30 PROCEEDINGS OF THE NATIONAL MUSEUM vol. V3 



Odoherms the slip representing this muscle split into three tendons 

 passing to the three middle digits. 



M. exlemor digiforum lateralis (figs. 9, 10, 20, 21) is, in most mammals, 

 a more fitting name for this muscle than its homologue, extensor 

 digiti quinti propriiis. In the Zalophus it was located between and 

 partly deep to those of the extensores communis and carpi ulnaris. 

 It arose from the distal part of the lateral epicondyle and the lateral 

 radial ligament in such a position that tension could be applied only 

 during flexion of the forearm. It was a weak and slender muscle 

 whose fine tendon split first into two. the lateral branch going to the 

 lateral border of the fifth metacarpal. The medial branch again 

 divided into two, sending one tendon to the medial side of metacarpus 

 5 and another to the adjoining border of the fourth. In the Phoca 

 this muscle was quite complex and occurred in three parts which 

 were not completely divisible proximad. Origin was considered to 

 be from the lateral epicondyle only, although there was quite firm 

 attachment to the capsule of the joint over the head of the radius. 

 Three tendons developed from as many muscular ^lips which passed 

 ectad of the long extensor of the pollex. The more ulnar of these 

 split into two branches wliich extended to metacarpals 4 and 5. The 

 more radial also split into two, extending to metacarpals 2 and 3, 

 while the deeper (not shown in fig. 21) inserted upon the ulnare. 

 For this muscle in Eiionetopias Murie recognized two divisions, equal 

 together to my one. One was a minimi digiti, with tendons to digits 

 4 and 5, and the other a medii digiti, with tendons to digits 3 and o. 

 In 0})odenus these tendons went only to digits 4 and 5. Miller con- 

 sidered that for Arctocephalus there was a single head of origin for 

 the communis digitorum and minimi digiti. The latter divided into 

 three main branches going to metacarpals 4 and 5. For Phoca, 

 Miller termed this division the extensor communis secundus, men- 

 tioning no divisions of the muscle itself but that it split into four 

 tendons, passing to the four lateral metacarpals. 



The structure referred to above as the lateral radial ligament de- 

 serves mention. It occurred in the ZaJophus only, as a broad, tough 

 band extending from the lateral epicondyle over the lateral aspect 

 of the radius to somewhat distad of its middle. It covered the 

 supinator brevis and was continuous along its border with the inter- 

 osseous membrane where this adjoined. Its function was as its 

 name implies — to add great strength to the joint. It was not an out- 

 growth of the normal capsular ligament of the elbow, for it not only 

 had some vestige of muscle fibers associated with it but seemed to be 

 served by the doi'sal interosseous nerve, which indicated that it may 

 have been a relic of some primitive division of the common extensor 

 group of the digits. No mention was made of such a structure in 

 other eared seals. 



