MUSEUM OF COMPARATIVE ZOOLOGY. 49 



Skull — The skull (Figs. 3 and 4, woodcuts, pp. 57-58, and Figs. 1 -4, PL 

 I) varies greatly in different individuals, not only in its general form, but 

 in the shape of its different bones. The occipital and median crests are 

 doubtless not much developed before the fifth or sixth year. The bones 

 thicken greatly after the animal attains maturity, and the palate becomes 

 more flattened. In the adult male the brain-box may be described as 

 subquadrate, narrower anteriorly, where the skull is abruptly contracted. 

 The greatest diameter of the skull is at the posterior end of the zygoma, 

 and is equal to three fifths of its length. The post-orbital processes are 

 strongly developed and quadrate ; the forehead is flat, and the facial pro- 

 file is either abruptly or gradually declined ; the muzzle is broad, equal 

 in breadth in front to the distance between the orbits. The palatal sur- 

 face of the intermaxillaries is flat, or slightly depressed anteriorly, and very 

 slightly contracted posteriorly. Laterally the intermaxillaries reach nearly 

 to the end of the palatals. The latter are much contracted posteriorly, 

 and terminate quite far in front of the hamuli pterygoidii. Both the 

 anterior and posterior nares are a little narrower than high. The nasals 

 are widest anteriorly. The last (fifth) pair of upper molars is placed 

 far behind the fourth pair, the space between them being about equal 

 to that occupied by two molars. The males in old age have exceed- 

 ingly high occipital and sagittal crests, most developed posteriorly ; an 

 teriorly they diverge and terminate in the hinder edge of the postorbital 

 processes. 



The lower jaw is massive and strong. Its coronoid processes are greatly 

 developed, as are the tuberosities at the angles of the rami, and a second 

 tuberosity on the lower inner edge of each ramus (see Figs. 9-11, 

 PI. III). 



It should be added that the above description of the skull refers ex- 

 clusively to the male. Having no skulls of the female, I am unable to 

 state definitely how the sexes differ in respect to the form of the skull. 

 Judging, however, from the sexual variations seen in Callorhinus ur sinus, 

 Otaria jubata, and other species of the Olariadce, the skull of the female 

 would be not only very much smaller, but it would lack almost totally the 

 high occipital and sagittal crests exhibited by the male, and have all the 

 processes for the attachment of muscles less developed. The teeth, es- 

 pecially the canines, are relatively much smaller, as is also the lower jaw. 

 In other words, the female skull would doubtless closely resemble the skull 

 of a yearling male. The annexed table of measurements indicates still 

 further the general form of the male skull and the relative proportions of 

 its different regions. 



