OCR Text |
Show 1900.] STRUCTURE OF TttE MUSK-OX. 701 wall of the skull behind the orbit. The length of this squamoso-frontal suture equals half the vertical diameter of the orbit. This remarkable arrangement seems to be peculiar to the Musk-ox. In Sheep, Goats, and most Antelopes \ as well as in Bos bubalis, the anterior lateral portion of the parietal meets the sphenoid and excludes the frontal from the squamosal. In Gazella clorcas there is a short suture between the squamosal and the frontal. Such a suture is also found in Bos taunts, in some specimens of which it attains a considerable length although not such an extent as in Ouibos. In the calf two interparietals are found in the median line between the parietals and the supraoccipital. They form together an oval figure with 19 m m . transverse and 13 m m . longitudinal diameter. In the adult cow they have been separated from each other in the median line, but are not anchylosed to the parietal or the occipital. In the adult bull they are not conspicuous. The angle between the parietal and occipital regions is straight. In tbe calf the occipital is visible from above, forming a zone as broad as its own thickness. In the adult cow the same condition is found, but in tbe oldest bull the parietal has extended more backward, so that the occipital zone of the coronal surface is more or less covered. It is evident from this description that the supraoccipital forms only the vertical posterior wall of tbe brain-case. This is a difference from the condition found in Sheep, Goats and many Antelopes2, in which the interparietal is anchylosed to the supraoccipital so that it looks as if the latter was angularly bent forward in the parietal plane and partook in the formation of the posterior roof of the brain-case. The sutura lambdoidea is in the Musk-ox plainly conspicuous even in old animals just behind the base of the horn-cores. It becomes first obliterated in the median line. The shape of the occipital region has been described by Bichardson (I.e.)and Biitimeyer. Strong muscles are needed, especially in the bull, for supporting the heavy head ; and for that purpose a strong occipital ridge extends downwards in the median line. Laterally under the crista lambdoidea there are deep grooves for the insertion of muscles. The supraoccipital does not reach the foramen magnum, but is excluded from it by the exoccipitals, as can be seen in the skull of the calf. Tbe thickness of the supraoccipital is exceedingly great, measuring in an old male 28 m m . (fig. 1, p. 688). The peculiar shape of the condyles is described by Bichardson (I. c. p. 69), who has also drawn the attention to the " exterior heel that occupies much of the space between the condyle proper and the paroccipital spine and furnishes a pulley or trochlea, which moves on a concave pretty broad articular surface, formed by a lateral notch in the brim of the atlas." In the calf this heel is not developed at all, and in the cow only a little. It is thus a 1 Nemorhcedus, Cepkalophus, Antilope, Saiga, Gazella (partly), Bubalis, &c. 2 Nemorhcedus, Antilope, Saiga, Gazella, Cephalophus, &c. PROC. ZOOL. Soc-1900, No. XLVI. 46 |