32 PKOCEEDINGS OF THE NATIONAL MUSEUM vol.73 



interosseous ligament, which occurs in Zalophus as the more usual 

 and extensive interosseous membrane with little or no osteological 

 indication. There may, however, be considerable variation m this 



detail. . . ., 



The medial or flexor surfaces of the ulnas of the two pmmpeds 

 are very similar, save for the relatively greater area proxirnad m 

 Zdophus. In this animal practically all of this area is occupied 

 by the origin of the very greatly specialized palmaris longus, and in 

 the Phoca., by the second head of the flexor digitorum communis. 

 Distad of the coronoid is the rugosity marking the insertion of the 

 brachialis tendon, and still distad along the radial border, a slight 

 crest in Zaiophus only for the second head of the flexor digitorum 

 communis. There are slight differences in the distal head of the 

 uhia of the two animals, conforming to variation of the articular 

 surfaces of the adjoining bones. ^ i ;. on 



Radius— In the ZalofKus and PJioca the radius comprises about 20 

 and 14 per cent, respectively, of the body length (30 in a cat), 29 per 

 cent in both of the arm length (36 in a cat), and 105 and 96 per cent, 

 respectively, of the humeral length (104 in a cat). The most signifi- 

 cant feature of this bone in the pinnipeds is the great expansion ot its 

 distal half. In the Fhoca the bicipital rugosity is much the better 

 developed, and there is also a well-marked rugosity for the interos- 

 seous ligament, absent as such in the Zalofhus, as previously men- 

 tioned The proximal part of the shaft is almost cylindrical, but at 

 the center in the phocid and proximad thereto there is h pronounced 

 expansion and process upon the radial side, which I have termed 

 the "pronator teres process" because it is covered by the insertion ot 

 that muscle. The muscle, however, did not include any pronounced 

 tendon or other feature which I considered would logically bring 

 about the development of such a well-defined process. In Zalophus 

 there are upon the flexor side of the distal part two broad shallow 

 Grooves for two groups of flexor tendons, and upon the radial part 

 li the extensor side, another for the extensor metacarpi polhcis ten- 

 don. Upon the flexor side in Phoca there are no grooves at^all, but 

 upon the extensor side these are numerous and deep. (See ng. 10.) 

 This would seem to indicate that in the Phoca the somewhat spe- 

 cialized function of the extensor is in powerful recovery of the 

 manus after flexion; which is in entire accord with the theory ad- 

 vanced partially to account for the greater phocid development ot 

 the lateral epicondyle of the humerus. / . • i v „ 



Hand—ThQ length of the manus, osteologically (not including 

 terminal cartilage in the otariid nor the nail in the phocid), com- 

 prises 29 per cent of the body length in Zalophus and 19 m the 

 Phoca (21 in a cat), while it measures 44 and 41 per cent, respectively. 



