254 THE HORSE AND ITS RELATIVES 



were really indigenous, and not the descendants of 

 European horses escaped from captivity (the date 

 appearing too early for European horses to have 

 established themselves in the country). If this 

 suggestion be well founded, it is quite certain that 

 Cabot's horses were survivors of the Onohippidium. 



Reverting to the North American members of 

 the group, the next genus for notice is Protohippus, 

 of the Loup Fork Miocene, which is closely related 

 to the undermentioned contemporary Merychippus, 

 but differs by the full development of cement in the 

 cheek-teeth of the milk or deciduous series, as well 

 as in those of the permanent set. Owing to the 

 shallowness of the jaws, the crowns of these teeth are 

 highly curved ; they are also relatively shorter than 

 in Equus, and have much the same pattern on the 

 grinding surface as those of Hippidium. The splint- 

 bones of the feet are complete, and terminate in 

 small, although perfect toes, so that Protohippus 

 was a three-toed animal. The typical species of 

 the genus stood only 9 hands at the shoulder. 



Certain equine remains from the Miocene of 

 Russia have been referred to Protohippus by Madam 

 Pavlow, 1 but, as the author herself admits, they are 

 too imperfect for definite generic determination. 



The aforesaid North American Miocene genus 

 Merychippus is the last of the genera in the direct 

 line of Equus which have the socket of the eye 



1 Bulletin de Socittt des Naturalistes de Moscou, 1903, p. 173. 



