TUSKS OF UINTATHERES. 21 



probable that those of the musk-deer and Chinese water- 

 deer are likewise of separate origin. With the exception of 

 the nmntjac, in which they are very small, all these deer- 

 like animals are devoid of antlers ; and it is thus evident 

 that their tusks have been developed in lieu of those 

 weapons. It is true, indeed, that the males of some of 

 the antlered deer have small tusks, but these are of no 

 use for offensive purposes, and are evidently organs in 

 process of degeneration. Moreover, in the hollow-horned 

 ruminants, such as oxen and antelopes, where the horns 

 are permanent and generally present in both sexes, not a 

 vestige of tusks remains. 



Although the Asiatic rhinoceroses have procumbent 

 tusks of considerable size in the lower jaw, none of the 

 odd-toed hoofed mammals, such as horses and tapirs, 

 have upper tusks of any size. In past times there were, 

 however, in North America a group of somewhat allied 

 creatures known as uintatheres, in which an enormous 

 pair of upper tusks, somewhat like those of the musk-deer, 

 was developed (Fig. 11). Like those of the latter, these 

 tusks grew permanently, and they were also protected by 

 a descending flange of the lower jaw, which was often 

 deeper than in the figured example. As these animals had 

 front teeth only in the lower jaw, we have here, therefore, 

 another curious instance of the parallel development of 

 similar conditions in totally unconnected groups. What 

 use these creatures could have made of their tusks is, 

 however, not very clear, as in the living condition they 

 could have projected but little below the lower jaw, while 

 they were too long to have been effectual when the mouth 

 was open. These uintatheres were also noteworthy on 

 account of having a number of bony projections on the top 

 of the skull, which in life may have been sheathed in horn ; 

 and it is not a little remarkable that another extinct 

 creature Protoceras (Fig. 19) belonging to the even-toed 

 group of hoofed mammals had a skull with very similar 

 bony projections and also similar upper tusks. 



Our last instance of animals furnished with per- 

 manently-growing upper tusks is afforded by the reptilian 

 class, in which the extinct South African creatures 



