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 Kabbit, 



Fig. 98. MOLAR TOOTH OF MASTODON. 



1. 2. 3. 



Fig. 99. MOLAR TEETH OF ELEPHANTS. 



1, African Elephant; 2, Indian 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. IOO.-SKULL OF BOAR. are ^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 



