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Show 702 DR. E. LONNBERG ON THE [June 19, special adaption for the Musk-bull. Biitimeyer says (I. c. p. 9) that he does not know any analogy to this except possibly slight traces " bei dem G n u und beim Schaf." H e thinks that it stands in connexion " zu dem unverhaltnissmassigen Gewicht des Kopfes." I do not think, however, that it is a structure formed only for the purpose of more easily carrying the weight of the head, as, in such a case, a similar arrangement ought to be found at least in some of the different animals with a head comparatively as heavy as that of tbe Musk-ox, for instance in Ovis poli Blyth. This form has, as I have had the opportunity of seeing in the Zootomical Institute of the High School in Stockholm, a very massive and stout occipital region, but no lateral extension of the condyles. It is rather an adaption for the strengthening of the occipital joint in a transverse direction, which is needed for the use of the horns as weapons. The horns are, as is w7ell known, placed so that their upturned points are situated at a considerable distance from the median line of the head. From their shape and arrangement it is evident that they are used sideways. That is, when hooking a foe, the Musk-bull does not move its head vertically up and down in the sagittal or median vertical plane ; in such a case the usual articulation would have been satisfactory, or the articulating surfaces would have extended in a median direction, as is often the case in Bos \ The movements of the Musk-ox when hooking are carried out obliquely or in a more or less transverse vertical plane 2. In such a way the horns become formidable weapons, but as the lever is rather long a strong fulcrum at the base of the head is needed, and this is afforded by the transverse extension of the articulation between atlas and occiput. The horns of the cow have not exactly the same position to the head as those of the bull. They are directed more forward and less outward, at least in the specimens I have seen. This, together with the fact that the horns of the cow are weaker and probably less used as weapons than those of the bull, may explain the difference in the development of the occipital articulation of the male and female of Ovibos. Nevertheless, the occipital region is also in the cow very stoutly built, and the interspace between the condyles and the processus paroccipitalis (paramastoideus) is more filled out with bone than in other Cavicornia. Boyd Dawkins (I. c.) and Biitimeyer;* compare the processus paroccipitalis of Ovibos to those of the Sheep and the Argali. Such parts as merely serve for the insertion of muscles are, naturally enough, easily subjected to changes in shape and structure, and thus of comparatively little value for systematic purposes. This 1 Such an extension of tbe articulating surfaces in a forward direction can also be observed for instance in Oreas canna; in species of Cervus, and in Antilocapra, it is remarkably great. 2 That the tips of the horns are used, and not only the basal parts, is proved by the fact that in some specimens the points are plainly sharpened by wearing or polishing against something hard, and moreover one of the bulls shot by Professor Nathorst had the tip of one horn broken off. 3 ' Die Rinder der Tertiar-Epoche,' Zurich, 1877 & 1878. |
