XI PALEONTOLOGY AND EVOLUTION 357 



are three, like those of the fore leg; and the 

 middle metatarsal bone is much less compressed 

 from side to side than that of the horse. 



In the Hipparion, the teeth nearly resemble 

 those of the Horses, though the crowns of the 

 grinders are not so long ; like those of the Horses, 

 they are abundantly coated with cement. The 

 shaft of the ulna is reduced to a mere style, anky- 

 losed throughout nearly its whole length with the 

 radius, and appearing to be little more than a 

 ridge on the surface of the latter bone until it is 

 carefully examined. The front toes are still three, 

 but the outer ones are more slender than in 

 Anchitherium, and their hoofs smaller in proportion 

 to that of the middle toe ; they are, in fact, re- 

 duced to mere dew-claws, and do not touch the 

 ground. In the leg, the distal end of the fibula is 

 so completely united with the tibia that it appears 

 to be a mere process of the latter bone, as in the 

 Horses. 



In JZquus, finally, the crowns of the grinding- 

 teeth become longer, and their patterns are slightly 

 modified ; the middle of the shaft of the ulna 

 usually vanishes, and its proximal and distal ends 

 ankylose with the radius. The phalanges of the 

 two outer toes in each foot disappear, their meta- 

 carpal and metatarsal bones being left as the 

 " splints." 



jaw was devoid of the posterior lobe which exists in the hinder- 

 most true molar. 



