SKULL AND SKELETON. 659 



It may be stated, however, in general terms, that the skeleton 

 indicates a general robustness of form, correlating with the 

 rather broad thick head. The relative length of the different 

 limb-segments and vertebral regions is about as in Plioca grcen- 

 landica, except that the caudal series of vertebrae is much 

 shorter. The bulk of the entire animal, however, must be con- 

 siderably greater than in P. grcenlandica. The scapula is long 

 and narrow, the proscapular and postscapular fossse about 

 equal, the latter not greatly produced at its posterior upper 

 border, as in Plioca vitulina and P. fcetida. Aside from the 

 absence of the acromion process, it thus differs in its nar- 

 row elongated form, and especially in the unusual length of 

 the shaft, from that of either of the three above-named species. 

 P. grcenlandica presents the opposite extreme, the scapula of 

 which is broad and short. 



The exceptional features of the skull are the small size of the 

 orbital fossse, the rather small size of the auditory bullas, and 

 the large size of the nasal passages. The general form of the 

 lower jaw is much as in P. vitttUna, especially resembling it in 

 the lateral convexity of the rami, and in the form of the con- 

 dylar portion, and in the abruptness of the angle. It is, how- 

 ever, small and weak for the size of the skull, and especially so 

 for the size of the animal.* Perhaps its most striking feature 

 consists in the large process on the hind border just below the 

 coudyle, which is twisted over toward the inner edge of the 

 jaw, and has its axis of development in that direction or trans- 

 verse to the longitudinal axis of the jaw. 



In comparison with the skeleton in the above-named species 

 of Plioca, the bones of the Bearded Seal are light and porous 

 (less so, however, than in the Cystophorince) ; the tuberosities 

 are all rather weakly developed, with a less tendency to anchy- 

 losis. To this general laxness of ossification may perhaps be 

 attributed the slight development and consequent lack of ab- 

 rupt eversiou of iliac crests of the pelvis already noted. The 

 subjoined table of linear measurements of the principal bones 

 of the skeleton is taken from that of a quite old female from 

 Cumberland Gulf, collected by Mr. Kumlieu. 



* I find that the lower jaw of a very old male P. vitulina just fits an adult 

 female skull of Erignathus bargains, except that the latter is slightly longer. 



