0. C. Marsh — Recent Polydactyle Horses. 355 



Fore Foot. Hind Foot. Fore-arm. Leg. Upper Molar. Lower Mol 



RECENT. 



EQUUS. 



PLIOCENE. 



PLIOHIPPUS. 



PROTOHIPPUS. 



(Hipparion) . 



MIOCENE. 



JIIOHIPPTJS. 



(Anchit/iermm) . 



MESOHIPPUS. 



EOCENE. 



OROHIPPUS. 



GENEALOGY OF THE HOESE. 



