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Show 1902.] OF HORNS AND ANTLERS. 215 are not primitive, they are the expression of degeneration, of the breaking up of a once powerfully developed bony growth. Fossil Giraffe-skulls are unfortunately still unknown, but Samotherium with frontal and posterior protuberances, Sivatherium with posterior growths hollow at the base and with frontal growths, lastly Brahmatherium with posterior and frontal armaments, are undoubtedly allied to the Giraffoid stock. "We leave out the unarmed Hydaspitherium and Helladotherium, which are suspected by experts to be female Sivatheria. It has been questioned whether these armaments, huge, and sometimes branched, were covered with skin and hair, or with horny sheaths. The antlers of the original specimen of the male Sivatherium clearly show deep and strong impressions of the blood-vessels, extending almost to the tips exactly as in Cervine antlers. They were undoubtedly covered with skin, and it would be hardly fair to assume that this and similar specimens happened to have died in the velvet stage. The same applies to Samotherium boissieri. But it does not follow that these armaments were true antlers in the sense that they were shed. Dr. Forsyth Major is inclined to think that there are sutures between them and their base. If there are any, they simply indicate the line of transition or demarcation which is usually seen between the pedicle and the rest. The hindmost pair of armaments of Sivatherium are hollow at the base, a fact which speaks decidedly against periodical shedding ; and the broadness of the base supports this view, since a good and permanent vascular supply from below was thereby ensured. The much shortened shape of the skulls of Sivatherium and Brahmatherium are unmistakable signs of specialization, excluding the possibility that these huge creatures of the latest Miocene or lowest Pliocene were the direct ancestors of Giraffes; but they were near relations and contemporaries. W e are now able to conclude that the evolution of Horns and Antlers and similar cranial armaments has passed through the following stages:- I. Exostosis. Subperiosteal ostotic outgrowths of the cranial bones, covered presumably with thickened skin-pads. These armaments were multiple, occurring on various parts of the skull. This type is rather old among the Ungulata, witness the Eocene Amblypoda, e. g. Dinoceras. It reoccurs amongst the Artiodactyla, which here alone concern us. Protoceras of the Lower Miocene of Montana is an almost ideal type in this respect, with its three or four pairs of facial, orbital, and posterior bony excrescences in the shape of uncouth ridges and neat cones. (Text-fig. 25, I, p. 216) II. Exostosis of the frontal bone producing a pedicle, with epichondrosis of apical growth, which by subsequent basal ossification becomes the antler. Skin originally unaltered, hairy ; this and the chondrosteoma are shed periodically.- Cervine type. (Text-fig. 25, II, p. 216) |