THE PEOBOSCIDEA. 431 



longitudinal belt of enamel, and, in tlie recent Elephants, 

 are developed only in the u^^per jaw. As their growth 

 continues for a long period, or throughout life, they 

 usually take the form of long tusks, which project on each 

 side of the upper jaw. The molar teeth are composed of 

 dentine, enamel, and cement, and their crowns, when un- 

 worn, are always ridged, the ridges very often being made 

 up of distinct tubercles. The intei-vals between the ridges 

 are sometimes, as in the Asiatic Elephant, exceedingly deep, 

 narrow, and completely filled up with cement ; or, as in 

 the Afi-ican Elephant, they may be shallow and open, the 

 cement forming only a thin coat. In the recent Elephants, 

 only the two incisors are preceded by milk teeth. The 

 molars are, altogether, six on each side, above and below; 

 they come into place and use successively, the hinder ones 

 moving forward, in proportion as the anterior ones are 

 worn do'vvn by the attrition of those which are opposed tc' 

 them. 



The stomach is simple and elongated, and there is a verj 

 wide ccecum. The trilobed liver has no gall bladder. The 

 heart has two anterior cavse. 



The cerebellum is left uncovered by the cerebral hemi- 

 spheres ; which, in the existing Elephants are large, and 

 have greatly convoluted surfaces. 



The male reproductive organs exhibit two very large 

 vesiculae seminales, and four prostates. The uterus of the 

 female has two coi-nua. 



Some, if not all, species of the extinct genus Mastodon 

 were provided with a pair of shoi-t tusks in the man- 

 dible, in addition to the large ones in the premaxillse. And 

 in some of these animals, as in certain other extinct Ele- 

 phants, the anterior grinding teeth had vertical successors. 

 The Miocene genus, Dinotherium, possessed two large, down- 

 wardly-dii'ected, tusks, one on each side of the symphysis 

 of the mandible, while there were none in the ujDper jaw. 

 The second and the third anterior grinding teeth had 

 vertical successors. 



The Probosciclea are, at present, restricted to Asia and 



