PROBOSCIDEA. 



443 



palms of the hand and the soles of the feet. There are no 

 clavicles. The testes are abdominal throughout life. There 

 are two teats, and these are placed upon the chest. 



The order Proboscidea comprises the three genera, Elephas 

 (with both living and extinct representatives), Mastodon, and 

 Deinotherium, the two latter being extinct. The order came 

 into existence in the Miocene period, in which it is represented 

 by all these three genera. The genus Elephas comprises the 

 living Asiatic and Indian Elephants. In all the Elephants, 

 whether living or extinct, the " tusks " are formed by an enor- 

 mous development of the upper incisors. The milk-tusks are 

 early shed, and never attain any great size. The permanent 

 tusks, however, grow from persistent pulps, attaining in old 

 males an enormous size. The lower incisors are absent, and 

 there are no other teeth in the jaws except the large molars, 

 which are usually two in number on each side of each jaw. 

 The molar teeth are of very large size, and are composed of 

 a number of transverse plates of enamel united together by 

 dentine. In the Indian Elephant the transverse ridges of 

 enamel are narrow and undulating, whilst in the African 

 Elephant they enclose lozenge-shaped intervals. 



The surfaces of the molars are approximately flat, and the 

 plates of enamel form patterns which are very characteristic of 



Fig. 360. Molar of the Mammoth (ElepJias primigeuius), upper jaw, right side, 

 half natural size. Post- Pliocene, a Grinding surface ; b Side view. 



the different species. Subjoined are illustrations of the molars 

 of three of the most important Post-Pliocene Elephants (figs. 

 360-362). 



