180 CLASSIFICATION OF MAMMALIA. 



line of his method, lie developes the principles on which his 

 divisions are founded. 



" The characters by which Mammalia differ most essentially 

 one from another are derived from the organs of touch, from 

 which results their degree of dexterity, and from the organs 

 of mastication, which determine the nature of their food ; and, 

 as a corollary to these, depends not only everything which is 

 connected with the digestive functions, but a variety of other 

 circumstances relative even to their degrees of intelligence. 



M The perfection of the organs of touch is estimated by the 

 number and mobility of the digits, and the extent to which 

 they are inclosed in a claw or in a hoof. A hoof which com- 

 pletely incloses that part of the digit which touches the ground, 

 precludes the exercise of it as an organ of touch or of prehen- 

 sion. The opposite extreme is where the nail, in the form of 

 a simple lamina, covers only one side of the end of the digit, 

 leaving the other side in possession of all its delicacy of tact. 



" The kind of food is indicated by the molar teeth, to the 

 form of which the articulation of the jaws invariably corre- 

 sponds. 



" For cutting flesh, the molar teeth must be trenchant and 

 serrated ; and the jaws fitted together, so as to move like the 

 blades of a pair of scissors, simply opening and closing in the 

 vertical direction. 



" For bruising grains and roots, the molar teeth must have 

 flattened crowns, and the jaws a horizontal motion : and 

 further, that the grinding surface may be always unequal, like 

 a millstone, the teeth must be composed of substances of dif- 

 ferent degrees of density, and consequently wearing down in 

 different proportions. 



" The ungulate quadrupeds are all of necessity herbivorous, 

 or with flat- crowned molaries, because the conformation of 

 their feet does not permit them to seize living prey. 



" The unguiculate animals are susceptible of more variety. 

 They are not limited to one kind of food ; and, besides the 

 consequent variation in the form of their molaries, they differ 

 materially from each other in the mobility and sensibility of 

 their digits. There is, moreover, a characteristic which pro- 

 digiously influences their dexterity, and gives variety to their 

 modes of action : it is the faculty of opposing a thumb to 

 the other fingers, so as to seize the smallest objects, which 

 constitutes a hand, properly so called. This faculty is carried 

 to its highest degree of perfection in man, in whom the whole 

 {interior extremity is free, and can be exclusively employed in 

 prehension. These different combinations, which strictly de- 

 termine the nature of the several mammiferous animals, have 



