1900.] STRUCTURE OF THE 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 l , as well as in Bos bnbalis, the 

 anterior lateral portion of the parietal meets the sphenoid and 

 excludes the frontal from the squamosal. In Oazella dorcas there 

 is a short suture between the squamosal and the frontal. Such a 

 suture is also found in Bos taurus, 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 mm. transverse and 13 mm. 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 aud occipital regions is straight. 

 In the 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 the 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 the brain-case. This is a differ- 

 ence from the condition found in Sheep, Groats and many Antelopes 2 , 

 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 sutwa 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 Richardson (I. c.)and 

 Riitimeyer. 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. The thickness of the supraoccipital is exceed- 

 ingly great, measuring in an old male 28 mm. (fig. 1, p. 688). The 

 peculiar shape of the condyles is described by Richardson (1. 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 NemorAadus, Cephalophus, AntUope, Saiga, Gazetta (partly), Bubalis, &c. 



2 Nemorhadus, AntUope, Saiga, Gazella, Ceplialophus, &c. 



Peoo. Zool. Soc— 1900, No. XL VI. 46 



