366 THE ANATOMY OF YERTEBRATED ANIMALS. 



which is strikingly different from that of other quadrupeds. 

 The tibia is relatively short. The fibula is distinct and com- 

 plete, and the bones of the pes have the same broad and short 

 form as those of the manus. The hallux has only a single 

 phalanx in some si:>ecies. 



The Prohoscidea have only two kinds of teeth, incisors and 

 molars, canines being entirely absent. The incisors are com- 

 posed of dentine and cement, with or without a longitudinal 

 belt of enamel, and, in the recent Elephants, are developed 

 only in the upper 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 up^oer jaw. The 

 molar teeth are composed of dentine, enamel, and cement, and 

 their crowns, when unworn, are always ridged, the ridges very 

 often being made up of distinct tubercles. The intervals be- 

 tween the ridges are sometimes, as in the Asiatic Elephant, 

 exceedingly deep, narrow, and completely filled up with 

 cement; or, as in the African 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 

 down by the attrition of those which are opposed to them. 



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

 wide csecum. The trilobed liver has no gall-bladder. The 

 heart has two anterior cavae. 



The cerebellum is left uncovered by the cerebral hemi- 

 spheres ; w^hich, in the existing Elephants, are large, and have 

 greatly-convoluted surfaces. 



The male reproductive organs exhibit two very large ve- 

 siculse seminales, and four prostates. The uterus of the female 

 has two cornua. 



Some, if not all, species of the extinct genus 3fastodon 

 were provided with q, pair of short tusks in the mandible, in 

 addition to the large ones in the premaxillce. And in some of 

 these animals, as in certain other extinct Elephants, the an- 

 terior grinding teeth had vertical successors. The Miocene 

 genus, Dinotherium^ possessed two large, downwardly-direct- 

 ed tusks, one on each side of the symphysis of the mandible, 

 while there were none in the upper jaw. The second and the 

 third anterior grinding teeth had vertical successors. 



The Prohoscidea are, at present, restricted to Asia and 

 Africa, where they are represented by two very distinct forms, 



