OF DIGESTION. 



81 



kind of teeth, with which they crush the shells of the 

 mollusks on which they feed. 



218. The Mammals, however, are almost the only verte- 

 brates which can be properly said to masticate their food. 

 Their teeth are well developed, and present great diversity 

 in form, arrangement and mode of insertion. Three kinds 

 of teeth are usually distinguished in most of these ani- 

 mals, whatever may 

 be their mode of life ; 

 namely, the cutting 

 teeth, incisors ; the 

 tusks or carnivorous 

 teeth, canines ; and 

 the grinders, molars 

 (Fig. 73). The in- 

 cisors (a) occupy the 

 front of the mouth ; 

 they are the most simple and the least varied ; they have 

 a thin cutting summit, and are employed almost exclu- 

 sively for seizing food ; except in the elephant, in which 

 they assume the form of large tusks. The canines (b) are 

 conical, more prominent than the others, more or less 

 curved, and only two in each jaw. They have but a single 

 root, like the incisors, and in the carnivora become very 

 formidable weapons. In the herbivora, they are entirely 

 wanting, or when existing they are so enlarged and modi- 

 fied as also to become powerful organs of offence and 

 defence, although useless for mastication ; as in the baby- 

 roussa, &c. The molars (c) are the most important for 

 indicating the habits and internal structure of the animal ; 

 and at the same time they are most varied in shape. 

 Among them we find every transition, from those of a 

 sharp and pointed form, as in the cat tribe, to those with 

 broad and level summits, as in the ruminants and rodents. 



Fig. 73. 



