R. S. Lull — The Evolution of the Horse Family. 179 



Oregon. The reference of P. gracilis, the Oregon specimen, 

 to this genus seems somewhat questionable, as the splint bones 

 are large rather than slender as in the typical species. 



Contemporaneous with Protohippus and like it a descend- 

 ant of Merychippus is JVeohipparion, a three-toed horse with 

 very complex teeth in which the anterior-internal column (pro- 

 tocone) is isolated from the anterior cross crest (protoloph), not 



13 



a 



Fig. 13. a, Forefoot and b, hind foot of Pliohippus pemix;- drawn from 

 the type specimen, No. 11376, Yale University Museum. One-fourth natural 

 size. (Original.) 



connected with it as in all other horses. One can trace the 

 evolution of this feature, for in Merychippus insignis the pro- 

 tocone, while attached, tends to become free, yet in JVeohip- 

 parion isonesum the reverse is true in that the protocone, 

 though free, shows a strong reluctance to leave its old associa- 

 tion with the anterior crest. In other species of JVeohip- 

 parion this is not apparent, the protocone being oval in 



