34 MAMMALIA. 
The young are nourished for some time after birth by a fluid (milk) 
peculiar to animals of this class, which is produced by the mamme at the 
time .of parturition, and continues to be so as long as is necessary. It is 
from the mamme that this class derives its name; and being a character 
peculiar to it, they distinguish it better than any other that is external*. 
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 intelligence. 
The degree of perfection of the organs of touch is estimated by the 
number and the pliability of the fingers, and from the greater or less ex- 
tent to which their extremities are enveloped by the nail or the hoof. 
A hoof, which completely envelopes the end of the toe, blunts its sensi- 
bility, 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 pos- 
sessed 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 corresponds. 
To cut flesh, grinders are required as trenchant as a saw, and jaws 
fitted like scissars, having no other motion than a vertical one. 
For bruising roots or grains, flat-crowned grinders are necessary, 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 flat-crowned 
grinders, inasmuch as their feet preclude the possibility of their seizing a 
living prey. 
Animals with unguiculated fingers were susceptible of more variety ; 
their food is of all kinds; and, independently of the form of their grinders, 
they differ greatly from each other in the pliability and delicacy of their 
fingers. There is one character with respect to this, which has immense 
influence on their dexterity, and greatly multiplies its powers; it is the 
faculty of opposing the thumb to the finger for the purpose of seizing mi- 
a 
* We shall find, however, in the sequel some doubts on this subject, arising from 
certain points in the family of the Monotremata. 
