1 68 



THE ARCTOG^IC REALM. 



[CHAP. 



detached 1 ; the feet being generally three-toed, although in one 

 Indian species the lateral digits are wanting. These three-toed 

 horses are met with in the Pliocene of Europe, Asia, and North 



FlG. 39. UNDER SURFACE OF SKULL OF Hipparion. 



America ; and it is suggested by Professor Cope that while in the 

 Old World the intermediate stage between Anchitherium and the 

 modern horses was occupied by this genus, in the New World this 

 gap was filled by Protohippus. The true horses (Equus\ charac- 

 terised by the one-toed feet and the union of the anterior inner 

 column of the upper cheek-teeth with the adjacent middle column,, 

 although now confined to the Old World, where they date from 

 the Pliocene, were formerly abundant in North America during the 

 Plistocene, and, as we have seen, were likewise represented during 

 the same epoch in South America. The oldest forms appear to 

 be those from the Siwalik Hills of northern India ; and it is thus 

 evident that the group was originally an Arctogseic one 2 . The 

 genus is now represented in all the regions of eastern Arctogaea, 

 with the exception of Madagascar, and its extinction in the New 

 World cannot be satisfactorily explained. 



1 This pillar forms the lowest part of the unshaded area in figure 38. 



2 Professor Scott, to whose views we have already alluded, in a paper pub- 

 lished in Tr. Amer. Phil. Soc. Vol. xvn. pp. in 112 (1894), is of opinion 

 that the genus Equus was evolved in North America, and that Anchitherium, 

 in its restricted sense, was off the direct line. He arranges the direct ancestral 

 forms of the upper Tertiary, from above downwards, in the order Protohipptis , 

 Desmatippus, Miohippus, and Mesohippus ; Anchitherium branching off from 

 Miohippus, and Hipparion from Protohippus. 



