234 ANIMAL LIFE PAST AND PRESENT. 



with skin or with very thin horn, and thus seem to 

 indicate that the difference between an antler and a 

 horn is not so great as appears to be the case when 

 our studies are confined to living animals. 



The last form of horn we have to mention among 

 existing animals is that found in the Rhinoceroses. 

 And here we have to observe that whereas the antlers 

 of the Deer and the horns of the Oxen are placed in 

 pairs on either side of the skull, in the Rhinoceroses 

 the horns or horn (for there may be either two or one) 

 are placed in the middle line one in front of the other 

 when two are present. In structure these horns would 

 be comparable to the horn of an Ox, if the latter had 

 no bony core, and were filled up internally with the 

 same horny material as that which forms its outer 

 surface. These horns have no solid attachment to 

 the underlying bone of the skull, and are thus only 

 excessive developments of skin-structure, more ana- 

 logous in structure to warts than to anything else 

 with which we can compare them. 



The extinct animals from the Tertiary deposits of the 

 United States known as Titanotheres, which were some- 

 what akin to Rhinoceroses, are distinguished by having 

 a transverse pair of bony horn-cores above the nose, 

 which during life were doubtless sheathed in horn. 

 Again, the Uintatheres (so named from the Uinta Moun- 

 tains), of the same region, form another strange extinct 

 type of huge Ungulates, having as many as three pairs 

 of bony horn-cores ; and thus being the most extraordi- 

 nary creatures of this group of animals at present known 



