AHT. 15 ANATOMY OF THE EAIIED AND EARLESS SEALS HOWELL 79 



no mention of complexity in connection with the sheath of the flexor 

 communis. 



M. abductor digiti quinti longus (figs. 10, 21, 23) was really a flexor 

 and was served by the ulnar nerve. Its homology is not certain but it 

 seems probable that it may be a division of the flexor carpi ulnaris. 

 It was present in Phoca only and arose by aponeurosis from the ulnar 

 termination of the olecranon and its tendon inserted upon the first 

 phalanx of digit 5. 



In the Zalophns the antibrachial extension of the pectoralis must 

 be included with the flexors of the lower arm. In the juvenal 

 specimen this detail proved puzzling, for after the part of the pec- 

 toral aponeurosis inserting upon the deltoid ridge had been removed 

 and the subdermal tissue of the manus dissected free, there remained 

 an apparently distinct structure wth muscle fibers attached arising 

 from the slight ridge extending from the deltoid crest to the medial 

 rim of the trochlea. This emerged from between the biceps and the 

 l)rachialis, and then fused with an extensive and tough sheet of 

 fatty fibrous tissue covering the radial border of the forearm and 

 metacarpus 1. With this were associated dark fibers apparently 

 muscular in character. In Figure 19 this detail is shown as en- 

 countered in this specimen after removal of the part of the pectoral 

 inserting upon the deltoid crest, except that the fibrous tissue ex- 

 tending farther upon the cranio-lateral part of the forearm is repre- 

 sented as having been cut away. In a fresh, adult female, however, 

 it was at once seen that this was a part of the deep pectoral, which, 

 in a tendinous sheet, inserted upon the humerus for the entire length 

 of its shaft, extending quite to the pollex, and with it was associated 

 a thick, fatty, fibrous layer, entirely nonmuscular in this adult, 

 that was most extensive over the anterior or radial border of the arm 

 and acted not only as a buffer or shock absorber, but materially 

 broadened the forearm. The fleshy part of the pectoralis that cov- 

 ered the proximal part of the medial forearm vv^as erroneously desig- 

 nated as a superficial layer of the palmaris longus by Murie for 

 pyumefopias, and by Miller for Arctocep holies. 

 The extensors of the antibrachium were as follows : 

 M. extensor digiiornm communis (figs. 9, 10, 20, 21) was the most 

 ^superficial of the forearm extensors, and arose in a thin sheet from 

 :he lateral epicondyle of the humerus. Its tendon passed beneath 

 ;he dorsal carpal ligament close to that of the extensor pollicis 

 [longus and in both animals a branch was sent to each of the four 

 lateral digits. This is Miller's primus division of this muscle in his 

 \Phoca. In Arctocephalus he stated that it split into two slips, one 

 >eing the same as I found the extensor communis in Zalophus and the 

 [second constituting an extensor minimi digiti. In Eumetopias and 



