342 LAND MAMMALS IN THE WESTERN HEMISPHERE 



contemporary ^Ccenopus the difference was merely one of 

 size, except for one small, but not insignificant feature. The 

 last upper molar had not perfectly acquired the triangular 

 form characteristic of all the true rhinoceroses, caused by the 

 complete fusion of the outer wall with the posterior crest, but 

 the wall projected a little behind the crest, as in perissodactyls 

 generally. Premolars (except the first) and molars were alike 

 in structure and of nearly the same size. While the grinding 

 teeth were thus hardly to be distinguished from those of the 

 true rhinoceroses, the anterior teeth, incisors and canines, 

 were totally different ; they were very small and had simple, 

 pointed and slightly recurved crowns, and were all very much 

 alike in size and form. Thus, there were in the front of the 

 mouth eight small, hook-like teeth, above and below, which 

 were obviously quite useless as weapons; and as the skull 

 had no horn, .the animal_ was defenceless, and must have de- 

 pended entirely upon 'speed for its safety from the attacks of 

 the larger and more powerful beasts of prey. 



The skull was short, deep and thick, and the head must 

 have been heavy and clumsy, quite out of keeping with the 

 body and limbs. The neck was surprisingly long, longer in- 

 deed proportionately than in the contemporary genus of horses 

 ('\Mesohippus), but the neck- vertebrae were relatively stout 

 and strong, as was required for the muscles to move and control 

 the heavy head. The body was rather elongate, but not deep 

 or massive, and the limbs were proportionately much longer 

 than in any of the known rhinoceroses. The limb-bones, one 

 and all, despite their length and slenderness, bore an unques- 

 tionable likeness to those of the true rhinoceroses. In this 

 elongation of the limbs the fore-arm and thigh were the parts 

 most affected, and the slenderness, though in notable contrast 

 to the proportions both of the true rhinoceroses and the jamyno- 

 donts, was yet much less marked than in the middle Eocene 

 representatives of the fhyracodonts themselves. The feet 

 were long and narrow, approximating, though not actually 



