334 Cell as Basis of Organic Activity 



PAD -FOOTED 



SPRING- FOOTED 



4 -TOED 



3 -TOED 



3 -TOED 



-TOED 



Equus 



Hipporion 



Hypohippus 



Pliohippus 



Merychippus 



Mesohippus 



Eohippus 



Fig. 106. — The evolution of the forefoot of the horse. The oldest stages are 

 below. Drawings are not to scale. (From Horses by George Gay lord Simpson. 

 Copyright, 1951, by Oxford University Press, Inc.) 



