HISTORY OF THE fLITOPTERNA 



501 



artery was in its normal position. The body was rather short, 

 hke that of a deer or antelope ; the number of trunk- vertebrae 

 is not definitely known in any of the genera, but was very prob- 

 ably 19 or 20, and the tail must have been short. 



The limbs were slender and of moderate length ; there was 

 no coossification between the bones of the fore-arm or the lower 

 leg. The feet were three-toed, except in one genus {^Thoa- 

 therium) in which they were single-toed, and nearly or quite 



Fig. 248. — Skull of \Diadiaphorus, Santa Cruz. American Museum. 



the whole weight was carried upon the median digit, the laterals 

 being mere dew-claws. The shape of the hoofs and the whole 

 appearance of the foot were surprisingly like those of the three- 

 toed horses, but there were certain structural differences of 

 such great importance as, in my judgment, to forbid the refer- 

 ence of these animals, not merely to the horses, but even to 

 the perissodactyls. In studying the fLitopterna, one is con- 

 tinually surprised to note the persistence of archaic and 

 primitive characters in association with a high degree of 

 specialization. 



The largest Santa Cruz representatives of the family were 



