REPORT ON THE SEALS. 169 



ulnaria ; and is inserted into the inner side of the base of the 1st phalanx. In Aretocephahis it 

 arises from the tendon of the flexor carpi ulnaris, from the pisiform bone, and from the tendon 

 of the palmaris profundus. It is well formed and is inserted into the ulnar side of the head of the 

 5th metacarpal ; and into the same side of the entire length of the 1st phalanx. Lucae names it 

 the M. flexor brevis digiti V. In Otaria Murie designates it the flexor brevis minimi digiti, and 

 in describing Trichcchus says " there is no trace whatever of the flexor orevis minimi digiti so well 

 developed in Otaria, PJwca fcetida, and Plwca vitulina." The origin and insertion coincide with those 

 of the corresponding human muscle, and the function is the same, being chiefly an abductor and 

 a flexor. The human muscle sometimes has accessory heads from the flexor carpi ulnaris and the 

 palmaris longus, and since a part of the origin in the Phocinse is from the former, and in Arcto- 

 ccphalus from the palmaris profundus and the flexor carpi ulnaris, there is much to support the name 

 abductor. 



In Triclicchus there is an opponens pollicis, and also a palmaris brevis. 



The Outer or Extensor Surface of the Forearm. — In PJwca vitulina, Plwca barbata, and 

 Plwca hispida the following muscles lie in this region: — Anconeus externus, supinator longus, 

 extensor carpi radialis, extensor communis digitorum, tensor fascise, extensor carpi ulnaris, supinator 

 brevis, extensor ossis metacarpi pollicis, extensor primi internodii pollicis. 



In Arctoccphcdus, besides the above muscles, there is an extensor proprius pollicis, and out of the 

 extensor communis is formed the extensor minimi digiti. The tensor fasciae is absent. All the 

 specimens want the dorsal interossei and the pronator quadratus. 



The Anconeus externus is a narrow slip and arises from the back of the external condyle of 

 the humerus, a little above the condyle ; it is inserted into the outer side of the tip of the 

 olecranon beside the inner head of the triceps, and into the upper half of the outer side of the 

 quadrilateral surface behind the sigmoid cavity. 



In Arctoccphcdus it arises from the posterior part of the supracondyloid ridge, and also, as in the 

 Phocinse, from the back of the external condyle ; and is inserted into the olecranon on the external 

 lip, between the 1st and 2nd tubercles. In Arctocepludus it did not run into the triceps so 

 intimately as in the Phocinas. It is an extensor and lateral supporter of the elbow-joint. It is 

 supplied by the musculo-spiral nerve. 



The Supinator longus is the most anterior of the extensors. It arises from the upper two- 

 thirds of the external border of the humerus, above the muscrdo-spiral groove on the outer border. 

 Below the head of the humerus it is covered by the external head of the triceps. After it crosses 

 over the external surface of the shaft of the humerus, it lies along the anterior border of the 

 radius, and is inserted into its anterior border, half an inch from the wrist, above the groove for 

 the muscle of the pollex. 



In Arctoccphcdus it arises from the external border as in Plwca, above, where the musculo- 

 spiral nerve turns round the supracondyloid ridge, lying to the outer side of the extensor carpi 

 radialis, from the neck of the humerus, and from the capsule of the shoulder-joint beneath the 

 external head of the triceps. The extent of origin from the neck is from the external border to 

 the outer border of the greater tuberosity. The fibres descend between the outer head (part one) 

 of the brachialis anticus, and the extensor carpi radialis along the anterior border of the radius. 

 At the middle of the anterior border it forms a round tendon, which is inserted into the external 



(ZOOL. CHALL. EXP. PART LXVIII. — 1888.) Yyy 22 



