186 COMMON r.lilTlSll ANIMALS 



males, and may be trausforined into tusks. The 

 molars are traversed by folds of enamel with short 

 tubercles and ridges which generally run transverse 

 to the long axis of the jaw. The ridges and 

 tubercles are worn down by use to an even masti- 

 cating surface, and a complicated pattern is thus 

 frequently produced on the crown of the tooth, 

 taking the form of four crescents. 



The Ungulates are the only mammals which pos- 

 sess horns. These weapons take the place of the 

 teeth and claws of the Carnivora, but they are 

 usually present in the males only, except in the case 

 of the reindeer, cows and some sheep and 

 antelopes. Horns vary in structure. The horn 

 of the rhinoceros is merely a collection of matted 

 hair borne upon a boss of bone. The horns of 

 the giraffe are, for all practical purposes, identical 

 in structure with those of the deer tribe. They are 

 masses of bone, at first separate from the skull, but 

 afterwards become fused with it, and they are 

 covered with skin. The horns of the deer tribe con- 

 sist of the same bony core, pedicle or " os cornu,^^ 

 covered, as the giraffe^s horns are, with skin, which is 

 known as '' velvet. ^^ This vascular skin is only present 

 while the horns are growing, and is rubbed off by the 

 animal as he uses his horns or antlers, when they 

 are full grown. In the stag, the horns or antlers 

 consist only of the bony core, which is not, as in 

 the case of the giraffe, permanent; but is shed 

 annually or every few years. During the process of 

 rubbing off the " velvet" the horns present a gory and 

 sore appearance, showing that the skin or " velvet ^' 



