X

o

^

THE STUDENT'S MANUAL

OF

COMPARATIVE ANATOMY,

AND

GUIDE TO DISSECTION.

DESIGNED FOE THE USE OE SCHOOLS AND OF JTJNIOE STIJDENT8
IN THE TTNIYEESITIES.

PAET I.
MAMMALIA.

(Anatomy and Dissection.)

BY

a HERBERT MORRELL, M.A., B.C.L.,

Late Assistant Demonstrator of Anatomy and Physiology
in the University Museum, Oxford.

LONDON : LONGMAN & Co.

OXFORD : Thos. SHEIMPTON & SON.

1872.

OXrOED : PRINTED BY H. ALDEN, CORN-MARKET STREET.

COMPARATIVE ANATOMY,

AND

GUIDE TO DISSECTION.

PAET I.

MAMMALIA.

(Anatomy and Dissection.)

ERRATA.

Page 6, line 5, for Proboscedia, read Proboscidea.

„ 16, „ 11 from bottom,/or Phascochaeres, reaf? Phacochserus.

^for Dycoteles, read Dicotyles.
„ 11, „ 3, /or PhaseolomydEe, r<ac? Phascolomidse.
for Hysipriminus, read Hypsiprimnus.
,,24^, „ 15, /or post-scapalar, reac? post-scapular.
„ 39, note, /or aromion, read acromion.
„ 53, note, /or Didelphydse, read Didelphidse.
„ 55, line 13, /or Phascolomyidae, read Phascolomidae.
„ 81, „ 7,/or t i^ , read t

1 or 2 . 1 or 2

2 . 2

85, „ 10, /or Hypsiprininus, rcac? Hypsiprimnus.

85, „ ^2, for Ornithorhynchus, read Ornithorhyncus.

88, „ 7, /or Arthodactyla, reac? Artiodacty la.

141 „ 7 from bottom, /or reptum, read septum.

146 „ 9 from bottom, /or occuli, read oculi.

159 , , 6 from bottom, dele pair of.

160 „ 5, /or of each pair of, read of the.

168 „ 4 from bottom, add in Man after temporal bone.

181 „ 2 from bottom, /or clavide, read clavicle.

182 „ 2, insert commas after syringe and made.
188 ,, 4, /or rena rea«5? renal.

235 „ 2 from bottom, /or Glasserian read Gasserian.

PREFACE.

In preparing the following short outline of the
Anatomy of the Mammalia, and of the Methods to be
pursued in investigating (a) the arrangement of parts
in the Mammalian Body, and (b) the special con-
struction of certain of these parts, e.^. the Heart,
Brain, Eye, and Cerebral I^^ervous System, frequent
reference has been made to, and almost verbatim
extracts taken from, the following books and papers,

Carpenter. Principles of Comparative Physiology.

Colhold. Cyc. Anatomy and Physiology, — art. Euminantia.

Mlis. Demonstrations of Human Anatomy.

Flower, Osteology of the Mammalia, in Journal of Anatomy and
Physiology, 1867 and 1869 (Mammalian Teeth). In Philoso-
phical Transactions, 1867 (Marsupial Teeth), and 1865, p. 633
(Marsupial and Monotreme Brain).

Oray. Human Anatomy.

Gulliver. Proceedings of Zoological Society, March, 1870 (Striated
Muscular Fibre of (Esophagus).

JETewson. Sydenham Society, 1846 (Blood Corpuscles).

Sulke. British Medical Journal, September, 1870 (Eye).

Huxley. Elements of Comparative Anatomy, 1864.

Mayer. Anat. TJntersuchungen liber das Auge der Cetaceen.

Marshall^ J. Phil. Trans., 1850, p. 133 (Azygos Veins).

Milne Edwards. Lemons sur la Physiologie.

Owen. Comparative Anatomy and Physiology of Yertebrata, Yds.
ii. and iii.

Parker. Shoulder Girdle.

Quatn. Human Anatomy.

Rapp. Cetaceen.

Rolleston. Forms of Animal Life.

Rutherford. Quarterly Journal of Microscopical Science, Jan. 1872
(Preparation of the Retina).

vi. Preface.

Strangeways. Veterinary Anatomy.

Turner (Edinburgh). In JS'atural History Review, 1862 (Orbit).

Van der JEoeven. Handbook of Zoology, Vol. ii.

Wagner. Comparative Anatomy of Yertebrata.

Waterhouse. Natural History. of Mammalia.

In making such extracts, it has been the object of
the Author to present to the Student, within the limits
of a few pages, a condensed summary of the salient
points to be noted in studying the Mammalian organ-
ism ; in other words, to point out shortly, and in one
handy volume, the essence of matter spread over many
pages in many different volumes. Although in some
respects the opening pages of the present volume may
bear upon their surface the impress of a species of
'' technical cram book '' ; it is hoped that the conclud-
ing pages, in which a series of Dissections are proposed
to the Student, may in some measure erase such an
impression, from the fact that in the pursuit of such
practical study as there put out the Student is so
brought face to face with many of the structures
treated of in the former part of the volume that they
cannot any longer remain to him mere abstract ideali-
ties, but must become well defined, tangible realities,
impressed upon his mind as things seen.

In conclusion, the Author would express his sincere
thanks to Mr. C. Eobertson, .Demonstrator of Anatomy
and Physiology in the University Museum, Oxford, for
his untiring supervision of the proof-sheets passing
through the press, and for his many valuable hints
and suggestions as the work proceeded.

3 Park Street, Oxford,

October, 1872.

CONTENTS,

Classification

PAGE

1

Classification Table

14

Osteology ......

19

Digestive System .....

58

ClECIFLATOEY SySTEM ....

98

Kespieatoey System ....

108

XJeinaey Oegans .....

115

Pecxjliae Glan^ds .....

117

Nervous System .....

119

Ceeebeal Convolutions (aftbe Geatiolet)

132

Oegans of Special Sense

139

Dissection of Sheep's Heaet

153

Dissection of Sheep's Beain .

161

Dissection of Common Eat . . . .

180

Dissection of Sheep's Head . . . .

208

Dissection- of Eye of Ox . . . .

260

Table of Ceeebeal Neeves, etc.

ad Jin.

Table of Ceeebeal Convolutions (aftee Geatj

[olet)

ad fin.

CLASSinCATIOK

The Class MAMMALIA lias been grouped with tlie
Sauroids, or Sauropsida, for that they both lack apparatus
for breathing air when dissolved in water. They have been
hence termed Abranchiate Vertehrata,

By virtue of being a Yertebrate, the Mammal is possessed
of well-marked characters, separating it from other Non-
Yertebrate living creatures {e. g. an endo- skeleton, &c., see
the Introduction) : and inasmuch as it is an air-breathing
Yertebrate, the ultimate sub-divisions of the appendages of its
scapular and pelvic arches will be found not to exceed five.

This Class includes fifteen

ORDERS :

I. BiMANA YI. Sectosialia XI. Cete

II. QUADKFMANA VII, PfiOBOSCIDIA XII. SlEEJTIA

III. Inskctivora YIII. Pkeissodacttla XIII. Ij^-examellata

IV. Cheiropteea IX. Hyracoidea XIV. Marsupialta

V. Rod en Ti a X. Aetiodactyla XV. Moxotremata

N.B.- — For examples see the annexed Table.

The Orders I. — XIII. inclusive form the Sub-class

'^PLACENTALIAr

The Orders I. — V^I. inclusive form part of a great section
of the Mammalia w^hich are possessed of claws, and are
thence termed

''UNGUICULATAr"^

I. In the Order BIMANA is included the genus Homo
alone ; set apart as possessed of, — hands (thumb opposable) to

* Tho remaining three Orders whicli come under this wide Section are the
In-enamellata, Marsupialia^ and Monotrcmata, treated of later on.

B

2 Mam. — Classifica tion,

the anterior extremities only, — special modifications of the
pelvic arch and limbs, and muscles thereto attached, whereby
the erect position is maintained, — the highest development of
brain, and, — no muzzle.

II. In the Order QUADRUMANA, the hand (innermost
digit opposable) is present on the posterior extremities ; and
the muzzle is more or less elongated. Three well-defined
Groups are comprised in this " Order,^' viz, :
1. Catarrhina 2. Platyrrhina. 3. Strepsirrhina

or Simiadae. or Lemuridae.

which are divided into two

Sub-orders :
First, SimiaDtE, or Monkeys, including the two first groups.
Second, Lemurid^, synonymous with the third group.

The Catarrhina have the nostrils oblique and approximated
below, and opening above and behind the muzzle. They are
restricted to the Old "World. This Sub-order includes the
Anthropomorphous (tail-less) Apes, Baboons, &c.

The Platyrrhina have the nostrils simple, sub-terminal, and
wide apart; and the tail generally prehensile. They are
peculiar to South America,

The Strepsirrhina have curved or twisted terminal nostrils.
They are confined to Africa, Madagascar, and India. In this
Sub-Order, the Cheiromys (Aye- Aye), is included, which was
classified by Cuvier among the Eodentia.

III. Among the INSECTIYORA, all of which have
molar teeth, bristled with cusps, the Galeopithecidce find a
place : these have by various authors been assigned to the
Cheiroptera (Cuvier), or to the Lemuridae of the Quadrumana.
The latest authorities, however. Professors Owen and Huxley,
classify them as here given. The other members of this
Order are the ErinaceidcB, which have the body covered with
prickles instead of hairs ; the Soricidce, with close fur, pointed
muzzle and scaly tail ; and the TalpidcBy which have amazingly
powerful fore-feet, and lack the organ of vision.

Mum. — Classification, 3.

IV, The distinctive character of the CHEIROPTERA*
consists in a delicate leathery membrane, which, uniting the
four long fingers, that radiate widely from the wrist, and filling
up the space between them and the side of the body, has the
appearance of a wing.

The Four Families composing this Order are

1. The Vesper tilionidce, or true bats; 2. the HhinolophtdcBy
or horse- shoe bats, with a leaf- like membrane on the nose ;
both chiefly insectivorous ; 3. the Phyllostomidce, or Yam-
pyres ; and, lastly, 4. the Pteropidce or Roussettes, with head
of dog- like form, both of which are chiefly frugivorous.

Y. The RODENTIAf are characterised by two large and
long curved incisors in each jaw, separated by a wide interval
from the molars, and the divided upper lip.

This Order comprises Eight Families:
1st, the Leporidce, at once distinguished from all the other
Rodentia by the possession of a small incisor behind each
normal one. 2nd, the CavidcB, in which the tail is either
rudimentary or entirely wanting. 3rd, the HystricidcBy dis-
tinguished by the spiny quills covering their bodies. 4th,
the Chinchillidcey with large broad ears and tufted tail.
5th, the Castoridce, distinguished from all other Rodents by
their horizontally flattened tail, of a nearly oval form, and
covered with scales. 6th, the Muridce, which have only four
toes on the anterior feet, and a sort of wart to represent the
thumb, and a long scaly tail. 7th, the Myoxidce, intermediate
between the preceding more or less mouse-like animals and
the true squirrels. And, lastly (8), the Sciuridce, which may
be recognised by their very compressed lower incisors and by
their long bushy tail. The Cheiromys, or Aye- Aye, classi-
fied by Cuvier among the Rodents, is now considered to
belong rather to the Lemuridge (Quadrumana).

• ;^»/j, hand : irrt^tv, wing.

t Synonymous with the Glires of Linnaeus.

4 Mam . — Class ifica tion .

•

YI. The species of the Order SECTORIALIA,* synonym-
ous with the Order Carnivora, as restricted by Profs. Owen
and Huxley, may be at once recognised by, — their four coni-
cal, curved, acute, canine teeth, — the gap between the incisors
and canines in the upper jaw for the reception of the lower
canine, — the molars either wholly trenchant or somewhat
tuberculated, but never studded with sharp conical projec-
tions, and — in each molar series the Dens Sectorius.

This Order is divided into four

Sub-orders :

1. DiGITIGRADA. 2. SeMI-PlANTIGRADA.

3. Plantigrada. 4. Pinnigrada.

1. The Sub-order Digitigrada includes the most typical
members of the Order : those whose short toes alone are ap-
plied to the ground, and that walk on tip-toe.

Such are the Families
of 1. the Canidce, in which the toes are all armed with non-
retractile claws, and the tongue is soft and destitute of horny
spines. 2. The Felidce, which have retractile claws, and a
tongue covered with small recurved prickles. 3. The Hycenidce,
with non- retractile claws (Canidae), a prickly tongue (Felidae),
and a pouch beneath the anus (Yiverridae). 4. The Viverridce,
whose glandular oval pouch secretes the odorous civet.

2. The second Sub-order, the Semiplantigr.U)a, is

synonymous with the Family
of the Mu&telidce ; animals which apply a portion of the sole
to the ground, but have the heel always raised : on account
of the length of the body and shortness of the limbs they

* The term Carnivora as used by Linnaeus included the Cheiroptera and In-
sectivora, as well as the so-called ' Carnivora proper,' and is synonymous with the
Carnaria or Carnassiers of Cuvier. The Cheiroptera and Insectivora being now
recognised as separate Orders, it seems inappropriate to use the same term to
denote the remaining group alone. The name Sectorialia has been here applied
having reference to the Dens Sectorius, or scissor tooth, found in the typical
members of this Order.

Mam. — Classification. 5

move with a peculiar gliding character, and have been termed
Vermi formes [PYermin].

3. The third Sub- order, the Plantigrada, in which the
whole or nearly the whole of the hind foot forms a sole, and
rests upon the ground, «

contains Three Families :
1. The MelidcB. — The members of this family have been clas-
sified sometimes among the Yiverridao, sometimes among the
Ursidae (Linna3us). 2. The Ursidce, which differ from all the
preceding families in the nature of the molar teeth, which,
although compressed in form, are furnished with tubercular
crowns. And 3. The Cercoleptidce, or Kinkajous, with very
long prehensile tail, short muzzle, and slender extensile
tongue.

4. In the last Sub-order, the Pinnigrada, both fore and hind
feet are short, and expanded into broad webbed paddles for
swimming, the hinder ones being bound in with the skin of
the tail.

It includes Two Families :
1. The Phocidce, which have incisor teeth in both jaws,
generally throughout life, — canines of moderate size, and —
molars trenchant ; and 2. Trichcecidce^ which lose most of
their incisor teeth early, — have upper canines enormously
developed, passing between the small canines of the lower
jaw, and projecting below the chin, and — molars of conical
form.

We now proceed to consider the purely vegetarian section
of the Mammalian Class, which is characterised by having
hoofs instead of claws, and is thence termed

*' ungulata:'

(Orders YIII. — X. inclusive.)
Cuvier divided his ^'sub-class" Ungulata into two Orders,
which he named Pachydermata and Ruminantia, and placed

6 Mam. — Classifica Hon .

under the order Pacliydermata the following three genera,
viz. Proboscidea, Ordinaria {e.g. Sus and Tapirus), and Solid-
ungula.

Modern classification has raised Cuvier's genus P. Probos-
cedia to rank as an Order, and has subdivided his genus P.
Ordinaria into three ; first, taking out those animals with an
"Even" number of digits fully developed ; and, secondly,
taking out of the remainder, which of course have an " Odd"
number of fully developed digits, the Hyracidae. With the
" Even" toed P. Ordinaria has been associated Cuvier's Rumi-
nantia, to form the Order called Artiodactyla (apnog even,
^aKTvXog digit). With his " Odd" toed P. Ordinaria has been
grouped Cuvier's Solidungula, to form the Order called
Perissodactyla (Trepiaraog odd, uneven, daKrvXog, digit). Lastly,
the family of the Hyracidae has been elevated to form the
Order called Hyracoidea.

TABLE OF UNGULATA.

CUVIER'S ORDERS. MODERN ORDERS.

Ruminantia . ! Ruminantia | aRTIODACTYLA

( even-toed = Omnivora )
/ ordinaria j hyracidae HYRACOIDEA

Pachydermata ) ( odd toed = Multungula \ T>T7-nT;2«nrk \ ptvt a

) solidungula ; . . Solidungula } i'J^^^^&^^^Abl ILA

\ proboscidea PROBOSCIDIA

YII. The PROBOSCIDIA. The members composing this
Order are characterised by the possession of two incisors, in
the form of long tusks ; and of a nose prolonged into a cylin-
drical trunk, flexible in all directions, highly sensitive, and
terminated by a prehensile appendage like a finger. Herein
are included

only the Family
of the Elephantid(2.

YIIL In the Order PERISSODACTYLA are included aU
those animals that have an unsymmetrical or odd number
of toes in the hind feet always, and generally in the fore
feet also. In the Tapiridae, however, the fore feet are "even"

Mam. — Classified tion . 7

toed, being tetradactyle, but tbe digits are still unsymmetri-
cal {viz.y inter se), for digit iii. is the largest and longest. If
the species be horned, tbe born or borns are placed on tbe
median line of tbe bead.

Tbis Order is divided into two

Sub-orders :

1. SOLID-UNGULA. 2. MuLT-UNGULA.

1. Tbe Sub-order Solidungula is

synonymous witb tbe single Family
of tbe Equidce, cbaracterised by baving only one digit (iii.)
completely developed in eacb foot ; and baving tbat digit
enclosed at its extremity in an entire boof.

2. Tbe species included in tbe Sub-order Mult-ungula
bave all tbree toes to tbe bind feet, and also to tbe fore feet,
witb tbe exception above named (Tapiridae). Tbey are

* divided into two Families :
1. Tbe Rhinoceridce bave, springing from tbe upper surface
of tbeir muzzle, a single or double born, composed of a solid
mass of borny fibres, supported on a bony protuberance of
tbe nose. Wben two borns. are present, tbey are placed one
bebind tbe otber, and tbe posterior born is mucb sborter tban
tbe anterior. 2. Tbe Tapiridce bave tbe nose produced into
a sbort proboscis.

IX. Tbe species of tbe Order HYRACOTDEA were long
placed among tbe Hodentia, on account of tbeir size : Cuvier
placed tbem next to tbe UbinoceridaD : Wagner made a
separate group of tbe Pacbydermata for tbeir reception, wbicb
be termed " Lamn-ungula," for tbat tbe feet are furnisbed
witb flattened nails instead of boofs. Tbis Order

contains but a single Family ^
tbe Hyracidts.-

X. Tbe AETIODACTYLA. Tbe species comprised in
tbis Order are cbaracterised by baving an even number of
boofed toes to eacb foot ; sometimes four, e.g. Hippopotamus,

8 Mam. — Classification.

sometimes two, e.g. Camelopardalis Giraffa ; and sometimes
two functional and two rudimental, e.g. most Rmninantia. If
the species be horned, the horns form one pair or two pairs ;
they are never developed singly, nor if there be two are they
placed on the median line of the head.

The Order Artiodactyla readily divides into two

Sub-orders :

1. OmXIVORA- 2. RUMIXANTIA.

The Sub-order Omxivora comprehends those species which
Cuvier grouped together as the " even- toed Pachydermata
Ordinaria," and of which he said, that they approximated
the Ruminants in various parts of their skeleton, and even
in the complication of the stomach, viz. the

Two Families
of the Hippopotamidce and the Suidcp. Of these the species
of the former have four toes, each terminated by a hoof to
each foot ; while the species of the latter have two hoofed
toes functional, i.e. available for walking, and twof others,
rudimental, placed at some little elevation on the back of the
foot.

2. The Sub-order Ruminantia (the Pecora of Linnaeus,
and recognised by Aristotle as a natural Order, under the
title fivpnica^oyra) , is one of the most distinctly circumscribed
groups of Mammalia ; one family alone, the Camelidac, pre-
senting any considerable exceptions to the general characters
of the Sub-order ; such as are, — the absence f of incisors in the
upper jaw, and their replacement by a callous pad ; — the
likeness and approximation of the lower canines to the lower
incisors ; — the wide diastema anterior to the molar series ; —
the true molars marked as to their crowns with two double

* In Dicotyles tlie hind feet are said to have only three toes, one of the
hinder ones being deficient.

t The Camelidce have a single pair of incisors in the upper jaw ; and lower
canines, and incisors dissimilar.

Mam. — Classification. 9

crescents, the convexity of which is turned inwards in the

upper and outwards in the lower jaw ; — the stomach divided

into four separate compartments : and — the * cloven foot/ the

two hoofs on each foot presenting a flat surface to each other,

appearing as though a single hoof had been cleft. It is on

the structure of the stomach that the faculty of returning

food to the mouth for remastication depends, and it is from

the name (rumen) given to the first of the compartments of

the stomach that the title of this Sub- order is derived.*

The species comprised in this Sub- order may be divided

into three well-marked groups, having regard to the presence

or absence of horns, and the condition in which the horns

when present exist, — viz.

Groups.

1. Carenticornua. 2. Solidicornua. 3. Cavicornua.

Of these, the first group, Carenticornua {careo, to be with-
out ; cornua, horns),

comprises the two Families
Ca?nelid(Bf and Moschidw, of which all the component species
are without horns ; generally have a cleft tumid lip ; and
modifications of claws rather than hoofs.

All the other Ruminantia, at least of the male sex, have
two horns, which may exist either as distinct bones uniting
directly with the skull ; or, as solid osseous developments aris-
ing from processes of the frontal bone ; or, lastly, as sheaths
of horny matter covering conical processes of the frontal
bone.

In the Group Solidicornua [sglidus, not hollow), are com-
prised those species which have dense osseous horns, viz.,
those composing the

Two Families
Cervidce and CamelopardidcE. The horns or antlers of the

* " Ruminatio dicta est a rumine eminente gutturis parte, per quani demiasus
cibus a certis revocatur animalibus." Serv. Virg. E. vi. 64.
t See note supra.

C

10 Mam, — Classification.

Cervidae are deciduous, and witli but a single exception, that
of Kangifer (Reindeer) are possessed only by males. The
boms of the Camelopardidae, on tbe contrary, are permanent,
and covered witb a bairy skin.

Tbe Cavicornua (cavus, bollow), tbe last Group of tbis Sub-
order, is

synonymous witb tbe Family
of tbe BovidcB. In these animals tbe prominences of tbe
frontal bones are covered eacb witb an elastic sbeatb, or
bollow born, formed as it were of agglutinated bair, wbicb
continues to increase by layers during life. Tbe prominence
wbicb tbe born envelopes grows witb it during life, and is
not deciduous.

TVe propose now to consider tbat group of animals wbicb,
as being devoid of bind limbs, possessed of pectoral limbs
only in tbe form of fins, and having tbe posterior part of tbe
body flattened out into a horizontal* caudal fin, were termed
by Cuvier

Mammalia MUTILATA.

This Sub-class (of Cuvier) contained one Order termed
Cetacea, and tbis again two Genera; 1. The C. Herbivora,
represented by tbe Dugong and cogeners, 2. The C. Ordi-
naria, or Blowers, represented by the Whale, &c. Modern
classification has elevated these two genera each to rank as
an Order. Some Zoologists have retained the name *' Cetacea"
for one of these Orders, using it to denote the C. Ordinaria
alone, thereby introducing confusion. To avoid tbis, the term
Cete has been here used instead, to designate tbe Order
synonymous with Cuvier's C. Ordinaria. The term Sirenia
has been adopted as tbe " Order "-name, synonymous witb
Cuvier's genus C. Herbivora.

* Fish hare the tail fin vertical.

Maryi . — Classifica tion . 1 1

XI. The species included by the modern Order CETE*
are either edentulousf or Monophyodont ; and all have the
external nostrils, spiracles, or blow-holes, situated on the top
of the head. They may be

divided into Three Families,
1. The BalmnidcB, or true Whales, in which the teeth are
deficient, t and the two sides of the upper jaw, furnished with
thin transverse serrated laminae, termed baleen or whalebone.
2. The Physeteridce, or Sperm Whales, which have no baleen
plates in the palate, nor teeth in the upper jaw, except in a
very rudimentary condition. The superior portion of the
enormous head consists of cavities filled with an oil which
solidifies by exposure, called spermaceti. 3. The DelphinidcBj
which always have one or more teeth in the upper jaw.

XII. The species included by the order SIEENIA have

teeth of difterent kinds, are Diphyodont, and have nostrils

situated at the upper fore part of the snout. In this order

there are

only Two Families.

1. The Rhytinidcey now extinct, are said to have had no

true teeth, but only a pair of bony plates, placed anteriorly,

on the palate and lower jaw. 2. The Manatidce are always

furnished with molar teeth.

The three following Orders complete the "Unguiculata."
XIII. The Order IJNT-ENAMELLATA J (teeth devoid of

• In the Linnsean classification the term Cete was used of the same Group
of animals as that to which it is here applied.

t In the adult.

X The term In-Enamellata has heen here adopted in order to avoid that ex-
treme confusion which has arisen from employing, in different schemes of clas-
sification, one and the same term to denote quite distinct aggregations of families.
When Cuvier entitled his sixth order of Mammalia " Edentata" he did so having
regard to certain groups of animals which were possessed in common of this
negative character alone, viz. that they lacked teeth in the fore part of their
jaws. With him the Order Edentata connoted the E. Tardigrada {e.g. Bradypus) ;

1 2 Mam . — Classifica tion .

enamel) is synonymous with Owen's Bruta, or Huxley's
Edentata, and

includes Three Families.
1. The Edentula (synonymous with the Myrmecophagidse),
are all devoid of teeth, and have a highly protrusible tongue
almost entirely composed of annular muscles. 2. The Basy-
podidm, which have numerous simple unenamelled teeth, and
the body covered with bony plates, arranged in the middle
in transverse bands (distinguishing them from the Manis, or
Scaly Ant eater). 3. The Bradypodidce, which also have teeth,
but they are devoid of true enamel, and are never replaced
by a second series * : the members of this family are almost
unique in having the fore legs much longer than their hind
ones.

The two next Orders compose the Section of

IMPLACENTAL MAMMALIA.
XIV. The species comprised in the Order MAESFPIALI A
have the so-called " Marsupial" bones in common with those
composing the following Order, viz. the Monotremata, but are
themselves distinguished by a peculiar pouch or duplicature
of the abdominal integument, within which in the female are
inclosed the teats, and which serves for the protection of the
immature young, termed the "marsupium" (whence they
have been termed Didelphia) ; and by the angle of the lower
jaw more or less inflected. They are

the E. Ordmaria|(e.5'. Dasjrpus) ; and the E. Monotremata {e.g. Echidna). All
modern Zoologists are agreed that the Monotremata form a distinct Order ; con-
sequently the term Edentata, as connoting less than it did in the well-known
classification of Cuvier, should he aholished. Again, the term Bruta was used
by Linnaeus to include the Proboscidean Elephant and the Zoophagous Trichaj-
cidse, and is therefore quite inapplicable here. The term here used is derived
from the peculiarity of the teeth of those genera herein included that possess
them, viz.^ that they are devoid of enamel.
* Monophyodont.

Mam . — Class ifica tio n. 13

divided into Seven Families.

1. Ttie Phascolomydce (Wombat) present, in ttie arrange-
ment of the teeth, a considerable resemblance to the Rodentia.
2. The Macropidce are at once distinguished by their exceed-
ingly long and powerful hind legs with elongated feet, resting
with their whole sole upon the ground ; and forelegs very
short. 3. The Phalangistidcc have all a large thumb, so
separated from the other digits that it seems to be directed
backward, as in birds ; it has no nail, and the two following
fingers are joined by the skin as far as the last phalanx ; from
this [circumstance they have derived the family name. The
three preceding families feed chiefly on plants ; the next four
on flesh or insects. 4. In the PeramelidcE the form of the
molars would seem to agree with those of the order Insecti-
vora : in structure of hind legs they approach the Macropidae.
5. The Didelphidoe are remarkable as alone of all the Marsu-
pials possessing eight incisors in the lower jaw. 6. The
Myrmecohiidce are distinguished from all other Marsupials
by the great number of teeth, viz. fifty-two. 7. The family
of the Dasyuridce includes the largest of the rapacious Mar-
supials.

XY. The Order MO:^OTEEMATA (iiovoq, single ; rpr^na,
orifice) is so called in reference to the single excretory and
generative outlet found in the three species comprised in it,
which however is not peculiar to them among Mammalia.
The members of this Order show most distinctly, in all their
characters, a relationship to the Oviparous Yertebrata, and
have been termed Ornithodelphia.

A TABLE

OF THE

ORDERS, SUB-ORDERS, GROUPS, AND FAMILIES,
WITH EXAMPLES

OF THE

Class MAMMALIA (/z/tyu^a, a teat).

Orders i. to xiii., inclusive. , . .M. Monodelpliia s. Placentalia.

Order XIV Didelpliia \ ^ -r ^i„_ .^i-

Order XV.., ,_,. Ornithodelphia } s. Implacentalia.

Orders i. to vi. and xiii, to xv. M. Unguiculata.

Orders vii. to x. Ungulata.

Orders xi. and xii Mutilata.

Most Mammalia are Diphyodont
Orders xi., xiii. and xv. are . . Monophyodont.

MAMMALIA PLACENTALIA.
Oeder I. — BIMAI«[A, {bi?ii, a pair; mamcSf a hand.)
Sole representative, the genus, Homo Man

Order IL— QUADRUMAI^A, (quatuor, four; m—)

Sub-order 1. SIMIyB {Simla, ape.)

Group 1. Catarrhina {xara, below ; fig, nose),
or SiMTiD^ (Old World Monkeys).

/ Troglodytes niger Chimpanzee.

Anthropomorpbous (tail-less) Apes s[j;^j^'''''^* ^''^^n' '

\ Hylobates Gibbon.

Semnopithecus Douc.

Cercopithecus IVIonkey.

Macacus Macaque.

Cynocepbalua Eaboon.

I'apio Drill.
„ 2. Platyrrhina («rX«r«y;, wide ; f~)

(New World or American M.) Mycetes Stentor or

Howling M.
A teles Spider Monkey.

Cebus Capuchin.

Callithrix Sagouin.

Hapale Jacobus Marmoset.

Sub-order 2. LEMURIDJE,

SjTionymous with Sxrepsirrhina [ffr^ixres, twisted; /»— )

Lemur

Lichanotus Indris.

Cheiromys Aye aye.

Stenops Loris.

Perodicticus Potto.

Mam . — Classifica tion.

15

Oedee'III.— INSECTIVORA {insecta, insect; voro, to eat).

Families, Galeopithecidse

GalcopitlK

ErinaceidsQ

Soricidae
Talpidte

Erinaceu3

Centetes

Gymnura

Sorex

Talpa

( Flying-
( Lemur.

Hedgehog .

Tenrec.

Gymnure.

Shrew.

Mole.

Ordee IY.— CHETROPTEHA (x«p, band; TrrepoV, wing).

Families | Vespertilionidae Vespertilio

Insect diet \ Ehinolophidse Ehinolophus

Vegetable diet ( PJ^jllo^tomidae Desmodus

® (. rteropidae rteropus

Bat.

Vampire.

Roussette.

Oeder Y. E0DE]S"TIA (rodo, to gnaw).
Sub-order 1. KON-CLAVICULATA\ {non, neg. ; clavicula, a clavicle).

Families Leporidae Lepus

Timidus

Hare

(except Claviculate Lagomys

Pika).

Cavidae Hydrochaerus

Capybara

Dasyprocta

Agoutis.

Cavia

Guinea Pig.

HystricidaB Hystrix

Porcupine.

Sub-order 2.

CLAVICULATA {c-).

Families, Chinchillidae Eriomys

Chinchilla.

Castorida0 ; Castor

Beaver.

Muridae Mus

Rat.

Arvicola

Vole

Dipus

Jerboa.

Myoxidse Myoxus.

Dormouse.

Sciuridaa Sciurus

Squirrel.

Pteromys

Plying Squirrel.

Arctomys

Marmot.

Oedbe YI.— SECTOEIALIA {dens sectorius,

or scissor tooth).

Sub -order 1.

DIGITIGRADA {digitus, a finger^; gradi

•or, to step).

Families, Felidae (typical) Leo

Lion.

Canidae Canis

Dog.

Hyaenidse Hyaena]

Viverridae Viverra

Civet.

Herpestes

Ichneumon.

Genetta

Genetts.

Sub-order 2.

SEMIPLANTIGRADA {semis,^^^; planta, mle; g—).

Family, Mustelidae M. Vulgaris

Weasel.

M. Martes

Marten.

M. Putorius

Polecat.

Lutra

Otter.

16

Mam. — Classification.

U. Arctos

Brown bear.

Procyon

Sacoon.

Nasua

Coati Mundi.

M. Taxiis

Badger.

Gulo 1USCU3

Glutton, or Fiael

Frass.

Cercoleptes

Kinkajou

fin ; g—).

P. Vitulina

Seal.

P. Otaria

Eared Seal.

Trichseciis

Walrus or M orse

Sub-order 3. PLANTIGRADAXp—\ g—)
Families^ Ursidae

Melidae

Cerco^eptidae

Sub-order 4. FIX NIG HAD A {pinna, fin; (/—).
Families, PhocidaB

TriebBecbidse

Oedee YII.— PEOBOSCIDIA {npoiioadQ, trunk).

Family, Elepliantidae Elephas Elephant.

Oedee YIII.—PEEISSODACTYLA(7r£pi<T<7oe, odd; ^afcrvXoc, digit).

Sub-order 1. SOLIDUNGULA (solidus, whole; ungula, hoof).

Family, Equidae E, Caballus

E. Asinus

Sub-order 2. MULTTINGULA (multus, mtLnj ; w— ).

Families, RhinoccridaB Rhinoceros

Tapiridas Tapirua

Oedee IX.— HYRACOIDEA.

Family, Hyracidaj Hyrax

Oedee X.— AETIODACTYLA (^pnoc, even ; 3-

Sub-order 1. OMNIVORA [omiiis, ererything; v — ).

Families, Hippopotamidae Hippopotamus
Suidae Sus

Babyrussa

Phascochaeres

Dycoteles

Horse.

Ass.

Tapir.

Daman.

Hog.

"Wart Hog.
Peccari.

Sub-order 2. RUMINANTIA (rwwm, paunch).

Group 1. Carenticornua {careo, to be without; cornua, horns).
Families, Camelidse Camelus Camel.

Moschidae Moschus Musk Deer.

Group 2. SoLiDicoRNUA {solidus, solid ; c — ).
Families,

Cervidae

i Flattened antlers
Round Antlers
Camelopardidaj

Platyceros Dama Fallow Deer.

C. Alces Elk.

^^^Sii^^. ] Reindeer.

1 arandus J

C. Elaphus Red Deer.

C. Capreolus Roe.

Camelopardalis \ p- «.

Giraffa } ^'■^^^^'

Mam. — Classification.

17

Group 3. Cavicornua {cavus, hollow; c — ).
Familj/ and syn., Bovidse

/ Gazella Dorcas

Gazelle.

f Bos-elaphus Oreas Eland.

\ Antilocapra

Prong-buck.

Antelopes

< Tetraceros

Chicarra.

i Bupricapra tra-

[ Chamois.

f giis

\ Cato Blepas

Gnu.

/ Capra

Goat.

I C. Ibex

Ibex.

Goats and sheep

< Ammo-tragus
/ Trag-elaphus

> Aoudad.

V Ovis

Sheep.

j Bos

\ Bonasus

Ox.

True bovine

Bison.

( Ovi-bos

Musk ox.

OiiDEii XI.— CETE ^r,Tug,

a whale).

Families, Balaenidse

Balsena

Whale.

Balaeuo-ptera

) Fin -backed
j whale or

boops

Rorqual.

Physetcridse

Physeter

Cachalot.

Delphinidse

Phocaena

Porpoise.

Delphinus

Dolphin.

Monodon

Narwhal.

Hyperoodon

Bottle-head.

Order XII. — SIEEXIA {aeipitv, a mermai

d).

Families, Rhytinidae

Rhytina

SteUerine.

(extinct since Dodo.)

Manatidas

Manatus

Manatee.

llalicore

Diigong.

Order XIII.— IX-EXAMELLATA (absence of enamel)

1 Families, Edentvda

/ Myrmecophaga

Ant-eater.

Insect-eating Syn. Myrmecophagidae (Manis

Pangolin.

( Dasypodidae

Dasypus

Chlamyphorus

Orycteropus

Armadillo

Leaf-eating Bradypodida)

Bradypus

Sloth.

B. Tridactylus

Ai.

B. Torquatus

[over.

D

18

Mam. — Classification.

MAMMALIA IMPLACENTALIA.

Oedee XIY. — MAESTJPIALIA (marsttpnim, a poucli.][

s.

DiDELPHIA

Families, Phascolomydoe
Macropidse

Plialangistidse

PeramelidgB
Didelphidse

Myrmecobiidae
Dasyiiridae

Phascolomya

Maeropus

Hysiprimniis

Phalangista

Petaiu'iis

Phascolarctos

Perameles

Chaeropus

Didclphys

Cheironectes

MpmecoTbius

Dasyxinis

Thylacimis

Phascosale

"Wombat.
Kangaroo;
Potoroo.
Pbalanger.

Koala.
Bandicoot.

Opossum.
Yapach.
Banded Ant-
eater.

Oedee. XY.^MONOTEEMATA {jiovoq, single; rpn^a, hole),
s.
Ornithodelphia

^ ^ .,1 , \ Duck-billed

Genera Ornithorhyncus j platypus.

i Spiny Ant-
\ eater.

Echidna

OSTEOLOGY— General.

I. — Skull. Tlie number of separate cranial bones is in
most Mammalia less than in Reptilia and Pisces. Tbe occi-
pital condyles are two in number, as in Amphibia, from
wbicb, bowever, tbey differ in development : the Mamma-
lian condyles being formed by the exoccipitah, in conjunction with
the well ossified basioccipital and not from tbe exoccipitals alone
(Amphibia). The foramen magnum is usually situated at the
back part of the skull, and generally in a position more or
less perpendicular (cf. i. and ii, 1).* Near to, or immediately
above it, there occasionally occur persistent fontanelles (cf.
vi, 4). The Paroccipital (= 'jugular process* in Man)
frequently exceeds the * Mastoid process' in size. The Sphe-
noid coalesces with the occipital at an early period. — The
Parietals are usually small and insignificant, flat, and fre-
quently united together, obliterating the sagittal suture
(cf. V. vi. viii, 1. x, 2). — An Interparietal bone is some-
times met with (cf. v. ix, xiv). — The Frontalis generally but
slightly arched, and consists originally of two lateral portions
which not unfrequently remain distinct : sometimes a single
frontal bone is found (cf. i. ii, 1. iv. vii. viii, 2). — The sutures
of the bones of the skull generally remain visible throughout
life, — The Temporal bone consists in the foetus of four pieces ;
the squamous, the tympanic, the petrous, and the mastoid :
of these the squamous portion is for the most part low and
compressed ; icith it each ramus of the lotcerjaw directly articu-

* These figures apply to the Orders and Sub-orders, as numbered in the
following section.

20 Mammalia.

lates ; and it sotnetimes forms part of the wall of the cranial
cavity : this last function of the squamosal is peculiarly Mam-
malian, but by no means constant in all members of the
class. The tympanic portion is attached to the petrous
either by suture or ligament, and is of various size and shape
(cf. V. vi. xi). The mastoid process is generally very slightly
developed. — The Styloid process frequently exists as a sepa-
rate ossicle. — The Facial bones are immovably connected with
each other (cf. Aves). — The Malar bone is seldom wanting,
but varies in size and shape (cf. vi. xi. xiii) ; its frontal pro-
cesses seldom reach the frontal bone (cf. viii, 1 ; x, 2) and
very rarely (cf. i. ii, 1) is there an inner plate developed,
circumscribing the orbit and zygomatic groove. The Lachry-
mals are very rarely wanting, but vary in size (cf. vi, 4 ; viii,
1 ; x, 2 ; xv), being usually more developed than in Bimana,
and contributing more to form the inner wall of the orbit,
where they seem to occupy the place of the ethmoid. The
Nasal bones are generally double, and very long (cf. ii, 1 ; viii,
1 ; X, 2). — The Intermaxillaries, which in Bimana are distinct
only in the earliest foetal periods (till the fourth month) occur
in all other Mammalia, and generally support incisor teeth
(cf. X, 2. &c.) : they frequently coalesce in old individuals
at the median line, and with the superior maxillary bones. —
The Superior MaxiUaries are more elongated than in Man,
and have a broader nasal process. The Palate bones have, in
most Mammalia, a large horizontal piece, by which the pos-
terior part of the hard palate is formed (cf. iv.) — ^Each of the
two Rami of the lower jaw, though developed from several
centres of ossification, consists in the adult of but one single
bone, which has generally an ascending process : and which
articulates directly with the squamosal element of the skull,
and not with the representative of the quadrate bone of the
lower Yertebrata, which in the Mammalia is appropriated as
malleus to the service of the organs of hearing : the articu-

General Osteology. 21

latin •^ condyle is of diverse form (cf. v. vi. x, 2), but usually
lias a convex or flat facet. The rami are united anteriorly
sometimes by symphysis, generally by ligamentous fibres :
tlie lower border of tlie symphysis is in Bimana alone
curved forwards and upwards (cf. ii, 1). — The Sphenoid, as
above said, coalesces early with the occipital ; the size of the
wings varies ; the pterygoid processes sometimes remain
separate tbroughout life (cf. xv.) ; sometimes coalesce with
the surface of the Palatal bones. The separation of the body
of the Sphenoid into two parts {vide Introduction) as seen in
the Human embryo persists in most Mammals for the whole
of life. The Ethmoid is more largely developed in this
than in the other classes of Yertebrata, and here alone de-
serves the • name which it has received in human anatomy,
from its perforated upper surface, or cribriform plate : in
very few Mammalia (cf. i. ii.) is the smooth lateral plate
forming the inner wall of the orbit (lamina papyracea)
present. — The Inferior Turbinate bones seem to be present in
all Mammalia. — The internal surface of the cranium presents a
cavity which, as in Aves, is entirely occupied by the brain,
and is thus the cast of its surface ; in Man it may be
divided into a posterior, middle, and anterior region, which
do not lie in the same plane, the posterior (cerebellar) being
the lowest : in other Mammalia these regions are less obvi-
ously distinct from each other, and lie more at the same
height. The depressions for the lodgement of the cerebrum
and cerebellum are sometimes separated by a bony tentorium,
prolonged inwards from the posterior part of the parietal
bones (cf. vi. viii, 1. xi.) and the superoccipital.

II. — The Vertebral Column. The articular surfaces at each
end of the well ossified centrum of a Mammalian vertebra are
generally flat : they are however sometimes cup- shaped
behind and spheroidal in front* (cf. x, 2.). This was also

• Opisthococlian centrum.

22 Mammalia.

a character of many extinct reptiles : but, as distinctive of
Mammalia, note that these articular surfaces are in this class
developed as separate, discoidal, epiphysial plates, which continue
for a longer or shorter period of life, and then coalesce with
the body. Each vertebra is developed from five centres .of
ossification : two for the epiphyses, two for the neural arch,
and one for the body : but the sutures between the elements of the
neural arch and the centrum are early ohliieratedy generally be-
fore the epiphyses coalesce with the centrum. The centra are
articulated by concentric ligaments, composed of fibrous tissue
and cartilage, forming the so-called " intervertebral cartilages."
The vertebral column is generally (? xi.) divided into the same
regions as in Man, viz., cervical, dorsal, lumbar, sacral, and
ca*dal. It exhibits great constancy in the number of verte-
brae in the Cervical region : there are generally seven (cf. xii,
xiii.) : the great variations in the length of the neck being
solely dependent upon that of the centrum of each vertebra
(compare centrum of cervical Y. of Giraffe with that of
Balasna). The first (atlas) and second (axis) cervical vertebrae
present a curious anomaly, in that the centrum of the atlas
has in the adult coalesced with that of the axis. The atlas
has constantly in Mammalia two articular cavities for the
reception of the two condyles of the skull. The cervicals are
generally all movable on each other (cf. xi.), and have their
transverse processes perforated for the vertebral artery. The
number of Dorsal vertebrce varies, but there are seldom fewer
than twelve (cf. iv.) or more than fifteen (cf. vii. xiii.) : the spi-
nous processes are seldom wanting (cf. iv.), and are generally
long and thin, and slope towards one in the latter half of their
series which is vertical, rises from the thence named *' anti-
clinal" vertebra, and indicates the centre of motion of the trunk.
To these spines is attached the ligamentum nuchae, and with
it they form what is termed the "withers." The ligamentum
nucha? has its anterior attachment on the spine of the second

General Osteology. 23

cervical, and often on the crest of the occipital bone also : it
is represented in Bimana by a condensed band of the fascia
nuchalis. The Rihs correspond in number with the dorsal
vertebrae ; and each rib is usually connected, by its head with
an articular cavity, formed by the bodies (cf. xi.) of two ver-
tebrae, and in addition (cf. xv.), backwards, by a tubercle, with
the transverse process of the posterior of those two vertebrae.
The continuations of the ribs by which they are united to the
sternum remain in most Mammalia cartilaginous (cf. xi. xiiL
XV.) during the whole of life (= costal cartilages). The ante-
rior ribs usually extend as far as the sternum*; in which
respect Mammalia differ from Aves. — The Sternum is usually
narrow, and consists of a simple longitudinal series of bones,
instead of having the second, third, fourth and fifth segments
fused, as in the adult Man. There is generally no epi-
sternum. The manubrium sterni presents considerable dif-
ferences, but generally receives the clavicles when present,
and the two first ribs (cf. iii. iv. xv.). The ensiform pro-
cess varies both in length and shape (cf. v. xiii.). The
Lumbar vertebrae are generally the larger, and vary in num-
ber from three to seven. A well defined Sacrum is generally
present (cf. xi. xii.) : as a rule it is very narrow (cf. i. ii.)
and is composed of from two to five vertebrae, generally united
(cf. XV.) together, and not anchylosed inferiorly to the pelvis
(cf. xiii.). The sacrum in Bimana retreats backwards, and
makes an angle with the lumbar vertebrae ; in the rest of the
Mammalia, on the contrary, it lies nearly, in the same plane
with the lumbar vertebrae, and is hence said to be ''straight.'*
Caudal vertebrae are generally present (cf. i. ii.): the anterior
ones are similar to those in other series, most of the usual pro-
cesses being present, f and generally inferior processes also,
[= haemapophyses, or " Chevrori' bones] articulated with the

* Exc. Bradypus tridactylus. f The pleurapophyses are absent altogether.

24 Mammalia.

centrum, leaving a canal for the blood-vessels of the tail :
but towards the end of the tail they dwindle gradually in size,
lose their processes, cease to have an arch, and assume the
form of a double cone, resembling the phalanges of fingers.
Anchylosis is an exception (cf. xiii.) in this region.

III. — The Scapular Arch and Appendages. The anterior
pair of limbs is never absent in Mammalia. As is the case
with the vertebral bodies of Mammalia so is it with the limb
bones ; almost all of which have the articular surfaces, in the
growing state, supported on distinct plates, called epiphyses,
which usually coalesce with the rest of the bone at maturity.
The Scapula is generally present as an expanded plate of bone,
but is of varied width (cf iii. xi.), length (cf. iii. iv.), and
size (cf. X, 2.) : the pre-scapular ("supra- spinous") or anterior
fossa is almost invariably larger than the post-scapular (in-
fraspinous) fossa. The Coracoidy though developed from an in-
dependent osseous centre, generally coalesces with the scapula,
of which it appears as a small process (cf. xv.). The Clavicle
(= the OS furculare of Aves), when present varies much in
shape and size (cf. vii. ix. x. xi. xii.) ; it is generally united
to the acromion (cf. xiii.) by ligament, and is usually single
(cf. XV.) on either side. The whole of the scapular arch is
specially modified in the Monotremata (cf. xv.). The JTumerus
and bones of the fore-arm (antibrachial) and hand are specially
modified according as the animal lives in air or water, or bur-
rows beneath the surface of the earth. There is no power of
rotation of the fore limb in any hoofed quadruped. There
are usually two bones in the fore-arm, the radius and ulna,
which admit of various degrees of rotation. The Humerus is
generally straight (cf. vi. ) ; in swimming and fossorial ani-
mals it is very short (cf. iii. xi. xv.), otherwise it may be
described as characterised in the normal Mammalia by having
a head, tuberosities, deltoid crest, twisted shaft, epicondyloid
processes, and intermediate trochlear articular surface for

General Osteoiuy<j. 25

synovial articulation with tlie proximal ends of radius and
ulna. The olecranal fossa is not always complete (cf. v. vi.),
nor is the internal condyle always imperforate (cf. v. vi. xiv.).
The Ulna is almost always longer than the radius (cf. iv. xiii,
1.), and generally provided with an olecranon (cf. xi.) of
variable size (cf. xiii.) : in those herbivorous quadrupeds
which are organised for rapid motion, both bones lie behind
each other, are immovably united, and more or less anchy-
losed. The Carpus consists usually of eight small bones,
ranged in a double row, varying in shape (cf. iii. xi.) and
number, but with this constant character, that the os unci-
forme always supports the two (when present, cf. Bpadypus)
outer metacarpals. The Metacarpus consists for the most
part of five separate (cf. xiii.) elongated bones : between the
metacarpals and the first row of phalanges are situated, very
generally, certain sesamoid bones (cf. viii, 1.). The number
of Phalanges in a finger rarely exceeds three (cf. xi.), and in
the thumb there are usually two. The number of fiugers
varies from one to five : of these five the third or middle
finger is the most constant, and commonly also the longest
(cf. viii, 1.) : the first or inner digit (the thumb) is the first to
disappear ; if there are two absent, the fifth or outer digit,
(the little finger) is the second to disappear : after these the
second, or index finger ; and then the fourth, or ring finger.

lY. — The Pelvic Arch and Appendages. The appendages of
the Pelvic Arch may be wholly wanting (cf. xii.) or rudi-
mentary. The Pelvis in other Mammalia is never so broad
as in Bimana, and its lateral walls are always smaller, flatter,
and longer. The Ilium seldom articulates with as many
sacral vertebrae as in Aves (cf. xii.). The Ischia and Pubes
are generally well developed. The pubic articulation (cf. iii.
iv.) is frequently very deep ; it is formed also by the ischia,
and is very often converted into bone. The Acetabulum is al-
most always complete ; and has frequently a depression for the

26 Mammalia.

insertion of the ligamentum teres ; it is generally imperforate
(cf. XV.). From the anterior or upper border of the pubic
bones there frequently arises a pointed spine-shaped eminence
(eminentia ilio-pectinea), which is the first indication of the
Marsupial bone (cf. iv. xiv. xv.). The Femur retains more of
the human form in the different orders (cf iv. vi.) than does
the humerus : the external trochanter is often very large, and
extends beyond the head of the bone : the internal trochanter
is occasionally wanting: a " third '* trochanter, a strong pro-
cess more or less in the middle line, is found in a number of
animals (cf. ix.). Whilst in Bimana the axis of the femur
deviates little from that of the vertebral column, in all other
Orders (including the highest Catarrhina, vk.j the tail-less
Apes), the femora are bent more forwards, and form an ob-
tuse angle with the pelvis. A Patella is very generally met
with. In the leg the Tihia is always the principal bone, and
main support of the femur. The Fibula presents many varie-
ties (cf. XV.), and is often very rudimentary (cf. iii, iv. viii, 1.).
The average number of the Tarsal bones is seven, and they
are generally separate. The os calcis has commonly a long
process for the attachment of the tendon Achilles (cf. iv.).
The Metatarsals vary in number ; those of the principal toes
in the leaping animals are long, and partly united together
(cf. v.). The same remarks apply to the toes as made above
on the fingers. Among Quadrupeds the Elephant furnishes
an example of the pentadactyle foot ; the Hippopotamus of a
tetradactyle foot, having digit i. (inner) withdrawn; the
Rhinoceros of a tridactyle foot, having digits i. and v.
(outer) withdrawn ; the Ox of a didactyle foot, with digits
i. and v., and ii. (index) withdrawn ; and, lastly, the Horse,
of a monodactyle foot, having digits i. and v., and ii. and iv.
withdrawn.

Special Osteology. Bimana. 27

OSTEOLOGY.— Special

The ShulL The united area of the cranial bones exceeds that of
the facial bones very considerably. The width between the outside
edge of each orbit does not exceed the extreme width of the cra-
nium between the parietal eminences. An inner plate is developed
from the Malar bone, which is united with the great ala of the
sphenoid, and forms with it a wall by which the cavity of the orbit
is so separated from the temporal fossa, that a fissure alone is left.
The Nasal aperture is frequently half as large as the orbit ; it is
situated between the lower borders of the orbit j the nasal bones are
arched transversely. The ethmoid has a crista galli. The peri-
hery or alveolar border of the Upper Jaw forms a continuous semi-
elliptic curve, uninterrupted by the projection of a:ny one excessively
developed alveolus. The bony Palate is deep and broad, though
short ; is arched both lengthwise and transversely ; and is formed
by the palatines, maxillaries, and small confluent pre-maxillaries,
supporting the incisor teeth. The plane of the alveolar border of
the upper jaw, passes through the floor of the cranial cavity ; the
whole cranium being much expanded backwards and downwards ;
and the Foramen Magnum^ which is placed near the centre of the
base of the skull, approaching the horizontal direction. The
Mandible has a well-defined and not^ rounded angle : the rami
become united in the median line at an early period before or after
birth : the symphysis menti forms with the base of the rami a
sharp angle, and has its lower border frequently slightly turned up
anteriorly. The body of the ITyoid bone (basi-hyal), is compressed
antero-posteriorly, and curved and extended transversely j but not
expanded or excavated behind. The lesser cornua of the hyoid
(cerato-hyals) are represented by mere tubercles. The Stylo-hyal
is anchylosed with the ' Temporal' bone, forming the 'styloid pro-
cess.' The Jugular processes are very small, but the Mastoids are
well developed. The Intermaxillaries are not distinct on the facial
surface.

28 Mammalia, Bimana.

The Vertebral Column. The number of vertebrae in each series is
generally constant, viz : Cervical^ seven ; Dorsal, twelve; and Lumbar,
five. The first and three posterior Ribs have a single aiticular surface
on the head ; the rest have it divided into two facets : the tubercular
articular surface is wanting in the last two pairs. Occasionally a
pair of tubercles on the anterior border of the manubrium indicate
rudiments of an episternum. A characteristic distinction of the human
Lumbar vertebrae is the backward production of the posterior
zygapophyses occasioning the deep posterior emargination of the
neural arch. The Sacrum is broad and slightly concave anteriorly,
both lengthwise and transversely. The Caudal series is reduced to
four or five aborted vertebrae.

The Scapular arch and app>endages. The Clavicles are always
present and complete, though slender in proportion to the length ;
and the curves are always fairly marked. The Scapulce are very
broad in proportion to their length : the direction of the spine and
acromion is distinctly transverse. In the Humerus the condyloid
processes are not very largely developed ; the intercondyloid per-
foration is occasionally seen. Both Radius and Ulna are slender and
short relatively to the humerus. The opposable thumb is restricted
to the upper pair of limbs. The terminal portions of the ungual
phalanges are long and broad, in order to support the surface specially
developed for a refined touch.

The Pelvic arch and appendages. The Pelvis is short, broad, and
wide, keeping the thighs well apart. The sacro-iliac symphysis is
subquadrate ; the symphysis pubis is short. In Man alone are the
boundaries of the brim or inlet of the pelvis {i.e., the cotylo-sacral
tract of the ilium, and the body of the pelvis), on one plane. The
Llium is broader than it is long ; concave internally, and concave
posteriorly,^' especially in the vertical direction. The whole of its
curved border is much developed, especially the anterior inferior
spine (for the straight tendon of ' rectus femoris'), the top of the crest,
or external labrum, and the large backward projection formed by the
posterior angle (for the ' glutasus maximus'),"each testifying to the
important share taken by the muscles thence arising in maintaining
the erect position. The Pubis is shoi't and thick ; an oblique
groove is present beneath the pubic boundary of the obturator
foramen. Anchylosis of the Tubes rarely takes place in Man.

* On account of the thickness cf the * crest.'

Special Osteologij. Quadrumana. 29

The acetabulum has a decided tendency to face out^Yards. In
proportion to the trunk the Pelvic Limhs are longer than in any-
other animal; they even exceed those of the Kangaroo (Macropus),
and are peculiar for tlie superior length of the femur, and for the
capability of this bone to be brought, when the leg is extended, into
the same line with the tibia. The neck of the Femur (cervix femoris)
is long, and forms an open angle with the shaft : as characteristic,
note the double obliquity of '^ neck'' and " shaft,'' whereby the
femora are brought to converge to the knee joints. The great
trochanter does not rise so high as the head of the bone. The linea
aspera is bent forward and developed like a buttress. The distal
end is considerably expanded, and the two condyles, especially the
inner one, much produced backwards. The Tibia is the second longest
hont of the skeleton, and is of tolerably equable diameter, though
expanded at its proximal end to form the knee joint. The slender
lihula articulates with the external aspect of the Tibia below the
knee. The outer or Fibular malleolus descends lower and more verti-
cally than the inner or tibial malleolus, restraining to a great extent
all lateral inflections of the foot upon the leg. The Foot is short in
proportion to the leg, and is so articulated that the sole is directed
downw'ards. The tarsal and metatarsal bones are co-adjusted so as to
form arches, both lengthwise and across, and receive the superincum-
bent w^eight from the tibia on the summit of a bony vault, which has
the advantage of acei'tain elasticity combined with adequate strength.
The Calcaneiim developes posteriorly a considerable tuberositj'. All
the five Toes have the same direction, forwards ; they are short, but
with the innermost longer, and much larger than the rest, forming
a " hallux," or great toe, w^hich is placed on the same line with,
and cannot be opposed to the other toes ; on the hallux the whole
force of the "flexor longus hallucis" is exclusively concentrated.

II.— QUADRUMANA.

The Skull. The form of the cranium has no approximation to
the oval type of Bimana. The facial area is unusually large
relatively to the cranial (cf. i.) ; and there is but slight, if any,
expansion of the cranium backwards or downwards. The Foramen
Magnum rarely assumes anything approaching co a horizontal
position, and is always placed towards the posterior part of the base
of the skull. The Mastoids are generally represented only by small
tubercles. The Paroccipital process is rudimentary. The Inter-

o

0 Mwmmalia. Quadrumana.

maxillaries are distinct on the facial surface. The Orbits are
completely circumscribed by an osseous ring; but the temporal
and orbital fossa are seldom entirely separated, except in the
Catarrhina. The Glenoid cavity is usually less deep than in
Bimana, and is bounded posteriorly by a well-marked post-
glenoid ridge (exc. Cheir^mys). The Alveolar border of the upper
jaw never forms a regular curve ; and even when it approaches
that shape, has some of the alveoli protruding beyond the rest.
The Bami, of the lower jaw, are rounded oif at each end, both at
the symphysis and at the " angle/' The Basi-hjal is generally
expanded and excavated posteriorly ; and the Cerato-hyals developed
into processes, being very rarely represented by mere tubercles
[e.g. in Gorilla). The JVasals are generally flat. In the Mhmoid
the crista galli is very rudimentary (exc. Cercopithecus). The
Clinoid processes of the sella are generally sinall or rudimentary,
except in the Catarrhina. Yery commonly a division of the Lateral
Cerelral venous sinus excavates the base of the petrosal, to terminate
at the post-glenoid fossa. (? Catarrhina.)

1. Catarrhina. In all Catarrliina the bony septiim bchvocn the orLital and
temporal fossa is complete. The nasals are flat, small, and generally coalesced.
In yoimg Apes ihe foramen may ?mm sometimes assumes a horizontal position.
The rami 'are generally coalesced early at the symphysis. There are seldom
any " post-glenoid " outlets of the lateral sinuses (exc. Hylobates.) The
tentorium is never ossified. The preclinoid and postclinoid processes are well
developed.

2. Platyrrhina. The frontal suture is obliterated in all, and the single hone
thence resulting is triangular, with the apex extending back between the
parietals, in some capuchins (cebus) as far as the superoccipital, thus repeating

■ a Piscine collocation of supra-cranial bones. In most of this group (exc.
Callithrix) the plate which divides the orbital from the temporal fossa, exhibits
a small unossified vacuity. The lachrymal foramen is within the orbit (cf. ii. 3),
and the orbital walls project considerably into the cranial cavity. The
mandibular rami of Mycetes are especially to be noted on account of the extra-
ordinary depth of their angular and ascending portions ; this development
relating to the protection and support of the still more extraordinarily developed
hyoidean and laryngeal apparatus. The Hyoid arch is reduced to the
basi- and thyro-hyals only ; but of these, the former is enormously developed
and expanded into a capacious sac, with thin walls, and a posterior opening
admitting a laryngeal pouch. — In other Platyrrhina the cerato-hyals are
present, and the basi-hyal is slightly exQavated, forming in Hapale only a
convex plate. The lateral sinuses have " post-glenoid" outlets, Atele*
furnishes an example of ossification continued into one half of the tentorium.

Special Osteology. Quadrumana. 31

3. Lemuridcc (or Strep sirrhma). In most LemiiridaD the cranial sxitures are
*' harmoniae*"; and the facial part of the skull is produced. The orbits are large
and expanded ; orbital and temporal fossce communicate freely ; the lachrymal
foramen is on the face. The coronoid process of the mandible is well developed.
In Cheiromys the ' symphysis ' menti is ligamentous. The anterior Cornua of
the hyoid are generally longer than the posterior, and inchide cerato- and epi-
hyals, supporting a cartilaginous stjdo-hyal. The glenoid cavity is generally
defended by a posterior ridge (exc. in Cheiromys, in which the absence of this
ridge admits of the free movement of the mandible backwards and forwards
requisite for the Rodent action of the great scalpriform incisors). The lateral
cerebral venous sinuses have a division in the base of the petrosal.

The Vertebral Column. — All have seven cervical vertebrae ; and
the majority have 19 vertebrae in the dorso-lumbar series : through-
out which interlocking joints are commonly found, except in the
highest Apes. In all, except in these same " anthropo-morphous'*
Apes the sternal bones are slender.

Catarrhina. In Anthropomorphous Apes, — the pleurapophysial part of the
vertebrae in the cervical region projects distinctly below the diapophysial part,
without however acquiring that antero-posterior breadth which gives it the
lamellifoi-m character in the inferior Apes ; — the sternum consists of the manu-
brium and generally of two or more broad and flat bones, coalesced to form
the 'body;' — the vertebrae never have interlocking joints -. — the sacrum is some-
times broad and slightly concave : — lastly, the caudal yextehrdd are frequently
reduced to five, anchylosed and aborted, but longer and narrower than in Bimana.

In most of the other Catarrhina, the centrum of the axis is much produced
backwards, underlapping that of the third vertebra. The posterior dorsuls and
anterior lumbar veitebrae frequently have the anapophyses developed as separate
processes, and the metapophyses provided with a facet for the accessory articular
surface of the posterior zygapophysis of the preceding vertebra : being thus
provided with an additional interlocking apparatus.

All Platyrrhina have a long tail, which is in most prehensile, and composed
of about thirty vertebrae (ex. Callithrix, 18.) The inter-cervical articulations
frequently tend to the ball-and-socket type. In Hapale ( M armoset ) the centrum
of the vertebra succeeding the Atlas is produced posteriorly into a convex pro-
minence which fits into a concavity on the forepart of the centrum behind. In
Ateles (Spider Monkey) the third to the sixth cervical vertebrae inclusive
show an anterior concavity and a posterior convexity on the articular ends of
the centrums in the transverse direction, an anterior convexity and jDosterior
concavity in the vertical direction, producing an interlocking joint, combining
strength with freedom of motion, and analogous to that in the neck of Birds.

• Of bastard or false (notha) sutures (?. e. sutures formed by rough surfaces),
those that are formed by the apposition of contiguous surfaces are termed
'suturae nothse appositae,' or in one word harmonice.

32 Mammalia. Quadntmana.

In the Leynuridre the cervical vertebrae are generally broad and short, and
their neural arch is low and flat, and sometimes fissured behind (Indri). The cen-
tra of the dnrsal vertebriE of the Cheiromys (Aye- Aye) are carinate ; the neural
spines are commonly all of equal strength, In the true Lemurs eight pair of
ribs join the sternum, which consists of seven bones and an ensifoim cartilage.

The Scapular Arch and Appendages. — The anterior pair of limbs
aid in support and locomotion. Clavicles are always complete. Tlie
Coracoid process of the scapula is usuallj' large and long. The
Elhoiv joint allows of both rotatory and flexile movcmonts of hand
and fore-arm. Most Quadrumana have the innermost digit opposable,
i.e. have a ^ rue 2yollex, or thumb.

Cntarrhina. The curves of the chvicles are usually not well mai'ked : these
bones are of excessive length in the " Long-armed" Apes. The humerus is
seldom perforated even slightly at its distal extremity : the condyloid processes
are considerably developed. The peculiar length of ai*m in the "Long-armed"
Apes {e.f/. Siamang, Hylobates) is chiefly due to the unusual length of the anti-
brachial bones. All Catarrhina have a true pollex, except Colobus.

PlatyrrJiina. In Ateles (Spider Monkey) the long and large coracoid has an
angular tuberosity, which sometimes joins the anterior costa. so as to circum-
scribe the prescapular notch. The humerus is in this group seldom perforated,
either above or between the condyles.

LemnridcB. In Lichanotus (Indri) the coracoid is especially large and strong.
The humerus is usually perforated above the inner condyle : when bent upon
the chest the humerus reaches to the tenth rib : — this length is characteristic in
this Sub- order. In Cheiromys the middle metacarpal is remarkable for its
extension, and sudden contraction in size towards the distal extremity. The
fourth digit is always the longest in this Sub order, except in Cheiromys, in
which the phalanges of digit iii. are attenuated to form the hooked probe-
like finger.

The Peine Arch and Appendages. The Pelvis is long and narrow.
The Iliac bones are long, more or less flat, slender, and extended
(except in the highest Api's) in a continuous line with the sacrum.
The Ischia are in a line with the ilia. The Acetahula have a tendency
to face forwards, and towards each other. The Femur has usually
a short neck, is itself short, and so articulated with the leg bones as
to retain habitually a ben I position of the knee : the great trochanter
usually rises to the height of the bead of the femur. The innermost
digit of the posterior pair of limbs is always opposable, i.e. in a
thumb-like condition, as in the hands ; hence the name of the Order,
QnadTu-mana.

Catarrhina. The posterior angle or spine of the ilium is above the sacral
surface, not behind it (as in Man). In all that have dermal callosities, the
ischia are expanded into rough flattened tuberosities. There is no oblique

Special Osteology. Insectivora. 3

A

groove beneath i\ie pubic botmdary of the obturator foramen (of. i.). The linca
aspcra of the fanur is little developed, and the outer articular condyle is nar-
rower than the inner one, the reverse being the case in Man. The articulation
of the bones of the leg with the tarsal bones favours the oblique position of the
foot, and adapts it for grasping. The ectoeiineiform has commonly a convex
articular surface for the hallux, which articular surface in Man is nearly flat :
the diiference being significant of the diiferent function of the hallux in the
two species : the chief fulcrum of the foot requiring a firm articulation in Man»
but in the higher Apes, e.g. Gorilla, requiring great extent of motion for the
function of this opposable grasping thumb.

Lemuridce. In the Spectres (Tarsius) the excessive length of the calcaneum
is remarkable : hence their generic name.

III.— INSECTIVORA.

The Shull. The cranial cavity is small, and the outer surface is
commonly smooth, and devoid of crests. The Orlital and Temporal
foss(B communicate freely (? Galeopithecus^). The Malar bones are
generally slender, and are usually either suspended in the zygoma
{e.g. Galeopithecus), or applied like a splint along the outer and
under side of the junction of the zygomatic with the maxillary
[e.g. Urinaceus, Gymnura). In Centetefi the Malar is entirely absentf
and the Zygomatic arch incomplete. The Tympanic is frequently
present as a delicate ring. In Talpa the pyriform skull is prolonged
by a prcenasal ossicle.

The Vertelral Column. All the processes are relatively small
throughout the vertebral column. The Sacrum, is narrow. The
Syraphysis Pubis is short or absent {Talpa, Bar ex).

In Tal'pa the first sternal bone, or Manubrium, is of unusual length, being
much produced forward, and has its under surface produced downwards, in the
shape of a deep keel, for extending the origin of the pectoral muscles.

Bones of the Limls, All the Insectivora have perfect Clavicles ;
the Scapula is generally long ; the Legs short and unguiculate ; the
Feet plantigrade, generally five-toed, none opposable.

The peculiar development of certain of the Limb-bones obtaining in Talpa
deserve special notice ; thus — The Clavicle is cubical (an unique form in Vertc-
brata), is articulated firmly to the anteriorly projecting breast-bone, but attached
to the acromion by ligament. The Scapula assumes Ornithic proportions, its
length being more than six times its extreme breadth, it is trihedral save in the
middle, where it is cylindrical. The Humerus, as in most fossorial animals, is of
great breadth, and provided with singular inequalities of surface for the attach-
ment of muscles; it is a sub-quadrate, lamelliform bone, wdth a proximal
articulation for the clavicle as well as for the scapula. f The Carpal series has
added to it a large supplementary sickle-shaped bone, extending from the radius
to the metacarpal of the pollex.

* The orbit is partly defined behind by long and slender processes of the frontal,
t And, as in 7nost animals that scratch, has the inner condyle perforated.

34 Mammalia. Cheiroptera.

IV.— CHEIROPTEEA.

The Skull. In most insect-eating Bats the Svperoecipital slopes
backwards, and contributes to the crista continued forward by the
interparietal and parietal bones. The Occipital Foramen \B\Qxj\^Yge
in most of the Order. The Mastoid is large and distinct, giving
attachment to the tympanic. The zygomatic parts of the Squamosal
and Malar are slender. The Frcemaxillaries are very small : in some
{e.g. Rhinoloplms) they are wanting. The Orbital and Temporal fossm
communicate freely. The Tympanies are very slightly connected
with the skull. In the frugivorous Bats (Pteropus) the Malar is
situated as in the Insectivorous Erinaceida).

The Vertebral Column. The Spinal Column gradually diminishes
in size, from the cervical to the sacral region. The neural spines
are generally of very small size in all vertebrae beyond the dentata.
The Sternum is carinate.

In Pteropus the keel of the large manubrium stemi is produced into a process
at each angle.

Scapular Arch and Appendages. — The Scapula is generally broad.
The Clavicle arched, long, and strong. The Humerus and Radius long
and slender. The Ulna rudimentary or absent. The Finger-bones radi-
ate widely from the wrist, the thumb is short, and furnished with a
long claw. The Metacarpals' oi the four clawlees fingers are exces-
sively elongated; these, together with the bones of the arm, are, in
the natural state, united by a delicate leathery membrane.

Pelvic Arch and Appendages. The Pelvis is feeble and slender.
The narrow subcylindrical Ilia coalesce with the sacral vertebra?,
and are parallel with the spinal column. The pubis is continued in
a line with the ilium to the ' symphysis,' which is generally but
slightly closed in the male, and remains open in most female bats.
The Sind Limbs are short. The Fibula is absent or rudimentary.
The Heel has generally appended to it a long and slender styliform
bone, which helps to sustain the Caudo-femoral membrane.

v.— RODENTIA.

The Skull. The confluence of the elements of the epencephalic
arch* is late. The squamosal maintains its individuality ; and fre-
quently has developed from it long compressed lamina, which serve
to clamp the tym^^anic and mastoid, or one or other of them to the
bide of the cranium. The malar is suspended in the middle of the

* ' Occipital hone ' of Anthroptomy.

Special Osteology. Rodentia. 35

Kygomatic arch. Anteriorly to each orbit there is usually present a
wide vacuity, termed the antorhital for amen y of variable size ; in Ilela-
mys Capensis (Cape Jerboa) it is larger than the orbit. An interorlital
foramen is also frequently found; the common outlet of the optic
nerves {e. g. Lepus) extending forward so as to occasion a small
vacuity at the back part of the interorbital septum. The temporal
and orhital fossce are Mended together in all Ilod-entia. The naml
^ndi frontal bones are frequently large and long, both being especially
developed in Hystrix Cristata (Porcupine). Osseous hullm are gene-
rally present, formed by the petro-tympanic. In most Eodentia the
anterior part of the vomer articulates with the median ascending
process of the praemaxillary, arching over the wide vacuities which
lead from the nasal passages to i}iQ prepalatine aperture. The lower
jaw is modified for the lodgement of the pair of long scalpriform in-
cisors, the sockets of which may extend to the middle (Lepus) or
even to the hind part (Castor, Hystrix) of the ramus. In all Hodents
the condyle is convex transversely and extended longitudinally
(? Lepus) in which direction it is chiefly moveable, to give a full
action to the gnawing incisors : there is sometimes found (^e.g. in
Capybara and Cavia Cobaya) a process directed backward from the
angle of the jaw.

The Vertebral Column. The neural spine is usually longest in the
second and seventh cervical vertebrse : it is obsolete in the interme-
diate cervicals in many Rodents. In all the agile, flexible bodied
Rodents the neural spines incline towards the 11th (? Lepus) dorsal,
the spine of which is vertical, and indicates the centre of motion.
The thoracic rils consist of bony pleur-,and gristly ha^m-apophyses.
In some Rodents, the Ensiform process is expanded behind into
a thin cartilaginous disc. Throughout the lumbar region both an-
and met-apophyses are generally well developed ; long hypapophyses
are also developed. In most Rodents with long tails h^emapophyses
are developed beneath the intervertebral spaces, e.g. Dipus (Jerboa).

Limh ho?ies. There are few generalizations deducible from the
limb bones ef Redentia, since the habits of the several species com-
posing this order are so various ; some have limb-s giving power in
running, some in swimming, some in burrowing, some in leaping,
some in climbing, and a few show modifications in relation to para-
chute-like expansions of integument for a kind of flight. The Clavi-
cles are frequently represented by slender ossicles freely suspended {e.g.
in Lepus timidus, — Dasyprocta, Capybara, — and Hystrix): when this

36 Mammalia. Sectorialia.

is the case, the radius and ulna are generally found in close contact,
or actually anchylosed ; — the humerus is generally perforated, but
only letiveen the condyles ; and — the tibia and fibula are distinct. On
the other hand, — when the clavicles are complete {eg. in Castoridae,
Sciurida3, Muridae, &c.) the bones of the fore arm are generally dis-
tinct (ex. Pteromys); — the humerus has the inner condyle perforated,
and, — the tibia and fibula are usually coalesced. In some Rodents
the spine of the Scapula is extended into an acromion at some distance
beyond the glenoid cavity and there developes a retroverted process :
the intermuscular cristse on the subscapular surface are usually well
marked. In Pteromys a strong accessory cartilage projects from the
ulnar side of the carpus, which aids in supporting the lateral fold of
integument there developed.

As in other burrowing animals, the lumbar and pelvic regions
of those llodents that burrow are narrow. In the Guinea-Pig
the ossa innominata can glide on the sacro-iliac joints, the sym-
physial ligament being extensible. In most Rodents i\ie femur has
a slender neck and lofty trochanter.

yi.— SECTORIALIA.

All the bones of the Skeleton are remarkable for their whiteness
and compact structure.

The SJcull. The upper contour of the Skull is generally rather
straight : an Occipital crest is always developed ; but though the
Temporal ridges usually meet, they by no means always form a
Sagittal crest of any size. Most Camivora have the Orbit incomplete
behind, and the Orbital and Temporal fossa3 continuous. The
Maxillaries usually contribute to form the anterior border of the
orbit. There is generally an Antorbital foramen ; its size is indicative
of the size of the nerve (2nd div. of V.) supplying the well developed
whiskers. The Frontal seldom, if ever, sends any process to join the
Malar. The Malar generally bifurcates posteriorly, and it alone in
most cases forms the post-orbital process ; the squamosal element
(zygoma) not extending so far. The Zggomatic-process is generally thick
and large, and forms an expanded arch. The Mandible is short and
strong ; the articulating condyle is much elongated transversely, and
locked in a deep cavity of corresponding form in the squamosal, so as
to admit of no lateral motion, and almost restricting the movements
of the mandible to one plane, for biting and dividing, not pounding
the food : the Coronoid process is broad and high, to give insertion

Special Osteology. Sectorialia. 37

to the large temporal muscles (the fossae from which these rise are
large and deep, and augmented by peripheral ridges of bone) ; there
is generally a process directed backwards from the angle of the jaw.
Acoustic bulled are commonly found, supported by the paroccipitals,
and developed either from the petrosal, or tympanic, or both, but
never from the Ali-sphenoid as in Thylacinus.^^ The Paroccipital and
Mastoid processes are sometimes distinct, sometimes connate, but
both tolerably developed. A narrow articular surface upon the Basi-
occipital is frequently found connecting the two condyles. The
Petrosals are generally perforated by the ento-carotids, and impressed
internally by a pit for the cerebellar ' flocculus.' The Tentorium is
always ossified, and usually the posterior part of the Falx also.f
The Rhin-encephalic fossae are generally well defined, and completely
divided both inter se by a thick Crista ff alii, and usually from the Pros-
encephalic compartment also by a low ridge. The Olfactory cTiamher
frequently extends above, and in some cases also underlies the Ehin-
encephalic fossae ; it always contains large and complicated turbinals.

Digitigrada. In most Digitigrada the frontal region is convex transversely,
but depressed in the median line : the sagittal crest is largely developed : the
paroccipitals and mastoids have coalesced on each side to form a triangular plate,
broad and thick, and supporting the back part of the acoustic bullae. The tri-
angular occipital region is remarkable for the depth and boldness of the sculptur-
ing of its outer surface, especially in Felidse, in which the carnivorous character
reaches its maximum. The pterygoids are perforated by the ecto-carotids only, in
the Yiverridae alone, in which group also are to be found instances of the fro7ital
developing orbital processes, which meeting the malar, circumscribe the rim of
the orbit {e.g. Ichneumon Mangusta).

Semi-plantigrada. The sagittal crest is small. There is a considerable post-
orbital constriction. In most Mustelidse the rhin-encephalic fossa is less distinctly
defined from the cranial cavity than in the Flantigrada : but in the Lutra the
cranial cavity is remarkable for its great posterior expansion, and its extreme
contraction between the rhin- and pros-encephalic divisions.

Flantigrada. Both Paroccipitals and Mastoids are large, except in Gulo. The
Pterygoids are generally perforated by the ectocarotids (except in MeHdae). The
skidl of Meles taxus (Badger) is remarkable for the closeness with which the
transverse condyles of the lower jaw are grasped by the borders of the articular
grooves at the basec^of the zygomatic processes.

* Marsupialia-Dasyuridae.

t This being the case in the Plantigrade Bears that do not move by hounds,
and in the Pinnigrade Seals, that can only shuffle along the ground, as well as
in the typical Digitigrade Felidae, tends to refute the theory that the final cause
of these ossifications is to prevent the concussion of the several parts of the brain
against one another when the creature leaps or boimds.

S8 Mammalia. SectoriaUa.

Pinnigrada. The temporal ridges often meet upon the sagittal suture {exc.
Cystophora), but seldom form more than a very slight crest (exc. Otaria). The
malar is frequently joined by the zygoma to bound the orbit posteriorly (exc.
Tricha3cus). The Lachrymals are wanting. There are no * bullae ' in Otaria
or Trichsecus. The Paroccipitals are generally distinct from the Mastoids : the
latter are often largely developed, especially in Trichsecus, in which their great
development causes considerable lateral expansion in the hinder part of the skull.
The Pterygoids are seldom perforated for the ecto-carotids (exc. Arctocephalus,
Otaria, Trichcccus). V er&isieni fontanelles are commonly present in the occipital.
The Palate has commonly a semi- elliptic botmdary posteriorly, but in Otaria it is
truncate, and in Cystophora proboscidea the posterior borders of the palatine
bones present three notches. The boundary of the jaw extends from below the
condyle forward, and rarely developes an angle.

The Vertehral Column is modified in relation to tlie medium in
whicli the species live, degree of carnivority, and mode of motion.
In no Sectorialia do Cervical yertebrae articulate by ball-and-socket
joints ; the seventh C. v. always has the transverse processes imper-
forate, consisting only of diapophyses. The Dorso-Limilar scries
numbers twenty vertebrce constantly ; the proportion of 'Dorsal' to
* Lumbar ' varies with the agility of the species, the most agile
Digitigrada having two or three less of free elongated pleurapophyses
than the stiffer trunked Plantigrada and Pinnigrada. A similar
variation is to be found in the development of Anapophyses, which
increase in size directly as the lithe action of the species tends to
dislocation of the vertebrae. Lastly, the Anticlinal vertebra is more
distinctly marked in direct correlation with the development of the
anapophyses. In the Planti-, Semi-planti-, and Digiti-grada, the
Pro-zygapophysis of one Lumbar vertebra is received into the inter-
space between the post-zygapophysis and the anapophysis of the
antecedent vertebra ; thus inducing an interlocking articulation.

Digitigrada. In Leo the spine of the axis has great height, length, and posterior
breadth, arching forward and backward, and overlapping the third Y. of which the
spine is obsolete : the spine of the fourth V. is short and vertical, indicating the
centre of motion of the neck. The anterior dorsal spines are lofty and strong for
the origin of muscles implanted in the ridged and pitted back part of the skull.
The Lumbar diapopJtyses are long and antroverted. The Sacrum of Canis rufus
(fox) is remarkable for its sudden diminution of size, as compared with the lumbar
vertebrae. Certain Viverridce, e.g. Paradoxiu'us (Palm-cat) have the tail organ-
ised for prehension.

Semi- Plantigrada. In Lutra the spines of the three sacral vertebroe have
coalesced to form a vertical crista, and the tail is longer and stronger than in the
terrestrial Mustelidoc.

Plantigruda. The number of true vertebrae is twenty-seven as a rule, and

Special Osteology, Sectorialia. 39

fourteen of these usually bear moveable ribs. In Ratehis the neural arches of
the last five cervical vertebrae are longer than their centra, and overlap each other
in an imbricated manner. In Cercoleptes (Kinkajou) the tail is prehensile.

Pinnigrada. The number of true vertebra} is the same as in the Plantigrada^
The perforated transverse processes of the third to the sixth ccrvicals inclusive
are generally remarkable for the distinctness of their di- and pleur-apophysial
parts. The anapophyses form mere rudimental projections from the back part of
the diapophyses. The neural arches of the middle dorsal vertebrae are frequently
vrithout spines and very narrow, leaving wide intervals of the neural canal impro-
tected. The manubrium is occasionally (P. Greenlandica) much produced. The
Lumbar vertebra) have a strong hyp-apophysial ridge which divides into two
tuberous processes indicative of the great development of the muscles of the trunk
necessary to the shuffling motion of this Sub -order.

The Scapular arch and appendages. The Clavicles are always more
or less rudimentary ; small clavicular styles'^* being usually present.
The Scapula is always broad and has a well developed spine ; the
acromion is developed sometimes simple, sometimes bifurcate ; the
coracoid also varies in size. The Humerus is much bent, the articu-
lar head lies out of the axis, the deltoid ridge is long and strong ;
there are strong ridges from the outer and inner sides above the con-
dyles for extending the origins of the muscles of the paw : and the
inner condyle is very commonly perforated, to defend the main nerve
(median) and artery (brachial) of the fore-leg from compression
during the action of those muscles. The Radius and Ulna are
entire, but not always distinct, being fixed when swift course is
their principal function. The compound ScapJio-lunar is common to
the Carpus of all Sectorialia. The innermost Digit is often stunted
or absent.

Digihgrada. All have the clavicular styles. The humerus is pierced between
the condyles but not above the inner condyle in all (exc. Felidse, in which the
reverse is the case). The radius and ulna, are closely and extensively united in
the Canidse and Hysenidse. The supplementary ossicle at the radial side of the
carpus is present in most Yiverridse and Canidse. Tha poUex, small in other
families, is retained in the Felidse, and, like the other toes, is terminated by a
large, compressed, retractile, unequal phalanx, forming a deep sheath for the firm
attachment of the large, curved, and sharp pointed claws.

Semi-Plantigrada. The acromion is generally distinctly bifurcate. The
humerus in Lutra is remarkable for the compression of the shaft, which is
strongly bent forwards.

Plantigrada. The clavicle is wholly wanting or very rudimentary. The
scapula is remarkable for its almost quadrate form, and for the strong develop-
ment of the ridge between the infraspinatus and teres major, constituting almost

• Ossicles suspended in the muscles and not extending from the aromion to
the Ptcrnum.

40 ' Mammalia. Prohoscidia.

a second spine. The inner condyle of the humerus is not perforated, except in
Ursus ornatus.

Finnigrada. There is no trace of a Clavicle. The humerus is generally-
shorter than the scapula : the inner condyle is perforated in Phoca (? alone).
The antihrachial hones are compressed and firmly united. The fore feet are
short and expanded into swimming paddles. The poUex or first digit exceeds i\ie
third, fourth, and fifth in length, but presents its characteristic inferior nimiber
of phalanges.

The Pelvic arch and Appendages. The Pelvis varies greatly in the
three principal Sub-orders, and so also its appendages ; but certain
characters appear to be common to each Sub-order, as follows: —

Digitigrada. The ilia are long and narrow, but thick : the ischia are also
long : the pubis is short, but the ischio-pubic symphysis long. The whole
* innominate ' bone forms a considerable angle with the axis of the lumbar series.
The toes alone touch the ground, the heel or calcancum being much raised. The
hallux is rudimentary in Vivenidce and Canidae.

Semi-Plantigrada. Only a part of the hind foot forms a sole to rest on the
ground.

Planiigrada. The ilia are shorter, thicker, and broader, than in the Digiti-
grada : the ischia are short and expanded, and form with the strong ^;?</ye« a
long symphysis: tho fet)iur is remarkable for its groat length, and superficial
resemblance to that of Man, though flattened from before backwards. In tho
Procyon (Raccoon) the fibula is characterised by three processes behind its distal
end. The hallux is rather shorter than the other toes, which are of subequai
length, and form the basis of a broad flat foot : the whole of the hind foot forms
a sole and rests upon the ground.

Finnigrada. The Pelvic arch is remarkable for the stunted development of
the ilia, and the great length of the ischia and pubes ; the symphysis is short, and
divaricable in parturition (cf. v.). 1h.c femur is equally peculiar for its short-
ness and breadth ; the shaft almost disappears and the two articular extrcmitiea
form nearly the whole mass. The tibia sm^ fibula are anchylosed at their prox-
imal ends. The bones of ihafoot are much developed, and are modified to form
the basis of a large and powerful fin : in Phoca, the middle toe is the shortest,
and the rest increase in length to the margins of the foot ; in Otaria and Trichae-
cus the toes are subequai in length. The hind feet are fettered by the continua-
tion of the integument to the tail.

yil.— PROBOSCIDTA.

The Shdl. The Sutures are soon obliterated. The Frontal bone
is excessively expanded by air cells ; as also are the short triangular
Nasals^ with which it coalesces. The Superoccipital is much expanded
and supports two Interparietals, which together with the Parietals,
Frontals, and jS"asals, form a dome of considerable size : hence the
cranial far exceeds the facial area. This dome is however filled al-
most entirely with contiguous air cells, and only a small proportion of

Mammalia. Prohoscidia, 41

the back part of the base forms the true brain case. The pneumatic
Maxillaries are remarkable for the large proportional size of their
alveolar part, in advance of which the bone extends upwards to be
wedged between the Frontal and Premaxillary, downward and for-
, ward to strengthen the socket of the Tusk, and lachward to form the
anterior pier of the Zygomatic arch and the lower part of the Orbit.
The pneumatic Premaxillary mainly consists of the part which
lodges the base of the great Tusk ; but its ascending portion reaches
the Prontal, and excludes the Maxillary from the Nasal. The
Upencephalic compartment of the cerebral cavity is wholly behind the
Pros- and Mes-encephalic ones, as is also the case in the Insectivora,
Cheiroptera, Eodentia, and Inenamellata.

The Vertebral Column. The Epiphyses continue detached from
the bodies of the Yertebrae to nearly full growth : the Centra are
remarkably short for their breadth, especially in the Cervical region.
The first and fourth Dorsal are remarkable for the strength as well
as the height of their neural spines. There is no Anticlinal Terte-
bra in the Dorso-lumbar series. The first and second Rils are
almost straight, and expand to join their short sternal parts. Five
pair of ribs directly join the sternum, which consists of four bones.
IS'early two-thirds of the Caudal vertebrae are reduced to the centrum
alone.

Anterior Appendages. There are no Clavicles : the Scapula is
broad and concave, and has thick epiphyses attached to the border ;
a process depends from the short pointed Acromion ; the Glenoid
cavity is shallow ; the Coracoid a mere tuberosity. The head of the
Humerus is sessile ; the great tuberosity rising above it and extending
antero- posteriorly ; each of these has a separate epiphysis. The
Radius, — crosses obliquely in front of the Ulna to the inner side of
the Carpus, — has its head wedged between two processes of the Ulna,
— and has its expanded distal half attached by a ligament to the
Ulna. The Feet have five toes, which are outwardly indicated only
by divisions of the hoof.

Posterior Appendages. The Ilium on each side is but narrowly
apposed, by the edge, to the three Sacral vertebrae, and stands out
from them so that its principal axis forms a right angle with the axis
of the Vertebral Column. The Ischia and Pules are short, and
form a symphysis, the axis of which is parallel with that of the
vertebral column. The Great Trochanter does not rise so high as

42 Mammalia. Perissodactyla.

tlie head of the Femur ; the small one is almost obsolete. The Tibia
and Filula are distinct throughout their length.

In the Proboscidia the following characters recall the ' Rodent ' type, viz. : —
the epencephalic wholly behind the pros- and mes-encephalic cerebral cavities ; —
the malar bone suspended in the middle of the zygomatic arch ; — the pj'cemaxil-
laries large and excluding the maxillary from the nasal ; — the large alveoli
for the single pair of incisors : lastly— the spine of the scapula extended into a
short pointed acromion and sending down a process.

YIII.— PERISSODACTYLA.

The Shull. The Nasals expand posteriorly. The slender Fterygoid
process has a broad and thick base, and is perforated lengthwise by the
ectocarotid artery. The major part of the Posterior Aperture of the
Nostrils is bounded by the Palatine bones of which only a small portion
enter into the formation of the bony palate ; the Bony Palate termin-
ates behind, generally in the neighbourhood of the penultimate Molar
tooth. The Post-tympanic process is well developed. The Jaws are
long and slender. If the species be horned the Horn is usually single,
but if there be two, they are of unequal size, and placed on the
median line of the head, one behind the other j each being thus a
single or odd horn.

SoUdungttla. The roof of the orbit is produced outwardly and the osseous
framework is completed posteriorly by the junction of the post-orbital with the
zygoma. The base of the post-orbital process is perforated for the superorhital
foramen. The lachrymal canal begins by a single foramen. The Prccmaxillaries
extend to the nasals, which are very long and conspicuous, and shut out the
maxillaries from the anterior aperture of the nostrils. The post-tympanic
process is separated from the paroccipital process by the intervention of the
tuberous mastoid. The tentorium is ossified.

Multungula. The orbit is incomplete. The superorbital foramen is absent.
The lachrymal canal commences by tioo distinct orifices. The prcemaxillariea
terminate before reaching the nasals. ^Ylq post-tympanic process either imites
with the lower part of the paroccipital, e.g., in Tapir ; or, seems to take the place
of the mastoid, e.g. in Ehinoceros.

The Vertebral Column. In both the Cervical and Dorsal vertebrae
the fore part of the centrum is convex, the hind part concave, i.e. the
joints of the centra are Opisthoccelian. The Dorso-lumhar vertebrae
are never fewer than twenty-two. There are commonly eight pair
of Ribs directly joined to the Sternum which consists of seven bones
and a xiphoid cartilage. The Sacral vertebrae are frequently five or
six in number, but ofthese only two or three articulate with the
Ilia.

Mammalia. Hyracoidea. 43

The Scapular Arch and Appendages. There is no po\rer of Eola-
tion of the Fore Limb in any Hoofed Quadruped. There are no
Clavicles. The Scapula is long in proportion to its breadth ; its
spine developes no Acromion : the Coracoid is a mere tuberosity
The Humerus is remarkable for the size and strength of the proximal*
tuberosities. The Os Magnum, and the Digitus Medius (iii.) which
it supports, are largely developed.

Solidungula. The ulna, represented by its well developed olecranal extremity,
is confluent with the radius in its proximal moiety. Digits iv. and ii. are rudi-
mental, and digit iii. alone encased in a Hoof,

Muitungi^la. The radius and ulna sometimes interlock, e.g. in Rhinoceros,
sometimes partially coalesce at their distal ends, e.g. in Tapims. Digits ii., iii.,
and iv. are fully developed, and each encased in a Hoof. In Tapir, the first or
trapezial digit is the only one absent ; and that articulated to the Magnum,
answering to the third, is the largest, and of symmetrical shape ; the whole fore-
foot plainly showing the Perissodactyle type, though with four toes.

Pelvic Arch and Appendages. The Ilium is generally rather
hammer-shaped, and articulates by its superior angle with two or
three of the sacral veitebra). The Ischium is produced backwards
considerably. The Femur has a third trochanter : and the medullary
artery penetrates the middle third of the back part of the shaft ; it
has no constriction between the head and shaft.

Solidungula. The Jibula is as rudimentary as the ulna.
Multungula. ThQjibula is fully developed.

IX.— HYEACOIDEA.

The SJcull. The elements of the Occipital bone are late in coales-
cing. An Interparietal is present in the back part of the sagittal
suture. The ascending process of the Malar articulates with the
post-orbital process which is formed by both Parietal and Frontal
bones. The Tympanic, which forms the Bulla Ossea at the basis
cranii, has not coalesced with the Petrosal. The hinder halves of
the Palatines enter into the formation of the Palato-Nares. The La-
chrymal canal commences by one or two foramina, protected by a pro-
cess. The Maxillary forms the floor of the orbit as in Perissodactyla
Multungula ; but the premaxillaries join the nasals. The Lower Jaw
is remarkable for the backward expanse of the ascending Ramus,
The Coronoid process is perforated lengthwise at its base.

The Vertehral Column. There are not fewer than twenty-nine or
thirty Dorso-Lumbar Vertebrae : the Dorsals in their form and pro-
portions resemble^those of the Rhinoceros : the Metapophysis exceeds

44 Mammalia. Artiodactyla.

the Diapophysis in length in all the posterior dorsals : no Anapophy-
ses are developed. In the eighth Lumlar vertebra the Diapophyses
suddenly acquire great breadth, and gradually increase in length to
the last lumbar. The first three Sacral vertebrae articulate with the
ilia.

The Liml Bones. There are no Clavicles. The Intercondyloid
part of the Humerus is perforated (as in the Tapir). The Fore Foot
is unsymmetrically tetradactyle : the Hind Foot has only three toes.

X.— AUTIODACTYLA.

The Shull. If the species be horned, the Horns form one pair or
two pair; they are never developed singly, of symmetrical form,
from the median line. The JVasals are usually long and conspicuous,
and do not expand posteriorly. The Zachrymal is very large,
especially in its facial part. The Super-orhital canals are large in
most species. The FrcB-tnaxillaries generally reach to, or are con-
tiguous with, the Nasals. The Post-tympanic does not project
downward distinctly from the Mastoid, nor supersede it ; and the
Par-occipital always exceeds both these processes in length. The
Bony Palate usually extends further back than in the Perissodactyles :
the hinder aperture of the Nasal passages being more vertical, and
commencing posterior to the last molar tooth. The base of the
Pterygoid process is not perforated by the ectocarotid artery.

Omnivora. The orbit is seldom complete : the prccmaxillaries reach the
nasals : the malar rarely reaches the frontal : the temporal fossa; are deep and
approximate on the top of the cranium : the zygomatic arch is strong : the arti-
cular condyle of the jaw is larger than in Euminantia. In Hippopotamus the
rim of the orbit is almost, sometimes quite, complete : the lateral series of molar
alveoH slightly diverge anteriorly : the basi-occipital forms no part of the occi-
pital condyles : each ramus has an antroverted angular process. Most of the
£uidceh.a.ye apraenasal bone.

Rurninantia. Processes are generally found on the frontal bone for horn core.
The parietals are frequently anchylosed together : the malar and frontal bones
generally complete the orbit. The articular condyle of the jaw is small, and
plays freely in all directions in a shallow glenoid cavity : the coronoid processes
are narrow, and the base of the ascending ramus expanded. The temporal fosses
are small : — the zygomatic arch weak : — the pramaxillaries generally edentulous.
The Jffyoid avch. includes long, compressed, hammer-shaped 'stylohyals' attached
to short epi- and cerato-hyals : the thyro-hyals are also small ; the basi-hyals
normal. [In Camelus no processes are developed from the frontal bone for horns :
the^Zygomatic arches, in relation to the laniariform teeth, are long and over-
span a wider temporal fossa than in the true Euminantia : the Prsemaxillaries do
not reach the nasals : the orbital plate of the Lachrymal shows two perforations :

Mammalia. Artiodactyla, 45

the angle of the Mandible is singularly elevated : and the palate extends as far
back as in the horse]. In Solidi-cornua the Horn cores are osseous, their bases
sometimes resting equally upon the parietals and frontals : the Lachrymal is
separated from the nasal by a large vacuity which intervenes between them,
the frontal, and the maxillary, [In Giraffa the articular surface of the prominent
occipital Condyles is so extended vertically as to admit of the head being raised
in a line with the neck : the Exoccipitals are largely developed for the ligamen-
tum nuchge. In Cervidce the Lachrymal is provided with a deep pit and groove
for the reception of the sebaceous sacs]. In the Cavi-cornua the Bovidue fre-
quently have Persistent Sutures between the exoccipitals, and between these and
the Superoccipital : the Occipital Condyles are wide apart : the Paroccipital
descends much below the Mastoid : the Malar generally extends largely upon
the face : the Nasals are frequently cleft anteriorly : the Frontals form the chief
part of, and alone develope the Horn cores (exc. in Antelopes) : a Lachrymal
pit is commonly found.

The Vertebral Column. The Borso-lumlar series generally num-
bers nineteen, except in Antilopidae and Ovida?.

Cmnivora. The Pleurapophysial parts of the transverse processes of the
posterior Cervicals generally develope hatchet- shaped plates or lamellae, which
progressively increase in size posteriorly, and overlap each other.

Ruminantia. The Cervical vertebra) have opisthocselian ball and socket joints :
the seventh cervical always has the transverse process imperforate : the anterior
Dorsals have long spines for the attachment of the ligamentum nuchas : the dia-
pophyses of the last lumbar vertebra do not articidat© with the sacrum. The
Camelidce have a remarkably long and flexible cervical region ; but the typical
number of vertebrae remains : the transverse processes of their cervical vertebrae
are never perforated for the vertebral artery* : their last sternal bone is greatly
expanded and protuberant below to support the pectoral callosity. The Giraffe
has the longest cervical vertebrae of all mammals.

The Scapular Arch and Appendages. Clavicles are wanting. The
spine of the Scapula is commonly produced into an acromial angle.
In the Carpus the os magnum does not exceed, and may be less than the
unciform. The Limbs are terminated by Feet with four or two toes,
the digit answering to the iii. in the penta-dactyle foot is unsym-
metrical, and forms with that answering to the iv., a symmetrical
pair.

Omnivora. The Scapula is short as compared with that of Ruminantia, and
the acromion is sometimes deficient, e.ff. in Sus scrofa. The Radius and Ulna are
generally coalesced, e.g. in Hippopotamus ; sometimes distinct, though in close
proximity, e.ff. in Sus.

Ruminantia. In the true Ruminantia the spine of the Scapula is not produced,
but terminates in an acute (Bos), or a right angle (Cervus) : in Camelidee, on the
contrary, it is produced. The Metacarpals coalesce early into a single bone, but

* The vertebral artery iu the CameUdae transverses the neurapophyses.

46 Mam^nalia. Cete.

the medullary canal of each remains distinct ; each moiety has its distinct distal
trochlea and phalanges ; and in each of them the second phalanx is modified to
be sheathed in a hoof : stunted portions of the other toes are'to be found in most
true Ruminantia suspended to the back part of the distal end of the so-called
* cannon ' bone, as ' spurious hoofs,' not reaching the ground.

The Pelvic Arch and Appendages. The Iscliia are long, and with
the dorsal angles of the broad and thick tuberosities produced to-
wards the caudal vertebrce. The Femur never has a third trochan-
ter: the Medullary artery^ except in the Camelid£e, enters the/or<9
part of the shaft usually in its upper third : the inner border of the
rotular channel never developes an irregular prominence (as in Peris-
sodactyla) though here produced. In the Carpus the Ectocuneiform
is less, or not larger than the Cuboid : the Cuboid and Naviculare are
distinct bones in all except the restricted or horned Ruminants.

Otnnivora. The Tibia and Fibula are generally distinct. In Dicotyles (Peccari)
the fifth as well as the first toe are wanting in the hind foot : the second toe is
small ; the third and fourth are very large, and form a symmetrical pair, show-
ing that the Artiodactyle structure essentially prevails, although the toes, by the
non-development of the fifth, are, exceptionally, reduced to three in number.

Ruminantia. The Oa innominaiiim is elongate, with the iliac portion concave
lengthwise, convex across, externally, with the expanded anterior end divided
by a ridge into two portions articulating with sacrum. The Ischium extends
back from the acetabulum with the tuberosity bending upwards. The Pubes are
slender. The Hind Limbs always exceed the fore limbs in length. The shaft
of the Fibula exists as a sclerous tissue in all Ruminantia. The Naviculare or
Scaphoid is almost always confluent with the Cuboid. The Metatarsal segment is
generally represented by the third and fourth metatarsals confluent : the distal
ends of the second and fifth being ossified and supporting the small digits termin-
ated by the ' spurious hoofs.' [In the Camelidce the scapula is broader than in
homed Ruminantia, and has its spine produced : the scaphoid is not confluent
with the cuboid : the canal for the medullary artery enters the back part of the
shaft of the femur; the borders of the rotular channel are subequal.]

XL— CETE.

The Skull is large, the size being due in most Cete to the develop-
ment of the jaws, which in some Whales [e.g. Bala^nidae, and Physeter
macrocephalus) is excessive. The Skull of the Balaenidas is more
symmetrical than that of the toothed Cete. T\iq Mastoids are always
distinct from the Petrosals. The Tympanic generally presents a
peculiar conchoidal shape, and is extremely dense in texture.
Laclirym,al bones are generally absent. The C rihr if orm plate is also
usually rudimentary, or absent (Physeter). The JVasal bones are
«hort, rudimentary, or absent (Physeter). The Frontal bones fre-

Mammalia. Cete. i7

quently assume the form of triangular plates with the outer and fore
angle produced into a superorbital process : they are joined to contigu-
ous bones by squamous suture. The bone formed by the coalesced Pre-
frontals (Phyaeter) penetrates the posterior part of the groove of the
vomer, and expands above it, forming the septum of the vertical
nasal passage ; it is not complicated with Turhinal or Rhinal capsules,
as in the so-called * Ethmoid ' of the other Mammals. The Malar
is generally small and slender. The Condyle of the Mandible projects
from the posterior part of the base or ascending ramus. In some
Cete the Pterygoid processes of the Sphenoid remain separated
throughout life. In Delphinus a bony Tentorium is found. In
Physeter the capacious basin on the upper surface of the skull, which
lodges the valuable produce called * spermaceti,' is formed by the
expanded and concave nasal processes of the Prsemaxillaries and
Maxillarics which overlap the Frontals. In the mature Balasna
mysticetus, the Maxillaries are disposed each like an expanded arch
along the outside of the co-extended Praemaxillaries ; their inferior
surfaces have two facets, separated by longitudinal ridges, to the sides
of which the plates of baleen are attached.

The Vertebral Column. The discoid terminal Epiphyses long re-
tain their individuality, especially in Balaena. There are no Anapo-
physes. The Cervical region is short; the Cervical vertebrae are always
seven in number, but each is flattened from before backwards into
a broad thin plate, and partly anchylosed with its fellow on either
side (except in Narwhal in which they are all free), and thus rendered
almost incapable of movement on one another : indeed in most of the
true "Whales (Balsena), Grampus, and Porpoise, the Cervical vertebrae
are blended together into a single bone. In many species of this group
the second Cervical vertebra lacks the Odontoid process. The number
of Ribs directly articulating with the Sternum is variable. The
ITcemapophyses, by which the Pleurapophyses or Eibs are joined to
the Sternum, are commonly cartilaginous, rarely osseous. The num-
ber of the component bones of the Sternum is also variable. The
Sternum of the Whale consists of but one short and broad bone, to
which is usually connected a single pair of Eibs. The vertebrae
without Eibs succeeding to the Dorsal are many in number, and,
since they are as free from anchylosis as in Pishes, cannot be differ-
entiated into * lumbar ' and ' sacral.' The Sacrum is never indi-
cated hy vertebral confluence^ and only obscurely by the position of the
Pelvic rudiments loosely suspended below. The Caudal vertebrae

48 Mammalia. Sirenia.

are distinguislied bj the ' chevron bones,' viz., haera apophyses
articulated in Cete, as in Crocodilia, directly to the under surface
of the centrum and coalesced at the opposite ends, thus forming
a haemal canal analogous to, but not homologous with, that in
Fishes. The Caudal vertebrae of Whales farther differ from those
in Fishes, in retaining the transverse processes, and in becoming
flattened from above downwards without coalescing.

Aiiterior Appendages. The Anterior Limbs alone are developed,
and are flat and fin-like. The Clavicles are wanting. The Scapula
is broad, flat, and without a spine along the outer surface; it has
a short stunted Coracoid anchylosed to it, and is freely suspended
in the flesh {cf. Fish). The Humerus is remarkably short in propor-
tion to its thickness, as in most Aquatic Mammalia. There is no
complete articulation between the bones of the Fore-arm and the
Humerus. The Olecranon, though generally present, is but slightly
developed. The two short bones* of the Fore-arm lie immoveably
behind each other, and are very flat. There is no complete articu-
lation between the bones of the Carpus, Fore-arm and Digits. The
Carpal bones are generally three to five in number, dice-shaped, and
lying between thick tendons and masses of ligament. Some of the
Digits have more than three phalanges ; in the Whales five to six, and
in the Dolphins even more. All the Digits in the natural state are
enveloped in a common fold of integument. The increase of the
Phalanges of certain Digits beyond the number three is a remarkable
instance of departure from the Mammalian type, and of affinity
with the extinct En-alio-saurus and Fishes.

Posterior Appendages. The Pelvic bones consist of two simple
elongated bones, lying near the anal and generative organs, which
converge together from opposite sides, or are connected by a trans-
verse piece: these traces of Innominate hones are remote from the
vertebral column and connected with the rest of the skeleton by
muscles only. There is never more than a trace of hind limbs;
these, when found, are represented [{e.g. in the Eight Whale) by a
two-jointed ray. This is the simplest condition of the limb, or ap-
pendage, of the Pelvic Arch known in the Mammalian Class.

XII.— SIRENIA.

All the bones of the skeleton are solid.

The Skull. The Facial, or rostral parts of the skull, anterior to
the orbits, is short. All the skull bones are massive, and, save in

Mammalia. In-Enamellata. 49

the instances of anchylosis, are somewhat loosely connected together.
The Frontals are not confluent. No distinct Nasals are found an-
terior to the frontal suture. The Prcemaxillaries of the Dugong
( Halichore) are remarkable for their very large and long deflected
alveolar portion. The Zygoma is unusually massive. The Basi-
sphenoid coalesces with the Alisphenoids; the Praesphenoid similarly
coalesces with the Orbitosphenoids, and is wedged between the
laminae of the Vomer as a compressed * rostrum.'

The Vertebral Column. The Cervical region is short, but longer
in proportion than in the Ceto. The cervical vertebrae are
generally free {cf. Cete) and short. In the Manatee and in the
extinct Rhytina (of Steller) they are hut six in number; thus forming
an exception to the generally constant number (seven) of cervical
vertebrae. The Ribs of the dorsal vertebrae are massive, and join
by cartilaginous haemapophyses the sternum, which in the immature
state is made up of two bones. There is no distinction of ' Lum-
bar' and 'Sacral' vertebrae. Most of the Caudal vertebrae have
long diapophyses and haemal arches.

iScapular Arch and Appendages. The Clavicles are wanting. The
Pectoral pair of limbs alone exist, and their supporting arch is
reduced to the Scapula, which has a short Coracoid process. The
Humerus has the normal Mammalian character, and a synovial
articulation {cf. Cete), with the Eadius and Ulna; the latter of
these bones developes an obtuse olecranon. The Phalanges are never
more than three in number.

The Pelvic Arch, The Pelvis assumes the Batrachian condition,*
and all appendages to the rudiment of the Pelvic Arch are wanting.

XIII.— IJS^-ENAMELLATA.

The Skull in the Insect-eating f In-Enamellata is long and slender,
these proportions reaching their extreme in the true Ant Eaters
(Myrmecophaga), owing to the great development of the facial part.
In the Brady podidae, on the contrary, the whole head is proportion-
ally small, the facial part of the skull being exceptionally short.
The cranial cavity is thronghout this order of small proportional size.
The Zygomatic arch culminates in regard to complexity in the Brady-
podidae, albeit in the small existing species, as also in the Ant Eaters,

* The Pelvic bones appear to be entirely wanting in Manatus.

t The Insect-eatiny In-Enamellata are the edentulous Myrmecophagid(B and
the Dasypodidce.

50 Mammalia. In-Enamellata.

the squamosal element fails to reach the malar one. The Malar bone
is remarkable in Brady pus for its size, shape, and connections; it is
freely suspended by its anterior attachment to the maxillary and
frontal, and bifurcates behind ; one division extending downwards,
outside the lower jaw, the other ascending above the free termina-
tion of the zygomatic process of the squamosal. The Intermaxillaries
are very small in most species of this Order, and support teeth only
in the six-banded Armadillo. The Pterygoids are frequently in-
flated in the Bradypodidce.

The Vertehral Column. — In no other Mammalian order are found
such complex vertehral articulations; e.g. In the Dasypodidae the
metapophysis presents an articular surface at the under and fore
part of its base, to be articulated with an anapophysis of the suc-
ceeding vertebra : and again the anapophyses upon the last dorsal,
each present an articular surface at the under part for connection with
the parapophyses. In this order alone are manifested the exceptional
instances of affinity to certain Ovipara, in the lower cervicals with
free ribs of the three-toed, and in the twenty-three costigerous
dorsals of the two-toed Sloths. The three-toed Sloths-"' {Bradypus
tridactylus) have nine cervical vertehrce ; and Cholcepusf Hoffmannii
has hut six cervical vertehrce ; two out of the four so-called exceptions
to the rule of there being always seven cervical vertebrae in Mam-
malia.J In the Loricate or Armadillo family (Dasypodidse) the
Tertebral column is remarkable for the prevalence of anchylosis in
unusual parts, eg. the cervical region ; and for the great size to
which the metapophyses attain (in the lumbar region especially).
The metapophyses (which are processes from the anterior zj^gapo-
physes) serve, together with the neural spines, to support the Cara-
pace. The Sloth and Armadillo have ossified hcemapophyses. The
spines of the Sacral vertehrce are very commonly anchylosed. In
Dasypus the Sacrum is exceedingly broad, and anchylosed inferiorly
to the Pelvis. Dasypus forms an exception to the rule of absence
of anchylosis in the caudal region.

Scapular Arch and Appendages. The Scapida in the Armadillos
and true Ant Eaters is broad, and presents two spines (in Manis it
has only one spine), and the acromion is long. Clavicles are present

* Bradypus torquatua is saiJ to have eight cervical vertebrae,
t Cholcepus : the genus of two 'toed Sloths.

Mammalia. Marsupialia. 51

in all Dasypodidae and Cholaepus; are small and rudimentary in
Myrmecophagida?, absent in Manis, and so short as not to reach the
sternum in the Sloth. The Humerus is generally well developed,
short and broad in the Armadillo, long in the Sloth, varying, as also
do the Antibrachial bones, with the burrowing or climbing habits of
the different species : it is generally perforated above the inner
condyle;]:. The Zflna is generally longer (ex. Manis) than the Eadius,
often much stronger {^.y. Armadillo), and usually possessed of a well-
developed Olecranon. In all In-Enamellata the Radius is free, and
rotates on the Ulna : in the Sloth these bones are so articulated as
to allow of pronation and supination. The Metacarpal hones in the
Sloth are united together posteriorly, and also with the front row of
Phalangeal bones. The Ungual Phalanx of the Ant Eater is charac-
terised by being split at the extremity by a longitudinal fissure,
commencing at the upper part of the base {cf. Perameles, Marsu-
pialia).

Pelvic Arch and Appendages. The Ischia are largely developed in
all except the Sloths: and except in Orycteropus unite with the
vertebral column. The Ilia are generally firmly and extensively
united with the Sacrum. The Pules are always slender, and form
but a narrow ossified symphysis. The large Pelvis, the union of
the Ischia with the Sacrum, and the speedy osseous confluence of
the several pelvic elements are common characteristics of the spinal
column of the In-Enamellata. The Armadillos are marked off from
the Sloth and Ant Eaters by having a third trochanter to the Eemur^
and the proximal and distal extremities of the Tilia and Filula
conate. In both Sloth and Ant Eaters, the Tibia and Fibula are dis-
tinct (in the former they are oppositely bent, leaving a wide inter-
osseous space), and both fore and hind feet have an inclination
inwards, owing in the latter case to the downward projection of
the outer Malleolus, which fits like a pivot into a socket in the
Astragalus.

XIY.— MAESUPIiLIA.

The Skull is generally more depressed and flattened than in the
Placental Mammalia ; and is remarkable for the small proportion
which is devoted to the protection of the brain, and for the great
expansion of the nasal cavity immediately anterior to the cranial
cavity : it usually converges ^gradually towards the anterior ex-

X Except Manis.

52 Mammalia. Marsupialia.

tremity. In the stronger carnivorous Marsupials the exterior of
the cranium is characterised by bony ridges • and muscular impres-
sions, varying directly with the development of the temporal
muscles, the extreme development being found in the Yirginian
Opossum, in which the sides of the cranium meet above at an acute
angle, and send upward from the line of their union a remarkable
elevated sagittal crest, which, in mature skulls, is proportionally
more developed than in any of the Placental Sectoiialia. In the
smaller Herbivorous and Insectivorous species the cranium presents
a convex surface, as in birds.

The Occipital region, which is generally plain, and vertical in po-
sition, forms a right angle with the upper surface of the skull, from
which it is separated by an occipital, or lamboidal crista. The ele-
ments of the occipital neural arch remain longer distinct in Marsu-
pials than in most other Mammals. The Condyles are each perforated
anteriorly by two foramina in most of the Marsupialia. The Fora-
men magnum is of great size in relation to the capacity of the cranium.
The Sagittal suture^ between the Parietals, is obliterated in those
species in which a bony crista is developed, as also in some aged
animals. An Interparietal hone is generally present. The Coronal
suture presents, in most of the Marsupialia, an irregular angular
course, forming a notch in the frontals on each side, and receiving
a corresponding triangular process of each frontal bone. The Frontals
are chiefly remarkable for their anterior expansion and the great
share which they take in the formation of the nasal cavity. The
JExtraorhital foramen is a good Marsupial character. The most
characteristic structui'e of the JVasal bones is the expansion of their
upper and posterior extremity. The Prcemaxillaries always contain
teeth, and the ratio of the development of these bones con'csponds
with the bulk of the dental apparatus which they support, they are
consequently largest in the Wombat. The Alalars are generally very
strong, and of great extent. The Zygomatic arches are always com-
plete, and usually strongly developed, but do not vary in size as
directly with the diet as in preceding orders. Most Marsupials
have a Sphenoidal hdla, foimcd by the expansion of the base of the
Sphenoid ; Acrobates and Perameles lagotis have a second bulla
formed by the expansion of the Petrous bone ; the Petrous lone is
generally of small size, and limited to the office of protecting the
parts of the internal ear ; the Glenoid cavity presents a character-
istic structure in most of the Marsupials in not being exclusively

Mammalia. Marsiiplalia. 53

formed by the Squamosal ; but presents various forms in direct cor-
relation with tlie structure of the teeth, and the movement required
of the jaw. The angle of the Jaw is as if it were lent inward* in the
form of a process. On looking directly upon the lower margin of the
jaw, in place of the margin of a vertical plate of bone there is seen
a more or less triangular surface, extended between the external
ridge and the internal process, or inflected angle (esp. in "Wombat).f
In all those Marsupialia which have few or very small incisors the
horizontal rami converge towards a point, the symphysis being more
or less complete. The Nasal cavity communicates with the mouth by
means of various large vacuities in the palatal processes. Two pos-
terior Palatal Foramina are generally present, of variable size and
position, especially noticeable in Perameles lagotis, in which the bony
roof of the mouth is perforated by a wide oval space, exposing
to view the Vomer and the convolutions of the inferior Spongy
bones in the nasal cavity. The Pterygoids long maintain their
individuality, and are always small and lamelliform. The Entocarotid
canals pierce the Basisphenoid, as in Birds. The Tentoritim is some-
times partially, but never completely ossified in any of the Marsu-
pialia. There is no ossification of the Falx, as found in Ornitho-
rhynchus [cf. Monotremata). There is no distinct pituitary fossa^
nor Clinoid processes. The Optic foramen is confluent with the
sphenoidal fissure.

The Vertebral Column. — The inferior arch of the Atlas frequently
remains permanently open in the middle line below {e.g. Phascolomys,
Phascolarctos, Phalangista, and Macropus). This opening is generally
occupied, in carnivorous Marsupialia and in Thylacinus, by a distinct,
and separate ossification. In all Marsupialia the spine of the Dentata
is well developed, both in the vertical and longitudinal directions.
The transverse processes of the Cervical vertebra? are generally more
or less expanded nearly in the axis of the spine, so that the pos-
terior part of one transverse process overlaps the anterior part of the
succeeding. The spine of the first Porsal is generally considerably
longer than that of the last cervical, and all the spines generally
slope towards the centre of motion. The Eils consist of bony pleur-
apophyses, and gristly ha3mapophyses, which acquire bone earth

* Except Tarsipes.

t The outer surface of the ascending ra7nus is imperforate in the Dasyuridae,
Didclpliyda?, Peramelidao, and Phalangistidse ; but in the Phascolomyd(e and
Macropidfc it is Aixecily perforated by a round aperture immediately posterior,
or oppoi^ite to the commencement of the dental canal.

54 Mammalia, MarsupiaUa.

only in the aged. In the Lumbar vertebrae the metapophyses attain a
great size. The number of vertebrse succeeding the lumbar, which
are anchylosed together in the Sacral region of the spine, varies
from seven, in "Wombat, to one, in Perameles: usually but one
vertebra supports the iliac bones. In most of the Marsupialia
which have a long Tail, whether used to support or suspend the
body, Y-shaped bones are found beneath the articulations of
most of the caudal vertebrae, which serve to protect the blood vessels.

The Scapular Arch and Appendages. — The Scapula varies in
form ; the coracoid exists as a process of the scapula, being anchy-
losed with it, as in the higher Mammalia, and not articulating with
the Sternum. The Subscapular area is generally more or less convex,
or undulating. The Clavicles are present in all except Perameles and
Chaeropus (?) ; are strongest and longest in the buiTOwing Wombat,
weakest and shortest in the great Kangaroo. In almost all, the in-
ternal condyle of the Humerus is perforated. The Radius and Ulna are
always distinct and well developed, but run nearly parallel and
€lose together. The olecranon is always well developed. There
is not any digit situated like a thumb, but all the fingers enjoy lateral
motion, and those at the outer side can be opposed to those at the
inner side, so as to grasp an object. The long ungual phalanges of
the Peramelidae are clelt mesially. Chaeropus has a manus much
resembling that of the Artiodactyla, but differing from it in having
digits ii. and iii. functional instead of iii. and iv.

The Pelvic Arch and Appendages, &c. — The Pelvis in the mature
Marsupial is composed of the os sacrum, the two ossa innominata, and
the characteristic supplemental bones attached to the pelvis, called
the ossa Marsupialia ; these last being ossifications of the internal
tendon of the external oblique muscle of the abdomen.* The length
of the symphysis of the Ischia (or the lower part of what is commonly
called the symphysis pubis), and the straight line formed hy the lower
margin of the Ischia, is a characteristic structure of the pelvis in most
Marsupialia. The shaft of the Femur presents no linea aspera, the
head is supported on a very short neck. The internal Malleolus is very
slightly produced in any Marsupial. The Fihula is well developed.
In the Scansorial and Gradatorial Marsupialia the bones of the
anterior and posterior extremities are of nearly equal length ; but

* These bones have no special function relating to the ventral pouch of the
female, being nearly equally developed in both sexes, and also in those species
in which the Marsupium is not present. — Flowtr.

Mammalia, Monotremata. 65

in the Saltatory species the disproportion in the development of
the bones of the hind leg is very great. In the Saltatory species
the Fibula is in close contact with or attached to the Tibia, so as
to ensnre fixity and strength : in others the Tibia and Fibula are so
loosely connected together, and with the Tarsus, that the foot enjoys
a movement of rotation analogous to that of the hand. A
degeneration of the Foot, common to many Marsupials, is to bo
observed in the slender condition of the second and third toes, as
compared with the fourth and fifth, and their enclosure nearly to
their extremities in a common integument : in the Saltatorial genera
they are reduced to almost filamentary slendorness. This condition
of the Pes called syndactylism prevails in all Marsupials, except the
Didelphidee, Dasyuridse, and Phascolomyidae. In most of the Plant-
eating Marsupials no rudiment of the innermost toe exists.

XV.— MONOTREMATA.

21w Skull. — The Monotremata differ from the Marsupialia in the
ahsence of the inflected process developed from the angle of the lower
Jaw. The Skull is long and low, the facial bones projecting in a
more or less beak-like form. The Sutures between the cranial bones
are eatly oUiterated. The Frontal bones expand as they rise, but do
not develope supra-orbital ridges. The Malar and Squamosal bones
are confluent (unless the slendqr process of the maxillary may repre-
sent the malar). The Lachrymals, also, are confluent with adjacent
bones. The Pterygoid processes of the Sphenoid often remain sepa-
rated throughout life. The Pterygoids are flattened, horizontal,
oval plates, attached to the obliquely truncated postero-external
extremities of the Palatines, and form part of the floor and the
inner wall of the tympanic cavity, an arrangement not met with in
any other Mammal. The Stapes is columelliform ; one cms of the
incus anchyloses with the reduced tympanic, the other is confluent
with the malleus. In many of these points the Ornithic affinity of
this order is apparent. In no Mammal is the proportionate size of
the lower Jaiv as compared with the skull so small as in Echidna, in
which it consists of two long styliform rami, loosely connected
anteriorly, and bound up with the superior mandible in a continuous
sheath of skin, except just at the apex. The lower jaw of Ornitho-
rhyncus, on the contrary, resembles very much a flattened duck's
bill ; it consists of two horizontal rami, united in the middle of
their length, diverging anteriorly and posteriorly from that point,

56 Mammalia. Monotremata.

and terminating towards the snout, as expanded spatulate processes.
- In both species theCoronoid process and the angle of the jaw are rudi-
mentary. Echidna has a well developed cribriform plate, but in Orni-
thorhyncus the olfactory nerve escapes by a single foramen (Sauroid
affinity). Lastly, we may note the lony falx found in Ornithorhyncus
only of this order (and rarely foand in other orders) attached internally
to the middle line of the coalesced parietals.

The Vertebral column. — The pleurapophyses in the Cervical region
retain their individuality. In Ornithorhyncus (but not in Echidna)
hypapophyses are present in the cervical vertebrae ; and are bifur-
cated in Atlas. The haemapophyses-'' of the first six Dorsal
vettebrse are ossified, and have cartilage interposed between them
and the pleurapophyses, f as in the Crocodile : the rest of tjie haema-
pophyses are cartilaginous, and overlap each other. A small tubercle
defines the neck of the Rih save in the last four, but save in the first
and second, the Ribs do not articulate with the diapophyses, but only
with the centra of the vertebrae helow the neuro-central suture, the
reverse of what occurs in the higher Mammals. The Frmsternum or
Manubrium is divided by an intervening layer of cartilage into two
parts : of these the posterior, or plcur-osteon, receives the haemapo-
physes of the first and second Ribs ; while the anterior, or pro-osteon,
is in relation with the Coracoids and Epicoracoids superiorly, and
with the body of the large T-shaped Inter-claviele[^/s^^r;^^^w, Owen]
(on which the Clavicles are supei-poscd) inferiorly. In Ornithorhyncus
the Sacral vertebrae remain permanently separated. In Echidna the
fluid central part of the intervertebral substance fills a more definite
cavity than in higher Mammalia ; and none of the Cervical vertebrae
have zygapophyses except the atlas. The (7(f)!w^<?/ vertebrae seldom have
haemapophyses articulated to the vertebral interspaces, as in many
Marsupials. The spinal nerves usually j9e;/oraif^ the neurapophyses. J

The Scapular Arch and Appendages. — The Scapular Arch is
arranged according to the type of the Sauropsida. The Scapula is
long, and sabre-shaped. The Coracoid, which in this order alone of
Mammalia attains its normal proportion, is developed as a distinct
bone, and extends from the Scapula to the Interclavicle, and also to

* Sternal Eibs. f Vertebral Kibs.

X The same arrangement obtains in Bovida?, and Tapir.

§ The Epicoracoid is a flat shield-like plate of bone, placed in front of the
inner end of the Coracoid, the rounded inner border of which passes beyond the
median line, overlapping the corresponding bone of the opposite side. — Floioer.

Mammalia. Monotremata. ,57

the Pro-osteon, with both of which it is in relation, as in Birds and
most Eeptiles ; it is anchylosed at full growth with the Scapula.
The Epi-coracoid^ (as in Lizards) articulated with the anterior margin
of the Coracoid is also an osteological characteristic of this order.
The Clavicles are represented by two curved styles, extending from
the acromion along the transverse arms of the Interclavicle. In this
Order alone of all the Mammalia are the Inter clavicles found. The
Humerus is remarkable for its shortness and breadth ; both condyles
are remarkably produced, especially the internal one, which is
perforated. The Radius and Ulna are pretty firmly connected to-
gether through nearly the whole extent, the ulna being chiefly
remarkable for the olecranon, which is bent forwards upon the
humerus and transversely expanded at its extremity. The number
of Phalanges is the same as in other Mammals, thus preserving the
type notwithstanding the Sauroid tendency in the scapular arch.

The Pelvic Arch and Appendages. — The Pelvis resembles that of
the Marsupialia in the presence of the ''marsupial" bones, which
are however relatively larger and stronger in this order; and it re-
sembles that of Reptiles in the length of time during which the
three components of each os innominatum remain distinct. In the
great development of the Ileopectineal spine* of Ornithorhyncus com-
pare Tortoise. In the perforated Acetabulum of Echidna compare
Aves. The Femur is short, broad, and flattened ; the Fibula is longer
than the Tibia by the extent of a process which rises upward some
way above the point of articulation with tibia, and like the ole-
cranon is greatly expanded at its termination. Both Monotremata
have a sesamoid bone placed at the interspace between the astragalus
and the naviculare ; and a second supernumerary bone articulated
to the posterior part of the astragalus which supports the perforated
spur, characteristic of the male sex.

§ See note on p. 56,

* In the Macropidse this is also strongly developed.

58 Mmnmalia.

DIGESTIVE SYSTEM— Gbneeal.

The Digestive Apparatus in this Class is of varied complex-
ity ; but in almost all Orders are to be found a Mouth, Tongue,
Salivary Glands, Teeth, (Esophagus, Stomach, Small Intes-
tine, Liver, Pancreas, Spleen, and Large Intestine (the com-
mencement of which is commonly marked by a Caecum). Of
these we shall treat in order.

The Mouth is almost always terminal, and bounded by fleshy
lips; these form the main characteristic of the Manmaalian
Mouth, inasmuch as the act of sucking is characteristic of all
young Mammalia, and this cannot be performed without
definite lips. The Lips admit of various modifications,
especially in the Quadrupeds, in which they are the main
agents in the prehension of food : the upper lip is generally
entire, but frequently marked with a median groove. The
Gape of the mouth is of variable width, but is rarely so small
as to admit only of the mere protrusion of the tongue. In
most Mammalia the Side Walls of the mouth are dilateable
and contractile, and Cheek Pouches are sometimes found
(chiefly in species of Insect-diet) : the Buccal membrane is
commonly smooth ; though sometimes beset with hard tuber-
cles. The Palate is usually more or less ridged transversely,
and the Velum palati* scooped out into a semilunar form, the
Uvulaf being absent in nearly all except the highest members
the class. Tonsils are generally met with ; and are largest in
the rapacious and carnivorous species.

• Soft palate.

t A conical process prolonged from the middle of the pendulous margin of
the Soft-palate in Man,

Digestive System — General, 59

The Tongue attains in this class its full development as an
Organ of Taste {q.v.) : it is commonly divided into a free,
gustatory, and sensitive part ; but in the matter of freedom
we meet with every gradation, from almost fixity to high
extensibility. It subserves several different mechanical offices,
being instrumental in the prehension, distribution, and some-
times even trituration of food.

Nearly all Mammalia have Salivary Gland^ ; the ratio of
their development varying directly with the nature of the
food and the time spent on mastication : they are larger in
those species which are Herbivorous than in those which are
Carnivorous, and are more highly developed in proportion as
the food is masticated for a longer period. The Glands com-
monly found pouring their secretion into the mouth are, the
Parotid, Submaxillary, and Sublingual: besides these there
are numerous Mucous Crypts* on the inside of the mouth and
on the Palate, e.g.^ Labial, Buccal, Zygomatic, Molar, and
Palatine. The Parotid, situated generally between the Ear
(irapa, near ; ovq, wt6q, the ear) and the lower Jaw, behind the
Masseter, penetrated by the Facial nerve, and whose duct
(ductus Stenonianus) opens between the Jaw and the Buccal
membrane in the neighbourhood of the upper Molar teeth,
is relatively the largest in Mammals that masticate most,
and feed chiefly on vegetables and fruit. The Submax-
illary, normally situated between or alongside the rami of
the lower Jaw, and whose duct (ductus Whartonianus) opens
inside the lower dental arch close to the fra3num of the Tongue,
upon the margin of the SubKngual, is largest in those species
that need the greatest amount of viscid lubricating secretion,
and have an animal or mixed diet. The Sublingual situated
by the side of the frsenum of the Tongue pours forth a viscid
secretion ; it is not always present. The Subsidiary Glands
are most developed in the Herbivorous Manimals in relation

* Termed collectively the Subsidiary Glauds.

GO Mammalia. Digestive System.

to tlie movements and mastication of tlieir coarse vegetable
food : tlieir secretion is more mucous than lubricating or
solvent. In sbort, the Parotid secretes tbe more fluid
>Saliva, wbich moistens in ordinary mastication the whole
mass ; the other glands secrete the slimy lubricating SaKva.
The Quantity of Saliva secreted by the Parotid {e.g. in Horse)
is in direct ratio to the dryness of the food and the difficulty
experienced in its mechanical division : while that secreted
by the Sublingual and Submaxillary flows in nearly equal
abundance, whether Mastication be exerted on dry or moist
forms of food.

The Teeth present remarkable difierences in Structure,
Replacement, Form, and Number, which stand in close
relation with the whole economy, mode of life, and form of
the species ; but generally agree in limits of Situation and
mode of Fixation. Structure. — In some genera JSorny LamincB
take the place of teeth*; but, as a rule, hard unvascular Dentine,
and Cement, exist in every Mammalian tooth ; and Enamel,
though not constantly present, is generally found. In the
newly formed tooth the Cement is always the outermost sub-
stance, and between it and the Dentine the Enamel is inter-
posed. The thickness of the coating of Cement in the adult
varies with the diet, being thin in those species that partake
of flesh or mixed diet, and thicker in those that feed on herbs.
According to the difierent arrangement of the Enamel, three
well vii^rk^di patterns of teeth are distinguishable : (i.) d. Simpli-
ces s. obducti, in which the Enamel forms an entire and uni-
form cap to the dentinal pulp ; (ii.) d. CompUcati s. semi-
compositi, in which the Enamel followed by the Cement is
inflected or penetrates into the Dentine and forms folds ; (iii.)
d. Lamellosi s. compositi, in which the folds of Enamel pene-
trate so far towards the root of the tooth as to divide it into

* Bakena. OrnithorhTncus.

Digestive Si/ste?n — General. 61

distinct lamina), eacli of whicli is at the same time separated
and held together by the softer Cement which external to
the Enamel follows its every fold. Replacement. — In almost
every species the teeth are formed in Alveoli ; but in some,
the tooth when completed and worn down is not replaced ;
while in others, two distinct sets are developed which have
been termed Permanent, and Temporary (Deciduous, or Milk)
teeth respectively. The Permanent and Deciduous teeth are
both formed simultaneously side by side from independent
portions of the primitive dental groove ; but the one destined
for early functional activity proceeds rapidly in its develop-
ment, while the other makes little progress until the time
approaches when it is called upon to take the place, by verti-
cal displacement, of the more precocious locum tenens*. The
process of Replacement is never repeated more than once in any
Mammal. Those species which generate only a single set of
teeth are termed Monophjdontsf (fioyog, once ; ^vw, I generate ;
odovg, tooth) ; those which generate two sets are termed
Diphyodonts {Ziq, twice, &c.). Some species, however, seem to
occupy an intermediate position in this respect, in that the
successional process is confined to a single tooth on each side
of the jaw+. Number. — A few genera and species are devoid
of teeth% The so called 'typicaV number of teeth in this Class
is forty-four||, but the number varies excessively ; from one
fully developed^, to one hundred and ninety**. The ^typical'
number of true Molars in the Placental Mammalia with two
sets of teeth {i.e., Diphyodonts) is three. The more purely
carnivorous the species and the more it feeds upon living prey,
the less numerous are the Molars. Situation. — True teeth im-
planted in Sockets are confined to the Maxillary, Premaxillaryff,

* FloM^er.

t Cete, In-Enamellata, Monotremata. + Infra. Marsupialia.

§ Myrmccopliaga, Manis. Echidna. || Cf. Insectivora. Artiodactyla.
If Cf. infra. Situaiion. ** Cf. In-Enamellata. f f or 7«^e>--nuixillar}-.

62 Mammalia. Digestive System.

and Mandibular or lower maxillary bones, and form a single
row in each : they may be a- symmetrical, either as comparing
one jaw with the other, or even one side of the same jaw with
the other, though this is rare. When there is but one fully
developed tooth* it is never median. The teeth never all make
an unbroken series in any existing f Mammal save in man.
Those teeth which are implanted in the Premaxillary bones
and in the corresponding part of the lower jaw are called
* Incisor a J* whatever their shape or size: the tooth in the
Maxillary bone which is situated at, or near to the suture
with the Premaxillary is the * Canine,^ as is also that tooth
in the lower jaw which, in opposing it, passes in front of its
crown, when the mouth is closed : posteriorly to these are
situated, in the Deciduous dentition, the ^Milk Molars '; and in
the Permanent dentition, the Premolars (succeeding the Milk
Molars) and the true Molars (without predecessors). Fixation.
— In no Mammal does anchylosis of the tooth xcith the jaw con-
stitute a normal mode of attachment. Each tooth has its
particular Socket, to which it firmly adheres, by the close
coadaptation of the apposed surfaces, and by the firm ad-
hesion of the alveolar periosteum to the organised Cement
which invests the fang or fangs. The complicated form of
Socket which results from the development of two or more
Fangs is peculiar to species of the class Mammalia. Form. —
Three parts are generally recognisable in a Mammalian tooth ;
the FangX, or E-oot, the inserted part ; the Crown, or exposed
part ; and the Neck, or constriction which divides the Fang
from the Crown. It is peculiar to this Class to have teeth
with two or more Fangs wherewith to be implanted in
Sockets ; but Fangs are not always present : for there are

* Narwhal.

t In Anoplotherium, Nesodon, and Dicliodon the teeth are said to have formed
an unbroken series.

X The term Fang is properly given only to the implanted part of a tooth of
restricted growth, which fang gradually tapers to its extremity.

\

Digestive Sy stein — General. 63

8ome teeth which grow perpetually during the life of the
owner ; such teeth require their base to be kept widely ex-
cavated for the Persistent pulp* and have therefore neither
Neck nor Fang. In most Mammalia particular teeth have
special forms for special uses : Incisors for cutting and scrap-
ing ; Canines for holding and tearing ; and Molars for
grinding ; but the Deciduous and Permanent representatives
of each series differ slightly inter se : thus the Permanent
Incisors and Caninesf differ from their Deciduous predecessors
in size ; and the Permanent Premolars which succeed the
Deciduous Molars have generally less complex Crowns than
their predecessors. The Molars, properly so called (i.e., those
posterior teeth which have no deciduous predecessors), are
usually the most complex in their form. Similarity of form
is characteristic of the teeth of Monophyodonts. The modi-
fications of the crown of the Molar teeth are those that are most
intimately related to the kind of food of the species possessing
them. Thus in the purely flesh-eating Mammalia the princi-
pal Molars are simple, trenchant, and play upon each other
like scissor blades : in those species that break bones the
Molars have conical Crowns : in the mixed feeding species, the
working surface becomes broader and more tuberciilated ; and
in the insectivorous species it is bristled with, sharp points:
in those that eat shell-fish the Molars are small and obtuse ;
and in the partly herbivorous species, the flat grinding surface
of the teeth is compKcated hj folds and ridges of Enamel
entering the substance of the tooth. When teeth are in ex-
cessive number they are generally small, equal, or sub-equal,
and of a simple conical form.

The cavity which is bounded anteriorly by the soft Palate,
and precedes the commencement of the alimentary canal
(or gullet), viz.y the Pharynx, is generally funnel- shaped,

* Cf. Eodentia, Proboacidia. In-Enamellata,
t Cf. Supra. Situation.

6'i- Mammalia. Digestive System,

wider above than below, formed by a continuation of tbe
integument of tbe nasal cavity and of tbe moutb, and ex-
tending from the base of tbe skull : it has 'seven openings
leading into it : at its upper part, in front and above the
level of the soft Palate, are the two posterior Nares, and,
on each side, the apertures of the Eustachian tubes ; below
the soft palate is the isthmus of the Fauces, opening into
the Mouth : posterior to the root of the tongue is the opening
into the Larynx protected by the Epiglottis : lastly, the con-
tracted part of the funnel forms the (Esophageal opening.

The (Esophagus is nearly cylindrical ; it is generally long
and narrow, and forms the narrowest part of the Intestinal
Canal : after passing into the Abdomen through a slit in the
Diaphragm it usually expands at once to form the Stomach :
its muscular coat consists of two layers ; the external fibres hav-
ing a longitudinal direction; the internal fibres surrounding
the canal generally in a circular or spiral manner : its mucous
membrane and the innermost covering of Epithelium form,
usually, longitudinal folds which become more conspicuous on
contraction of the muscular coat : it is rarely provided at its
termination with valvular spiral folds : but as a rule passes
to the stomach without any valve. The Qj]sophagus of Mam-
malia is never wholly destitute of a Sheath of striated muscular
fibre (as is that of Sauropsida)*.

The Abdomen, as a definite and circumscribed visceral
chamber, is peculiar to the present class ; the Heart and
other thoracic viscera being shut out by the complete trans-
verse septum or * Diaphragm ' from the major part of the
trunk cavity.

The Stomach presents remarkable diversities. In the
greater number of Mammalia it is simple as in Man, though
frequently with the pyloric portion reverted. Sometimes
the Cardiac portion is divided from the Pyloric by a constric-

* Gulliver,

Digestive System — General. 65

tion, visible externally; sometimes such division existing
internally is scarcely visible outside ; in either case the Pyloric
end may be itself further sub-divided. Again, though very
rarely, there is found a sort of glandular ProventriculuSj
separated by a constriction from the wide muscular part of
the Stomach. Further, the Stomach may be complex ^ made
up of many compartments, and this even in some flesh- eating
species. Lastly, the Stomach is sometimes found intesUni-form.
The size of the Cardiac portion of the Stomach is mainly
dependent on the nature of the food ; it attains its maximum
in the herbivorous Ruminantia (in which the first three
stomachs are apparently divisions of the * Fundus ventricuK *
of Man), and is much reduced in most flesh feeders ; this
correlation is further demonstrated by the fact that the
fourth Stomach of the Ruminant is the largest as long as
the animal sucks. In Mammalia a capacious and complex
alimentary canal, as a whole, is almost invariably correlated
with a restricted vegetable diet ; though the extent to which,
and the mode by which the complexity is attained is variable :
either a highly developed and concentrated glandular appa-
ratus may be added to the Stomach, as in Castor, Myoxus,
and Phascolomys ; or the Stomach itself may be amplified,
subdivided, or sacculated, as in the Ruminantia, and Her-
bivorous Marsupialia ; or both these complexities may be
combined, as in the existing Sirenia and the Bradypodidae ;
or, lastly, if a simple condition of the Stomach is retained,
the compensation of complexity may be attained by the pre-
sence of a large sacculated colon and caecum. The Pylorus
is occasionally defended by a valve. Accumulation and de-
tention of vegetable food in the stomach occasions frequently
'bezoar* concretions.

The relative length of the Intestinal canal varies, being, in
general, longest in the vegetable feeders, and short in the flesh

K

6Q Mammalia, Digestive Si/stefn.

feeders : but, taking all Orders together, it is usually more
extended in Mammalia than in other Yertebrata.

The presence of a Caecum and ileocaecal valve generally
marks off the Intestinal Canal into the two main divisions,
called from the difference of their calibre in Man, ' Small' and
* Large ' intestine, names which lose their significance in
many lower Orders : of these two, the Small Intestine is
usually the longer, and beset on the inside with Villi of
various size, or with elongated longitudinal folds in the place
of Yilli. The 'ductus communis choledochus' conveys the
Bile into the Duodenal segment, and, prior to opening into the
Intestine, is generally joined by the Pancreatic duet ; and
runs for a space between the muscular and mucous coats of
the Intestine, where a dilatation of the duet is sometimes
found. The Ccecum may be small and conical, large, or
sacculated, and occasionally, though very rarely, double.
The presence and size of the Caecum varies directly with
the nature of the food, being either absent or small in
flesh feeders, and highly developed in vegetable feeders.
Further, it would appear, from the Rodentia, that the Caecum
is large, when food is but slightly nutritious and little
varied ; while it is small when nutritious food is readily
obtainable. A Veroniform appendix to the Caocum is most
exceptional.

• The clusters of Peyer's glands are as a rule considerably
developed.

The Mesentery is usually of greater extent than in Man :
a large and small Omentum are regularly present ; but the
great Omentum, which is said to be peculiar to Mammalia,
CO- existing with the diaphragm, does not always overlie the
same parts. Large Omental processes with accumulated fat
are never continued from the urinary bladder, and rarely
from the pelvic or other regions of the abdominal walls, as
they are in most Reptilia. Small processes from the serous coat

Digestive System — General, 67

of the large intestine are developed in many Ungulata, and
are called ' appendices epiploicse' in the human subject.

At the end of the Rectum glands are frequently situated,
which secrete a fatty and strongly odorous fluid. The termin-
ation of the Intestinal Canal is usually distinct from the
sexual aperture.

The Liver is situated ventrally* to the Diaphragm, chiefly
on the right side as in Man : it is usually divided distinctly
into two principal lobes : in many species it is tri-lobed, in
others multi-lobular : the greater the number of its divisions,
the more does it extend to the left side. The right third of the
gland is in most Quadrupeds sub- divided into two or more
lobules, the left third more commonly remains single. The
Liver is generally divided into a greater number of lobes in
the flesh feeders than in the vegetable feeders : in other
words, it is most subdivided in those species whose food
presents the greater amount of hydro- carbonates for elimi-
nation, and hence it is least subdivided in the purely herbi-
vorous Ungulates. It is small and little divided in Mammals
with divided or compound stomachs. The lobulus spigelii
is constant in its position behind the small Omentum. A Gall
Bladder is usually present, though frequently wanting : it is
wanting in a greater number of species of this class than of
any other ; in the flesh feeders the gall bladder is always
present ; and generally also in insect feeders : it is usually
single. When the gall bladder is present, a ^ Cystic,' * Hepatic,*
and 'Comment' Bile Duct exist, as in Man. The number of
branches which unite to form the hepatic duct vary ; thus, in
Man, two emerge at the portal fissure ; but, in more divided
livers, the liberated ducts are more numerous. The Portal
Vein in Mammals is formed by (1) the Coronary vein of the
stomach, (2) the superior Mesenteric vein, which returns the

* i.e. in the Abdominal cavity. Vide supra, Abdomen,
t * Ductus Communis Choledochus.'

68 Mammalia. Digestive System,

blood not only from the Spleen, but also from the Pancreas,
the Duodenum, the greater part of the Stomach and Omen-
tum, the descending Colon, and part of the Rectum.

The Pancreas lies a little dorsad* of the stomach, and between
the Spleen and the Duodenum : it is commonly divided into
two lobes, though occasionally it is tri-lobed : it may have one
or two excretory ducts ; when the duct is single it usually
joins that from the Liver before reaching the Intestine ; if a
second duct is present it enters the Duodenum by itself.

DIGESTIVE SYSTEM.— Special.

1. — Month.

— Not always terminal.

A rostral production sometimes makes the oral opening sub-ter-
minal, or inferior {e.g. Sorex, Elephas, Tapirus). Ornithorhyncus
is provided with a mouth nearly resembling the flat and sensitive
bill of the Aves Chenomorphaj.

2. — Lips.

— J^ot always presetit.

Cete. In the Delphinidae they are barely represented.

Monotremata. They are manifest at the suckling period only.

— Modified for prehension or uprooting.

In animals that feed on succulent and luxuriant herbage, the Lips
are capacious, strong, and pendulous, for the purpose of grasping
and detaching their food.

JProloscidia. The under lip alone is free : the upper lip blends
with the nose, and is with it produced into an elongated cone,
moveable in every direction, and terminated by a thumb-like ap-
pendage, endowed with exquisite sensibility, and capable of picking
up the smallest objects, {cf. Organs oi Sense, !N^ose.)

Ferissodaetyla. The Multungulate Tapir has a similar arrange-
ment to that found in the Elephant.

* «.tf._bet-weeii the Stomach and the Vertebral Column.

Digestive System — Special, 69

Artiodactyla. The mouth of the Hog tribe has the upper h'p
and nose modified to form the * snout.'
— Do not always form entire segments of an ellipse.

Cheiroptera. In !N"3'cteris the two converging ridges of the lower
lip enclose a triangular prominence of the upper lip.

Hodentia. In some Hodentia the upper lip is partially cleft.

Proloscidia. In Elephas the under lip is produced into a pointed
form.

Artiodactyla. In the Camelidae a mid-fissure divides the upper

lip- _ \

Marsupialia. The upper lip is partially cleft in the Macropidse.

3. — Gape of the Mouth.

Cheiroptera. Those species that feed on insects have a very wide
gape.

Sectorialia. The mouth is characterised by the width of its gape.

In-Enamellata. In the Edentula (Myrmecophagidae) the long
and tubular mouth seems to serve mainly as a sheath for the slender
tongue when retracted.

Monotremata. The mouth of Echidna is long and tubular, as in
the Ant-Eater, and terminates by a small orifice.

4. — Cheeh Pouches.

Quadrumana. Cheek Pouches are never found in the highest
Apes. But in the lower Catarrhina, and in these alone of this
Order, they are found.

Rodentia. In Cricetus (Hamster) the wide orifice of the pouch
is just within the commissure of the short lips : the bag itself ex-
tends along the side of the head to the neck. In Saccostomus it
reaches back as far as beneath the ear.

Sectorialia. Cheek pouches have not been found in any species.

Marsupialia. A few species have Cheek Pouches. In Koala
they are wide and shallow. In Didelphys Yapock they are large.

Mofiotremata. Ornithorhyncus has an oblong Cheek Pouch, in
which it may stow away fresh water Insects, Crustacea, &c.

5. — Buccal Memhrane.

Artiodactyla. In the Euminantia the cavitj' of the mouth is
lined with retroverted papillse.

In-Enamellata. In Myrmecophaga the Buccal membrane rises in

70 ' Mammalia. Digestive System. ^

two ridges, just anterior to tlie angle of the jaw, which become
very callous, and seem to occupy the place of teeth : in Myrmeco-
phaga Didactyla they form horny plates.

6. — Palate.

In Bimana and the higher Quadrumana the Palate is smooth and
unridged.

Rodentia. The roof of the mouth is commonly beset posteriorly
with two rows of hard oblique ridges, and in Capromys three hard
tubercles are found anteriorly. In Capybara the constriction of
the soft Palate reduces the communication between the mouth and
pharynx to a small aperture.

Artiodactyla. In the Camelidae a broad pendulous flap hangs
down from the fore part of the soft Palate, and usually rests upon
the dorsum of the tongue, though it is sometimes greatly enlarged.
Its surface shows the pores of innumerable mucous crypts : the
secretion these provide aids in keeping the surface of the pharynx
and root of the tongue moist when water is scarce. The back of
the mouth appears to be as completely closed in the Giraffe as in
Capybara.

Monotremata. In Ornithorhyncus the soft Palate is thick, broad,
and divided posteriorly into three fimbriated lobes. In Echidna
the Palate is armed with six or seven transverse rows of sharp short
retroverted spines.

7. — Uvula.

Bimana. The Uvula is almost characteristic of the Order.

Quadrumana. In the Catarrhina a short Uvula is apparent. In
the Platyrrhina the fauces are but slightly divided. In the Le-
muridae there is sometimes found* a median longitudinal fold from
the back of the soft palate close to the margin, but this never pro-
jects so far as to divide the fauces into two arches.

In-Enamellata. In Dasypus 9-cinctus the soft palate is thick-
ened in the middle, like a rudimental Uvula.

8. — Tonsils,

Rodentia. The Tonsils are perhaps the most feebly developed in
this Order.

» e.g. in Aye Aye.

Digestive System — Special. 71

Sectorialia. Tlie Tonsils are largest in the Digitigrada, especially
in Leo and some other Felidse, in which each tonsil forms a sac :
they are very small in the Semi-plantigrada, but large in the Plan-
tigrada.

9. — Tongue.

(For Tongue as Organ of Taste, cf. Special Sense Organs.)
— Protrusihility.

Rodentia. The Kodentia have the least power of protruding and
moving the tongue, in the whole Mammalian class.

In the Prohoscidia, Cete, and Sirenia, the Tongue is but slightly
moveable.

In the In-Enamellata the tongue of Myrmecophaga affords an
example of one the most protrusible of all in this Class.
— Subserving prehension.

Cheiroptera. The tip of the Tongue is furnished in many species
"with long pencillate papillos at its apex, useful for probing night-
blowing flowers for minute Insects {e.g. in Monophyllus). In Des-
modus (Yampiro) the terminal papillae resemble wart-like elevations,
so arranged as to form a circular suctorial disk when required.

Sectorialia. The Felidae have horny spinules on the fore part of
the dorsum of the Tongue, which form a powerful rasp, to cleari
bones.

The act of lapping may be noticed as an instance in point.

Artiodactyla. The Tongue of Giraffa affords an instance of one
long and prehensile.

In-Enamellata. In the Edentula the most obvious office of the
Tongue is that of prehension : the soft viscous apex, presenting an
adhesive surface, is insinuated into the Ant-hills, whence the Ter-
mites are withdrawn, entangled in the viscid saliva that covers it.
— Subserving distribution of food in the mouth.

This is a common function of the Tongue, but is especially notice-
able in Ornithorhyncus, where the posterior or intermolar portion of
the Tongue is provided anteriorly with two projecting, short, conical,
horny bodies, which can impede the passage of unmasticated food
to the pharynx, and direct it on each side into the cheek pouches.
— Subserving trituration of food.

In-Enamellata. In the Ant-Eaters the Tongue is used to crush
the termites against the callous ridges [supra 5) on each side of
the mouth.

72 Mammalia. Digestive System.

Monotremata. The dorsum of the Tongue in Echidna is broad,
flat, callous, and beset with hard papillae (representing in these lowly
organised Mammals the lingual teeth of Fishes), between which and
the palatal spines {supra 6) insects are crushed. The conical pro-
cesses on the Tongue of Ornithorhyncus may also subserve the same
purpose.

10. — Salivary Glands.

— Ratio of their development.

Cheiroptera. In the Insect-eating Bats the Maxillary exceeds
the Parotid gland in size : but in the fruit-eating Pteropines the
Parotids are the larger glands.

Rodentia. In the Omnivorous Eats with ferine tendencies, the
Submaxillaries are in excess : in most other Rodents, which subsist
mainly or exclusively on vegetable products, the Parotids are the
largest.

Marsupialia. The proportions of the Parotid and Submaxillary
difi'er according to the nature of the food, as in Rodentia.

- — The Parotid Gland.

Rodentia. In Castor (Beaver) the Parotids are enormous, extend-
ing from before the ears, forward and downward, to meet the Sub-
maxillaries (which are about one-twentieth their size), the whole
forming a sort of glandular collar. A similar development is found
in the Leporidse. In Cricetus (Hamster) the Parotids are applied to
the back of the cheek pouches.

Sectorialia. In the Seal tribe the Parotid is either very small or
wanting. In the Dog it is comparatively small ; relatively larger
in the Cat ; and more so in the Bear tribe.

Proloscidia. The salivary glands are all largely developed.

Perissodactyla. In the Horse the Parotid forms a considerable
mass, extending from its normal position behind the Masseter up-
wards to the Ear Conch, the base of which it embraces, and down-
wards to the Larynx, where it meets its fellow.

Artiodactyla. The Parotids are large in all Ruminantia.

Cete. In the Piscivorous Cete, which bolt their food like Pishes,
the Parotids are absent.

Sirenia. The Parotids are large (the species of this Order
browze on fuci).

In-Fnamellata. In the Great Ant-Eater the Parotid gland is

Digestive System — Special. 75

small in proportion to the animal ; but the duct, about eleven inches
in length and half a line in diameter, is perhaps the longest duct,
in proportion to the size of the animal, in the animal kingdom.*

Marsupialia. In the Great Kangaroo the Parotid is very large,
extending from below the auditory meatus three or four inches
down the neck : in the Potoroos it reaches as far as the clavicle :
but in both is separated from the Sub-Maxillary.

Monotremata. In Ornithorhyncus the Parotid is divided into
flat lobes, thinly applied to the fundus of the cheek pouch {ef. Cri-
cetus, Rodentia).

— The Sub -Maxillary Gland.

Sectorialia. This Gland in the Dog is large and globose.

Perissodactyla. These Glands are about one fourth of the size of
the Parotids, by which they are covered.

Cete bolt their food, and have no such Glands ; except the Balaeni-
dae, in which they are present in a diffused form.

In-Enamellata. Those which have long tongues (e.g. Myrmeco-
phaga, Dasypus,) have a hladder superadded to this Gland, both
for storing up the quantity of secretion needed in a sudden excess
of outflow in lubricating the tongue, and also for increasing the
tenacity of the secretion so poured out by the absorption of some of
the serous part of the saliva during its detention therein.

Monotremata. In the Echidna this Gland is of unusual dimensions ;
it extends from the meatus auditorius along the neck, and upon the
anterior part of the thorax. The duct subdivides and dilates when
it reaches the interspace of the lower jaw; serving the same end as
the pyriform bladder of some In-Enamellata [vide supra). This
modification of * Wharton's duct' appears to be unique.*

11.— The Teeth.

Bimana. — Structure. All the teeth are 'simplices' s. obducti :
the coronal Cement is of extreme tenuity, seldom so thick as to
show a bone cell. The Dentine is 'unvascular' {i.e. the tubules
are not large enough to admit capillary vessels with red blood
corpuscles).— Replacement. The * Deciduous' series consists of

.2.2 1.1 2.2
^2T2'^ni'^2T2 = 20.

* Owen,

74 Mammalia. Digestive System.

The Permanent series consists of

.2.2 1.1 2.2 3.3

' 2-72' ' rri'^ '^ 27^' ^ 37-3 = ^^-

The outer Incisor and the two anterior Premolars of the ' typical '
series being suppressed. — Number, They are the same in number
and in kind as in the Catarrhine Quadrumana. — Situation. They
stand in one continuous unbroken row, describing a regular parabolic
curve, and seldom have any, even the slightest, interval or 'diastema*
between the lateral Incisor and Canine on either side of the upper
jaw. The Incisors are vertical, or nearly vertical, in position,
— Form. They are of equal length or depth of crown, and show no
sexual distinctions. The Incisors are characterised by their truo
wedge-like form, equality of sizt), and small size relatively to the
other teeth and to the entire skull. Both upper and lower Pre-
molars are bicuspid and implanted by a single conical fang (or, two
conate, in upper jaw) : the outer curve of the premolar part of
the dental series being greater than the inner one, the outer cusp of
each Premolar is the larger. The third Molar (dens sapientice) is the
smallest in both jaws. In the Upper Jaw the first and second true
Molars support four trihedral cusps which present strong sigmoid
curves, and are generally implanted by three diverging fangs ; the
first Molar is considerably worn before the completion of the Molar
series by the acquisition of the Bens Sapientiae. In the Lower Jaw
the crowns of the true Molars are quinque-cuipid, and these teeth
are implanted by two fangs with median grooves.

2 2

Quadrumana. — Numler. The Incisors are commonly ■ and

(3 . 3\ '

r-— 5 I. — Situation. The Incisors generally

incline forward from the vertical line*. A break or diastema* in the
dental series is generally found for the reception of the crowns of
the Canines when the mouth is closed. The Canines and Premolars
generally form nearly a straight* line with the Molars. — Form. The
lower Incisors are broad and thick. The Premolars, which are
bicuspid, have the outer cusp of the first and the inner* cusp of the
second the largest ; alternating thus by reason of the teeth being
situated in a straight line. The Molars are broad and tuberculated,
and the four cusps rise distinct and independently of each other.

Catarrhina. — Structure. All the teeth are simplices ; the coronal cement is

2 2

thin. — Kumher. Haye the same number and kind of teeth as Bimana : « m — '- —

^ 2.2

Cf. Bimana, supra.

Digestive System — Special. 75

— Form. Each Incisor has a prominent posterior hasal ridge : the middle pair
are generally larger than the lateral Incisors ; and all four bear a larger propor-
tion both to the entire skull and to the rest of the teeth than in Bimana. The
Canines of the Baboons are deeply grooved in front, like the poison fangs of
some Snakes. The Premolars as well as the Molars are severally implanted by
one internal and two external fangs.

Tlatyrrldna. — Number. Have four more teeth in the Molar series than the

3 3

Catarrhina, viz. p m ^5-^. The ' Marmosets/ however, have but two true Molars

2.21.1 2.2
on each side of both jaws, their dental formula being i n""^; <^ T~\ > f^ T~o'

— Form. Molars have blunt tubercles.

3.3 33

Lemuridcv. — Number. Incisors are commonlv — ' — , and Premolars — '■ —

■^ 3 . 3 3 . a

2 2
(Lichanotus), or in number. — Situation. In the upper jaw of Otoclinus

and Lemur the small Incisors are vertical. — Form. The Incisors are generally
modified somewhat toward the Eodent and Marsupial type, the inferior onea
are long and narrow. The Molars have sharp tubercles. The dentition of
Cheiromys (Aye Aye) is modified in analogical conformity with the Eodent
type, to which it makes a very close approximation, in the absence of Canines,
and, the wide vacancy between the single pair of scalpriform Incisors and the
short series of Molars ; it may be distinguished from that of Eodentia in that
a. the crowns of the upper incisors project obliquely forward, and do not extend
vertically downward (Rod.) ; b. the lower Incisors are more curved, and c. all
the Incisors are entirely invested with Enamel, which is however thicker upon,
the front than upon the back part of the tooth.

Inseetivora. The dental system in this Order is remarkable for
the many varieties and even anomalies which it presents ; almost
the only characteristic predicable of it being the presence of
sharp points or cusps upon the crowns of the molar teeth. — Struc-
ture. The teeth consist of a basis of hard Dentine, with a thick
coronal investment of Enamel (especially in Soricidae), and the usual
outer covering of Cement : around the fangs the Cement usually
assumes the character of true bone, traversed by medullary canals.
— Replacement. The Deciduous teeth of the Talpidas and Soricidae
are uterine, i.e., are developed and disappear before birth. — JVumier.
Two species in this Order have the * typical' number of teeth, viz.,
Talpa and Gymnura, each having the dental formula
^.3.31.1 4.4 3.3

'STS'^ITI'^^ 474' ^3"T3 = ^^-
Chrysochlore approaches, in the number of its Molar teeth, the

remarkable condition which a solitary genus of existing Marsupials;
(Myrmecobius) also presents ; judging from the form of the teeth, it

has at least r~~^ true Molars. In Ehynchocyon (African Shrew)

76 Mammalia. Digestive System,

the upper Incisors are absent ; the premaxillary bones terminating in
a trenchant edentulous border, as in the true Euminant. — Situation.
In Galeopithecus the two anterior Incisors of the upper jaw are
separated by a wide interspace. In Chrysochlore the true Molars
are separated from each other by vacant intervals, as in many Rep-
tiles.— Fixation. In the Shrew the roots of the lower Incisors
become anchylosed to the jaw-hone, a Eeptilian character oJffered by
the Soricidse alone in the Mammalian Class. — Form. The crowns
of the first two Incisors of Galeopithecus present the form of a
comb, and are in this respect unique in the Class Mammalia : the
second upper Incisor presents the peculiarity of an insertion by two
fangs. In Amphisorex and Ehynchocyon the lower Incisors are
notched, or bilobed. In Chrysochlore the three anterior teeth in the
upper jaw, situated in the premaxillary bone, and therefore ' In-
cisors,' are laniariform. The crowns of the Molar teeth are gene-
rally bristled with sharp points or cusps, and are always broader in
the upper than in the lower jaw. In Chrysochlore the crowns of
the upper true Molars assume the form of thin plates, narrowed
from before backward, with two notches on their working edge, and
a longitudinal groove along the outer and thicker margin ; the lawer
true Molars are of unusual length.

Cheiroptera. — Replacement. The Deciduous teeth make their
appearance above the gum before birth, as in Soricida), but they
attain a more completely developed state, and are retained till a
short time after birth. — Numler. Incisors may be present as

2.21.1

o — «, or :j — r, or absent. Canines are always present in both jaws.

6 . 6

The Molar series never exceeds r — -^ and in the Yampire is re-

2.2
duced to - — -. — Form. Incisors, when present, are always very

small, and, in the upper jaw, commonly unequal : in Chilo-
nycteris the mid-incisors above and the outer ones below have the
crown notched : in Phyllostoma the mid-pair above are large and
laniariform: in Desmodus they are two in number in the upper
jaw, with large, compressed, curved, and sharp-pointed crowns. The
Canines are always of the normal form. The Molar series are
bristled with sharp points in the great bulk of the Cheiroptera.
In Desmodus (Vampire) the true Molars with the bristled crowns
are absent, and the Molar series have simple compreBsed conical

Digestive System — Special. 77

crowns. In the great frugivorous species (Pteropidac) the Molars
have broad flat crowns.

Rodentia. The Eodentia are characterised by two large and long
curved Incisors in each jaw, separated by a wide interval from the
Molars ; for no Rodent is possessed of Canines. — Structure. The
Incisors consist of a body of compact Dentine, more dense anteriorly
than posteriorly, with a plate of Enamel laid generally upon the
anterior surface of the tooth alone (the Enamel consisting of two
layers, of which the external is denser than the internal) ; and a
general investment of Cement, which is very thin upon the Enamel.
In Leporidse the Enamel is traceable to the back of the tooth. The
Molars have always a coating of Enamel, the vertical folds of which
generally penetrate the crown of the tooth : these folds have a general
tendency to a transverse direction. In those Rodentia that have
rootless Molars the folds of Enamel extend inwards for the entire
length of the sides of the tooth, which may be thus distinguished
from the rootless Molar of the In-Enamellata. The Chinchillidae,
and Capybara, aiford good examples of the Dentes * compositi,' with
plates of Enamel, followed by Cement, parallel. In all Rodentia,
vascular Dentine forms but a small constituent of the Molar tooth ;
the pulp, after forming a certain thickness of tubular Dentine,
becomes converted into Osteodentine. — Replacement.^' The first or
anterior tooth of the Molar series, whether the number be 2-2, 3-3, or
4-4, is a Premolar {i.e., has displaced a deciduous predecessor in a
vertical direction). — Number. The Incisors (= Dentes Scalprarii),
are never more than two in number in either jaw, except in the
Leporidse, which have two pair, placed one pair (the smaller) behind
the., other, in the upper jaw. The Molars are not numerous in any
Rodent. — Situation. The Molar teeth are obliquely planted, the
series on each side converging anteriorly in both jaws. — Form. The
upper pair of Incisors describe a larger segment of a small circle,
the lower ones a smaller segment of a larger circle : they are of
unlimited growth {i.e. with ^ persistent^ pulps), and therefore without
'neck' or 'fang:' they have a sharp anterior margin, from which
they slope obliquely back, like a chisel, and are thence named dentes
scalprarii: when an opposing incisor is lost, following the curve
prescribed to their growth by the form of their socket, their points
often return against some part of the head, completing the circle.

* Cf, Marsupialia, id, infra.

78 Mammalia. Digestive System.

The Molars are sometimes rootless ; sometimes have short roots,
tardily developed; and sometimes ordinary roots soon acquired.
These differences in the mode of implantation relate to the differ-
ences of diet. Those Eodentia which subsist on mixed food, and
which have a tendency to carnivorous habits, or subsist on nutri-
tious vegetable substance (e.g. oily kernels) have their Molars,
* simplices,' rooted, and with shallow crowns: e.g. most Hystricidae,
Muridae, and Sciuridse. Those Rodentia which feed exclusively on
vegetable substances, especially on the less nutritious kinds, have
their Molars ' complicati,' with incomplete and lately developed roots,
and a limited growth of crown ; e.g. Castoridae. Those Eodentia
which are strictly herbivorous have their Molars *lamellosi,' and
rootless ; e.g. the Leporidte and most Cavidae. The rootless and
perpetually growing Molars are always more or less curved.

Sectorialia. Throughout the Order the Incisors are small, and,

3 . 3

except in a few Seals, ~—^ in number ; the Canines are long, largely

o . o

developed, r-^ in number, the lower passing anteriorly to the

upper, as usual, when the mouth is closed. The Molars follow the
general rule, both as to number and form, in accordance with the
variation of diet ; but, in all, the last Premolar [p m 4) of the upper
jaw works upon the anterior true Molar {m 1) of the lower jaw,
and in the strictly flesh-feeding genera, scissor fashion ; each of these
two teeth was denominated by P. Cuvier ' dent carnassiere,' which
has been rendered ' dens sectorius,'' the 'sectorial' or scissor tooth;
hence the name here given to this Order. A tubercle is generally
present at the inner side of the base of the anterior part of the crown
of the 'sectorial' tooth; the development of the tubercle bears an
inverse relation to the carnivorous propensity of the species. In
general the crowns of the teeth of the upper and lower jaws inter-
lock.

Digitigrada. The Incisors have broad and thick creams, shaped as a trefoil in
Hysonidae ; indented by a transverse cleft in Felidse ; or with two notches in
Canidce ; and are situated in a transverse row ; the exterior Incisors above being
larger than the four middle ones. Canines are slightly curved, and have a fang
as long or longer (Felidae) than the crown. In all Digitigrada there is a pit
internal to the last Premolar of the upper jaw, which receives the crown of the
first true Molar of the lower jaw. Both Felidro and HysenidoB have hut a single
minute tubercular true Molar on each side of the upper jaw ; and the inferior
Molar series are all of the ' sectorial' form, and so set as to shut within the upper,

Digestive System — Special. 79

like shears : but the Hysenidse may be distinguished by a. the shape of the crowng
of the Incisors, b. the relative strength of Molars and Canines, c. the additional
Premolar on each side in both jaws; and d. the basal ridge which girds the coni-
cal (for breaking bones) Crown of the second and third Premolar in both jaws,

4 . 4
and defends the subjacent gum. The Viverridse and Canidse have both^? m — — -

2.2
and m — '—;■ in the upper jaw ; but in the former, the Canines are more feeble,

and have smoother crowns ; the Molar series are less trenchant and more tuber -

2.2
cular; and the inferior true Molars fewer in number, viz., m — -. than in tho

latter. The Canida? are distinguislied by the form of the Incisors ; by having
the first lower true Molar anteriorly sectorial, and posteriorly tuberculate ; and

3 3

the true Molars below m . — '- — ,
3 . 3

Semi-Planiigrada. The Mustelidoo have great development of the inner tu-
bercle of the Sectorial tooth : the Molar series nearly approaches that of tho
Hysenidse.

Plantigrada. All approximate more or less to the dentition of the families
of the Ursidse : the dental formula is essentially the same, both in number and
kind of teeth, in the genus Ursus, as in the genus Canis. But the chief charac-
teristics of the dentition of the Bears are, the development, in the lower jaw, of
the true Molar teeth to their typical number in the placental Mammalia ; their
general manifestation, in both jaws, of a tuberculate grinding surface : and the
reduction in size of the Premolars, of which, the last in the upper jaw {p m 4),
becomes more directly and completely opposed to its homotype in the lower jaw
than is the case in those species more nearly allied to the typical family of the
Order, viz. the Felidse. The true Molar in Meles deserves special notice, on
account of its enormous size as compared with its homotype in the two preced-
ing Sub- orders. In the Ursidse m 2 is generally considerably developed.

3 . 3

Pinnigrada. The Incisive formula never exceeds r— -f, ; and in the adult

"Walrus is reduced to zero in the lower jaw, and one pair in the upper jaw.
All possess powerful Canines in both jaws, except Walrus, in which they are
absent in the lower jaw; here, however, as if byway of compensation, the
upper Canines are of enormous size, tusk-like, with 'persistent pulps,' and com-
pelled to pass outside the lower jaw when the mouth is shut. The Molar series

4.4 1.1

usually consists oi p m - — -; m ~ — , a second true Molar being rarely {e.g.

Otaria) present. In the Phocidee the fang or fangs of all the teeth are usually
remarkable for their thickness, which commonly surpasses the long diameter of
the crown. There is no special modification of the crown of any tooth by which
it can merit the name of a ' sectorial :' and the co- adaptation of the crowns of
the upper and lower teeth is completely alternate, each tooth in the lower series
being anterior to its fellow in the upper series.

Proloscidia. Incisors are wanting in the lower jaw, but project

80 Mammalia. Digestive System.

as long tusks in the upper jaw, one in each premaxillary bone.
The Molars are large and complex : of these there are never more
than two in place or in use on each side at any given time. — Struc-
ture. The Incisors, here called tusks, have * persistent pulps/ and
consist of ivory, i.e. a modification of dentine, with exceedingly small
dentinal tubes, arranged in almost angular gyrations, and which
shows, in section, strise, proceeding in the arc of a circle^ from the
centre to the circumference in opposite directions, and forming by
their decussations curvilinear lozenges ; the ivory is lowly vascular.-
The Molars afford striking examples of dentes lamellosi^' ; the
growth of each plate begins at the summit, consequently they remain
as separate denticles until their bases become contiguous and blend
together. The number of plates in the first Molar is four, and each
succeeding tooth has on the average four more plates than the one
immediately preceding it. — Replacement. The Molar teeth succeed
each other from behind, moving in the arc of a circle. — Numher.

2.2 6.6

The total number of teeth developed appears to be i - — - . m ^ — -

JPerissodactyla. The Incisors and Canines are near together, and
a long diastema intervenes between them and the Molar series.
The crown of from one to three of the hinder Premolars is as com-
plex as those of the Molars. The outer side of the Upper Molars
is generally impressed by two wide longitudinal channels.

The Incisor teeth of the Equidae are distinguishable from those of the Ru-
minants by their greater curvature ; and from those of all other animals by the
fold of Enamel which penetrates the body of the crown fi-om its broad flat sum-
mit, like the inverted finger of a glove, followed externally, as usual, by the
cement, constituting the * mark 'f of veterinary authors. The Canines are large
in the Horse; rudimentary in the Mare. The lower Canine, though situated
as in the Ruminants, close to the outer Incisor, is distinguished by its cuspidate
form. The Molars of the Equidae may be distinguished from the complex teeth
of other Herbivora corresponding with them in size by the great length of
the tooth before it divides into fangs. In the Tapiridse, the existence of a
transverse without an antero -posterior valley results in the division of the
crowns of the Molar series into a pair of transverse ridges.

* Cf. Capybara (Rodentia), supra.

t The cavity in the lower Incisors, or ' mark,* is usually obliterated, in the
first or mid-Incisors at the sixth year, in the second Incisors at the seventh year,
and in the third or outer Incisors at the eighth year.

Digestive System — Special. 81

Hyracoidea. The Incisors are large, and, to a certain extent, Eo-

dent-shaped : the Canines are wanting : the Molar series is of the

* typical' number. The first Premolar differs from the rest only by

a graduated inferiority of size, which in the last Premolar, p m 4,

ceases to be a distinction between it and the true Molars. The

pattern of the upper Molars is unsymmetrical.

1.1 0.0 4.4 3.3

Dental formula : i — r- ; c - — ~ ; p m ^ — - ; m -~ = 34.

Artiodactyla. The crowns of the Premolars are smaller and less

complex than those of the true Molars, usually representing half of

3.3 ^ ^
such a crown. The true Molars are constant, m ~ — r ; the Pre-

o . o

molars are subject to variety.

Omnivora. — Structure. The Canines generally have Enamel only on the
anterior convex surface. The tusks of the Hippopotamus exhibit the maximum
density in their component tissues : the compact dentine differs from true
ivory by showing in transverse section simple concentric, instead of curvilinear
decussating lines. The last true Molar of Phacochserus is perhaps the most
peculiar and complex tooth in the whole class of Mammalia : the surface of the
crown presents three series of enamel islands, in the direction of the long axis
of the grinding surface, blended into a coherent crown by abundant cement.
— Number. Sus. Scrofa has the typical dental formula. — Form. Excessive de-
velopment of Canines characterises all Omnivora : in Hippopotamus the Inci-
sors are affected in the same way ; the two median inferior incisive tusks being
cylindrical, and of great size and length. The Molars of Hippopotamus are
characterised by the trefoil shape of the two divisions of the crown, one valley
bisecting the middle of the crown transversely, with two shorter indents parallel
to it, one on either side. In the Suidae the upper Incisors decrease in size from
the first (i 1) to the third {i 3), receding from each other in the same degree : and
the teeth of the Molar series progressively increase in size from the first to the
last. In Babyrussa the upper Canines are bent abruptly upwards, and curve
backwards, penetrating the upper lip.

liuminantia. The development of horns bears an inverse relationship to the
development of the anterior teeth. The typical Euminantia (Cavicornua) never
have upper Incisors (their place is taken by a callous pad), and very rarely
upper Canines : their inferior Canines are procumbent, and are similar to, and form
part of the same series with the Incisors : most of their deciduous Molars re-
semble in form the true Molars, which are separated by a wide interval from
the Canines, and have their grinding surface marked by two double crescents,
the convexity of which is turned inward in the upper and outward in the lower
jaw. The last true Molar of the lower jaw in all Ruminantia is" characterised
])y the addition of a third posterior lobe : and in all Ruminantia the outer con-
tour of the entire Molar series is shghtly zigzag, the anterior and outer angle of
one tooth, projecting beyond the posterior and outer angle of the next in

M

82 Mammalia, Digestive System.

advance. The dentition of the Solidicomua follows that of the Cavicomua
pretty closely, ^except that the males sometimes hare Canine teeth in the upper
jaw (esp. Cennis Muntjak). The Carenticomua presents considerable anoma-
lies ; though, agreeably to the rule as to horns above noted, all have Canines
in the upper jaw (especially developed in Moschus moschiferus). The Camelidaa
have a pair of laniariform Incisors in the upper jaw; the inferior Canines
distinct from the Incisors in their laniariform development, and more erect in
position than in the ordinary Ruminantia ; and, lastly, the anterior Premolar
laniariform in both jaws.

Cete. All are Monophyoclont, none truly edentulous : for the
Balenidae manifest in their foetal state a true dental system, in the
shape of a series of minute calcified denticles in an open groove
extending along the alveolar border of both the upper and the
lower jaws. In no Cete, except the common Dolphin, are teeth
implanted in the Intermaxillaries. The primitive seat of the de-
velopment of the tooth matrix is maintained longer in the Cete
than in other Mammalia ; and, except in the rudimental tusk of the
Narwhal, is at no period enclosed in a bony cell : in this respect the
Cete offer an interesting analogy to true Fishes. The teeth in the
Cete are all of one kind, and usually of a conical shape.

The Whales proper (Balaenidae) have the footal dentition of the upper jaw
succeeded by homy substitutes in the form of plates, terminated by a fringe,
situated on either side of the upper jaw, behind each other : the plane of each
plate is at right angles with the axis of the skull, and depends vertically from
the palatal surface of the maxillary, and of the anterior part of the palatine
bones. The lower jaw of the Whale that has passed its foetal existence has
neither teeth nor baleen. The plates are shaped like an obtuse-angled triangle,
the fringed side being that subtending the obtuse angle ; one side enclosing the
angle forms the outer margin of the baleen plate ; the other is hollow and has this
cavity filled with baleen pulp, which is formed of parallel descending tubes
passing into bristly fibres at the inferior margin of the horny lamina, of which
the external or cortical substance of each plate consists ; and is imbedded in a
compact sub-elastic substance, attached to the palate. The Sperm "Whale
(Physeter) has teeth in both jaws, but they are visible only in the lower jaw,
in which they are situated in a wide and moderately deep groove in the dense
semi-ligamentous gum. The first formed extremity of the tooth in the young
Physeter (Cachalot) is capped with enamel, which however gets worn off when
the tooth is fully developed. In Phocoena Orca (Grampus) the laniariform
teeth are as large in proportion to the length of the jaws, as in the Crocodile,
and are separated by intervals, so that the upper and lower teeth interlock. In
the Narwhal two rudimental teeth are enclosed in a horizontal alveolus at the
junction of the intermaxillary with the maxillary ; one of which, the left, is in
the male further developed into a tusk nine feet long, marked exteriorly by
Spiral ridges ; and with a pulp cavity throughout its entire length internally.

Digestive System — Special. 83

In tlie common Dolphin the number of teeth amounts to 190; the maximum
number in the Class Mammalia.

Sirenia^ are Diphyodonts*, and have teeth of different kinds,
Incisors and Molars. In Halicore (Dugong) the superior Incisors alone
project in the male, and in the female neither upper nor lower
Incisors are visible. The Molars have flattened or ridged crowns
adapted for vegetable food. Those of Halicore consist of a large
body of dentine, a small central part of osteo-dentine, and a thick
external investment of Cement; Enamel is absent. In Manatus
Molars are present in both jaws. In Halicore abortive teeth alone
are found in the deflected portion of the lower jaw.

InSnamellata. This Order includes two genera, which are de-
void of teeth, Myrmecophaga and Manis ; the rest are possessed of
those organs. The Bradypodidae generate only one set ; they are,
therefore, Monophyodont. The Dasypodidse probably all generate
two sets, and are therefore Diphyodont. The teeth are very rarely
implanted in the intermaxillary bones. No true enamel is present on
any tooth (hence the name here given to this Order). The teeth
are of uninterrupted growth, and are concomitantly implanted by
a simple, undivided, and generallj' deeply excavated base.

The teeth of the Dasypodida3 (Armadillos) are harder than those of other
species of Inenamellata : those of Orycteropus are continued solid, and of the
same dimensions, to the bottom of the socket ; where they terminate in a tnm-
cate undivided base, and may be looked upon as an aggregate of small denticles.
D. Sexcinctus has the anterior tooth, which is shaped like the succeeding Molar,
implanted in the Intermaxillary bone. Of the eight teeth habitually found in
each side of the mouth of the nine-banded Armadillo, both in Maxilla and Man-
dible, all except the most posterior in each set are preceded by well-developed
functional milk teeth, which closely resemble the permanent teeth in form, and
nearly equal them in size, and are not shed until the animal has almost attained
its full developmentf. An example of excessive number of teeth occurs in this
family in the Priodont Armadillo, which has ninety -eight teeth. In the Brady-

5 5
podidse the teeth seldom exceed — ^ in number ; of these the anterior one on

each side is generally much prolonged.

Marswpialia. Replacement. The animals of this Order present
a peculiar condition of dental succession, uniform throughout the
Order, and distinct from that of all other Mammalia. This peculi-

* Cf. infra. Marsupialia, Replacement.

r Flower. Journal of Anat. and Phys. 1860.

84 Mammalia. Digestive System.

arity may be thus briefly expressed. The teeth of Marsupialia do
not vertically displace and succeed other teeth, ivith the exceptionjof
a single tooth on each side of eachjaiv. The tooth in which a vertical
succession takes place is always the corresponding or homologous
tooth, being the hindermost of the Premolar series, which is pre-
ceded by a tooth having the characters more or less strongly ex-
pressed of a true Molar. If you divide the Mammalia in regard to
the succession of teeth into Monophyodonts and Diphyodonts, the
Marsupials occupy an intermediate position, presenting as it were a
rudimentary Diphyodont condition, the successional process being
confined to a single tooth on each side of the jaw; to which, how-
ever, analogous examples may be met with in the Placental series
in the Dugong and Elephant, in which the successional process is
limited to the Incisor teeth ; and in those members of the Eodentia
which have but four teeth in the Molar series, i.e., three true Molars
and one premolar {e.g. Beaver, Porcupine), in which the latter is,
exactly as in the Marsupialia, the only tooth which succeeds a
deciduous tooth*. — Number, Incisors are present in all the species,
but are variable in number ; in some genera {e.g. Peramelidse and
Didelphidae) of the flesh-eaters, exceeding that of the Mammalian
type in the upper jaw (e 5 . 5). Canines are present in all the
flesh-eaters, but are not constant in the plant-eating genera, being
absent in the Phascolomydae and Macropidae (except in upper jaw
of Hypsiprimnus, and the foetal Macropus ; in the latter they are
never functional), and but feebly represented in the Phalangistidse
(absent in lower jaw of Phascolarctos). The typical number of teeth
in the Molar series is seven on each side of both jaws. Those pos-
terior teeth of either side of each jaw which have no deciduous pre-
decessors are as a general rule, four in number, instead of three, as
in most Placental Mammalia ; but in Myrmecobiidae the number of

true (m ^-~^) and false Molars is eighteen in each jaw, exceeding

that of any other known existing Marsupial {cf. supra ; Insectivora ;
Chrysoclore) ; and Petaurus pymaeus is said to have only three true
Molars on either side of each jaw. The dental formula of the Phasco-
lomydae is the same both in number and kind to that of Eodentia.
The dental system of the Dasyuridae corresponds generally with that
of the Sectorialia ; it diff'ers in having the Incisors in greater num-

• Flower. Phi^, Trans. 1867.

Digestive System — Special. 85

ber and the Molars of a more uniform and simple structure.
Situation. In tlie Dasyuridae the points of the lower Canines are
received in hollows of the interraaxillarj palatal plate, and do not
project, as in the Sectorialia, beyond the margins of the maxillary
bones. In the Myrmecobiidse the inferior Molars are directed
obliquely Inwards, and the whole dental series describes a slight
sigmoid curve. — Form. All the Incisors in the Myrmecobiidae are
slightly compressed diudi pointed. In Phascolomydse and Macropidae
they have persistent pulps. The anterior tooth of the Molar series
in Hypsiprininus has a peculiar trenchant form, indented especially
on the outer side, and in young teeth, by many small vertical grooves.
In the Phascolomyda3 the false and true Molars have persistent pulps,
and are consequently devoid of true fangs, in which respect the
"Wombat diifers from all other Marsupials, and resembles the denti-
gerous In-Enamellata and herbivorous Rodentia. The Premolars of
the Macropidae are distinguished by being compressed, and narrower
in front than behind, having two cusps behind and one in front. In
the omnivorous Peramelidae the Molars (originally quinque-cuspi-
date) early assume a smooth oblique grinding surface. In the
Myrmecobiidae the Molars are multicuspidate.

Mbnotremata. In Echidna teeth are wanting. In Ornithorhyn-
chus two horny plates, consisting of a series of close-set vertical
hollow tubes, and situated on each side of each jaw, eight in all,
serve for teeth : the anterior pair, above and below, are narrow and
somewhat trenchant, the posterior pair are subquadrate and slightly
tuberculate, each tubercle being separately developed, and becoming
confluent with its fellows in the course of growth. (For lingual
teeth, see above, p. 72.)

12. — The Phanjnx.

Ferissodactyla. In the Horse the Pharynx is capacious and com-
municates with a pair of large sacculi at the ends of the Eustachian
tubes.

Artiodactyla. In Giraffa the back part of the mouth terminates
by a transverse slit, through which projects the broad upper margin
of the Epiglottis, which is folded upon itself.

In-Enamellata. In Dasypus (Q. Cinctus) the Epiglottis projects
through the arch of the Soft Palate.

13. — The (Esophagus.
— is short and wide in all Sectorialia.

SQ Mammalia. Digestive System.

The GEsophagus is of small area in the largest species of Cete.

— extends beyond the diaphragm in Cercopithecus, the small
Platj'rrhines, and Cheiromys [\ inch), of iheQuadrumana ; in most
Insectivora, Rodentia, and Uijracoidea ; in the DidelphidaB and Ma-
cropidse (M. major. 5 in.) of the Marsupialia ; and in the Monotre-
matous Ornithorhyncus.

— has in Leo ( ? all Felidse) {Sectorialia) a third layer of longi-
tudinal fibres applied to the inner side of the circular ones at the
terminal part of the (Esophagus.

— has in Leo (? all Felidae) (on account of the special arrangement
of the muscular fibres) the lining membrane puckered up into numer-
ous narrow alternating transverse rugae. A similar structure is
present in Didelphys Virginiana (Marsupialia).

— in ^quus [Perissodactyla) presents a more or less large sickle-
shaped fold, developed close to the Cardiac orifice of the stomach,
which prevents the return of food, so that the Horse cannot vomit.

— has a sheath of striated muscular fibre. Several different Orders,
or Families of Mammalia have a sheath of striated muscular fibre
extending all along the CEsophagus, to or even on the Cardia, as may
be well seen in Euminants, Rodents, Bears, and many others : it
may, however, stop short of the Cardiac end of the (Esophagus, e.g.
in Man, Quadrumana, Felidae, the Horse, and many others.*

14. — The Stomach.

{a) — is Simple in

Bimana, in which the Cardiac pouch is relatively small, and the
(Esophagus enters near the Cardiac end, thus admitting of an ex-
tensive lesser curvature.

In most Qtcadnwiana, e.g. the tail-less Apes, the Lemurida? (in
which last the Cardiac portion is large), and Cheiromys, in which the
Stomach is subglobular.

In nearly all Insectivora^ the Cardiac and Pyloric orifices being
approximate.

In the Insect-eating Cheiroptera.

In the Sectorialia, where the Cardia and Pylorus are generally
wide apart; the * blind sac' is of small extent, and the Pyloric end
is bent abruptly and closely upon the middle of the stomach. The

* Gulliver.

Digestive System — Special. 87

epithelial lining of the gullet terminates abruptly at the Cardiac
orifice.

In the Proloscidia, where however the stomach is longer than
usual, with the Cardiac sac much produced and conical.

In most Perissodactyla.

In the Hyracoidea, in which two-thirds of the cavity are lined
with a thick white epithelium; and the stomach is bent upon itself
where this lining ceases.

In nearly all Dasypodidae, and some Myrmecophagidre of the In-
Bnamellate Order, where the muscular coat is more or less thin at
the Cardiac end, and thick, with a tendinous spot externally, at the
Pyloric end : especially in Manis, in which the structure is made
the more gizzard-like by its thick papillose cuticular lining.

In all Marsupialia^ whether flesh-, insect-, or leaf-eaters, except
the Macropidae.

And in the Mbnotremata ; in Ornithorhyncus the stomach is mem-
branous, and chiefly remarkable for the close approximation of the
Cardiac and Pyloric oriflces : in Echidna the tunics of the stomach
are thin to near the Pylorus, where the muscular coat assumes
something of the gizzard character.

(h) — is simple, lut with glandular patches, in

The insectivorous BatSy in which the gastric membrane at the
Pyloric end of the stomach assumes a glandular character.

The Castoridae among the Rodentia, where the gastric glands are
situated near the Cardiac orifice, arranged in longitudinal rows.

And the Phascolomydoe of the Marsupialia, where the conglomerate
gastric gland is of a flattened ovate form, near the Cardiac orifice,
and with its excretory orifices scattered.

(c) — is CoxsTEiCTED iuto two Of three portions, e.g.

In the Phyllostomidoe and Pteropidse of the Cheiroptera, of which
in Desmodus the Cardiac portion is produced into a long intestini-
form reservoir, the rest of the stomach being long and narrow, bent
upon itself.

In most Rodentia, and is especially noticeable in Cricetus externally
and Meriones internally. In Mus Rattus, the oesophageal epithelium
is usually continued upon the inner surface of the Cardiac compart-
ment, which is constricted from the middle portion, and that again
from the * blind sac' at the other end of the stomach ; in Arvicola am-
phibius, and Lemming, the Cardiac and middle compartments form

88 Mammalia, Digestive System.

one elongated cavity, separated by constriction from the Pyloric
portion, which again throws off a small sacculus above ; in Lepus,
there is a well-marked tendinous patch on the Pyloric compartment.

In the Perissodactyh Horse, the thick cuticular lining of the
Cardiac Cul-de-sac terminates abruptly by a prominent indented edge,
separating it from the Pyloric half with its villous surface.

In the Omnivorous Arthodactyla.

In the In-Enamellate Ant Eater, the spherical stomach has a
subglobular appendage, as it seems, intervening between the main
cavity and the intestine : on both the anterior and posterior sur-
faces of the stomach is a sheet of tendon : the Pyloric division is
remarkable for the thickness of its muscular tunic, and the^density
of its epithelial lining, which convert it into a veritable gizzard.

(d) — has a quasi-glandular Proventeictjlits attached.

A long glandular proventriculus, separated as in Birds by a con-
striction from the wide muscular stomach, is found in Myoxus Avel-
lanarius (Kcd Dormouse).

{e) — is Complex.

In the Artiodactyla the Stomach is generally made up of four
distinct cavities, respectively called 1. Rumen, or Ingluvies ; 2. Re-
ticulum, or Honeycomb ; 3. Psalterium, Maniplies, or Omasus ;
4. Abomasus. The Pv-umcn is the largest of the four cavities, and
the reservoir for the food previous to re- mastication : the inner sur-
face is covered with papilla? (cuticular villi), except in the Camelidoe,
where large cells below and at the sides are found for the retention
of water; it secretes an alkaline fluid. The Reticulum, situated
directly below the entrance of the oesophagus, always receives the
water. The cells vary in depth in different Pamilies, but generally
are directly correlated with the nature of the food, being very
shallow when {e.g. Giraffa) the food takes the shape of juicy leaves
and buds. A passage leads from the oesophagus to the third cavity,
bounded by two low parallel ridges. The Maniplies is occupied
by deep parallel crescentic folds, like the leaves of a book ; in pass-
ing through this the. food is deprived (by squeezing) of superfluous
fluid : in the Camelidoe and most Moschidae these longitudinal la-
mella? are wanting. The Abomasus has the usual structure of the
true digestive stomach ; here the food is penetrated by acid gastric
juice ; this is therefore the seat of the true digestion. The Pylorus
is protected by a valvular protuberance, placed above it, just within

Digestive System — Sjpecial, 89

the Stomach. The food is first swallowed only half masticated ; the
coarse bolus opens the lips of the groove, and falls into the Eumen ;
after maceration there, portions of the mass are transmitted into the
Eeticulum, and from thence into the demi-canal to he moulded into
the form of pellets, which are carried up to the mouth by an anti-
peristaltic action of the muscular coat of the (Esophagus : remasti-
cation renders the food softer, so that when it is again swallowed it
passes through the groove (the walls of which are stimulated to
contract) into the Maniplies, and then to the Abomasus.

In the Cete the Stomach is divided into several cavities : the first
is a continuation of, and similar to the (Esophagus ; its commence-
ment is indicated by the orifice, surrounded by large irregular pro-
jections, leading into the second stomach, beyond which it dilates
into a heart-shaped cavity; the second stomach is round, and leads
by an oblique orifice into the third, which is likewise round, but
small, and not visible externally ; the fourth cavity is long and
narrow, and pursues a serpentine course, almost like an intestine.
The digestive process goes on in, or is assisted by the fluids in each
and all of the cavities. This complex Stomach, being found even in
the predaceous Phocaena orca (Grampus), affords an example of
special development to meet special need ; here, the need of extract-
ing all the nutriment available, to maintain animal heat in a system
in constant contact with a heat-absorbing medium.

It is singular, when this is considered, to find in the vegetable-
feeding Sirenia a less complex Stomach than in the carnivorous
€ete ; in the Sirenia the Stomach assumes the constricted type, but
has two appended sacculi opening on the pyloric side of the con-
striction, and a special spiral gland in the conical pouch that projects
from the extremity of the cardiac portion : the (Esophagus enters
the cardia in a valvular manner.

Among the In-Enamellata^ Cholsepus (Two-toed Sloth) has a com-
plex Stomach : the cardiac compartment is divided into' a left and
right portion, of which the left terminates below in a short ca3cal ap-
pendage : between the right-cardiac and the pyloric portion a second
cavity intervenes : the third, or pyloric cavity, being quite distinct,
and separated by a constriction from the rest of the Stomach.

— is Intestini-form, e.g. —

Quadrumana, In Semnopithecus EntelluSj where the left, or car-
diac half forms a large cavity, many times constricted, while the
right or pyloric portion is long, narrow, and intestini-form, and

90 Mammalia. Digestive System.

sacculated along the line of the greater curvature, by means of
a pair of strong muscular bands, like the human Colon.

Marsiipialia. In Macropus (Kangaroo) the sacculated Stomach re-
sembles the human colon, both in its longitudinal extent, structure,
and disposition in the abdomen ; three narrow longitudinal bands of
muscular fibres extend the whole length, except near the Pylorus j
the cardiac extremity is bifid, or subclavate.

15. — The Small Intestine.

— Dilatation of the Duodenum,

Rodentia. The Intestinal Canal usually begins by a well-marked
dilatation. In Coypu this dilatation is so large that it projects
towards the GEsophagus, like a Cajcum : the whole Duodenum is more
continuously and loosely suspended than in most higher Mammals.

Perissodactyla. Commencing from the Pylorus, the Duodenum
is considerably dilated, but its diameter soon contracts.

Artiodactyla. The Duodenum is always dilated at its commence-
ment ; it there forms a distinct pouch in the Camel.

Cete. The Duodenum always commences by so considerable a
dilatation that it has been sometimes reckoned among the divisions
of the complex Stomach.

In-Miamellata. In Dasypus the Duodenum is dilated at its com-
mencement.

Marsupialia. In Phascolarctos the Duodenum commences with a
small pyriform sacculus, nearly an inch in breadth, but soon con-
tracts to a diameter of five lines, which is the general calibre of
the small Intestines.

— Mucous Lining y Villi, Folds, Glands, &c.

JBimana. The surface of the Mucous Membrane is extended by
transverse folds, or valvulse conniventes, in the Jejunum and Ileum ;
where also are to be found, situated opposite the line of attachment
of the mesentery, numerous patches of ' agminate follicles.'

Insectivora. As a rule, the Intestinal Canal is uniform in diame-
ter, and devoid of Csecum. The lining membrane of the intestine
of Talpa is disposed along part of the canal in close-set longitudinal
folds; but is remarkable for its smoothness, and the absence of
visible Yilli.

Frohoscidia. The termination of the Ileum projects as a conical
valve into the CfEcum. The mucous coat of the Jejunum is throwa
into small irregular folds, both transverse and longitudinal.

Digestive System — Special. 91

Perissodactyla. In Ehinoceros the lining membrane of the Duo-
denum is, at the commencement, jpuckered up into irregular rugce ;
flattened triangular processes begin to make their appearance about
six inches from the pylorus ; in the Jejunum three or four of these
processes are often supported on a common base ; as they approach
the Ileum they begin to lose breadth and gain in length, until they
assume the appearance, near the end of the Ileum, of vermiform
processes, like tags of worsted, from two-thirds of an inch to one
inch in length.

JByracoidea. The agminate follicles are lodged in fossae of the
mucous membrane. The small Intestines present internally a series
of twelve small pouches, which make no projection externally, being
situated wholly beneath the muscular coat.

Artiodactyla. In many species of Euminantia, especially Giraifa,
the same arrangement of the Agminate Pollicles is observed as in
Hyracoidea.

In-Enamellata. In Myrmecophaga the inner surface of the Duo-
denum and Jejunum is smooth, presenting no villi to the naked eye.
In Dasypus peba there is a well-marked zone of racemose glands
beyond the Pylorus, In Orycteropus the small Intestines are of
unwonted length, about thirty-seven feet, and their lining membrane
without folds, but beset with fine villi.

MarsupiaUa. In most species, even the most carnivorous, there
is a zone of glands at the commencement of the Duodenum. In
Phascolarctos the end of the Ileum protrudes for the extent of a
quarter of an inch within the Caecum.

Monotremata. The mucous coat of the Intestine of Ornithorhyn-
cus contrasts with that of Echidna in the presence of numerous
transverse and oblique folds, which are absent in the latter.

16. — The Cmcum

— is absent in

most Insectiwra^ except the Tupaias and some snouted Shrews ;
all Cheiroptera^ except Rhinopoma and Megaderma Spasma ;
the Myoxidoi of the Eodentia, which hybernate, like the Bear ;
the Semiplantigrade and Plantigrade Sectorialia ;
and in the Bradypodidce (Inenamellata).

— is small and simple, though occasionally bifid, in
Bimana, where it is short, wide, and sacculated ;
the Catarrhine and Flatyrrhine Quadrumana ;

92 Mammalia, Digestive System.

the Murida, SciuridcB, and Hystricidce of the Eodentia [cf. Teeth) ;

most Digitigrade and Pmnigrade Sectorialia, especially in the
typical Eelidee, e.g, Leo [being longer in Hyaena than in Leo, and
again longer in Canis than in Hyaena] ;

all Artiodactyla ;

all Sirenia [that of Manatus being bifid] ;

the Entomophagous Marsupialia, and all Marsupials that have a
saccnlated Stomach ;

and the Monotremata [that of Echidna being vermiform and
glandular].

— is long, wadi frequently sacculated m

all LemuridcB, or Strepsirrhine Quadrumana [in Cheiromys, and
Stenops Javanicus, it contracts at its termination, and becomes
glandular] ;

many Rodentia [in Eathyergus (Mole Rat) and Arctomys (Mar-
mot) the inner membrane of the Caecum is augmented by transverse
or circular folds. In Coypu the Caecum is puckered into sacculi by
two muscular bands. In Capybara the enormous Caecum occupies
almost the whole of the posterior half of the abdomen. In most
vegetarian Eodentia the Caecum is long, especially so in the Leporidae.
Two oval patches are usually found on either side of the ileocaecal
valve. In the Leporidae the termination of the Caecum is slender
and glandular, like the vermifonn appendage in Man] ;

the Frohoscidia, in which the large Caecum is sacculated on three
longitudinal bands ;

the Perissodactyla [in Equus Caballus the Caecum is sacculated on
four longitudinal bands ; but in Rhinoceros on a single broad band
on the anterior surface] ;

the Balmno]ptera (Cete) ; where the Caecum, though simple, is of
considerable length ;

and in the Carpophagous Marsupials [the Phalangers having a
Caecum sometimes twice the length of the body ; the Koala having
a Caecum three times the length of the body, with its inner secreting
membrane further augmented by several nearly parallel plaits, con-
tinuing from the Colon three-quarters of the way towards the blind
extremity],

— has a Vermiform Appendix in
JBimana ;

Digestive System — Special. 93

the Higlier Catarrhine Apes, e.g. Simla (Orang), and Hylobates
(Gibbon);
and in Fhascolomys (Wombat) of the Marsupials.

— is double in

the Uyracoidea, where there is, first, a sacculated Caecum, whose
length, from the orifice of the Ileum, is three inches, and circumfer-
ence eight inches : and, secondly, two conical Caeca, proceeding
from the dilated part of the Colon ; each of these lower Caeca being
an inch and a half in diameter at its base, and gradually contracting
till it terminates in a glandular vermiform appendage, about half
an inch long — ;

and in the little Two-toed Ant Eater, and Six-handed Armadillo.
Tn the last named, the large Intestine expands into a pair of short wide
pouches, one on each side the insertion of the Ileum ; the terminal
orifice of the Ileum being a slit with tumid margins on the middle
of the ridge, between the two Cseca.

1 7. — The Large Intestine.

Rodentia. In Arvicola (Water Yole) the Colon begins by a pair
of large sacculi, but quickly contracts to the same calibre as the
Ileum.

Artiodactyla. The Colon, in part of its course, is disposed in five
spiral coils, like a screw, coming nearer the centre : these spiral
turns form one of the characteristics of the Order.

In-Enamellata. In Bradypus (Sloth) the Colon is short and
straight (Avian point).

Marsupialia. In Koala the inner surface of the large Intestines
is extended by longitudinal valvula) conniventes. In the Kangaroo
the lining membrane is disposed in a very fine network.

Monotremata. Ornithorhyncus has no valvula coli ; the first half
of the Colon has longitudinal folds, the remainder a smooth inner
surface.

18. — Termination of Intestine.

In-EnameTlata. In the Bradypodidae (Sloth) the anus in the female
is not distinct from the generative outlet.

Marsupialia. In all Marsupialia two sebaceous follicles open into
the termination of the rectum. The anus has its proper sphincter,
but it. is also surrounded, in common with the genital outlet, by a
larger one. When the Penis is retracted, the faecal, urinary and

94 Mammalia. Digestive System.

genital canals all terminate within a common external outlet ; so
that in the literal sense the Marsupialia are monotrematous.

Monotremata. The rectum terminates at the anterior and dorsal
part of the vestibular compartment of the Cloaca.

19. — The Great Oraentum

— is small, and does not cover the Intestines
in Prohosciclia^ Perissodactijla, and Sirenia.

20.— The Liver

— is simple

in Bimana and Cete.

— is Multifid, to a greater or less degree in

most other Orders, the average being seven to eight lobes.

Rodentia. In Capromys each lobe is subdivided into almost in-
numerable angular lobules, which, though closely in contact, are quite
detached from each other, being appended by their apices to the
large branches of the vena portse and hepatic arteries and veins.
Each of the lobules is partially subdivided into still smaller ones,
the whole structure approximating to a complete natural unravel-
ling of this conglomerate gland to its component acini.

Ungulata. The Liver is least subdivided in the purely herbivor-
ous Ungulates. The Perissodactyles have in general a larger and
more subdivided Liver than the Artiodactyles, especially than the
Euminants, in all of which (E.) the Liver is confined to the right
hypochondriac (vtto, under; ■xpydpog, cartilage, of ribs), and epigastric
(«7ri on ; yaarrjp the stomach) regions.

Marsupialia. The Liver is subdivided into many lobes in all ;
but especially in Koala, where the under surface is subdivided into
thirty or forty lobules.

21.— The Gall Bladder

— is absent in

some Cheiroptera, e.g. Roussettes and Colugos ;

some Rodentia J e.g. Mus, Cricetus (Hamster), and Helamys (Jerboa);

the Prohoscidia, where however the hepatic duct is wide and
very long, with a reticulate inner surface, and expands between the
coats of the duodenum into an oval receptacle, irregularly divided
into compartments ;

all Perissodactyla ;

some Artiodactyla, e.g. Camelidce and Cervidse ;

Digestive System — Special. 9-")

all Cete;

and some In-Unamellata. [Bradypus ^rf'dactylus has no gallbladder,
though Bradypus fMactylus is possessed of one.]

— is generally present

in all the other Orders ; and in most genera of the Cheiroptera,
llodentia, Artiodactyla, and In-Enamellata, with the exception of
those noted above.

In the Insectivora it is for the most part of considerable size.

In the Sectorialia the inner surface of tlie gall bladder is minutely
rugous and villous. In some Seals {e.g. Otaria) the ductus commu-
nis, after it is joined by the pancreatic duct, terminates in a dilated
sacculus, within the duodenal coats.

In all Cmicornua (Artiodactyla) a gall bladder is present.

Of the In-Enamellata^ the gall bladder is present in Bradypus
didactylus, and all DasypodidaD. In Orycteropus two separate gall
bladders are found.

All MarsupiaUa and Monotremata have a gall bladder.

22. — The Pancreas

— is Iranched, or dendritic,

in several species of JRodentia and MarsupiaUa.

— has a single duct, yet entering alone,

in most Rodentia, where it enters the duodenum lower down than
the bile-duct ; and

in the Monotrematous Echidna, where it enters the duodenum,
between the bile duct and the pylorus.

90 3fam77ialia,

DUCTLESS, OE YASCULAE GLAXDS.

i.— The Spleen-.

The Spleen is always present, lies near the Stomach, and
is commonly elongate and simple; but varies in form and
size in the several Orders. Its development is directly cor-
related with that of the Pancreas. It is larger in the om-
nivorous and quasi-carnivorous Eodents, e.g. the Eats, than
in the vegetarian species of the Order ; it is also relatively
larger in the Sectorialia than in the Ungulata.

Cete. In some Cete, e.g. Dolphin, the Spleen is remarkable for
its sub-divisions.

Marsupialia. In most Marsupials the Spleen is bent, or bilobed.

2.— The Thyroid.*

A Thyroid gland is generally present, situated in close
relation to the Larynx, from the shield-shaped cartilage of
which it has received its name. It usually consists of a pair
of oblong lateral lobes, united by ligament.

3._The Thymus.

This gland, which is formed towards the end of foetal
existance, and attains its greatest development during the
period of lactation, is present in most Mammals at birth ; the
bulk of the gland lies behind the manubrium. It is distin-
guished from the Thyroid by its wide central cavity, and
generally by its diminution in volume, or disappearance,
early in life.

* QvptoQj a shield ; iihoQy shape.

Ductless^ or Vascular Glands, 97

— is persistent and large in

all diving animals ; e.g. Castor (Eodentia), Lutra and Plioca
(Sectorialia), and Cete.

In the Artiodactyla,- whether Euminantia or Omnivora, the cer-
vical portions of the Thymus are much developed, often extending
to the mandibular angles.

4. — The Supra-Renal Capsules

are generally present, and always larger in the foetal tlian
in tlie adult animal : in lower Mammals they are not alwaya
in contact with, the kidney, as they are in Man.

98 Mammalia.

CIECULATOEY SYSTEM— Geneeal.

Absorbent Glands are mucli more numerous in Mammalia
tlian in any other class ; but are usually less numerous and
more blended together in other orders than in Bimana ; they
present themselves on the lymphatics as well as on the
lac teals ; those on the lac teals (* mesenteric ') sometimes
cluster together into a single mass, named the Pancreas
Asellii, at the root of the Mesentery. In the Mam-
malia alone of all Yertebrata are conglomerated or
conglobate glands met with in the Mesentery. The Lacteals
all discharge their contents into a Receptaculum Chylij which
is situated in the Lumbar region close to the spine, at which
point the superficial l^nnphatics of the lower limbs communi-
cate with them. One, or sometimes two, Thoracic ducts are
continued anteriorly from the E-eceptaculum, and terminate at
the junction of the Jugular and Subclayian Yeins. When
the Thoracic duct is single, it is always on the left ; it often
resembles rather a plexus of vessels than a single tube ;
branches proceeding from it and then re-uniting again ; when
there are two ducts, that on the right usually joins its fellow
on the left prior to joining the venous system. In some of
the lower Mammalia, however, a double thoracic duct is con-
stant, one terminating on the left, the other on the right.
JS^o rhythmically pulsating sacs have been detected in the
absorbent system of Mammalia. When a distinct waU can

Circulatory System — General, 99

be defined the Lympliatioe of Mammalia are seen to be more
numerous, minute, and bigbly organised than in tbe Lower
Yertebrata ; and to have tbeir inner tunic folded to form
many and efficient valves of the ' semi-lunar ' type, commonly
in pairs, rarely single.

The Heart consists of two auricles and two ventricles ; the
auriculo- ventricular chambers are usually quite distinct inter-
nally, but the division is seldom indicated externally. The
venous and arterial parts of the vascular system have no com-
munication beyond the heart, save at the peripheral capillaries.
The Heart is invested by a pericardium. In the prone trunk
of quadrupeds the pericardium adheres to the sternum, rarely
to the diaphragm : from which in many Mammals it is more
or less separated by a lobe of the lung. The form of the
Heart is in general more rounded than in Man, the Apex is
occasionally indented, and, most exceptionally, cleft. In Man
the heart is placed obliquely ; in lower Mammalia it is almost
always placed more in a line with the axis of the body. The
right auricle is less definitely divided into * sinus ' and ' auri-
cle ' proper than in Birds. The Foramen ovale, though
generally closed in the adult, yet is sometimes found open
some time after birth. The Eustachian valve is frequently
wanting. The Precavals* (* descending cavae ') sometimes
terminate in the auricle by distinct orifices. The right auri-
culo-ventricular valve resembles in structure the left, as beings
membranous and attached by tendinous threads to muscle ;,
it rarely takes on the form of the single muscular valve of
the Bird. Occasionally there is found as a normal formation,
in the septum ventriculorum, below the origin of the aorta, a
cruciform ossification called the bone of the heart. In most
other particulars the Heart of other Mammals is the same
as that of man.

. * Owen.

100 Mammalia. Circulatory System,

The Arteries. In the Mammalian class the Aorta bends
over the left bronchial tube : the chief primary branches of
the Arch are given off at a little distance from its origin in
variable order. But before forming this arch, it gives off
close to its origin generally two (' coronary ') arteries for the
heart. The Aorta in some diving animals forms near to its
exit from the heart a considerable dilation : and so also some-
times the Pulnionary artery. There are four principal
varieties of form in which the vessels leave the arch. (1.)
The Human type, viz., a right arteria innominata, from which
the right * carotid ' and right ^ subclavian ' are given off ; the
left ' carotid ' and left * subclavian ' having each a separate
origin. (2.) The Bat t}^e, viz. two arteriao innominata^, each
giving off the * carotid ' and * subclavian ' of its own side.
(3.) The Feline type, mz. one arteria innominata giving off
both * carotids' and the right * subclavian' ; the left subclavian
having a separate origin. (4.) The Ruminant type, in which
the single arteria innominata gives off both carotids, and both
subclavian arteries. The great Arteries of the posterior
extremities are in most Mammals derived from a single*
trunk on each side — the common iliac artery. Retia Mirahilia
are found in various situations, and are constant characteristics
of some genera : they have been found in the Skull, Orbit,
and Nasal cavity, in the Thorax, round the Spinal cord, in
the Arm, and in the Leg.

The Veins. The major part of the Yenous sj^stem, after
the vessels have gained, in returning from the capillary area,
a conspicuous size, is furnished with valves f which occur
usually in pairs. As a general rule valves are wanting in

* In Birds they are derived from two primary branches of the aorta, one cor-
responding with the external iliac and femoral, the other with the internal iliac
and ischiadic arteries.

t No valves are met with in the veins of Reptiles and Fishes, and not many
in those of Bii-ds.

Circulatory System — General. 101

tlie superior and inferior cavao, subclavian and iliac veins, and
in the veins of the liver (both portal and hepatic), heart, lungs,
kidneys, brain, and spinal cord. Many of the veins within
the Cranium are included in spaces formed by the separation
of the laminae of the dura mater, and do not admit of being
dilated beyond a certain size ; these are termed ' sinuses/ In
all Mammals may be found the ' superior longitudinal sinus,'
united at the Uorcular Herophili'* with the lateral Sinuses.
It is very rarely that the veins have an outer coat of circular
fibres. In most higher Mammals there is one superior cava as in
Man, but there are instances, by no means uncommon, of two
anterior or descending vena3 cava) as in Birds. The posterior
or inferior cava is commonly dilated in diving animals
previous to entering the heart. The Portal circulation is
limited in Mammalia to the Liver, the Kidney being supplied
with arterial blood only. The veins of the Kidney are con-
tinued from the Renal artery, and communicate solely with
the inferior cava. The Iliac veins combine to form the
inferior cava in all Mammals, without conveying any part of
their blood to the Kidneys. The external jugular veins are
often very wide where they convey the blood from the brain
sinuses as well as from the neck ; in Man, the Quadrimiana,
and Sectorialia, the blood from the brain sinuses is conveyed
by a separate channel, viz. the Internal jugular veins. A
plexiform disposition of the veins is sometimes met with.

The Blood of Mammalia is hot and red : the blood corpuscle
is, as a general rule, a circularf disc ; and, whether circular or
oval, instead of being swollen in the centre by a nuclear part,
it is there thinnerij:; the disc is consequently slightly biconcave.
The average diameter of the human blood disc is — ^^ : they

* In Man tlie sinuses which are contained in the several processes or folds of
the dura mater converge to a common point, which corresponds with the occipi-
tal protuberance, and is called the confluence of the sinuses, or torcular (a wine-,
or oil-press) Herophili.

t Camelidae alone excepted. % Non-nucleated.

102 3fammaUa. Circulatory System.

are commonly somewhat smaller in other orders. In Mam-
malia tlie blood discs are most numerous, and most minute
relatively to the bulk of the body, of all Yertebrata.

CIECULATORY SYSTEM— Special.

1. — Ahwrhent system.

Quadrumana. The mesenteric glands are specially numerous-.

Sectorialia. The mesenteric glands are aggregated in one mass,
known to old anatomists as the Pancreas Asellii.

TJngulata. The mesenteric glands are numerous.

2.— The Heart.

— The ^pericardium seldom reaches the diaphragm

in any of the species composing the following orders, vi%. : —
Insectivora, CheirojJtera, Rodentia^ In-Enamellata^ Marsupialia, and
Monotremata.
— The Heart shows external signs of division

in some Rodentia. The apex of the heart is sub-bifid in the Hare
and Acouchi.

In some Cete^ e.g. the Cachalots and Whales, the apex is rounded
or rather flattened, and sometimes indented.

In all Sirenia, the outward division of the ventricles indicated in
some Cete is carried to an extent very characteristic of the Order ;
but in Ehytina and Manatus the cleft is not quite so deep as in the-
Heart of Halicore.

— The fossa ovalis.

Marsupialia. There is no trace of a * fossa ovalis ' nor of an ' annulus
ovalis ' ; and the absence of these structures, which are present in the
heart of all the Placental Mammalia, relates to the very brief period
during which the auricles intercommunicate in the Marsupials, and
to the minute size, and in other respects incompletely developed
state, at which the young Marsupial animal respires air by the Lungs,
and has the mature condition of the pulmonary circulation established.

Circulatory System — Special. 103

— The foramen ovale.

In the Seals (Sectorialia) and other animals that live in water the
foramen ovale may remain open"^* for some time, but it is rare : in all
Cete, and in the Dugong (Sirenia), the fossa ovalis is closed.
— Each precaval has a separate orifice into the auricle

in many Insectivoray Cheiroptera, Rodentia, In-Enamellata, MarsU'
pialia, and Monotremata.

— Eustachian Valve.

Sectorialia. The Eustachian valre is wanting in most species.

Proloscidia. In the Elephant the Eustachian valve is large and
spirally twisted.

Cete. The Eustachian valve is generally wanting.

— Right Auriculo- Ventricular Valve.

Monotremata. In the Ornithorhyncus the right 'tricuspid' valve
consists of two membranous and two fleshy portions : the smallest of
the latter is situated near the origin of the pulmonary artery,
corresponds with the lesser fleshy valve in the heart of certain Birdsy
e.g. Pelican (Dysporo-morphse : Desmognathae), and is attached to
the whole of the side of the first or adjoining membranous portion r
the second fleshy portion answers to the larger muscular valve of
the Pelican. The two edges of the lower half of the second fleshy
portion of the valve in the Ornithorhyncus are free ; but those of
the upper half are attached to the two membranous portions of the
'tricuspid' valve ; the margin of the membranous part of the valve is
attached to the fixed wall of the ventricle by two small chordae
tendineae ; and the structure of the valve thus offers an interesting
transitional state letween that of the Mammal and that of the Bird.
— Bone of the Heart.

Artiodactyla. In most adult Huminantia and some Omnivora (^.y.
Hog), there is a bent bone at the base of the heart, on the septal
side of the origin of the aorta, and imbedded in the tendinous circle
which gives attachment to the muscular fibres of the ventricle.

3. — Arterial System.

— The Coronary Artery is said to be singlef in the Elephant.

* Vander Hoeven, ii., 584.
t Camper.

104 Mammalia. Circulatory System.

— Arch of Aorta.

a. The Human type obtains in

Bimana ; the higher Caiarrhine Quadrumana ; the Claviculate
Rodentia {e.g. Muridse, Castoridae) ; most Finnigrade Sectorialia ;
most Bala^nidce^ of the Cete ; most Sirenia ; the Basypodidce and
BradypodidcB of the In-Enamellata ; a few broad-chested Marsu-
pialia, e.g. Koala and Wombat ; and the Monotrematous Ornithorhyn-
cus.

h. The Bat type obtains in

the Erinaceidce and Talpidce of the Insectivora ; most Cheiroptera ;
and some Delphinidae (not Phocsena) of the Cete.

c. The Feline type obtains in

the Strepsirrhine, Platyrrhine, and lower Catarrhine Quadrumana ;
most Noyi-claticulate Rodentia ; nearly all Sectorialia (except Pinui-
grada) ; the Prohoscidia^'; some Artiodactyla, e.g. the Omnivorous
Suidce, and the Ruminants Auchenia^ and Giraffa ; the In-Enamellata
JEdentvIa ; and most Marsupialia (exc. see above).

d. The Ruminant type obtains in

most Ferissodactyla {e.g. Tapir and Horse) ; and most Ruminant
(Bovidae) Artiodactyla.

— Arterial Retia Mirahilia.

Quadrum.ana. The Limb arteries of the Slow Lemurs (Stenops)
exhibit a plexiform arrangement as in the Sloths (Bradypodidae).

Sectorialia. The Ophthalmic artery (a branch of tho external
Carotid) forms in the Cat a vascular plexus in the Orbit. The
Brachial artery has a plexiform arrangement in the Walrus.

Artiodactyla. In the Euminantia a similar orbital plexus is found
as in the Cat {supra) : in the Hog and Euminantia ' retia ' are
also found in the nasal cavities, formed by the Sphenopalatine artery :
again, there is an intracranial * rete ' at the base of the skull in
Ruminants ; it is large in grazers (esp. Bovidae), is less in browsers,
and least in the Giraffe, which habitually feeds with the head raised.

CetCi In Phocaena the Intercostal arteries divide into a vast
number of branches, forming by their close tortuous interlacement a
plexiform mass : from which branches pass into the neural canal, to
surround the spinal cord with a similar plexus which increases in
thickness near the skuU. Thus the neural axis can receive its

* Owen. Wagner (p. 45) says that both the Carotids are given off from a
single common trunk, situated between the two subclavian arteries ; and quotes
it as a very rare arrangement.

Circulatory System — Special. 105

appropriate stimulus of oxj^genated blood during the periods of long
submersion and consequent interruption of respiration to which the
Cete are subject. The brachial artery also of Phocaena has a plexi-
form distribution.

Sirenia. The littoral and herbivorous Sirenia, which never
go so deep, or stay so long submerged as the whales, are said not to
possess either of the plexuses above described. The brachial artery
has a plexiform arrangement in Manatee.

In-Enamellata. The brachial artery is remarkably modified in
the Sloths, where, after bending over the first rib and traversing the
axilla, it suddenly sends off, or seems to break up into a fasciculus
of minute longitudinal branches which surround and conceal the
main trunk which exists in the middle of the plexus. A femoral
plexus is also given off at the brim of the pelvis by one or two
branches which subdivide, but not, as in the axilla, by many ramus-
cules from one point. Rete have been noticed on the blood vessels of
the limbs in Myrmecophaga didactyla, and Dasypus sexcinctus also.

Monotremata. The arterial system of both genera is characterised
by the subdivided plexiform disposition of many of the arteries.

— Origin of arteries of posterior extremities.

Mursupialia. In the Kangaroo and Yulpine Phalanger the Aorta
gives off, opposite the interspace of the two last lumbar vertebrse,
the iliac arteries ; but these are afterwards resolved into the ordinary
branches of the external iliac of the placental Mammals, with the
addition of the ilio-lumbar artery. The trunk of the Aorta, much
diminished in size, maintains its usual course for a very short
distance, and then gives off the two internal iliacs, and is continued
as the ' arteria sacra media ' to the tail. The transitional character
of this part of the Marsupial sanguiferous system, between the Ovi-
parous and Placental types, is manifested in the large size of the
external"^' iliacs as compared with the internal iliacs, their greater
share in the supply of blood to the hinder extremities, and the
brevity of the Aortic trunk between their origins. In Marsupialia
the inferior mesenteric artery does not arise primarily from the Aorta.

4. Venous system.
— - Valves,

* In most Birds the femoral, or external iliac, are smaller than the ischiadic,
or internal iliac, arteries subsequently given off.

106 Mammalia. Circulatory System.

Artiodactyla. The Portal vein shows valves in some Euminants.
Cete. The non- valvular structure of the veins is remarkable.

— External circular fibres.

Sectorialia. The hepatic veins in the Seal have an outer coat of
circular fibres. Wagner remarks that a peculiar annular muscle,
about an inch in breadth is met with in the Seals on the trunk of
the inferior cava above the diaphragm and venous sac, which can
cut off the return of blood to the heart.

— A right and a left vena cava superior are found in

some Insectivor a f e.g. Hedgehog; some Cheiroptera, e.g. 'Bat; most
Eodentia, e.g. llabbit, Squirrel, Rat, Mouse ; in the Proloscidia ;
and in all Marsupialia and Monotremata.

— A right vena cava superior and a left azygos venous trunlCf prevails
in most of the larger quadrupeds : it is found in

some Insectivora, e.g. Talpa ; some Eodentia, e.g. Cavia; some
Perissodactyla, ^.^. Horse; and some Artiodactyla, e.^. the Omnivorous
Suidce, and many Euminantia Cavicornua.

— A right vena cava superior and a left cardiac venous trunh or coronary
sinus, prevails in the higher Mammalia,

e.g. in Bimana; many Quadrumana ; most Bigitigradej Semi-
plantigrade, and Pinnigrade Sectorialia ; and nearly all Cete.

— The Inferior cava is more or less dilated

in some Eodentia, e.g. Castoridcd;

in some Sectorialia, e.g. Lutra and Phoca (in the latter thi8
dilatation reaches to the greatest extent ; it occurs close to, and al-
most within the liver, and extends to the diaphragm, above which
the vein is again of the common width) :

in the Belphinidce (Cete) and the Monotrematous Ornithorhyncus.

— Venous plexuses.

Cete. The veins at the back of the Thoracic-abdominal cavity
have a characteristic expansion and plexiform multiplication. The
chief abdominal reservoir is formed by the vast psoadic* plexus
which extends from behind the hinder end of the kidney to the
hinder end of the abdomen : in the Porpoise it forms a mass of
reticulate veins upwards of an inch in thickness. The caudal vein

* So called, as being situated between the psoas muscle and tbe peritoneum.

Circulatory System — Special. 107

is represented by a plexus, and occupies mucli of the haemapopliysial
canal.

5. "IhQ Blood.

— Oval discs.

Artiodactyla. The Camelidce, (e.g. Dromedary, Llama, Vicunga)
have elliptical blood discs : but these are equally non-nucleate with
the ordinary circular blood discs ; and adhere to the Ruminant
characteristic of minuteness of size.

— Sue of discs.

The two extremes of size observed in the Mammalian class are in
Elephas Indicus 2745, and Moschus Javanicus y^^^.

Artiodactyla. An unusually small size of the blood discs is asso-
ciated with the peculiarities of the Ruminant structure.

• W. Hewson.

108 Mammalia,

EESPIEATOEY SYSTEM— General.

The Larynx, Trachea, and Lungs, in the Mammalia are
fashioned after the type of the same organs in Man.

The cartilages of the Larynx are upon the whole the same
as in Man, viz., a Thyroid ; a Cricoid ; an Epiglottis ; two
Arytenoids*; two Cartilagines Santorianae, articulated with
the summits of the arytenoids ; and two Cuneiform Cartilages
(Wrisberginao), situated between the arytenoids and the epi-
glottis : but in addition there is sometimes found an ' Inter-
articular f cartilage, situated between the two arytenoid car-
tilages, upon the upper border of the cricoid. These cartilages,
some of which are occasionally found ossified, are united to-
gether by ligament. Two pair of elastic fibres are commonly
found stretched between the arytenoid and thyroid cartilages,
viz. the * upper' and ' lower ' Yocal Chords, between which the
lining membrane bulges outward to form the * laryngeal ' sac
or S^entricle.' The alse of the T/^yro/c? cartilage are generally,
though not always, united, and form anteriorly an angle ;
though usually larger than the cricoid the thyroid is not
always so : it may have no upper cornua ; its lower cornua may
be produced to meet the first tracheal ring ; from its upper
part sacculi may be continued into the interspace between the
epiglottis and the Hyoid ; and it may be itself hollowed out

"^ apvTaivaf a pitcher or ladle ; el^OQy shape,
t Brandt.

Respiratory System — General, 109

like a bulla, to receive a sacculus. The Cricoid is generally
smaller than the thyroid, but may be even three times greater
in size ; it is usually complete anteriorly, but may be almost
divided by a cleft : it is sometimes so extended posteriorly as
to cover the five anterior tracheal rings. The Epiglottis is
almost universally present, protecting the entrance into the
Larynx ; it may be entire, or notched at its apex ; its sides are
sometimes attached to the apices of the arytenoid cartilages ;
together with the arytenoids it may be enclosed by a sheath
of pharyngeal mucous membrane ; it may contain no true
cartilage ; and may be perforated by apertures leading into
sacculi. The Arytenoids sometimes extend half way across the
rima glottidis ; they maj'- be, as above said, enveloped with
the epiglottis in a membranous sheath ; and, together with
the cartilages of Santorini, are sometimes confluent at their
apices. The Vocal Chords are subject to great variations in
point of development ; both upper and lower ^chordae vocales '
may be reduced to half their normal extent, owing to the
anterior extension of the arytenoids ; the superior ^ chordae '
may be represented by a slight thickening of the lower border
of the lateral membranes continued from the arytenoids to the
base of the epiglottis ; again, the lower vocal chords may be
alone manifested, and the interchordal ventricle obsolete : or
there may be no vocal chords, and quasi- ventricles alone
present ; lastly, both the vocal chords and ventricles may be
wanting. Certain species vibrate their vocal chords by
currents of air in alternate opposite directions, but this is
exceptional. The interchordal ventricles when present vary
much in relative size ; they may be subdivided into several
pouches. Above the convergence of the upper chords is some-
times found the opening of a ' hyoid sac,' the basi-hyal bone
being hollowed out to receive this sac. Some species of Mam-
malia are always mute : others are mute except at the sexual

110 Mammalia, Respiratory System.

season : Gibbons (Hylobates) alone of brute Mammals may
be said to sing.

The Trachea is kept open by cartilaginous hoops, wbich
may be complete or cleft : when cleft, tbe ends of each
ring may meet and touch, or overlap, or (as is commonly
the case) may be separated even to the extent of a quarter
of the circle, the intervening space being occupied by mem-
brane : this separation very rarely occurs on the anterior sur-
face. The cartilages of the rings may be continued spirally
into one another ; and the rings themselves may be occasion-
ally found ossified. The number of rings varies, from three
(Dugong) to a hundred (Camel). The entire tube is lined
by a mucous membrane with a ciliated free surface. The
trachea as a rule passes with a straight course until its sub-
division into bronchial tubes. As a rule there are two
Bronchi, but there is occasionally found a third smaller
bronchial tube which passes to the right lung. The bronchi
when within the substance of the lung divide and gradually
lose their tracheal structure ; the cilia ceasing when the
divided bronchial tubes again subdivide to form the numerous
'intercellular' passages : the intercellular passages intercom-
municate, which the bronchial ramifications never do. The
arborescent subdivisions of the intercellular passages terminate
in air cells, in size from \ to ^^ of a line : on the parietes of
these cells the pulmonary capillaries offer only one side to the
respiratory medium, instead of being wholly immersed in the
extra-bronchial air as in Birds. Air sacs in connection with
the lungs, as are observed in Birds, are not present in
Mammalia.

The Lungs, minutely cellular throughout, are suspended
freely in a thoracic cavity, separated by a musculo-tendinous
partition or ' diaphragm ' from the abdomen. A complete
Diaphragm is peculiar to Mammalia; it is attached to the
vertebra?, the ribs, and the sternum, and is tendinous in the

Respiratory System — General. Ill

middle ; occasionally a small bone is found in its tissue. Tlie
serous membrane covering each, lung is reflected from the root
of the lung upon the walls of the thorax, thus constituting a
so-called * pleural ' sac. The pleural serous sacs are peculiar to
Mammalia. The right lobe of the lung is usually the larger,
and is very commonly subdivided : the left lobe is frequently
undivided, and when divided has generally fewer lobes than
the right. The lungs may be simple and undivided, as in
Man, but exceptionally. The most common Quadrupedal dif-
ference from the Bimanal type is the lobe called * azygos,*
or ' impar,' detached from the right lung to occupy the space
between the heart and the diaphragm.

EESPIRATOEY SYSTEM— Special.

1.— The Thyroid.

Quadrumana. In most Platyrrhina the upper border of the
Thyroid is emarginate. In Mycetes (Howler) the Thyroid is twice
the size of that of Man, and has a strong anterior prominence, bulg-
ing out there to lodge a pair of sacculi continued from the fore part
of the long interchordal cleft or ventricle. In Stenops (LemuridaB)
the lower cornua of the Thyroid are produced over and beyond the
Cricoid to be connected with the first tracheal ring.

Artiodactyla. In the Hog there are no upper cornua to the
Thyroid ; and in the Camelidse the upper cornua are represented only
by tubercles.

Sirenia. The cartilaginous wings of the Thyroid are not conflu-
ent, but are joined anteriorly for a short way by sclerous tissue, and
below this by membrane and areolar tissue.

Monotremata. In Ornithorhyncus the lateral alse of the Thyroid
are bony, and each of them bifurcated : one of the processes extend-
ing to the posterior part of Pharynx, where it becomes cartilaginous,
and is confluent with the corresponding process of the opposite side.

112 Mammalia. Respiratory System.

2.— The Cricoid.

Bectorialia. In Vrms the Cricoid is almost divided by an anterior
cleft.

Prohoscidia. The Cricoid extends posteriorly over the first three
tracheal rings.

Artiodactyla. In the I^lh (Alces) the Cricoid is expanded behind
and thence produced downward so as to cross the five anterior
tracheal rings.

Cete. In Phocwna the Cricoid is incomplete at the fore part.

Sirenia. The Cricoid is larger than the Thyroid, and forms a
complete ring.

3.— The Epiglottis.

Rodentia. The Epiglottis generally has a bifid apex, and at its
base small cartilaginous styliform bodies, separated by a triangular
space.

Perissodactyla. In the Ass and Tapir the root of the Epiglottis is
perforated by two apertures, leading to two sacculi continued upon
part of the inner surface of the Thyroid.

Cete. In Phocrena the long Epiglottis is enclosed with the Ary-
tenoids in a sheath of pharyngeal mucous membrane so as to form
therewith a long pyramidal projection, with a slightly expanded
apex, which is encircled, as it were grasped, by a sphincter-like
disposition of the muscles of the soft palate.

Sirenia. There is no true Cartilage in the Epiglottis of Dugong.

In-Enamellata. In the Armadillos the Epiglottis is deeply notched
at the apex.

Marsupialia. The Epiglottis is remarkable for its large size and
generally for its emarginate apex. There is no muscle passing from
the Epiglottis to the tongue. In Perameles and Phascogale the sides
of the broad and short Epiglottis are attached to the apices of the
Arytenoid Cartilage.

Monotremata. In Ornithorhyncus the apex is notched.

4. — The Arytenoids.

Perissodactyla. In Ehinoceros the base of the Arytenoid cartilages
extends half way across the aperture of the Larynx, and from the
anterior extremities of these produced bases, the upper and lower
* chordae vocales' extend forward to the Thyroid cartilage and base

Respiratory System — Special. 113

of the Epiglottis. Only the anterior half, therefore, of the ' rima
glottidis ' is bounded by vibratile vocalising material.

In most Insectivora and Cheiroptera, and some Artiodactyla [e.g.
Hog), the Arytenoids are united at their apices by the conjunction
of the Santorinian cartilages.

For Arytenoids (1) sheathed with, or (2) attached to Epiglottis,
cf. supra^— 3. Cete, and Marsupialia.

5. — Interarticular Cartilage.

In most Cheiroptera and Insectivora {e.g. Hedgehog) there is a tri-
angular cartilage between the bases of the Arytenoids and the
Cricoid called by Brandt * Interarticular.'

6. — ChordcB Vocales, and Ventricles.

Quadrumana. No tail-less Ape has a hyoid sac : but in the Orangs
the sacculi continued from the interchordal ventricles pass out
between the Thyroid and Hyoid, and in the adult males extend over
the fore part of the neck and upper part of the chest, being subdi-
vided into several pouches.

Mycetes appears to have four sets of sacs : («) from tlie fore part of the inter-
chordal space, a pair of sacculi are developed which occupy the thyroid bulla ;
{b) from the upper part of the thyroid-sacculi are continued a pair of 'pyramidal
oval' sacculi, which occupy the sides of the interspace between the epiglottis and
the hyoid ; {c) from the fore part of the thyroid sac is continued the neck of the
large ' infundibular sac,' which expands^to occupy and line the biilla of the basi-
hyal ; lastly, [d) between the glottis and arytenoids are the orifices of a pair
of pouches, continued rather from the pharyngeal than the laryngeal membrane,
which extend forward and upward on each side of the epiglottis.

Rodentia. In the Porcupines both the Yocal Chords and the
Yentricles are wanting.

Sectorialia. In the Badger the laryngeal sacs are deep and bifid :
one portion extending to the root of the tongue, the other to between
the Thyroid and Cricoid cartilages. In the Eelidse the upper Yocal
Chords are unusually prominent, and by their vibration cause the
purring sound.

Proloscidia, most Perissodactyla, and many Artiodactyla [e.g.
Camelidse, A Ices, &c.) have the upper Chords barely definable.

Cete have no Yocal Chords ; but at the base of the Epiglottis are
two lateral glandular fossae representing the 'Yentricles.'

In-Enamellata. In both Dasypodida3 and Bradypodidas the superior
Yocal Chord is absent, and the Yentricles are obsolete or shallow.

Q

114 Mammalia. Respiratory System.

7. — Species that are Micfe.

Of the Eodentia, the Porcupines are mute, save at the rut, when
the male emits a low grunt.

Of the Artiodactyla, the Giraffe is mute, save at the sexual seasoD.

The Marsupialia as a rule have little or no voice.

8.— The Trachea, &c.

— Rings ossified.

In Ornithorhyncus the bronchial annuli are bony.

— Eings not closed anteriorly.

Cete. In the BalcenidcB the rings are interrupted by a membranous
portion on the anterior surface ; a peculiarity which is unique
among Mammals.

— Bings are complete

in some Perissodactyla {e^g. Horse), Artiodactyla {e.g. Ruminants)^
Cete, and Marsupialia.

— Kings overlap
in most Sectorialia.

— Trachea convoluted.

In-Enamellata. In Bradypus tridactylus the trachea is convoluted
as in the Nilotic* Crocodiles ; it descends nearly to the diaphragm,
and then curves upwards again before it divides into the two bronchi.

— Trachea divided ly median senium.

Modentia. In the Cape Jerboa (Helamys) is found a tracheal
structure recalling the early division of the tube in Reptiles ; the
Trachea being divided a littlebeyo i i the Larynx into two canals by
a median septum; as if the bronchi began there, and were continued,
adhering, some way before diverging to the lungs.

— Trachea divides into three m'<in bronchial trtcnh

in most Artiodactyla {i.e. Ruminantia and Hog) and in the Cefe.

— Bronchi with spiral coils.

Sirenia. In the Dugong the cartilages of the bronchial tubes are
continued spirally into one another.

9. — The Lungs.

— Simple and undivided

in Bimana, Proloscidia (where, however, the right lung sends off
a lobular process), and Cete.

* Not in the Alliffatov orGaviaL

Mammalia. 115

UEINAEY OEGANS— General.

The Mammalian Kidney is distiny,uislied from tliat of all
otlier Yertebrata by tbe bipartite division of its substance
into a * cortical ' and a ' medullary ' portion. The Cortical f
secretory portion, is highly vascular, and composed mainly of
tortuous tubes, which, taking their origin from the Malpighian
bodies, converge towards the interior and do not spread to the
exterior of the gland. The Medallari/y excretory portion, is
composed mainly of straight tubes converging to meet at the
apex of the medullary pyramid : it contains no Malpighian
bodies. The secreting tubuli generally terminate by one
or more papilla) in a dilatation at the commencement of the
ureter called the pelvis. In many Mammals the right kidney
is placed higher than the left ;• the reverse of that commonly
observed in the Human subject. The Eenal artery alone,
derived directly from the aorta, supplies both the substance of
the kidney and the secreting organism : in discharging the
latter function, the afferent vessels form vascular tufts in the
Malpighian bodies, and the efferent vessels proceeding thence
form capillary plexuses surrounding the uriniferous tubes.
The Capillaries after they reunite to form venules round the
papillae sometimes assume a starlike, or an arborescent dispo-
sition, or even form a network on the surface of the kidney
prior to dipping down through the cortical septum to emerge
at the hilus. In all cases the ultimate venous trunks teim-
inate in the vena cava inferior and their component veins
never anastomose ivith the Intestinal veins. In the Human
Embryo the Kidneys consist of several masses or lobes, as it

116 Mammalia. Urinary Organs.

were a multiplication of simple kidneys ; in some species they
continue in this form during the whole of life : this is par-
ticularly the case in those that live in water. When a
kidney, is thus subdivided, each ' venule ' has its oion excretory
duct. The Ureters almost invariably terminate in a Urinary
bladder, and have an oblique valvular course through its
coats. The Bladder appears to be smaller in those species
that feed on flesh than in those that feed on herbs.

URINARY ORGANS— (Special).

1. — Lohdes.

Sector ialia. In the Phocida) (Pinni-gr.) the kidney is divided
into from seventy to one hundred or more lobules, and its surface
has in consequence a tesselated aspect.

Cete. The kidneys have a racemiform appearance ; in the
Dolphins two hundred separate lobules can be counted.

2. — Papillcd.

The following Species generally have only a single papilla into
wliich all the renal tubuli open, viz.:

all Catarrhine Quadrumana : and most Hodentia, Sectorialiaf In-
Enamellata, and Monotremata.

3. — Termination of Ureters.

In the Monotremata the ureters do not terminate in the bladder^
but in the urogenital canal; the orifice of the sperm duct, or oviduct,
intervening between that of the ureter and the bladder. The urine
may dribble out with the faeces, or may pass by a retrograde course
into the bladder ; but in either case it is expelled ^er cloacam^ not
per urethram.
4. — Superficial ramijications of veins, Sfc.

In most Bigitigrade Sectorialia (Felidae, Hya^nidae, Yiverridae, and
Suricate), the kidney is remarkable for the arlorescetit disposition of
the veins on or near the surface. In Pkoca (Pinni-gr.) the veins
unite to form a netivork on the surface of the kidney.

Mammalia, 117

PECULIAE GLANDS.

In certain Genera and Species peculiar glands are found
subserving special functions ; e.g. sebaceous follicles of tbe
skin secreting a strong smelling, unctuous fluid ; anal sacs,
or glands ; and others on the back, legs, and feet.

Quadrumana. In Cheiromys, and some other Lemuridae, the
anal glands are reduced to two shallow cutaneous pits at the sides
and upper part of the vent ; in higher Quadrumana this trace dis-
appears.

Insectivora. In many Shrews two longitudinal series of glandular
tubes open upon the sides of the body opposite to the anterior feet,
the secretion of which has a more or less musky odour; and in
certain large Shrews {e.g. Macroscelides) the under part of the base
of the tail is tumid, through the development of the glandular
follicles.

Cheiroptera. In certain tropical bats {e.g. Cheiromeles) a glandu-
lar exuding sac is situated near the axilla : and in some Yesperti-
tiones upon the sides of the upper jaw.

In the Rodentia and Sector ialia anal sacs, and preputial glands
close to them, are of frequent occurrence, especially noticeable in
Castor idse (Eodentia) and Viverridae (Sectorialia).

Prohoscidia. In Elephas a large gland is situated in the temporal
region, especially^^developed in the rutting season.

Artiodactyla. Interdigital glands are generally found which
exude their lubricating secretion from an orifice at the upper and
fore part of the cleft between the principal hoofs. In Dicotyles is
found a gland situated rather posteriorly upon the mid-line of the

118 Mammalia. Peculiar Glands.

back*-. In many Ruminants and Hogs an inverted fold of skin just
below the orbit ('suborbital sinus') receives the secretion of numerous
sebaceous follicles by which it is perforated. Glandular depressions
of the skin situated in the groin ('inguinal pits') are found in many
Antelopes, and are especially noticeable in the small Ruminant
called on account of the odour of the secretion * Musk Deer.'

In-Fnamellata. The short vestibule or cloacal passage of the two-
toed Sloth shows orifices of many sebaceous follicles.

In all Marsupialia there arc two cavities with sebaceous follicles
opening into or near to the termination of the rectum.

Monotremata. In the male Ornithorhyncus and Echidna there is a
considerable triangular gland on the outer side of the leg, between
the femur and the long olet^ranoid process from the head of the
fibula ; the duct from this descends down the back of the leg to the
tarsus, where it suddenly expands into a vescicle applied to the base
of the spur (cf. Osteology) and is thence continued as a minute duct
into the canal which traverses the spur, and which terminates by a
fine longitudinal slit about one line distant from the point.

* The resemblance of this orifice to the navel on the opposite part of the trunk
ftiiggestcd to Linnajua the term Dicotyles for this genus of S. American porcine
animals.

Mammalia. 119

NEEVOtJS SYSTEM.— Geneeal,

The Spinal Cord, or Myelon (of Owen), exists in varioits
proportions relativel}^ to the neural canal in different Mam-
mals : but the mass of the Myelon, with but few exceptions,
bears a direct ratio to that of the body throughout the series,
has essentially the same structure, and is much less than
that of the brain. It extends considerably further posteriorly
in other Mammalia than in Man, as a rule reaching as far as
the Sacrum*. As in the rest of Yertebrata, a central canal
is often found in the Mammalia, especially in the foetus ; it
is more obvious in lower Mammals than in Man. Two en-
largements are generally found in the Cord ; one in the region
of the attachment of the anterior limbs (brachial); the other
where the lumbar and sacral nerves arise, which form the
plexus for the hind limbs (pelvic) : the pelvic enlargement is
wanting when the hind limbs are rudimentary ; it never ex-
hibits a rhomboidal sinus {cf. Aves) : the brachial enlargement
is distant from the medulla oblongata, according to the length
of the *neck.' The Spinal Cord generally terminates pos-
teriorly by breaking up into threads, forming the so-called
' Cauda equina,' which is scarcely ever met with in the cord
of the other Yertebrata.

«

The Oruithorhj-ncns hardly departs from the condition of the Lizard, the
Myelon extending into the sacrum, and having the intravertehral nerve roots
limited to the shori canal of the caudal region.

120 Mammalia. Nervous System.

The Brain, or Encephalon, presents four primary segments
or divisions, named respectively from back to front. 1.
Epenceplialon. 2. Mesencephalon. 3. Prosencephalon, and
4. E-hinencephalon.

1. The hindmost division, or Ep-encephahn, consists of the
Macromyelon (= ' medulla oblongata,' + the intracranial pro-
longation of the myelonal columns as far forwards as their
emergence from the Pons), and the Cerebellum, together with
its transverse Commissure, called * tuber annulare,' or Pons
Yarolii. From the Macromyelon the cerebral nerves, from
the fifth to the hypoglossal (or ninth) inclusive, arise. In
most Mammals below Man, a transverse section of the Me-
dulla oblongata, in the region of the first cervical nerve, pre-
sents the form of an ellipse, as opposed to that of a circle, as
in Man. The Olivary bodies do not always present internally
a * corpus dentatum,' or nucleus with plicated capsule of
white neurine : they are frequently crossed before reaching
the Pons by the trapezoid homologues of the arciform fibres
in Man. The Trapezium^ which is found in most Mammals,
except Man, consists of a quadrangular elevated layer of
transverse medullary fibres, which lies close behind the Pons,
near to the pyramidal bodies, and abuts against the origin of
the auditory and facial nerves. The middle lobe of the
Cerebellum is the most constant part in the Vertebrate series,
but by no means always holds a large proportional size, as
compared with the lateral lobes. The addition of Lateral lobes
to the Cerebellum is characteristic of the Mammalian Class. An
* appendicular lobe,' a subspherical lateral process or append-
age to the hemispheres of the Cerebellum, is sometimes found.
To the * flocculus ' the origin of the acoustic nerve can be
traced; it is generally associated with large external ears,
and a well-developed auditory organ. In Mammals the ven-
tricle of the Cerebellum, which is persistent in Fish, Heptiles
and Birds, is obliterated. The Pons is found in all Mammals,

Nervous System — General. 121

and by it the Mammalian brain may be distinguished at its base
from that of other Vertebrata : the size of tlie Pons is directly
correlated with the development of the lateral lobes of the
Cerebellum.

2. The division of the Brain next anterior to the Epen-
cephalon is termed the Mesencephalon : it includes the Nates
and Testes, third Yentricle, and Pineal and Pituitary glands*.
The Nates, or 'optic lobes,' are expansions of the processus
ad testes, or crura ad cerebrum (superior peduncles of An-
thro.) ; the layer (valvula) uniting these two crura becomes
thickened by transverse white fibres behind the optic lobes,
and these in the higher Mammals swell into a second pair of
tubercles, the Testes, which usually exceed the Nates in
breadth, but are less in length. In the groups in which the
eyes are relatively largest, the large proportional size of the
homologue of the optic lobes is significant of their important
relationship with the origin of the nerves of vision. These
* Corpora quadrigemina ' form a much smaller mass of the
brain than in the lower Vertebrata, are not hollow internallyf ,
and, though in most Mammals covered by the Cerebral Hemi-
spheres, are in some genera more or less exposed between the
Cerebrum and Cerebellum. The third Yentricle has no con-
tinuation into the optic lobes, which it has in oviparous
Vertebrata ; its ascending canal to the Pineal appendage is
obliterated, but the descending canal to the Pituitary body is
retained as the Infundibulum. The third Ventricle is formed
by the vertical expansion of the ' iter a quarto ad tertium
ventriculum,' which is itself a forward continuation of the

* The third ventricle extends upwards into the pedicle of the Conarium
(pineal gland) and downward into that (infundibulum) of the hypophysis
(pituitary gland). Owen iii. 97.

t Van der Hoeren. Wagner says (p. 23), ' the Corpora Quadrigemina are
very frequently provided with an internal cavity.' In the fcetus of Man and
Mammals these eminences are at first single on each side, and have an internal
cavity, communicating with the ventricles. Q. and S. 554.

122 Mammalia. Nervous System.

primitive Myelonal cavity, traversing the Mesencephalitf
basis.

3. The third primary division of the brain, anterior to the
Mesencephalon, is termed the Prosencephalon : it includes the
Crura Cerebri anterior to the Nates, the Thalami Optici, Cor-
pora Striata,and Cerebral Hemispheres with their commissures.
The Cerebral Hemispheres attain a greater development than
in any other class of Vertebrata : they are connected together
in all Mammals, as in Birds, by the cord-like fasciculus of
transverse fibres, called the * anterior commissure ' : but the
main distinction lies in the superaddition, to the * diverging'
or 'crural* fibres, of other commissural tracts ; either longi-
tudinal, connecting parts of the same Hemisphere ; or trans-
verse, bringing the greater portion of the two Hemispheres
into mutual communication. The Hemispheres are always
connected by a more or less extensive Corpus Callosum : but
in descending the series from Man to those Placental Mammals
of lowest cerebral organization, a great change is seen in the
condition of the Corpus Callosum, in the disappearance of the
rostral portion, and coincident greater development of the
posterior folded or psalterial portion ; the latter being con-
nected with the relative increase of the hippocampal region
of the Cerebrum : a change of precisely the same nature is
seen carried to an excess in the brain of the Marsupial. The
anterior Commissure diminishes in size in proportion as the
Corpus Callosum increases in extent. The Corpus Callosum
increases directly as the growth and complexity of the Hemi-
spheres. As the Hemispheres increase, in the Placental
series, so does the extent of the filmy inner walls of the lateral
ventricles (' septum lucidum,' Anthro.) between the body of
the Fornix and the Corpus Callosum. Each Hemisphere of the
Cerebrum begins as a vesicle of neurine, the'cavity of which
receives the growth from the 'crura,' forming the 'Corpus
Striatum' ; this^ in Birds, mainly fills the ' Yentricle ' or rem-

V

Nervous System — General, 123

mant of the primitive cavity of the sac : but, in Mammals,
the wall of the vesicle is augmented by folds, of which the
first and most constant is pushed from the mesial or inner
side of the ventricle into its cavity, giving rise to the con-
vexity, representing the part called ' hippocampus* in Anthro-
potomy. The anteriorly continued and transversely connected
longitudinal fibres of the Hippocamp constituting the Fornix,
furnish a further distinctive characteristic of the Mammalian
as compared with the Avian brain. An intercommunication
between the two Prosencephalic cavities (lateral ventricles)
defined in Anthropotomy as the foramen of Monro, exists in
all Mammals. The extent to which the Hemispheres are
developed posteriorly is very variable, being in some genera
so slight as to leave the Corpora Quadrigemina exposed, and
being seldom sufiicient to entirely cover the Cerebellum.
In proportion to the increase of the Cerebral Hemispheres
there is a diminution in the size of the ganglia immediately
connected with the organs of sense. The external surface of
the Hemispheres is generally convoluted, but there are several
Orders and Genera in which the surface is smooth, as it is in
the brain of the Oviparous Yertebrata.

4. The foremost primary division of the Brain, termed the
Rhinencephalon, includes the anterior termination of the co-
lumnar tracts (the * roots of the olfactory nerves' in Anthro.),
and the appended vesicular mass called 'olfactory lobe' (the
*bulb of the olfactory nerve' in Man). In most Mammals
the * lateral ventricles' of the Prosencephalon are continued
into the Rhinencephalon. As a very rare -exception the
* olfactory bulbs' may be absent*.

Membranes of the Brain. A fold of dura mater is commonly
found between the Cerebral Hemispheres termed the ' Falx ';
a second duplicature is found between the Cerebrum a^^'^ Cere-

* In a few Cete, e,g. Dolphin.

124 Mammalia. Nervous System.

bellum, called the ' Tentorium ;', and, exceptionally*, a third
process between the lobes of the Cerebellum termed the ' Falx
minor -J ossification is occasionally extended into both the
Tentorium and Falx (major).

Nerves. — Olfactory nerves are present in all saye one Order
of Mammals, and are sent off in greater number from the
Rhinencephalon than in lower Yertebrata : in one known
instance alone does the olfactory nerve quit the skull by a
single foramen {i.e. one from each Rhinencephalon), as in
Birds and Lizards.

The Optic nerves, which rise chiefly from the ' nates,' de-
velope in almost all Placentalia an oblong nodule of grey
matter (corpus geniculatum of An thro.) prior to bending
round the outer and back part of the ' thalami,' from which
they receive accessory filaments. At their confluence beneath
the brain there is no trace of the laminated arrangement
commonly found in the 'chiasma' of Birds and E/cptiles : they
generally leave the skull each by a special ' foramen opticum'.
In those animals which have very small, rudimentary eyes,
the optic nerves are very delicate.

The Sixth Nerve, besides supplying the ' rectus externus,'
is also distributed in most Mammals to an additional, ^ sus-
pensory', muscle of the eye, not found in Man, viz. the * re-
tractor oculi.'

The Fifthy or Trigeminal Nerve, is frequently very much
developed, being commonly the largest of the Cerebral nerves.
The size of this nerve varies directly with the perfection of
sensitiveness ip. the parts to which it is distributed, not with
the proportion of the facial to the cranial part of the head.
A distinct gustatory nerve, communicating with a motory
'facial' nerve by a 'chorda t^^mpani' is an arrangement charac-
teristic of the Mammalian trigeminal nerve.

* On account of the large vermiform lobe of the Cerebellum projecting beyond
its Hemispheres.

Nervous System — General, 125

Of the ' Seventh Pair,' the portio dura (or facial nerve), tra-
verses the parotid gland in those Mammals in which that gland
is well developed. The large development of that part of the
'portio mollis ' (or auditory nerve) which supplies the cochlea is
characteristic of the Mammalia; in which the posterior division,
answering to the main part of the acoustic in lower Yertebrates,
is spent upon the vestibule and semicircular canals.

Of the Eighth Cerebral Nerve j the *glosso-pharyngeal' division
is relatively smaller in Mammals than in Birds : it is mainly
distributed to the back part of the tongue, and to the pharynx
in all members of this Class. The Vagus, or ' pneumogastric
division' has, as in the other Yertebrata, the longest course,
widest distribution, and most numerous connexions of any
of the Cerebral nerves ; but is characterised, in Mammals, by
receiving the * accessory ' nerve from a greater extent of the
myelon. The * recurrent ' branches of the Yagus are more
exclusively distributed to the trachea and larynx, and send
a smaller supply of nerves to the oesophagus than in Birds or
Reptiles. In most Mammals the Yagus after its exit from
the jugular foramen, exhibits a grey enlargement ; but this
is less distinctly divided into an upper and lower ganglion
than it is in Man.

The Ninth, or motor nerve of the tongue (hypoglossal)
varies in size according to the length of the tongue and the
frequency and extent of its muscular motion. In most Mam-
mals the filaments of this nerve are collected into two bundles
which pass out each by a single precondyloid foramen, but
two foramina are occasionally found on each side.

The Sytnpathetic nerve system is much the same as in Man :
it influences the contractile power of blood vessels, the coats of
which, in all Mammals, show a considerable plexiform supply
therefrom. In all Mammals the parts regarded as * trunks,' or
*main cords' of the sympathetic, form a symmetrical pair,
extending along the sides of the centrums of the Yertebrao,
forw^ard to the basioccipital, and backward to the coccvx.

126 Mammalia. Nervom System,

NERYOTJS SYSTEM.— Special.

1. — Spinal Cord, or Myelon.

— The proportmi of, to Neural Canal,

is greatest in the Pinnigrade Sedorialia {e.g. Seal), the Cete, and
the Sirenia. The space between the myelon and neural arches i&
occupied by blood vessels, which are chiefly arterial plexuses.

— The Mass of, is in direct ratio to that of the body.

except in certain Insectivora, e.g. HedgeJwg, a fsw Cheiroptera,
and the Monotrematous Echidna.

— does not extend as far as Sacrum

in some Cheiroptera, the Hedgehog (Insectivora), and the Echidna,
(Monotremata); the myelon being concentrated into the dorsal region.

— presents only the anterior enlargement
in the Cete, and Sirenia.

2. Brain, or EncephaJon.

i. Bimana. — Membranes. In Man (as also in most Quadrumana)
the sole ossification co-extended with any part of the dura mater is
that called * crista galli' (in Anthro.). An unossified process from
the middle of the posterior border of the tentorium, extending from
the internal occipital crest, projects into the notch between the
hemispheres of the Cerebellum, and is termed falx minor, or falx
cerebelli. — Epenceplmlon. A thin layer of superficial fibres, which
in lower Mammals with non-prominent * olivary' bodies pass out-
ward as a ' trapezoid' layer, in Man curve round the exterior of the
olivary prominences and constitute the arciform fibres. The ' corpus
dentatum' is well marked. The transverse section of the medulla
oblongata is nearly circular. The lateral lobes of the cerebellum
acquire the largest proportions (as compared with other Mammals),
and reduce the middle lobe to the semblance of a subordinate ad-
junct, called * vermiform process.' — Mesencephalon. The corpora
quadrigemina are small in comparison with those of the lower Mam-
malia.— Prosencephalon. The Human Brain surpasses that of all
Mammalia in its greater proportional bulk to that of the body, and

Nervous System — Special. 127

in the still greater proportional size of the cerebrum to the rrst
of the brain, viz. as 8 to 1. The anterior commissure has but
insio^nificant dimensions. The cerebral hemispheres completely
overlap the cerebellum : the middle lobe is well defined.

ii. Qiiadrumana. — Membranes. In the matter of the * crisl a
galli,' see Bimana. In Cebus and Ateles the tentorial margin of
the petrosal is slightly produced. — Epencephahn. In the Anthro-
poid Apes the arciform disposition of fibres in conjunction with the
olivary bodies prevails instead of the ' trapezoid ' found in all other
Orders below. The 'appendicular lobe' of the cerebellum is present
in most Lemurida) [e.g. Aye Aye), and is lodged in a special pit of
the petrosal : but in the large Catarrhiua the lateral lobes increase
in size, and lose or incorporate the appendix. The flocculus is pre-
sent in all Quadrumana, and is well ma ked in he timid and sharp-
eared nocturnal Aye Aye. — Prosencephalon. In the Lemurida) the
cerebrum does not extend over the whole of the cerebellum. In
the diminutive Midas the upper surface of the hemispheres is
smooth. The brain of several genera of Apes reeembles that of Man*
in the posterior development of the cerebral hemispheres specialized
as the * third lobe ; * in the possession of a posterior horn to the lateral
ventricle {e.g. in Orang-utan) ; and in the presence of a hippocampus
minor (Orang-utan)f .

iii. Insectivora. All the four primary segments are in view from
above and succeed each other from behind forward (e.^. Ehynchocyon, '
African shrew) as in Reptilia. — Epencephalon. The cerebellum
presents few transverse convolutions ; the median, or vermiform lobe
is large relatively to the lateral lobes ; he pons rather small. — Mesen-
cephalon. The corpora quadrigemina;]: are large and exposed between
the cerebrum and cerebellum. — Prosencephalon. The cerebrum does
not extend over the cerebellum ; each hemisphere is much contracted
anteriorly. The corpus callosum is of limited extent; the hippo-
campi relatively large : there is no septum lucidum. The lateral
ventricles are continued into the rhinencephalon. The cerebral

* Huxley. Comp. Anat. (Ed. 1864) pp. 98-100.

t For the complete elaboration of the comparison of the convolutions of the
Brain of Man as compared with that of the Apes the student should consult M.
Pierre Gratiolet's " Memoire sur les Plis Cerebraux des Hommes et des Primates,"
of which the Appendix to this chapter is a summary.

X The 'optic lobes' of Talpa show no reduction of bulk commensurate with
that of the visual organ.

128 Mammalia. Nervous System,

hemispheres are devoid of sulci {e.g. Sorcx, Talpa, Erinaceus).
The RMnencepliala are long, large, and pyriform.

iv. Cheiroptera present the same type of brain as the Insectivora,
except that the cerebral hemispheres present a few simple folds on
their exposed surfaces.

V. Rodentia also, have a similar brain to the Insectivora, except
that the lateral lobes of the cerebellum are larger relatively to the
median lobe (esp. in Hare), though that still retains its large size.
The cerebellum is as a vrhole proportionally greater to the rest of
the brain in liodentia than in other Mammals. The anterior pair
(nates) of the corpora quadrigemina are larger than the posterior.
The cerebral hemispheres in the smaller species {e.g. Lepus,
Cavia) have only a very few shallow depressions ; they do not
always, though generally {e.g. Lepus, Castor), leave the corpora quad-
rigemina exposed. The cornu ammonis and corpus fimbriatum are
usually found very large : and the corpus callosum is of greater
relative extent than in Insectivora.

vi. Sectorialia. — Membranes. For the ossification of the tentorium,
see Osteology, sub. Sectorialia. In seals both the tentorium and
hind part of the/a/.r are ossified, and a thick ridge enters the fore
and under part of the falx between the rhinencephalic fossae. — JEpen-
cephaloji. The cerebellar hemispheres are more highly organised than
in the Rodentia : the smallest species have the smallest lateral lobes
in proportion to the middle one. — Mesencephalon. The posterior
pair (testes) of the corpora quadrigemina are the larger. — Prosence-
phalon. The cerebral hemispheres extend over part of the cerebellum :
in many of the Sectorialia they exhibit nothing more than a few
shallow grooves. In the Dog, Otter, and Seal, the convolutions are
far more numerous than in the feline tribes. The corpus callosum
is connected with the fornix by a septum lucidum.

vii. Prohoscidia. In the TJngulata the relative size of the lateral
lobes of the cerebellum increases with the bulk of the species, and
attains its maximum in the Elephant. This genus is remarkable for
a well developed cerebrum overlapping part of the cerebellum, and
for the excess of convolutions on the cerebral surface.

viii. Perissodactyla. The cerebrum always extends over part of
the cerebellum. In the Solidimgula the cerebral convolutions are
more numerous than in the majority of Sectorialia : the ' nates '
exceed the testes in size.

ix. Hyracoidea. The cerebral hemispheres present but few and
simple fissures.

Nervous System — Special. 129

X. Artiodactyla. In Muminantia the nates exceed the testes in
size.

xi. Cete. The olivary bodies are not covered by a * trapezoid '
layer of fibres. The brain is remarkable for its rounded form, and
for the proportional size of the cerebellum, especially of its lateral
lobes : the pons is large and prominent. The cerebral hemi-
spheres are highly organised in the Dolphins ; the sulci are very
numerous.

xii. In-Enamellata. The cerebellum is not covered by the
cerebrum ; its vermiform portion is considerable. The corpora
quadrigemina are not reached by the cerebral hemispheres. The
smaller and especially the insectivorous species have smooth low tri-
angular hemispheres, with small corpus callosum.

Impl AGENT ALIA. The Prosencephalon presents the following
differentiating characters*:

(«.) A peculiar arrangement of the folding of the inner wall of
the cerebral hemisphere : a deep fissure, with corresponding pro-
jection within, continued forwards from the hippocampal fissure,
almost the whole length of the inner wall. In other words, a
hippocampus major (instead of being confined, as it is at least in the
higher forms of Placental Mammals, to the middle or descending
cornu of the lateral ventricle), extending up into the hodij of the ven-
tricle, and constituting its inner wall.

(5. ) An altered relation (consequent upon this disposition of the
inner wall) and a very small development of the upper transverse
commissural fibres (corpus callosum).

{c.') A great increase in amount, and probably in function, of the
inferior set of transverse commissural fibres (anterior commissure).

xiii. Marsupialia. Epencephalon. — The Cerebellum presents trans-
verse convolutions, few in the climbing Koalas and Opossums, more
numerous in the locomotive Kangaroos : it is remarkable for the
large proportional size of the median or vermiform lobe as compared
with the lateral lobes, and the concomitant diminution of the
' Pons'. In nearly all there is a small, subspherical, lateral process or
appendage more or less projecting and sometimes lodged in a peculiar
fossa of the petrosal above the internal meatus. Mesencephalon. — In
most Marsupials (Dasyurus, Didelphys) the corpora quadrigemina
are more or less exposed between the Cerebrum and Cerebellum.

♦ Flower. Phil. Trans. 1865, p. 647.

130 Mammalia. Nervous Syste7n.

Prosencephalon. — The Cerebral Hemispheres do not extend over the
Cerebellum in any of the species : their external surfaces are un-con-
voluted in most Phalangistidae, Peramelidae, Didelphidse (Opossum),
and small Dasyuridse

xiv. Monofremata. JEpenceplialon. — The grey matter does not form
a corpus dentatum in the olivary tracts. The lateral lobes of the
Cerebellum are very small, and, concomitantly, the Pons also,
especially in Ornithorhyncus, where it assumes the form of a narrow
band ; but the median lobe is large, and in Echidna forms the main
bulk of the Cerebellum. Mesencephalon, — The posterior pair (testes)
of the corpora quadrigemina are not separated by a longitudinal
groove. Prosencephalon. — In Ornithorhyncus the Cerebral Hemi-
spheres overlap the Mesencephalon and reach to the Cerebellum : with
the exception of the hippocampal fissure and the depression lodging
the Hhinencephalic crus, the surface is unbroken and smooth. In
Echidna the outer surface of the hemispheres is extended by convolu-
tions. The ventricles are continued into the Phinencephalon, which
in Echidna is enormous.

3. — Nerves,
{a.') Olfactory

— are ahsent

in all the Cete save those with baleen, in which they are few and
small.

— exit from skull.

In the Ornithorhyncus is the sole known instance of the Olfactory
nerves quitting the skull by a single foramen, i.e. one for each Rhinen-
cephalon.

(5.) Optic.

— origin.

The optic nerves seem to be derived more wholly from the thalami
in Man than in most lower Mammals.

— exit from the skull.

In some Marsupials the optic nerve escapes by a cleft continuous
with the 'fissura lacera anterior.'

— size.

The Optic nerves are smallest in the Moles ; largest in the Giraffe,
(c.) Trigeminal or Fifth.

— This nerve attains its largest relative size in Ornithorhyncus

Nervous St/ stem — Special. 131

paradoxus, which, like the duck, uses its beak as a tactile instrument
in the detection of its food.

— The infraorbital branch is often of remarkable size, particularly
in those animals that are provided with a snout, or with large
vibrissas upon the upper lip, to the follicles of which it gives con-
siderable branches.

— The third division^ which supplies, from its ganglionic part,
the sensitive and secreting surface of the long tongue, is much
developed in Echidna. The size of the lingual branch of the
trigeminal is still more marked in the Pangolins and Ant-eaters,
esp. in Myrmecophaga jubata.

— The denta/ry branch of the Maxillary is large in Rodentia and
Froloscidia, to meet the demands of the active and persistent matrix
of the Incisors.

— The palatine nerves attain their maximum size in the Balcenida
in relation to the active and extensive growth of baleen.

{d) Hypoglossal or Ninth.

— exit from the skull.

The main roots of each hypoglossal, which quit the Macromyelon
usually in two bundles, escape in many Marsupials by two precon-
dyloid foramina.

— size.

In the Giraffe the motor nerve of the tongue is larger in propor-
tion to the body than in the Ox ; it is largest in the Pangolins and
Ant-eaters in relation to the great length of the tongue, and frequency
iand extent of its muscular motions.

132 ' Mammalia,

CEEEBEAL CONVOLUTIONS OP THE ANTHEOPID^
(MAN) AND SIMIAD^ (APES AND MONKEYS.)*

(Based on M.Gratiolet's jT/(???joe;Ve stir lesplis Gcribraux de V Homme et des Primates.)

Four structural peculiarities serve to distinguish the Brains of
Man and of the Apes from those of all other animals : — these are

1 . The rudimentary condition of the Olfactory lobes.

2. A perfectly defined Fissure of Sylvius.

3. A posterior lobe completely covering the Cerebellum.

4. The presence of a posterior Cornu in the lateral ventricles.

In the Brain of no other animal are these characters found to co-
exist simultaneously.

The Lemurs are excluded from this group, because in them the
Olfactory lobes are large, the Cerebellum is not completely covered,
and there is no posterior Cornu in the lateral ventricles.

Although these four characteristics are sufficient warrant for class-
ing an animal amongst the Apes, even if the external surface of its
Brain be absolutely devoid of Convolutions, still wherever Convolu-
tions do exist, they are always found to be parts of a definite ground-
plan or type, which pervades the whole series.

Owing to its medium development, the Brain of Cercopithecus
Saba3us displays most clearly the outlines of this ground-plan, as no
obscurity arises either from obliteration of the component primary
Convolutions, or from the development of secondary ones. In fact the
surface of the Cerebral Hemispheres of the higher Apes and of Man
is only a complication of that seen in the Cercopitheci, whilst that
of the lower Apes is a simplification of it.

* This paper was communicated by S. J. Sharker, Esq., B.A., Jesus College,
Oxford.

Cerebral Convolutions. 133

In the Cercopithecus Sabaeus the great Median Fissure divides the
Brain into two Hemispheres ; each Hemisphere having an external
surface, and an internal surface. The external surface comprehends
all that can be seen on taking a profile view of the Brain : the
internal, all that is seen on looking at the surface exposed by severing
the two Hemispheres from each other by a perpendicular section
through the great Median Fissure and Corpus Callosum. The line
formed by the junction of these two surfaces above, is the superior
border : that formed by their junction below, is the inferior border.
The most prominent point of the Frontal lobe, where the two borders
meet anteriorly, is the anterior or Frontal extremity : the point
where they meet posteriorly, is the posterior or Occipital extremity.

A. External Surface,

The lobes on the External Surface are,

1. Frontal.

2. Parietal.

3. Temporo-sphenoidal.

4. Occipital.

The Central lobe, or * Island of Eeil ' is hidden within the lips of
the Fissure of Sylvius, and corresponds with the inferior aspect of
the Corpus Striatum.

The External Perpendicular Fissure divides the External Surface
into an anterior and a posterior part: the posterior comprehending
the Occipital lobe : the anterior being divided again into two by
the Fissure of Sylvius. The portion above this fissure- embraces the
Parietal and Frontal lobes, that below it the Temporo-sphenoidal
lobe.

1. The Frontal lobe is limited posteriorly by the ascending branch
of the Fissure of Sylvius, or, as Mr. Huxley names it, the Antero-parie-
tal Sulcus. It is divided into an Orbital lobule and a Frontal lobule,
the former corresponding to that part which rests on the orbital plate
of the Frontal bone. The convolutions of the Orbital lobule are in-
constant: those of the Frontal lobule are three in number and all
longitudinal in direction, viz. : —

a. Superior Frontal. — h. Middle Frontal. — e. Inferior Frontal,
or Supra-ciliary.

2. Parietal Lohe. This Lobe is bounded anteriorly by the Antero-
parietal Sulcus, posteriorly by the External Perpendicular Fissure.

134 Mammalia.

Three well marked Convolutions belong to this lobe : two of them
are vertical in direction, and are separated from each other by the
Pissure of Rolando ; these are, («.) the anterior of the two, the First
Ascending Convolution, [h.) the Second Ascending convolution : {c)
the third is the Curved Convolution, which winds round the superior
extremity of the Parallel Fissure : this Convolution has an as-
cending branch, and a descending branch which is continuous with
the Middle Temporal Convolution.

3. Temporo-sphenoidal Lobe, This lobe lies below the Fissure of
Sylvius. It embraces three Convolutions, which are usually oblique
in direction ; they are

a. Superior Temporal. — l. Middle Temporal. — c. Inferior Tem-
poral.

The superior and middle convolutions are separated from each
other by the Parallel Fissure, around the summit of which winds the
Curved Convolution.

4. Occipital Lohe. The convolutions in this lobe are three in
number, and take a longitudinal direction. They are

a. Superior Occipital. — h. Middle Occipital. — c. Inferior Occipi-
tal.

The anterior border of the Occipital lobe often, as here, is thin,
and projects forward over the external perpendicular fissure : it is
then called the * Operculum.'

There are moreover on the external surface four Bridging Convo-
lutions, two of which are of considerable classificatory importance ;
mz. those which connect the Parietal lobe with the Occipital.

The first passes from the posterior extremity of the Second Ascend-
ing Convolution to the Superior Occipital Convolution. The second
passes from the summit of the descending branch of the Curved Con-
volution to the Superior Occipital. The third external Bridging Con-
volution connects the Middle Temporal with the Middle Occipital j
the fourth connects it with the Inferior Occipital Convolution. The
two latter are always superficial. The others are sometimes super-
ficially, sometimes deeply placed.

B. Internal Surface.

About the middle of the Internal Surface is seen the Great
Central Aperture, round which the Convolutions are ranged and
through which the Crus Cerebi passes upwards. It is divided into

Cerebral Convolutions. 135

two parts by the Fissure of the Hippocampus, which bifurcates
posteriorly. That portion of the Brain which is placed below this
Fissure, together with the Fascia Dentata (Pli Godronne, Grat.)^
which does not come into view on the surface, is called the Occipito-
Temporal Lobe. The rest of the internal surface is again divided into
two by the Internal Perpendicular Fissure, which runs down from
the superior border of the Hemisphere and stops short about on a
level with the posterior extremity of the Corpus Callosum. That
part of the Brain which is below or behind the Internal Perpendicular
Fissure, and between it and the posterior part of the Hippocampal
Fissure is the Internal Occipital LohuU ; that above and in front of it
is the Fronto-parietal Lobe.

1 . The Fronto-parietal Lobe is divided by the great Fissure of the
Frontoparietal Lobe into

a. An Inferior Convolution, Convolution of the Internal Zone, s.
Convolution of the Corpus Callosum. — h. Convolution of the External
Zone.

The Convolution of the Internal Zone expands posteriorly to form
the Quadrilateral Lobule.

2. In the Occipital Lobule the Convolutions are inconstant.

3. The Occipito-Temporal lobe comprehends,

a. The Superior Internal Temporal Convolution (Pli Godronne^
Grat.), which is placed above, and externally to the so-called anterior
part of the Hippocampal Fissure and does not appear on the surface :

h. The Middle Internal Temporal, placed below the Hippocampal,
and above the Collateral Sulcus of Huxley. This convolution ends
anteriorly in a large Lobule — lobule of the Hippocampal Convolution
(lobule de I'Hippocampe, Grat.)^ — and from the extremity of this
lobule a little hooked process curves backwards, which is the Hook
of the Hippocampal Convolution (Crochet de I'Hippocampe, Grat.) :

c. The Inferior Internal Temporal which consists of parts of three
Convolutions which also take part in the formation of the External
surface of the Hemisphere ; viz. the Inferior External Temporal, —
Inferior External Occipital, — and the Middle External Occipital
Convolutions.

Two Bridging Convolutions also belong to the Internal Surface.
They connect the Quadrilateral with the Occipital Lobule, and are
sometimes superficially sometimes deeply placed. They are the
Superior Internal Bridging Convolution which passes from the summit

136 Mammalia.

of the Quadrilateral Lobule, to the summit of the Occipital Lobule,
where it is continuous with the Superior External Bridging Convo-
lution: and, — the Inferior Internal Bridging Convolution which unites
the base of the Quadrilateral Lobule with the Inferior extremity of
the Occipital Lobule.

If the Brain of Man be taken as the standard of Cerebral develop-
ment, the position of any Ape in a classification, which has the
Kervous system for its basis, will depend upon the degree in which
its brain resembles that of Man.

The most striking features of the Human Brain are —

1 . Its great size and complexly convoluted surface.

2. The great development of the Frontal Lobe ; and especially of
the Superior Frontal Convolution, which is indicated,

{a.) By the position of the upper extremity of the Fissure of
Rolando, which reaches the superior border of the Hemisphere at a
point much further back than in the Apes' Brains : —

(5.) By the Antero-Parietal Sulcus meeting the Fissure of Sylvius,
not just above the Bend of the Fissure of Sylvius, as in most Apes,
but considerably further back : —

{c. ) By the horizontal position of the Fissure of Sylvius, which is
more especially due to the great development of the Superior
Frontal Convolution.

3. The small extent of the Occipital Lobe.

4. The comparatively small, and but slightly projecting Tcmporo-
sphenoidal Lobe.

5. The Obliteration of the External Perpendicular Fissure, owing
to the great size of the two Superior External Bridging Convolutions,
both of which are superficial.

6. The great Antero-posterior extent of the Corpus Callosum.

Amongst the Old "World Apes there are three groups, headed
respectively by the Orang-Ftang (Simla Satyrus), the Chimpanzee
(Simla Troglodytes), and the Gorilla, in each of which Cerebral
development seems to be progressing on a different plan.

Thus, in the group of which the Orang is chief, in which the brain
appears to be developing in the same direction as that of Man, the
Frontal and Parietal Lobes gradually increase in size and complexity,
the Occipital d^x^iim.'&iim^ pari passu: — in the Chimpanzee the Frontal
and Occipital lobes are most developed: — whilst in the Gorilla the
Parietal and Occipital Lobes predominate.

Cerebral Convolutions. 137

The Brain of the Orang is more massive than that of the Chim-
panzee, and that of the Chimpanzee than that of the Gorilla : but the
Occipital Lobe in the Gorilla is larger than in either of the other two
(a point of inferiority, since this lobe is so small in Man) ; and the
Frontal lobe is lower : moreover the Convolutions are probably less
complicated in the Gorilla's Brain : therefore the Gorilla has the
least highly developed Brain of the three.

In the Chimpanzee the Occipital lobe is large, — its Operculum
complete — the ascending branch of the Curved convolution generally
rises in front of the Fissure of Sylvius, and ascends a considerable
distance towards the superior border of the brain. The superior
External Bridging Convolution is generally absent ; the second is
large, but does not usually come to the surface.

In the Orang the Occipital lobe is of moderate size. — the Opercu-
lum scarcely perceptible — the Curved convolution rises on a level
with the summit of the Fissure of Sylvius — the superior Bridging
convolution is large and superficial — the second present, but hidden.

In Man the Occipital lobe is very small, and there is no trace of
an Operculum ; the origin of the ascending branch of the Curved
convolution is on a level with the summit of the Fissure of Sylvius,
and both the superior Bridging convolutions are large and superficial.
Therefore these three leaders will rank as follows

1. Orang-Utang.

2. Chimpanzee.

3. Gorilla.

The convolutions of the Brain are arranged after the same plan in
the Platyrrhine as in the Catarrhine Monkeys : and yet the former
have very distinctive Cerebral characteristics, and such as are not
found in the latter. Thus, besides the extreme reduction in the size
of the Frontal lobe, and the enormous development of the Parietal
in some, we find the second External Bridging convolution always
superficial in Cebus Capucinus ; the convolution limiting the summit
of the Fissure of Sylvius hidden in Ateles, without any part of the
fissure itself being covered ; and the ascending branch of the Curved
convolution continuous with the Superior Temporal in the same
Monkey — arrangements which do not find a parallel in the Old
World Series. The highest group (Sapajous, Grat.) contains
Mycetes, Ateles, &c.; they take the first rank, owing to their having
a comparatively larger Frontal lobe, and both superior External
Bridging convolutions present. Next to these come Cebus Capucinus,

138 Mammalia.

and Cebus Apella (Sajous, Grat.). The third group embraces, Callith-
rix, iNyctipithecus, Pithecia (Sagouins, Aotes, Sakis, Grat.). The
fourth, the Hapalidse, Hapale (Edipus, and Hapale Jacchus (Pinches
and Ouistitis, Grat.).

The importance of such characters as the slanting direction of the
ascending convolutions of the Parietal lobe, the elevation or depres-
sion of the Fissure of the Hippocampi, the height to which the
summit of the Curved convolution rises, and others of a similar kind
put forward in the table, depends on their being indications of the
greater or lesser development of certain parts of the Brain ; thus, the
convolutions of the Parietal lobe slant when they are pressed back-
wards by the increasing size of the Frontal lobe : — the Hippocampal
Fissure rises high in the connection with the greater development of
the Occipital lobe, or is depressed by increase in the lobes placed
anteriorly to it : — the Curved convolution is beaten down by the
development of the superior Bridging convolutions.

The following is Gratiolet's Classification according to Cerebral
Characters : —

1. Homo.

/ Simia Satyrus (Orang-Outang, Grat.)
2 \ Hylobates (Gibbons, Grat.)

j Semnopitheci (Semnopitheques, Grat.)

\ Cercopitbeci (Guenons, Grat.)
2 { Siruia Troglodytes (Cliimpanze, Grat.) \ Catarrhini (Pith^qiies, Grat.).

( Macaci (Yrais Macaques, Grat.) [

! Gorilla (Gorille, Grat.)
Cynocephali (Baboiiins, Grat.)
Macacus Ehesus (Macaques U queue courte,
Grat.)
[ Mycetes (Hurleurs, Grat.)
6 I Ateles (Ateles, Grat.)

( Lagothrix (Lagotriches, Grat.)
g ( Cebus Capucinus (Sai, Grat.)
( Cebus Apella (Sajou, Grat.)

iCallithrix (Sagouins, Grat) [ Platyrrhini (Cebes, Grat.).

Nyctipithectis (Aotes, Grat.)
Pithecia (Sakis, Grat.)
J. ( Hapale ffidipus (Pinches, Grat.)
\ Hapale Jacchus (Ouistitis, Grat.)

Organs of Touch, 139

OEGANS OF SPECIAL SENSE.

A. Organs of Touch.

There are but few examples of the special adaptation of
parts for tactile exploration ; such, however, may be noted
in the shape of tactile 2^cipillcB on the fingers or tail, or on tho
naked terminal integument of the nose, especially when pro-
duced as a snout or proboscis ; or again in the form of
vibrisscB (that is, hairs so connected by their sclerous basal
capsule and bulbs with sensory nerve filaments, as to receive
very delicate impressions by contact with extraneous objects
or impulse), which are commonly found on the upper or
lower lips, and at the angles of the mouth : or, lastly, as
expansions of highly sensitive membrane, in the shape of
wings, ear-conchs, &c.

Special.

— Tactile Papillce.

In Man the broad tips of the fingers are richly supplied with
penicellate plexuses of nerves, the terminations of which occupy
each the centre of a papilla.

In Quadrumana, tactile papillae are developed on the fingers and
on the prehensile tail (when present, e.ff. Ateles).

In the Shrew, Mole, Elephant, Tapir, and Pig, these papillae are
specially developed on the produced exploratory snout.

— JExpansions of Membrane.

The extent of surface and delicate organisation of the parts of the
skin forming the wings and ear-conchs of those of the Bat tribe that

140 Mammalia. Organ of Taste,

pursue volant insects, and the antennal nose-leaves of many species
(RhinolophidEe) relate to the perception of atmospheric impulses
rebounding from surfaces near which the Bat approaches in flight.

B. Organ or Taste.

The Tongue is more highly developed in Mammalia than
in the rest of the Yertebrata. There is occasionally found
underlying the tongue a flattened process bifid at the apex,
and presenting the appearance of a second tongue, this has
been termed the frsenal or sublingual plate. Beneath the
tongue, posteriorly to the tip, is frequently found a fibrous
or sclerous rudiment of the ' glosso-hyal,' called ' worm,' or
* lyttaJ The tongue is commonly divided into a free, gusta-
tive, prehensile part ; and a deeper, intermolar, masti-
catory or deglutitional part : of these — the former may be
developed to such an extent and have such mobility as to
suggest the predominance of the prehensile function, or, on
the contrary, may be capable of very little motion ; — the
latter may lack the intermolar enlargement. As a rule, in
Mammalia, the vascular and sensitive lingual membrane ad-
heres closely to the muscular tissue : occasionally its sanguine
tint is obscured by pigment, and presents a leaden colour.
Horny spines are sometimes found on the superior surface
anteriorly, and (though very rarely) at the base, on either
side the mouth.

Special.

— Frmnal Plate.

This lingual character prevails throughout the Strepsirrliine
group of Quadrumana.

— The Lytta

is well marked in the flesh-feeding Dasyuridm (Marsupialia) and
in the Sector ialia.

— The Intermolar Milargement

is well marked in the Rodentia and Ruminantia;
is absent in Qiiadrmnana, Secforialia, and others.

Organ of Smell. 141

— Molility.

The Rodentia offer the least, and the In-Enamellata the greatest
power of protrusion and mobility of the tongue in the whole Mam-
malian class.

— Structure^

Host Cetd offer a marked contrast to the other Mammalia in hav-
ing the skin of the tongue separated from the flesh by a layer of
blubber.

— Spines.

In the Felid(B (Sectorialia), JPteropidcB (Cheiroptera), and especi-
ally in Ornithorhyncus (Monotremata), the anterior part of the
tongue is covered with hard horny spines.

In the Bugong (Sirenia) a large but short thick retro verted horny
process projects from each side of the base of the tongue.

C. Organ of Smell.

The Olfactory organ of Mammalia is seldom absent ; it
differs from that of other Yertebrata both in the cribriform
lamina of the Ethmoid (of which the apertures transmit the
branches of the first pair of nerves to the nasal cavity) — in
the sinuses, subsidiary cavities usually divided into mutually
communicating cells, which may exist in the frontal, sphenoid,
and superior maxillary bones ; and- — in the great provision
made by bony and gristly laminae for the support of the
olfactory membranes. It is very exceptional to find this
organ wanting, but the extent of its development is very
variable, especially in the matter of the accessory cavities.
There is frequently* found, on each side of the cartilaginous
reptum of the nose, a longitudinal sac, surrounded by a car-
tilaginous sheath, and lined internally by a glandular mucous
membrane, which communicates with a duct running through
the foramina incisiva to the palate. Of the three turbinated
bones, the inferior is generally most developed. In animals
provided with a snout the nasal cartilages are lengthened
out into a tube, w^hich is covered with muscles that move it

* Ruminantia and Rodentia.

142 Mammalia. Organ of Hearing.

in many directions. Diving animals have valves*, or an-
nular sphincter musclesf, whereby the nasal passages may be
closed internally.

Special.

Olfactory Organ absent.

All Cete possess the * crura rhinencephali '; but the baleen-bearing
"Whales alone of this Order have olfactory nerves ; the family Del-
phinidce presenting the exceptional instance of the absence of the organ
of smell.

— Cribriform plate.

Ornithorhyncus forms the single exception in the Mammalian class
to the constant presence of a cribriform plate : in this species one
olfactory nerve quits each rhinencephalon and escapes from the skull
by a single foramen ; not dividing until it enters the nasal cavity.

— Accessory cavities : Turbinated bones.

The Cete have no accessory cavities in the cranial bones in con-
nexion with the nasal cavity. In the Dolphin and Narwhal there
are no turbinated bones.

D. Organ of Heading.

The Organ of Hearing is commonly formed throughout
the Mammalian Class on the same general plan that it is in
Man : the chief distinctive features of the Class being

1. The extension of the Cochlea into coils, suggestive of the
name :

2. The ossification of the Cartilages between the stapes
and tympanum, forming the * malleus ', and commonly also
the * incus': and

3. The presence, save in most swimmers and burro wers,
of an external ear or conch.

It is only in the Orangs and Chimpanzees that the parts
defined in the human auricle are represented : the Concha^
when present, may be quite rudimental, and is sometimes
represented only by a small scale-like fold of thin integu-
ment, contrasting very markedly with the trumpet- shaped

* Ornithorhyncus. f Seal.

Organ of Hearing, 1^3

cartilage commonly found, and with the pendulous flaps of
the Elephant. The Meatus externuB is generally osseous.

The Tympanic cavity is by no means always concealed in
the petrous bone, as it is in Man ; it is sometimes expanded
into a ^ bulla'; and may extend into the Squamosal and
Pterygoid bones*. The tympanic bone frequently retains its
freedom, and is more or less subservient to the support of the
drum membrane. The Basisphenoid sometimes f enters into
the formation of the tympanic cavity.

The Three Auditory Ossicles (Otosteals) can in general be
distinguished ; viz., the Malleus, the Incus with the Os orbicu-
lare, and the Stapes, although their forms undergo consider-
able changes. Thus, the Malleus occasionally bears a close
resemblance to the * cartilage columellse' of Birds ; or it may
assume an expanded lamelli-form type ; or be bent, complet-
ing the circle for the drum-membrane, and expanding for its
attachment thereto ; or, lastly, it may be perforated. Again,
the Stapes may have a wide vacuity and slender crura, and
be traversed by a bony canal surrounding the trunk of a
nerve and vessel (arteria ophthalmica and maxillaris, or
arteria meningea media :|:) which pass through the stapes and
the tympanic cavity : or it may be columelliform, its oval
base supported on an imperforate stem, which may or may
not develope processes marking out the Incus : or it may
retain the normal Mammalian shape, and have very thick
crura, by which the perforation is obliterated or reduced to
a minimum.

The bony Semicircular Canals occasionally project from the
petrosal capsule within the cranium : in many, though not
in all of the Mammalia, these canals open by five orifices
into the vestibule : there are nearly always three ampuUaj
present.

* Sloth. t In Hedgehog (Insectivora) and Marsupialia.

X In Cheiroptera.

144 Mammalia. Organ of Hearing.

Of all parts of the Labyrinth the Cochlea varies most;
m., in the number of its coils, which may present all
degrees of complexity, from half 2^ turn to nearly ^i?tf complete
turns.

While in Man the muscles of the external ear are only
feebly developed, so that it can be but slightly moved,
very numerous muscles turn the Ear of the lower Mammalia
in all directions. In many diving animals peculiar valve-
shaped projections are found, by which the external meatus
is closed and protected against the entrance of water.

Special.

1 . The Concha is absent or rudimentary

in the 7a/j!?/'</<s(Insectivora); — in the Phocidce^TA Tnch(ecid(B{^eQ'
torialia Pinnigrada) : — in the CeteivfYiero, in a full-sized Cachalot, the
external opening of the ear is a longitudinal slit, one inch in length,
admitting with difficulty the end of the fore-finger ; and in the com-
mon Porpoise and Dolphin is so small as to require search in detect-
ing) : — in the Sloth (rudimeutal) and Mams (scale-like) of the In-
Enamellata : and — in the MoJiotremata. (In the Echidna the external
aperture presents the form of a vertical slit, shaped like the italic aS,
an inch and a half in length.)

2. Meatus externus.

In Echidna the remarkably long Meatus is strengthened by a
series of incomplete cartilaginous hoops, connected together by a
narrow longitudinal cartilaginous band, so that its structure closely
resembles that of a trachea. The narrow tortuous meatus of Orni-
thorhyncus has a valve externally.

In the Water Shrew the antitragus can be brought forward so as
to close the external meatus at will.

3. Malleus.

— Bird-like : e.g. Perameles (Marsupialia).

— Lamelliform : e.g. Shrews (Insectivora).

— Circular: e.g. in the Armadillos (In-Enamellata) where the
Malleus is bent, almost, as in the Monotremata, completing the circle
for the drum membrane.

— Perforated : e.g. in the "Wolverine (Plantigrada ; Guh^ and Otter

Organ of Hearing. 145

(Semiplantigrada, Lutra) of the Sectorialia the Malleus is perforated
near the origin of the process.

4. Stapes and Incus.

— Terf oration transversed hy osseous cylinder.

In most Insectivora {e.g. Mole) part of the osseous wall of the
labyrinth conducts a vessel and nerve through the opening of the
Stapes.

This is also the case in many Rodentia {e.g. Squirrels, Cavies,
Marmots).

— Avian type.

In some Bats (Cheiroptera), e.g. Vespertilio noctula, maybe noted
a retention of the columelliform confluence of Stapes and Incus.

In most Marsupialia {e. g. in Perameles), and Monotremata, the
Stapes is columelliform ; its base oval, supported on an imperforate
stem ; its apex being more expanded in the former than in the latter
Order.

— Stapes imperforate.

In addition to the above-named instances ; note this also in the
Walrus (Sect. Pin.) and Delphinus leucas (Cete).

5. Semicircular Canals.

In most Insectivora the bony semicircular canals project from the
petrosal capsule within the cranium, and conspicuously so in the
Mole (Talpa), in which the petrosal is large and cellular.

All insectivorous Cheiroptera and Monotremata likewise show this
same projection.

6. Vestibule, &c. '

In the Whales the Vestibule of the labyrinth is all but wanting.
In the Sloths there are only two * ampullae,' none being met with
upon the external canal.

7. Cochlea, &c.

In the Monotremata the Cochlea has only a half coil ;
in Bimana, Quadrumana, Cheiroptera, SoUdungula (Perrisso-d.),
and Rumiiiantia (Artio-d.), two and a half qotI^ ;
in Sectorialia three coils ;
in most Rodentia four ; in Caelogenys Paca nearly ^t^e coils.

146 Mammalia. Organ of 8ight,

E. Organ of Sight.

It is only in Man and the Apes that the eye is situated in
a complete bony cavity ; in all the rest of the Mammalia the
Orbital fossae are completed, and separated from the Temporal
fossae by membrane only. Eyes are always present in this
Class, but they are occasionally very rudimentary, and covered
by the skin, which passes over the eyeball without any palpe-
bral opening or loss of hair. They frequently hold a lateral
position, and if, when this is the case, the Cornea is also pro-
minent, they are susceptible of receiving the image of a pur-
suer without turning the head.

The Eye is commonly moved by six Muscles, as in Man ;
of these, the ' Superior oblique,' (which arises from the back
part of the rim of the orbit with the Recti, advances to the
upper part of the rim, glides there through a tendinous pulley,
returns towards the eyeball, is reflected backward and out-
ward beneath the Hectus superior, and is inserted into the
Sclerotic between this muscle and the Rectus Extemus), de-
mands special notice inasmuch as the trochlear arrangement
thereof is peculiar to the present Class. — Besides these there
exists in all Quadrupeds up to the Quadrumana another
muscle which runs from the margin of the Optic Foramen,
surrounds the Optic nerve, and expands like a funnel as it
approaches the back part of the eyeball to which it is fixed ;
this is termed the * Choanoid Muscle,' or Suspensorius Occult;
it is generally single, but may be bifid, or even quadrifid ;
and occasionally, though very rarely, is the only muscle
present. — The lower eyelid has occasionally a special depressor,
or apertor muscle. — And the Third eyelid a special ' nictitator*
muscle, which however has not the same arrangement as in
Birds. — Lastly, an ' Orbicular' muscle, to close the circular
eyelid, may be present.

The longitudinal axis of the eye is generally of less extent

Organ of Sight. 147

tlian the transverse*: but the relative size of the eyeball
seems to increase directly with the increasing power of loco-
motion of the different species, even in those of the same
Order. The eyes are generally small in those species that
burrow.

In no Mammal is bone developed in the Sclerotic ; but this
investing membrane is itself occasionally ^fibro-cartilaginous',
and may be present in great thickness especially round the
entrance of the Optic Nerve. The Cornea, which generally
presents a more or less convex surface externally, is flat in
the Aquatic Mammalia. In all Mammalia, Monodelphous,
and Didelphous, as far as at present observed, the Lem and
Ciliary muscle do not differ in any essential point from those
of Man. In all other Mammalia the Lens is more spherical
than in Man, especially in Aquatic species : in most, the
central planes are three, as in the human foetus : in a fewf
there is but one. The Capsule, its epithelium, and the lens-
fibres, are essentially like those of Man. The Ciliary pro-
cesses are simple ; the suspensory ligament and its connexions,
the arrangement of the Ciliary muscle (which derives its
nerves from the lenticular ganglion), and the kind of muscular
tissue (imstriped), are such as we find in the Human eye:|:.
The Pupil is almost invariably circular, but is sometimes
capable of being contracted to form a vertical slit : occasion-
ally also the pupil is found transversely oblong, with the
upper border somewhat festooned by the presence of a Liga-
mentum pectinatum.

Tuft-shaped flakes of pigment, called the Racemiform, or
sponge-like bodies, are occasionally found projecting from the
pigment layer (Uvea) at the posterior surface of the Iris, and
tending to interrupt the regular margin of the Pupil.

* Except in Man and Apes,
t Cete and some Rodentia.

148 Mammalia. Organ of Sight.

Crepuscular and Nocturnal Mammals {e.g. Pteromys, Aye-
Aye, Lemur) have a large convex Cornea, very wide Pupil,
and convex Lens (esp. Bats and Nocturnal Eodents). —
Aquatic Mammals, on the contrary, have an excessively
convex Lens, but very slightly projecting Cornea.

In many Mammals the Choroid^ instead of being uniformly
lined with dark pigment, as in Man, presents, on a greater or
less extent of its back part, a brightly coloured layer, named
Tapetum, on the inner surface of which is the tunic of Ruysch
{i.e. the inner part of the Choroid Coat formed by the capil-
laries of the Choroidal vessels), as well as the layer of hexago-
nal cells, which, however, is here, as in the eye of the Albino,
destitute of pigment. The Tapetum consists sometimes of
tendinous fibres, sometimes of cells, filled with granular
matter *: it is of various colours, e.g. silvery, white, white
edged with blue, light blue, green, amber, chocolate : it occu-
pies a broad transverse tract of the Choroid ; and may present
a Crescentic form, the greater extent being below the entrance
of the Optic nerve, and only a small portion above. No Ta-
petum is found in Bimana, nor in Quadrumana, above the
Lemurs.

The Macula lutea of the Petina, or * yellow spot ' of Soem-
merins:, appears to be confined to the eye of Bimana, and of
the higher Quadrumana.

The eye is occasionally closed by a single circular Eyelid
with a small round opening in it, and protected by a car-
tilaginous plate continued from the upper part of the Orbit,
comparable to the palpebral plates in the Crocodile : such
circular eyelid may however have the division of the hori-
zontal eyelids indicated by an external groove at the inner
Canthus*. As a rule there are three eyelids present, two being
horizontal : of these the lower one is generally the largest

* Leidig. * jtnvhs, the coi-ner of the eye.

Organ of Sight, 149

and most movable, and rarely has a proper * depressor' muscle,
but falls down by its own elasticity on the relaxation of the
* orbicularis ' which draws it up. The upper eyelid is occa-
sionally provided with cilia. The third, innermost, eyelid is
vertical, and termed the membrana nictitans, it contains
muscular fibres, and extends over the eye when that is drawn
back by the action of the * suspensorious' muscle ; it is some-
times small, rudimentary, or absent.

The Lachrymal Glands are often small, and sometimes ap-
pear to be wanting. A special gland, subserving the move-
ments of the third or nictitating eyelid, termed the Harderian
gland, is present in all quadrupeds up to the Quadrumana,
though occasionally represented merely by an aggregate of
follicles, somewhat more complex than the 'Meibomian,' at
the inner side of the eyeball*. The group of glandular fol-
licles sometimes found occupying the recess of the inner
canthus, and named the * Caruncula Lachrymalis,' are gener-
ally absent when the Membrana Nictitans is much developed,
and therefore seldom coexist with the Harderian gland. In
all Mammals with divided or horizontal eyelids there is found
a provision for carrying ofi" the waste lubricating fluid of the
ej^eball, similar to that in Man.

Special.

1. Uye.

— Rudimentary y &c.

In certain burrowing Insectivora, and Rodentia, e.g. Chrysoehloris
and Talpa caeca (Insectivora); Spalax typhlus (mole rat), Mus typhlus
(Rodentia).

— Situated laterally with prominent Cornea.

e.g. in JerloidcB and Leporidce (Rodentia) ; and Horse (Pcrissodac-
tyla, Solidungula).

in Ruminantia (Artiodactyla) the eyes are lateral.

♦ e.g. in Cete and Proboscidia.

150 Mammalia. Organ of Sight,

2. Suspensory Muscle

— is divided

in Cete into four short muscles, paralleling the longer recti, but
of greater breadth, and almost continuous.

In Rhinoceros (Perissodactyla, Multungula) the fasciculi of the
Choanoid Muscle have coalesced into two masses.

— is alone present

in the Balcence (Cete), in the absence of the other muscles of the
eye*.

— is rudimentary

in lower Quadrumana; where a few fibres detached from the
inner part of the origin of the recti to be inserted into the sclerotic
nearer the entry of the Optic Nerve represent it.

3. * Depressor' of lower eyelid.

In Rhinoceros and Monotremata the lower eyelid has a depressor
muscle.

4. ^ Nictitator'* muscle.

In Elephas (Proboscidia) there is a special * nictitator' muscle,
the fibres of which pass at first over the base of the membrane in a
curve, then form an angle to include the extremity of the nictitating
cartilage, which is consequently moved in the diagonal of the con-
tracting forces.

5. ' Orbicular^ muscle.

In Cete, and Seals (Sectorialia) the circular palpebral opening is
closed by an * orbicular' muscle, or sphincter, and is expanded by
four broad, thin, almost continuous muscles {e.y. Porpoise).

6. The Sclerotic coat.

In the Ornithorhyncus the * Sclerotic' ib Jihro-cartilayinous.
In the Cete the Sclerotic is excessively thick, as also in the Pro-
boscidia, at the entrance of the optic nerve.

7. The Pupil

— contracts to a vertical slit

In the Pradypodidce (In-Enamellata) and the small crepuscular f
Felidae (Sectorialia).

— is transversely oblong
in Camel, Ox, and Sheep.

* Mayer. t In the large diurnal Felidse it is circular.

Organ of Sight, 151

8. The Lig amentum pectinatum

in Man consists of slight festoon-like processes of the fihres of the
Iris, lying in a transparent elastic fibrous tissue, continuous with
the posterior elastic layer of the Cornea :

in the eyes of the Sheep and Ox it is a more developed structure
than in the Human eye, and in them the festooned processes are
prominent, giving a milled appearance like that of the edge of a
coin.

Racemiform bodies projecting from the Uvea are found in the
Solidungula and Euminantia generally.

9. The Tapetum

— in colour is

— usually green in Perissodactyla* (except in Horse, in which it
is light Hue) ; in most Artiodactyla (being, however, chocolate in the
Hog), and in Proboscidia : but is silvery white in the Cete, and most
Sectoralia (except in the Felidae, in which it is amber, and the Canidse,
in which it is white, edged with blue) :

— in structure

it consists of tetidinous fihres in Euminantia and Proboscidia : and
of cells filled with granular matter in Sectorialia.

— in form

it is broadly crescentic in Felidce (Sectorialia).

10. The Retinal spot.

Quadrumana. This spot, situated in or very near the axis of
vision, exists in the Catarrhina as in Man : but has been found in
no Lemurine (in which a minute fold or crease occupies its place).

11. HhQ Eyelids

— are single and circular
in Monotremata.

In Cete the eyelids are represented by a continuous circular fold
of the skin, leaving a round opening in front of the eye, with a
narrow margin unprovided with eyelashes : this is also the case

in Seals (Sectorialia), where however an external groove indicates
the division of the horizontal eyelids.

— The upper Eyelid is provided with Cilia

in all Euminantia ; they are especially long in Giraffe.

* It is absent in Ehinoceros.

152 Mammalia. Organ of Sight,

— Memhrana nictitans may he rudimentary or absent .

In Man and the Quadrumana, at the inner Canthus, opposite the
puncta lachrymalia, there intervenes a vertical fold of conjunctiva,
the plica semilunaris, resting on the eye ball, which is a rudiment of
the membrana nictitans.

The presence of this eyelid in the Sirenia distinguishes them from
the Cete, in which it is absent.

12. The Lachrymal glands.

In the Cete there are no true Lachrymal glands : but in the
Dolphins a ring-shaped gland behind the eyelids is present*.

— Caruncula Iqchrymalis coexists with Harderian glands in the
Hog tribe and the Sheep.

Rapp.

Dissections, 153

DISSECTIONS.

I. SHEEP'S HEART*.

Preparatory. — Inject with coloured size the Coronary
arteries from their orifices in the sinuses at the root of the
Aorta.

The only difficulty in dissecting a Sheep's heart lies in
the mass of fat you have to contend with round its base
(i.e. that portion which is directly attached to the great blood
vessels). Now in order to remove the fat, do not attempt to
slice it away from the outer surface ; if you do, you will
assuredly cut through superficial vessels (i.e. the coronary
arteries and veins) and cut into others : but taking each
portion of fat separately, carefully separate it by dissection
from the subjacent tissue, and never cut across any structure
until you are perfectly satisfied as to what it is.

EXA.MINATI0N OF THE ExTERiOR. — When the fat has been
cleaned away ; taking the Heart in your hand you will note
one half to be more easily indented than the other ; this
marks the area of the thin- walled right f Ventricle : the thick-
walled left Ventricle occupying the larger part of the anterior
surface.

* In order to eec the first course of the vessels after learing the heart, it will
be well to obtain the heart and lungs together : as, however, we purpose tracing
them when dissecting the complete specimen of a Mammal, we have described
here the heart alone.

t In using the terms right and left we speak of the heart as situated in the body.

X

164 Mammalia,

Placing tlie heart before you, with the apex towards you,
and this right ventricle to your left, you will observe (1) a
large vessel rather to the right of the median line, and arising
from the base of the Heart : this is the Pulmonary Artery
which conveys venous blood to the Lungs ; (2) a distinct
groove crossing the anterior surface of the Heart diagonally
from the left centre of the base to a point a little below the
middle of the right margin : this groove marks the line of the
interventricular* septum and carries the proper nutrient vessels
of the Heart, viz. the Coronary arteries and veins, in its
channel ; (3) a large vessel immediately posterior to the Pul-
monary artery : this is the Aorta which conveys arterial blood
to the body generally ; (4) folded ear-like appendages at the
base of each ventricle : these are the Auricles ; and (5) a groove
between the auricles and ventricles termed the Auriciilo-
ventricular Sulcus.

By the aid of the coloured injection thrown into them
it will be well now to trace out the principal branches
of the Coronary Arteries. There are normally two Coronary
arteries, one arising from the left, and the other from the
right sinus of Valsalva (two small internal pouches in the
anterior segment of the root of the Aorta) as in Man ; their
distribution is, however, different : for in the Sheep the right
Coronary Artery takes a short course in the groove between
the right auricle and the ventricle, behind the cone at the
base of the Pulmonary artery, and then sends off a short
branch posteriorly to the auricle, its main stem continuing
along the right margin of the Heart : while the left Coro-
nary Artery immediately on leaving the Aorta divides into
three branchesf, one running along the anterior interven-
tricular groove ; the second traversing the left border of the

* i.e. the Septum, wliicli separates the cavities of the two ventricles.

t As an abnormality the third branch is sometimes found commencing by a
distinct orifice in the left sinus.

Dissection of Sheep^s Heart, 155

Heart ; and the third taking a course close under the left
auricle in the Auriculo-ventricular sulcus, and reaching to the
back of the heart and the posterior interventricular groove.

Lastly, we may note on the exterior of the ventricles
several white lines running across the superficial branches of
the vessels ; these are Nerves derived from the Cardiac plex-
uses*, which are themselves derived partly from the Cerebro-
spinal and partly from the Sympathetic systemf.

Turning the Heart over, the transverse groove which goes
round the base of the Heart between the Auricles and Yentri-
cles, and which is interrupted only by the trunk of the Pul-
monary artery anteriorly, is readily traced : the vessel in close
relation with and posterior to the Aorta, and opening into
the right Auricle at its superior border, is the Vena Cava
Superior, which conveys to the Heart the blood which is re-
turned from the Head, Neck, Upper Limbs, and Thorax, and is
remarkable as being a vein without valves : the vessel nearly
in the middle line, and terminating in the right Auricle a
little above its inferior margin, is the Vena Cava Inferior,
which returns the blood from the Lower Limbs, from the
Viscera, Pelvis, and Abdomen : that vessel which passes down
to the side of the left Auricle immediately behind the Appendix,
and continues its course along the back of the left Auricle and
Auriculo-ventricular groove to reach the lower and back part
of the right Auricle, on the left of the Orifice of the inferior
cava, close to the interauricular septum, and below and behind
the fossa ovalis (like the left superior cava in the lower
Mammalia and in Birds), is the large Left Azygos Veinp, it

* The deep Cardiac plexus is situated inferior! y to the Trachea at its hifurca-
tion ; close to the point of division of the pulmonary artery, and above the
arch of the Aorta. The superficial Cardiac Flexus lies within the arch of the
Aorta and beneath the right Pulmonary artery.

t In order to expose these more clearly, let the heart be placed in a Nitric acid
and spirit bath, consisting of 6| drs. of acid to one quart of spirit, for three
or four days. — C. Robertton.

1 J. Marshall.

156 Mammalia.

receives all the Intercostal veins of its own side, and the lower
right Intercostal veins also : its lower part is alwaj^s dilated
and muscular : the Coronary vein opens into it, as also a series
of small veins from the back of the heart, the mouths of which
are all provided with valves, while, on the contrary, no valves
exist along the continuation upwards of the large venous
trunk (azygos), at least in the neighbourhood of the Heart.
We find then in the Sheep, as in most large Quadrupeds, a
right Yena Cava Superior and a left Azj^gos Venous Trunk,
instead of a right Yena Cava Superior and a left Cardiac
Yenous Trunk or Coronary Sinus as in Man. The size of the
left Azygos is complementary to that of the right : hence we
find the right Azygos in the Sheep is insignificant ; whereas
in Man, in whom the left Azygos is all but obliterated*, the
right Azygos is large. A further correlation of growth may
be noted, viz. that whereas the Thebesian valve is present in
every instance in which the left venous trunk forms a ' Coron-
ary Sinus ' receiving veins from the heart alone (as in Man) ;
it is certainly absent in those animals which have a left Azygos
or left Superior Cava, being represented in the Sheep merely
by a slight ridge of the Auricular Parietes. Situated superi"
orly to the dilated portion of the Left Azygos may be seen
the cut orifices of the Pulmonary Veins, which return the
blood from the Lungs and are without valves. Hence we see
that the Auricular portion of the Heart is immediately con-
nected with the great Yeins : and the ventricular portion with
the great Arterial trunks.

* The remnant of the obliterated left Azygos trunk of the Foetus exists in the
adult, as (i.) an oblique Auricular yein running in a direct course from the back
part of the left Auricle to open into the ' Coronary Sinus,' unprotected by any
valve at its mouth, (ii. ) lines or streaks continued upwards from this vessel on
the wall of the right Auricle, (iii.) a further prolongation in the shape of a small
duplicature of the serous layer of the pericardium, passing between the left
Pulmonary artery and the subjacent Pidmonary vein, termed by Marshall the
Vestigial Fold of the Fericardiiim,

Dissection of Sheeph Heart. 157

Dissection of Right Aurict.e. — In order to examine tlie
interior of the right Auricle it will only be necessary to make
one incision, viz. from the point of entrance of the Yena Cava
inferior to the Auricular appendage ; and to remove and wash
out the blood.

Around and in the interior of the Appendix are fleshy bands,
named Musculi Pectinati, which form a net-work contrasting
with the general smoothness 6f the Auricle. Immediately
opposite the termination of the Inferior Cava is a large oval
depression. Fovea, seu Fossa Ovalis, which is the vestige of the
Foramen Ovale of the Footal Heart, and indicates the original
place of communication between the two Auricles ; it is bounded
by a prominent ridge of muscular fibre called Annuhis, seu Isth-
mus Vieussenii : a thin semitransparent structure closes the
Fossa and forms the Septum Auricularum. In front of and be-
neath the Inferior Cava is a thin fold of the lining membrane of
the cavity, a rudiment of the Eustachian Valve, a remnant of a
much larger structure in the Foetus by which the blood from the
Inferior Cava was directed through the Foramen Ovale into
the left Auricle. Immediately beneath the Eustachian Yalve
is the dilated orifice of the left Yena Azygos ; at its termination
and almost within the Auricle may be seen the mouths of the
smaller veins of the Heart (venae cordis minimse; named the
Foramina Thehesii. Between the openings of the Superior and
Inferior Cava, on the right side of the wall of the Auricle is
a small projection termed the Tubercle of Lower : it was sup-
posed by Lower to direct the blood from the Superior Cava
towards the Auriculo-ventricular opening {i.e. the opening
between the Auricle and Yentricle) . The orifice of the Superior
Cava is not provided with a valve.

In the Adult there is but one current of blood in the right
Auricle, viz. towards the Yentricle : but in the Foetus thero
are two streams in the cavity of the Auricle : one of pure and
the other of impure blood, which cross one another in early

158 Mammalia.

life, but become more commingled as birtb approacbes. Tbe
Placental or pure blood, entering by tbe Inferior Cava, is
directed by tbe Eustachian Yalve chiefly into tbe left Auricle
tbrougb tbe Foramen Ovale ; wbile tbe current of tbe Sys-
temic or impure blood, coming in by tbe Superior Cava, flows
downwards in front of tbe otber to tbe rigbt ventricle*.

Dissection of Right Yentricle. To examine tbe interior
of tbe rigbt Yentricle tbe dissector will pass tbe forefinger
of tbe left band tbrougb tbe Auriculo-ventricular orifice, and
make an incision witb tbe scalpel a little to tbe rigbtf of tbe
anterior interventricular groove, from tbe base or origin of
tbe Pulmonary Artery to near tbe apex of tbe Heart, and carry
tbe incision round posteriorly a little to tbe rigbt of tbe
posterior Inter- ventricular groove up to tbe Auriculo-ventri-
cular groove.

On raising tbe Y-sbaped flap tbus formed, tbe base of tbe
ventricular cavity will be seen to be perforated by two
apertures ; tbat on tbe rigbt, leading into tbe Auricle, is tbe
right Auriculo-ventricular opening; tbat on tbe left, and bigber
up, is tbe Infiindibulum, or moutb of tbe Pulmonary Artery.
Tbat wall of tbe Yentricle comprised in tbe Y-sbaped flap is
comparatively tbin, and bas its internal surface marked by
projecting flesby bands of muscular fibres, called ColumncB
CarnecB : of tbese, tbose tbat project freely into tbe cavity and
give attachment by their free ends to tbe little tendinous cords
of the valves of tbe auriculo-ventricular opening are named
Musculi Papillares. The left or inner wall of tbe Yentricle is
much smoother, especially near the aperture of the Pulmonary
Artery. A strong moderator band will be noticed passing
from one wall of tbe Yentricle to tbe other ; this band is
generally found where the life of the animal depends upon its
speed. Surrounding the Auriculo-ventricular orifice is a strong
fibrous band, from which is prolonged a thin membranous

* Ellis. t See note, p. 153.

Dissection of Sheeph Heart. 169

valve which projects into the cavity of the Ventricle : near
its attachment to the Heart this valve is undivided, but it pre-
sents three chief points at its lower margin, and is thence
named the Tricuspid Valve ; to the free margin of this valve
are attached the small tendinous cords, Chordoe Tendinece,
above mentioned.

During the contraction of the Yentricle the valve is raised
by the blood, so as to close the opening into the Auricle ; but
the further protrusion of it into the auricular cavity is arrested
by the small tendinous cords.

From the funnel- sHaped part of the right Yentricle the
pulmonary artery arises ; at its mouth are seen three Semi-
lunar or Sigmoid valves : these should be further brought to
view by prolonging the incision in the anterior wall of the
Ventricle upwards, into the pulmonary artery, between two of
the segments of these valves. In the free margin of each
valve there is seen a slightly thickened nodule called the
Corpus Arantii; and in the wall of the artery, within each
valve, and on a level with the free margin, is seen a slight
hollow, called the Sitius of Valsalva*

When the blood is entering the artery these valves are
pressed against the wall ; but when the distended artery re-
acts upon the contained blood, the valves are thrown towards
towards the centre of the cylinder and arrest the return of the
blood to the Ventricle.

Dissection of Left Auricle. — A cut should be made with
the scissors from the entrance of the right pair of pulmonary
veins {i.e. just above and to the left of the fossa ovalis) to the
free extremity of the Auricle.

The Musculi Pectinati, and the Auriculo-ventricular orifice
will be seen to resemble those in the other Auricle : and on
holding the septum between the Auricles to the light, a slight

* These are better marked in the Aorta.

160 Mammalia.

indication of the superficial semi-lunar fossa (whicli is well
marked in man), may be seen ; i.e. the now adherent border
of a membranous valve which during foetal life is applied to
the left side of the then open Foramen Ovale. The mouths
of each pair of Pulmonary veins open close to one another ;
those from the right lung open into the extreme right of the
Auricle, near the septum ; those from the left lung open in
both cases close to the left Yena Azygos. The Pulmonary
veins are not provided with valves.

Dissection of Left Ventricle. — In order to expose the
internal aspect of the left Ventricle, an incision should be
made through its anterior wall, just below the Coronary
artery that supplies the left side of the Heart, and to the left
of the septum ; and should be continued parallel with the ven-
tricular groove round the right of the Apex to a point a little
to the left of the middle line posteriorly, and then upwards
until it; meets the left Coronary artery at the point where it
descends to run along the ventricular groove at the back of
the Heart : on raising this triangular flap it will be necessary
to cut across several small fibrous bands which run from the
free outer wall of the Ventricle to the Inter-ventricular
Septum.

The walls of this Ventricle will at once be noticed to be
considerably thicker than those of the right Ventricle. Its inter
nal surface is much marked by the projecting Columnae Car-
neae, except near the Aortic opening. The Musculi Papillares
are collected for the most part into two great bundles, whence
proceed the numerous Chordae Tendineae with which the two
segments of the Auriculo-ventricular valve are furnished.
This valve, which is called * Mitral' from a fancied resemblance
to a Mitre, is attached both to a fibrous ring surrounding the
Auriculo-ventricular aperture, and, in part, to the Aortic ring :
the right segment of this valve alone intervening between the
the Aortic and Auriculo-ventricular apertures. The open-

Dissection of Sheep^s Brain, 161

ing of the Aorta is close to the Septum Ventricularum, and is
guarded by three Sigmoid valves, larger and stronger through-
out than those in the Pulmonary artery : from the two
anterior Sinuses of Yalsava arise the Coronary arteries.

The bone of the Heart (cf. supra, Circulation) though gen-
erally present in Buminants does not appear in the Sheep till
in advanced years* : consequently is seldom found in the
Heart of a Sheep killed for food.

II. SHEEP'S BRAm.

N.B. — It icill he icell to place a fresh Braki in spirit for a
week at least ])rior to commencing the dissection, in order that it
may he thoroughly hardened.

Examination of the Exterior. — The whole exterior of
the Brain will be seen to be closely invested by a membrane,
called the Pia Mater, which dij)s into all the sulci between
the convolutions, and forms a medium in which the arteries
and veins may ramify. Besides covering the exterior of the
brain, this membrane sends processes into the interior, in
which the vessels that supply the walls of the enclosed space
can be conveyed ; thus one process penetrates into the Cere-
brum below the Corpus Callosum and is termed the Velum
Interpositum ; and two vascular fringes project into the fourth
ventricle, known as the choroid plexuses of that cavity.

* Milne Edivards. Lecons siir la PAysto%2c,t.iii.,p.492, note, " Chez le Mou-
ton il ne parait se former qu'^ un age avance. [Duvernoy, Lecons d'Anatomie
Comparee de Cuvier, t. vi. p. 292. F. S. Leuckart. Bemerkungen (Meckel's
Deutsches Archiv,, t. vi. p. 136).]

162 Mammalia.

Looking at the upper surface of the Brain (i.e. that surface
on which the convolutions chiefly appear) it will be noted
that {a) the large lobes of the Cerebrum do not cover the
posterior twisted nodule or Cerebellum, in other words the^os-
terior lobe of the Cerebrum of Man is absent (i.e. that lobe which,
in Man, rests upon the tentorium and whose extent forwards
is limited by the anterior margin of the Cerebellum) ; (b) the
Cerebellum does not consist of two distinct lateral lobes con-
nected by an elevated median portion, as in Man ; but, rather,
the median lobe holds the chief position.

Looking at the under surface or base of the Brain the student
should note, (a) the large size of the Olfactory bulbs on either
side of the anterior lobes of the Cerebrum ; (b) the very slight
extent to which the so-called ' middle ' lobe appears, owing
to the great development of the lobe of the Hippocampus
immediately internal to and underlying it; (c) the small
size of the Pons ; and (d) the broad Medulla Oblongata. The
structures in the median area, and the nerves, will be noted
after the removal of the Pia Mater.

Dissection of PRiNciPAt Arteries. — The student should
now proceed to follow out the principal trunks of the Arteries
that supply the Brain with blood ; viz. the Vertebral and
Internal Carotid Arteries. It may be well to be reminded of
the course of these vessels after leaving the heart.

In all Ruminants, both right and left subclavian arteries,
and both * common' carotids, arise from one arteria innominata
springing from the arch of the Aorta.

Each Vertebral artery is generally the first branch of the
Subclavian of its own side ; it passes through the foramina
in the transverse processes of the cervical vertebrae from the
sixth forwards, and enters the Skull through the Foramen
Magnum : it then passes round the medulla oblongata to
blend with its fellow in a common trunk at the posterior
border of the Pons : the two vertebral arteries united form

Dissection of Sheep^s Brain. 163

the Basilar artery ; this vessel receiving its name from the
fact of its being in close relation with the basilar process of
the Occipital bone : after traversing the Pons in the median
line and reaching the anterior border of the Pons, the Basilar
artery divides into two terminal branches, named the posterior
Cerebral arteries, which run in an oblique direction forwards
just internal to two nerve twigs (the third pair of nerves), and
then bifurcate, one branch returning in a posterior direction,
the oih.Qv continuing forwards to join the internal Carotid arteries
which enter the Brain posteriorly to the Optic Commissure,
i.e. that mass of nerve matter lying transversely, limiting, as it
were, the longitudinal furrow between the Cerebral Hemi-
spheres posteriorly.

The * Common ' Carotids^ after leaving the arteria innomi-
nata, divide each of them in the neighbourhood of the Thyroid
cartilage into two branches, named * external' and 'internal'
carotids ; of these, the former is distributed to the external
parts of the cranium, viz. the head and face ; the latter to
the internal parts of the cranium. After the bifurcation of
the * common ' carotid, the * internal ' branch passes ventrad
of the three transverse processes of the three upper cervical
vertebrae to the Carotid foramen in the lesser wing of the
sphenoid, forms a plexus in the cavernous sinus just external
to the sella Tursica, and, passing just within the clinoid pro-
cesses, reaches the base of the Brain a little posterior to the
Optic Commissure*. Immediately on their reaching the base
of the Brain the two internal Carotids are each met by a branch
of the posterior Cerebral Artery\ of its own side ; they then pro-
ceed forwards round the Optic Commissure, and bifurcate,
one branch (the ' middle cerebral ') running up the fissure of
Sylvius (i.e. the depression between the anterior and middle

* "When the Brain has been removed from the Skull the cut ends of the
internal Carotids are sometimes so short as to require careful search.

t Proceeding from the Basilar Artery, vide supra.

164 Mammalia,

lobes of the Cerebrum), but not covered (as it is in Man) by
tbe anterior development of the middle lobe; tbe second
branch Q anterior Cerebral') of each, side coming into close
relation in front of the Optic Commissure, and sending off
anastomosing twigs to each other as they pursue their parallel
course along either side of the base of the longitudinal fissure
between*the Cerebral hemispheres. These remarkable anas-
tomoses, first between the branches of the vertebral and inter-
nal Carotid Arteries ; and secondly between the anterior
Cerebral Arteries inter se, constitute the Circle of Willis, and
form a means for equalising the circulation in the brain.

Removal of Membranes. — The student should now care-
fully remove the adherent membranes from the surface of one
half* of the brain, being especially careful at the followiDg
points, viz. the origin of the third pair of nervesf; — the division
between the Cerebrum and Cerebellum, especially the external
part of that division in which the fourth nerve lies ; — the
lateral extremities of the Pons where is the origin of the fifth
pair ; — the anterior end of the Medulla adjoining the Pons,
where are the origins of the seventh pair (laterally), and of
the sixth pair (near the median line) ; — the lateral border of
the Medulla oblongata for the eighth pair ; and a little inter-
nal thereto for the ninth pair — and lastly, at the posterior end
of the longitudinal fissure of the Cerebrum superiorly, so as not
to tear away the pineal gland or velum interpositum.

In all cases it is best to leave the membrane round the roots of
the nerves f cutting round them with the scissors : and in clean-
ing the fissures, to open them out with the handle of the
scalpel.

This done, the following structures present themselves for
notice at the base of the Brain.

* In order to be able to compare tbe two sides after removal of tbe membrane,
t Supra, p. 163.

Dissection of Sheep's Brain, 165

Anteriorly there is the median longitudinal fissure between
the Cerebral hemispheres ; and, at some little distance within
the fissure, is the anterior border of the great transverse Cere-
bral commissure, called the Corpus Callosum.

At the base of the anterior lobes of the hemispheres, are
situated the First Pair of Nerves, termed Olfactory , as being
the special nerves of the sense of smell : on reaching the
Cribriform plate of the Ethmoid bone they expand into a bulb
from which are given ofi" numerous filaments which pass
through the cribriform foramina and are distributed to the
mucous membrane of the nose.

JSText may be noticed the Optic Commissure which rests upon
the Olivary process of the Sphenoid bone : the Optic Nerves
which proceed thence and are distributed exclusively to the eye
ball, have been cut away ; the optic tracts which remain pos-
terior to the commissure, and diverge laterally may be traced
back into the optic thalami and corpora quadrigemina. Just
within the angle of the optic tracts, immediately behind the
commissure, is the Tuber Cinereum : this forms part of the
floor of the third ventricle, and from it proceeds the Infundibu-
lum*, through which the cavity of the third ventricle above,
is continued into the remnant of the cavitj^ that existed in the
foetus in the Pituitary body below.

Next, behind the Tuber Cinereum, is the Single f Corpus
Albicans, formed by the anterior Crura of the Fornix, which
after descending to the base of the brain are folded upon
themselves before passing upwards to the Thalami optici.

The two cylindrical bundles of white matter which emerge
from the anterior border of the Pons, diverge as they pass
forwards, give origin from their inner margin to the 3rd pair

* When the Brain is removed from the Skull, the Infundibulum is almost
ahvays cut through, leaving only a tubular orifice : and so also the Pituitary
body which was situated in the Sella Turcica of the Sphenoid bone.

t In Man there are two Corpora Albicantia, except at an early period of foetal
life, when they are blended together in one large mass.

166 Mammalia.

of nerves {i.e. th.e chief Motor nerves of the muscles of the
eyeball), and are crossed just before entering the hemispheres
by the optic tracts to which they are adherent, are the Crura
Cerebri.

Posterior to the Corpus Albicans, bounded on either side
by the Crura Cerebri, and limited posteriorly by the Pons
Varolii, is the Posterior perforated space, which forms the back
part* of the floor of the third ventricle, and is perforated by
numerous small orifices for the passage of blood vessels to the
Thalami optici.

Winding round the outer side of either Crus from above,
having origin in the upper part of the Yalve of Yieussens,
immediately behind the Testes, and above the Pons Varolii,
will be seen the Fourth Pair of Nerves. They are also called the
Trochlear'^ nerves, and supply the orbital surface of the su-
perior oblique muscle of the Eye.

The broad transverse band of white fibres which forms the
great transverse cerebellar commissure, and whose extremities,
contracted into a thick rounded form, constitute the middle
crura, or peduncles, of the Cerebellum, is the Pons Varolii. Its
under surface presents a groove in the median line, in which
was lodged the basilar artery ; its upper surface forms part of
the floor of the fourth ventricle ; and from its sides, the Fifth
Pair of Nerves f nerv. trigeminus, or Trifacial, take their super-
ficial origin.

The Trifacial^ is the largest cranial nerve, and somewhat
resembles a spinal nerve in its origin by two roots, one motor,
the other sensory, and in the existence of a ganglion (Gasse-
rian) on its sensory root : it has three great divisions. The

* Cf. supra, Tuber Cinereum.

t The Superior Oblique Muscle in Man passes through a fibrous loop at the
inner angle of the orbit before reaching the eyeball, thus as it were, passing
through a pulley or trochlea, (Gr. vgax,i7^ia) whence the name given to the nerve
supplying it.

X Also called Trigeminal.

Dissection of Sheep^s Brain. 167

first two trunks proceed exclusively from the ganglion, and
are entirely sensory, viz. (a) the Ophthalmic, which enters the
Orbit and supplies the eyeball, the lachrymal gland, the
mucous lining of the eye and nose, and the integument and
muscles of the eyebrow and forehead : and (b) the Superior
Maxillary, which is continued forwards to the face below the
orbit, and supplies the side of nose, the lower eyelid, upper
lip, and upper teeth. The third or Inferior Maxillary trunk
receives a considerable part from the ganglion, and has asso-
ciated with it also the whole of the fibres of the motor root.
It therefore becomes a mixed nerve : and supplies the teeth
and gums of the lower jaw, the integument of the temple and
external ear, lower part of the face and lower lip, and the
muscles of mastication : it also supplies the tongue with its
special nerve of the sense of taste.

The enlarged anterior part of the spinal cord immediately
succeeding the Pons is the Medulla Oblongata ; it rests its in-
ferior surface on the basilar groove of the occipital bone, and its
superior surface forms the floor of the fourth ventricle. Its
inferior surface, which we are now considering, is marked by
a median groove in which ran a small artery, a recurrent
branch of the conjoined Vertebral arteries : and, a little to the
right and left of this median groove, it is marked by a second
groove commencing at the Pons and bending outwards like a
hook : this marks the track of the Arciform Fibres, within the
bend of which is situated on either side an oval mass, termed
the Olivary Body ; and at the commencement of which, just
behind the Pons, is situated the Sixth Pair of Nerves : one
arising from each lateral half of the Medulla.

The Sixth Nerve {abducem) is distributed to the ocular sur-
face of the External Rectus muscle of the eye.

Between the Olivary Bodies and the median groove are the
* Anterior ' Pyramids.

Between the Olivary body, and the Trifacial Nerve is the

168 Mammalia.

origin of the Seventh Pair of Nerves. This pair of nerves con-
sists of two portions, named respectively Portio Mollis =
Auditory, and Portio 'D\x.vq.=^ Facial Nerve. The former is the
special nerve of the sense of hearing, being distributed ex-
clusively to the internal ear ; the latter is the motor nerve of
the face, and is situated a little nearer to the middle line than
the Portio Mollis.

Immediately behind the Olivary body, a little further back
than the origin of the Seventh Pair of Nerves, will be seen the
superficial origin of two of the three components of the Eighth
Pair ofNerveSy viz. the Glosso-Pharyngeal and the Pneumogastric
or Vagus ; the third component, viz, the Spinal Accessory,
arises by several filaments from the lateral tract of the cord
below the Yagus. Of these three components the Glosso-pharyn-
geal is distributed, as its name implies, to the Tongue and
Pharynx, being the nerve of sensation to the mucous mem-
brane of the fauces and root of the Tongue ; and of motion to
the Pharyngeal muscles. The Pneumogastric has a more
extensive distribution than any of the other cranial nerves,
passing through the neck and cavity of the Chest to the
Abdomen : it is composed of both motor and sensory fila-
ments : it supplies the organs of voice and respiration with
motor and sensory fibres; and the Pharynx, GEsophagus,
Stomach, and Heart with motor fibres. The Spinal Accessory
consists of two parts ; one, the accessory part to the Yagus,
to whose pharyngeal and superior laryngeal branches it con-
tributes filaments ; the other the spinal portion, which is dis-
tributed to the Sternomastoid* and Trapezius! muscles.

* The Sterno-mastoid is a muscle which passes obliquely across the neck, arises
by two distinct heads, from the Sternum and Clavicle (when present), and is in-
serted by a strong aponeurosis into the outer surface of the Mastoid process of
the Temporal bone : it is a flexor and depressor of the head.

t The Trapezius is a muscle covering the upper and back part of the neck and
shoulders ; arising from the Occipital protuberance, ligamentum nuchse, and
spinous processes of cervical and dorsal vertebrae, and inserttd into the upper

Dissection of Sheep^s Brain, 169

Posteriorly to tlie origin of the eighth Pair of Nerves, from
the groove between the Pyramidal and Olivary bodies, the
Ninth or Hypoglossal nerve takes its origin : it is the motor
nerve of the Tongue.

On looking at the Superior Surface of the Brain, in
addition to the points enumerated before, there may be seen,
by slightly separating the Cerebellum from the Medulla
oblongata, the triangular cavity of the Fourth Ventricle, the
apex of which, from its resemblance to the point of a pen, is
called the Calamus Scriptorius. On either side of the Medulla,
and continuous with the ' posterior '* columns of the Cord, are
the Restiform Bodies, which as they proceed forwards diverge
from each other, assist in forming the lateral boundaries of the
fourth ventricle, and then enter the corresponding hemisphere
of the Cerebellum, forming ii^ posterior-\ peduncles : in the me-
dian line is a furrow which terminates at the apex of the fourth
ventricle in the Ventricle of Arantius, which is the remains of
a canal which in the foetus extends throughout the entire
length of the Cord : — on each side of the median fissure, and
separated from the Pestiform bodies by a very slight groove,
are two narrow white cords called the Fasciculi seu Eminentia
teres. Projecting into the fourth ventricle on either side are
two delicate vascular fringes, processes of the Pia Mater,
called the Choroid Plexuses of the Fourth Ventricle.

On slightly separating the Cerebral Hemispheres, the longi-
tudinal fissure will be seen to be floored, as it were, by the
Corpus Callosiim, a thick stratum of transverse fibres, connect-
ing the two hemispheres of the brain, and forming the roof of
a space in the interior of each hemisphere, called the Lateral
Ventricle.

border of the spine of tlie Scapula, the Acromion, and the Clavicle : if the head
is fixed it elevates the point of the shoulder ; if the shoulder is fixed it draws the
head more or less directly backwards.

* i.e. Superior in Qitadruped. f Cf. supra, Pons Varolii.

Z

170 Mammalia,

On pressing tlie Cerebellum backwards so as to gain a view
of tbe parts intervening between tbe Cerebrum and Cerebel-
lum, the following structures will be disclosed. At tbe
posterior margin of tbe Corpus Callosum there will be seen in
tbe median line tbe posterior extremity of the Velum Inter-
posifum, a vascular membrane reflected from the Pia Mater into
the interior of the Brain. The Velum will be seen to pass
beneath the posterior rounded border of the Corpus Callosum,
and above the Corpora Quadrigemina : on slightly raising
Hs posterior border it will be found to form an almost complete
investment for a small conical reddish body, which rests upon,
or rather in, the division between the anterior pair (nates) of
Corpora Quadrigemina. This conical reddish body is the
Pineal Gland (Conarium) so named from its peculiar shape
(pinus, the fruit of the fir) ; in its base, as we shall afterwards
see, is a small cavity communicating with that of the third
ventricle. Posteriorly to these are the Corpora Quadrigemina
(optic lobes) ; four rounded eminences, separated by a crucial
depression ; the anterior larger pair are called JSfates, the
posterior pair the Testes : they will be found to be situated
immediately behind the third ventricle : and are seen to be
connected with the Cerebellum by means of a large white cord
on each side, the processus a cerehello ad testes, or * superior ' *
peduncles of the Cerebellum ; stretched between these two
peduncles will be seen a thin translucent lamina of medullary
substance, called the Valve of Vieussens ; it covers-in the
canal leading from the third to the fourth ventricle {iter a
tertio ad quartum ventriculum) and forms part of the roof of
the latter cavity: from the upper part of the valve, im-
mediately behind the testes, arises the fourth or trochlear
nerve, as above mentioned.

Examination of the Interior of the Brain.

* Cf. supra. Restiform bodies.

Dissection of Sheep^s Brain. 171

1st Section. — To the Level of the Corpus Callosum.
The Hemisplieres should now be sliced off to a level with the
Corpus Callosum, when the white substance of that structure
will be seen connecting together both hemispheres, and
marked in the middle line by a longitudinal, central, ridge, or
raphe. The Student should here note the large expanse of
medullary matter* now exposed, surrounded by the convoluted
margin of grey substance.

2nd Section. — To Expose the Lateral Ventricles.
In order to see the thickness of the Corpus Callosum, and to
bring into view the parts in contact with its under surface,
a cut should be made through that body on each side near the
middle line, and continued parallel with it forwards and back-
wards as far as the limits of the underlying ' lateral ' ventri-
cles ; the rest of the Corpus Callosum, external to the above
longitudinal incisions on either side, which forms the roof of
the space within, should then be removed ; and inasmuch, as
a part of either ventricle extends down, in the middle lobe
towards the base of the Brain, the course of that cavity
should be followed by incisions along each side thereof ; and
the superjacent substance of the hemisphere should be re-
moved. The cavity passes at first backwards, outwards, and
downwards ; then curves around the Crus Cerebri, forwards
and inwards, nearly to the point of the * lobe of the Hippo-
campus,' close to the fissure of Sylvius.

The two large irregular cavities exposed on removal of that
part of the Corpus Callosum, above described, are the Lateral
Ventricles, serous cavities separated by the vertical Septum
Lucidum ; each consists of a central cavity or body, and twof
smaller cavities or cornua ; of these the anterior cornu curves
forwards, outwards, and downwards in the substance of the

* The centrum ovale majus of Vieussens.

t Since the 'posterior' lobe of the Human Cerebrum is deficient in the Sheep,
the posterior cornu is also wanting.

172 Mammalia,

anterior lobe ; while the descending cornu traverses the
* middle ' lobe of the Brain, forming in its course a remark-
able curve round the back of what will be shown later to be
the Optic Thalamus.

The Corpus Callosum will be seen to present a somewhat
arched form from before backwards, and to be thicker at
either end than in its central part. Anteriorly it forms a
bend or genu (of which the reflected portion is termed the
rostrum), and is attached to the anterior cerebral lobe ; poste-
riorly it is continuous with the fornix which immediately
underlies it ; and in the intermediate portion of its length it
is connected with the Septum Lucidimi (the vertical partition
between the two lateral ventricles).

In the external wall of the anterior portion of the central
cavity will be seen a pear-shaped prominence, which also
forms the posterior boundary of the anterior cornu. This is
the Corpus Striatum^ so named from the striated appearance
which it presents in section. The inferior border of
the intraventricular portion of the Corpus Striatum is
bounded by a slight depression in which lie some longitudi-
nal fibres of white medullary substance : but these are barely
traceable ; however they form the Tcenia Semicircularis, which
anteriorly descends in close connection with the anterior pillar
of the Fornix, and posteriorly is continued, along with the
pointed end of the Corpus Striatum, into the roof of the ' des-
cending ' cornu. Beneath it is a large vein (Yena Corporis
Striati), which receives numerous smaller veins from the
surface of the Corpus Striatum and Thalamus Opticus, and
terminates in the Yena Galeni.*

The highly vascular fringe-like membrane which comes
next posteriorly, extending in a curved direction across the
floor of the lateral ventricle, and following down the descend-

* Vide infra, in the Velum Interpositum.

Dissection of Sheep* s Brain. 173

iiig cornu, is the Choroid Plexus : in front it is conjoined
with, the Choroid Plexus of the other side, through a large
oval aperture (as it appears in this section), termed the Fora-
men of Monro : it rests upon the Corpus Fimbriatum or Tcenia
Hippocampi, which is a narrow white tape- like band attached
along the inner border of the curved elongated eminence that
extends along the entire length of the floor of the descending
cornu, and is called Hippocampus Major or Cornu Ammonis
(from its resemblance to a ram's horn). The Corpus Fimbria-
tum is a continuation of the lateral edge of the posterior
pillar of the Fornix. Just anterior to the edge of the Corpus
Fimbriatum, and underlying it, is a part of the eminence,
called the Optic Thalamus, into which the Optic tracts at the
base of the Brain are distinctly traceable. Running along
the part of the Optic Thalamus just mentioned is seen the
Choroid Arterij ; it arises either from the trunk of the inter-
nal carotid or from the middle cerebral artery, just at that
point where the inferior end of the fissure of Sylvius
meets the anterior end of the transverse fissure ; enters the
horn of the lateral ventricle, beneath the edge* of the
' middle ' lobe of the Brain ; and is distributed to the Hippo-
campus Major, Corpus Fimbriatum, and Choroid Plexus.
The arteries of the Choroid Plexus, after ramifying through
its substance, send branches into the substance of the Brain ;
the veins of the Choroid Plexuses terminate in the Yenee
Galeni.

On holding up the Brain to the light, and gently raising
the Corpus Callosum into its normal position, the thin semi-
transparent Septum Lucidum, which is attached above to the
under surface of the Corpus Callosum, and below to the
anterior part of the Fornix, is apparent. The Septum con-

* Through the same part of the transverse fissure that the Choroid artery
enters the Brain, the Choroid Plexus joins with the Pia Mater.

174 Mammalia,

sists of two laminae, separated by a narrow interval, the
interval being called the Fifth Ventricle.

3rd Section. — To Expose the Fifth Yentricle. Tbe
space of the very minute fifth, ventricle * will come into view
by cutting across the part of the Corpus Callosum that re-
mains in the middle line ; detaching the anterior half from
the Septum Lucidum below, and reflecting it forwards. This
ventricle is in the sheep not more than iV*^. in length, and
close within the anterior fold or genu of the Corpus Callosum.

4th Section. — To Expose the Fornix. The posterior
half of the Corpus Callosum should now be detached with care
from the structures iminediately subjacent to it, and reflected
backwards ; and the Septum Lucidum should also be removed
by section along its inferior margin : by this means the
Fornix^ will be exposed, and seen to be a longitudinal lamella
of fibrous matter, triangular in shape, with the ap^x pointing
forwards : its free lateral edges (Corpora Fimbriata) form-
ing on each side part of the floor of the lateral ventricles ; and
the edges of its posterior crura being in contact with the
Choroid Plexuses : we have seen also that its upper surface is
connected in the median line to the Septum Lucidum in front,
and to the Corpus Callosum behind : lastly, at the apex it is
seen arching over the Foramen of Monro at a point which
will be shown later to be the front of the Optic Thalamus.

The two openings (one on each side) known as the Foramina
of Monro, besides being the passage for the Choroid Plexus,
form also a transverse communication between the lateral
ventricles.

5th Section. — To Expose the under Surface of the
Fornix, the Yelum Interpositum, and the Transverse
Fissure of the Cerebrum. The Student should now divide

♦ Flower. PhU. Trans., 1865, p. 638.
t Fornix, an arch or Vault.

Dissection of Sheep's Brain. 175

the Fornix across anteriorly, just above the Foramen of
Monro, and reflect the posterior portion backwards.

When the posterior part is raised the Fornix will be found
to be supported on a vascular membrane, named Velum Inter-
positum ; the apex of the Fornix will be seen to end in two
processes, the Anterior Crura, separated from each other by
a narrow interval, and which afterwards descend in a curved
crescent form to the Corpus Albicans, where they each make a
turn like half the figure 8, and furnish a white envelope
to the grey matter of that body. The Foramen of Monro will
be seen to be merely an enlarged portion of an interval that
exists between the whole under surface of the body of
the Fornix and subjacent structures ; and the Choroid Plex-
uses will be seen to have their anterior origin from the bifur-
cated anterior extremity of the velum interpositum (just
posterior to the anterior crura of the Fornix), and also to be
connected with its lateral margins. By removing the Choroid
Plexus the lateral ventricles will be seen to descend towards
the middle line, where they afterwards join together and lead
into the upper part of the third ventricle. The Yelum Inter-
positum is reflected from the Pia Mater into the Interior of the
Brain through the transverse fissure*, passing beneath the pos-
terior rounded border of the Corpus Callosum and Fornix, and
above the Corpora Quadrigemina, Pineal Gland, and Optic
Thalami : it separates the under surface of the body of the For-
nix from the cavity of the third ventricle, and its posterior
border invests the Pineal Gland. The arteries of the Yelum
Interpositum are derived as well from the Choroid artery as
from the Superior Cerebellarf Artery, which enters from be-
hind, beneath the Corpus Callosum. Its veins, the VencB Oaleni,

* Vide infra, p. 176.

t The Superior Cerebellar Arteries arise near the termination of the Basilar
artery : they wind round the Crus Cerebri, close to the fourth nerve, and in ad-
dition to supplying the Pia Mater covering the Cerebellum, also give several
branches to the Pineal Gland and Velum Interpositum.

176 Mammalia.

two in number, run along its under surface, beginning at tbe
Foramen of Monro by tbe union of branches from the Yense
Corporis Striati and Yense Plexus Choroides (noted above).
The Yense Galeni unite posteriorly in a single trunk, which
terminates in the ^ Straight '* sinus.

On separating the Corpus Fimbriatum from the Thalamus
Opticus, the position and boundaries of the great cleft at the
posterior part of the Brain, called the Transverse Fissure, will
be readily comprehended. This fissure is situated beneath
the Fornix, extending downwards, on each side, from the
Foramen of Monro in the middle line to the end of the des-
cending cornu ; its central part lies beneath the Fornix and
Corpus Callosum, and its lateral part is placed between the
edge of the Fornix, the Optic Thalamus, and Crus Cerebri.
Through this great slit, as above noted, the Pia Mater passes
into the Erain, and forms the Yelum Interpositum and
Choroid Plexus.

6th Section. — To Expose the Thalami Optici and Third
Yentricle. The Yelum Interpositum should now be raised
and removed ; the Hippocampus Major of one side dissected
away from subjacent structures and folded over on the other
side ; and the adjacent portions of Pia Mater removed : in
doing so the student must be especially careful at the posterior
border of the Yelum, where it invests the Pineal gland, so as
to leave that gland in situ.

On the under surface of the Yelum Interpositum will be
noted two very short vascular fringes projecting into a narrow
oblong fissure which lies beneath and extends to the base of
the Brain called the Third Ventricle ; these are termed the

* The * Straight ' Simcs, i.e. that which runs along the line of junciion of the
Falx Cerebri {i.e. the process of dura mater, which descends vertically in the
longitudinal fissure between the two hemispheres of the Cerebrum) with the
Tentorium {i.e. a horizontal process of dura mater between the Cerebrum and
Cerebellum), from the termination of the inferior longitudinal sinus (which is
contained in the lower /ree margin of the Falx Cerebri) back to the torcular
Herophili (or point where the longitudinal and lateral sinuses are confluent).

Dissection of Sheeph Brain, 177

Choroid Plexuses of the Third Ventricle^ and resemble tlie
like parts in the lateral ventricles. On either side of this
Third Ventricle are the Optic Thalami ; in front are the ante-
rior Crura of the Fornix, with the anterior Commissure of the
Cerebrum, lying in front of them and visible in the interval
between them ; behind is the Pineal Gland, and in front
of, and beneath it, the Posterior Commissure ; crossing the
centre of the space from one Optic Thalamus to the other
is the Middle or Soft Commissure.

The Third Yen tricle communicates with the other ventricles
of the Brain in the following way : — In front it joins each
lateral ventricle through the Foramen of Monro : and behind,
by a passage which is called the aqueduct of Sylvius, beneath
the posterior commissure, it joins the fourth ventricle. At
the lower part in front there is a deep pit, which leads down-
wards to the funnel-shaped cavity of the infundibulum [iter
ad infundibulum).

It has been shewn that the Thalami Optici enter into the
lateral boundaries of both the lateral and third ventricles,
that they are separated from the Corpora Striata by the groove
in which is the Taenia Semicircularis, and are partly covered
by the Fornix : it will now be noted that along the upper
part of their inner borders lie the peduncles of the Pineal
Gland. The optic tracts which have already been referred to
in connection with the base of the Cerebrum may be traced
back to the Thalami : each tract, somewhat cylindrical towards
the Optic Commissure, becomes flattened and broader as it
approaches the Thalamus, and makes a bend as it turns round
the Crus Cerebri to reach the back part of that body. Near
this bend (which is called the Genu or knee), and to the outer
side of the Corpora Quadrigemina are placed two small, oblong,
and flattened eminences connected with the posterior extrem-
ity of the Optic tract : these are called the Corpora Geniculata.

The four rounded eminences placed in pairs, and situated

A A.

178 Mammalia,

immediately behind the third ventricle and posterior com-
mtissure, beneath the posterior border of the Corpus Callosum
and above the ' iter a tertio ad quartum ventriculum/ are the
Corpora Quadrigemina. Each pair will be seen to be situated
on the cerebral aspect of the peduncle of the Cerebrum of the
same side : the anterior eminences {nates) far exceeding the
posterior {testes) in size ; and from each a lateral white band
{hrachia) proceeding beneath the Corpus Geniculatum internum
to join the Optic tract. These bodies are also connected with
the Cerebellum by means of a large white cord on each side,
the Processus a Cerebello ad Testes, or superior peduncles of the
Cerebellum : the thin white layer between these peduncles,
the Valve of Vieussens, covers in the canal leading from the
third to the fourth Ventricle, and gives origin to the fourth
nerve.

To Expose the Iter a Tertio ad Quartum Ventricu-
lum, Fourth Ventricle, Arbor Vitje of Cerebellum, &c.
— The student should now make a vertical median incision
through the whole length of the Brain, down to, but not quite
dividing, the base.

By this means he will obtain a longitudinal section disclos-
ing the following points from the front : the thickened genu
and rostrum of the Corpus Callosum ; the anterior extremity
of the Fornix and the anterior Cerebral Commissure (very
small) in close relation ; the crescent of the third Ventricle,
the anterior arm descending to the infundibulum, the bend
passing beneath the middle or soft commissure (very large),
the posterior arm ascending to the Pineal Gland ; the floor
of the third ventricle formed by the Optic Commissure, In-
fundibulum, and Corpus Albicans : from the middle of the as-
cending arm and proceeding backwards above the Crus Cere-
bri, and just beneath the posterior Commissure (which is itself
just beneath the Pineal Gland) and the Corpora Quadrigemina
is the 'Iter': further back, the 'Iter' is seen floored by the

Dissection of Sheep's Brain. 179

upper surface of the Pons, roofed in by tlie Yalve of Yieus-
sens, and then passing into the fourth Yentricle beneath the
Cerebellum, to terminate at the Calamus Scriptorius and Yalve
of Arantius, the anterior extremity of the closed central canal
of the spinal cord. In the Cerebellum there will be noted the
absence of any enclosed cavity or ventricle, such as was found
in the Cerebrum ; but, instead, the presence of a mass of
white matter in the centre which sends out spreading and
gradually thinning layers into the interior of all the laminae of
the grey substance which forms a continuous covering on the
surface ; and, as the consequence of this arrangement of the
grey and white substances, the presence of a beautiful foliation
or arborescence, named * Arbor vitae ;' the section, above made,
crossing the laminas and dividing the grey and white sub-
stances together.

180 Mammalia,

III. DISSECTIOIS' OF A MAMMAL.

COMMON RAT— Mus Decumanus.

Rodentia. Muridce,

Introductory. — Mus Decumanus (Pallas), the Brown Eat,
Le Surmulot (Bujffon) of the FrencLi, is supposed to have
penetrated into Western Europe from Persia and the East
Indies, where it lives in burrows, about 1730 ; for it was not
till 1727* that, after an earthquake, it arrived at Astracan
by swimming across the Yolga. Though frequently styled
the Norway Kat, it was not known to exist in Scandinavia f
when the name was first applied to it. It is somewhat larger
than the Black Pat (Mus Pattus), which also originally came
from the East ; and has in many countries expelled it.

It is of a brownish grey colour above, and a whitish grey
colour beneath. The Tail is furnished with annulate scales, and
hairs between each ring, but is on the whole thinly haired and
shorter than the head and body, by both of which points it
may be further distinguished from the Black Pat. The Ears
are rounded, somewhat naked, and exsert. The Eyes are late-
ral. The upper Lip is distinctly cleft : the Muffle is sliglitly
hairy but not divided by any vertical groove J separating the
nostrils, the only indication of which is a small seam imme-
diately above the incisors. The external nasal apertures,
underneath the muffle, are lateral, and shaped somewhat like
a comma. The Fore-feet are furnished with four toes, and on
the sole are several warts, one being especially developed, for

* Cuvier. Buifon, viii., p. 206. t Pennant.

t Waterhousl says, " A distinctly cleft upper lip, combined with a small
naked muffle, divided by a vertical groove, and separating the nostrils, is char-
acteristic of nearly the whole of the Great Murine and Sciurine sections" (Nat.
Hist. Mam. vol. ii., p. 7) ; but this does not appear to be so here.

Dissection of Common Rat, 181

the thumb, and unguiculate. The Hind-feet are pentadactyle.
The Incisor teeth are two in number in each jaw, large, in-
curved, and separated from the Molars by an interval or dias-
tema, the result of the withdrawal of the Canines : their depth
is greater than their width, and their sides are somewhat
flattened.

The creature before us bears the following external charac-
teristics of a YERTEBRATE : its body seems bilaterally
symmetrical, and presents no appearance of segmentation ;
it has not more than two pairs of limbs ; its jaws appear to
be modifications of the walls of the head rather than modifi-
cations of limbs ; the organs of smell, sight, and hearing,
are limited to the head, and consist of single bilaterally sym-
metrical pairs ; lastly, it is possessed of an anus, — no Verte-
brate being aproctous.

It bears the following characteristics of a MAMMAL, viz.:
the covering of hair ; the vibrissae on the snout ; the under-
jaw alone moveable ; the external ear ; the cartilaginous pro-
longation of the bony parts of the nasal cavity, forming a
nose, or muzzle : and the intromittent organ of generation.

It would be placed with the Rodkntia, as being possessed
of two scalpriform Incisors in each jaw, and having these
separated by a diastema from the molars, i.e. lacking Canine
teeth : and from its scaly thinly- haired tail, it would be
grouped with the Muridce.

Injection. — The animal is best injected from the jugular
vein, which may be readily found by first making a straight
incision through the skin, about an inch long, from the end of
the sternum to the symphysis of the jaw, and reflecting the
the skin on one side ; and then with the scalpel making
a slight incision through the muscle underlying the skin ;
when the vein will be found holding an antero-posterior
course across the clavide about half way between the middle
of the chest and the anterior border of the shoulder. A

182 Mammalia.

sliglit incision should be made into the vein ; the pipe of the
injecting syringe inserted into the incision then made pointed
towards the body, and a hgature passed round the vein en-
closing the pipe.

We may conveniently divide the course of the dissection
into two parts.

I. Abdominal region. II. Thoracic region.

The dissection of the Head will be more conveniently
treated of in a larger subject.*

N.B. The student should have the skeleton of a Rat before him.

The animal should be laid upon its back on a cork of suffi-
cient width to allow of the limbs being pinned out on either
side, by which means the body may be kept firmly in position.

Eemoval of the Skin. To raise the skin from the ventral
aspect of the body one longitudinal cut should be made,
severing the skin only, in the middle line, the entire length of
the body, and the skin should be reflected to either side.

Abdominal Muscles. After removing the skin, the first
muscle which presents itself, and which adheres very closely
to the skin, is peculiar to Quadrupeds, viz., the Panniculus
Carnosus, or Musculus Subcutaneus. This fleshy pannicle
is spread over the whole body ; the abdominal portion forms
a broad expansion, its fibres running from the shoulder to
the flank; on the supero-lateral area of the abdomen it is
thick and fleshy, especially behind the arm, below which it
sends a tendinous expansion which penetrates between the
caput muscles and the chest, and gets attached to the Pecto-
ralis Major and internal trochanter of the Humerus. It is
related externally with the skin ; internally with abdominal
tunic and muscles : its action is to corrugate the skin, bind
down other muscles, and assist in difficult expiration.

This Panniculus should be removed, and there will then be
apparent a thin white median line, extending from the ster-

* Tide Dissection IV., Sheep's Head.

Dissection of Common Rat. 183

num, posteriorlv, the whole length of the abdomen. This is
the fibrous cord called Linea Alba; about midway in its
length is an enlarged white spot, which is the remains of
the Umbilicus. Situated on either side of, and attached to
the Linea Alba, on the inferior and middle part of the abdo-
men are the Recti [s. Sterno-pubiales) muscles, bounded su-
perficially by a tendinous aponeurosis.

External to the Recti Muscles on either side is a white
line, marking both the outer edge of these muscles and the
union of the fleshy and aponeurotic portions of the pair of
muscles that together occupy the whole area of the abdomen,
viz.y the External Oblique (s. Costo-abdominalis) muscles. The
External Oblique may be traced upwards to its origin by
fleshy processes from the outer surface of several of the poste-
rior ribs ; and the alternation of these processes with similar
processes which form the origin of the Serratus Magnus*
muscle beneath the arm should be noted.

From the front of the Sternum there arises the Pectoralis
Major muscle, triangular in shape, with the base at the Thorax^
and the apex at the Arm, where it is inserted into the Humerus.

The External Oblique tnuscle should be now raised^ — by carry-
ing the scalpel through the digitations near the ribs, continu-
ing the incision along the side, and reflecting it towards the
middle of the body, — in order to expose {a) the Eibs and the
Intercostal Muscles which lie just within its anterior fibres ;
and {b) the Internal Oblique muscle posteriorly. In raising
it care must be taken not to detach the Rectus muscle from
the Eibs above, and to avoid cutting through the tendon of
the Internal Oblique at the upper part, towards the sternum.

The Internal Oblique muscle (s. Ilio-abdominalis ) rises
from the crest of the Ilium, and its fibres have a general
oblique direction forwards towards the middle line ; it is in-

* The Serratus Magnus arises by pointed processes from the ribs, and is in-
serted into the Scapula.

184 Mammalia.

serted into the inner surface of the cartilage of all the false
ribs, the symphysis pubis, and the linea alba.

Cavity of Abdomen. The cavity of the abdomen is now to
he opened, by a longitudinal cut with the scissors from the
Ensiform Cartilage at the end of the Sternum to the PelviSy
through the conjoined aponeuroses of the muscles of the ab-
domen ; followed by a lateral incision on each side along the
edge of the posterior ribs ; care being taken not to pierce or
prick any of the subjacent organs or their surroundings. The
fl,aps thus marked out should be reflected to either side.

On first opening the Abdomen the glistening appearance
of the peritoneum or lining membrane of the cavity should
be noted : and before the natural position of the viscera is
disturbed, their general arrangement and connection with
surrounding parts should be examined : which will be found to
be much as follows, slight variations occurring according to
the season of the year and the gender of the species on which
the dissection is made.

Extending across the whole of the anterior moiety of the
abdomen is the Liver, in part concealed by the ribs ; as many
as four lobes present themselves. On the left side a piece of
the Stomach is visible, but this viscus is to a considerable ex-
tent hidden by the Liver. In the median line a deep red
body above an inch in length is seen, lying in a transverse
direction, slightly hidden in the centre by the Liver : this is
the Spleen. At the left end of the Spleen, and between it
and the Stomach, is situated the Kidney. Continuing in
the middle line, we come next posteriorly to the small intes-
tines, coiled about the whole of the posterior moiety of the
Abdominal cavity: and almost adjoining the Spleen, separated
therefrom by a coil of small Intestine, are the Large Intestine
and Caecum, both of a greyish colour ; the Caecum being gene-
rally rather to the animal's right, but free and not bound
down to the right iliac fossa, as is the case in Man.

Dissection of Common Rat. 185

The specimen before us being a male, we come next to the

small whitish bladder in the middle line, and on either side

of it the pinkish tinted Cowper's Glands, external to which

. again are the vesiculae seminales : and lastly in the median

line the Penis and Scrotum.

On gently pressing away the Liver from the cavity it oc-
cupies anteriorly, two structures will be apparent : — first, the
Diaphragm^ which forms a vaulted moveable partition between
the Thorax and the Abdomen, and which, by its movement up
and down alternately, during respiration, causes enlargement
of the Thoracic cavity in inspiration, and of the Abdominal
cavity in expiration ; and, concomitantly, a slight alteration in
the position of certain of the Abdominal Viscera, especially
the Liver, Stomach, and Spleen ; — secondly, in the middle, a
reflection of the Peritoneal lining between the Liver and the
Diaphragm forming one of the suspensory ligaments of the Liver.

On raising the posterior free border of the Liver, the whole
oi the Stomach is apparent : the left or cardiac portion of this
viscus is ovate and strongly recurved ; the (Esophagus will be
readily seen to enter near the middle of the anterior or concave
border, immediately to the right of which the Stomach will
be seen to assume a difierent hue, marking the commencement
of the right or pyloric portion whose parietes are thicker than
those of the cardiac, and are glandular internally : the Pyloric
stricture should also be noted, and the small tendinous spot
immediately preceding it, at the end of the pyloric portion of
the Stomach whence a ligament proceeds to be attached to the
abdominal surface of the large left lobe of the Liver.

On turning forwards the Stomach, and at the same time
gently pulling the Spleen away, the difiused Pancreas* comes
into view, spread throughout the Omentum (a process of peri-
toneum found only in Mammals), which is attached to the
postero- superior segment of the Stomach, and to the Spleen.

* Cf. p. 187.

B B

186 Mammalia,

The Pancreas may be distinguished from the fat by its rather
fleshy hue.

The Large Intestine, which is often of a greenish colour,
should now be turned down towards the tail, disclosing the short
simple Caecum about an inch in length, — the termination of the
small Intestine thereat in the shape of a white cord-like tube
about \-in. in diameter, coming down rather from the left side,
and — the commencement of the large Intestine as a greenish
tube of larger calibre. The large Intestine may be traced
further by moving the small intestines to the left of the animal ;
and be seen to continue up the right side, and then straight
across the body to the middle line, at which point it assumes
an antero-posterior direction. By turning the Intestines over
to the right, the last section is seen to contract abruptly about
ll-in. from the anus to which it proceeds as ' rectum' in a direct
antero-posterior line. The size of the Intestinal canal of the
Rodent varies directly as the teeth. It is largest in those
species which have rootless molars, but is of moderate size,
and is more simple in form in those species, as the Rat
before us, which subsist less exclusively upon vegetable sub-
stances, and have rooted tubercular molars.

As noted above, it will be now distinctly seen that the Large
Intestine (excepting Rectum) and Caecum are not kept in place
nor connected to the abdominal walls by folds of Peritoneum,
as is the case in Man, but are free, and not bound down.

The Student should now turn over and spread out all across
the body, away from the Liver, the whole of the small intes-
tines, taking each coil separately, and placing them in order,
without tearing them, or injuring any structures in connection
with them. By this means he will be enabled to see the whole
of the Mesentery* supporting the Small Intestines, together
with the Mesenteric vessels, and the aggregation of Mesen-
teric glands, which form a knotted dark-coloured band, in the

* jj.€(Tog, middle; errefiov, intestine.

Dissection of Common Rat 187

centre of the Membrane. Next, let him turn over the Intes-
tines on the right of the body, and trace the first three inches
of the Small Intestine after leaving the Pylorus, laying it out
on the left, towards the tail ; by this means a light white
cord is seen, to the right, which would seem to prevent the
complete extension of the Intestine in the direction indicated,
and which appears to issue from the right centre of the dorsal
margin of the Liver. The white cord is the Bile duct, which
enters the Intestine about two inches from the Pylorus.
Between the Bile duct and the Intestine is stretched a process
of Omentum in which a further portion of the diifused Pancreas
is visible. This low dendritic type of gland prevails in Roden-
tia : here the main part of the gland is that which extends
from the end of the duodenal fold to the left, into the gastro-
splenic omentum, where it ramifies : the chief part of the
duodenal Pancreas following the curve of the gut, but rami-
fying in its wide mesentery. In these creatures the Pancre-
atic ducts are many in number, and paired ; not single, as is
usually the case in Man. This may be readily demonstrated
by means of injection. Having tied one end of the Hepatic
duct, inject a cold blue injection into the other end, and it will
run, on either side, into the many Pancreatic ducts. If this
last portion of Intestine, Pancreas, and Bile-duct, be now
turned over to the right front, the spleen remaining as it was
left above, viz., over the left thigh, a little way from the
stomach, the student will be able to trace the principal
factors of the Portal vein, viz.: the Splenic coming from the
Spleen, the Mesenteric vein coming across from the centre of
the Mesentery, and both uniting at a spot in the median line
prior to entering the substance of the Liver just dorsad of the
Bile-duct.

The Mesenteric Arteries (which supply the Intestines, and
arise from the Aorta just posterior to the Liver) and also the
Penal Arteries may be next traced. This will be best

188 Mammalia.

achieved by — first, following out the left renal or emulgent
vein from the point at which it emerges at the hilus of the
kidney to its junction with the Yena Cava on the right side,
being a vein of considerable size, longer than the right rena
vein, and passing ventrad of the aorta ; and then carefully dis-
secting through the Peritoneum a little in advance of the
Benal Yein, when the course of the right Renal artery will be
found from the Hilus of the Kidney to its origin from a
longitudinal vessel in the median line, i.e., the Aorta : and
close to this point, but slightly in advance of it, and on the
right side, will be seen the commencement of the Mesenteric
Artery.

The intervening space between these two aortic branches
gives the site of the Solar or Epigastric Plexus, that is a
plexus of nerves, offsets of a reddish ganglion, near the side
of the Aortic trunk. Mixed up with the nerves of this plexus
are numerous small lacteal glands*, and a dense tissue,
which require to be moved with care.

In the Abdomen the Aorta will be noted to be in the me-
dian line, dorsad of all the viscera, just ventrad of the centre
of the vertebrae, and with the Yena Cava to its right side,
except at its point of bifurcation to form the two common
iliac arteries, where the Yena Cava will be found to be
exactly dorsad of the Aorta.

The Vena Cava, which lies to the right, and partially dor-
sad of the Aorta, may be followed forward as far as the pos-
terior border of the Liver, where it disappears ; and backward
to its origin at the junction of the two commonf iliac veins.

By pulling the lobes of the Liver forward from within
the vault of the Diaphragm on the left side, and dividing
the ligaments by which they are attached to it, a clear view

* A deeper extension of the Mesenteric Glands.

t The common Iliac Vein is formed by the confluence of the external and in-
ternal Iliac Veins,

Dissection of Common Rat. 189

may be obtained of {a) the (Esophagus, from the point where it
perforates the Diaphragm up to its arrival on the anterior
concave margin of the stomach ; and of {h) the white line of
the Pneumogastric nerve closely adherent to the dorsal segment
of the circumference of the (Esophagus.

To the right of the (Esophagus will be seen the anterior
abdominal portion of the Yena Cava, after it has left its
hiding-place in the Liver notch, and at the point where it
receives the many large branches of the hepatic veins, these
veins being in greater numbers here than in Man, on account
of the less degree of concentration of the lobes of the Liver. —
And, lastly, to the left of the (Esophagus, and nearer to the
back- bone, after a little careful dissection, will be seen the
Aorta.

Removal of Stomach, Spleen, Pancreas and Intestines.
Let a double ligature be now placed around the (Esophagus,
near to its entrance into the Stomach ; and a second double
ligature round the rectum about an inch from the anus ; and
let the intestinal tube be cut through with the scissors be-
tween the ligatures at these two points ; and the detached
piece be taken away by cutting through the vessels and other
connections which would retain it in the abdominal cavity ;
leaving the bile-duct about an inch long from the liver. The
right Kidney is thus exposed a very little further forward in
the body than the left. The smooth external surface of the
Kidneys should be noted, as characteristic of the class Mam-
malia.

The more minute examination of the Intestines should be
now proceeded with, in two portions ; by cutting through
the small intestine beyond the entrance of the Bile and Pan-
creatic ducts.

First note the form of the Stomach \ the pyloric portion
being more glandular and highly vascular than the cardiac ;
the (Esophagus entering the middle of the upper curvature ;

190 Mammalia,

the rudiment of a circular tendon, developed on its pyloric
division* ; and the Omentum, attached to its convex border :
also the diffused fleshy- coloured Pancreas, with its ducts ; the
relatively large size of the Spleen ; and the Bile duct.

The Stomach should now be pinned out on a cork, under
water, and a window should be made in one side of it in order
to expose the interior arrangement as much as possible in
situ.

The Student will then note the dense white Epithelium of
the cardiac half of the Stomach, projecting with a smooth
outline into the pyloric half, and easily separable from the
outer coating of the Stomach : also the extreme vascularity of
the pyloric portion, and the patches of gastric glands specially
visible in that part, immediately opposite as well as near to
the entrance of the (Esophagus : this vascular coat terminating
equally abruptly with the epithelial coat of the cardiac por-
tion just beyond the oesophageal opening. If the (Esophagus
and Pylorus be now slit down, the extra- muscular develop-
ment around each will be noted, especially around the former '■>
while the villous appearance at the commencement of the
small intestine contrasts markedly with the smooth or pitted
appearance of the mucous membrane of the pyloric portion
of the Stomach. A small piece should be teazed up and placed
under the microscope, by which means the membrane may be
seen to be formed almost entirely of minute vertical tubes,
which lie side by side.

The exit of the vessels of the Spleen along one regular line
should be noted ; and, in section, the network of fibrous or
trabecular tissue, of which the mass is formed. No duct
exists in connection with the organ.

The first inch and a-half of the small Intestine should be
slit down along the line of attachment of the mesentery : a

* A bird-like characteristic.

Dissection of Common Rat, 191

bristle passed into the ' common ' duct from its opening into
the Intestine ; and the villous coating noted, a small portion
being placed under a low power of the microscope.

The student should next direct his attention to the division
of large and small Intestines, marked by the presence of the
CcBCum^ or head of the colon {caput ccecum coli) viz. the rounded
pouch-like projection of the large Intestine, which receives, at
about an inch from its blind extremity, the termination of
the small Intestine. The Caecum should be cut open by mak-
ing a window in the side opposite the entrance of the small
Intestine, and making two incisions, — one along the attached
border of small Intestine to meet this aperture ; and the other,
opening the large Intestine, towards the same direction. The
absence of internal septa, dividing it into cells*, so commonly
found in Rodentsf will be noted ; as also, on the contrary, its
simple form and moderate size, which appears to be correl-
lated in this Order, with rooted tubercular molars, and a non-
exclusive vegetable diet. The Caecum is bounded towards
the small Intestines by a tumid white ring, representing the
ileocaecal valve, close to which is the commencement of the
large Intestine marked by longitudinal rugae and the absence
of villi ; the calibre of the large Intestine is about half that
of the Caecum. The longitudinal rugae do not extend beyond
three inches from the Pylorus ; after which the Intestine be-
comes both thinner and even- surfaced, except a slight pucker
here and there where a bend occurs.

Portions of the Small Intestine above the CcECum (for
Peyer's glands) ; of the Caecum itself ; and of the Large In-
testine, one piece taken near to the Caecum, and another near
to the Pectum, should be put under the microscope, in order
to see well the difference of the mucous lining.

The Intestines should now be separated from the mesentery,

* e.g. The spiral membrame found in the Hare ; or the honeycomb arrange-
ment ef the walls found in other species,
t Waterhouse.

1 92 Mammalia.

and tlie length taken, botli by a tape, and relatively to the
body, from snout to anus. The whole length will measure
seven times that of the hody, and, of this, one-seventh will be
Large Intestine : or, in inches, the whole will measure from
47 to 50 inches, the large intestine and rectum 6 to 7 inches,
and the small intestine 41 to 43 inches ; the Caecum measur-
ing from 1^ to 2 inches.

The Bile duct, which was left about one inch long from the
Liver, should next be traced up to that organ and the several
branches into which it breaks up, agreeably to the many
lobes of the multifid liver, noted. The absence of the gall
bladder in this species should also be noted: the anterior
lobe of the Liver {i.e., the lobe immediately in apposition
with the Diaphragm), corresponding to the " cystic " lobe in
Man, being here notched only for the suspensory ligament.
The lobe immediately posterior to the cystic lobe and extend-
ing mainly to the left is the " left lobe " ; while the numerous
lobes to the right of, and forming the posterior section of the
organ are homologous with the '* right lobe *' of the human
Liver. This follows the usual rule in the Multifid Liver, viz.:
that the cystic, suspensory, or middle lobe is the largest : the
portion of the gland to the right of this lobe being subdivided
into two or more lobules, of which the extreme right may be
the larger, and marked on its posterior aspect by a depression
for the kidney ; and that portion to the left more commonly
remaining as a single lobe.

The Hepatic artery is readily seen coming from the Aorta
about a quarter of an inch posterior to the Diaphragm : and
within half an inch of this, farther back, may be seen the great
trunk of the Inferior Cava (or Post-caval of Owen), crossing
just ventrad of the anterior extremity of the right Kidney
to pass through the accumulated attachments of the right lobes
of the Liver, and through a groove in the middle or cystic
lobe prior to piercing the Diaphragm.

Dissection of Common Rat. 193

Removal of Liver. — The Liver should be now removed
from the Abdomen by cutting across the remaining ligaments,
and the vena cava (leaving it as long as possible, so as to be
easily distinguishable after removal of the Liver).

The general structure of the Liver should be examined
under the microscope, sections being made in various direc-
tions, to expose the lobular arrangement with the intervening
interlobular veins, and the intralobular radicles ; the specimen
before us having been injected from the jugular vein, will
have the hepatic veins coloured by the injection*.

The Kidney may be next removed for examination, by
dividinor its vessels about the middle : at the anterior ex-
tremity and rather underlying it is the supra-renal body, much
resembling the surrounding fat. The Ureter and the Renal
vein and artery lie close together in the longitudinal fissure,
or hilum, that marks the inner excavated border. Opposite
the fissure is a hollow in the interior of the Kidney, called a
sinus, into which the hilum leads.

In order to see the interior, it will be necessary to cut
through the Kidney, from its concave to its convex border, a
little to the side of the vessels, and then to slit up the latter.
The section of the Kidney presents the typical Mammalian
arrangement, viz.: an external, granular, or cortical part,
and an internal, pyramidal, or medullary part ; but diflPers
from that in Man in that there is but a single papilla into
which all the renal tubuli open. The investigation of the
secreting tubes, &c., must be conducted with specially injected
specimens of this organ ; and is not easily conducted with the
Kidney of a small animal as that before us.

Returning again to the body of the animal, the student
should trace hack the Ureter from the Kidney left in situ.
Of the three vessels in the hilum, that which is anterior is

• In order to expose the persistent companionship of the vena porta, hepatic
artery, and hepatic duct, the liver must he specially injected and hardened.
Vide Introduction,

CC

194 Mammalia.

the renal artery ; next comes tlie renal vein, and posteriorly,
of a rather dark color, is the Ureter. This tube, by which the
fluid secreted in the Kidney is conveyed to the bladder, is
directed obliquely backwards and inwards towards the middle
line along the dorsal wall of the abdomen, and passes vent r ad
of the common iliac artery of that side, and of the anterior
crural nerve which meets it at that point. A slight incision
should be made into the ureter close to the Kidney, and a
bristle passed along it. A probe should be passed up the
Rectum ; the sudden contraction of the last inch of the In-
testine noted ; and also the relative position of the anus.

In Examination of the Diaphragm*, the Student should
note this muscle to be made up of a central tendinous (or
aponeurotic) part, and a fleshy periphery. The fleshy portion
takes its origin from the cartilages of all the false ribs and of
the last true rib, and from the superior (internal) surface of the
ensiform cartilage : its fibres converge towards the centre ;
and it is inserted between the ribs and the spine. In the
centre, close to the right of the tendinous part, is an opening,
foramen dextrum, through which passes the inferior vena
cava : to the left of the middle line, near the foramen dex-
trum, is a second opening, foramen sinistrum, for the passage
of the oesophagus and pneumo- gastric nerves : close up to
the vertebral column, ventrad of which the course of the
aorta has been already noted, are two large muscular pro-
cesses, of which the right is the longest and largest, termed
the crura or pillars of the Diaphragm, forming an inverted arch
beneath the aorta ; this arch is known as the hiatus aorticus,
and through it the thoracic duct passes, as well as the aorta.

Dissection of the Thorax. — The Pectoral muscles over
the chest must now be carefully cleaned away and reflected on
each side. First, let the skin be severed and reflected along
the arm ; secondly, let the Panniculus Carnosus be reflected

* ha(ppaffaio, to separate two parts.

Dissection of Common Rat. 195

outwards ; next, let the Pectoralis major be detached by-
dividing the muscle along its attachment to the Clavicle (but
being very careful not to injure the injected jugular vein
which will be seen to pass superficial to the" Clavicle) and by-
making a vertical incision through its substance a little ex-
ternal to its line of attachment to the sternum and costal
cartilages. This muscle should then be reflected outwards,
and its tendon, attached to the Humerus, carefully examined.
By this means the Pectoralis minor, situated at the upper part
of the Thorax immediately beneath the Pectoralis major, will
be exposed, arising from near the cartilages of the anterior
ribs, and inserted into the Coracoid process of the Scapula.
The costal attachment of the Pectoralis minor should be
divided across, and the muscle reflected outwards, by which
means the axillary vessels and nerves are brought fully into
view, and should be next examined.

In the Axilhy or space between the upper and lateral parts
of the chest, and inner side of the arm, are contained
the axillary vessels and the brachial plexus, with their
branches. This cavity is filled with a good deal of areolar
tissue, which must be carefully removed, and the vessels and
nerves cleaned from the clavicle to the elbow. The chief
vessel crossing the outer portion of the space is the axillary
vein ; close to this is the (white) median nerve, and just in-
ternal to these is the axillary artery ; the axillary vein always
being on the Thoracic side of the artery, and of greater
calibre. The Biceps muscle, which extends from the Scapula
to the Radius, fills up the rest of the outer space. A bristle
should, be passed up the artery for further investigation later
on. The axillary vein bringing the blood up from the fingers
terminates about a quarter of an inch posteriorly to the
Clavicle, and becomes the subclavian vein. The axillarij artery
is the continuation of the subclavian artery, which comes from
the Arteria innominata on the right side ; but direct from the

196 Mammalia,

Aortic arch on the left side. The median nerve, so called from
the course it takes along the middle line of the arm to the
hand, arises by two roots from the Brachial Plexus, which the
student should now trace up, being very careful not to injure
any of the injected vessels^ We may here give a caution
which should in every case be observed, namely, always to
work with th6 scalpel along the line of direction of a vessel or nerve,
and never across it. The Brachial Plexus is formed by the
union of the anterior branches of the lower cervical and first
dorsal nerves, and extends from the lower part of the side of
the neck to the axilla, being plexiform only in one part, and
that not far from the neck. Around the plexus and the
axillary vessels may be found traces of lymphatic glands im-
bedded in the areolar tissue.

Beneath the axillary vessels and nerves, with its deep
surface resting upon the ribs and intercostal spaces, is the
Serratus magnus muscle noted above ; this muscle is covered
in front by the Pectoralis major. The sternal digitations of
this muscle in part overlie the small serially repeated ex-
ternal Intercostal muscles which extend from the tubercles of
the ribs nearly to the outer end of the cartilages. The fibres
of the Inter costals are attached to the adjacent margins of each
pair of ribs, and are directed nearly parallel with the sternum.
The action of the external intercostals is to elevate the ribs .
they are, therefore, muscles of inspiration : in this action they
are aided by part of some deeper muscles just within the ribs>
termed the internal intercostals, viz., that part apparent
between the costal cartilages (from their outer end to the
sternum), and whose fibres have a general oblique direction
downwards (towards the sternum) and forwards (towards the
head), therefore, to some degree crossing those of the
external intercostals. The lateral portions of the internal
intercostals, underlying the external intercostals, act as de-
pressors of the ribs, and therefore aid in eorpiratory eflPorts.

Dissection of Common Rat. 197

Removal of Sternum. — The student should now carefully-
clean the ribs and sternum from the junction of the clavicle
with the manubrium*, down to the ensiform cartilage, until
he can distinctly verify each rib. The sternal half of the
diaphragm should then be separated from its attachment to
the ribs with the scissors, and allowed to fall back ; the student
taking special care not to detach anything from its thoracic
aspect, lest in doing so he separate the Phrenic nerves which
reach the diaphragm right and left of its centre. The Ribs
should then be divided on either side, following the line of
junction between the true ribs and the costal cartilages ; and the
clavicle dislocated from the manubrium. Great care will be ne-
cessary to avoid puncturing the vessels anteriorly. The inter-
nal surface of the thoracic wall should be freed from the lining
membrane (pleura) with the handle of the scalpel as it
gradually admits of separation from the enclosed organs ; this
done, the sternal wall of the thoracic cavity should be
removed.

The bag of the Pleura being now opened, the cavity with
its contents will be ready for examination. Anteriorly is the
Sternal attachment of the sterno-mastoid muscle, and the
Thymus gland. Next is the Heart in its pericardium, and on
either side the Lungs. The size of the thoracic cavity varies
during life, both transversely and in depth, concomitantly
with the situation of the ribs and diaphragm in breathing.
The Pleura are two serous membranes or closed sacs, which
are reflected around the Lungs in the cavity of the thorax.
These pleural sacs approximate, but do not blend, along the
middle line ; and this median portion thus constructed of two
membranes is termed the mediastinum^ . The part of the
mediastinum in front of the Heart extends from the pericardium

* Manubrium^ a handle : the Sternum being looked on as a short broad dirk,
the ensiform cartilage being the point.

t Mediastinum, medius the middle ; sto, I stand.

198 Mammalia,

to the inner surface of tlie sternum : and if the student will
hold up gently with the forceps this upper portion, he will
see the sort of inverted A thus formed ; the stem being
mediastinum anterior ; the branches, the internal side of the
pleural sac on each side ; the space between the branches being
occupied by the pericardium, or membrane surrounding the
heart. On gently pulling down the diaphragm, the thin
white cords of the Phrenic nerves will be apparent ; coming
down nearly in a straight line ventrad of the roots of the
Lungs and by the side of the pericardium {i.e., between it and
the mediastinal portion of the pleura), to the Diaphragm.

Exposure of Yessels, &c., in the Neck, — When the
Student made the incision in the median line through
the skin from the symphysis of the lower jaw, and
reflected the skin on either side ; he by this means exposed
the sub- maxillary gland, as a large pinkish mass. This should
be divided in the middle line, as also the sterno-mastoid,
sterno-thyroid, and other muscles more or less closely connected
with it in the neck, and reflected to each side, by which means
the trachea will be exposed, and the vessels and nerves on either
side of the neck.

And here the Student will observe — first, that it is the
external, and not the internal jugular that is the main
trunk by which the blood from the interior of the skull
returns to the heart in these Rodents, and which by its con-
fluence with the vein from the anterior limb constitutes the
vena cava descendens : the internal jugular being here repre-
sented only by a small vein passing dorsad of the clavicle, and
forming the third confluent tributary in the same relative
position as in Man ; and — secondly, that in forming this union
the external jugular crosses the clavicle on the outside, and then
together with the subclavian penetrates into the thoracic
cavity in the interval between the clavicle and the first rib,
the two veins uniting as they enter the cavity. Thus in two

Dissection of Common Rat 199

points does the arrangement of these vessels differ from that
in Man, where the external jugular runs parallel with the
posterior border of the sterno-mastoid muscle as far as its at-
tachment to the clavicle, and then perforates the deep fascia
dorsad of the clavicle to join the sub-clavian vein ; and — the
internal jugular is the chief vein from the head.

Dissection of Phrenic Nerves. — The Student should
now remove the mass of Thymus gland that hides the
continuation of the jugular and subclavian veins in their
course towards the Heart ; and be careful not to cut away
the pericardium with it, nor injure the vessels covered
by it.

To find the left Phrenic nerve, he will first note
the curve made by the descending cava round the first rib,
and the crescent it forms immediately afterwards, of which
the second left rib might form the centre. If then he
carefully dissects on the concave side of the crescent, he
will find close adherent to the vessel, at a point just oppo-
site the second rib, a thin white cord, which is the left
Phrenic nerve. This he should trace back nearly in a straight
line ventrad of the root of the single-lobed left lung, by the
side of the pericardium, between it and the mediastinal
portion of the pleura ; and by the left side of the fourth lobe
of the right lung, to the diaphragm. The right Phrenic
nerve may be traced in the same way, from the internal as-
pect of the concavity of the crescent of the right descending
cava, along the outer side of its posterior termination, across
the roots of the right lung, and along the course of the ascend-
ing or inferior cava to the diaphragm. These diaphragmatic
or Phrenic nerves take origin from the posterior cervical
nerves, and are therefore spinaly not cranial nerves.

The existence of a left vena cava descendens is again a point
to be noted, as different from the arrangement of vessels
usually found in Man, where the left jugular and subclavian

200 Mammalia,

yeins cross over by an * innominate ' vein to form, with the
corresponding vessels on the right side, one vena cava superior.

Examination of Lungs and Heart. — The Lungs
will be seen to be freely suspended in the Pleural
cavity, and to bear no marks of the ribs, &c., on their
exterior. They are made up of five lobes, of which some are
apportioned to the right and some to the left section of the
organ, according as they are supplied from the right or left
primary branch of the pulmonary artery. In this specimen
four lobes enter into the composition of the right Lung ; the
fourth lobe being in the middle line in relation with the
apex of the heart above, and the left Phrenic nerve on its left ;
this lobe, in excess of the three-lobed constituents of the right
Lung in Man, is termed the post-caval lobe, as being notched
on its dorsal surface for the passage of the inferior cava,
after it has pierced the diaphragm en route to the Heart.

Between the post-caval lobe and the left Lung, dorsad of the
left Phrenic nerve, the student will readily perceive the
(Esophagus with the Pneumogastric nerve lying on it, which,
after piercing the diaphragm, continues forward dorsad of the
root of the left Lung. Further he will note the anterior
margin of the left Limg, and of the anterior lobe of the right
Lung to be indented by the descending cava of each side ;
that of the left side passing ventrad of the root of the left
Lung, and winding round the left contour of the Heart to
reach the back of the right ventricle. The two descending
cavse thus enclose in their grasp the roots of all the vessels
leaving the heart.

The root of the Lung will be seen to consist, on its ventral
aspect, of the vessels proceeding between the Lungs and the
Heart, viz., the pulmonary arteries and veins ; dorsad of
these, and hidden by them, are the air tubes or Bronchi, which
by their union, as will be shown presently, form the Trachea :
dorsad of the Bronchi, as may be seen by lifting up the left

Dissection of Common Rat, 201

Lung, the (Esophagus passes, as above noted : dorsad of the
CEsophagus, close to the back and slightly to the left of the
median line, being partially hidden by the left lobe of the
right Lung, will be found the Aorta, of which the abdominal
portion (up to the Diaphragm) has been previously traced :
and lastly, in the anterior portion of the Thorax, coming away
from between the ventral aspect of the spinal column, and
the Aorta, will be seen the Vena Azygos of the left side,
which, after passing round the root of the left Lung, joins the
left vena cava descendens.

The stratification of the three chief sy sterns of the body may
be here noted, and should be well borne in mind, for it is
characteristic of all Yertebrata to have the Vertebral column
tvith its cotitained nervous system dorsal, the Heart ventral, and
the Digestive system intermediate to the other two.

Dissection of Vessels and Nerves in the middle line

BETWEEN THE CUT ENDS OP THE FlRST AND SeCOND RiBS ON

EITHER SIDE. — The Heart lies opposite the middle of the
Sternum, its longitudinal axis inclined obliquely from above
downwards, slightly backwards and to the left : being, as it
were, dependent from the vertebral column ; consequently,
the apex alone comes near the Sternum.

By cleaning carefully the vessels at the anterior part of
the base of the Heart, their relative positions will be found to
be as follows : to the right, the right vena cava descendens ;
and next, the commencement of the arch of the Aorta (not
colored by the injection), from which a branch proceeds
straight forwards between the vena cava and the Trachea,
which is the Innominate Artery. This Artery should be traced
forwards with great care to about opposite the cut end of the
first rib, where it will be found to bifurcate, one branch con-
tinuing onwards as before, which is the right common carotid ;
the other branch bending under the point of junction of the

D d

202 Mammalia,

jugular and subclavian veins, and forming the right subclavian
artery. Now the Student will see the reason of his care, for
crossing the subclavian artery at its point of origin, and run-
ning forwards parallel with the Trachea, at first external to the
carotid, and then crossing it about a quarter of an inch further
forwards than the bifurcation, is the right Pneumo- gastric
Nerve. This Nerve may now be traced back between the
Innominate Artery and the right cava, and forwards in com-
pany with the carotid artery. "We have thus demonstrated
on the right side, the Phrenic nerve on the right of tl\e right
cava, and the Pneumo -gastric on the left of the right cava,
at the point just opposite the cut end of the second rib.

Now let the Student cut through the vena cava as it courses
round the^rs^ rib, and immediately dorsad of this vessel he will
find the Phrenic nerve continuing its straight course, and pass-
ing ventrad of the subclavian artery, about one eighth of an inch
from the spot where the Pneumo- gastric crosses it. This nerve
may be now followed up in the neck, and by this means its whole
course is exposed, which, briefly summarized, is as follows : —
commencing in the cervical region near the Thyroid cartilage,
it courses down the neck, crosses the subclavian artery dorsad
of the vena cava superior, on the side of which it continues
to the Heart ; it then crosses ventrad of the roots of the
right Lung, and follows the course of the inferior cava to the
Diaphragm.

If now the left vena cava descendens be slightly raised at
the corresponding point, the Student may, by careful dissection,
make out the difierence between the arrangement of arterial
branches on this side, as compared with the other. First
he will come upon, near the middle line, the left common
carotid artery, arising direct from the Aortic arch, across
which, closely adhering to the inner side of the left cava, he
will find the left Pneumo -gastric nerve to run ; and secondly,
a little deeper, he will come upon the left subclavian artery, also

Dissection of Common Rat 203

arising directly from tlie arch of tlie Aorta, but external to
the carotid. The arch of the Aorta will be seen to turn over
towards the back and left side, then to cross over a highly-
injected vessel, which is the pulmonary artery arising from
the right ventricle, and then to disappear dorsad of the left
cava, and proceed towards the back-bone. If the cleft between
the right auricle and ventricle be looked into, the root of the
Aorta will be seen to take origin dorsad of, and rather
behind the root of the pulmonary artery.

Removal of Left Lung. — The Left Limg should be now
removed by section through its root, and the left descending
cava cut across, leaving the Phrenic nerve in situ, and the
Pulmonary artery and Aorta untouched. By this means may
be seen the intermediate course of the Pneumo- gastric nerve,
which will be best traced from the point we left it last, m.,
where crossing the subclavian artery ; from this point it is
readily followed downwards ventrad of the Aorta, almost
adhering to the dorsal aspect of the Pulmonary artery, and
reaching the Oesophagus at the point where the Trachea
comes first into apposition with the (Esophagus, just dorsad
of the root of the left Lung.

By this section, also, may be traced the course of the
Aorta, after giving off the left subclavian artery ; at first in
close apposition with the left of the Trachea, then of the
(Esophagus, and lastly, taking up a position almost dorsad of
the Oesophagus, but slightly to the left, in which position it
continues its course down the back, in the inter-pleural space
ventrad of the spine, until near the Diaphragm, at which
point, *as above noted, it is directly dorsad of the Oesophagus.

It will thus be seen that the Aortic trunk is sinorle,
which is a characteristic of all warm-blooded animals ;
and secondly, that this single trutik arches over towards the
left, encompassing the root of the left Lung, a matter to be

204 Mammalia,

noted in contradistinction to the direction of the Aortic arch
in the Bird.

By turning up the apex of the Heart, the course of
the left vena cava may be traced round the base of the
ventricles behind, dorsad of the pulmonary vessels (which
may be seen on either side towards the Lungs), to be joined
some distance to the left of the right auricle by the ascend-
ing cava, forming a large sinus at the back of the Heart.

Examination of Trachea. — The Student should now
cut across the right vena cava descendens near the auricle,
and the Aorta near the Heart, and pressing the Heart
backwards dissect awav the connective tissue and remains
of pericardium at its base. By this means he will be
enabled to see the bifurcation of the pulmonary artery,
and just internal to this, but following the same direc-
tions, the subdivision of the Trachea into the two Bronchi :
the swelling contained within the angle of the pulmonary
artery being the point of junction of all the pulmonary veins
on their entrance into the left auricle. By cutting through
these Pulmonary vessels as they come into view, and lastly by
cutting through the ascending cava near its entrance into the
right auricle, the Heart may be removed.

The Heart differs little from that of the Sheep, and it will
therefore be unnecessary to enter here into a particular in-
vestigation. The enormous thickness of the walls of the left
ventricle, and the extreme tenuity of the walls of the right
ventricle should, however, be noted, as also the great extent
of the sinus at the back.

Removal of Right Lung. — The Trachea may be now
cut through just posterior to the arch of the Aorta; but
care must be taken not to cut through, at the same time,
the (Esophagus, which is closely adherent to the dorsal
aspect of the Trachea at this point : and the right Lung
removed. Here the Student should remark that the

Dissection of Common Rat, 205

Trachea consists of a series of pieces of cartilage, segments
of rings, which are connected together by fibrous tissue, each
piece of cartilage forming an incomplete ring. By placing a
piece under a low power of the microscope, he will further note
that between the ends of the cartilages is a continuous trans-
verse layer of unstriated muscle, which is attached to the
truncated ends and the inner surface of the cartilages, under-
lying a few superficial longitudinal fibres. The mucous
membrane lining the tube is furnished (when fresh) with a
columnar, ciliated epithelium. Again, it will be noted that
the right Bronchus is subdivided near the Lung, into as
many primary branches as there are lobes, and that in point
of position each Bronchus is situated dorsad of the pul-
monary arteries and veins.

If now the Student will make a flat section of one lobe of
the Lung, cutting it in the direction of its largest superficies ;
and a second, straight through and across the lobe, he will be
enabled to see the larger branches of the bronchi, and their
mode of branching ; also the blood-vessels, and the general
cellular structure throughout. If specially injected and
hardened (when fresh), the structural changes in the air-
tubes should be examined under a microscope ; the pieces of
cartilage seen in the Trachea becoming broken up in the
smaller bronchial tubes, and scattered over the wall as ir-
regular fragments, and lastly disappearing : the fibrous and
elastic tissues of the bronchial tubes being alone continued to
the air cells.

Dissection of Sympathetic Cord, &c., in the Thorax.
— Yentrad of the spinal column, lying in the interpleural
space, are the Aorta, Azygos Veins, CEsophagus, and
Splanchnic Nerves, all of which should be traced out.

If the Student will examine the wall of the Thorax, about
a quarter of an inch to the right of the middle line, he will
trace a slight seam taking a longitudinal direction. This

206 Mammalia.

should be carefully followed with the point of the scalpel ; and
at a little depth below the surface he will come upon a white
cord. This is the cord of the Sympathetic Nerve, which lies
just ventrad of the bodies of the Yertebrae : its fibres may
be traced forwards dorsad of the Azygos Yein, to about the
level of the second rib, and backwards to the diaphragm.
In such a small subject, the Sympathetic is not easily traced,
except by a practised hand, through the anterior aperture of
the Thoracic cavity ; and should the Student attempt to trace
the right Sympathetic cord, he must follow it up dorsad of
the subclavian artery, about one eighth of an inch from its
origin at the Aorta ; and then along the side of the carotid
artery. Under a lens the ganglia on this cord should be
noted : especially opposite to the cut ends of the first and
second ribs. There may also be noted branching from it,
about an inch anterior to its perforation of the diaphragm, a
smaller nerve, the great Splanchnic, which perforates a cms
of the Diaphragm. On the left side of the body, the left
Azygos Yein, the entrance of which into the vena cava
descendens was noted above, should be traced back alongside
of, but slightly dorsad of, the Aorta ; on its dorsal aspect will
be found the corresponding cord of Sympathetic Nerve.

The Aorta and Oesophagus should both be cleaned, and the
Pneumo- gastric nerves left in situ, one on each side of the
(Esophagus.

In the neck, the Phrenic nerve being very fine is not easily
traced to its origin ; but the Sympathetic and Pneumo-
gastric should be traced up to the Head, closely adhering to
the Carotid artery. The common Carotids should be followed
up on either side to the point of their bifurcation into the
internal and external Carotids, which will be found to take
place on the level of the anterior termination of the Trachea,
viz.^ opposite the Larynx.

Dissection of Salivary Glands. — The Student should

Dissection of Common Rat. 207

now with the scissors make the two following cuts : one from
near the angle of the mouth to the anterior corner of the eye,
and another from the front of the ear, in a direction above
the level of the eye ; and join these two cuts along the lower
margin of the eye. This piece of skin should be dissected
away, and also the underlying superficial muscles and fascia.

There will then be apparent the outer margin of the
almost conjoined Hybernating and Submaxillary Glands,
which were reflected in a previous dissection ; and between
them and the Ear the Parotid Gland. From the lower
margin of the Parotid Gland, a duct will be seen pass-
ing to the angle of the mouth : this is the duct of the Parotid
— Steno's duct. The muscle over which it passes on a level
with the teeth of the lower jaw, is the Masseter muscle.
Between the upper margin of the Parotid Gland and the Eye,
a second perfectly distinct gland of a darker hue (in the
fresh state) than the Parotid may be made out, from which
a rather broad duct proceeds to enter the orbit ; this gland
is the facial, extra- orbitally placed portion of the Lachry-
mal Gland. The orbital portion of this gland may be brought
to view, together with the Harderian Gland, by gently press-
ing the eyeball upwards and forwards.

Dissection of Anterior Factors of Descending Cava.
— The Student should now clean and separate the three
glands just seen from one another, turning the Submaxillary
downwards, the Lachrymal up over the Ear, and leaving
the Parotid in situ. By dissecting in the substance of the
Parotid Gland, the Student will find the vessels from the face
uniting to form the commencement of the temporal vein,
which reaches from the Zygoma on which it rests to the
angle of the jaw, and is succeeded by the external jugular
vein. He should then trace this back along its course, which
is marked by a line from the angle of the lower jaw to the
clavicle, crossing the sterno-mastoid muscle ; and will note

208 Mammalia.

that it is joined, a little distance anterior to the clavicle, by
the anterior jugular vein, which arises from the convergence
of some superficial branches in the submaxillary region.

The further dissection of the Head will be better traced in
a larger subject, e.g., the Head of a Sheep, to which we
propose to call the attention of the Student for his next
dissection.

lY. THE CEEEBRAL NERYES, &c.

AS DISSECTED IN THE

SHEEP'S HEAD.

General Examination. The Sheep's Head as usually
supplied from the market is devoid of skin, and without its
external ears ; the junction of the Ear with the Head being
indicated by the cartilaginous portion attached to the ex-
ternal auditory meatus.

The occipital condyles stand out clearly, denuded of their
connections with the first cervical vertebra or Atlas ; between
them is the cut end of the spinal cord, surrounded by its
loose sheath of Dura Mater ; loose, that is, around the cord
which is much smaller than the sheath ; but attached to the
ventral segment of the circumference of the Foramen Mag-
num. The cord itself presents in its section the shape of a
flattened cylinder, and will be found to be closely invested
with a dense white coating, or Neurilemma,* formed by the
membrane called Pia Mater ; between this Neurilemma and
the sheath of Dura Mater is the cavity enclosed by the
delicate, serous, Arachnoid membrane. The section of the

* Neurilemma, pevpop, a nerve ; Xf/x/^a, a peel or coyering.

Dissection of Sheep's Head. 209

cord also displays — the dorsal and ventral fissure by whicli it
is divided into two equal and symmetrical portions ; — the ar-
rangement of grey matter in two crescentic masses, placed
one in each lateral half of the cord, with their convexities
towards each other, each crescent having a dorsal and a
ventral horn, of which the ventral is much the larger and
fuller ; and lastly — in the centre, the central canal of the
spinal cord, which opens anteriorly into the Calamus Scripto-
rius of the fourth ventricle. The cord in its sheath rests
upon the basi-occipital, and is roofed over by the supra-
occipital bone ; the main bulk of the condyles being made up
of the ex-occipitals, though also containing a portion of basi-
occipital.

In the middle line, on the crest of the supra- occipital bone,
will be found some yellow elastic substance, which is the
anterior extremity of the ligamentum nucha3. This ligament
extends from about the second dorsal spine posteriorly, and
supports the weight of the head and neck. Likewise on the
supra- occipital crest, but external to the ligamentum nuchas,
on either side will be seen a muscle cut short : this is the
origin of the Splenius muscle, which is situated along the side
of the neck, and is inserted into the transverse processes of
the posterior cervical vertebra), and the spinous processes of
the anterior dorsal vertebrae ; — taken together, their action is
to elevate the Head ; singly, they flex the Head to one side.

About half an inch ventrad of the external margin of each
occipital condyle, the firm point of a bone will be felt ; this
bone will be the par-occipital process, a development of
a process homologous with the jugular process in Man.

From the root of the par- occipital (close to the condyle) an
imaginary line drawn forwards to the ventral margin of the
orbit will pass through the Ear cartilage, and along the
Zygomatic arch.

Just anterior to the Ear is the situation of the condyle of

E s

210 Mammalia.

the jaw, ventrad of the Zygomatic process ; and in a relative
position dorsad of the Zygoma is the situation of the coronoid
process of the jaw.

Immediately above the cartilage of the Ear will be seen a
knob of muscle : this is the Temporalis vel Temporo-
maxillaris ; it fills up the Temporal fossa of the Skull.

The limit of the Brain cavity anteriorly may be marked by
a line drawn between the orbits, just in front of the ridge of
the Frontal bones ; hence to expose the Brain with a view to
getting it out entire, the saw should be passed through the
skull bones in a horizontal line from the occipital condyle to
the middle of the Frontal ridge.

Attached to the Head will be generally found the anterior
portion of the Trachea, recognised by its ringed structure ;
and dorsad of the Trachea, in close connection with it, the
anterior end of the CEsophagus.

If a line be drawn from the outer margin of the occipital
condyle, passing just internal to the point of the par-occipital
process, to the outer margin of the QEsophagus ; such line
will pass the generally patent orifice of the cut end of the
* common carotid,* about an inch ventrad of the par-occipital
process.

Dissection of Parotid Gland, &c. — Placing the Head
with the side of the Face towards him, the Student
will first consider the position of the superficial structures
he is about to dissect, as follows : — The Parotid Gland
lies almost in a straight line along the posterior margin
of the ramus of the jaw, coming round on to the face but
slightly at the angle of the jaw, but extending further for-
wards close by the Ear. From just within the anterior
margin of this gland, there issue across the face several
nerves and one duct, in the following order : first, there are
two fine nerves in a line from the ear to the angle of the
mouth ; half an inch below these, in a line from the occipital

Dissection of Sheep* s Head, 211

condyle to tlie angle of tlie mouth, is a larger nerve brancli ;
an inch, and a quarter below this, in a line from the par-
occipital process to a point about two inches along the
'body' of the jaw, is a duct; lastly, a quarter of an inch
below this duct, running in a parallel direction, is another
nerve.

The fat should he now removed from the surface of the
Parotid Gland, and it will be best to begin between the Ear
and the par- occipital process, and then work forwards, being
specially careful (when the anterior edge of the gland is
reached) to work towards the mouth, not across, in order to
avoid dividing the nerves and duct, which mainly lie in the
direction of the mouth.

The Parotid Gland will be found to be limited above by
the Zygomatic arch, to present a lobulated appearance, and
to be of a reddish brown colour.

The Student will next trace out the nerves, &c., in the
following order :

First, the large nerve twig (the second noted above), an
inch and a half from the top of the gland, should be cleaned
forwards as far as is possible*, and then should be traced
back in the substance of the Parotid, where it curves up-
wards as it gets deeper, in a direction between the Ear and the
condyle of the jaw ; and here the Student must be careful not to
injure a second nerve he will meet with deep down, coming in
from the direction of the angle of the jaw. When this last
nerve is reached, it should be traced forwards through the
substance of the gland, in a direction towards the angle of
the jaw ; it will be found to be the lowest of the four men-
tioned in the first instance ; and should be traced forwards
across the face, following close along the edge of the ramus.
These two nerves thus traced out are the two terminal

* The anterior branches of it are frequently removed with the skin.

212 Mammalia.

brandies of the Portio dura of tte seventh nerve, the motor
nerve of the face ; consequently, generally known as the
Facial Nerve. The larger, and superior, of these two branches,
emerging upwards and forwards through the Parotid Gland,
and crossing the ramus of the jaw just below the neck of the
condyle, is the Temporo -facial branchf. The other division,
emerging obliquely downwards and forwards through the
Parotid Gland, and dividing opposite the angle of the jaw
into branches which are distributed on the lower part of the
face and upper part of the neck, is the Cervico- facial branch.

The Student should next continue tracing the Facial Nerve
further down in the substance of the Gland, and only just a
quarter of an inch beyond the junction of the Cervico-
temporal and Cervico-facial branches, and on the opposite
side of the Cervico-temporal to that on which the Cervico-
facial was found, he will come upon a nerve twig passing from
the main stem just below the Ear, and curving round and
upwards to reach the surface between the posterior margin of
the orbit and the knob of muscle above the Ear which fills
the Temporal fossa, above noted as the Temporalis or Temporo-
maxillaris muscle : this is the Auricular branch of the Facial
JNFerve.

By continuing the dissection of the main nerve stem a
bare eighth of an inch further into the Gland, the Facial
Nerve will be traced down to its exit from the Skull, through
the Stylo-mastoid foramen.

Secondly, he should trace the fine nerves near the top of
the gland, in front of the Ear ; these will be found to run
forwards towards the angle of the mouth, and backwards,
united, within the Parotid Gland, or rather between it and the
internal layer of muscle, and not penetrating the substance of

t This nerve will be seen to be connected with the auriculo- temporal nerve,
to be described below, as it crosses the ramus.

Dissection of Sheep's Head. 213

the gland ; they should be traced deep down in front of the
external auditory meatus, internal to the auricular branch of
the Facial, and there left for the present. The Nerve of
which some of the branches have been thus traced back, is
the Auricula- Temporal Nerve, a branch of the larger sub-
division* of the Inferior Maxillary division of the Fifth or
Trigeminal nerve. At the point at which we leave it, it has
just turned up between the external ear and the condyle of
the jaw, under cover of the Parotid ; and we have seen it
escape from beneath this structure and divide into several
branches, some of which are branches of communication with the
facial nerve, which they meet on the superior border of the
Masseter muscle.

Lastly, the duct that intervenes between the two branches
of the Facial Nerve should be traced in a curved horizontal
direction (like the middle of the letter co), across the Masseter
muscle ; at first inclined to follow the direction of the Cervico-
facial nerve ; then, about an inch from the border of the
Gland, curving upwards to the angle of the Mouth, which it
passes by; and finally opening on the inner surface of the cheek
by a small orifice opposite the second molar tooth of the upper
jaw. In dissecting this out, it will be of great assistance to
pass a bristle along it, or a fine probe, to give the direction.
Yery frequently the middle part of the duct is removed with
the skin, but even then both ends should be traced; the
anterior inch, which is much dilated as it perforates the buc-
cinator muscle, and passes in company with the facial vein
internal to the facial nerve and artery, being readily found
in the detached gland connected with the Parotid, viz.,
the Glandula Socla Parotidis, situated at the angle of the
mouth, and whose duct opens into that of the Parotid. The

♦ This, the larger hranch of the Inferior Maxillary, receives only a few
filaments from the motor root ; and hence is more of a sensory than of a motor
nerve.

214 Mammalia,

course of tlie Parotid duct is frequently marked by pigment.
By tracing it a sliort distance within the substance of the
gland, the component radicles of the main duct will be ap-
parent coming in alternately from either side.

The Nerves and duct should he next cut across about the
middle of their course, and reflected together with the sub-
cutaneous fat, in order to expose the chief muscle of the face,
which has been incidentally mentioned above, viz., the
Masseter Muscle. This muscle consists of several layers, in-
tersected by tendinous bands, enclosed in aponeurosis. A
superficial portion is marked out, arising from a tuberosity on
the superior maxilla by a thick tendon, its fibres passing
obliquely downwards and backwards, to be inserted into the
outer surface of the posterior border and angle of the inferior
maxilla. A middle portion of the muscle lies rather deeper,
and arising from the ridge of the malar bone and anterior half
of the Zygomatic arch, its fibres also passing to the angle
posterior external surface of the ramus. A third and
deepest portion, rising from beneath the Zygomatic process,
is inserted into the external surface of the ramus, just below
the Sigmoid notch, between the condyle and the Coronoid
process.

One other muscle may be noted in close relation with a
nerve, viz., the Levator lahii superioris alseque nasi, which is
situated on the side of the face, arising close to the point of
origin of the most superficial part of the Masseter, and ex-
tending forwards to the upper lip. By reflecting this muscle
from its upper side, and cleaning away the subjacent fat by
longitudinal scraping, the anterior termination of the infra-
orbital nerves will be disclosed. It will be remembered that
from the Gasserian ganglion, near the commencement of the
Fifth Nerve, three large branches proceed : the Ophthalmic,
Superior Maxillary, and Inferior Maxillary. Of these the
two first are purely sensory ; at the present point in the dis-

Dissection of Sheep^s Head. 215

section we come upon the termination of the second branch,
viz., the Superior Maxillary, which, after leaving the cranium
together with the Ophthalmic through the Sphenoidal fissure*,
crosses the lower part of the Zygomatic fossa, enters the
maxillary hiatus, passes through the infra -orbital canal, and
emerges on the face at the infra-orbital foramen, where we
now find it dividing into numerous facial branches, especially
nasal and labial, and in close relation with the ultimate
fibres of the temporo-facial nerve.

The anterior inch and a half of the body of the inferior
maxilla should be carefully examined (especially about an
inch behind the teeth), for the anterior appearance of the
dental nerve through the mental foramen : that nerve, namely,
which traverses the dental canal in the inferior maxilla ;
entering the canal by the dental foramen, an opening
one inch below the sigmoid notch on the inner side of the
maxilla. The Dental Nerve is the largest of the three
branches of the Inferior Maxillary Division of the Fifth Nerve.

The Temporal muscle above the cartilage of the Ear should
next be cleaned, and its origin from the parietal ridge, part
of the occipital crest, and zygomatic process, noted ; as also
its insertion into the coronoid process of the inferior maxilla,
which will be found about an inch and a half behind the orbit.

If the Student will place a loose ramus of a sheep's jaw
on his dissection in its proper position, he will be better able
to make out the situation of the condyle, coronoid process,
neck of condyle, ramus, &c., and the points of attachment
of the Temporal and Masseter muscles.

And here (as in all Herbivora) he may note that the
muscles more directly worked in mastication, e.g., the Mas-
seter and the Pterygoids (to be seen hereafter), are propor-

* In Man, tlie Ophthalmic leaves by the Sphenoidal fissure, and the Superior
Maxillary by the foramen ovale.

216 Mammalia.

tionally more developed than the biting muscles, e.g., the
Temporales.

Dissection of Gland Duct, I^erves, and Muscles just
Internal to the Angle of the Jaw. — The Student wiU
now turn the Head partially over, so that it rests on the side of
the nose ; and placing a block under the angle of the jaw, will
strain the Larynx and QEsophagus over it, hooking them down
to the table by means of a chain and hooks. In this way the
Submaxillary Gland will be apparent, placed close below and
behind the Parotid, on the outer side of the Pharynx ; also
the Paroccipital process, with a sharply defined muscle* pro-
ceeding therefrom in the direction of the lower jaw, beyond
the angle ; and lastly, a fleshy muscle extending all along
the inner side of the ramus and angle of the jaw. These,
together with the Duct of the Submaxillary Gland, will form
our next objects of dissection.

The submaxillary duct will be found on the continuation of
a line drawn from the extreme anterior margin of the orbit to
the angle of the jaw : hence in dissecting away the gland-
lobules from the fat and mucous membrane, care must be taken
to avoid cutting across the duct ; the best way to proceed being,
first to dissect the mucous membrane, &c., in one sheet away
from the muscle lying within the jaw, and reflect it ; and then
to stretch the sheet of membrane thus reflected, by which
means the vessels and ducts ramifying in it may be readily
detected. Proceeding from the middle of the gland in the
direction indicated will be seen a pinkish aggregation of lines
and vessels ; this requires special and careful investigation,
for, at the final reunion of the ducts from the lobules, just
where the duct of Wharton commences, will be easily seen a
nerve ganglion of grey mattery as large as a medium-sized pin's
head ; about one-eighth of an inch from, and rather larger

* The Digastric muscle.

Dissection of Sheep^s Head. 217

than the first, is another ganglion ; and lastly, there is one
on each nerve strand which crosses the primary bifurcation of
the duct, tracing it backwards : the whole forming as it were
a second and posterior factor of the submaxillary ganglion,
which will be noted later on in connection with the Chorda
Tympani, after removal of the jaw.

Having found the duct and nerve plexus, a stoutish bristle
should be passed up the duct, and the fat and connective tissue
dissected away from the surface of the gland and adjoining
structures : and here again care must be taken between the
border of the gland and the occipital condyle, lest a large
nerve cord be cut away which runs from the direction of the
condyle parallel with the posterior margin of the, ramus and
angle of the jaw.

The submaxillary duct will be seen to run forwards between
two muscles : of these, that inserted into the inner posterior
border, and angle of the inferior maxilla, is the Internal Ptery-
goid muscle, which takes its origin mainly, as its name would
imply, from the inferior part of the crest of the Palatine and
Pterygoid bones. When acting singly these muscles produce
a lateral motion, together they raise the jaw and close the
mouth.

The second and internal of the two muscles is the Digastric*,
a long thin muscle that runs alongside the inner edge of the
ramus of the maxilla, attached to the inner edge of the
horizontal part of the jaw, and to the Paroccipital process :
it is so called from its consisting of two fleshy bellies united
by an intermediate tendon. In two points its arrangement
difiers from that in Man ; first, in that its tendon does not per-
forate the Stylohyoid muscle ; and, secondly, in that it does
not arise from the digastric groove on the inner side of the
mastoid process of the temporal bone ; which would be impos-

* diQ, twice ; yaaTrip, a belly.

F F

218 Mammalia.

sible, for the mastoid process of Anthropotomy is here
represented by a small separate stunted bone intervening
between the paroccipital process (external jugular of occipital
in Man), and the post-tympanic process of the squamosal.

And here it may be noted as a general statement that all
the muscles attached in Man to the Mastoid process, in this
animal are attached to the paroccipital process instead.

The small muscle running across, and external to the
posterior belly of the Digastric, will be traced back to arise
from a moveable bony head just internal to the point of the
paroccipital process ; this moveable ossicle is the end of the
styloid bone (a process of the tympanic in man) : forward it
will be traced internal to the Submaxillary gland and duct ;
and by reflecting forwards the gland substance posterior to the
duct (carefully leaving the duct and nerve plexus in situ) this
muscle may be seen to be inserted into a moveable ossicle, in
the middle line between the rami, and a little anterior to the
angle of the jaws, the ossicle being a portion of the Hyoid
bone. This muscle is therefore known as the Stylo- Hyoid ;
and its action is to draw back and elevate the os hyoides.

Internal to the Stylo- Hyoid Muscle is a large nerve trunk
winding from within the Paroccipital process, in a course
almost parallel with the posterior margin of the jaw. This is
the ITyjwglossal Nerve^ the motor nerve of the tongue. This
will be traced back later on, when examining the back, or
base of the skull.

Removal of Lower Jaw. — The Student will now clean
away and reflect upwards from the surface of the Masseter
muscle the Parotid gland, and nerves ramifying therein ;
and then take a saw and make the three following cuts, only
partially severing the bone, and completing the fracture by
working a chisel in the groove, so as to avoid injuring the
structures immediately internal to the bone by cutting too
deepwith the saw, viz. : — 1, from the angle of the mouth

Dissection of Sheep^s Head. 219

across the ramus of the jaw, about an inch and a quarter
from its lower margin. — 2, in a sloping direction across the
anterior part of the body of one jaw, about two inches from
the teeth and symphysis respectively, posterior to the mental
foramen; — and 3, a similar cut in the same direction and
situation on the other jaw. Then, taking a scalpel, he should
scrape away the muscular attachments, &c., along the margin
of that jaw the ramus of which has been fractured, and con-
tinue the same operation on the inner surface of the jaw,
removing as far as possible the periosteum at the same time,
so as to avoid cutting any structures internal to it ; pressing
the bone away with the thumb of the left hand, and following
close to the bone with the scalpel in the right hand. The saw
will have cut through the Inferior dental nerve (mentioned
above), just as it has penetrated the substance of the Inferior
Maxilla to pass forwards in the dental canal beneath the
teeth; and again, just before its appearance on the outside of
the jaw at the mental foramen. This nerve being the second
branch of the Inferior Maxillary division of the Fifth Nerve
we have seen ; the first being the Auriculo Temporal branch
distributed on the face.

Examination of Body of Jav^. — The Student will do
well now to follow the Dental Nerve in the canal contained
within the maxilla. This may be accomplished by taking a.
chisel and mallet, and making a fracture along the inner side
of the anterior two- thirds of the jaw, and then placing the
chisel just under the upper edge of the fracture, chipping the
bone away towards the teeth and gums along their entire
course. By removing this inner plate of bone the implanta-
tion of the molars will be well seen ; and generally, at the
age a sheep is killed for food, a sac will be disclosed contain-
ing a molar tooth in process of formation, posterior to the
last molar visible through the gum ; as also three more
sacs with teeth, beneath the three anterior teeth that have

220 Mammalia.

reached tlie surface. Lastly, underlying the whole series of
teeth will be seen the enormous Inferior Dental Nerve, from
the dental to near the mental foramen ; and along with it the
Inferior Dental branch of the internal maxillary artery (one of
the terminal branches of the External Carotid) which sup-
plies the teeth.

IsTow the fact of the three anterior teeth in the body of the
jaw having other teeth beneath them, shows them to be
deciduous or milk teeth ; and the two next teeth having
no such reserve supply, are thereby shown to be two of
the true Molar series. But, supposing the internal economy
of the jaw were not laid bare, we could still predicate
of the three anterior teeth that they were milk teeth ; on
this ground, — most of the deciduous molars of the Rumi-
nantia resemble, in the form of their crowns, the true molars,
i.e.f the crowns present throughout a similar complexity;
and again, the last milk molar has three lobes like the
last true molar (which in this case has not yet cut the
gum) ; whereas the premolar permanent series that replace
the milk deciduous molars have more simple, or less complex
crowns than their predecessors, and are, therefore, less com-
plex than the posterior teeth of the series :

Determination of Age — this is of value in ascertaining
the age of the beast, for if on examining the jaw the third
tooth presents a greater number of lobes than those in advance
of it, and all the series look pretty much alike, it is quite
certain that none of the premolar series are yet in place.
In other words : since

In the Sheep —

Both anterior and second Premolar appear from the
twenty-fourth to the thirtieth month, and the posterior Pre-
molar appears from the twenty-seventh to the thirtieth
month, it is quite clear that the beast has not attained its
second year.

Dissection of Sheep's Head. 221

Being satisfied that the milk molars are still in place, the
next point to note is how many true molars have cut the
gum, for

In the Sheep —

The anterior molar cuts the gum from the third (early) to
the ninth (late) month ; the second molar cuts the gum from
the ninth (early) to the twelfth (late) month ; and the pos-
terior (tri-lobedj cuts the gum from the eighteenth (early) to
the twenty-fourth (late) month.

Hence if, as here, two molars only can be felt, each bilobed,
posterior to the trilobed milk molar, you know the sheep to
be over nine months and under eighteen months old. But
there remains a simpler test of age than this, by referring to
the teeth that fringe the anterior margin of the jaw.

These teeth will be seen to be eight in number, of which
the three on each side nearest the middle line are called
Incisors ; and the outer one on each side is called a Canine
tooth. All this series, in course of development, goes through
a process of replacement ; and in this process the teeth assume
a difierent shape ; the first set being small and narrow, with
an almost circular blunt grinding surface ; the second set
broad and large, with a trenchant edge, and brown markings,
like two leaves, on the inner surface. The central pair alone
represents the permanent series in the case before us.
Now in the Sheep —

The permanent central incisors appear from the twelfth
(early) to the twentieth (late) month ; the permanent internal
lateral appear from the eighteenth (early) to the twenty-
eighth (late) month ; the permanent external lateral appear
from the twenty- seventh (early) to the thirty- sixth (late)
month. The corner pair, or Canines, appear from the thirty-
sixth (early) to the forty-second (late) month.

In this case the central pair of permanent Incisors, com-
monly called the Nippers^ being up, and no others, we

222 Mammalia,

know the beast to be under eighteen months and oveDf" twelve
months old ; from the Molar series we concluded it to be
under eighteen months and over nine months old. Hence we
may certainly conclude the animal before us to have been
from twelve to eighteen months old*.

Examination of the Developing Tooth and others.
— By removing the capsule around the posterior tooth of the
Molar series, the different structures of a tooth may be made
out. The soft pulpy material at the base is the Dental pulp,
a soft, highly vascular, and sensitive substance, accurately
filling the central cavity of the tooth. The lower paTt of the
solid portion of the tooth is composed of Dentine, which
forms the principal mass or foundation of the body of the
tooth, gives the general form, and immediately encloses the
cavity. The upper part is formed of Enamel. It will be well
now to remove this Tooth and place it in a solution consisting
of two parts of Nitric Acid and one part of Chromic Acid in
one hundred parts of water, with a view to making a longi-
tudinal section through the tooth when it is soft enough to
admit of cutting, to show the external coating of enamel, the
inner coat of dentine, and the central pulp cavity in their
relative positions.

"We may note here, as in all Ruminants, — that the outer
contour of the entire Molar series is slightly zigzag, the
anterior and outer angle of one tooth projecting beyond the
posterior and outer angle of the next in advance ; also, — that
in most of the deciduous series, but in the three posterior
teeth onlyf of both upper and lower jaws in the perma-
nent series {i.e., the True Molars), may be seen the character-
istic complexity of the Ruminant grinder ; the grinding

* The Head under dissection having been purchased in September, it is
probable that the lamb was born late, about March.

t The three first or premolars have, as before said, more simple crowns than
those which they displace.

Dissection of Sheep^s Head. 223

surface being marked in the centre by double crescent-shaped
ridges of enamel, so disposed as to present along with the
central mass of dentine, and external crust of cement, alter-
nate layers of hardened tissue, having different degrees of
density: the complexity in question being the result of peculiar
plications of the formative capsule, some of which are longitu-
dinal, or project inward from the sides of the capsule, and form
peninsular folds of enamel upon the grinding surface of the
tooth, whilst others depend vertically from the summit of the
matrix into the body of the tooth, and form islands of enamel
when the crown begins to be wornf ; and, lastly, — that the
last true Molar of the lower jaw presents the character found
in all E/uminants, viz., a third, posterior, lobe.

Dissection of Digastric and Mylo-Hyoid Muscles, and
Mylo-Hyoid Nerve. — By the removal of the jaw as described
above, the Student will be enabled to investigate from the
side the relative positions of the muscles, nerves, ducts, and
vessels : and will first note that the main bulk of the muscle
that was removed along the inferior margin of the jaw was
the anterior belly of the Digastric muscle ; next that the
more fleshy and massive muscle scraped away from the inner
surface of the angle of the jaw was the insertion of the
Pterygoid ; and lastly, will observe the cut end of the Dental
nerve where it was cut across in removing the jaw.

He should now dissect close along the internal aspect of
the Pterygoid (being especially careful not to injure any of
the delicate nervous structures near its anterior margin) ; and
then turn it upwards, with a view to exposing the posterior
inch of the duct of the Submaxillary Gland, and the tendon
of the Digastric Muscle. Then dissect the long anterior
belly of the Digastric away from the edge of the mouth,
leaving in situ the muscle that lies internal to it, and whose

t Owen.

224 Mammalia,

fibres are arranged at right angles to those of the Digastric,
being very careful not to cut away the nerve that lies
between these two muscles, whose apparent posterior ex-
tremity, i.e., as far as at present traceable, is internal to the
ramus of the jaw where it was cut across (and which may be
therefore sometimes destroyed in the fracture).

The muscle immediately underlying the anterior belly of
the Digastric is the Mylo-hyoid* ; it forms with its fellow of
the opposite side a muscular floor for the cavity of the mouth ;
and arises from the whole length of the internal superior
margin of the body of the jaw (the mylo-hyoid ridge), from
the symphysis to the last molar tooth. The posterior fibres
pass obliquely backwards, and may be traced, internal to the
Digastric, to be inserted into the body of the os-hyoides ; the
middle and anterior fibres (as will be later shown) are inserted
into a median fibrous raphe, where they join at an angle
with the fibres of the opposite muscle. This Mylo-hyoid is
distinctly double ; the anterior bundle having an extended
longitudinal development, while the posterior division is
short, and has its fibres directed transversely outwards.

The nerve exposed, running the whole length of the Mylo-
hyoid muscle, is the Mylo-hyoid nerve, a branch derived
from the Inferior Dental Nerve, just as that nerve is about
to enter the dental foramen. It descended in a groove on the
inner surface of the ramus of the jaw, in which it was re-
tained by a process of fibrous membrane. It supplies the
cutaneous surface of the Mylo-hyoid muscle, and the anterior
belly of the Digastric.

Dissection of Chorda Tympani, Gustatory Nerve,
Whartonian Duct, and Submaxillary Plexus. — The

* ixv\r)y a mill, the jaw ; and v (the letter upsilon) tlZos, shape, the thence-
named Hyoid bone.

Dissection of Sheep's Head. 225

MylO'hyoid muscle should he next dissected away* from its
superior margin, and reflected downwards towards the middle
line. In order to do this, the Mylo-hyoid nerve will have to
be cut across by the fracture of the jaw, and turned over
with the muscle. Excessive care will he needed along the pos-
terior margin of the muscle, in the line hetween the last upper
molar and the duct of the Suhmaxillary Gland, beneath which
runs the Chorda tympani, and is located the anterior
fraction of the Submaxillary ganglion. Just within the
posterior- superior corner of the same muscle, and overlapped
by the anterior margin of the (internal) Pterygoid above
described, may be seen the broad white stem of the Gustatory
Kerve. Close within the median raphe of the Mylo-hyoid
above noted is lodged the submaxillary duct, in the middle of
its course ; and between the two branches of the gustatory
nerve is situated the long sublingual gland, whose duct runs
forwards a little above the Whartonian duct.

The terminal course of that branch of the Facial nerve
called the Chorda tympani, is alone here brought into view.
It has descended between the two Pterygoid (external and
internal) muscles, and met the Gustatory nerve. It should
be carefully dissected out, and will be seen again to quit the
Gustatory nerve, and working backwards and downwards on
the segment of a circle, to join the direction of the Sub-
maxillary duct, in company with which we have noted it in a
previous dissection. A reddish ganglionic mass may be made
out in the fat about one-eighth of an inch in advance of the
lower fifth of the Chorda ; this is the anterior Suhmaxillary
ganglion. From this ganglion filaments radiate ; one larger
filament going back to the Submaxillary gland and forward

* We must here again caution the Student to be extremely cautious'to remove
only the muscle, and leave the inter-muscular adipose tissue to investigate when
the superjacent muscle is reflected.

G G

226 Mammalia.

in a direction parallel with the jaw, where it may be traced
in the fat across the Gustatory nerve to end in the mucous
membrane of the mouth. This ganglion also receives fila- •
ments from the Chorda tympani, and from the Gustatory
nerve, which form a fine plexus in the triangle enclosed by
the Chorda, Gustatory, and main ganglionic filament.

The Whartonian Duct takes very nearly a straight course
along a line drawn from the Symphysis to the angle of the jaw ;
which line also marks the lower margin of the Styloglossus
muscle. Three inches from the gland it is crossed by the in-
ferior branch of the Gustatory nerve. By the aid of the
bristle inserted into the duct, its course may be traced forwards
in close connection with the Gustatory nerve, along what
would be the inner side of the jaw, had it not been removed,
between the Styloglossus muscle and Sublingual gland, to
open into the mouth rather in front of the frsenum lingua3,
where it is protected by a thick papilla of mucous membrane,
called a harb in cattle, the opening being guarded by a plate
of cartilage.

The Gustatory Nerve or lingual branch of the inferior
Maxillary division of the Fifth nerve will be notecf to have
descended under the anterior border of the internal Pterygoid
muscle, and to lie internal to, and to the front of the inferior
Dental Nerve* as it enters the jaw, at which point the Chorda
tympani is in close relation with it. It then crosses ob-
liquely to the side of the Tongue over the Superior Constrictor
muscle of the Pharynx, and reaches the Styloglossus muscle,
on the external surface of which it runs, and shortly after
divides into two branches ; the smaller branch continuing
straight along the margin of the tongue to the anterior
attachment of this organ, the larger branch descending to
cross the Whartonian (submaxillary) duct about an inch and

* Cut short in the jaw.

Dissection of Bheep's Head. 227

three quarters in advance of the Submaxillary ganglion, and
disappearing beneath the duct soon after.

The Sublingual is the smallest of the salivary glands, and
is of a narrow oblong shape, situated between the two
branches of the Gustatory nerve posteriorly, and between the
upper branch and the Whartonian duct anteriorly ; the lower
branch of the Gustatory bending upwards internally to the
gland about the middle of its length. The principal duct
should be followed forwards, and at a point about three
quarters of an inch from the papilla at its termination it will
be seen to be crossed by the superior branch of the Gustatory
nerve, and from the same point to become enclosed in the
same sheath with the Whartonian duct, to the end of its
course. A bristle passed along this duct will, however, shew
that in many cases the two ducts remain distinct in the sheath,
and open separately in the mouth ; though in many cases the
two ducts blend before opening into the mouth. This single
canal from the Sublingual gland, entering the mouth an-
teriorly, is known as the duct of BarthoUni; the several
smaller ducts which unite to form the single canal being
called the ducts of Rivini.

Of the three salivary glands now seen, the Submaxillary is
said to be the first formed in the Mammalian foetus ; then
the Sublingual, and lastly the Parotid.

Investigatiox of the Chain of Hyoid Bones. — The
Student will do well now to raise the Pterygoid muscle and
that part of the ramus of the jaw which remains in situ, and
stretch it over towards the top of the skull b}^ hooks, in order
to expose the Stylo-hyal bone, with the muscles thereto
attached.

Before noticing the muscles connected with the Os Hj^oides
more particularly, it may be well to direct the attention to its
osseous framework. The Hyoid bone is made up* of a

* Cyc. Anat, S., art. Ruminantia.

228 Mammalia.

congeries of nine ossicles more or less consolidated, arranged
in four pairs, the ninth piece being represented by the *body '
or Basi-byal bone. The first pair, the Stylo-hyalSj immediately
internal to the posterior border of the ramus of the jaw, have an
enormous longitudinal development, being also somewhat
hammer- shaped and compressed laterally; their peculiar
figure being due to the presence of two apophyses at the
temporal extremity, by the superior of which the bony chain
is connected by a short ligament with the cranium. The
second pair, or Epi-hyaky are intercalated between the first
and third pair of ossicles ; the third pair (placed nearly
vertical) make a right angle with the first pair (which lie
horizontally forwards), and the second pair fill up the apex of
this angle, which is directed forwards. The third pair, or
Cerato-hyalSy have a nearly vertical position when the head is
raised. The body of the hyoid, or Basi-hyal, of a triangular
form, is placed below the cerato-hyals, and anterior to the
greater cornua or thyro-hyals. This fourth pair, the Thyro-
hyals, articulate to the extremities of the lateral apophyses of
the Basi-hyal, and lie nearly horizontally backwards, the
whole series forming on each side a figure like the italic S
sloping the wrong way.

In Man,

The Stylo -hy ah are represented by the ' Styloid process of
the temporal bone' ; the Epi-hyals by the ' styloid ligament';
the Cerato-hyals, by the * lesser cornua ' ; the Basi-hyal by
the 'body '; and the Thyro-hyal by the 'greater cornua.' In
the Ruminant, the so-called ' greater cornua ' (of anthropoto-
my) are subordinate to the so-called ' lesser cornua ' in the
extent of their development.

Removal of Parotid Gland ; and Dissection or
Stylo-Glgssus, Genio-Hyo-Glossus, and Genio-Hyoid
Muscles ; and Hypo-Glossal Nerve. — The Student should
now remove the posterior part of the Parotid Gland along

Dissection of Sheep^s Head, 229

the track of the cervico-facial branch of the Seventh nerve, but
leaving the nerve in situ. In so doing, a branch of the
external jugular vein will be cut across, lying internal,
and almost at right angles to this cervico-facial nerve :
but the external carotid artery which lies in the same direction
as the vein, only a quarter of an inch deeper, should if possible
be kept in situ running between the posterior belly of the
Digastric muscle and the Stylo-hyal bone. The head and
proximal processes of this bone should be cleaned, and the bone
exposed (freed from fat only) throughout its length. Within
half an inch of the inferior extremity of the stylohyal bone
will be seen the origin of the Stylo-glossus muscle, which extends
forwards along the under surface of the tongue as far as the
tip, and on whose external surface the Submaxillary plexus
and the course of the Gustatory nerves have been exposed :
the Whartonian duct has been shewn to run along its
inferior margin.

The long tendon of the Stylo-hyoid muscle proceeding from
the posterior apophysis at the superior extremity of the Stylo_
hyal bone will be now readily seen, and the inferior attach,
ment of the muscle to the base of the Thyroid cornua may be
traced, out.

Immediately above the origin of the tendon of the Stylo-
hyoid muscle may be seen the insertion of the short triangular
Masto-styloid* muscle, which arises from the paroccipital
process, and is inserted into the inferior apophysis of the
hammer-shaped extremity of the Stylo-hyal bone.

The ultimate course of the Hypoglossal nerve may be
next traced ; and in order to this, the Mylo-hyoid muscle
should be dissected quite down to the median raphe : care
being taken not to injure the broad nerve tract that lies in-

* A special muscle found in the Carnivora Ruminantia and Pachydermata
(of Cobbold). — Ci/cl. Anat. and Phys., art. Ruminantia, p. 527.

230 Mammalia.

ternal to it, and very little below the margin of the Stylo-
glossus : the Whartonian duct should also be left in situ along
the lower margin of the Stylo- glossus.

After removing the adipose tissue intervening between the
fascia of the under-lying muscles, the following arrangement
of the principal muscular strata will be disclosed.

From the direction of the last molar tooth, towards the
H5^oid arch, just internal to the posterior part of the Stylo-
glossus, will be seen the obliquely-placed fibres of the Syo-
glossus, arising from the side of the body of the Hyoid (or
Basi-hyal), and inferior part of large cornua (or Thyro-hyals),
and inserted into the side of the Tongue : being in relation there-
fore externally, with the Stylo -glossus superiorly, and the
Mylo-hyoid and Digastric inferiorly ; crossed by the Hypo-
glossal nerve and Wharton's canal ; and in relation internally
with the two horizontal layers of muscles, next to be treated
of, viz., superiorly the Genio-h5^o-glossus, and inferiorly, next
to the median raphe, the Genio-hyoid. Just anterior to the
upper margin of the Hyo-glossus, and blending with it, will
be noticed a thin band of muscle getting thicker anteriorly,
situated on the under surface of the tongue between the Hyo-
glossus and the muscle next to be described, (viz., the Genio-
hyo- glossus), and whose fibres blend with the fibres of the
Stylo-glossus in front of the Hyo-glossus : this is the
external aspect of the Lingualis inferior muscle, one of the
intrinsic muscles of the tongue.

Next there will be seen an upper stratum of longitudinal
fibres proceeding from within the anterior edge of the Hyo-
glossus and Lingualis, along the inferior surface of the tongue
to near the symphysis of the jaw. These are the fibres of
the GeniO'hyo- glossus muscle, which arises from the lateral
aspect of the inferior maxilla, near its symphysis, and is in-
serted first into the substance of the tongue, and further back
into the Cerato- and Epi-hyal bones (or lesser cornua) of the

Dissection of Sheep's Head. 231

Hyoid arch. It will be seen to be in relation superiorly,
therefore, with the substance of the tongue : externally, with
the Stylo-glossus in its posterior moiety ; and the sublin-
gual gland and duct, and Whartonian duct in its anterior
moiety ; and lastly, to be crossed in its middle third by the
larger factor of the Hypo- glossal nerve.

Thirdly will be seen an inferior stratum of longitudinal
fibres just internal to the raphe found between the Mylo-
hyoids : these are fibres of the Genio-hyoid muscle, arising
from the jaw near its symphysis and inserted into the Basi-
hyal (or *body ' of the hyoid bone). The Genio-hyoid may
be said to be between the Genio-hyo-glossus and the median
raphe of the Mylo-hyoid.

The Hypo- glossal nerve will have been thus traced to take
the following course. After passing internal to the Digastric,
it proceeds beneath the Mylo-hyoid and inferior margin of
the Stylo- glossus, lying between it and the Hyo-glossus ; and
is then continued forwards along the external surface of the
Genio-hyo- glossus, which it finally penetrates, to reach the
tip of the tongue.

At the same time a considerable part of the course of the
Lingual artery will have been made out ; arising from the ex-
ternal carotid artery as it crosses about the middle of the Stylo-
hyal bone, it continues in the direction of that bone across the
origin of the Stylo-glossus, dips down internal to the Hyo-
glossus, between it and the Genio-hyo-glossus (where it runs
parallel with the Hypo-glossal nerve), then ascending and
working forwards on the under surface as far as the tip of
the tongue under the name of the ranine* artery.

The actions of the various muscles hitherto described may be
thus briefly stated.

First Group. — The Temporal, Masseter, and Internal Ptery-

* Rana, a frog ; also a swelling under the tongue.

232 Mammalia.

gold raise the lower jaw against tlie upper ; and tlie two latter
muscles, from tlie obliquity in the direction of their fibres,
assist the External Pterygoid (to be seen later, after the
removal of the Zygomatic arch) in drawing the lower jaw for-
wards upon the upper ; the jaw being drawn back again by
the deep fibres of the Masseter and the posterior fibres of the
Temporal.

Second Group. — The Digastric depresses the lower jaw.

Third Group. — The Stylo-hyoid, Mylo-hyoid, and Genio-
hyoid together raise the Hyoid hone, and with it the base of
the tongue, during the act of deglutition.

Fourth Group. — The Genio-hyo-glossi, Hyo-glossi, and
Linguales act separately. The Genio-hyo-glossi, by means
of their posterior and inferior fibres draw upwards the Hyoid
bone, bringing it and the base of the tongue forwards, so as
to protrude the apex from the mouth : — their anterior fibres will
restore it to its original position by retracting the organ
within the mouth. The whole length of this pair of muscles
acting along the middle line of the tongue will draw it down-
wards, so as to make it concave from before backwards, and
form a channel along which fluids may pass to the Pharynx.
The Hyo-glossi draw down the sides of the tongue, so as to
render it convex from side to side. The Linguales by drawing
downwards the centre apex of the tongue render it convex
from before backwards.*

Examination of Internal Pterygoid, and Stiperior
Constrictor Muscles. — The Student will now take a fine
saw, and cut through the zygomatic arch in two points ; an-
teriorly, just behind the orbital ring ; and posteriorly, about
an inch from the same : he will then raise that part of the
ramus of the jaw which still remains, and will first cut across
a small muscle in the neighbourhood of the molar teeth,

Gray.

Dissection of Sheep^s Head. 233

which is the Superior Constrictor Muscle ; and next will scrape
away from the anterior margin of the ramus the attachment
of another muscle, viz. the anterior and larger belly of the
external pterygoid muscle. The object of the removal of the
section of zygomatic arch is now apparent, viz. in order to
admit of the extraction of the coronoid process of the jaw,
which is next to be drawn outwards through the gap made, and
turned over backwards ; access being by this means gained
for the examination of the second and shorter belly of the
external pterygoid muscle which is attached to the under
side of the internal angular prominence of the condyle of the
jaw.

The External Pterygoid muscles are thus seen to occupy
the major part of the zygomatic fossa: they arise by two
heads placed close together, occupying a considerable area on
the Sphenoid, Pterygoid, and posterior aspect of the Superior
Maxillary bones. The fibres from both heads are marked
with tendinous intersections, and have a general downward
direction. When the muscles of both sides act together, the
lower jaw is slightly drawn forward ; but when the muscles
of one side act alone, the result is the advancement of one
condyle only, and hence the lateral motion of the jaw, throw-
ing the teeth to the side opposite to that on which the muscles
act. This action repeated alternately on both sides induces a
lateral grinding movement of the lower teeth.

The inferior dental nerve should be removed from the
dental foramen in the jaw, and left (as to its upper course) in
situ, together with the mylo-hyoid branch which lies just
posterior to it, and which will be, later on, traced back to the
motor root of the inferior maxillary nerve : the buccal nerve
should also be traced up, and cleaned. In laying bare these
nerves towards the temporo-maxillary articulation, a large
vessel will be noted crossing them at right angles ; this is the
internal maxillary or deep Facial artery y the larger of the two

H H

234 Mammalia.

main terminal branches of the external carotid. It may be
traced back into the internal substance of the Parotid gland,
by which its origin below the condyle of the jaw is concealed ;
and at the point at which it crosses the inferior dental nerve it
maybe seen to curve horizontally forwards between the jaw and
the internal lateral ligament of the temporo-maxillary joint ;
thence it may be traced obliquely forwards and upwards on
the outer surface of the smaller belly of the external Pterygoid
muscle ; and then inwards between the two bellies of this
muscle, just internal to the buccal branch of the inferior
maxillary nerve (which crosses it at right angles), to the
spheno-maxillary fossa, where it divides into two main
branches : the bifurcation taking place immediately internal
to a hooked process which projects backwards from that
upper part of the sphenoid bone known as the Ali-sphenoid.

In tracing the Internal Maxillary Artery backwards care
must be taken not to cut across that branch of the external
carotid which supplies the Parotid gland, and which leaves
the upper side of the bend of the internal maxillary much in
the same way as the carotids themselves leave the aortic arch.
And secondly, care must be taken to avoid cutting through
the auriculo-temporal branch of the inferior maxillary nerve
which was first exposed as the superior nerve tract in the
dissection of the Parotid gland.

Hemoval of Coronoid Process, part of the Condyle,
AND REMAINS OP Ramus OF LowER J AW. — The Student
should now take a fine saw, and cut part of the way through
the internal angle of the condyle of the jaw, completing the
fracture with the ' bone-nippers ' so as to avoid injuring
the subjacent structures ; remove the bone ; and also cut
away the unattached portions of the anterior belly of the ex-
ternal Pterygoid, avoiding any injury to the buccal nerve
which lies internal to it, as it courses from the posterior angle
of the superior maxilla towards the inner aspect of the

Dissection of Cheep's Head. 235

temporo-maxillary joint. The point of intersection of the
internal maxillary artery and tlie buccal nerve well defines
the separation between the two bellies of the external Ptery-
goid muscle.

The Student should have before him at this stage of the
dissection the following nerve branches between the Par-
occipital process and the orbit, m., — on the posterior aspect of
the Parotid gland, the Cervico-facial, Temporo-facial, and
Auricular branches of the Facial or portio dura of the Seventh*
nerve, converging to meet just behind the external meatus of
the Ear : — on the internal aspect of the Parotid, the Auriculo-
temporal branch of the Inferior Maxillary nerve passing in-
wards close to the remains of the condyle of the jaw: — on the
external aspect of the Internal Pterygoid muscle, in order from
behind forwards, first the small Mylo-hyoid nerve closely
attached to the Inferior Dental nerve ; and then the Chorda
Tympanif in juxtaposition with the Gustatory nerve, each
making for the external extremity of the broken condyle : and
lastly, the Buccal branch of the Inferior Maxillary nerve, cours-
ing from the direction of the posterior molars of the upper jaw,
back between the two bellies of the External Pterygoid mus-
cle towards the antero-internal aspect of the fractured condyle.
The Student will now pursue the Chorda tympani to the
Skull. He will find it leave the posterior side of the Gustatory
nerve at a point a little before this last nerve crosses internal
to the Inferior Dental nerve : and then pass internal to the
Inferior Dental, and Auriculo-temporal nerves, to reach the
skull by an aperture at the inner end of the Glasserian fissure,
i.e. that fissure which separates the articular part of the glenoid-

♦ Some anatomists consider Portio dura = vii.; and Portio mollis, or auditory,
= viii. cf. p. 238.

t By means of the Chorda Tympani the Gustatory nerve is put in relation
with the Facial nerve : and it is also in communication with the Hypo-glossal
nerve by means of the plexus which its own branches form with branches of the
Hypo-glossal nerve at the inner border of the Hypo-glbssus muscle.

236 Mammalia.

fossa (on which rests the cartilaginous disc) from the remain-
ing part behind, which is formed by the Tympanic subdivision
of the Temporal bone. The rest of the course of this nerve
lies within the Ear : it leaves the trunk of the Facial while
within its canal, enters the back part of the tympanic cavity
through a short canal close to the membrane of the Tympanum,
and crosses this membrane and the handle of the Malleus to
gain the aperture above noted at the inner end of theGlasserian
fissure. Its after course, as we have seen, is downwards and
forwards under cover of the posterior belly of the External
Pterygoid, internal to the Auriculo- temporal and inferior
Dental nerve, to unite with the Gustatory nerve at an acute
angle : with this nerve it ascends, in close contact, to a point
about opposite the posterior molar teeth, then curves down-
wards and backwards to the sub-maxillary ganglion, and along
the course of the duct of the sub-maxillary gland to the
second factor of the ganglion near the gland, and there
it becomes too fine to trace its terminal twigs.

!N^ext let him take the posterior belly of the External Ptery-
goid with the inner angle of the condyle of the jaio attached to it,
and pass it, beneath the internal maxillary artery , forwards between
the Buccal and Gustatory nerves^ in order to expose the junction
of the four great branches of the Inferior Maxillary sub-
division of the Trifacial, viz., the Buccal, Gustatory, Inferior
Dental, and Auriculo- Temporal : these may then be traced
up to the skull and cleaned ; and the united trunk noted to
perforate the skull at a point a little anterior and internal to
the site of the temporo-maxillary articulation. The Fora-
men thus arrived at, inasmuch as it transmits the third
or inferior division of the Trifacial, is homologous with the
so-called foramen ovale of the human skull.

Dissection of Internal Pterygoid Nerve ; Eustachian
Tube ; and Otic Ganglion. — Having thus two fixed points to
start from, vi%., the Chorda tympani and the united Inferior

Dissection of Sheep^s Head, 237*

Maxillary, we may, by careful investigation of the intervening
area, arrive at the Eustachian tube, and Internal Pterygoid nerve.
Just at the point where the Auriculo- temporal nerve runs in
to the main trunk, but internal and posterior to it, will be
found the short branch of the Internal Pterygoid nerve
leaving the Inferior Maxillary to penetrate the Internal
Pterygoid muscle; when this is cleaned there will be seen
underlying it, at a slight angle, a small strip of muscle ; and
between this strip of muscle and the Inferior Maxillary root
a bluish hard tube will be readily distinguishable, which is
the proximal end of the Eustachian tube, i.e., the canal which
leads from the cavity of the tympanum to the upper part of
the Pharynx.

The Eustachian tube and Internal Pterygoid nerve thus
found, give us the bearings of the anterior portion of the
diffused Otic ganglion. This ganglion is of a reddish-grey
colour, and situated on the deep surface of the Inferior
Maxillary trunk, around the origin of the Internal Pterygoid
branch. Its inner surface is close to the cartilaginous part
of the Eustachian tube. It is perhaps best seen by pressing
back the united Gustatory and Inferior Dental branches :
the ganglion occupying the apex of a triangle of which these
nerves form the left side, the Buccal nerve the right side,
and the Internal Maxillary artery the base.

The Facial branch of the seventh nerve may be now cleaned up
to the sJmll, i.e. to the Stylo-mastoid foramen, situated between
the Paroccipital process, the external auditory meatus, and the
commencement of the Stylo-hyoid chain of bones and liga-
ments.

The large compressed Stylo- hyal bone may be now cleaned
at its proximal end, and the prominent posterior process
exposed : the normal anterior boundary being traced up
internal to the Parotid gland and Carotid artery (which
should both be slightly turned over to the front) to its short

238 Mammalia,

ligamentous attacliment, a little anterior and inferior to the
Stylo-mastoid foramen whence issues the seventh nerve.
Removal of Part of the Cranial Wall in order to

EXPOSE THE EoOT OF THE TRIFACIAL NeRVE. It will be

well, before making the above dissection, to gently press away
from the cranial wall with the handle of the scalpel, the portion
of brain thereto adjoining, in order to see clearly the origin
of the cranial nerves in that part. In this way there will be
seen beneath the Cerebellum two stout nerve roots leaving
the Medulla, just opposite the external auditory meatus ; of
these, that directed forwards is the root of the Trifacial, and
that directed straight outwards is the Seventh nerve. Pos-
teriorly is seen a group of nerve fibres, mainly directed out-
wards; these constitute the group sometimes called the Eighth
Nerve*; but which really consists of three distinct nerves : the
Glosso-pharyngeal, Pneumo- gastric, and Spinal Accessory :
the two first of these being attached to the Medulla Oblongata
in the same line ; the last, the Spinal Accessory, taking its
origin chiefly from the spinal cord, and coming forward to
join the Pneumo- gastric in the foramen of exit, called the
jugular foramen. Lastly, anteriorly to the Trifacial will be
seen two fine nerves, one arising from the Yalve of Yieussens,
between the Cerebrum and Cerebellum, and extending for-
wards in the Dura Mater in the same direction as the main
bulk of the Trifacial, m%., the Fourth JN^erve (pathetic, or troch-
lear) ; the other, coming from the Cerebrum and directed
obliquely outwards, being the Third Nerve, or motor oculi.

The Student will now take a saw, and make two incisions in
a general direction from the middle of the Brain to the root
of the Tongue. Of these the anterior should be taken just
behind the orbital ring, through the middle of the anterior

* According to another arrangement, in wliicli the Cerebral nerves are
reckoned as twelve pairs, the Glosso-pharyngeal =: ix. ; the Pneumo-gastric =:
X. ; and the Spinal Accessory =r xi.

Dissection of Sheep* s Head. 239

belly of the external pterygoid ; in other words, through the
Frontal, anterior margin of Parietal, and Sphenoid bones, in
the direction of the sphenoidal fissure ; and here care must
be taken not to saw through too deep, or otherwise the second
subdivision of the Trifacial, which goes horizontally forwards
from the sphenoidal fissure, viz., the Superior Maxillary
subdivision, will be injured or even cut through. The posterior
incision should be made on a line drawn from a point about
two inches in advance of the posterior margin of the occipital
condyle, through the glenoid fossa, down to the upper surface
of the Inferior Maxillary nerve ; in other words, from the
upper margin of the occipital bone to the foramen ovale,
keeping clear of, and to the front of the external auditory
meatus and glasserian fissure, so as to leave the Chorda tym-
pani uninjured. Neither of these incisions should be carried
with the saw quite down to the points indicated ; but when
within a short distance thereof, a few strokes with the mallet
on the outer table of the part to be removed, will complete
the fracture along the line of the foramina required; and
then by carefully scraping the dura mater from the inner
surface of the bones with ,the scalpel, the portion of the
cranial wall may be removed without injury to the nervous
structures lying just within.

Removal of Posterior Margin, and Superior Internal
Wall of Orbit, and Dissection of Orbital Membrane and
Lachrymal Gland. — Three cuts should he made with the saw;
one just below the junction between the frontal and malar
bones ; a second a little distance, about three-eighths of an
inch, above this point ; and a third along a line drawn from
the anterior margin of the orbit to the Optic nerve where it
leaves the skull through the optic foramen. This last incision
must not be made too near the middle line of the skull or the
pulley of the superior oblique muscle will be destroyed. The
Student, with the skull before him, will bear in mind through

240 Mammalia.

how mucli bone he will have to saw in each case, and will
take care not to cut too deep ; to avoid which, it is always
best to finish the fracture by the introduction of a chisel into
the groove made, and forcing the crack by a sort of lever
action on the bone surfaces. The two pieces of hone included
between these three incisions should he removed after that the
contents of the orbital cavity have been detached from all
connection with their inner surface. Special care will be
needed as the dissector approaches near to the optic foramen,
to avoid injuring the Fourth nerve.

The Orbit contains the following structures within the
orbital membrane, viz. : the Eyeball, the Lachrymal, and
Harderian glands ; six muscles connected with the eye —
four straight and two oblique : and one muscle connected
with the upper eyelid : also numerous nerves, viz., the Second,
Third, Fourth, Ophthalmic division of the fifth, and the Sixth,
with part of the Sympathetic : and, lastly, the Suspensory
(or Choanoid) muscle.

Some of the mass of fat which fills up the lower part of
the orbital cavity may be removed, care being taken not to
cut down on the Superior Maxillary branch of the Fifth nerve,
which runs horizontally forward from the inferior limit of
the sphenoidal fissure.

It will then be found that the lower part of the orbit,
which is completed in Man by an osseous framework, is here
only completed by membrane. This membrane is the orbital
membrane or periosteum, which thus becomes a structure of
much importance, for it stretches across the floor of the orbit
from its outer to its inner wall, extends backwards to the
optic foramen, and completes the boundary of the cavity at
the spot where the bony wall is wanting. Intimately connected
with the membrane, and forming an essential part of it, is a
thin layer of a pale-reddish substance, which extends across
the greater part of the floor of the orbit, passing backwards

Dissection ofSheep^s Head. 241

to the optic foramen and sphenoidal fissure. This reddish
mass* may be seen under a quarter-of-an-inch object glass, to
be composed for the most part of flat, pale, non-striped fibres,
collected together in bundles, with which is mingled both
white and yellow ordinary fibrous tissue : the pale non-
striped fibres having all the characters of the involuntary
muscular fibre. By irritation of the cervical sympathetic,
these membranes project the contents of the orbit, especially
the bulb, forwards. Retraction is produced by the trans-
versely-striped ^ retractor '. In Man, the orbital membrane
is much reduced in size, and the * retractor' is wanting, so
that no distinct projection of the bulb follows irritation of
the sympathetic! .

The pink glandular mass, situated in the upper and back
part of the orbit, is the Lachrymal gland, which secretes the
tears ; it resembles in structure the saKvary glands ; and has
numerous fine ducts which open on the inner surface of the
upper eyelid. As the eyelids are generally removed with the
skin before the head is sent in to the market, their arrange-
ment can only be seen in a specimen specially reserved.

Removal of Okbital Membrane and Dissection of the
Nerves, Ganglion, and Muscles contained therein. —
The orbital membrane should be now divided towards the bach
of the orbit, and taken away ; and then the fat internal to
the membrane carefully removed : by this means the fine
Fourth nerve, which was traced before along the commence-
ment of the Ophthalmic branch of the Fifth nerve, may be
followed up to the inner side of the orbital cavity, and to its
termination in a muscle there situated. This muscle, by the
entrance of the Fourth nerve into it, is recognised as the
Superior Oblique muscle. It will be seen that the Fourth

* If specially prepared by soaking in diluted nitric acid,
t Turner (Edinburgh), Natural History Eeview, January, 1862 ; and Strange-
way's Veterinary Anatomy, p. 475.

I I

242 Mammalia.

nerve enters the orbital surface of the muscle, and not the
ocular surface, as is generally the case with the other nerves.
In close apposition with the Superior Oblique muscle will be
seen the most superficial of the muscles of the orbit, viz.^ the
Levator Palpehrce Superioris, in contact with the periosteum
externally, and the Superior Eectus internally : it will be seen,
later on, to arise close to the optic foramen, and may be now
traced forwards to its insertion into the forepart of the tarsal
cartilage of the eyelid.

The Fat should be cleaned away round the Superior Oblique
muscle, and it will then be seen to be a thin and narrow muscle
arising from the outer end of the optic foramen, and passing
through a fibrous loop at the upper internal surface of the
orbit, before being inserted into the sclerotic coat behind the
middle of the eyeball. The pulley, or trochlea, consists of a
fibre- cartilaginous ring, attached by fibrous tissue to a
small tubercle on the frontal bone at the supero-internal aspect
of the orbit. The thin insertion of the muscle passes internal
to the superior rectus muscle, and terminates between this
and the external rectus.

The Superior Rectus muscle should be next cleaned out (the
upper one of the two just noted), and its origin from the outer
margin of the optic foramen, where it is connected with the
other recti muscles around the Optic nerve, noted.

At this point it will be advisable to trace the anterior ter-
mination of the Lachrymal and Supra- orbital branches of the
Ophthalmic division of the Fifth nerve. The Ophthalmic, the
smallest of the three great divisions of the Fifth, is divided in
the Sheep into two principal branches : one, the smaller, going
towards the back ; the other, the larger, going towards the
inner front of the orbit. Of these, the first is made up of two
principal factors, vi%., a Lachrymal and Suprarorbital branch ;
the second enumerates but one factor, the Nasal branch. The
Lachrymal and Supra-orbital branches lie just within the

Dissection of Sheep's Head. 243

orbital membrane on the outer margin of the orbit ; united
at the origin of the principal muscles of the eye, they proceed
about three-quarters of an inch further together, ascending
along the direction of the most external muscle of the eye,
mz.y the external rectus, and then they part company ; one
small twig passing straight up to the Lachrymal gland, the
other continuing on in its first direction, to be distributed to the
muscles and integument on the superior and posterior margin
of the orbit. Of the Nasal branch we shall treat later on.

The tendinous insertion of the superior rectus into the
sclerotic coat beneath the lachrymal gland should be next
noted. The inner surface of this muscle is in apposition,
near its insertion, with the suspensorius muscle (found in all
Quadrupeds up to the Quadrumana), and with the tendon of the
superior oblique ; and, near its origin, with two stout nerves,
m%., the Third, by which it is itself supplied, and the Nasal
branch of the Fifth. A twig from the fifth will also be found
supplying this muscle.

The External Rectus muscle may be next cleaned. This
muscle has a similar origin and insertion to the Superior
E-ectus, hut is supplied by a separate nerve, the Sixth nerve, —
a very fine thread, which reaches the muscle near its origin,
and on the edge nearest to the Superior Rectus.

Factors of the Pedicle of the Eyeball. — We have
now, at this stage of the dissection, disclosed the following
factors of the stalk, or pedicle, of the eyeball : — ^nearest
to the middle line is the tmj Fourth nerve ; next to it the
origins of the levator palpebrae superioris, and superior
rectus muscles ; then the Third nerve, the Nasal branch of the
Ophthalmic division of the Fifth nerve, the twig from the Fifth
supplying the superior rectus, and the Sixth nerve, all occupy-
ing the narrow slit between the origin of the rectus superior,
and that of the rectus externus, which comes next ; and lastly,

244 Mammalia.

most externally, the Lachrymal and Supra-orbital branches of
the Ophthalmic division of the Fifth nerve.

The orbital membrane may now be further reflected on the
outer side, and the fat carefully removed ; by which means
the origin of the inferior rectus will be disclosed, adjoining
that of the external rectus ; and between the edges of these two
muscles will be seen a stoutish nerve running forwards, and
a thin nerve running backwards, both meeting at a spot about
half an inch from the origin of the muscles. Of these two
nerve- cords, — that running forwards is the continuation of
the Third nerve, and that running backwards is a factor from
the Fifth nerve, en route to the CiKary ganglion.

The Student should now carefully separate the contiguous
margins of the superior and external recti muscles; turn
each away from the other, and remove the fat.

The further course of the Nasal branch of the Ophthalmic
division of the Fifth wer^^e will then be made out, tending inwards
across the stalk of the Choanoid or Suspensorius muscle, and
then across the origin of another muscle arising close to it,
vis:., the internal rectus. Arrived at this point, the nerve
will be found to bifurcate, — one branch, after gaining the
anterior edge of the superior oblique muscle (between which
and the internal rectus it has just passed,) re-enters the cranial
cavity through a foramen in the orbital plate of the frontal
bone, to pass through the cribriform plates of the Ethmoid
bone, and be distributed on the walls of the nasal fossae : — the
other branch continuing further forwards to the margin of the
orbit, to be distributed to the lachrymal sac, eyelids, and side
of nose.

If now the stalk, or origin of the suspensorius, be gently
pushed on one side away from the superior rectus, the large
white Optic nerve will be brought into view, and a little more
of the course of tlm Third nerve, vi^., where it dips under the
pedicle of the Suspensorius in company with the Optic nerve.

Dissection oj Sheeph Head. 245

At this point the Third nerve will be found to send off a
branch tending to the inner aspect of the orbit, to supply the
inferior rectus muscle ; the main stem continuing rather
towards the outer side of the eyeball.

It will next be well to gently separate the suspensorius
from the external rectus : these two muscles will be found
intimately united at their origin ; and more, they are both
supplied by filaments from the same nerve, viz.y the Sixth.

Dissection of Lenticular or Ciliary Ganglion. —
We previously directed attention to the line of demarca-
tion between the superior and external recti muscles : it
will now be well to separate their apposed edges in the same
way that the others have been treated: only in this case
with more care, for, within their lips, where the two difierent
nerves seem to converge, will be found the Lenticular or Ciliary
ganglion, a knot of nervous matter, not very readily distin-
guished from the surrounding fat, except by its slightly
reddish tint. In situation it may be described as occupying
the centre of a triangular cavity enclosed by the Optic nerve,
and the external rectus, and suspensorius muscles. By its
inferior border, the ganglion will be seen to have branches
of communication with other nerves ; and in the ganglion
sensory, motor, and sympathetic filaments are combined. A
short thick branch passes from its lower margin to join the
branch of the Third nerve, which is now seen to continue
forwards towards the anterior external boundary of the orbit ;
and a second branch, or rather main factor, comes from the
Fifth ; it is also connected with the sympathetic system by a
nerve emanating from the cavernous plexus of the Sympathe-
tic. From the superior border of the ganglion proceed two
branches, each of which consists of a bundle of small twigs ;
these extend along the Optic nerve to the eyeball, which they
enter by apertures in the back of the sclerotic coat ; and are

246 Mammalia,

eventually lodged in grooves on the inner surface of the
sclerotic, pierce the ciliary muscle, and ramify in the Iris.

The Third nerve should now be traced forwards ; first
along the posterior edge of the inferior rectus, then across the
outer surface of the upper part of this muscle, to terminate
in the Inferior Oblique muscle. This muscle is situated near
the anterior margin of the orbit, and differs from the other
muscles in being directed across, instead of parallel to, the
axis of the orbit. It arises from the lachrymal bone, immedi-
ately beneath the lachrymal duct. From this spot the mus-
cle passes outwards above the internal rectus, and between
the suspensorius and external rectus, to be inserted into the
upper margin 'of the sclerotic coat at this point, close to the
insertion of the superior oblique muscle.

The next stage of the dissection requires very great care,
viz., in tracing back the several nerve branches above enume-
rated through the dura mater and upper part of the cavernous
sinus to the Brain.

The Cavernous sinus is so named from the reticulate
structure in its interior ; the space results from the separation
of the layers of the dura mater. The piece of dura mater
bounding the sinus externally is of some thickness, and con-
tains in its substance the following nerves. The most super-
ficial is the Fourth Nerve : it lies almost on the surface of the
internal aspect of that ridge of the dura mater which passes
along the tips of the clinoid processes : next below it, is the
Third Nerve ; and below this, again, the two quite distinct
though apposed branches of the Ophthalmic division of the
Fifth Nerve. Through the cavity of the Cavernous sinus the
Sixth Nerve passes.

It will require considerable patience to trace these nerves,
and the dura mater in which they are imbedded should be
kept moist during the dissection by applying a damp sponge.

To complete the dissection of the Orbit there only remains

Dissection of Sheep's Head. 247

the investigation of the Membrana Nictitans, and its accom-
panying gland, viz. the Harderian Gland.

In tracing back the Inferior Oblique muscle to its origin
below the Lachrymal duct, a light pink gland will have been
noted in the interval between the Inferior and Internal Recti,
and the Inferior Oblique muscles : this is the Harderian gland,
by which a thick whitish humour is secreted. Associated
with this gland, in the angle of the eye, between the globe
and the side of the orbit, will be found the accessory eyelid
or Membrana Nictitans, a fibro-cartilaginous structure con-
tinuous posteriorly with the pad of fat which is insinuated
between all the muscles of the eye. When the eye is in its
natural position the margin of this membrane is only to be
seen, the rest being buried in the ocular sheath ; but when
by the contraction of the Hecti and Suspensorius muscles, the
globe of the eye is drawn back against the pad of fat, the
membrane protrudes across the eye. The secretion of the
Harderian gland is poured forth from two openings under the
Membrana Nictitans, in order to facilitate the motion of this
membrane over the eyeball.

Nerves of the Orbit.

Eyeball is supplied by Second Cerebral (sensory).

Levator Palpebrae „ „ Third Cerebral (motor).
Rectus Superior „

Rectus Inferior „

Rectus Internus „

ObKquus Inferior „

{i.e. the Third Nerve supplies all but three of the muscles
of the eye)

Obliquus Superior is supplied by Fourth Cerebral (motor).
Fore-part of the Head, Nose, \ „ Fifth Cerebral, Ophthalmic

and Lachrymal Gland ) Division (sensory).

Rectus Externus is supplied by Sixth Cerebral (motor).
Choanoid or Suspensorius „ „ „

248 Mammalia,

The position of the parts in the Orbital Cavity may be
shortly reviewed as follows : — The Supra-orbital and Lachry-
mal nerves lie close to the outer wall of the cavity ; and the
small Fourth nerve near the inner wall : all entering the Orbi-
tal cavity above the muscles. The Superior Oblique muscle is
recognised by the Fourth nerve entering it : the Levator
Palpebrse and Superior Rectus are crossed by the Fourth
nerve : the External Rectus is seen between the Supra-orbital
and the Lachrymal nerves.

A small nerve, the Temporo-malar, or orbital branch of the
Superior Maxillary trunk, lies in loose fat, along the outer
angle of the floor of the orbit, and should be traced before
further dissection is made in that part, as it is soft and easily
broken : it is distributed to the eyelids and to the integu-
ment.

Dissection of Spheno-Palatine Ganglion. — The Perios-
teum, or Orbital Membrane, should now be dissected away
from the subjacent fat, and, together with the contents of the
orbit, turned towards the top of the skull ; and the fat removed.

By this means the cancellous bony structure that projects
backwards along the base of the orbit in the direction of the
optic nerve will be disclosed ; and, immediately beneath it,
the Superior Maxillary division of the Fifth nerve : this stout
bundle of nerves should be traced back to the Gasserian
ganglion, and forwards to the point where it enters the
maxillary hiatus to pass through the infra- orbital canal and
emerge on the face at the infra- orbital foramen, where it
divides into numerous branches. In the orbit this nerve is
accompanied by the internal maxillary artery.

Internal to the Superior Maxillary Branch, and between it
and the nerves to the Eye will be found the much difi'used
SphenO'Palatine Ganglion, also known as Meckel's Ganglion.
The junction of the Orbital branch with the Superior maxil-
lary division takes place about the middle of the ganglion.

Dissection of Sheep's Head.

249

The ganglionic mass is of a reddish grey colour, but is not
easily distinguished from the surrounding fat ; this ganglion
resembles the other ganglia in connection with the Fifth
nerve, in having sensory, sympathetic, and motor roots con-
nected with it. Its motor root is formed by the Yidian nerve,
which does not here run in a separate osseous canal as it does
in Man, and so may be traced, as the principal branch, back
as far as the under or internal aspect of the Fifth nerve ;
beyond this point it is not easily traced, but its course may
be here noted, — through the back part of the cavernous sinus
to the superior cervical ganglion, which will be exposed later
on, hidden now by the par-occipital process and the muscles
thereto attached. The emergent branches of the Spheno-
palatine ganglion are distributed to the muscles and vessels
of the orbit, to the soft and hard palate, and to the nose.

Close adjoining the line of the Spheno -palatine ganglion
and its several cords, is the line of the Dental nerve, which
quits the main trunk of the Superior Maxillary soon after it
leaves the Gasserian ganglion, passes along the floor of the
orbit, enters a canal in the maxilla, and then supplies the teeth.
We have now traced the principal branches of the Fifth nerve,

as follows '. — [ i Supra-orbital, to fore-
Ophthalmic diyi- j \ head.
/ sion (with Ciliary { \ Lachrymal, to 1. gland
ganglion). | ' ~~^ — ^'^

Fifth
or

Trigeminal

or

Trifacial

Nerve.

Sensory root,
through Gasserian
Ganglion to all
three divisions.
Motor root.
InferiorMaxillary
division alone.

Superior Maxillary

division
(with Spheno-Pala-
tine Ganglion).

Inferior MaxiUary

division
(with Otic & Sub-
maxillary ganglia) .

and eyelid.
— Nasal, to nose & eyelid
— Orbital, to eyelid and

side of face.
— Infra-orbital, to lower
eyelid, side of nose,
and upper lip.
— Dental, to teeth of up-
per jaw.
/ Buccal, to cheek and
J angle of mouth.
j Auriculo - temporal :
' through parotid gland
Gustatory or Lingual,
to tongue.
/ Inferior Dental, to
j teeth of lower jaw,
j lip, and chin.
\ Mylohyoid, to Mylo-
hyoid muscle.

K K

250 Mammalia.

Dissection of the Eighth and Ninth Pair of Cerebral
Nerves, and of the Sympathetic System at the base of
THE Skull. — The Student will first cut througli the par-
occipital process near to the Skull, and turn it forwards, and
fix it in that position with a set of hooks and chains : by this
means he will be enabled to get at, and dissect out, the bundle
of nerves that lie but little below the fat in the cavity between
the par-occipital process and the external aspect of the occi-
pital condyle.

This bundle of nerves consists of, in order from back to
front, the following principal factors : — the Ninth or Hypo-
glossal Nerve leaves the skull through the anterior condyloid
foramen, and is crossed at about ^in. from the foramen by
the Spinal branch of the Spinal Accessory ; this spinal branch
joins the course of a stout nerve called the Pneumogastric or
Vagus just before it crosses the Hypo- glossal, and these may
be traced back together to the * foramen lacerum basis cranii,'
by which they take exit from the skull. Next adjoining this
stout nerve-branch is the fine Glossopharyngeal Nerve , which
leaves the skull at the same spot with the Yagus ; an& then
lies along the external surface of a nodulation of a pinkish
hue ; this nodulation is the First Cervical Ganglion of the
Sympathetic System.

But in order to get at the roots of these nerves it will be
necessary to take the saw and first cut through the occipital
condyle down to the condyloid foramen, and break it ofi"
with the chisel, thus exposing the root of the Hypo-glossal
nerve ; and, secondly, to saw down from the posterior side of
the Facial nerve to the cranial exit of the conjoined Eighth
pair of nerves, separate the grooves with the chisel, and then
cut through the remaining pedicle of bone with the bone nip-
pers, by which means the ganglia at the root of the Eighth
pair of cranial nerves will be disclosed. It will now be well
to trace each of these nerves forwards.

Dissection of Sheep^s Head. 251

The Hypo-glossal is a motor nerve ; after passing from the
cranium by the condyloid foramen, it crosses first the Yagus
(being embraced between it and the spinal branch of the
Spinal Accessory), and then the carotid artery; near this
point it gives off a branch, the descendens noni, which de-
scends in the sheath of the carotid artery, and is distributed
to the depressor muscle of the os hyoides. The further pro-
longation of the main stem of the Hypo-glossal to its disap-
pearance beneath the mylo-hyoid muscle has been traced in a
previous dissection (p. 231).

The Spinal Accessory is a motor nerve ; its origin from the
cervical portion of the spinal cord, and entrance into the
cranium by the foramen magnum was noted above :
after leaving the cranium through the foramen lacerum it
divides, the Accessory part gives twigs to the Yagus, and the
Spinal part continues backwards under the superior extremity
of the submaxillary gland, passes down the neck, supplies
the Sterno-mastoid muscle, and is lost in the Trapezius muscle.

The Pneumogastric or Vagus is a mixed nerve, originating
by motor and sensory roots, and is the largest of the cranial
nerves in the neck. In its passage through the foramen
lacerum in the same sheath of dura mater with the Spinal
Accessory, it has developed a distinct ganglion, termed the
ganglion of the root ; and after it has escaped from the foramen,
and received the Accessory part of the Spinal Accessory, it
presents a second and fuller enlargement, termed the ganglion
of the trunk : it then descends behind the guttural pouch, and
proceeds down the neck in the same sheath with the common
carotid artery.* The principal branches in the upper part of
its course, near the head, are two, mz., (1) a Pharyngeal
branch, which comes off near the ganglion of the trunk and

* The further course of this nerve has been previously seen in the dissection
of the Rat.

252 Mammalia,

terminates in tlie Pharynx, and(2) a Superior Laryngealhranch,
rather larger than the preceding ; which comes off about one
inch from the skull, inclines slightly forwards internal to the
carotid artery, and passes to the side of the Larynx, which it
enters near the margin of the thyroid cartilage.

The Qlosso- Pharyngeal, the third Cranial nerve that comes
through the foramen lacerum, is the smallest of the three, and
a mixed motor and sensory nerve, but pierces the dura mater
through a distinct opening : presenting in the aperture of
exit- two small ganglionic swellings, from the larger of which
spring the branches that unite this with the other nerves in
this part. Leaving the cranium, it passes internal to, and in
the same direction with the stylohyal bone to join the back
and side of the tongue. In its course it gives off, close to
the ganglion, a nerve to the tympanum called Jacobson's
nerve, and at about one and a-half inch lower down a branch
to the tonsils ; in the neighbourhood of this last it anasto-
moses freely with fine branches from the Yagus forming a
plexus.

The Anterior Termination of the Sympathetic System.
— In the dissection of the Rat the Student will have traced
the main cords of the sympathetic system up to the head : he
has now before him the superior cervical ganglion, the largest
of the three ganglia in the neck. From this ganglion nerve-
twigs communicate with the ganglia on the Pneumogastric and
Glossopharyngeal nerves. The apparent continuation from
the upper part of the ganglion enters the skull by penetrating
the back part of the cavernous sinus, where it forms the
Cavernous Plexus. A branch from this plexus joins the larger
(or superior) Superficial Petrosal nerve (the first branch of
the Facial nerve), and the two conjoined are termed the
Yidian nerve, which, as above said, is in connection with the
Sphenopalatine Ganglion.

Dissection of Sheep^s Head. 253

Dissection of Mouth, Tongue, Palate, Posterior Nares,
Pharynx and Larynx. — The Student should now take a saw,
without a back, and make an antero-posterior vertical section
of the Head ; carrying the incision right through the base of
the Skull down to the level of the posterior part of the Thy-
roid Cartilage and the dorsum of the Tongue. The two halves
may then be laid out on each side, like the leaves of a book,
leaving the Tongue in the middle line.

The osseous frame-work, within which are contained the
several parts and organs next to be described, demands the
first attention. The upper part of the cranium, or brain-
case, was removed in an early stage of this dissection ; but
the longitudinal central axis, above which are the brain, nose
and face, and below which are the posterior nares and the
palate, still remains. Posteriorly, and forming the support
of the Medulla Oblongata, will be seen, in section, the anterior
boundary of the foramen magnum, formed by the Basi-occi-
pital factor of the occipital bone ; this is about an inch long :
then follows the 'body' of the sphenoid bone, or Basi-sphenoid,
limited anteriorly by a suture (in appearance a greyish line) ,
and hollowed out superiorly to receive a pink oval body : the
hollow is known as the sella turcica : the pink oval gland
depending from the brain, just posterior to the Optic com-
missure, is the pituitary body. Next, anteriorly, is a rather
broader bone, notched superiorly by the groove in which is
lodged the optic commissure ; and terminated anteriorly
by the upright perforated bone through which the olfac-
tory nerve fibres penetrate ; this is the Pre-sphenoid. The
Basisphenoid and Presphenoid form in man two of the
factors of the ' Sphenoid bone.' The anterior boundary of
the cranial cavity is formed, as just said, by the perforated
Ethmoid bone, and next above that come the cells in the
Frontal bone. Thus the floor of the Cranial cavity is seen
to be made by the following bones, arranged serially, mz..

254 Mammalia.

Basioccipital, Basisphenoid, Presplieiioid, and Ethmoid ; the
roof being formed by the Frontal, Parietal and Supraoccipital,
which have been cut away. The Ethmoid bone consists of
two perforated parts and a median partition, the perforated
parts being opposite to, and transmitting the olfactory nerves
arising from the olfactory lobes. That which comes into
view under the vertical section is the middle plate, or * lamina
perpendicularis' of the Ethmoid bone; and its prolongation
forwards, as the median cartilaginous septum of the nose.
Considering this septum to be a continuous structure, ossified
in the neighbourhood of the cribriform plates, but not ossified
beyond the first inch and a-half from the cranium. Professor
Flower applies the term ' Mesethmoid' to the whole of this
element of the skull, whether ossified or not, including the
'crista galli' of human anatomy. On either side of this
Mes-ethmoid are the Turbinal bones, contained in either
nasal cavity. These Turbinals are formed by two distinct
sets of convoluted spongy bony plates ; a lower set, which
come close down to the nasal orifice, and which are
attached to the Maxilla by one of their folds, whence they
are called Maxillo- turbinals, and an upper set, extending
from the cribriform plate to the posterior and superior mar-
gin of the Maxillo-turbinals, from which however they are
quite distinct and separate, and called, from their attach-
ment to the cribriform, ethmoid, or sieve-like plate, the JEfh-
mo- turbinals. " It will be observed* that while the Ethmo-
turbinal is placed high in the nasal cavity, and above the
direct channel by which the air passes to the posterior nares,
the Maxillo-turbinal, situated near the front of the chamber,
before it has divided into an upper true olfactory chamber
and a lower nasal passage, nearly blocks up the whole cavity,
so that air passing through in inspiration is filtered between

* Flower. Ost. Mam. p. 108.

Dissection of Sheep's Head. 265

its meshes. The moist membrane which covers its bony-
plates in life is supplied with nerves chiefly from the Fifth
pair, and not from the Olfactory ; so that it does not perform
the function of an organ of smell like the Ethmoturbinal,
but rather serves to guard the entrance of the respiratory
passages from foreign substances, and perhaps to warm the
inspired air.'*

The lower part of the median partition between the nasal
cavities is formed by the Vomer, a bone which in a trans-
verse vertical section presents the form of a capital Y,
receives the lower margin of the Mesethmoid between the
lips that rise from its superior surface, and itself com-
pletes the nasal septum below, by the development of a thin
vertical plate from its inferior surface. The Yomer extends
back so far as to be in apposition with the anterior termina-
tion of the Presphenoid ; and forwards so as to meet the Prae-
maxillse, being in the anterior half of its course in apposition
with the superior surface of the Maxilla, as far back as the
suture between the Palatine and Maxilla. The opening between
the Palatine and the Yomer constitutes the Posterior Nares.

If now the Student will press with his finger the external
wall of this Posterior Nares on the line between the posterior
ends of the Palatine and the suture between the Basioccipital
and Basisphenoid, he will feel the broad Pterj^goid bones, and
distinguish their inferior termination in a narrow lamella
with a hamular process projecting backwards. It is round

T , 1 o -1 ^ Cribriform plate ; \

Lateral mass of the Superior and middle Ethmotvrbinals
Ethmoid ("turbinated bones")

Ethmoid" \ " Crista G alii" and ] | Posterior ossified

of \ " Lamina Perpen- > < part

Anthropotomy. j dicularis " ) (of Mesethmoid.

^ , ( Cribriform plate ; )
Lateral mass of the J Superior and middle J Ethmoturbinals
Ethmoid ( u turbinated bones " )

256 Mammalia,

tMs process that the tendon of tlie tensor palati muscle passes ;
a muscle that fixes and renders tense the lateral parts of the
soft palate.

Tracing the edge of this bone backwards, a small lip will
be found, in the mucous membrane, covering the termination
of a tube. This tube, which is closely united to the pterygoid
plate, covered by the mucous membrane, and opens into
the Pharynx, is the Eustachian tube, a canal by which the
cavity of the tympanum is rendered continuous with the
cavity of the Pharynx ; in other words, a canal by which the
tympanic cavity of the ear communicates with the external
air. The upper part of this canal was noted in a previous
stage of this dissection (p. 237).

The Pharynx is that cavity that extends obliquely down-
wards and backwards above the velum palati (which separates
it from the mouth), and forms the backward prolongation of
the posterior nares. We have just noted the slit-like open-
ings of the Eustachian tubes on each side ; below these we
oome to the Isthmus of the Fauces^ a narrowed channel between
the Pharynx and the mouth, or rather between the free bor-
der of the velum palati and the Epiglottis, whose size is
altered by the elevated or pendent position of the soft palate.

The posterior border of the soft palate in man presents in
the centre a conical pendulous body called the Uvula, but
this is absent in nearly all other animals. In the Horse, the
velum palati is so much developed that the isthmus is kept
constantly shut, except during the passage of food or water,
and the animal is unable to breathe through his mouth;* but
in the Sheep it is not so complete and pendulous, conse-
quently the isthmus is generally open, thus allowing the
animal both to breathe through the mouth and to regurgitate
its food in the act of rumination.

* Strangeways.

Dissection of Sheep^s Head, 257

The anterior and inferior surface of the velum forms the
posterior boundary of the mouth, and is united laterally to
the base of the tongue. Between the velum and the base of
the tongue are two lateral spaces, in each of which are two
or three openings, the mouths of the ducts from the Tonsils^
each tonsil being a collection of follicular capsules.

The Hard Palate^ or anterior part of the roof of the mouth,
consisting of the palatine bones and palatine processes of the
superior maxilla, is covered by a dense membrane, equally
divided by a median longitudinal ridge, which terminates
anteriorly in a small tubercle. From this ridge proceed
transverse ridges, dividing the palate into a number of super-
ficial folds, the edge of each posterior fold underlying the
posterior margin of the fold next in front of it, so that an
abrupt edge is always presented towards the back of the mouth.

The Tongue* presents three distinct portions ; the most
anterior constitutes the tip, and its upper surface may be
called dorsum planum : this portion is limited abruptly
posteriorly by the hump or elevation which forms the second
portion, and whose upper surface may be denominated dorsum
gibbosum : that part which gradually declines to the base of
the epiglottis forms the third part, and its surface may be
called dorsum radicis. The tip assists in the prehension and
mastication of the food ; the gibba, like a piston, pushes the
bolus towards the pharyngeal cavity ; while the root, by
means of the exterior parts of its muscles, enables the organ to
move as if connected by a joint to the hyoid bone.

In the Human tongue the whole ante- gibbous portion is
deficient : it is therefore truncated as compared with the
Huminant tongue. It is by means of the ante- gibbous por-
tion of the tongue that quadrupeds lap up water.

The under surface of the tongue is connected laterally to

* Cf. J. Zaglas. Annals of Anat. and Fhys., 1850. Parts i. and ii.

T- L

258 Mammalia^

the lower jaw by the genio-liyo-glossi muscles, in front of
which the mucous membrane beneath the tip forms a fold
called the Frcenum Linguce. A little anterior to the fraenum
on either side are the openings of the ducts of the sub-max-
illary and sub-lingual glands.

The upper surface or dorsum of the tongue is covered with
papillae of various form throughout its whole extent, except
in the neighbourhood of the epiglottis. Four varieties of
papillce are found, viz. (a) circiimvallate, i.e. papillae resting in
cup-like depressions of the mucous membrane ; these are found
only along the lateral margin of the gibbous portion of the
tongue ; (b) fungiform, i.e. larger processes of the mucous
membrane than the circum vallate, wider at the free end than
at the part fixed to the tongue ; these are more numerous
than the circumvallate, and are principally situated in the
middle of the dorsum ; (c) conical, i.e. small cones like white
specks, principally along the sides of the tongue ; and, lastly,
(d) filiform, i.e. hair-like processes of the epithelium, sloping
generally towards the back of the mouth ; these papillae cover
the anterior two-thirds of the tongue and vanish towards the
base.

Behind the Tongue and in front of the orifice of the
Larynx is the leaf- shaped cartilage, termed the Epiglottis ;
which during respiration is placed vertically, but during de-
glutition takes a horizontal position so as to close the open-
ing of the Larynx and prevent food passing into it during its
passage through the Pharynx into the (Esophagus.

The rounded eminences posterior to the Epiglottis, and on
which the Epiglottis rests when depressed backwards, are the
Arytenoid Cartilages.

Dissection of the Larynx. — The (Esophagus, which lies
above the Larynx and Trachea, should be now dissected away
from the Trachea, in order to enable the Student to expose
the internal arrangement of the Larynx by a longitudinal cut

Dissection of Sheep^s Head. 259

with the scissors between the arytenoid cartilages through
the tracheal rings and cricoid cartilage.

The base of the Epiglottis will then be seen to be attached
to the upper margin of the thyroid cartilage, the largest of
the cartilages of the Larynx, and which consists of two lateral
expansions or also, which meet and unite anteriorly at an acute
angle, forming a projection answering to the 'Adam's Apple '
in Man.

The upper Yocal Chords are small and inconspicuous.
The Tracheal rings are complete, but not absolutely joined,
the division being traceable all down the right side.

By pressing outwards the mucous lining of the upper part
of the Larynx between the Arytenoids and the base of the
Epiglottis, a hard substance will be felt holding an antero-
posterior direction : this is the Thyro-hyal bone.

Dissection of the Hyoid Boxes. — Without going into
the detail of the muscles, the Student should acquaint himself
with the position of the series of Hyoid bones, of which the
Thyro-hyal is the posterior.

Turning the side of the head up again, he will find this bone
almost underlying the tendinous part of the di- gastric muscle,
parallel with which it continues for about an inch ; at this
point, and underlying the Hypo- glossal nerve, a joint will be
found ; as also what appears to be a single bone (running at
right angles to the Thyro-hyal, prolonged a little way down
and continuing up towards the last molar of the upper jaw), but
which really forms two of the factors of the arch, the downward
prolongation being a small round nodule representing the basi-
hyal, and the upward prolongation being the cerato-hyal. At
the upper end of the cerato-hyal will be found another bone
running towards the stylo- hyal ; this is the epi-hyal, and thus
the S of the hyoid arch is completed, — the top of the S be-
ing attached to the Skull, the convexity of the bend support-
ing the Tongue, and the return end supporting the Larynx.

260 Mammalia.

As before noted (p. 228), the bones follow one anotber tbns :
stylo-byal, epi-byal, cerato-byal, and thyro-byal ; the basi-
byal forming an angular prominence between the thyro- and
cerato-hyals.

Y.— D ISSECTION

OF THE

EYE OF THE OX.*

External. — To see the general form of the ball of the Eye,
and the outer surface of the external coat, the attachment of
the different muscles should be taken away, and the fat re-
moved which surrounds the white chord of the optic nerve :
by this means we shall be enabled to see from back to front
the following structures : posteriorly, is the Optic nerve,
attached to the back of the globe but considerably to one side
of its axis ; next, the Sclerotic ((TKXrjpogf hard) coat, i.e. the
opaque posterior five- sixths of the ball ; and, anteriorly, the
Cornea {corneus, horny), i.e. the smaller transparent sixth part
of the ball. The outer surface of the Sclerotic coat is smooth
except where the muscles have been attached. The Cornea
and front portion of the Sclerotic are covered by mucous
membrane, called the Conjunctiva, being the reflected portion
of the under lining of the eyelids, much simplified in
character ; and where the tendons of the four Itecti expand
over it anteriorly, partly covered by the Conjunctiva, a thin
tendinous layer is seen, called the " white of the eye." The
Cornea is seen to be elliptical, transparent, and convex

♦ N.B. — A general notion of the structure of the Eye may be gained by pur-
suing the following shorter method of dissection, viz. —

After all the muscles have been removed, pin the Eye to a loaded cork ; then
place the cork in a deep pie-dish, and fill the dish with water so as to cover the
Eye, and proceed to expose the coats of the Eye by a series of windows, thus :

1. Kemove about half of the Sclerotic and Cornea : 2. Remove a smaller por-
tion of Choroid and Ciliary processes : and 3. Remove a small portion of the
Retina.

By this means all the coats are seen at the same time, and in situ. C.Robbrtson.

Dissection of Eye of the Ox. 261

anteriorly, i.e. like a watch-glass, and, at the circumference,
blended with the Sclerotic coat by continuity of tissue ; and
will be found to be smooth and firm, though soft to the touch.

On looking into the eye, there will be seen behind the
transparent Cornea, a coloured membrane which gives the
tint to the eye ; it is the Iris, and the central aperture by
which it is perforated is the Pujnl. The small bodies situated
on the pupillary margin of the Iris are called Corpora nigra.
The pupillary opening is entirely filled by a portion of the
anterior surface of the Capsule of the Crystalline Lens. The
space, between the Cornea in front and the Lens behind, in
which the Iris is suspended, contains a clear watery fluid,
named the Aqueous Humor. These several parts act as
follows : the Cornea transmits, but also deflects (refracts, or
bends towards the axis of the cone) the rays of light trans-
mitted ; the movements of the Iris regulate the quantity of
light admitted to the Lens ; the Lens has the power of
refracting and causing the convergence of the rays of the cone
of light, not only on their entrance from a rarer medium
(aqueous humor) into its anterior convex surface, but also at
their exit from its posterior convex surface into the rarer
medium (vitreous humor).*

Removal of Cornea.! — The Student should now cut with

• Kirke's Phys., Ed. 7, p. 647.

t The following mode of operation is suggested in "Gray's Anatomy." In
order to separate the Sclerotic and Cornea, so as to expose the second tunic, the
eyeball should be immersed in water contained in a small vessel. A fold of the
Sclerotic near its anterior part being then pinched up, an operation not easily
performed from the extreme tension of the membrane, it should be divided with
a pair of blunt-pointed scissors. As soon as the Choroid is exposed, the end of
a blow-pipe should be introduced into the orifice, and a stream of air forced into
it, so as to separate the slight cellular connection between the Sclerotic and
Choroid. The Sclerotic should now be divided around its entire circumference
{i.e. midway between the Cornea and Optic nerve), and may be removed in
separate portions. The front segment being now drawn forwards, the handle
of the scalpel should be pressed gently against it at its connection witb
the Iris, and, these being separated, a quantity of perfectly transparent fluid
will escape ; this is the aqueous humor. In the course of this dissection, the
Ciliary nerves may be seen lying in the loose cellular tissue between the Choroid
and Sclerotic, or contained in delicate grooves on the inner surface of the latter
membrane. P. bbQ (Ed. 1858).

262 Mammalia,

the scissors tlirougli the Cornea, all round, at its junction
with the Sclerotic, and remove the Cornea from the front of the
eyeball. On piercing the Cornea the Aqueous humor, above
mentioned, will escape from the chamber of which the Cornea
forms the outer wall.

The Aqueous humor differs little from water in its physical
characters : but it contains a small quantity of some solid
matter, chiefly chloride of sodium (in the human subject), dis-
solved in it.

The Cornea is readily separable into two layers, one fibrous,
and the other firm but structureless, retaining its transparency
for a long time ; of these, the former, made up of a series of
fine superposed layers, and lined posteriorly by a very thin
structureless membrane, known as the membrane of Demours,
is the Cornea proper ; the latter, consisting of a basement
layer (anterior elastic lamina) covered by Epithelium, is the
Corneal Conjunctiva. The Epithelium in front of the
* anterior elastic lamina ' demands special notice ; for in the
Horse, the Ox, and the Sheep, it has a much more remarkable
appearance than in Man, and one not to be accounted for by
the ordinarily presumed mode of growth of stratified epithelia ;
for the deepest cells are greatly elongated and larger than
those which are immediately superimposed, and have precisely
the appearance of true columnar epithelium, the flat ends
resting on the subjacent elastic lamina, and the pointed ex-
tremities directed forwards.*

The Chamber of the Aqueous Humor^ which has been thus
opened into, was formerly said to be partially divided into
two chambers which communicated through the Pupil ; but
it has now been ascertained that in Man the pupillary margin
and part of the posterior surface of the Iris are in contact
with the Capsule of the Lens, thereby closing the chamber

* Quain and Sharpey, ii. 715 (Ed. 7).

Dissection of Eye of the Ox. 263

posteriorly. There exists, however, a distinct and separate
middle chamber, anterior to the circumference of the Lens
(= the posterior chamber of old anatomists), viz.y in the
angular interval existing at the circumference between the
ciliary processes, the Iris, and the suspensory ligament of the
Lens.

Reflection of Sclerotic. — Let four cuts be now made
with the scissors through the Sclerotic from the edge whence
the Cornea has been removed, towards the optic nerve — being
careful to cut through the Sclerotic alone, — and let the four
resulting flaps be pinned down upon a cork so as to support
the Eye in an upright position : a thin structure* will be found
to unite the fore part of the Sclerotic to the front of the un-
derlying dark tunic called the Choroid ; this must be broken
through with the handle of the scalpel, as also some connec-
tions further back towards the optic nerve.

The Choroid coat. Ciliary {cilium, an eyelash) processes, and
Iris are supplied by vessels from the Ophthalmic (6(j)daXfxoQ, an
eye) artery , named the anterior and posterior Ciliary vessels : of
these the posterior (short) ciliary branches pierce the Sclerotic
coat around and close to the Optic nerve : the anterior (long)
branches, arising in front of the orbit chiefly from muscular
branches, pierce the Sclerotic just behind the Cornea. The
Ciliary veins also perforate the Sclerotic at different points to
go to join the Ophthalmic veins.

The inner aspect of the Sclerotic coat will be seen to be of
a dark colour, resulting from the presence of a delicate con-
nective tissue (Membrana Fused) through which branches of
the ciliary vessels pass obliquely : and which is thickest at the
back part of the eyeball, becoming thinner and whiter towards
the Cornea. On the inner surface of the Sclerotic, at its corneal
margin may be seen a circular groove passing round ; which

* Vide infra, Ciliary muscle.

264 Mammalia.

groove is the outer wall of a venous canal (sinus circularis
iridis), the Canal of Schlemm ; the inner wall of this canal is
to be seen on the middle coat of the eye, just within the
thickest part of the white ring which by the removal of the
Sclerotic coat has been disclosed (around the eye just beneath
the anterior boundary of the Sclerotic). The white ring just
named marks the ciliary ligament and muscle, which limit
the extent forwards of the black Choroid coat.

The Ciliary muscle forms a ring of unstriped muscular tissue ;
its fibres are attached in front to the inner surface of the Sclerotic
coatf and are also connected with the terminal fibres of the
posterior elastic layer of the Cornea. The Ciliary ligament, in-
ternal to the Ciliary muscle, surrounds the Iris nearly opposite
the junction of the Cornea with the Sclerotic tunic : it may
serve the purpose of supporting the other coats at the fore
part of the Eye.

It may now be noted that the Iris is connected by its cir-
cumferential border with the Choroid, the Cornea, and the
Ciliary ligament and muscle ; whilst its inner edge is the
boundary of the Pupil : its anterior surface is variously
coloured.

The outer surface of the Choroid is flocculent, and is covered
by remnants of a pigmentary areolar tissue (membrana fusca)
between it and the Sclerotic coat : in it may be seen small
veins arranged in parallel arches (vasa vorticosa) ; and lying
upon its surface are the ciliary arteries and nerves.

Reflection of Half of the Iris. — The student should now
carefully lift up a portion of the Iris in the forceps, and with
the scissors separate it (for half its circumference), from its
attachment along the inner margin of the ciliary muscle, and
reflect it.

By this means an anterior view of the Ciliary processes may
be obtained. These Ciliary processes are a series of plaits or
folds, disposed in a circle, and projecting inwards, at the back
of the circumferential portion of the Iris ; they form the an-

Dissection of Eye of the Ox, 265

terior termination of the Choroid coat. The plications of the
Ciliary processes of the Choroid coat fit into, or interdigitate
with corresponding plications of the suspensory ligament of
the Lens : this the Student should note carefully before
making the following

Reflection of the Circle contained within the Ciliary
Ring. — Let the Student divide the Choroid coat, and the
Retina which lies beneath it, circularly, with the scissors, about
i-in.behind the white ring of the Ciliary muscle, being specially
careful not to cut the Hyaloid* membrane ; and raise this
piece of Retina and Choroid coat, together with the Ciliary
ligament and the attached Iris in one piece ; detaching the
Ciliary processes of the Choroid coat from the digitations
which they form with the plications (also called Ciliary pro-
cesses) of the suspensory ligament of the Lens ; and float this
in water over a piece of whitened cork or wax : then gently
wash the pigment from the back of the Iris. Great care is
necessary to leave the Lens, its capsule, and its suspensory
ligament, and the Hyaloid membrane, in situ : but it is of the
utmost importance in order to the right understanding of this
middle section of the Eye.

We by this means obtain a posterior view of the same
ciliary processes of which we have just examined the anterior
aspect beneath the Iris.

The posterior surface of the Iris is covered with a deep
tinted pigment, called the Uvea {uvea, a cluster of grapes)
from the purple colour it assumes in man : after removing
this, the membrane of the Iris should be treated with acetic
acid, and then there may be seen (under the microscope) at
the margin of the pupil a narrow circular band of non-striated
m,uscular fibre {Sphincter muscle of Pupil) with which, lines
radiating from the centre to the circumference {Dilator mus-

* Vide infra, Hyaloid membrane, p. 266.

M M

266 Mammalia,

cle) are blended : — there may also be seen prominent festoon-
like processes of the fibres of tbe Iris lying in a transparent,
elastic, fibrous tissue continuous with the posterior elastic
layer of the Cornea, and giving a milled appearance like that
of the edge of a coin ; this constitutes the Ligamentum pecti-
natum : — and, lastly, the finely indented border, ora serrata,
which forms the anterior boundary of the nervous tunic or
Retina, extending forwards nearly to the outer edge of the
Ciliary processes of the Choroid, whence nucleated, elongated
cells (not nerve elements), constituting the pars cilia ris retina,
are continued onwards as far as the tips of the Ciliary processes.
The anterior face of the eye after the performance of the
various sections above described (viz.: 1. Removal of Cornea,
2. Heflection of Sclerotic, and 3. Reflection of Circle contained
within Ciliary Ring) now presents to our view(«) a transparent,
though firm and elastic Capsule encompassing the Lens ; (b)
a transparent membranous structure placed around the Lens,
termed the Suspensory ligament, or Zonule of Zinn, on which
dark lines of pigment covering the surface may be traced,
which when washed, reveal plaits or folds less prominent but
longer than the processes of the Choroid coat which have
been just removed therefrom (these two sets of folds having
been dovetailed together, the prominence of one membrane
being received into the hollow of the others) ; (<?) the fine
transparent Hyaloid membrane which encapsulates the Vitreous
Humor, and is at its fore part closely united with the posterior
aspect of the suspensory ligament of the Lens, which however
it underlies, and, passing beyond, ends by joining the back of
the capsule of the Lens : {d) the cut edges of the Retina and
of the Choroid coats. It will be apparent from the above
description that it is possible for an interval to exist, surround-
ing the edge of the Lens capsule, bounded in front by the
suspensory ligament, and behind by the hyaloid membrane (in
that it passes posteriorly to the suspensory ligament, though

Dissection of Eye of the Ox, 267

attached to its outer border, en route to reach the Lens capsule).
Such an interval does exist, and is known as the Canal of Petit.

At this point in the dissection we have then three concen-
tric rings apparent in front of the eye ; in the centre, the Lens
and its capsule ; immediately external to, and placed around
the lens capsule comes the transparent, membranous, suspen-
sory ligament of the Lens, and, next, the cut edge of the
Betina, of which the anterior termination (ora serrata) was
removed in a previous dissection.

The Student should now cut across the thin membranous
capsule in which the crystalline Lens is enclosed, and with-
draw the Lens (which is a transparent double convex body) from
its seat in a hollow on the front of the Yitreous body to which
it is inseparably united.

The Lens should be dried, or hardened by immersion in
spirit*, or boiled f in a test tube until it becomes opaque, and
then split with a knife, by which it may be demonstrated to
consist of a whole series of concentric laminae, arranged one
within another, like those in an onion, which may be separately
detached from one another. Under the microscope each layer
may be teased out with needles and seen to be constructed of
minute parallel fibres : and in the Lens of the Ox, now
under consideration, these fibres in some parts of the Lens
will be seen to be irregularl}'- serrated at ' their edges ; but
this is not the case in every layer, nor in the same layer in all
subjects.

The Yitreous body will be seen to fill four-fifths of the space
within the coats of the eyeball, and reaches forwards external to
the circumference of the Lens, nearly to the Iris : but is slightly
hollowed in front to receive the Lens. In looking to the

* Or Chromic Acid.

t The water in which the Lens has heen hoiledwill he opaque ^^ith Globulin.
It will bring out the Fibres better if 1 per cent, of Sulpburic Acid be added,
and the boiling be continued for five or ten minutes.

268 Mammalia.

inside of tlie eye through the vitreous body, the surface of the
Hetina, as long as it remains properly supported by this 'body/
will be seen to be quite smooth, except at one spot, rather to
the side of the axis of the eyeball, where the optic nerve
expands, and the central artery of the Retina enters.

The Yitreous body in its Hyaloid membrane should now
be removed in order to see the inner surface of the Nervous
Tunic or Retina : i.e. the delicate, almost pulpy membrane,
which — contains the terminal part of the optic nerve, — lies
within the Choroid coat, — rests on the Hyaloid membrane of
the Vitreous humor, and, — extends forwards nearly to the
outer edge of the ciliary processes of the Choroid, where it
ends in a finely indented border — viz. the ova serrata.

"We do not find in the Eye of the Ox, nor indeed in the
Eye of any Mammal, except that of Man and of the higher
Quadrumana, the yellow elliptical spot in the axis of the eye-
ball known as the* macula lutea'or yellow spot of Sommerring.

The Retina is easily separable from the investing membrane
next external to it, viz. the Choroid coat ; and when this is
detached, the outer surface will be seen to be rough or slightly
flocculent, from the fine shreds or fragments of a structure at
first called JacoVs Membrane, but which is now generally
recognised as the columnar layer of the Retina.

To prepare the Retina for Microscopic investigation, the
Student should take a perfectly fresh specimen and harden it
by immersing it in Miiller's fluid (consisting of 2^ parts of
Potassium Bichromate, 1 part of Eodium Sulphate, and 100
parts of Distilled Water) ; then he should make a mixture of
bee's- wax and olive oil (equal parts), and pour these substances
when melted (at as low a temperature as possible) round the
piece of Retina from which the sections are to be cut ; or
place the piece of Retina (if flat), sandwich- fashion, between
flat plates made of these same substances. By this means

Dissection of Eye of the Ox. 269

the tissue is supported and held firm while the section is
being made.*

A vertical section of the Retina should be made and examined
under the microscope, when three layers or strata of dissimilar
materials will be apparent, viz. 1. an external layer consisting
of rods and cones, called the columnar layer (stratum bacil-
lorum) ; 2. an intermediate or granular layer, made up of two
collections of rounded and oval corpuscles separated by a
clear striated internuclear space ; 3. an internal nervous layer,
made up of three distinct structures : {a) externally {i.e. ad-
joining the inner stratum of nuclei in the ' granular ' layer)
is a stratum consisting chiefly of nerve cells (the celhilar
stratum) ; (/;) intermediately is a stratum of nerve-fibres
directed forwards from the optic nerve, and terminating in
the nerve cells on which they lie : — both these strata — the
cellular and the nerve fibre — diminish in thickness concomi-
tantly as they extend forwards from the middle of the back
of the eye ; — and, (c) internally, a limiting membrane (mem-
brana limitans), which lines the inner surface of the Retina,
separating it from the vitreous body.

* Retina of Calf or Pi^, prepared by Klein's method. 1. Take a perfectly
fresh eye, and pierce the Sclerotic and the (..oinea with areeillein several places.
2. Place it in Miiller's fluid for three weeks. 3. Cut the eye transvirscly into
two portions. 4. Take the Retina out and place it in dilute alcohol for three to
five days. 5. Place it in dilute animoniacal solution of Carmine (carmine, 10
grains; strong ammonia, 30 minims ; glycerine, 2 oz. ; distilled water, 20 oz. ;
rectified spirit, \ oz.) for twenty-four hours. 6. Wash it in wattr and place it
in absolute alcohol for half to one hour. 7. Place it between two plutes of wax
and oil (equnl parts) or paraffin, and make scctums. 9. Mount in Dammar (a
solution of Dammar resin in benzole). — Rutherford, in Quarterly Journal of
Microscopical Science, N.S. ilv., January, 1872.

H. Aldbjt, Printer, Oxford.

5 X

By tha mme Author.
A VES.— Anatomy and Dtsskctiox.

Price 1/6.

t

OPINIONS OF THE PRESS.

The book -will be found very convenient by students at Oxford, and elsewhere,
who are carefully studying the Anatomy of the Vertebrata. — Nature.

Practical hints (which are good) for young dissectors are also given. — Zoo'
logical Record.

The larger part of the publication is taken up by a condensed summary of
tbe principal points to be noted in the Anatomy of Birds, which certainly gives
more useful information on the subject than any other English book with which
we are acquainted ; and the whole concludes with a most practical chapter on
dissection. — The Ibis. (Quarterly Journal of Ornithology).

Mr. Morrell appears to have hit off successfully the happy mean between
being too rudimentary for a tolerably advanced worker on the one hand, and
that hypertechnicality which is so common in recent anatomical works on the
other. — Oxford Up^dergraduales Journal.

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