140 THE VITAL FUNCTIONS. 



§ 3. Mastication by means of Teeth. 



The teeth, being essential instruments for seizing 

 and holding the food, and effecting that degree 

 of mechanical division necessary to prepare it 

 for the chemical action of the stomach, perform, 

 of course, a very important part in the economy 

 of most animals; and in none more so than in 

 the Mammalia, the food of which generally re- 

 quires considerable preparation previously to its 

 digestion. There exist, accordingly, the most 

 intimate relations between the kind of food 

 upon which each animal of this class is intended 

 by nature to subsist, and the form, structure, 

 and position of the teeth ; and similar relations 

 may also be traced in the shape of the jaw, 

 in the mode of its articulation with the head, 

 in the proportional size and distribution of 

 the muscles which move the jaw, in the form of 

 the head itself, in the length of the neck, and its 

 position on the trunk, and indeed in the whole 

 conformation of the skeleton. But since the 

 nature of the appropriate food is at once indi- 

 cated by the structure and arrangement of the 

 teeth, it is evident that these latter organs, in 

 particular, will afford to the naturalist most im- 

 portant characters for establishing a systematic 

 classification of animals, and more especially of 

 quadrupeds, where the difterences among the 



