1900.] STBUCTUBE OF THE MUSK-OX. 703 



can also be seen in the ontogenetic development of the Musk-ox. 

 In the calf these processes are quite flattened from the sides as 

 in Bos and many Antelopes, which perhaps is the primitive shape, 

 as it is found in so many different forms. Later, in adult animals, 

 the processes become thickened in such a way that they become 

 triangular in section through the development of a lateral crista 

 whereby a broad posterior face is produced. Distally the processes 

 become compressed in an antero-posterior direction and end iu a 

 transverse edge. These modifications are of course effected for 

 the purpose of getting larger space for the insertion of the muscles, 

 and I do not lay much weight upon them : I mention them only 

 to show that the processus par occipitalis of the Musk-ox does not 

 much resemble those of the Sheep, which are posteriorly narrow, 

 slender and tapering towards the tips. These processes of the 

 Musk-ox are slightly curved towards the median line ', although 

 not so much so as in the Sheep, Oxen, Buffaloes, and many other 

 ruminants. They cannot be termed small (cf. Riitimeyer), as 

 their length in an adult bull measures about 3 cm., which is as 

 much as | of the height of the occipital region from the lower 

 surface of the condyles to the sulura lambdoidea. The same 

 relation is already found in the calf (resp. 2 cm. and 8 cm.). 



" The basi-oceipital bone in Ovibos moschatas is quadrate in 

 outline," Boyd Dawkins says (I.e.). In the young calf it is quite 

 hexagonal, but with age the posterior sides are shortened so that 

 the corpus of the bone becomes quadrate in outline ; and therein 

 lies of course a certain similarity with the Sheep, but also with 

 several Antelopes. It seems, therefore, contrary to Dawkins's 

 opinion, questionable whether this characteristic can be of any 

 other value than that of separating these animals from the Oxen, 

 which have the basioccipital bone differently shaped. Dawkins 

 also points out the difference between Bos and Ouibus with regard 

 to the anterior muscular impressions of this bone, the former 

 having them " supported on a tuberosity.'' Such things are of 

 little importance; but as the question is open to discussion, it may 

 be mentioned that in Sheep and Goats these impressions are 

 situated at the sides, partly on the lateral surface, of the bone, and 

 separated by a smooth area nearly as broad as the bone. In the 

 Musk-ox, on the contrary, the same impressions cover the ventral 

 surface of the bone so that they nearly meet in the median line in 

 the adult male, but do not extend laterally (fig. 7). The basi- 

 occipital of the Musk-ox is traversed by a low median keel which 

 is already indicated in the calf. Richardson's exact description 

 (I. c. p. 69) of these parts need not be repeated. 



The auditory bulla is subjected to considerable ontogenetic 

 changes, as can be seen from the following measurements. In the 

 calf it is rather large and inflated. Its length is 39 and its 

 greater width 20 mm. In the adult cow it also looks inflated, 



1 This may be subject to variation, as Richardson saj-s that they " descend 

 straight," but Rutimeyer found them " einwartsbogen wie beim Argali.'' 



40* 



