RECENT. 
EQUUS. 
PLIOCENE. 
PLIOHIPPUS. 
PROTOHIPPUS. 
(Hipparion). 
MIOCENE. 
MIOHIPPUS. 
(Anchitherium). 
MESOHIPPUS. 
EOCENE. 
OROHIPPUS. 
O. C. Marsh—Polydactyle Horses. 
Fore Foot. Hind Foot. Fore-arm. Leg. 
i 
GENEALOGY OF THE HORSE. 
