlea represents a
curved horn, as in birds and reptiles, and the semicircular canals
project into the cranium. The Eustachian tube is wide in the ceta-
cea, it opens at the blowing hole, where it is furnished with a valve;
the cochlea is short and convoluted in one plane in the cetacea, long,
narrow, and spiral in the rodentia, and in the guinea-pig, porcupine,
and aguti, it forms three turns and a half; the other essential parts
of the labyrinth agree on the whole with those of the human
subject.

Smell. — No organs subservient to this sense have been detected
in the cyclo-neurose animals, but in the annelidesof the diplo-neura,
the sense is said to reside in the parietes of their mouths, or the pores
of their air-sacs, and in the palpi, and autennag of insects. The
entrance to the respiratory passages, the sensitive tentacula, and
even the whole surface of the body in the higher orders of the mol-
lusea, are capable of receiving odorous impressions. The lami-
nated organs of smell in fishes are placed in two small depressions on
the anterior part of the face ; they are protected by cartilage, lined
by a delicate mucous membrane disposed in radiated folds in the
pike: tufted in the cyprinus, and arranged like the barbs of a quill
in the carp, ray, and shark. These cavities have no communication
with the mouth or pharynx ; they are closed in front by a valve
formed of skin and cartilage, and a similar structure partly divides
each into two.

In the perennibranchiate amphibia, as the proteus and siren, the
organs of smell in every respect resemble those of fishes, and in the
more highly developed genera, as frogs and salamanders, they
approach in characters to those of reptiles. The nostrils are partly
cartilaginous, partly osseous, and open into the cavity of the mouth.
The olfactory nerves enter by two foramina in the ethmoid bone,
and are distributed to every part of the soft pituitary membrane. In
serpents the nasal cavities present rudimentary turbinated bones,
and open posteriorly by a single orifice. The turbinated bones are
larger and more curved in the sauna, and in the chelonia the olfac-
tory surface is greatly extended and concealed by a strong osseous
covering.

In birds the external nostrils vary much as to size, shape, and
situation, they are generally free and wide, but in some instances
very small, as in the heron and gannet. The septum narium is
partly bony, partly cartilaginous, and covered by a highly vascular
pituitary membrane in the swan. The nasal cavities in birds con-
tain three turbinated bones and open separately into the pharynx,
except in the cormorant, where they join previous to their opening.
The olfactory nerves are distributed exclusively to the membrane
covering the septum narium and superior spongy bone. It is gene-

64 EVERS'S COMPARATIVE ANATOMY.

rally supposed that birds of prey are gifted with an acute sense of
smell, but the experiments of Mr Audubon go to prove the reverse
opinion ; and according to the researches of Scarpa, the following is
the order in which it is enjoyed, beginning with those in which it
is most acute ; grallatores, natatores, raptor es, scansores, inses-
sores, rasores.

The organs of smell in the mammalia are distinguished by the
more perfect formation of external nose, by the large size of the
nasal cavities, and by the latter receiving several new openings,
such as the frontal, nasal, ethmoidal, sphenoidal, and maxillary
sinuses. The external openings are valvular in the beavers, seals,
and camels, and variously modified in other animals, according to
their different habits, as in the hog, elephant, &c. The turbinated
bones are long and simple in the rodentia, ruminanlia, and pachy-
dermata, and they form a complicated series of labyrinths in the
carnivorous tribes, where an acute sense is so necessary to enable
them to pursue their prey through their dark retreats. The large
olfactory nerves pass through the numerous openings of the cribri-
form plate, except in the cetacea, to be distributed on the surface of the
turbinated bones. These nerves are large and hollow in the human
foetus, like the olfactory tubercles of quadrupeds, and it is interest-
ing to observe how the sense of smell preponderates over all others
in the new born child, this can be easily tested during the nuzzling
of the infant at the mother's breast, when the loudest sounds may
assail its ears without effect, and when its visual powers are limited
to the mere perception of intense light.

Taste. — A considerable degree of obscurity prevails, respecting
the enjoyment of this sense in the different classes of animals, and
although we cannot display any organ especially appropriated to it
in the inferior tribes of animals, yet it is supposed that all enjoy it,
from the polygastric animalcules up to man. It is generally seated
in, but by no means confined to the tongue, this organ being absent
in some instances even in the human subject, where the existence
of the sense has been proved; and in other cases, where the tongue
does exist, its dense horny nature excludes it from such an enjoy-
ment. The form of the tongue differs considerably in different
animals; in none, not even in the simiae, is it exactly like that of
man. In the cephalopoda distinct gustatory villi cover its surface ;
in many fishes it has no papillae, and in others it is set with teeth ;
in the chameleon it is an organ of very peculiar mechanism, and
admits of being protruded for several inches in pursuit of prey, with
amazing celerity and precision. This power, for a long period a
paradox with naturalists was discovered by Dr. Houston to be of an
erectile nature. In birds it serves chiefly as an organ of prehension,
in a few only does it possess papillae, being generally sheathed in
front by horn. With few exceptions among the edentata, the
tongue in the mammalia serves as an organ of taste. In the bisulca
it is covered with a thick epithelium ; in the bat, the opossum, and

ORGANS OF SENSE. 65

especially the lion, and others of the cat kind, it is beset with strong
sharp prickles, for prehensile purposes.

Touch. — This is the most general as well as the most simple of
the senses, and the degree in which it exists has reference to the
state of the tegnmentary membrane, and I he condition of the nervous
system. In the invertebrata no organs solely devoted to the per-
ception of sensitive impressions have been detected, yet there is little
doubt but that the cilia of most poly wastries, the ten taenia of zoo-
phytes and mollusca, and the antennas of ray ri a pods and insects are
subservient to this sense. Some fishes have fleshy sensitive fila-
ments arranged around the month after the manner of ten taenia,
and others have only the skin on the abdomen, or about the mouth,
uncovered with scales, and capable of receiving- external impres-
sions. The tongue among serpents, and the tail among saurian
reptiles, and some mammalia, constitute their chief tactile organs.
The organs of touch in birds are the bills, the cire in the falconidce
the wattles of the cock, and the caruncles of the turkey. It must
be acknowledged, however, that this sense is very limited in birds,
which is in some degree compensated for by the free distribution of
the fifth pair of nerves to their horny bills, especially those of the
aquatic species, which procure their aliment from mud.

In many of the mammalia the skin is shielded from external im-
pressions by the presence of horny or spiny coverings, dense furs.
or thick hides; and it is not till we arrive at the higher orders of
quadrupeds, carnivora and quadrumana, that the organ of touch
makes any approach to the perfect development of it observed in
the human subject.

RECAPITULATION.

1. Organs of vision exist in every class of animals, and in the
lowest orders the eyes vary in number from one to near 100.

2. In the vertebrata the eyes are two and vary much in form and
situation.

3. No organs of hearing or smell have been detected in the
radiata.

4. Our knowledge concerning the organ of taste is involved in
much obscurity.

5. No organ of touch has been detected in the invertebrata.

CHAPTER. X

ORGANS OF DIGESTION IN THE INVERTEBRATA.

General observations. — The organs engaged in the function of
digestion may be arranged under two heads: the primary, or
8 — f evers 5

66 EVERS'S COMPARATIVE ANATOMY.

essential — including the alimentary tract; and the secondary, or
tributary, embracing the liver, spleen, pancreas, salivary, and
mucous glands.

There is no organ so universally present, nor so essential, as an
internal digestive cavity, and hence so often alluded to as consti-
tuting a line of distinction between the animal and the vegetable
kingdoms ; indeed there is no class of animals without it, although
it is not found in every species of each class. The peculiarities
presented by the digestive apparatus will vary according to the
rank an animal holds in the scale of the creation, the kind of food
on which it is destined to subsist, and the elaboration that food
may require to undergo. The alimentary surface of a plant is the
exterior of its root spread out in the earth, and absorbing, by its
spongioles, the materials for its nutrition, but the alimentary surface
of an animal is internal, and continued from the skin, like the in-
side of a lady's muff.

Cyclo-neura, Grant — Radiata, Cuvier. — In the very low
tribes of animals the digestive apparatus presents characters equally
diversified as the forms of the creatures themselves. The aliment-
ary cavity has often but one orifice; there are seldom teeth or
glandular organs, and the food is generally of the simplest sort. In
the polygastrica, as the term signifies, the cavities are numerous,
and their various forms have been well observed by Ehrenberg,
who caused these transparent animalcules to swallow fluids coloured
with carmine, indigo, or sap-green. The monads and several other
genera have but one orifice which receives the openings of the several
cavities, and from the absence of intestine the entire group has been
named anentera. in the higher forms, however, the alimentary
canal is furnished with an oral and an anal orifice, the straight,
curved, or spinal intestine receives the openings of numerous ccecal
appendices through its whole course. In some of the small monads
no internal cavity has been detected, and in other genera the num-
ber varies from one up to two hundred, as seen in a paramascium.
Many species are provided with dental organs in the form of stiff
spines disposed around the mouth, but in none of the class have
tributary or glandular organs been observed.

The porifera present a very simple form of alimentary appa-
ratus, their absorbent canals closely resembling the ramified roots
of plants, and as we ascend through the diversified series of the
polypifera or zoophytes we perceive the system increasing in com-
plexity from the simple genito-digestive sac of the hydra up to the
complicated structure presented by the actiniform polypi, where the
stomach is provided with a muscular and mucous tunic lined with,
vibralile cilia, and communicates inferiorly with the genital cavities.
The greater number of the acalepha possess a simple broad and
radiated alimentary cavity, suited to their highly organised and
minutely divided food, but in the monostomatous species, which
live on coarser aliment, a cartilaginous masticatory apparatus and
biliary secretion are superadded. The torpid predaceous echino-

ORGANS OF DIGESTION IN THE INVERTEBRATA. 67

dermata afford in the structure of their digestive organs, connecting
links of transition from the radiated to the articulated classes. In
the higher forms of the echinida strong masticating and salivary-
organs are provided, the anal orifice, which in the lower tribes is
placed on the inferior surface, gains a dorsal aspect, which it con-
tinues to hold in the holothuriae and articulated classes. Thus we
perceive the digestive cavity, from being a simple monostome sac,
gradually acquires the form of a long narrow canal, open at both
ends, and furnished with salivary and biliary organs.

Diplo-neura, Grant — Articulate Cuvier. — The carnivorous
character of this great division of the animal kingdom bespeaks an
alimentary canal, limited in its capacity, straight in its form, and
simple in its structure. This canal usually takes a horizontal
direction, opens at the two opposite extremities of the body, and is
provided at its commencement with prehensile, destructive, or mas-
ticating organs. In consequence of the simple nature of the food
on which the entozoa subsist, many of them have but a single orifice
to their digestive sac. In the higher and more perfect forms, how-
ever, of these as well as of the rotifer a, the canal passes straight
or slightly winding through the body, presenting an oral and anal
aperture, and surrounded by the genital and biliary organs. The
cirrhopoda are remarkable for the great size of their salivary and
biliary apparatus, and the wide ducts of the latter, which open into
the stomach, as in most of the invertebrated tribes.

Among the annelida the earth-worm is remarkable for its capa-
cious mouth, a small salivary gland, a sacculated stomach, consist-
ing of three continuous cavities, and a narrow, slightly bending
intestine. The leech has three horny maxillae, furnished with sharp
teeth, with which it inflicts its tri-radiate wound, the straight, irre-
gularly sacculated intestine is furnished with ten pairs of lateral
coeca, and enlarges into a small sac near ihe anus. The carnivo-
rous rnyriapods are provided with three pairs of salivary and two
poison-glands, by their contracted oesophagus and elongated mem-
branous stomach, they resemble the higher species of worms, and
by their small, narrow intestine, ending in a wide colon, they are
allied to the ophidian reptiles.

The digestive organs of the insecta present in an embryo state
nearly all the essential elements of the chylo-poietic system in the
highest classes of animals, as masticating organs, salivary and
mucous glands, liver, pancreas, &c. : they will be found to vary,
however, according to the peculiar living habits of the species, and
the quality of their food. The alimentary canal usually consists
of a wide pharynx, a narrow oesophagus, a dilated crop, a muscular
gizzard, provided with sharp, conical, horny teeth, a capacious chy-
lific stomach, a straight, narrow intestine, a short, dilated colon,
and a contracted cloaca. In the herbivorous insects, the alimentary
canal is long, capacious, and complicated. The gall-bladder is
usually single, but occasionally double. The cunning carnivo-
rous aracknida resemble the insects in the arrangement of their

masticating organs, whilst their straight narrow alimentary canal
and the compact state of their liver, ally them to the Crustacea.

Like most other carnivorous articulata, the cunning, cruel,
aqautic crustaceans are provided with prehensile and masticating
organs well suited to destroy the prey in the rich element they in-
habit. The maxillae vary from one to five pairs, but are wanting
in the lower orders. The alimentary canal is generally without
convolutions, and opens by two apertures. The decapods present
a narrow oesophagus, leading to a capacious muscular stomach,
furnished with numerous solid calcarious teeth, and a straight in-
testine occupying the dorsal portion of the trunk, and receiving-
near its commencement the biliary and pancreatic ducts. The
salivary glands are absent except in the higher orders, where rudi-
ments of them are perceived surrounding the oesophagus. The
mucous membrane forms rugae in the oesophagus and stomach,
but not in the intestine, and the peritoneum ibrms no mesentery.

Cyclo-gangliata, Grant — Mblluscq, Cuvier. — This great divi-
sion of the animal kingdom being destined chiefly to subsist on
soft food, masticating organs are little required by them, hence they
are often but sliohtly developed, and in some cases wholly absent.
But their food is greatly varied and often coarse, so as to require a
complicated form of alimentary canal, and a high development of
glandular apparatus. The digestive organs of the tunica t a closely
resemble those of the conchifcra, being a little more complicated in
the latter. Both are destitute of prehensile or masticating organs,
and depend for their supply of food on the respiratory currents.
They possess a short wide oesophagus, opening into a capacious
muscular stomach, without teeth, and receiving the biliary ducts.
The intestine is generally short, wide, and convoluted. The con-
chifera differ from the tunicata by their long and convoluted intes-
tine passing between the two aorta?, through the fleshy substance
of the ventricle, and the mass of the liver. The terrestrial pulmo-
nated gasieropnds present a more complicated digestive apparatus
than the acephalous mollusca, especially those which feed on vege-
table substances. They are provided with a pair of horny jaws, a
muscular tongue and proboscis armed with sharp recurved spines, a
large pharynx, a long oesophagus, and a capacious stomach, divided
in the phytophagous species, into several compartments, fur-
nished internally with teeth, and receiving the biliary and pancre-
atic secretions. One or two pairs of salivary glands lie around the
oesophagus, and the liver is of considerable size. The intestine
is long and convoluted, and opens in common with the genital or-
gans on the right side, near the anterior extremity of the body. In
the pteropods and cephahpods, the oesophagus passes through the
cranial cartilage and ganglionic ring, sometimes dilating into a
crop before entering the muscular gizzard, which is often lined
with a thick coriaceous epithelium. The intestine is short and
wide in the carnivorous species, destitute of coecum-coli, not dis-
tinguished into large and small as in the vertebrata, and no where

VERTEBRATA. 69

imbedded in the substance of the liver, as in many of the inferior
mollusca. The mollusca are without gall-bladder^ and as yet no
portal circulation has appeared. The entrance of the hepatic duct
into the stomach is guarded by a pair of prominent valves, pro-
longed so into the intestine as to allow of the passage of the pan-
creatic and biliary secretions into the gut during a state of vacuity
without entering the stomach or duodenum.

CHAPTER XI.

VERTEBRATA.

In this great department of the animal world the digestive appa-
ratus presents a higher development and a greater degree of com-
plexity than we have met with before. The alimentary canal
always swells out into a distinct gastric enlargement, and is provided
with a large conglomerate liver, spleen and pancreas. The duode-
num invariably receives the biliary and pancreatic secretions, and
he salivary glands are rarely absent. The teeth are generally
confined to the alveoli, and there are none found in the stomach.
As a general rule the canal is longer, larger and more sacculated,
and the masticating; and glandular apparatus more developed in
the phytophagous than in the carnivorous tribes.

PISCES.

Since vegetable food cannot be procured in the unfathomable
depths of the sea, we are prepared to meet with a short and simple
form of alimentary canal in fishes, suited to their predaceous habits.
Vegetable substances might even endanger their lives by an evolu-
tion of gas which would render them specifically lighter than the
water, and cause them to float upon its surface with the belly up-
wards. The teeth of fishes are generally numerous, destitute of
fangs, laminated, deciduous, thinly covered with enamel, and
movable on the surface to which they adhere, till maturity, when
they become permanently fixed. The teeth of fishes are often
implanted in the tongue as in many gasteropods and birds, in the
vomer as in amphibia, in the palate bones as in serpents, in the
pharyngeal bones, branchial arches and os hyoides, as well as in the
maxillary and inter-maxillary bones to which they are confined in
the saurian reptiles and mammalia; the teeth are most numerous
in the pike and salmon, and are altogether wanting in some genera,
as the sturgeon. As in serpents, crocodiles, dolphins, and other
predaceous non-masticating vertebrata, the teeth are not opposed to
each other but placed alternately, adapting them to their prehensile
office.

The tongue is broad, short, and almost destitute of papillae. The
salivary glands are only rudimentary, and even wanting where the
liver and pancreas are well developed, but the mouth is well sup-
plied with mucus. The short, wide infundibuliform oesophagus
has an external circular, and an internal longitudinal layer of mus-
cular fibres, and is lined with a pale, villous, longitudinally plicated
mucous membrane provided with numerous mucciperous follicles.
The large gastric cavity is sometimes long and tapering as in the
herring, and sometimes globular as in the lophius: its two orifices
are closely approximated, so that the food is retained in it for a long
period, hence, if we feed a tame perch till it is gorged, it will not
eat again for ten or fourteen days ; both orifices of the stomach are
sphinctorial, its mucous membrane is plicated and forms a valve at
the pylorus with a fringed margin, surrounded by a ring of carti-
lage. The intestine, in many cases, does not measure more than
half the length of the body, in others, however, as the sword fish, it
forms several convolutions, but rarely does it admit of any distinc-
tion into large and small. In the sturgeon, ray, and shark the anal
is smaller than the cardiac portion, and the reverse obtains in the
pleuronectes, gadi, murcenae, &c. In order to compensate for the
shortness of the canal and the absence of valvulse conniventes, the
lining membrane is peculiarly disposed, being reticulated in the
sturgeon, forming spiral turns in the shark and ray, and serpentine
folds in the eel. The rectum here as in oviparous vertebrata, ter-
minates in the cloaca through which are discharged feces, urine,
semen, and ova. On either side of the anus there is an oblique
valvular opening, admitting of free egress, but prohibiting any
thing from without, and the air-sac, or rudimentary lung commu-
nicates by a membranous tube with the oesophagus, stomach, or
upper portion of the intestine.

The large elongated liver is of a soft texture, light colour, and
divided into many lobes, it is provided with arterial and portal cir-
culation, and generally with a large gall-bladder as in other pre-
daceous vertebrata. Several long hepatic ducts join the cystic, and
many short ones run at once into the fundus of the gall-bladder,
and the short but wide choledochus either opens separately or in
common with one or more of the pancreatic ducts into the upper
portion of the intestine. The spleen is small, of various forms,
attached to the side of the stomach, generally simple, but lobulated
in the shark and sturgeon, as in some of the cetacea, and in the
lamprey, which has neither pancreas nor gall-bladder, it is wholly
absent, as in the invertebrata. The pancreas which is wanting in
the centriscus, presents every stage of development, from one or
two simple follicles as in the lophius, choetodon, (fee, up to a large,
compact, reniform mass, enveloped in a muscular tunic, as in the
sturgeon and xiphas. The large pancreatic follicles are connected
by loose cellular tissue, and admit the digested food info their in-
terior, like the biliary tubes of some mollusca. The peritoneum
lines the walls of the abdomen, and surrounds the viscera in the same

VERTEBRATA. 71

manner as in snails, and the sepias: it form a small mesentery and
a rudimentary epiploon, and it presents the remarkable peculiarity
of its cavity communicating with the surrounding medium by the
tvyo small openings, placed at the side of the anus.

AMPHIBIA.

These animals, like the fishes, are predaceous in their habits,
and swallow their food without mastication. The whole of them
have prehensile teeth in the palate ; salamanders have them in both
jaws, frogs in the upper only, and the toad and pipa in neither, but
in the toad two small transverse rows exist behind the posterior
nares. The teeth in the proteus nearly resemble those of the sala-
mander, but in the siren they are arranged in a quincunx order as
in many fishes, and amount nearly to two hundred. The salivary
glands are absent in the aquatic, and merely rudimentary in the
terrestrial amphibia. In the toad and perennibranchiate amphibia
the tongue is short, thick, and fleshy, but in the frog it is
long, free, bifid, covered with papillae and mucous follicles, as in
reptiles The short, dilatable, fleshy oesophagus, leads to a narrow,
transversely elongated stomach, muscular in it parietes, and over-
lapped by a large bilobate liver with a distinct gall bladder. In
the young tadpole of the frog the almentary canal is very long, the
intestine which is narrow and coiled, measures ten times the length
of the space from the mouth to the anus, but after the metamorphosis
has occurred, and that the mixed food of the tadpole is changed for
that of a more nutritious nature, as snails, worms, ccc, the canal
becomes gradualy shortened to one fourth of its former length. The
duodenum has transverse folds like valvular conniventes, and the
short, wide colon ends in the cloaca, together with the openings of
the genital and urinary organs. The mucous membrane forms
longitudinal folds in the proteus, the triton, the pipa, and the sala-
mander; transverse folds in the froo-, and quadrangular cells in
the hyla. A small pyloric valve exists in the toad and pipa, and
the valve of the colon is distinct in the frog, the triton, and the
hyla. The liver, the spleen, and the pancreas are found in all the
amphibia, varying in shape according to the form of the animal.
Thus we perceive in the lower orders of amphibia, an evident
approach in their digestive organs to those in fishes, in the great
number of teeth, shortness and width of oesophagus, absence of
fundus to the stomach, want of distinction between large and small
intestine, and the magnitude of the liver. But in many we discover
an approximation to the higher vertebrata, in having fewer teeth,
an elongated tongue, fundus to the gastric cavity, distinction between
large and small intestine, absence of pyloric and colic valves, and
the development of transverse folds in the duodenum.

72 EVERS's COMPARATIVE ANATOMY.

REPTILIA.

The ophidian and saurian reptiles chiefly subsist on animal food,
therefore their digestive apparatus will be found to differ from that
of the chelonia which live on vegetable substances. The teeth of
serpents are sharp, conical, inverted, unopposed, and set in loose,
movable bones, adapted for seizing and lacerating their prey, they
are attached to the maxillary, inter-maxillary, sphenoid, and palate
bones, and the poison fangs of the venomous species are perforated
and grooved in front to transmit, the secretion of the poison gland
forced out by muscular pressure. The tongue is long, smooth,
sheathed, and bifurcated. The salivary glands vary in the differ-
ent species; the sublingual is always present, and the poison gland,
which is analogous to the parrotid, is confined to the noxious spe-
cies, and is placed below and behind each orbit. The long, disten-
sible oesophagus, copiously supplied with mucus, leads to the long,
straight, capacious stomach, longitudinally plicated and capable of
being distended to many times the size of the body ; it tapers to the
pyloric orifice, which is provided with a distinct valve, and embraced
by sphinctorial fibres. The duodenum presents a villious surface,
and receives the pancreatic and biliary ducts; the remainder of the
small intestine is narrow and convoluted to the commencement of
the short, dilated colon, where there is generally a circular valve
and a small coecum. The colon ends in the cloaca together with
the ureters, oviducts, or vasa deferentia, and the male organ of
generation, single or divided, also passes through the cloaca, as in
other oviparous vertebrata. The liver, spleen, pancreas, the kid-
neys, the testes, and the ovaria present an elongated form conform-
able to the shape of the body. The small intestines are attached
to a mesentery, and the large are often sacculated for the purpose
of retarding the passage of the food.

As most of the sauria are carnivorous like the ophidia, they pre-
sent a form of alimentary apparatus equally simple. Their prehen-
sile teeth are fewer and chiefly restricted to the jaws; the stomach
is short and round in the form of a gizzard, with a pair of central
tendons ; the small intestine is long in the phytophagous species
as the scincus and iguana, and in all other respects they resemble
the ophidian reptiles.

The phytophagous chelonia present a higher development of
alimentary canal than the carnivorous species. The place of teeth
is supplied by the sharp horny margins of the jaws ; the tongue is
covered with long papilla?; and the salivary glands are variously
developed in the different species. The long, wide, muscular oeso-
phagus leads to a large fleshy stomach, extended transversely, and
without a pyloric valve. The intestine is about six times the length
of the body, and the colon presents a short, wide coecum, and a
circular valve at its commencement in the terrestrial, but not in the
aquatic species. The alimentary canal is wide and muscular, and

VERTEBRATA. 73

the mucous membrane folded longitudinally so as to form a surface
of considerable extent. The rectum dilates into a cloaca which
receives the openings of the urinary and genital organs.

AVES.

Nothing can be more beautiful to observe than the rigid economy
which is displayed in the accurate adaptation of the digestive
apparatus of birds to the various and dissimilar kinds of iood on
which, from their diversified living habits they are destined to subsist.
The absence of teeth in this class is supplied by strong horny
beaks and powerful muscular gizzards, the former performing the
part of cutting, and the latter of grinding teeth ; the form of the
bill will vary according to the food of the different species of birds
and their mode of procuring it, thus in the climbing frugivorous
maccaws, parrots, and cockatoos, it is broad and powerful to break
the hard shelly coverings of seeds, and most of the granivorous
order have a similar structure. The broad bills of ducks, geese,
and other aquatic species are well adapted for obtaining worms and
other substances from watery or muddy situations, whilst the eagle,
the hawk, the owl, and other rapacious birds have short, strong,
arched, dense bills, with cutting edges, equally suited to seize, cut,
or tear their living prey. The tongue, which in birds serves the
purpose of a prehensile organ, is as variable in form as the bills,
being long, broad, and covered with recurved spines in the swans;
short, round, and flexible in the parrots and cockatoos, and short
and muscular in the struthious birds. The tongue of the flamingo
is very remarkable, it is composed of an elastic, cellulo-fatty sub-
stance, its form is nearly cylindrical, the pointed apex being sup-
ported by an osseous plate iuferiorly. A deep groove runs along
the centre of the upper surface with a row of recurved spines on
either side. The os hyoides in this class very much resembles that
of reptiles, and the length of its glosso-hyal element chiefly deter-
mines the length of the tongue.

Since the food for birds remains but a short time in the mouth
and undergoes very little change there, their salivary glands are
small. In the crow they consist of a series of conical follicles
situated along the sides of the mouth, and opening separately on
its mucous surface; in most other birds, however, there are four
pairs, one under the tongue, another at the junction of the angles
of the lower jaw, another close to the cornua of the os hyoides, and
the fourth is placed at the angles of the mouth: they are most
developed in the frugivorous species. The uvula and velum are
not present, and the narrow laryngeal aperture is protected by the
retroverted papillae at the base of the tongue, except in the coot, the
albatross, and a few others where the epiglottis exists merely in a
rudimentary form quite insufficient to cover the opening.

There is a remarkable pouch under the jaw of the pelican which
serves as a net for seizing fish, and is capable of containing ten

VE ANATOMY.

quarts of water; a similar provision is found in the swift, the rook,
the male bustard at maturity, and other insectivorous birds. The
alimentary canal is much longer and more capacious, and the glan-
dular apparatus better developed in the phytophagous birds than
in those which subsist more exclusively on animal food. The long,
wide, fleshy oesophagus, with a cuticular lining-, passes down
behind and to the right side of the trachea, behind the heart
and between the lungs. In rapacious birds it is capable of enor-
mous dilatation, but in the flamingo its diameter does not exceed
half an inch. In the frugivorous, insectivorous, and omnivorous
birds, the oesophagus presents nearly a uniform capacity all through,
but in the raptorial eagles and vultures, which gorge themselves at
uncertain periods, it forms a lateral dilatation at the lower part of
the neck termed the ingluvies or crop. And in those birds which
live exclusively on, and require to take a large quantity of vegetable
food, the crop is large, globular or oval, single in the common fowl,
and double in the pigeon ; it is altogether wanting in the swan and
goose. The oesophagus and crop are supplied with an abundant
mucous secretion, and are provided with an external circular and
an internal longitudinal set of muscular fibres, the reverse of the
disposition observed in the human subject. Mr. Hunter has re-
corded in his animal economy, some interesting observations on
the crop of the pigeon, from which it appears that this macerating
paunch takes on a secreting function during the breeding season,
and supplies the young pigeons with an abundance of milk, a diet
suitable to their tender a^e, and the analogy of the pigeon's milk to
that of the mammalia has not escaped popular notice.

That part of the oesophagus which extends from the crop to the
gizzard, was called by Mr. Hunter the lower oesophagus ; at its in-
ferior part, just above the gizzard, it dilates into the glandular divi-
sion of the stomach, variously termed the jjroventriculus, ventri-
cular succenturiatus, bulbus glandulosus, echinus, infundibulum.
In the omnivorous and piscivorous tribes there is no perceptible
dilatation here, but in all it presents increased vascularity as it is
provided with a number of glands which secrete a fluid analogous
to the gastric juice. Beneath the infunbulum is the powerful
muscular gizzard directed transversely like the stomach of the
vertebrita, overlapped by the lobes of the liver, and lined internally
with a thick, dense epithelium. At the upper part of the gizzard
are two openings, one large, to the left side, and communicating
with the proventriculus, the other smaller, and a little to the right,
leads into the duodenum. In those birds which feed on grain and
other hard substances, the muscular fibres of the gizzard are dis-
tinguished by their density and red colour, they are arranged in
four masses, two lateral, called the digastric muscles, and connected
to anterior and posterior tendons, and two smaller ones between
these, at the end of the gizzard, termed musculi intermedii. In
rapacious and carnivorous birds the parietes of the gizzard are thin
and membranous, yet distinctly presenting the anterior and posterior

VERTEBRATA. 75

tendons. The gallinaceous birds, in which the gizzard is most
powerful, swallow pebbles and other hard bodies, which serve the
purpose of reducing their food, like the gastric teeth of crustacea,
insects, and gasteropods ; but in the carnivorous birds, with a thin
membranous gizzard, no such substances are required, all the neces-
sary changes being effected by the activity of the gastric secretions.
The parietes of this organ are subservient in a remarkable manner
to a known law, to which the whole muscular system yields, that
of increasing its growth in proportion to the functions imposed on
it; this was strikingly illustrated in the case of a sea-gull, which
Mr. Hunter kept for a year, living, contrary to its nature, upon grain.
At the end of that period he contrasted its gizzard with that of
another sea gull, which had been living on fish, and found that the
digastric muscles of the former had acquired nearly three times the
development of the latter. He accomplished similar phenomena by-
changing the food of an eagle and of a tame kite, the former throve
very well on bread, but that it was dissatisfied with its fare, is to be
inferred from its seizing the earliest opportunity of breaking its
chain, and effecting its escape. These facts show in a clear manner
the provision of nature for the preservation of life under a variety
of circumstances.

The intestine is shorter in birds than in mammalia, its different
divisions are better marked than in the lower classes, and in the young
bird a remnant of the entrance of the vesicula umbilicalis may be
seen on the interior part of the small intestine in the form of a
small ccecal appendage, and in many gallinaceous and some aquatic
birds it remains through life. The course of the small intestine
varies much in the different orders of birds; the duodenum always
makes a long fold, which embraces the long, bilobate pancreas in
its concavity. The large intestine is about a tenth part of the
length of the body, and usually has two coeca at its commencement,
except in the bustard and ostrich, it runs a straight course from
the cceca to the cloaca ; it is generally a little larger than the small
intestine, and its villi are shorter, coarser, and fewer. The coeca
coli are of great size in the gallinaceous and other granivorous
birds, where they arise by two narrow canals, and enlarge into
wide sacs, often several times the size of the intestine, as in the
turkey. In the ostrich they have the mucous membrane disposed
in the form of a spiral fold. They are least developed in the gral-
latores and the nocturnal rapacious birds. In the herons and several
other birds there is but one, as in the invertebrate and lower ver-
tebrate animals, and as in the plantigrade carnivora, they are alto-
gether wanting in the zygodactylous birds.

The rectum terminates by a round valvular orifice in a dilatable
cavity, the upper part of the cloaca, which is the remains of the
allantois, and now forms a rudimental urinary bladder, and in the
ostrich it serves for the retention of the urine as in the higher
viviparous animals. At the lower and back part of this urinal por-

76 EVERs's COMPARATIVE ANATOMY.

tion of the cloaca are the openings of the ureters, and external to
these, the openings of the oviducts, or vasa deferentia.

To this urethro-sexual canal, succeeds the preputial cavity, or
lower portion of the cloaca, which lodges the organs of excitement,
clitoris or penis, as in reptiles, marsupial, and monotrematous mam-
malia. In the median plain, and on the dorsal aspect of the prepu-
tial cavity is the opening of a conical sac, named Barsa Fibricii,
which lodge's the anal follicles, and is analogous to Cowper's glands.

The liver is large in birds, especially in the aquatic species, it
generally consists of two lobes, but occasionally of three, as in the
pigeon, goose, and swan ; the right lobe is usually larger than the
left, the latter, however, is larger in the bustard, where it extends
into the pelvis. The bile is discharged by two ducts, one goes
directly to the duodenum, the other to the gall-bladder, and when
the latter is absent, they both open separately into the duodenum,
but in no case is there a ductus choledochus. The pancreas, long,
narrow, and trihedral, is lodged in the fold of the duodenum, its
ducts are two, sometimes three in number, as in the pigeon, raven,
and common fowl, and they terminate separately in the duodenum.
The small, round, oval, flat, or elongated spleen is placed beneath
the liver, and to the right of the proventriculus; its texture is loose,
and the blood would seem to be deposited in cells, from which the
veins take it up.

When we contemplate the different lengths and forms of intestine
met with in this class, we cannot help attributing it to some wise
purpose, and a little reflection on the greatly diversified nature of
the food on which the various tribes of birds are destined to subsist,
irresistibly leads us to infer that economy seems to be the main
design ; for instance, the colon and coeca of the African ostrich,
which has to subsist on the scanty and uncertain fare of the desert,
are fifty times the length of the same parts in the cassowary, which
inhabits Java, one of the most fertile countries on the globe.

MAMMALIA.

The digestive organs vary more in this than in any other of the
vertebrated classes, and the varieties will be found to refer chiefly
to the type of development and living habits of the sundry species.
The teeth present infinite varieties as to form and position ; however,
their density and fixedness are well calculated to disintegrate ali-
mentary substances, and blend them with the mucous and salivary
secretions. The teeth are wanting in the ant-eaters, pangolins, and
the whalebone whale. The young ornithorhynchus paradoxus has
two molar teeth in each jaw on each side: these are shed in the
adult animal, and replaced by one large one on each side. But in
the hystrix there are twenty small, blunt, horny teeth, near the base
of the tongue, and seven transverse rows in the corresponding sur-
face of the palate. The incisor, canine, and molar teeth exist in
the quadrumana. carnivora, ruminantia, without horns, and in most

VERTEBRATA. 77

of the pachydermata ; but it is only in the extinct anoplotherium
among mammalia, that the three kinds of teeth are arranged
in an uninterrupted series, as in man. The superior incisors are
wanting in the ruminantia, and the inferior in the walrus. The
Ethiopian hog and certain bats lose their incisors at a particular
age. The canine teeth are absent in the rodentia, some ruminants,
and in most of the female solipeda. The rodentia have but two
incisors in each jaw, with the exception of the hare and rabbit,
which have them double in the upper jaw; the kangaroo has two
below and eight above ; the daman two above and four below. The
molar teeth are the most essential, and are the last to disappear:
hence the ornithorhynchus paradoxus, the tatu, and the two-horned
rhinoceros, are restricted to them. The molar teeth are renewed
eight times in the elephant, the incisors are shed twice in many
rodentia ; and most of the teeth are renewed once in the other
orders of the mammalia. In most mammalia which feed on animal
substances, the crowns of the teeth are entirely covered with enamel,
and only partially so in the phytophagous quadrupeds.

The following is an outline of the process by which the teeth
are produced. About two months after conception, a gelatinous
substance lies alonsf each alveolar arch: at 'the third month this
substance is firmer, and lodged in a shallow groove in the bone. It
is next divided into separate pulps by transverse filaments passing
from one side of the alveolous to the other. These pulps are en-
closed in, and connected by vessels to a thin vascular membrane,
which, between the third and fourth month begins to secrete the
ossific laminae from its outer surface. This membrane, with its
contained pulp, is supplied from the dental vessels, and nerves, and
is surrounded by a thick vascular sac, separable into two layers ;
• he latter membrane is attached to the pulp only at its base, but is
firmly connected by its outer layer to the gum, from which it derives
its vascular and nervous supplies. It is from the inner surface of
the internal layer of this sac that the enamel is secreted, and at
this period it becomes thick and vascular, whilst the outer layer,
which is only rudimentary in man, secretes the crusta petrosa in
the graminivorous quadrupeds. After the enamel has been secreted,
both layers of this sac become wholly absorbed, hence they have
been termed the deciduous membranes, in contra-distincti< n to the
permanent, which are described as three in number, one being the
periosteum of the alveolus, another the periosteum of the root,
and the third the periosteum of the dental cavity, which secreted
the tooth. But in fact these three permanent membranes are simply
a continuation of the periosteum of the jaw which first lines the
alveolus, then descends, to form the periosteum of the root, and
lastly passes up in the form of a hollow cone to enclose the pulp.
The period at which the teeth appear in the human subject is very
variable, some children being born with two or more, whilst in
others they may not appear for two or even three years. From five
to eight months, however, is the most usual period ; they generally

appear first in the lower jaw, and proceed in the following order : —
From 5 to 8 months, the four central incisors; from 7 to 10, the
lateral incisors; from 12 to 16, the four anterior molars ; from 14
to 20, the four cuspidati ; and from 18 to 36 months, the four pos-
terior molars.

The purposes of prehension are accomplished by sensitive fleshy
lips, as in herbivorous quadrupeds, by a long, flexible tongue, as in
the giraffe and ant-eaters, and by other organs such as the proboscis
of the elephant. The salivary glands are largest in herbivorous
quadrupeds, less in the carnivora, and least in the aquatic mamma-
lia. The sublingual glands are wanting in cats. The velum palati
is large, but the uvula is confined to the quadrumana. The os
hyoides, is most developed in the herbivorous quadrupeds, and has
been shown by Geoffroy to consist of twelve elements, a glosso and
basi-hyal piece for the body, an apo a cerato, and a styl-hyal ele-
ment tor each of the anterior corn u a, and an ento and uro-hyal for
each of the smaller posterior cornua. This condition is sometimes
found as an abnormal state in man. The oesophagus is wide and
dilatable in the carnivora, and narrow and fleshy in the herbivora.
The arrangement of its muscular fibres is the same as in man ; and
its mucous tunic, wh'ich usually forms longitudinal and but rarely
transverse folds, is lined with cuticle, which in the carnivora termi-
nates at the cardiac orifice in a fringed margin, but lines half the
stomach of the horse, the rat, the hog, and some others of the pecora,
and in the ruminantia it lines the three first cavities of the stomach.
The oesophagus of the ornithorynchus hystrix is furnished with a
peculiar valve at its commencement, and numerous papillse at its
termination, directed upwards, and its cuticular lining is continued
through the stomach.

The animal nature of the food of the carnivora bespeaks a short
and simple form of alimentary canal. In some, as the lion and the
cat, the stomach is elongated in form, and its orifices remote from
each other, this is particularly the case in the lynx; in others, as
the racoon, it is nearly globular, and in all, with the exception of
the seal, its interior is smooth, and almost without villi. The
monotremata, cheiroptera, insectivora, and marsupialia, also present
a simple stomach, a coecal portion being but little developed.
When, however, the food is of a more mixed character, the stomach
becomes more elongated transversely, as in the quadrumana and
others of the less carnivorous tribes. In most of the rodentia the
thin cardiac portion forms a distinct coecum, and is separated by a
constriction from the pyloric muscular portion. Several of the
pachydermata, marsupialia, edentata, and quadrumana, form a link
of transition to the more complex stomachs of the cetacea and
ruminantia in the formation of folds or coeca with cuticular linings.
Thy intestinal canal is very short in these animals, the whole tract
not exceeding three times the length of the body in the lion and
wild cat. In the badger there is scarcely any distinction between
small and large intestine: but in the lion, seal, and others, it is well

VERTEBRATA.

marked. The coecum is small in cats, spiral in dogs, and generally
absent with the colic valve in the mustelidae. Valvulse conniventes
are scarcely developed.

In thecetacea the tongue is short, thick, fleshy, and but. little sus-
ceptible of motion, and in the whale it often affords three barrels of
oil. The teeth are prehensile, the salivary glands rudimental or
deficient, and the oesophagus short and wide. In the phytophagous
cetaceans the stomach is divided into a large cardiac, and a small
pyloric portion, by a contraction which gives origin to twotubiform
prolongations. The coecum is simple in the dugong, and bifurcated
in the manatee. In the zoophagous cetacea the stomach consists of
four or five compartments, none of which, except the first, have any
communication with the oesophagus, therefore no rumination can
occur. The first cavity is small and lined with cuticle, which ter-
minates abruptly at the narrow opening leading into the second. A
smal| pyloric orifice leads to a dilated duodenum. There is scarcely
any distinction between small and large intestine, and the coecum
coli is but little developed. Why so complicated a stomach should
exist in animals nourished by the most digestible and highly organ-
ised food, is an anomaly for which we can offer no explanation, but
one which, from its interest, courts early investigation.

The stomach of the kangaroo resembles the human colon and
caecum; the oesophagus enters near its left extremity, which is
small and bifid; the stomach first extends towards the right side,
and then upwards and to the left, in such a manner as to completely
encircle the entrance of the oesophagus, and terminates at the py-
lorus by a contracted orifice. Its cavity gradually enlarges from the
left extremity till it nearly reaches the pylorus, it then dilates into a
round cavity with two lateral processes, and finally ends by a
narrow orifice. It presents a sacculated appearance arising from
the presence of anterior and posterior bands like those of the human
colon, and the cuticle lines it to a certain extent on either side of
the entrance of the oesophagus. This animal has been known to
ruminate when fed on hard ifood. The kangaroO-rat and the vam-
pyre bat present similar modifications of stomach but have no part
of it lined with cuticle, and in the former there is a valve at the
cardiac orifice. The intestine of the kangaroo corresponds in its
great length and convolutions with the coarse nature of its vegetable
food, and the coecum is about fifteen inches long. At the cardiac
orifice of the stomach in the beaver and wombat there is a large
gastric gland, like the glandular infundibulum in birds.

The ruminating animals possess four stomachs ; the first magnus
venter, or paunch, receives the crude unrnasticated food, while the
animal is grazing. When this cavity is filled the animal retires to
rest, and begins to ruminate; the unmasticated food, softened in
the paunch, now passes in small portions into the second cavity,
called reticulum, or honey comb ; from this it passes as a bolus up
through the oesophagus to the mouth, where it is thoroughly mas-
ticated and insalivated ; it is next couducted by the oesophagus to

80 EVERS'S COMPARATIVE ANATOMY.

the third stomach, termed mam/plies, or omasum, aid from thence
into the fourth stomach called abo?nasum, or rennet bag-. Of these
cavities, the first is the largest, and the third the smallest. The three
first are lined with cuticle, and the fourth, which is next in capacity
to the paunch is lined with a soft mucous coat folded in the longitu-
dinal direction. This is the proper digestive stomach, and is analo-
gous to the digestive sac of carnivorous and higher quadrupeds.
The fourth stomach of the ruminantia is the first developed ; in the
earlier periods of life it is the largest, and the only one employed in
digestion. The mechanism by which milk is transmitted directly
into the fourth stomach during the period of suckling is this, the
G3Sophagus enters just where the three first cavities approach each
other, here it can open directly into the first or second stomach, but
instead of terminating there, it is continued in the form of a groove
with prominent lips, which admit of being drawn together so as to
form a complete canal, which then constitutes a direct continuation
of the oesophagus into the third stomach, but this cavity not having
been distended with solid food in the young animal, it merely forms
a tube through which the milk passes into the fourth stomach. In
the adult animal the same mechanism continues, but here the third
cavity having been already distended, receives the bolus after
rumination.

In the ruminants without horns, as the dromedary, the camel,
and the lama, a somewhat different but not less beautiful mechanism
prevails, fitting them to live in the sandy deserts and arid plains
they inhabit. In these animals the paunch consists of two com-
partments, the first of which receives the un masticated food from
which it is returned to the mouth, moistened by the fluid of the
second or cellular compartment. After the cud has been chewed,
the food passes along the upper part of the second cavity into the
third, and from that to the fourth. When the camel drinks, the
water passes directly into the second cavity, and when this is full
it flows into the neighbouring cellular compartment of the paunch.
In the bullock, the three first cavities are lined with cuticle ; in the
camel it lines only the two first, and terminates just within the ori-
fice of the third, the surface of which has a faint appearance of
honey-comb structure. From the comparative view which has
been taken of the stomach of the bullock and camel, it appears, that
in the bullock there are three cavities formed for the preparation of
of the food, and one for its digestion. In the camel, the two com-
partments of the first cavity answer the purposes of the two first
stomachs of the bullock ; the second is employed as a reservoir for
water only ; the third is so small and simple in its structure, that it
is not easy to ascertain its particular office, whilst the fourth is that
in which the process of digestion is accomplished.

As a general rule, it may be stated that the intestinal canal is
long, large, and sacculated in the herbivorous tribes, and short,
straight, and without sacculi, in the carnivora. Some remarkable
exceptions, however, present themselves, for instance in makies,

VERTEBRATA. 81

mice, and shrews which are purely frugivorous, and in sloths,
which live on vegetable food, the intestine measures only about
three times the length of the body; whilst in the porpoise and seal,
which live on animal food, it measures in the former 11 times, and
in the latter 28 times the length of the body. But this apparent
anomaly is explained by recollecting that the caecum plays a com-
pensating part with respect to the other portions of the alimentary
canal, indeed the researches of the Heidelberg professors authorise
us in believing that it acts the part of a second stomach, and that
where the latter is simple, the coecum presents a complex and
highly developed condition, and vice versa. Hence by a reference
to the highly developed coecnm and vermiform appendix of the
rodentia, we are enabled to reconcile their simple form of stomach
with their herbivorous food. In the elephant, the small intestine
measures 3S feet, the colon and rectum 20£ feet, and the coecum 1£.
In the camel, the small intestine is 71 feet, the colon and rectum
56, and the coecnm 3. The intestine is 10 times the length of the
body in the horse, and 28 times in the sheep. In an ornitho-
rhynchus 17£ inches long, the small intestine measured 4 feet 4
inches, and the colon and rectum 1 foot 4 inches. In this animal,
the rectum, urinary, and genital organs terminate in a cloaca, as in
birds and amphibia.

The solidungulous pachydermata masticate their food before it is
swallowed, therefore they do not ruminate, and require but a simple
digestive stomach ; but they have the same narrow lengthened form
of intestine, and a capacious sacculated coecum and colon. The
liver is largest in the cetacea and those animals that dive or burrow ;
smaller in the herbivora, and least in the carnivorous tribes. There
seems to be no general law for the presence or absence of the gall-
bladder in mammalia more than in birds and fishes ; it is for the
most part wanting in the herbivorous species, as the deer and
the camel ; it is also absent from most of the rodentia and pachy-
dermata ; and here the hepatic duct is generally much dilated, as in
the horse and elephant. In the otter a similar dilation exists in
conjunction with a gall-bladder. It is remarkable that all the
mammalia which want this reservoir, except the porpoise, are
phytophagous.

In the course of my dissections during my pupilage at the college,
I, together with my esteemed friend, Surgeon Bewley, of Moate, met
with a female subject about nine years of age, in which this recep-
tacle was absent. I invited the attention of Dr. Houston to this, I
believe, unique anomaly, who has prepared and deposited the
biliary apparatus in the museum of the college.

The spleen is long, flat, and attached to the paunch in the rumi-
nantia, narrow and lengthened in the carnivora, and in the porpoise
it consists of several portions. The pancreas is long, flat, and
attached to the right end of the first stomach in the cetacea, in other
mammalia it is longer, and often divided into several portions, its
8 — g evers 6

duct, which is double in the elephant, usually opens separately into
the duodenum.

RECAPITULATION.

1. A digestive cavity is the most universal organ in animals, and
exists in all, with the exception of some of the monads.

2. Masticating, salivary, and biliary organs are found in the
higher radiata.

3. All these parts are more highly developed in the articulata,
and one or two gall-bladders are present.

4. There has been no gall-bladder found in the mollusca.

5. The stomach receives the biliary and pancreatic fluids in all
the invertebrata.

6. The invertebrated animals possess no portal circulation.

7. In the vertebrate the alimentary canal always swells out into
a gastric enlargement. The tributary organs are large and conglo-
merate, and the salivary glands are rarely absent.

8. The duodenum receives the biliary and pancreatic secretions,
and there are no teeth found in the stomach.

9. As a general rule the alimentary canal is larger and longer in
the vegetable-eating animals, than in those that live on flesh.

10. Fishes have a simple form of alimentary canal, their teeth are
often numerous, as in the pike, rarely absent as in the sturgeon,
their salivary glands are rudimental, or entirely wanting, and their
whole canal often measures but half the length of the body.

11. The digestive apparatus undergoes interesting changes during
the metamorphosis of the frog, &c.

12. The teeth are absent in birds, and their place supplied by bill
and gizzard.

13. The crop is double in the pigeon, single in the fowl, and
absent from the goose. The gizzard is thick and powerful in the
granivorous, but thin and membranous in the carnivorous species,
and the great intestine terminates in the dilatable rectal vestibule
which receives the openings of the ureters, of the oviducts, or vasa
deferentia, and of the Bursa Fabricii.

14. The teeth are greatly modified in the mammalia, being
rarely absent, as in the man is or pangolin, the myrmecophaga and
the echidna.

15. The digestive system is most complex in the herbivorous
ruminantia, and most simple in the carnivora ; in the latter the
food requires but little elaboration, hence the form of the teeth, and
the great strength of the jaws are admirably adapted for seizing and
tearing their living prey, here also we have a simple stomach, and
a short intestine, without any provision to retard its contents. In
the ruminantia, on the contrary, the jaws are elongated, and admit
of free lateral motion with flat grinding teeth, the stomach is com-
plicated, and the intestine long and sacculated ; in fact all things

ABSORBENT SYSTEM. 83

conspire to ensure perfect comminution of the food, retardation of
its passage, and a due absorption of its nutritious particles.

CHAPTER XII.

ABSORBENT SYSTEM.

Although Monro, Poli, Sheldon, and Carus, have described chy-
liferous vessels in many of the invertebrated classes, their existence
in these animals has not yet been satisfactorily proved, and it is more
than probable that their function is performed by the veins, the white
blood of which resembles the chyliferous fluid of the vertebrata.
The chyle varies much in its composition and properties in the
various tribes of vertebrated animals, and even in the same animal
according to the sort of food it lives on, being of a pinkish tint, with
abundance of crassamentum in the different animals which subsist
on nutritious animal food, while it is limpid and pale, with a great
proportion of serum in the inferior animals. The chyliferous, like
the other systems of the body, presents different grades of develop-
ment in the different vertebrated classes. Thus, in fishes the
vessels seem to consist of a single tunic, destitute of valves, and
without conglobate glands ; they form two strata of vessels between
the coats of the intestine, and carry a limpid fluid to the recepta-
culum chyli, from which one or two thoracic ducts lead to the
jugular veins or other branches of the cavee. The lymphatics and
lacteals communicate frequently with one another, and with the
neighbouring veins, and when injected they present a beaded ap-
pearance owing to the presence of rudimentary valves.

The chyliferous system in the amphibia is the same as in fish,
but in the reptilia it presents a higher degree of formation in the
existence of valves, and the milkish appearance of the chyle, the
place of glands is still supplied by the convoluted condition of the
vessels as in fishes ; here also, two or more thoracic ducts, fre-
quently communicating, pass to the jugular or subclavian veins, or
the angle between them, previously receiving the lymphatics from
the head, neck, and arms. In the tortoise, the anastomoses of the
thoracic ducts nearly conceal the trunk of the aorta. This system
presents a somewhat higher grade of development in birds, both
sets cf vessels being more numerous and distinct, the valves are
more abundant, but yet admit of the passage of fluids from trunks
to branches. Glands appear now for the first time, in connection
with the lymphatics, but not with the lacteals. Two thoracic ducts,
having but few anastomoses, terminate by several openings at the
junction of the jugular and subclavian veins.

In the mammalia the absorbent system is better developed and

84 EVERS'S COMPARATIVE ANATOMY.

mora distinct from the sanguiferous than in any of the preceding
classes, as manifested in the sanguineous characters of the chyle,
the elaborate structure of the vessels, the perfect condition of their
valves, the increased number of conglobate glands, and the unity
and distinctness of the thoracic duct. Sometimes this duct is
double, as in the dog, and sometimes its branches open into the vena
azygos, as in the hog. Occasionally its trunk divides, and having
enclosed a narrow elongated space, called insula Halleri, the
branches again unite. The mesenteric glands are of great magni-
tude in the cetacea, more detached in the pachydermata, and grouped
into a mass, named pancreas Assellii, in the carnivora.

RECAPITULATION.

1. Lymphatics have been described, but not saticfactorily demon-
strated, in the invertebrata.

2. No conglobate glands have been found in fishes ; their absorb-
ents are thin, convoluted, and furnished with rudimentary valves,
and occasionally two thoracic ducts exist.

3. This system is the same in amphibia as in fishes, but in the
reptilia the valves are more perfect.

4. In birds the absorbents are very numerous, the valves still
more perfect, and glands for the first time met with.

5. In mammalia the entire system is marked by a higher type of
formation : the thoracic duct is sometimes double as in the dog,
and occasionally opens into the vena azygos as in the hog.

CHAPTER XIII.

SANGUIFEROUS SYSTEM IN THE INVERTEBRATA.

The systemic, or red-blood circulation was discovered in the
higher animals by Harvey, in 1619; and by the researches of
modern comparative anatomists, it has been found to have a much
more extended existence ; there is a considerable number, however,
of the cycloneurose classes of animals, in which no distinct vascular
system has as yet been detected. The first appearance of it which
we observe in the lower animals, as in the earliest condition of the
human embryo, consists of vessels alone, through which the fluids
move in a circle, like the colourless blood in the cells of a plant.
In the asterias, echinus, and holothuria among the echinodermata,
a large vessel, in the form of a ring, surrounds the commencement
of the alimentary canal, from which the systemic arteries are
derived ; the systemic veins send branches to the gills, from which
the blood is returned by one large vessel to the heart.

SANGUIFEROUS SYSTEM IN THE INVERTEBRATA. 85

Diplo-neura. — In the earth-worm two vessels, one above and the
other below, extend the entire length of the body; they communi-
cate by several cross branches, and join at their extremities, where
small dilatations are observable, supposed to aid in propelling the
blood, which moves in opposite directions. The large vessels of the
annelida are endowed with a contractile power, and in insects,
spiders, and the lower species of Crustacea, large dilatations occur,
capable of considerable contractility.

In the leech, hirudo vulgaris, the two principal vessels are placed
on the sides, and lesser ones above and below, all anastomosing
freely by transverse branches ; of these the superior longitudinal
and the inferior transverse only pulsate. It is the opinion of
Miiller that the lateral vessels alternately empty themselves from
behind forwards ; and others state that the blood is moved forwards
in the upper vessel and backwards in the lower.

The arachnidans, which breathe by means of trachae, seem to have
a dorsal vessel only, without any ramifications. Those, on the
contrary, which possess branchial lungs, have a well developed cir-
culatory apparatus. The blood leaving the heart by the arteries is
distributed to all parts of the body ; having become venous it is
returned to the pulmonary branchiae by sinuses which supply the
place of veins, and having undergone arterialisation, it is returned
to the heart by the branchio-cardiac vessels, again to be propelled
through the arteries.

In the higher Crustacea the heart consists of two sinuses and a
ventricle ; from the latter, in the stomopoda, six vessels arise which
distribute the blood to the eyes, liver, antennas, (fee. This fluid
is next returned to venous sinuses in the neighbourhood of the
branchiae, through passages without any apparent parietes ; the
arterialised blood is brought from the branchiae to the sinuses of the
heart by vessels named branchio-cardiacs, from which it is received
by the ventricle and sent into the arteries issuing from it, each of
which is provided with a valve at its origin.

Cyclo-gangliata. — The greater number of the animals which
compose this class are aquatic, and enjoy a branchial respiration.
In the ascidiae the heart is very simple, consisting merely of a thin
membranous ventricle destitute of valves. The conchifera have
two auricles and a ventricle; the gasteropoda and pteropoda possess
a strong auricle and ventricle provided with valves. In the cepha-
lopoda there is an aortic heart, and two branchial hearts, or dilata-
tions ; in these animals, the blood having been carried to the system
by the arteries is returned by the veins to the branchial fringes ; in
some bivalves, however, a portion of it is sent direct to the heart
without passing through the respiratory organ. In the gastero-
podous and other mollusca the rectum passes through the ventricle.

86 EVERS'S COMPARATIVE ANATOMY.

CHAPTER XIV.

SANGUIFEROUS SYSTEM IN THE VERTEBRATA.

In the greater number of the invertebrate animals which we have
hitherto examined, the heart and principal artery were placed above
the alimentary canal and the chief part of the nervous system ; but
in the vertebrate classes the converse order obtains, the heart
being below the alimentary tract; in the former division the blood
generally arrives at the heart after having passed through the re-
spiratory organ, while in the latter the blood flows from the heart
to the respiratory organ. In the invertebrate classes, too, there is
no vena porta, the liver being supplied by an hepatic artery alone.

PISCES.

The gills, which are the only respiratory organs of fishes, are
placed in the course of the arterial circulation. The venous blood
from all parts of the body is conducted to a single auricle which
propels it into the ventricle, from which it is brought by the
arterial bulb to the gills, where it is arterialised, and from which it
is distributed by the branches of the aorta to all parts of the body.
The caudal vein of the eel presents a contractile dilatation, to which
Dr. Hall has applied the name of caudal heart; this doubtless
assists in promoting the circulation in the caudal branches of the
vena cava. Many look upon the heart of fishes and the artery
issuing from it as analogous to the right heart and pulmonary
artery of higher animals ; but it is much more just to consider the
heart as corresponding to the whole heart of the warm-blooded
vertebrata, seeing that in some of the reptiles possessing gills, the
blood is sent to these organs through the great systemic trunk. In
fact, the heart, in these animals, acts at once the part of a pulmo-
nary and a systemic heart in propelling the blood not only to the
gills, but through all parts of the aortic system.

Portal-circulation. — The porta in fishes carries to the liver the
venous blood from the stomach, intestines, spleen, pancreas, and
occasionally from the genital organs, swimming bladder, and tail.
In the gadus, however, as in reptiles, the venous blood from the tail
and the central parts of the abdomen goes to the kidneys. In the
silurus the blood from the posterior part of the body is distributed
to the liver and kidneys : and in the carp, pike and perch, to these
organs and to the vena cava. This vessel also receives the blood
from the testicle, ovary, kidneys, and frequently from the swimming
bladder.

AMPHIBIA.

The metamorphosis which this class of animals undergoes in
passing from the pisciform to the reptilian state, is strikingly

SANGUIFEROUS SYSTEM IN THE VERTEBRATA. 87

illustrated in their circulatory system : beginning life with the
single heart of a fish, and ending it with the double heart of a
reptile. In the water salamanders the venous blood which has cir-
culated through the body, is returned to a systemic auricle, and
having passed through the ventricle, it is received by the bulbus
arteriosus, and sent by the branchial arteries to the branchial
leaflets. The pure blood is now received by the pulmonary veins,
the confluence of which constitute, as in fishes, the descending
aorta.

From this latter vessel a small branch passes off to the rudiment-
ary lung, which is afterwards to become the pulmonary artery. As
the animal changes from an aquatic to an atmospheric respiration,
the branchiag become absorbed, and the lungs proportionally deve-
loped. Their arteries experience corresponding changes, those of
the former organs diminishing, while those of the latter increase
with the growth of the lung. The two veins which return the
blood from the rudimental lung also enlarge, and as they arrive at
the heart, they undergo a remarkable dilatation, which constitutes
the left auricle. Till lately the bi-auricular form of heart was sup-
posed to be confined to the caducibranchiate amphibia, as frogs,
toads, salamanders, and tritons, but the researches of Owen have
proved its existence in the perennibranchiate amphibia also.

At the same time that the systemic auricle receives the impure
blood from the cavae, the pulmonic auricle receives the aerated
blood from the lungs. From both of these cavities the blood is sent
into, and mixed in, the single ventricle, from which it is sent by
the one impulse to the lungs and to the system generally. From
this description it is obvious that the blood is but partially purified,
mixed blood being sent through the pulmonary arteries, as well as
through the aorta and its ramifications.

REPTILIA.

In this class of animals we perceive a still higher grade of deve-
lopment than was met with in the amphibia; the ventricle is par-
tially divided by a septum into two compartments, corresponding
in most particulars to the two ventricles of warm-blooded animals.
In some the septum is so imperfect as to be incapable of preventing
the admixture of the blood derived from both auricles. In others,
however, as the crocodile, the ventricles are separated completely,
or communicate by a small orifice provided with a valve, which
prevents the blood passing from one compartment to the other. In
fact the heart in this singular animal is double, as in the higher
vertebrata, so that the venous blood returned by the cava? to the
right auricle, passes from the right ventricle through the pulmonary
artery to the lungs, while the pure blood returned from this organ
to the left auricle is directed from the left ventricular compartment
through the systemic arteries. The auriculo-ventricular orifices are
provided with a muscular valve, and in the crocodile there are two.

It is curious, however, that in the whole of this class the descending
aorta is formed by the union of two branches, the right branch
arises from the left ventricular compartment, consequently carries
pure, or nearly pure blood, which it distributes to the head, neck,
chest, and upper extremities. The left branch, on the contrary,
arises either from the right ventricular compartment, or what is
tantamount to it, from the pulmonary artery. It is obvious, then,
that the descending aorta carries a mixed quality of blood to the
parts it supplies; but it is interesting to observe, that previous to
the junction of the two aortic arches, the left gives off the cosliac
axis which supplies the entire alimentary canal and digestive organs
with venous blood. In the turtle, lizard, and some serpents, where
the septum ventriculorum is imperfect, the pulmonary artery and
aorta at once carry mixed blood, and in some of the chelonia,
as the tortoise, the existence of ductus arteriosus ensures a more
complete mixture of venous and arterial blood. The arteries arising
from the ventricles are each provided wtth two valves.

Portal system. — In amphibia and reptiles, as in fishes, there
are two lesser venous circulations; the one belongs to the liver,
and the other, which does not exist in birds or mammals, belongs
to the kidneys. In some reptiles ail the venous blood from the
posterior parts of the body is distributed to the liver and kidneys,
while in others a portion is sent to the inferior cava ; this latter
vessel also receives the venous blood which has circulated through
the kidneys.

AVES.

The heart, in this highly organised class of oviparous animals
consists of four separate and distinct compartments, and indeed pre-
sents a more perfect typical form than is met with in even the mam-
malia. Its form is conical, being sometimes short and wide, as in
the crane, and sometimes more elongated, as in the emeu. Its
situation is mesial, its axis parallel to that of the trunk, and in con-
sequence of the partial development of the diaphragm its apex rests
between the lobes of the liver. The right auricle seems consider-
ably larger than the left, and the auricular portion is distinctly
divided from the sinus by two semilunar muscular valves; one
attached along the anterior, and the other along the posterior side
of the sinus. The venous blood is returned to the sinus of the
auricle by an inferior and two superior venas cavae, and it is re-
markable that the left superior cava receives the coronary vein just
before its termination. The orifice of this vessel is opposite to that
of the inferior cava, but separated from it by a semilunar mem-
branous valve. The auriculo-ventricular opening is a small oblique
slit, and reflux from the ventricle is prevented by a thick strong
muscular valve so disposed as to give considerable impulse to the
flow of blood through the pulmonary artery. There is a small
muscular column at the upper part of the orifice, but it is only one

SANGUIFEROUS SYSTEM IN THE VERTEBRATA. 89

of the carnese columnse, of which few exist in the ventricle. In
the left auricle a mere rudiment of valve is found between the sinus
and the appendix. The parietes of the left ventricle are very thick,
and the auriculo-ventricular opening1 is guarded by two mem-
branous folds corresponding to the mitral valve in mammalia. The
pulmonary artery and aorta are provided at their origins with three
semilunar valves, those of the former vessel being thicker and
stronger than those of the latter. The extremities of these valves
will be found by careful dissection to be attached to cartilaginous
or osseous points imbedded in the fibrous tunic of the vessels.

The pulmonary artery having arisen from the right ventricle at
once divides into two branches, one for each lung; from these or-
gans the blood is returned by two veins, which unite before they
reach the left auricle. From the left ventricle arises the aorta,
which immediately sends off two branches analogous to arteriae
innominatae, for the supply of the head and wings. It may be
observed that birds possess no palmar arches, nor, strictly speaking,
a radial artery. The cerebral, orbital, temporal, and spermatic
arteries are remarkable for their free and plexiform anastomoses.
But of all the arterial plexuses, that of the organ of incubation
requires special notice. It is formed by branches from the posterior
thoracic, abdominal, cutaneous, and ischiadic arteries, immediately
under the integuments of the abdomen. This plexus becomes
enormously enlarged during the period of incubation.

The venous system in birds is remarkable for the frequency of
its communications, especially one which exists between the united
caudal, hemorrhoidal, and iliac veins and the vena porta, by means
of which the blood from the viscera and posterior parts of the body
may flow either into the cava or porta, a disposition obviously de-
signed to guard against congestions: as yet it is a question con-
cerning which contradictory opinions prevail, as to whether the
branches of the pulmonary artery extend to the air-cells distributed
over the body, or whether the blood in the systemic capillaries un-
undergoes any change tending to its purification in the parietes of
these cells.

MAMMALIA.

The form of the heart, and the distribution of the blood vessels in
the whole of this class so closely resemble the human type, that it
becomes necessary to notice only a kw individual peculiarities ; in
the dugong and rytina for instance, among the cetacea, the heart is
cloven by the deep separation of its two ventricles, and the orifice
of the inferior cava is guarded by a fleshy Eustachian valve, which
is wholly absent in the lion, the bear, and the dog. In the mono-
tremata, the marsupiata, the porcupine, and the elephant, the right
auricle receives one inferior and two superior cavae as in birds, and
the coronary vein terminates in the left superior cava. In the
ourang-outang and the mole, only, is the apex of the heart inclined

90 EVERS's COMPARATIVE ANATOMY.

to the left side as in the human subject. In the upper part of the
substance of the left ventricle of the pig, the stag", and other bisulea,
are two small flat bones, cruciformly disposed in the stag, they are
formed about the third year of the animal's life, and are but slightly
developed in the female. It has been generally supposed that the
foramen ovale and ductus arteriosus remain permanently open in
seals, otters, and cetaceans, and although the dissections of Cuvier,
Home, Blumenbach, and T. Bell, go to prove that they have
remained unclosed in a few instances, still we must look upon these
as exceptions, admitting, however, that these passages continue
longer pervious in these diving animals than in other mammalia.

As regards the arterial system some remarkable peculiarities are
observed in the branches arising from the arch of the aor^a, thus
in the horse, the camel, and many of the long necked mammalia,
this great trunk just after its origin divides into two branches, one
becomes the descending aorta, the other ascends vertically and
divides into a right innominata, a left subclavian and a left carotid,
which latter appears in direction the continuation of the trunk. In
the elephant there is but one coronary artery, and both carotids
arise by a common trunk between the two subclavians.

The dolphin has an innominata on each side, this constitutes the
type of the cheiroptera. In the marmot and the guinea-pig, the
right innominata gives rise to the two carotids, and the right sub-
clavian. This also is the type of the order quadrumana, and most
of the carnivora. Among the peculiarities in the distribution of
arteries we may notice the rete mirabile formed by the internal
carotid at its entrance into the cranium in several carnivora and
ruminant bisulca ; the plexifonn arrangement of arteries which
exists under the pleurae and between the ribs in the cetacea ; and
the remarkable anastomosing divisions of the arteries of the extre-
mities and tail in the slow moving and climbing animals as the
bradypus, myrmecophaga, pangolin, and stenops. This condition
of the arterial system doubtless has reference to the peculiar living
habits of the animal it exists in, thus in the cetaceans these serpen-
tine vessels constitute so many reservoirs for containing arterial
blood during the obstructions to the circulation which are almost
inseparably connected with the aquatic habits of these mammalia,
whilst in those with depending heads, the rete mirabile is admirably
calculated to . obviate the injurious effects of sudden influxes
to the brain, and in the edentata the arterial divisions alluded
to are no less indicated, lest the large trunks of the extremities
should suffer from pressure during their long continued action
in climbing.

The plexiform disposition, which characterises so many parts of
the arterial system, is no less strikingly displayed in the venous.
This is well seen in the tortuous sinuses which receive the inter-
costal veins in the porpoise, the vena azygos being absent in this
animal. A beautiful distribution of veins constituting the rete
mirabile venosum, is met with on the foot of the horse, where these

SANGUIFEROUS SYSTEM IN THE VERTEBRATE. 91

vessels run in innumerable parallel branches on the anterior surface
of the coffin bone. Another peculiarity in this system is presented
by the inferior cava, in the porpoise, the seal, the common and the
sea otter, consisting in a considerable dilatation of this vessel
between the liver and the diaphragm, similar to what is observed
in tortoises and diving birds.

A general review of the vascular system indicates that the heart
in its simplest form resembles a vessel endowed with contractility,
as exemplified by the vessel-like multiple hearts which constitute
the vascular trunks of the annelides, the contractile trunks on the
alimentary canal of the holofhuria, the dorsal vessel of insects, &c.
In the embryo of the highest warm-blooded animals the heart is at
first tubular, and it is interesting to observe, that during the progress
of its development it passes through, and resembles the several forms
which constitute its permanent type in the adult state of fishes and
reptiles, even the clefts in the neck, with the arched divisions of the
aortic trunk, which are persistent in reptiles, may be seen in the
human embryo at a very early stage of its development, and the
ductus arteriosus, which is single in mammalia, but double in birds,
is the last of those arches which remains unclosed in the foetus.
These arches may be well seen by inspecting the embryo of a bird
on the third day of incubation.

The frequency of the heart's action varies much in different ani-
mals, and even in the human subject, from a variety of causes.
In a fish it beats in a minute from 20 to 24
In the frog, about - - 60

In birds, from - - 100—140

In the bat, - - 200

In rabbits, - 120

In the cat, - J 10

In the dog, - - 95

In the sheep, - 75

And the horse, - 40

In the human embryo, - 150

At birth, - - 130 to 140

During the first year - - 115 — 130
During the second year - 100 — 115

During the third year, - 90 — 100

During the seventh year, - 85 — 90

About the fourteenth year - 80 — 85

in the middle period of life, - 70 — 75

In old age, - - 50—65

RECAPITULATION.

1. The systemic circulation was discovered by Harvey in 1619.

2. In the higher radiata a large artery surrounds the beginning
of the alimentary canal, in the form of a ring, from which the
systemic branches arise.

EVERSS COMPARATIVE ANATOMY.

3. A distinct heart is first seen in the Crustacea.

4. In the gasteropodous mollusca, as the snail, the rectum passes
through the heart.

5. There is no portal circulation in the avertebrata.

6. The heart of a fish consists of a single auricle and ventricle,
and the blood of the porta is distributed to the liver and kidneys.

7. All the amphibia have at first the single heart of a fish, but
the caducibranchiate species terminate life with the double heart of
a reptile.

8. The heart of birds consists of four distinct compartments, as
in mammalia, but rather more perfect, owing to the existence of its
fleshy valves.

9. The heart of the higher warm-blooded mammalia, even that
of man, in the course of its development, represents the several
grades which constitute the permanent types of the lower animals.

CHAPTER XV.

RESPIRATORY SYSTEM IN THE INVERTEBRATA.

The respiratory organs are sometimes placed in the interior of
the body in the form of lungs sometimes towards its exterior in the
form of lamellated, ramified, pectinated, tufted, ciliated, or pin-
nated processes, termed gills, or branchiae, and a third form of re-
spiratory apparatus is obtained by the development of a system of
tracheal tubes, ramified to an exquisite degree of minuteness, and
widely spread through all the organs of the body. Animals pro-
vided with lungs generally breathe atmospheric air, whilst in those
furnished with branchiae respiration is accomplished by means of
water. An exception to the former, however, is met with in the holo-
thuria; and to the latter, in the terrestial Crustacea. It will appear
in the progress of this article that some of the vertebrated animals
commence life by a branchial respiratory and terminate it by a pul-
monary, and that others enjoy a mixed form of respiratory organ all
through. In fact, nature seems almost to have exhausted her
ingenuity in the construction and development of respiratory
apparatus.

Cyclo-neura. — In the lowest classes of this division the only
respiratory organs detectible are small cilia pervading the entire
surface, but so minute as to require high magnifying powers to
render them visible. The tentacula and the whole surface of the
body are subservient to the function of respiration in the polypifera.
In the asterias and sea-urchin among the echinodermata, the water
passes into and out of the cavity lined by peritoneum, in which the
viscera are lodged. In the holothuria the water is alternately re-

RESPIRATORY SYSTEM IN THE INVERTEBRATA. 93

ceived and emitted from a tube which is ramified in an arborescent
manner, with terminal cellules.

Diplo-neura. — The highly vascular skin of the entozoa performs
the function of respiration — in some, through the medium of water ;
and in others the blood is oxygenated on the mucous surface of the
animals they infest. In the cirrhopoda respiration is performed by
the arms and by the leaf-like fringed membranes attached to the
anterior part of the sides of the body. The surface of the body is
in general the seat of respiration among the annelida, but in the
lumbrici, nereides, and hirudines respiration is in part effected by a
series of minute membranous sacs under the skin of the abdomen,
each having a separate external opening. Respiration is aerial in
the greater number of insects, the air being received through a
number of stigmata, and carried by the tracheae in some cases into
vesicles, and in others into longitudinally ramifying trunks.

Many insects in their larval state breathe by means of branchiae
in the water, and some in their perfect condition breathe water,
although they have an internal tracheal apparatus ; from the water
in these branchiae the air is separated, and passed in the gaseous
state through the ramified tracheae. There is a very curious fact
connected with the eristalis, this disgusting insect has the last ring
of its body elongated into a membranous tube, within which there
is a second horny tube, which the animal can extend to the surface
for the purpose of respiration, whilst it lives at the bottom where it
procures its food in the filth of sloughs, sewers, and stinking privies.
The tracheary aracknida resemble insects in their tracheal tubular
respiration, whilst the respiratory organs of the pulmonary arachnida
consist of small sacs opening externally, and situated at the under
surface of the abdomen. Both sets of organs are enjoyed by the
segestria and dysdera. In tracing the progress of development of
the respiratory apparatus in the higher Crustacea, as the astacus
fluviatilis, it will be found to present four principal periods ; lstly,
that which precedes the appearance of this apparatus ; 2dly, that in
which the branchiae are not distinguishable from the organs dedi-
cated to locomotion or mastication ; 3dly, that characterised by the
transformation of these into organs wholly dedicated to respiration,
and distinct from the extremities ; and 4thly, that during which the
branchiae sink inwards, and become lodged in the branchial cavities.

By reviewing the respiratory apparatus in the different groups of
crustaceans, it will be found that the several stages of development
of the higher orders constitute the permanent types of the lower
series ; thus, to the first stage of organisation belong the greater
number of the entomostraca and copepoda ; to the second, the bran-
chiopoda ; to the third, the amphipoda ; and to the fourth the entire
order of the decapoda. The greater number of the Crustacea live
under water; some, however, as the gecarcini, or land-crabs, con-
stantly live out of water, but it is necessary t! at their ^piratory
membrane shall be kept humid, and for this purpose the membrane
is thrown into folds in the form of reservoirs for containing water.

94 EVERS's COMPARATIVE ANATOMY.

Gyclo-gangliata. — The greater number of this division breathe in
water, by means of gills, some however, breathe by lungs in the air.
The first mode of respiration is enjoyed by the tunicata, conchifera,
pteropoda, cephalopoda, and some of the gasteropoda, the remainder
of this class breathe atmospheric air, by means of a lung in the form
of a large cavity, placed beneath the mantle. A curious circumstance
connected with the conchifera is, that the eggs on escaping from the
ovary, are deposited between two layers of the branchial membrane,
where they increase in size and undergo incubation.

CHAPTER XVI.

ORGANS OP RESPIRATION IN THE VERTEBRATA.
PISCES.

This entire class is covered with branchiae, by means of which
they abstract the free oxygen contained in the water. In the sharks
and rays, and in all the osseous fishes there are four gills on each
side, supported by as many branchial arches of cartilage or bone,
connected to the os hyoides.

Each gill consists of a double series of lance-shaped lammellae
closed in by a movable cover, operculum. Generally there is but
a single opening for the passage of the water, but in some
instances, especially among the cartilaginous fishes, there are
several. In consequence of the swimming bladder of fish being
supposed by Cams, Blumenbach, and many others, to be subservient
to the purposes of respiration, it merits some notice in this place.

This organ, which is sometimes divided by a septum, as in the
genus cyprinus, and sometimes absent, as in the pleuronectes,
Jophius, and mackerel, is placed in the abdomen, close to the spine,
and below the kidney ; consists of an internal vascular lining
membrane, a strong fibrous tunic, and a partial investment of peri-
toneum. In fresh-water fishes, it has been found to contain nitrogen,
and in salt water fishes, chiefly carbonic acid gas. From its
anterior part a canal, ductus pneumaticus, passes forwards and
opens into the oesophagus, except in the sturgeon where it
opens into the stomach. This duct is double in the cod, in the
carp it possesses valves so disposed as to admit of the egress, but
prevent the ingress of air; it is absent in the sciura, cobitis, burbot,
and others. When we consider that this organ is largest in such
fishes as swim with greatest velocity, and wanting in those where
large fins or a powerful tail compensate for its absence, we are dis-
posed to agree with those who regard it as an organ of progressive
motion.

ORGANS OF RESPIRATION IN THE VERTEBRATA. 95

AMPHIBIA.

Progs and salamanders in their tadpole state, breathe by gills,
which during the earliest periods of their existence are placed ex-
ternally; they also possess rudimentary lungs, which become deve-
loped as the animals change from the aquatic to the aerial respira-
tion. The perennibranchiate amphibia, as the proteus, siren, and
axolotl also possess both sets of organs, and retain them through
life, but here the lungs always present the rudimentary type, and
it is even doubted whether they subserve at all to the function of
respiration. In these as well as in the larval condition of the
caducibranchiate genera, the pulmonary organ is in the form of a
mere sac, and it is only during the metamorphosis that it assumes
the cellular character. In the adult state of all the higher orders
of amphibia respiration is accomplished in a manner different from
all other air-breathing animals, viz., the mouth being fully distended
by the air which enters through the nostrils, these passages together
with the pharyngo-oesophageal are closed, the mouth then suddenly
contracts by the action of the surrounding muscles, and the air is
forced by an effort of deglutition through the glottis and trachea
into the lungs. Hence, one of the most effectual ways of killing a
frog is to keep its mouth open for a short period ; this mode of
inspiration is accounted for by recollecting that the ribs are
absent in these animals.

REPTILIA.

In most of the amphibia the trachea is very short and perfectly
membranous. In this class it is somewhat longer, and cartilaginous
plates begin to appear in it ; these plates which are first seen in the
dactylethra, do not form perfect rings, but present the appearance
of perforated lamellse irregularly disposed. In the bronchi of the
casciliae, however, the cartilaginous rings are much more complete.
In lizards and serpents the lung is a mere cavity with cellular
parietes, having perforations which communicate with the neigh-
bouring cells. Turtles have a more complicated structure, approach-
ing that of warm-blooded animals.

AVES.

The lungs, in this class, are confined to the back parts of the
cavities of the thorax and abdomen by the serous membrane com-
mon to these cavities ; they are of a flattened, elongated form, smooth
anteriorly, and grooved posteriorly by the ribs, between which they
are impacted ; they are of a bright red colour, and of a loose spongy
texture; on the surface of the lungs there are openings through
which air passes from the bronchial tubes into large neighbouring
cells. In birds not organised for flight these cells, are confined to

96 EVERS'S COMPARATIVE ANATOMY.

the abdomen, but in others they extend along the neck, and even
into the extremities: they also penetrate the cavities and diploe of
the bones, a discovery for which we are indebted to Mr. Hunter.
This great physiologist injected the medullary cavities of the bones
from the trachea: he also tied this tube, and having broken the
humerus of a fowl, and the femur of a hawk, he found that the
birds respired for a short time through the artificial openings. The
proportion in which the osseous system of birds is permeated by
air has reference to their respective modes of progression, thus
almost every bone in the body admits air in the kite, the hawk, the
eagle, and other birds of high flight; and in the hornbill even the
phalanges of the toes contain air. Four uses have been ascribed
to this extension of the respiratory system in birds — first, to sub-
serve the function of respiration ; secondly, to aid by mechanical
pressure the action of the lungs; thirdly, to render the body spe-
cifically lighter for the purposes of flight : and fourthly, by the dis-
tension of the cells in the extremities to assist in maintaining the
wings in a state of extension, during long-continued flight. Mr.
Hunter supposed it contributed to sustain the song of birds and to
give it strength and tone.

The air passages in birds consist of a superior larynx, a trachea,
and inferior larynx, and two bronchi with their ramifications. The
superior larynx is situated behind the root of the tongue, resting
on the uro-hyal element of the os hyoides ; it is composed of from
four to ten bony or cartilaginous pieces, and two pairs of muscles ;
thyro-arytenoidea and constrictores glottidis. The trachea is com-
posed of a series of bony or cartilaginous rings, which form com-
plete circles, with the exception of the two first ; they are closely
approximated, and sometimes overlap. Many birds, as the rasores,
have no inferior larynx ; in others it presents different degrees of
development, thus, in the genus falco there is but one pair of
muscles; in the parrot tribe three, and in the insessores, where this
organ attains its greatest decree of perfection, five. The rings of
the bronchi do not form complete circles, but gradually become
smaller, and finally disappear.

MAMMALIA.

In the entire of this class there is great similarity in the respira-
tory organs, not only to each other but to the human type of for-
mation. An epiglottis exists in all, and is divided at its superior
extremity in the seal, the hare, and the ant-eater. The larynx in
all the mammalia consists of the same parts generally as in man,
but occasionally modified in obedience to particular circumstances.
Thus, in the cetacea this organ ascends as far as the posterior
nares, and communicates with the spouting hole, which opens at
the top of the head by a single or double orifice, closed by a fleshy
valve in the form of two semicircles. The great size of the larynx
in the lion accounts for the powerful and terrific roar of that ani-

ORGANS OF GENERATION IN THE INVERTEBRATA. 97

mal. The peculiar grunting voice of the pig is produced by large
lateral cavities communicating with the small ventricles of the
larynx, and the neighing of the horse results from the vibrations of
membranous folds connected with the chordae volcales.

The trachea varies considerably in the length, breadth, and num-
ber of its rings; thus, in the seal, the porpoise, the cheiroptera, and
several rodentia, its rings form complete circles as in birds ; their
number varies from 14, presented by the mouse, to 78, as seen in the
seal. In the sloth the trachea descends considerably in the chest,
and again ascends to divide into the bronchi. The lungs present
very few varietes in the class mammalia. In the cetacea they
are remarkable for their elongated, flattened form, and for the free
communication of their cells with each other.

RECAPITULATION.

1. The respiratory apparatus is very extensive and greatly varied
in the invertebrata, in the lowest orders of which it is usually con-
fined to the surface of the body.

2. Respiration is performed by gills in fishes, and in the caduci-
branchiate amphibia, during the tadpole state ; in the siren and
proteus it is in all probability performed all through life both by
gills and lungs.

3. In birds this system is extended into the bones and into the
large cells of the thorax and abdomen.

4. The organs of respiration throughout the class mammalia,
are very similar to those of man.

CHAPTER XVII.

ORGANS OF GENERATION IN THE INVERTEBRATA.

Notwithstanding the varied modifications observed in the organs
of generation throughout the animal kingdom, the reproductive
function will be found to conform to a few leading types, as the
fissiparous, sfemmiparons, oviparous, viviparous, and ovo-vivipa-
rous. Fissiparous generation consists in the division of an animal
into two or more, similar in every respect to the original being. In
this form of generation, which is met with in some of the infusoria,
cestoidea, and annelida. the line of separation takes different direc-
tions, being transverse in the paramoecuim, and vertical in the vor-
ticellae. In gemmiparous generation the young appear as sprouts
from the body of the parent: it is more extended than the last,
being met with in the polypine and coralline animals, in sponges,
cystiform entozoa, and in some acalephae. These two forms of
9 — e evers 7

EVERS'S COMPARATIVE ANATOMY.

reproduction appertain to animals unprovided with special organs
of generation.

In oviparous generation, which belongs to birds, many reptiles
and fishes, the egg^ after fecundation, passes through the oviduct
from the body of the parent, to be hatched by the influence of
external agents. Most mammalia afford examples of the viviparous
form of generation, here the ovum remains within the uterus of
of the female until it is capable of independent life. Many animals,
however, besides mammalia, bear their young alive, examples of
which are to be met with among the reptiles, fishes, mulluscous
and articulate animals. The last form of generation above alluded
to is the ovo-viviparous, which implies the production of living
foetus, the ovum being hatched within the body of the parent;
but never contracting a vascular connection with the uterus, this is
the case with the monotremata, as the echidna, and ornithorhynchus,
and also with the monotrematous marsupiata, as the opossum, and
kangaroo.

All the higher classes of animals possess generative organs of
two kinds, the co-operation of which, for the purposes of reproduc-
tion, constitutes the distinction of sex, into male and female.

The following table exhibits a view of the reproductive process
in the different classes of animals, as given by Dr. Thomson, of
Edinburgh, in his matchless article on generation, in the "Cyclo-
paedia of Anatomy and Physiology."

f Parent splits, each part a new ani-
mal.
J 1. Transverse,
f Fissiparous . . \ 2. Longitudinal.
3. Irregular.
I Parent splits and discharges the

Non-sexual

J-H

youn<

v Sexual

I r«o™™^o™„„ $ Budding upon the parent stock.
^Gemmiparous . J Separatbed Duds, gemmae, or sporules

1. On all parts of the body.

2. On one part or organ only.

f Hermaphrodite Both sexual organs on one individual.

1. Self-impregnation.

2. Mutual impregnation.
'Oviparous laying eggs which are

hatched.
1. External fecundation.
L Dioecious . . <{ 2. Internal fecundation.

Ovo-viviparous, eggs hatched within

the maternal body.
.Mammiferous, suckling the young.

1. Monotrematous.

2. Marsupial.

3. Placental or strictly viviparous.

Prom the above table, it appears that there are a vast number of
animals wholly destitute of generative apparatus, and where organs
first appear, the animals seem to have the power of pro*J5agati ng by
means of ova, without copulation ; in many of the lower animals,

ORGANS OF GENERATION IN THE INVERTEBRATA. 99

however, as the annelida, the acephalous, and gasteropodous mol-
lusca, both sets of organs are placed on the same individual, con-
stituting it an hermaphrodite. Some of animals of this class, as
the holothuriae, possess the power of self-impregrmtion, whilst
others, though possessing double organs, require mutual impregna-
tion ; this is the case with the leech, and the common earth-worm.
In all the insect tribes the sexes are separate, the male organs being
the testicles, the vesiculae seminales, the excretory tubes, and in
many, the prehensores.or organs for seizing the female during
coitus. The female organs consist of the ovaria, the oviducts, the
spermotheca, or receptacle for the male semen, and the ovipositor,
an instrument for directing the ova to their proper location at the
period of extrusion.

The generative system of the arachnida and Crustacea is very
simple, consisting in the male, of testes and vasa deferentia, and in
the female, of membranous ovaries with their excretory ducts.
These organs are double in each sex, and quite distinct from each
other.

In the mollusca, the generative organs present some peculiarities;
there is but one testicle in the male, and one ovary in the female,
each placed on the right side of the neck. The penis is of huge
dimensions in the gasteropoda, while in the cephalopoda it is quite
rudimentary; but, by way of compensation, the vas deferens is
large, convoluted, and muscular.

When two snails amorously disposed, meet, as Professor Jones,
of London, lucidly observes, they begin their blandishments by
rubbing the surfaces of their bodies together; after some hours
the generative orifice on the side of the neck is seen to dilate, and
to display within its cavity three apertures, one from the penis,
another from the female organs, and the third from the sac which
contains a calcareous quadrangular spike, called the dart; the use
of which seems to be to excite to love its sluggish, sleepy, apathetic
associate, by pricking the surface of its body; at length his dart is
broken, and he becomes in turn the object of a similar attack ; both
the reptile cupids having thus exhausted their quivers, and received,
each, the love inspiring wound, the other two orifices now dilate,
from one the Ions: whip-like penis protrudes, and is received by the
vaginal orifice of the other; these phenomena being reciprocal, they
mutually embrace and impregnate each other.

100

CHAPTER XVIII.

ORGANS OF GENERATION IN THE VERTEBRATA.
PISCES.

In this extensive class, the generative apparatus is comparatively
simple, consisting in the female osseous family of two large mem-
branous ovaries, with short oviducts, opening in the vicinity of the
anus. The ova are generally very numerous, and are deposited in
shallow water where they receive the fecundating influence of the
male, and the genial heat of the solar rays. In the males the tes-
ticles are of great size and composed of a congeries of convoluted
tubes; the semen is discharged by the vasa deferentia, and diffused
through the water in the neighbourhood of the ova, which are thus
impregnated. The presence of a penis in this class is not necessary,
seeing that copulation does not occur; to this, however, there are
a few exceptions, in which the ova are fecundated prior to their
discharge; and in the blennius viviparus, the young are produced
alive, being hatched within the oviduct. In these rare instances,
the vas deferens protrudes externally in the form of a little penis.
In the eel, the lamprey, and many cartilaginous fishes, the ova are
suspended in the interior of the abdomen where they receive the
influence of the semen, and are discharged by a simple orifice near
the anus.

AMPHIBIA.

The ovaria of these animals are smaller, but in other respects
similar to those of the lamprey ; the oviducts are long and tortuous;
they commence by a fimbriated extremity, and previous to their
termination in the cloaca they enlarge to retain the ova for some
time before expulson. In the frog, the testicles, which are two in
number, are placed on the kidneys, and their excretory tubes dis-
charge themselves into the ureters. In the majority of instances,
the ova are fecundated in exitu by the sprinkling of the semen from
the male which is placed on the back of his mate. In the triton,
and a few others, the semen diffused through the water passes into
the genital organs and produces internal impregnation. The sala-
mander alone possesses a rudimentary penis, and in this case, too,
the eggs are hatched within the oviduct.

The reptilia, for the greater part, possess a generative system,
the same as the amphibia ; the higher orders accomplish internal
impregnation. The males of serpents' are generally provided with
two penises which, instead of being perforate, are grooved for the
passage of the semen into the cloaca of the female. In the sauria
the penis is bifid, and its extremities covered with recurved spines.

ORGANS OF GENERATION IN THE VERTEERATA. 101

AVES.

In the males of this class, the testes, two in number, are placed
high in the abdomen, beneath the kidneys; they are subject to re-
markable variation of size, according to the period of the year their
office is required; thus, in January the testicle of the sparrow is
about this size, o, and by April it attains the size of a large pea.
The vasa deferentia, seldom much curved, pass down and terminate
separately on a rudimentary penis in the urethro-sexual pouch.
The epididymis is quite rudimentary, and varies much in colour,
being black, yellow, or green. Coitus is usually effected simply by
an eversion of the cioacag, therefore the intromittent organ is only
rudimentary:, in those birds, however, which copulate in water, as
the drake, swan, &c, it necessarily attains a larger size. It is
sometimes double as in serpents, and is always grooved along its
upper surface, for the passage of the semen. The ovarium and
oviduct are confined to the left side, they primarily, however, exist
on both sides, but rarely continue their development on the ri<rht.
A clitoris is present in the females of those species whose males°are
provided with a penis.

MAMMALIA.

The male organs of generation in this class consist of the testicles,
vasa deferentia, penis, urethra, vesiculas seminales, the prostatic
and Cowper's glands, and with one interesting exception, supplied
by the monotremata, the genito-urinary systems are quite distinct
from the digestive. In by far the greater number of mammalia the
testicles descend into the scrotum as in man ; in some, however, as
the amphibious mammalia, the cetacea, the elephant, and the orni-
thorhynchus, they never leave the abdomen, and in others, as the
bat, the mole, and the hedge-hog, among the insectivora; the rat,
the guinea-pig, the porcupine, and the squirrel, among the rodentia,
they descend during the rutting season, and return into the abdomen
after it is over. The communication between the tunica vaginalis
and the peritoneum remains unclosed in those animals in which the
testicles descend, except man, and where these glands occasion-
ally pass into and out of the cavity, the communication is very
free. The vasa deferentia are very serpentine in those ani-
mals where the testicles remain in the abdomen, and in ruminants,
the elephant, and especially the horse, they are greatly dilated near
their termination in the urethra.

Vesiculce Seminales.— There seems to be no general law for the
presence or absence of these accessory bodies. They are met with
ID the camel, elephant, bull, ram, horse, boar, guinea-pig, rabbit,
hedge-hog, &c. In these animals they have either no communica-
tion, or a very imperfect one, with the vas deferens. In man and
the simiae only is the communication free and direct. The prostate

102 EVERs's COMPARATIVE ANATOMY.

is more constant in its existence than the vesiculae, being found in
all orders of the mammalia, excepting perhaps the greater number
of the rodentia and insectivora. It is double in the elephant, the
camel, the horse, and some others. Compels glands, which are
small, and situate behind the bulb of the urethra in the human
subject, are large, and often increased in number in other animals,
thus in the opossum and kangaroo-rat there are four, and in the
wombat, kangaroo, and others, as many as six. They are absent
from the greater number of carnivora, ruminantia, and cetacea. In
the marsupiata they are covered by a strong muscular stratum, and
in the icheneumon, their ducts run forward, and open near the
extremity of the penis.

Penis. — This organ is modified considerably throughout the
class. Thus, in the digitigrade carnivora, as the dog and the lion, its
two crura are separated by a distinct fibrous septum, which is absent
in the cetacea, pachydermata, and plantigrade carnivora. In the
cheiroptera, qnadrumana, cetacea, rodentia, and carnivora, with the
exception of the hyena, and a few others, the penis is occupied by
a cylindrical bone occasionally grooved. Remarkable peculiarities
exist in the intromittent organ of the marsupiata; in the opossum
the glans is bifid, and has three openings, one for the urine, and
two for the semen. In the ornithorhynchus paradoxus the penis is
double anteriorly, and in the hystrix, it divides into four glands,
each furnished with sharp papillse perforated for the discharge of
the semen, but in neither of these strangely organised animals does
the urine pass through it, this organ being concealed within the
cloaca. The urethra shall be deferred till the consideration of the
urinary organs.

The female organs of generation in the mammalia consist of the
vulva, clitoris, nymphse, vagina, uterus, Fallopian tubes, and ovaries.
These latter organs are invariably double; in the marsupiata
their structure is racemose as in birds, but in all the other genera
they are more solid, and approach more or less the human type.
The Fallopian tubes present but few peculiarities, except in the
echidna and ornithorhynchi, where they experience a dilatation in-
feriorly to supply the place of a uterus, and afterwards open sepa-
rately into the short vagina, on each side of the orifice of the urin-
ary bladder. In the lower orders of mammalia the urethral and
sexual passages are blended together, the uterus is elongated in form,
and thin in its walls; in the carnivora, ruminantia, pachydermata,
and cetacea, a mesial cleft appears, and the cornua are greatly deve-
loped ; and in the marsupiata and most rodentia, the organ is
divided into two lateral halves, each opening separately into the
vagina, which, in the virgin state of the sloth, the ass, the mare,
the pig, and the cow, is divided by a narrow ve3itical septum. The
external organs of generation afford no striking peculiarities, except
in the deficiency of nymphae and hymen.

From a review of the above details of the generative organs in
the marsupial and monotrematous orders, one must expect to find

ORGANS OF GENERATION IN THE VERTEBRATA. 103

some peculiarity in their mode of generation. In all the other
mammalia the ovum is fecundated in the ovary, from which it de-
scends through the Fallopian tube to the uterus, in the higher
orders about the twelfth day. An intimate vascular connection is
now established between the ovum and the uterus, by means of the
placenta, and continues till the embryo is fully formed, and as we
say, capable of enjoying an independent existence. This consti-
tutes the period of utero-gestation, which, in the human subject is
ten lunar months, but varies in almost every species of the class.
A very different process, however, takes place in the animals above
alluded to, thus in the kangaroo, the foetus, small and imperfect,
leaves the uterus about the thirty-ninth day after conception, and
is lodged by the mother in the marsupium or pouch formed for its
reception on the lower part of the abdomen, by a fold of integument
in which the mammary gland is placed. Shortly after it reaches
the pouch, it is found attached by its mouth to one of the nipples,
from which it receives a constant supply of milk ; this is rendered
more secure by the gland being covered over by a stratum of mus-
cular fibres, which enables the mother to feed the foetus at pleasure.

The mode of breeding of the monotremaia is as yet involved in
some obscurity. The word monotremata means animals with a
single outlet from the genito-urinary and digestive organs, called a
cloaca; and is applicable to all the marsupiata, but is at present
confined to the edentate species of them, as the echidna and orni-
thorhynchi. Previous to the late valuable researches of Mr. Owen,
the existence of mammary glands in these animals was denied,
which, combined with the structure of their ovaries, and their pe-
culiar development of uterus, led to the supposition of their being
oviparous in their generation.

Although the structure of their generative organs, the presence
of mammary glands, their bearing their young alive, and suckling
them, confer on them the ovo-viviparous type of generation, it must
be acknowledged they possess many characters in common with
reptiles.

RECAPITULATION.

1. All forms of generation conform to the fissiparous, gemmipa-
rous, oviparous, viviparous, and ovo-viviparous.

2. These organs are separate and distinct in the insecta, the
annelida, and the Crustacea. In the mollusca they are single, and
confined to one side.

3. This system is simple in fishes, and a rudimentary penis oc-
casionally present.

4. Internal impregnation rarely occurs among the amphibia or
reptiles.

5. In birds the size of the testicles varies according to the season,
and the penis is often absent.

104

6. In some orders of mammalia the testicles never leave the
abdomen, and in others they descend at certain periods.

7. There is no general law for the presence or absence of vesi-
culae seminales or prostate, the latter is more generally present .

8. The penis in many instances is furnished with a bone ; in
some it is bifid, and in the ornithorhynchus no urine passes
through it.

9. The generative organs and mode of generation are peculiar
in the monotremata.

CHAPTER XIX.

URINARY ORGANS IN THE INVERTEBRATA.

The urinary, like the biliary and lachrymal apparatus, consists
of four principal parts, each having its peculiar office consigned to
it, and all jointly contributing to the same end — namely, the sepa-
ration from the blood, and the discharge from the system, of certain
decomposed and effete animal and saline matters. The urinary
organs, when complete, as they are in the higher orders of animals
consist of the kidneys, the ureters, the bladder, and the urethra.

Although the mollusca secrete urine, and uric acid has been de-
tected in the long convoluted caeca of insects, and even through
the bodies of cantharides ; yet no perfect urinary system has been
discovered in the great invertebrate division of animals. It is more
than probable that the function of the kidneys in the majority of
instances devolves on the respiratory, the cutaneous, and the biliary
systems, together with certain glands, many of which serve not only
for the elimination of noxious materials from the system, but as or-
gans of defence on the approach of danger; in this latter light may
be regarded the acrid secretions of bees, beetles, wasps, and spiders ;
as also the ink of the cuttle-fish which has the effect of blackening
a considerable extent of the surrounding water, and thus baffling
the attacks of its enemies : and among the vertebrata, a striking
example is presented by the yagouare of Azara, one of the mephitic
weasels of Chili, whose urine is rendered so intensely offensive by
the secretion of some adjoining glands, that dogs or other animals
which have been sprinkled with it during their pursuit of this crea-
ture, are said to have torn portions of their own skins off from dis-
gust, notwithstanding careful and repeated ablutions.

URINARY ORGANS IN THE VERTEBRATA. 105

CHAPTER XX.

URINARY ORGANS IN THE VERTEBRATA.
PISCES.

The kidneys in this class are long and narrow, sometimes extend-
ing the whole length of the abdomen, as in the burbot. They
generally present the appearance of forming but a single mass,
their separation being only indicated by the presence of the ureters
and the cava. The ureters, which arise by numerous fine radicles,
soon unite in all the osseous fishes, into a single tube, which forms
a heart shaped dilatation previous to its termination behind the
anus, in common with the sexual organs.

Bladder. — This reservoir is absent from all the osseous, and
several of the cartilaginous fishes, as the ray and shark, in which
the ureters open as in birds, into a cloaca: when it is present as in
the lump-fish, it receives the ureters anteriorly, and opens behind
the anus in common with the vasa deferentia.

AMPHIBIA.

The kidneys are more distinct in this class than in fish. They
are greatly lengthened in the aquatic genera, but are much shorter in
the frog. The ureters convey the urine to the bladder, which is
situated in front of the rectum : in the frog it is of considerable size,
its walls are thin, and its fundus presents' two cornua. In the rep-
tilia the kidneys afford but few peculiarities, being elongated in the
lizard, as in fish, and somewhat oval in the tortoise. The ureters
are longer in this class than in the amphibia, and discharge them-
selves either into the cloaca or bladder. This organ is absent from
the ophidia, and several of the sauria, as the lizard, and the croco-
dile. It is very large in the chelonia, as the tortoise, and it is sin-
gular, that the ureters instead of going to it, empty themselves into
the urethra in front of it, so that the urine has to re-ascend to the
urinary reservoir.

AVES.

In this extensive oviparous class the kidneys are of great length,
extending along the spine, from the lungs to the lower end of the
rectum. These organs are relatively larger in birds than in the
terrestrial mammalia — a circumstance which is explained by recol-
lecting the nature of their integuments, and the little transposition
they admit of. They are of small size in the bustard and heron,
and their lower extremities are somewhat blended together in the
coot. Their structure is remarkable for the absence of cortical
portion ; the tubuli uriniferi run to the surface, and by their con-

106-

fluence form the commencement of the ureter, which descends
along the surface of the kidney, and posterior wall of the rectum,
and terminates in that part of the cloaca called the urethro-sexual
cavity. The space between their termination and that of the rec-
tum is large in the owl and many aquatic birds, and is looked upon
by some as a rudiment of urinary bladder.

The supra-renal capsules are small, of a bright yellow colour,
and placed on the inner and upper part of each kidney, in contact
with the testicle or the ovary. They are erroneously supposed by
some to have some functional relation to the generative system.

MAMMALIA.

The kidneys are lobulated in the cetacea, seals, otters, bears, the
elephant, the ox, &c, as in the human foetus. In the otter each
kidney consists of about ten lobules; in the bear of about fifty, and
in the seal as many as a hundred and thirty. They present a lobu-
lated appearance in many other mammalia during the early periods
of existence. The ureters enter the bladder in an oblique direction,
a little behind its neck, in all the animals of this class, with the ex-
ception of the echidna and ornithorhynchus, in which they open
into the urethra near its commencement, so that the urine must ?G-
ascend to the bladder, as in the chelonian reptiles. In the mamma-
lia generally the bladder lies more loose in the abdomen than in
the human subject, owing to its more perfect peritoneal investment.
For the greater part it is more muscular and less capacious in the
carnivora than in the herbivorous tribes. In the rodentia, however,
it is small and fleshy. The shape of the bladder will be found to
vary in obedience to age, sex, and species, the younger the animal,
however, the more elongated will it be found, and in the human
embryo it is cylindrical, tapering towards the urachus above, and
the urethra below.

The renal capsules, like the kidneys, are lobulated in the cetacea,
and other aquatic mammalia, and are found relatively very large
in the young of animals possessing them. The urethra, as in the
human subject, consists of a membranous or muscular, and of a
spongy portion, the former receiving the accessory secretions. In
the boar and many ruminants these two portions join at an angle.
The corpus spongiosum arises by two roots in most of the marsu-
piata, and in the kangaroo, the urethra runs through the centre of
the penis to its extremity.

RECAPITULATION.

1. In the great invertebrate division of animals, the functions of
the kidneys seem to be performed by other parts, as the surface of
the body generally, and certain glands.

2. Kidneys exist in all fishes, but a urinary bladder is confined
to the cartilaginous tribes.

NAMES OF AUTHORS CONSULTED. 107

3. Birds have kidneys and supra-renal bodies, but no bladder.

4. The kidneys are lobulated in the adult state of many, and in
the foetal state of most mammalia.

5. The ureters open into the bladder in all the mammalia,
excepting the monotremata.

LIST
OF THE PRINCIPAL AUTHORS CONSULTED.

Baron Cdvier.— Leeons D'Anatoraie Comparee— Regne Animal— Bv

Griffith, &c.
Linnjeus. — Systema Naturae.
Grant. — Outlines of Comparative Anatomy, &c.
Lamark.— Histoire Naturelle des Animaux sans Vertebres.
Owen.— Clycopaedia of Anatomy and Physiology, &c.
Coldstream.
Edwards.

Lawrence. — Zoological Lectures.
Bell. — Cyclopaedia of Anatomy and Physiology.
Auduin.
Todd.
Sir C. Bell.— Mechanism of the Human Hand— Bridgewater Treatise.
Blumenbach. — Comparative Anatomy, by Lawrence.
Deshayes.— Cyclopaedia of Anatomy and Physiology.
Harrison.
Sharpey.
Carus by Gore.— Introduction to the Comparative Anatomy of

Animals.
F. Cuvier.— Histoire Naturelle des Mammiferes.

Houston.— Descriptive Catalogue of the preparations in the

Museum.
Fyfe. — Outlines of Comparative Anatomy.
Thomson.— Cyclopaedia of Anatomy and Physiology.
Jacob.
Jones.
Sir E. Home.— Lectures on Comparative Anatomy.
Mueller. — Elements of Physiology.
Hunter. — Animal (Economy.
Roget— Bridgewater Treatise.
Rees. — Cyclopaedia.
Blainville.— De l'Organisation Des Animaux, ou Principes

d'Anatomie Comparee.

CONTENTS,

CHAP. I. Preliminary Observations,

Cuvier's Classification of Animals,
Grant's Classification of Animals,
II. Skeleton in the Invertebrata — General Remarks,

III. Vertebrata — General Observations,

— Pisces,

Amphibia,

Reptilia,

Aves, ...

Mammalia, ...

Recapitulation, -

Fossil Bones of Animals, ...

IV. Ligamentary System, ...

V. Muscular System in the Invertebrata,
VI. Vertebrata,

VII.
VIII.

Pisces,

Amphibia,

Reptilia,

Aves,

Mammalia,

Recapitulation, -

Nervous System in the Invertebrata

Vertebrata,

Pisces,

Amphibia,

Reptilia,

Aves,

Mammalia,

Recapitulation,
IX. Organs of Sense — Vision,

Hearing,

Smell,

Taste, -

Touch,

Recapitulation,
X. Organs of Digestion in the Invertebrata,

XI.

Development of Teeth,
Recapitulation,
XII. Absorbent System,

Vertebrata — Pisces,

Amphibia,

Reptilia,

Aves, -

Mammalia,

PAGE

7
. 8

10
. 11

- 15
18

- 19
22

. 29
38

- 38
39

. 40
42

. 42
42

- 43
44

- 45
46

. 47
48

- 48
50

. 51
51

. 53
56

. 56
61

- 63
64

. 65
65

. 65
69

- 71
72

. 73
76

- 77
82

. 83

112 CONTENTS.

XIII. Sanguiferous System in the Invertebrata, 84

XIV. Vertebra ta— Pisces, - - .86

Amphibia, .... 86

Reptilia, ' - - .87

. Aves, .... 88

Mammalia . - . 89

Recapitulation, --,.... 91

XV. Respiratory Organs in the Invertebrata, - - - - 92

XVI. Vertebrata— Pisces, ... 94

Amphibia, - - . .95

Reptilia, - - - 95

Aves, - . . . .95

Mammalia, ■ . . - 96

Recapitulation, - . - - - - - 97

XVII. Organs of Generation in the Invertebrata, ... 97

XVIII. Vertebra I a— Pisces, . - - 100

Amphibia, - - 100

Reptilia, . - - - 100

Aves, . . . .101

. Mammalia, - - . - 101

Recapitulation, - - . ... . - 103

XIX. Urinary Organs in the Invertebrata, .... 104

XX. Vertebrata— Pisces, - - . 105

Amphibia, ..... 105

Reptilia, - - - - .105

Aves, . . . - .105

Mammalia, . - - .106

Recapitulation, ....... 106

Names of Authors who have been consulted, - - - 107

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