10 



ELEPHANTS, RECENT AND EXTINCT. 



grinding surface of the tooth of such an elephant con- 

 sequently consists of a solid mass, made up of alternating 

 vertical transverse layers of various substances, arranged 



FIG. 6. Molar Teeth of Indian () and African (J) Elephant. 

 In a the anterior half is worn, and the remainder unworn. 

 Much reduced. (After Owen.) 



in the order of cement, enamel, ivory, enamel, cement ; 

 and since each of these constituents differs in hardness, it 

 will be obvious that the millstone-like apparatus is now of 

 a far more efficient type than it was in the mastodon. 

 Moreover, since the crowns of the molars of the true 

 elephants are very much taller than are those of the 

 mastodons, it is evident that they will require a longer 

 period of time before they become worn away, and that 

 they will therefore allow a longer life to their owner. 

 Even, however, among true elephants there is a con- 

 siderable amount of difference in regard to the number 

 and narrowness of the component plates of their molar 

 teeth, and it will be seen from Fig. 6 that in this respect 

 the African elephant departs far less widely from the 

 mastodon than does its Indian cousin. Since the food of 



