160 



ODOB^ENUS OBESUS PACIFIC WALRUS. 



species there is a thinness and anterior deflection not seen in 

 the other. The sculpturing of the occipital plane (after allow- 

 ing for a considerable range of individual variation in this 

 respect) is quite different, as well as the relative degree of 

 verticality. The occipital breadth of the skull, as compared 

 with the total length of the skull, is not greatly different in the 

 two forms. In the Pacific species, the occipital condyles are 

 narrower than in the other, and are placed at a somewhat dif- 

 ferent angle, both laterally and vertically. 



FIG. 20. Odobcenus rosmarus. 



The difference in relative development of the anterior and 

 posterior portions of the skull in the two species is best seen 

 from above (Figs. 20 and 21). In this view, the narrow facial 

 breadth in the Atlantic species (Fig. 20) is in striking contrast 

 with its great occipital breadth, whereas in the Pacific species 

 (Fig. 21) the two regions are more equally developed. Another 

 difference brought out in this view is the greater interorbital con- 

 striction in the Pacific species, which is not only relatively but 

 actually much narrower than in the other, while the point of 



