42 MAMMALIA. 
this class derives its name, and being a character peculiar to 
it, they distinguish it better than any other that is external.(J) 
Division of the Mammalia into Orders. 
The variable characters which form essential differences 
among the Mammalia are taken from the organs of touch, on 
which depends their degree of ability or address, and from 
the organs of manducation, which determine the nature of 
their aliment, and are all closely connected, not only with 
every thing relative to the function of digestion, but also with 
a multitude of other differences relating even to their intelli- 
gence. . 
The degree of perfection of the organs of touch is esti- 
mated by the number and the pliability of the fingers, and 
from the greater or less extent to which their extremities are 
enveloped by the nail or the hoof. 
A hoof which completely envelopes the end of the toe, 
blunts its sensibility, and renders the foot incapable of seizing. 
The opposite extreme is when a nail, formed of one single 
lamina, covers only one of the faces of the extremity of the 
finger, leaving the other possessed of all its delicacy. 
The nature of the food is known by the grinders, to the 
form of which the articulation of the jaws universally corres- 
ponds. 
To cut flesh, grinders are required as trenchant as a saw, and 
jaws fitted like scissars, having no other motion than a verti- 
cal one. 
For bruising roots or grains, flat-crowned grinders are ne- 
cessary, and jaws that have a lateral motion; in order that 
inequalities may always exist on the crown of these teeth, it 
is also requisite that their substance be composed of parts of 
unequal hardness, so that some may wear away faster than 
others. 
Hoofed animals are all necessarily herbivorous, and have 
(1) We shall find, however, in the sequel some doubts on this subject, arising 
from certain points in the family of the Monotremata. 
