1364 



CLASS MAMMALIA. 



Family Rhinocerotim;. — With this family we enter upon the 

 consideration of another branch probably derived from the primi- 

 tive Lophiodont stock, which attained great development in Ter- 

 tiary times, and is still represented in Asia and Africa by at least 

 five well-defined species. It is not easy to distinguish this family 

 from the Lophiodontidce, as represented by Hyrachyus (which Dr 



Fig. 1237. — Left half of the palatal surface of the cranium, and left lateral aspect of the skull 

 of Metamynodon planifrons ', from the White River Miocene of North America. One-sixth 

 natural size. Na, Nasal ; Fr, Frontal ; Pa, Parietal ; So, Supraoccipital ; sm, United post- 

 glenoid and posttympanic processes; 1, 2, 3, Alveoli of incisors; c, Alveolus of canine; 2, 3, 4, 

 Premolars ; 1, 2, 3, True molars. (After Scott and Osborn.) 



Schlosser includes in the Rhinoce?'otid<z), but the upper true molars 

 (fig. 1239) generally have a very thick outer wall, which is often 

 produced in advance of the first ridge ; their transverse ridges are 

 but slightly bent, and are intimately connected with the outer wall ; 

 the upper premolars are usually nearly or quite as complex as the 

 true molars ; the lower cheek-teeth are more or less completely 



