INTRODUCTION. xiii 



" The variable characters which form essential differences 

 among mammals are taken from the organs of touch, on 

 which depend their degree of ability or address ; and from 

 the organs of mastication, which determine the nature of their 

 food, and are all closely connected, not only with everything 

 relative to the digestive function, but also with numerous other 

 differences concerning even their intelligence. The degree of 

 perfection of the organs of touch is estimated by the number 

 and 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 layer, 

 covers only one of the surfaces of the end of the finger, leaving 

 the other surface 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 always corresponds. To cut flesh, 

 grinders as trenchant as a saw, and jaws fitted like scissors, 

 having merely a vertical motion, are required. For bruising 

 roots or grains, flat-crowned grinders, and jaws having a lateral 

 motion, are necessary : and in order that the crowns of these 

 teeth may always possess inequalities, their substance is com- 

 posed 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 incapacitate them for seizing living prey. Animals 

 with fingers are susceptible of more variety, their food is of 

 all kinds ; and, independently of the form of their grinders, 

 they greatly differ from each other in the pliability and sen- 



