702 DR. E. LONNBERG ON THE [June 19, 



special adaption for the Musk-bull. Riitimeyer says (Z. c. p. 9) 

 that he does not know any analogy to this except possibly slight 

 traces " bei dein Gnu und beim Schaf." He thinks that it stands in 

 connexion " zu dem unverhaltnissmassigen (xewicht 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 

 the 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 well 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 i . 

 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, to- 

 gether 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. jNTevertheless, the occipital region 

 is also in the cow very stoutly built, and the interspace between 

 the condyles and the processus paroecipitdlig (paramastoideus) is 

 more filled out with bone .than in other Cavicomia. 



Boyd Dawkins (7. c.) and Riitimeyer 3 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. 



