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 vacaities 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 the 

 latter. 



From this it may be seen that Ovibos, in which the 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 Oapra and Ovis are in this respect. In Nemorhcedus the 

 sinuses extend through half or more than half of the horn-core, 

 according to A. Mil ne-Edwards's figures 2 ; but in liupicapra the 

 horn-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 up- 

 ward 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. tig. 5, p. 697), so that their 

 diameter in an old bull is 47 mm. measured a little 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 been 

 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. Biitimeyer 3 seems inclined to 

 assume this for the purpose of more easily explaining the, according 

 to his opinion, ovine origin of the Musk-ox 4 . 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 band. 



2 Milne-Edwards, Eech. pour servir a l'hist. nat. des Mammiferes (Paris, 

 1868-74), pi. 71 a, pi. 73. 



3 Versuch einer nat. Gesch. d. Eindes, 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. 



