R. S. Lull — The Evolution of the Horse Family. 171 



the genus Ryr mother ium from the London Clay, known only 

 by the skull. 



The genus Eohippus has teeth of a very similar pattern, but 

 more advanced in that the cross crests are somewhat more dis- 

 tinct than in Hyr mother ium and, unlike the latter, the fourth 

 premolar is beginning to assume the form of a true molar. 

 The hand bore four digits, with a vestige of the first (thumb) 

 in the form of a splint bone probably entirely concealed within 

 the skin. The more progressive hind foot had but three toes, 

 with a remnant of the fifth. 



Eohippus was a small animal about eleven inches in height 

 at the shoulder and in general suggestive of the carnivores 



Fig. 7. a, Fore foot and b, hind foot of Eohippus pernix. 

 ze. (After Marsh.) 



One-half natural 



rather than of the ungulates of to-day. The back was arched, 

 the head and neck were short, and the limbs of moderate length, 

 showing no especial adaptation for speed. This genus has a 

 remarkable geographical range, having apparently originated in 

 western Europe (England) and migrated by way of Asia and 

 what is now Bering Strait as far southeast as New Mexico. 

 This migration of Eohippus shifted the scene of the evolution- 

 ary drama to our own country, for, while the remains of suc- 

 ceeding genera are increasingly numerous in North American 

 rocks from the Wasatch on, it is only from time to time that 

 European representatives appear, in each case evidently derived 

 from migratory North American types. The Yale Museum 



