118 PROCEEDINGS OF THE NATIONAL MUSEUM vol. T:; 



It is quite remarkable that during the reduction in the size of the 

 pinniped arm the relative proportions of the humerus and radius 

 have remained virtually the same both in the Zaloplms and the Phora, 

 as in the cat. There are two other measurements of this segment that 

 are also worthy of mention — the length of the ulna and the width 

 of the radius. In the cat the length of the ulna is 114, in the- 

 Zalojyhus 123, and in the Phocu 131 per cent of the radial length. 

 This is not a great difference but the disparity is not in the expecte.l 

 direction. A great length of the olecranon is associated with strength 

 of extension of the antibrachium, which one would expect to be an 

 attribute of Zalophus — not a Phoca with its small, weaker manu>. 

 One can readily understand how an increased width of the anti- 

 brachial bones is correlative to the use of the forelimb as a swimming 

 organ, this being an inevitable result of the turning of this limb into 

 a broad, thin paddle. The Cetacea show this character .to a strong 

 degree and it is an expected characteristic of Zalophus,, in which the 

 greatest width of radius is 29 per cent of its length, but w^hy this 

 same proportion should be 35 per cent in the PJioca is unknown. Save 

 for the deep grooves upon the distal part of the radius of Phoai. 

 the other details of this bone mentioned in the osteological descrip- 

 tion are without any especial significance in the present connection. 

 These grooves would be developed by agility rather than strength, 

 and it is likely that they have been deepened by the same sort of 

 " fiddling," water-treading movements of the flipper already men- 

 tioned, but there may be additional reasons for their appearance. 

 There is no indication in the pinnipeds of any twisting of the shafts 

 of the antibrachial bones, as so oftens occurs in fissipeds for the pur- 

 pose of directing the manus straight craniad for increased facility 

 in walking. 



The proximal part of the ulna is of great depth, especially in 

 Zalophus. This is due in this animal to the enormous width upon 

 the medial face of the bone, of the head of the palmaris longus. 

 arising from all this broadened portion, while in the Phoca thi> 

 muscle is confined to the olecranol border, and the medial face of the 

 ulna is occupied by a part of the origin of the flexor digitorum com- 

 munis. Another muscle that has apparently acted to deepen the 

 proximal part of the ulna of Zalophus is the extensor pollicis longus, 

 occupying the ulnar two-thirds of the lateral face, while in the 

 Phoca the origin of this muscle is very ftiuch narrower. 



After transection of the antibrachial muscles it was found that 

 through the forearm, chiefly the radius of course, the pronation-sus- 

 pination movement of the wrist in respect to the humerus is about 40' 

 or 45° in Zalophus and fully 80° in Phoca. 



