IV.] PERISSODACTYLES. 169 



The rhinoceroses (Rhinocerotidce) originally had a distribution 

 very similar to that of the horses, with the exception that they 

 never entered Neogaea; and they also agree with the latter in their 

 present extinction in North America, where they are unknown 

 after the Pliocene. On both sides of the Atlantic the true 

 rhinoceroses appear to have commenced in the lower Oligocene ; 

 and in both areas the earliest forms were hornless. Early species 

 with a pair of horns placed transversely on the nose are likewise 

 met with both in Europe and North America; but the modem 

 two-horned rhinoceroses appear to be restricted to the Old World, 

 where one extinct species (Rhinoceros antiquitatis] ranged as far 

 north as the Arctic circle during the Plistocene period. On the 

 whole, it seems preferable to include all the living and most of the 

 extinct species in the typical genus Rhinoceros ; the existing forms 



FlG. 40. SECOND RIGHT UPPER MOLAR OF Rhinoceros. 



A. median valley ; D. anterior, and E. posterior crests ; F. posterior valley ; 



H. crochet. 



being confined to the Oriental and Ethiopian regions. Rhino- 

 ceroses, it may be observed, differ from all the preceding families 

 of the suborder by the upper cheek-teeth having a continuous 

 outer wall, instead of being divided by a vertical ridge into two 



