HISTORY OF THE PERISSODACTYLA 301 



carry the very low-crowned teeth, and, for the same reason, the 

 ascending ramus of the lower jaw was short. The face was 

 relatively short and the eye-socket, which was incompletely 

 surrounded by bone, was directly above the hindmost teeth ; 

 the cranium was proportionately large and capacious and the 

 brain, as is shown by the cast, was richly convoluted. The 

 neck was relatively far shorter than in the Miocene genera, 

 the ball-and-socket joints between its successive vertebrae 

 were less elaborated and the odontoid process of the axis was 

 in the first stage of assuming the spout-like form, being semi- 

 cylindrical, with convex lower and flat upper surface. The 

 trunk was proportionately long and the back sloped forward, 

 owing to the greater length of the hind legs. The limbs and 

 feet were elongate and very slender, but the fore-arm bones 

 are only partially coossified, and the ulna, though greatly 

 attenuated, was still complete. The same is true of the bones 

 of the lower leg ; the shaft of the fibula was hardly more than 

 a thread of bone, but its full length was preserved. In the 

 fore foot there were three functional digits, the median one 

 enlarged and supporting most of the weight, but its hoof was 

 much thinner and flatter than in the corresponding digit in the 

 Miocene and subsequent genera ; the lateral digits touched the 

 ground and were not entirely functionless and, in addition, 

 there was a small splint, the rudiment of the fifth digit. The 

 hind foot was three-toed, without splint. 



The little Uinta horse {\Epihippus) is still very incompletely 

 known, but gives us one point at least of greater primitiveness 

 than the White River genus in that only the last two premolars 

 had taken on the molar-pattern, the forward two being smaller 

 and simpler. The known species of the Uinta genus was very 

 much smaller than any of the "^Tiite River forms and even 

 smaller than some of those of the preceding Bridger formation ; 

 but it should be remembered that the Uinta has been but par- 

 tially explored and much remains to be learned regarding its 

 fauna. 



