HISTORY OF THE PERISSODACTYLA 293 



otherwise, on account of their great height, would press upon 

 the eye itself ; the orbit is completely encircled in bone. The 

 lower jaw is deep vertically and the ascending ramus (see p. 66) 

 very high, on account of the hypsodont character of the teeth, 

 which thus necessitates a remodelhng of the skull in several 

 respects. The neck is long, each of its seven vertebrae being 

 elongate; except in the atlas and axis, the anterior face of 

 each centrum is strongly convex and the posterior of all except 

 the atlas is deeply concave ; the odontoid process of the axis 

 (see p. 71) is spout-shaped, concave on the upper and convex 

 on the lower side, lodging and protecting the spinal cord. The 

 spines of the anterior dorsal vertebrse are very high, making 

 a low hump at the withers between the shoulder-blades ; the 

 trunk-vertebrse are so arranged as to make the back almost 

 straight and horizonta,l. The limbs and especially the feet 

 are very long. ' The two bones of the fore-arm, the ulna and 

 radius, are coossified into a single piece (Fig. 30, p. 81), but 

 the Umits of each are still plainly to be seen, especially in a 

 young animal ; and it is evident that the ulna is greatly re- 

 duced in size and has lost its middle portion, while all the 

 weight is borne by the radius. Similarly, in the hind leg the 

 enlarged tibia, or shinbone, alone supports the weight; and 

 only the two ends of the fibula are preserved (Fig. 38, p. 87), 

 and these are indistinguishably fused with the tibia in the 

 adult animal, but may be made out in the colt. The thigh- 

 bone has a very characteristic shape, which is difficult to. de- 

 scribe without an undue use of technical terms, but the unusual 

 prominence of the great trochanter (Fig. 35, p. 85) and of the 

 rotular groove is an important factor in producing this ap- 

 pearance. 



The very long and slender feet are so raised from the ground 

 that the animal walks upon the very tips of the toes, the 

 wrist being what horsemen call the "knee" and the heel is the 

 "hock," and the gait is thoroughly unguUgrade. Each foot 

 has but a single functional toe, the third or middle one of the 



