THE FORERUNNERS OF THE HORSE 277 



Condylarthra of lower grade than either Perisso- 

 dactyla or Artiodactyla. All the members of this 

 group had five-toed fore and hind feet, and like- 

 wise rested a considerable portion of the sole 

 upon the ground in the original plantigrade 

 fashion a feature in which they differ markedly 

 from the horse and its relatives, which walk only 

 on the very tips of their toes in the extreme of 

 the modern digitigrade style. The two series of 

 small bones of the wrist (carpus) and ankle (tarsus) 

 joints are also arranged in distinct vertical rows, 

 without that interlocking which characterises these 

 portions of the skeleton in the Perissodactyla. . 



In concluding this chapter brief reference may 

 be made to a few of the more striking features 

 which characterise the long chain of progressive 

 evolution from the Eocene Hyracotherium to the 

 modern Equus. Two factors have evidently been 

 predominant in guiding this evolution, namely, the 

 necessity of collecting and assimilating food and 

 of attaining a high degree of speed. " To the 

 one," as Dr. Lull remarks, "the horse owes the 

 marvellous perfection of the grazing mechanism, 

 as seen in the lengthened jaws and in the teeth ; 

 to the other, the fleet limbs and graceful contour 

 of the body and the increase in stature. These 

 adaptations are entirely mechanical, and, while 

 tending toward greater and greater perfection 

 on the whole, are not always of a progressive 



