HISTORY OF THE PERISSODACTYLA 



345 



a common term, even though that common ancestor should 

 elude discovery, 



]Hyrachyus may be described as a generalized, relatively 

 undifferentiated perissodactyl, from which almost any other 

 family of the order, except the horses and the ftitanotheres, 

 might have been derived. The incisors, present in undi- 

 minished number, were well developed and functional, but not 

 large, and the canines were moderatel}' enlarged, forming 

 small tusks. The premolars were all smaller and less complex 

 than the molars, which had a strong resemblance to those 

 of the tapirs ; in the lower jaw they were identical with the 

 latter, but in the upper jaw there was more than a suggestion 

 of likeness to the rhinoceroses. The skull was long, narrow 



Fig. 183. — Skull of t Hyrachyus. (After Osborn.) 



and low, hornless, and with thin, slender nasals and straight, 

 horizontal upper contour. The neck was short, the body 

 very long and the limbs of medium length and weight ; though 

 relatively stouter than in ^Triplopus of the upper Bridger and 

 Uinta beds, they cannot be called heavy. The feet were not 

 especially elongate and rather slender ; the manus had four 

 toes and the pes three. 



A brief and short-lived branch of this stock existed in the 



