30 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 7S 



absent in Zalophus, for in the latter this muscle inserts narrowly 

 upon the extended base of the lesser tuberosity. Just below the head 

 in Phoca is a definite ridge, this being in line with the proximal 

 extension of the entepicondylar ridge which marks the origin of the 

 supinator longus. In Zalophus this origin is much more extensive 

 and there is no ridge. In Zalophus the lateral epicondyle projects 

 hardly laterad of the trochlea, but much more in Phoca, while in 

 Zalophus the medial epicondyle is greatly developed and slightly so 

 in the phocid. The only explanation which can be offered for these 

 conditions is the inference that in the otariid the flexors of the lower 

 arm, some of which arise from the medial epicondyle, are consider- 

 ably more developed as regards angle of leverage and, therefore, 

 effectiveness, than the extensors ; and the flexors are the ones needed 

 for powerful backward thrusts of the flippers in swimming. In the 

 Phoca, however, it appears as though the stimulus for the develop- 

 ment of the extensors has been at least as great as in the case of the 

 flexors. The extensors are used in such motions as upward thrusts 

 of the manus to assist in submergence or depressing the anterior part 

 of the body. The Phoca, but not the Zalophus, has an entepicondy- 

 lar foramen; but this is not a uniform character distinguishing the 

 two families, for Thomson (1909) examined a number of skeletons 

 of seven species and genera of the Phocidae in which this faramen 

 was absent. 



Forearm: Ulna. — Although the ulna of Zalophus appears the more 

 massive, the greatest length of this bone is 123 in the otariid, and 

 131 per cent in the phocid (114 in a cat), of the articular length of 

 the radius. The chief feature of this bone in the pinnipeds is its 

 broadness proximad. In Zalophus the lesser sigmoid cavity is rela- 

 tively deeper and the coronoid higher. A well-defined ridge occurs 

 upon the lateral surface, separating the origins of the extensores 

 metacarpi pollicis radiad, and the pollicis longus ulnad, the latter 

 being about half the size of the former. In the Phoca the last- 

 mentioned muscle occupies but a very restricted area near what is 

 termed the ulnar process of the olecranon. This is considerably more 

 falcate than in the otariid. Extending in Phoca from the radial 

 process of the olecranon to below the sigmoid cavity is another small 

 ridge, marking the insertion of the anconeus extrenus, but this ridge 

 does not occur in the otariid and the muscle inserts by fascia upon 

 the posterior border of the olecranon. Instead, there is a ridge far- 

 ther radiad, marking with greater sharpness in this animal the lat- 

 eral boundary of the triceps medialis. Just distad of the middle of 

 the shaft from the lateral aspect there is a pronounced rugosity in 

 the phocid but not the otariid, and in the former a corresponding one 

 adjoining upon the radius marking a restricted but very strong 



