HISTORY OF THE fLITOPTERNA 



507 



connections that they originally had in the 

 pentadactyl manus, a very great difference 

 from the horses. The ankle-joint also was of 

 the same primitive character as in the other 

 fLitopterna. The feet were relatively longer 

 and more slender than in the other fpro- 

 terotheres and the metapodial of the single 

 functional digit longer in proportion to the 

 phalanges. 



The appearance of the hving animal, aside 

 from the character of the hair, colom'-pattern, jf 

 etc., may be closely inferred from the skeleton. 

 It was a much smaller and more graceful ani- 

 mal than its contemporary and relative \Dia- 

 diaphorus, as Ught and agile as a gazelle. The 

 head had some resemblance to that of a small 

 horse, but the neck was much shorter than in 

 the horses ; the body also was shorter than in 

 the latter, and the proportions of the trunk 

 and limbs were quite as in the smaller ante- 

 lopes. But these likenesses to horses and an- 

 telopes were, it must again be emphasized, 

 superficial ; the fundamental characteristics 

 of structure were more primitive than in the 

 most ancient known artiodactyls and perisso- 

 dactyls. 



With the aid of the fragmentary material 

 which alone represents the fproterotheres in 

 the formations preceding and following the 

 Santa Cruz in time, it is not practicable to 

 trace the development of the various phyla in 

 a satisfactory manner. Two of the Santa Cruz 

 genera, ^Diadiapfiorus and ■\Proterotherium, 

 continued into the lower Pliocene (Parana), 

 and two additional ones have been named, 



Fig. 253.— Left pes 

 of fThoaiherium. 

 Princeton Uni- 

 versity Museum. 

 Letters as in Fig. 

 250. 



