ART. 15 ANATOMY OF THE EARED AND EARLESS SEALS HOWELL 1 13 



is no skeleton of this genus at hand but I can not find any modifica- 

 tions in other Phocidae examined that might permit such an unusual 

 position to be assumed. 



No very significant differences in the thorax proper can be detected, 

 save a tendency toward broadening in the phocid and apparently the 

 lengthening in the otariid, possibly due in the latter to the advantage 

 of having bony protection against hydrostatic pressure over the 

 greatest possible area of the abdomen. The presternum that is well 

 developed in both animals has undoubtedly been lengthened by a 

 forward extension of the pectoralis, which is of such prime impor- 

 tance to the swimming of the otariid, and probably secondarily so ir 

 the phocid. 



In the present paper there will be no attempt to calculate by for- 

 mulae the leverage and potential strength of the limb segments and 

 their muscles. Such treatment of the subject gives the result a pro- 

 found and scholarly appearance, but the writer views with the great- 

 est distrust all such treatments, for they can not take into considera- 

 tion the differences of fascial attachment, and no one can tell exactly 

 what any particular muscle either can or will do. 



The anterior limb of the Pinnipedia as it now occurs is the result 

 of three stimili which are hard to unravel — the fact that the prox- 

 imal part is within the body, operative in both; phylogenetic influ- 

 ences, of an unknown degree of resemblance; and the fact that the 

 forelimb is the primary organ of propulsion in the Otariidae and 

 practically inoperative for this function in the Phocidae. In the 

 otariid the foreflipper is one of the most important, and in the 

 phocid, one of the least important, parts of the body. On land the 

 former animal uses this member as normally as its proportions will 

 allow. It is extended at the wrist at a right angle to the antibra- 

 chium, the toes being directed almost directly laterad. In the latter 

 the manus may be used to help the animal from the water or over a 

 rough spot, but its shortness and the thick blubber layer often pres- 

 ent over the chest raise the manus too far from the ground for it to 

 be of great use. Hence it is usually held somewhat pendant and 

 abducted (from the forearm). As far as I can tell the most natural, 

 static position of the anterior limb in both animals is with the 

 humerus at slightly less than 90° to the scapular spine. In the 

 otariid the antibrachium is almost extended, and in the phocid flexed 

 to almost 90°. In the former the manus is almost on a line with the 

 antibrachial axis, and in the latter, abducted to at least 45° — usually 

 more. The static posture of these segments with relation to each 

 other is shown in Figure 30. 



In the water the otariid moves with broad sweeps of the powerful 

 manus, recovery being made with the radial border of the arm pre- 

 86377—28 8 



