84 SEXUAL DIMORPHISM 



was a peculiarity not originally connected with them, but 

 acquired at a later stage of their evolution. The short horns 

 of the giraffe are covered with hairy skin, which, however, is 

 nearly hairless and rather horny on the blunt extremities. 

 They are present, too, in both sexes, though larger in the 

 male. It is curious that the bones of these horns are at 

 first united with the skull by suture, and are not, therefore, 

 strictly speaking, outgrowths of the skull bones. In the 

 extinct Sivatherium, which, though allied to the giraffes, had 

 a neck and legs of ordinary proportions, there were two 

 pairs of horns, the anterior short and conical like those of 

 the giraffe, the hinder long and palmate, somewhat like those 

 of the elk. As there is no burr, it is fairly certain that the 

 latter were not shed, but it is not so certain whether they 

 were covered with horn or soft skin. The latter seems more 

 probable, because appendages covered with horn are not 

 usually branched. It must be noted, however, that these 

 giraffe-like forms are not more ancient, but more recent, than 

 the extinct deer of the genus Dremotkerium, which belong 

 to the Miocene, while the former are found in the Pliocene. 

 They indicate, however, that large and to some degree 

 branched antlers might exist which were permanent and 

 covered with skin. 



Our second hypothesis, therefore, is that the original 

 antlers of deer were in this condition. Then they may have 

 grown and branched gradually in consequence of pressures 

 and blows received in fighting. We may suppose that at a 

 certain stage of evolution the fighting became more severe, so 

 that the skin and periosteum were torn off the bone. This 

 may have happened first in old stags in which the bone of 

 the antler was harder. The loss of the periosteum would cause 

 the death and shedding of the bone, and this process would 

 not at first be annual. The renewal of the lost part might 

 be due to renewed irritations at first, and became normal by 



