HISTORY OF THE fTOXODONTIA 



473 



tremely small in comparison with the size of the animal ; in 

 structure, they were almost identical with those of ^[Toxodon, 

 but were far narrower and more slender. The heel-bone (cal- 

 caneum) articulated with the other bones of the tarsus in a 

 normal manner. The digits were well separated and the hoof- 

 bones quite strongly developed, indicating that the hoofs were 

 functional, supporting most of the weight. In short, the 

 difference in the external appearance of the feet between 

 the two genera was much the same as between 

 the tapirs and rhinoceroses. 



The species of ^Nesodon, of which many 

 have been named on very questionable grounds, 

 differed but little in size and were of such vari- 

 able and fluctuating character that a proper 

 discrimination of them is exceedingly difficult. 

 One of these species {^N. cornutus) gives in- 

 dications of having possessed a small dermal 

 horn on the forehead and was thus a possible 

 ancestor of \Trigodon. 



A second phylum of the suborder was 

 represented in the Santa Cruz stage by the 

 genus ^Adinotherium, the species of which, 

 not equalling a sheep in size, were very much 

 smaller animals than those of ^Nesodon, but 

 closely Uke them in other respects. The denti- 

 tion, including the pre-lacteal series, and the 

 skull were almost identical in the two genera, 

 with the exception that a large proportion of the individuals 

 of ^Adinotherium had the small frontal horn, while others had 

 no trace of it. While it is quite possible that the presence or 

 absence of the horn, which was always inconspicuous, may 

 have been a matter of specific distinction, a more probable 

 explanation is that it was a sexual character, the males horned 

 and the females hornless. Much the same thing is to be 

 observed in the modern Javan Rhinoceros {R. sondaicus) in 



a- 



Fig. 239.— Left pes of 

 fNesodon, Prince- 

 ton University 

 Museum. Letters 

 as in Fig. 238 and 

 scale of reduction 

 the same. 



