OCR Text |
Show 1900.] STRUCTURE OF THE MUSK-OX. 699 which the vacuities extend through the whole length of the horn-core. In the horn-core of Goats the vacuities extend through three fourths of the length of the horn-core, but in Sheep only a little more than a fourth 1 ; the bony tissue is much more spongy in tbe latter. From this it may be seen that Ovibos, in which tbe sinuous portion of the horn-core is only about a sixth of its length, represents a stage more like that of the greater number of Antelopes, or is, in other words, perhaps in a more primitive condition. It is, however, doubtful how much importance ought to be ascribed to the extension of the air-cells or sinuses in the horn-cores. By the above statements, it is shown how different the closely allied genera Capra and Ovis are in this respect. In Nemorhcedus the sinuses extend through half or more than half of the horn-core, according to A. Milue-Edwards's figures 2; but in Rupicapra the born-core is only hollow at its base for one-tenth of the length. In both the latter genera the horn-cores have the same straight upward direction, so that such a condition does not seem to influence the development of the sinuses, as perhaps might be supposed from the difference in this respect between Goats and Sheep. On the other hand, the Buffalo with its horizontal horn-cores has large sinuses extending to the tips. The parietals of the Musk-ox do not contain any sinuses or air-cells but are very thick and massive (cf. fig. 5, p. 697), so that their diameter in an old bull is 47 m m . measured a bttle in front of the sutura lambdoidea. It has been said above that the frontals and parietals lie in the same horizontal plane. This is already the case in the young calf, and is thus a primitive condition which has beeu retained ; not an acquired characteristic, as it must have been if Ovibos were the direct descendant of the fossil Bootherium Leidy, and the latter derived from the Sheep. Biitimeyer3 seems inclined to assume this for the purpose of more easily explaining the, according to his opinion, ovine origin of the Musk-ox *. It is, however, so far as I can judge, less probable that a form originating from ancestors with an even fronto-parietal region, such as the primitive ruminants must have had, should have acquired a specialization in form of a frontal elevation or " Knickung " as a base for the horns ; and then again, without reduction of the horns, returned from such a specialization to the original arrangement of the frontals and parietals and devised, so to speak, a new plan for fixing the horns in a more suitable manner. That is, in other words, a reversion from the ovine specialization of the skull to the primitive antilopine 1 This may be subjected to some variation, but I make my statements from the material at hand. '2 Milne-Edwards, Rech. pour servir a l'hist. nat. des Mammiferes (Paris, 1868-74), pi. 71a, pi. 73. 3 Versuch einer nat. Gesch. d. Rindes, ii. pp. 17-20. 4 But if Ovibos was descended from Bootherium which had a " Knickung " of the frontals, it would be expected that the calf of the former would show some traces of likeness in this respect to its supposed progenitor, which however is not the case, as already stated. |