22 
INTRODUCTORY. 
neath the cerebellum. The crura of the cerebellum always 
form under the medulla oblongata, a transverse prominence, 
termed the tuber annulare. 
The eye, lodged invariably in its orbit, and protected by two 
eyelids, and a vestige of a third, has its crystalline humour 
fixed by the ciliary process. Its sclerotic coat is simply cel¬ 
lular. 
In the ear there is always found a cavity, called the tympanum 
or drum, closed from without by a membrane called the mem - 
brana tympani; it has also four small bones, called the incus , 
malleus, stapes, and os orbiculare, at the entrance of which is 
placed the stapes, which communicates with three semicir¬ 
cular canals; finally, a spiral canal, called the cochlea, which 
terminates by one of its canals in the tympanal cavity, and by 
the other, in the vestibule. 
The tongue is always fleshy, and is attached to a bone called 
the hyoid, suspended by ligaments to the cranium. 
The lungs are two in number, composed of an infinity of small 
cells, and are always inclosed, without adhesion, in a cavity 
formed by the ribs and the diaphragm, and lined by the pleura. 
The organ of voice is always at the superior extremity of the 
trachea; and a fleshy continuation denominated the velum palati, 
or soft palate, establishes a direct communication between the 
larynx and the back part of the nostrils. 
Living on the earth’s surface, these animals are exposed to 
the transitions of heat and cold. Their bodies have a covering 
of hair, which is thicker in the northern regions, and more 
scanty as they approach the warm latitudes. The Cetacea, how¬ 
ever, which inhabit the sea, are totally devoid of this covering. 
The internal canal in the Mammalia, is suspended by a fold 
in the peritoneum, called the mesentary, which contains a 
number of conglobulated glands for the lacteal vessels. Another 
production of the peritoneum, termed the epiploon, hangs on 
the front of, and underneath the intestines. 
Cuvier divides the Mammalia into orders, whose essential 
characters are founded on the construction of the feet or organs 
of touch, and the number and kinds of teeth. On the perfec¬ 
tion of the organs of touch, the power of expertness depends ; 
and from the dentition may be ascertained, in a great measure, 
the nature of their food and digestive functions. 
