1402 



CLASS MAMMALIA. 



premolars are nearly always absent ; while the mandibular symphysis 

 is never produced into a long rostrum, but usually terminates in a 

 short spout-like channel, as in fig. 1278. The ridges of the true 

 molars extend straight across their crowns, and generally show no 

 sign of division into inner and outer columns ; there is always a 

 certain quantity of cement in the valleys between the ridges ; and in 

 those species in which these ridges become developed into tall thin 

 plates, the cement forms equally tall laminae filling the intervening 

 spaces. In the least specialised forms the number of the ridges in 

 the " intermediate " molars may be as low as five ; while those in 

 the last true molar may vary from seven in the least specialised to 

 upwards of twenty-four in the most specialised species. Finally, it 

 is only in a few of the more generalised species that the " interme- 

 diate " molars have an isomerous ridge-formula. 



Like the Mastodons, this genus is divided into two groups, 

 according to the structure of the teeth. In the first, or Stegodont, 

 group, which is entirely confined to the Eastern parts of the Old 

 World, the number of ridges in the cheek-teeth is comparatively 

 low, and there may be only five or six of such ridges in the " inter- 

 mediate," and from seven to eleven in the last upper true molars. 



The structure of the molars of Elephas Cliftt, from the Pliocene of 

 India, Burma, and Japan, which is the most generalised species of the 



llJkl- 





I 





Fig. i2jg.—£/ep/zas Clifti. The first left upper true molar ; from Burma. 

 One-half natural size. (After Clift.) 



genus, is shown in fig. 1279 ; where it will be seen that the ridges are low 

 and roof-like, and that the cement is confined to the bottom of the inter- 

 vening valleys. The molars of this species (in which premolars were 

 developed), it will be seen, are but one step in advance of those of the 

 Tetralophodont Mastodons. In other species of this group, like E, in- 



