1900.] STRUCTURE OF THE MUSK-OX. 697 



answer must be the first, or Antilopine, in fact the primitive one. 

 The fronto-parietal region forms a perfect plane without the 1 

 slightest trace of " Knickung," and the parietalsare fully developed 

 and partake in the roofing of the brain-case. It is accordingly 

 quite evident that this part of the skull of the Musk-ox shows no 

 affinity either with the Oxen or with the Sheep, but is of . the 

 more primitive Antilopine type l . The origiu of the horn-cores in 

 Ovibos is different from that of the Antelopes, as it is perfectly 

 lateral. In the skull of a young Musk-calf shot by Professor 

 Nathorst on the 26th of August, and thus probably about three 

 months old, the beginning of the horn-core appears as a small 

 tubercle situated about 4 cm. behind the orbit, and about 1 cm. from 

 the sutura coronalis 2 . The horn-core thus originates only on the 

 frontal bone, but its base expands gradually with age in a median 

 as well as backward direction, so that in an old bull, as is well 

 known, it covers not only the posterior portion of the frontal, but 

 also the whole parietal as far as the sutura lambdoidea. In this way 

 the same effect is produced in Ovibos as in the Ovina and Bovina, 

 viz., the horns get their insertion on to the vertex of the skull. The 



Fig. 5. 



Section of skull of Musk-ox. 



result is, however, obtained by quite different means in the three 

 types, and the vertex is not situated in the same cranial region. 

 It must also be remembered that the Musk-ox ontogenetically and 

 gradually passes through all intermediate stages of its development 

 from the primitive one ; but this is not the case in the others. 



1 The fronto-parietal and the occipital planes form a right angle with each 

 other, and the highest point of the Musk-ox skull is therefore at the sutura 

 lambdoidea. 



2 There is a more pronounced tubercle situated at the edge between the 

 upper and lateral surfaces of the skull, and divided by the sutura coronalis. 

 This cannot, however, be the origin of the horn-core, as it becomes evident from 

 Sir John Richardson's figure that the horn-core in a 16 months old animal is 

 still situated only on the frontal bone. 



