236 
number and persistency of their sutures, are 
intermediate in character to those of Birds and 
Reptiles. The anterior extremity of the skull 
is always formed by both the upper and lower 
jaws. The scapula is generally an expanded 
plate of bone; the coracoid, with two excep- 
tions, appears as a small process of the scapula : 
the clavicle is inconstant as to its presence ; the 
sternum consists of a narrow and usually simple 
series of bones; the sternal portions of the ribs 
are generally cartilaginous, and fixed to the 
vertebral portions without the interposition of 
a distinct articulation ; there are no abdominal 
ribs or abdominal sternum. The pubic and 
ischial arches are generally complete, and 
united together by bony confluence on the 
sternal aspect, so that the interspace of the two 
bony pelvic arches is converted into two holes, 
called foramina obturatoria, or thyroidea. 
The brain in Mammalia consists of cerebral 
and optic lobes, cerebellum and medulla ob- 
longata, but the optic lobes are placed on the 
upper part of the crura cerebri, are solid, are 
always divided by a transverse fissure, and are 
generally concealed by the cerebral lobes, in 
consequence of the large relative size of these 
masses; the decussation of the corpora pyrami- 
dalia is always distinctly marked: the tuber 
annulare and lateral lobes of the cerebellum 
have a correspondingly conspicuous develop- 
ment; the ventricles of the cerebrum are large, 
and contain a corpus striatum and cornu am- 
monis; the fornix is always well developed, 
but the following aphorisms in Cuvier’s cele- 
brated abstract or condensation of M. Serres’ 
rize essay are applicable only to the placental 
ammalia, viz. “ The corpus callosum as well 
as the pons Varolii are peculiar to Mammalia. 
The corpus callosum is developed in direct 
proportion to the size of the corpora striata 
and hemispheres. It increases progressively 
from Rodentia to Man. The corpus collosum 
is developed in direct proportion to the de- 
velopment of the tuber annulare.” 
In the Marsupial Order, as in the Kangaroo 
and Wombat, the cerebral hemispheres are 
relatively larger and more complicated with 
convolutions than in any Rodent, yet the trans- 
verse commissure which represents the rudi- 
ment of the corpus callosum connects only the 
hippocampi majores ; it is not separated from 
the fornix by any septum lucidum ; and, upon 
divaricating the cerebral hemispheres, the la- 
teral ventricles are as much exposed as when, 
in placental Mammalia, the corpus callosum 
has been removed. The tuber annulare, how- 
ever, exists in the Marsupial as in the Placental 
Mammalia, and illustrates its correlation with 
the lateral lobes of the cerebellum. The class 
Mammalia is the only one in which the cere- 
bral hemispheres are observed to have their 
vascular superficies multiplied or increased by 
convolutions, which arrive at ther maximum 
of development in Man. 
The olfactory nerves of mammals are soft, 
and divide into numerous branches in the 
cranium, which out by the orifices of the 
cribriform plate of the «thmoid. 
Themervi vagi principally supply the larynx, 
MAMMALIA. 
form a plexus around the cesophagus, and do 
not wie into a single trunk eons x to 
the stomach. The left recurrent ot 
the right, bends round the trunk of the aorta. _ 
The cervical portion of the sympathetic nerve 
passes along the neck on the sternal aspect 
the transverse processes of the vertebra; ai 
its trunk in the thorax and abdomen is m 
immediately connected with the ganglia of tl 
spinal nerves. The splanchnic nerves fo 
large ganglia before giving off the 
plexuses. 
The sclerotic coat of the eye is a fibr 
membrane, and never contains bony pl 
In the quantity of aqueous humour and th 
convexity of the lens, Mammals are gene 
intermediate to Birds and Fishes; b 
have no marsupium or pecten, nor any ¢l 
roid gland. 
The organ of hearing is characterized 
Mammalia by the full development of © 
cochlea with a lamina spiralis ; there are th 
distinct ossicles in the tympanum ; the met 
brana tympani is generally concave external! 
and the meatus auditorius externus often & 
mences with a complicated external ear, havit 
a distinct cartilaginous basis. ~~ 
The external apertures of the of sm 
are provided in Mammalia wit ub 
cartilages and muscles, and the extent of 1 
internal organ is increased by accessary cavill 
or sinuses which communicate with the p: 
sages including the turbinated bones, 
The tongue is always soft and fleshy, ai 
gustatory surface is provided with conical, fo 
sulate, and fungiform papille; it is suppl 
by a large proportion of the third division 
the fifth pair of nerves, as well as by the ninth 
and glosso-pharyngeal. “ 
Classification —The Mammalia were first 
separated from other four-footed animals and 
distinguished as a class or particular group — 
(genos) by Aristotle, the founder of natural 
history, by whom they were denominate 
Sootoka, or Viviparous animals. The Greek 
philosopher divided the Zootoka, according to 
the nature of their locomotive organs, into 
three sections: 1st, Dipoda, or bipeds; 2d, 
Tetrapoda, or quadrupeds ; and 3d, A pode 
or impeds, which comprehends the Whale- 
tribe. The second of these primary division 
—the quadrupeds,—which includes by far the 
largest proportion of the class, and in common 
parlance is considered as the class itself, is 
subdivided by Aristotle into two great natural 
groups, according to the modifications of the 
organs of touch. In the first of these groups, 
the extremities of the digits are left free for 
the exercise of the tactile sense, the nail or 
claw being placed on one side only (Ungui- 
culata of Ray); in the second group, the 
digits are inclosed in hoofs (Ungulata of Ra’ y)- 
For the convenience of treating of the different 
forms of the Unguiculate quadrupeds, Aristot 
employs for their further subdivision anothe 
system of organs, viz. the teeth. His first ya 
or family is composed of those Unguicu 
which have the front teeth trenchant, or termi- 
nating in a cutting edge, and the back teeth 
