172 
DIFFERENT KINDS OF TEETH. 
namely, the African and the Indian; as also between each 
of these and the great extinct species known as the Mam¬ 
moth (fig, 99). In the great gnawing teeth of the Eabbit, 
Fig. 98. —Molar Tooth of Mastodon. 
Fig. 99. —Molar Teeth of Elephants. 
1, African Elephant; 2,1 ndian Elephant; 
3, Mammoth. 
&c., the front surface only is covered with enamel; and as 
this is worn away more slowly than the ivory, it stands up as 
a sharp edge (fig. 91), which is always retained, however 
much the tooth may be worn away. 
183. Of all the teeth, the molars may be regarded as the 
most useful. They are seldom absent in the Mammalia; and 
their office is usually essential to the proper digestion of the 
food. Animal flesh (the most easily digested of all substances) 
needs but to be cut in small pieces; but the hard envelopes 
of beetles and other insects 
must be broken up; and the 
tough woody structure of the 
grasses, and the dense coverings 
of the seeds and fruits on which 
the herbivorous animals are 
supported, must be ground 
down. The incisors and canines 
Fig. loo. Skull of Boar. are c h{ e fly employed among 
Carnivorous animals for the purpose of seizing their living 
prey, and are never deficient in them; but they are less re¬ 
quired in Herbivorous animals; and either or both kinds are 
not unfrequently deficient. Sometimes, however, they are not 
