6 THE ANCESTORS [CH. 



forms ill the Eocene of both Europe and America. In the 

 Phenacodiis of the American Lower Eocene the feet still retain 

 the primal five digits, whilst in the Eocene of both Europe and 

 America occur the diminutive Hyracotherium, which had its 

 fore-limbs four-toed, but its hind three-toed (as is the case with 

 the tapir, which is in many respects the most ancient of existing 

 forms referable to the Perissodactyle order), and also Eohippus 

 belonging to the same sub-family, but which is slightly more 

 primitive, as its hind feet have a vestige of the first digit. 

 Pachynolophus (or Orohippus), found in both Europe and 

 America, shows molars somewhat more advanced towards the 

 equine type. From this last form the Anchitherium found in 

 the Upper Miocene is not far removed in structure ; but, though 

 it is a little nearer to the horse in several respects, it is not 

 now considered to be in the direct line of descent, as it is 

 considerably larger than some succeeding forms. Since both 

 Hyracotherium and Pachynolophus occur in both the Old and 

 New Worlds, from them may have sprung the true horses of 

 both hemispheres. But from this point there is now a bifur- 

 cation, for Mesohippus, the next step towards Equus, is as yet 

 only known in America, as is also the case with its successors 

 Miohippus, Desmatippiis, and Protohippus. The last-named 

 (found in the Lower Pliocene), and which was about the 

 size of a modern donkey, had three toes on each foot. As 

 Mesohippus has not been discovered in the Old World we are 

 left only with Anchitherimn (already described) and Hipparion 

 (which had come from America) in that area. The latter was 

 very widely distributed, occurring not only in North America, 

 but also in Asia, Europe and Africa. Its remains have been 

 recently found in considerable numbers at Pikermi near Athens 

 (a fine specimen from which place is now in the National Museum 

 of Natural History), in the isle of Samos, and in Egypt. In 

 the typical North American and European forms there were 

 three digits, but in the Indian Hipparion antelopinum the 

 lateral digits seem to have disappeared. 



We have already given reasons for not placing Anchitherium 

 in the direct line of ancestry of the horse, and zoologists now 

 hold that Hipparion must likewise be excluded. It became 

 extinct probably owing to excessive specialization. 



