108 



THE THEORY OF EVOLUTION 



separate history, the horses have been individually 

 abundant and thus have had a much better chance of 



McH- 



~/y e .X. 



-Atczz: 



m. 



Fig. 9. Fore foot of Plio- 

 hippus, Pliocene, hind- 

 er view, showing the 

 very long splint-bones 

 (Mc. II and IV) and 

 rudiment of fifth digit 

 (Mc.V)(fromTroxell). 



Mc. 



-McJT. 



Fig. 10. Fore foot of Horse (Equus) 

 posterior view, showing short 

 splint-bones. Wrist- and toe-bones 

 omitted. 



being preserved as fossils than those of their con- 

 temporaries which were less common. But there are 

 several other families whose history is only less com- 



