OCR Text |
Show 700 DR. E. LONNBERG ON THE [June 19, type is improbable, at least as long as the armature-the horns- which have been the cause of the development, are retained. But there is no difficulty in assuming that from the same indifferent type have been developed forms which have specialized their armature differently, the one as Ovibos moschatus and the other as " Bootherium" or Ovibos bombifrons; and that in such a case the latter has acquired a characteristic, the frontal elevation, which offers some resemblance to the ovine type. But then this is only a parallel, and proves no affinity with the ovine type. There seems also no need for assuming Bootherium as being older than Ovibos, as both have occurred in the Pleistocene l. In a young calf of Ovibos, the length of the parietals near the median line is 40 per cent, of the length of the frontals measured in the median line. This relation, however, diminishes with age, so that in an old bull the corresponding percentage is 30-35. It is, however, a little difficult to perceive the sutures at the surface between the frontals and the parietals, but the sutura lambdoidea is distinguishable, although nearly obliterated, even in the oldest skull I have seen. The parietal zone on the top of the head is thus already in tbe calf, compared with the frontal region, shorter than in many Antelopes (Gazella, Cephalophus, Nemorhcedus, Bupi-capra, &c). In the Sheep and the Goats the relation varies a good deal, but in many cases the parietal zone is not even 30 per cent, of the frontal, and is accordingly more reduced than in the Musk-ox. The latter seems thus, with regard to the development of the parietal region, to occupy an intermediate position between the Sheep and the more primitive Antelopes. On the sides, the parietals of the Musk-ox extend with a rather short and truncate portion forward between the frontal and squamosal. The anterior end of this portion reaches only halfway between the orbit and a vertical line drawn through the meatus auditorius externus. This shortness of the lateral portion of the parietal in the Musk-ox has the result that the frontal meets the squamosal, and forms with it a rather long suture on the lateral 1 I must confess, however, that I only know Bootherium from the figures published by Boyd Dawkins (Palasontographical Society, vol. xxv. Monogr. on the Brit. M a m m . of the Pleistocene, genus Ovibos, pi. v.), and from descriptions. Fig. 3 on the plate quoted is said to be a coronal view of the skull of Bootherium bombifrons Leidy, and is regarded by Dawkins as belonging to an adult female. It is, however, rather similar to the aspect of the skull of a young Musk-ox, and ought to be compared with Sir John Richardson's figure (Zoology of the ' Herald,' pi. iv. fig. 2). Fig. 4 on Dawkins's plate is said to be a lateral view of the same, which nevertheless is hardly possible, to judge from the general appearance as well as from the dimensions. Dawkins's fig. 4 of Bootherium cavifrons Leidy is regarded as belonging to an old male, which seems very probable from comparison with the Musk-ox, in which the large exostoses at the base of the horn-core get reabsorbed in old age. These forme may belong to the same species, representing the female and the male form, as Riitimeyer and Boyd Dawkins have suggested, but their ovine affinities I cannot see. When Riitimeyer says (op. cit. p. 18) that the horns of Bootherium have been " ohne Andeutung einer riickwarts Beugung der Spitzen," it must be remembered that the horn-cores of these animals are so short that they indicate onlv the direction of the basal parts of the horns. |