HOW ANIMALS EAT. 
71 
may be still farther 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 Eodents 
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 
Fig. 36.—Upper Molar Tooth of Indian Elephant (Elephas Indicus), showing trans¬ 
verse arrangement, of dentine, d , with festooned border of enamel plates, e; c, 
cement; one-third natural size. 
ridges, well adapted for grinding. The cutting teeth of 
the Eodents 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 Eeptiles, 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 
