THE TEETH OF MAMMALS 169 



Only two species are now living, — the African and 

 Indian Elephants. The Mastodons, Dinotherium, 

 Mammoth, and several Elephants are now ex- 

 tinct on the earth, and can only be studied in 

 fossil remains. The order is almost entirely ex- 

 tinct, and the living species of Elephants can only 

 be preserved by domestication and care, as they 

 have been remorselessly destroyed for the ivory 

 furnished by the long tusks. The order is dis- 

 tinguished by the long incisor tusks, which are 

 implanted in deep sockets in the premaxillary 

 bones, and grow continuously from persistent 

 pulps. The bulk of the tusk consists of finely- 

 tubed dentin which constitutes the ivory of com- 

 merce. The tubules bend and curve, which makes 

 the fine ivory lines and causes the refraction of 

 light which is one of the beauties of fine ivory. 

 The present trade in ivory is enormous, and 

 comes from Africa, where the elephants have been 

 destroyed by thousands, so that the wild species 

 will soon become extinct. Formerly the fossil 

 beds and Arctic shores and islands of Siberia 

 yielded great quantities of the tusks of the extinct 

 Mammoth, and they are yet washed up by the 

 waves. Of the two living species of the Elephant 

 the formula is, — 



i.Hm.y = 26. 

 0-0 6-6 



The two upper central incisors are greatly pro- 



