DIFFERENT KINDS OF TEETH. 
171 
cutting edges, which work against each other like the blades 
of a pair of scissors (fig. 94); whilst in animals that live on 
insects, these teeth are raised into conical points, which lock 
Fig. 94 .—Teeth of Carnivorous Animai. Teeth of Insectivorous Animal. 
into corresponding depressions in the teeth of the opposite 
jaw (fig. 95). When the nourishment of the animal con¬ 
sists principally of soft fruits, these teeth are simply raised 
into rounded elevations (figs. 97, 98); and when they are 
Fig. 96. 
Teeth of Herbivorous Animal. Fig. 97 .—Teeth of Frugivorous Animal. 
destined to grind harder vegetable substances, they are termi¬ 
nated by a large flat and roughened surface (figs. 96, 99). 
The roughness of this surface is maintained by the peculiar 
arrangement of the three substances of which the tooth is 
composed. The enamel, instead of covering its crown, is 
arranged in upright plates, which are dispersed through the 
tooth ; and the space between them is filled up by plates of 
ivory and of cementum (§ 54). These last, being softer than 
the enamel, are worn down the soonest; and thus the plates 
of enamel are left constantly projecting, so as to form a rough 
surface admirably adapted to the grinding action which the 
tooth is destined to perform. The mode in which these 
plates are disposed, affords a most characteristic distinction 
between the two species of Elephant at present existing, 
