164 



ODOB^ENUS OBESUS PACIFIC WALRUS. 



considerably broader than in the other, and the plane of artic- 

 ulation is more nearly vertical. This seeins correlate with the 

 greater incurvation of the tusks ; these, being almost vertical 

 in the Pacific species, allow a greater declination of the head. 



Another .difference apparent in this aspect of the skull is the 

 relative posterior extension of the condylar portion, which, in the 

 Pacific species, extends much further beyond the posterior bor- 

 der of the mastoids than in the other. This is obviously due to 

 greater length of the basioccipital segment of the skull in the 

 Pacific species, which is clearly shown in the annexed figures 



FIG. 26. Odobccmis rosmarus. 



(Figs. 26 and 27). The position of the foramina of the basal 

 portion of the skull is also quite different in the two, as is 

 especially seen in respect to the condylar foramina, which are 

 situated more posteriorly in the Atlantic species than in the 

 other, due, perhaps, to the shortness in this form of the basi- 

 occipital region. 



