AHT. 15 ANATOMY OF THE EARED AND EARLESS SEALS HOWELL 117 



higher distad. It can not play the same part in the economy of 

 this animal as in the otariid, for the forelimb is practically useless 

 as a swimming organ. Of course the high deltoid crest may be a 

 relic from a time when the foreflipper may have been so used, but 

 I believe another explanation is the proper one, and this is that the 

 high deltoid crest of the PJwca was developed in response to stimuli 

 provided by strong antagonistic action of the muscles attached 

 thereto; in other words, that it has acted as a static fulcrum while 

 the animal is swimming. The more caudal part of the pectoralis and 

 tlie latissimus dorsi are both of decided aid in the rhythmic lateral 

 swimming movements of the posterior body. These insert upon the 

 deltoid crest, which is held static as a fulcrum by the atlantoscapu- 

 laris inferior and humerotrapezius. It is not meant to imply that 

 this has been the only stimulus, but it was probably the most 

 important. 



The lesser tuberosity of Phoca is enormously developed and is much 

 higher than either the head or the greater tuberosity ; but in Zalophus 

 it is low, although very prominent. The condition in the phocid 

 is not attributable to any complexity of muscles attached to this 

 tuberosity, for almost the sole influence is the subscapularis. At 

 least a part of the height of the process is due to the fact that in 

 this animal the normal position of the humerus is a bit more ab- 

 •ducted ; but this seems insufficient to account in full for the condition 

 and other logical reasons are obscure. The medial epicondyle, giving 

 rise to a number of the forearm flexors, is larger than the lateral in 

 Zalophus^ as is the usual case in fissipeds, but both epicondyles are 

 unusually massive. The flexors of this animal are, of course, of the 

 utmost importance in operating the powerful backward sweeps of the 

 flipper employed in swimming. In the Phoca the lateral epicondyle 

 is fully as large as, if not actually larger than, the medial, and it is 

 readily seen that in the phocid function of the arm while swimming, 

 extension, in the way of brisk dorsal motions, is fully as important 

 in steering movements as ventral ones. In consideration of the 

 difference in the function of the forearm in the two animals it is 

 rather unexpected to find precise similarity in the direction that the 

 origins of the antibrachial muscles have migrated, which may be 

 interpreted as evidence of some strength in favor of the uniphyletic 

 origin of these two families of pinnipeds. This migration, as already 

 mentioned, consists of a movement distad from the femur to the 

 antibrachium of the palmaris longus, flexor carpi ulnaris (part), and 

 flexor hallucis longus. In both animals there has been a movement 

 distad of other muscle attachments which are characteristically of the 

 humerus, but it is likely that this has been due to a more speedy rate 

 of shortening for the distal than for the proximal part of the humerus. 



