HOW ANIMALS EAT. 71 



may be still further strengthened by having two or more 

 diverging fangs, or roots, a feature peculiar to this class. 

 The incisors and canines have but one fang; and those 

 that are perpetually growing, as the incisors of Rodents 

 and Elephants, have none at all. The teeth of flesh-eat- 

 ing Mammals usually consist of hard dentine, surrounded 

 on the root with cement and capped with enamel. In the 

 herbivorous tribes, they are very complex, the enamel and 

 cement being inflected into the dentine, forming folds, 

 as in the molar of the Ox, or plates, as in the compound 

 tooth of the Elephant. This arrangement of these tissues, 

 which differ in hardness, secures a surface with prominent 



er Molar Tooth of Indian Elephant (Elephas Indicus), showing trans- 

 verse arrangement of dentine, d, with festooned border of enamel plates, e; c, 



FIG. 36. Upper Molar Tooth 



verse arrangement of de _, 



cement ; one-third natural size. 



ridges, well adapted for grinding. The cutting teeth of 

 the Rodents consist of dentine, with a plate of enamel on 

 the anterior surface, and the unequal wear preserves a 

 chisel-like edge. Enamel is sometimes wanting, as in the 

 molars of the Sloth and the tusks of the Elephant. 



In Fishes and Reptiles, there is an almost unlimited 

 succession of teeth ; but Mammalian teeth are cast and 

 renewed but once in life. 



Vertebrates use their teeth for the prehension of food, 

 as weapons of offence or defence, as aids in locomotion, 

 and as instruments for uprooting or cutting down trees. 

 But in the higher class they are principally adapted for 

 dividing or grinding the food. 30 While in nearly all other 



