34 MAMMALIA. 



Tlie young are nourished for some time after birth by a fluid (milk) 

 peculiar to animals of this class, which is produced by the mammse at the 

 time of parturition, and continues to be so as long as is necessary. It is 

 from the mamma; 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- 



* We shall find, however, in the sequel some doubts on tliis subject, arising: from 

 certain points in the family of the Monolremafa. 



