168 THE VOYAGE OF H.M.S. CHALLENGER. 



digiti V. It is not present in Otaria and Trichcchus. It arises from the inner surface of the ulna 

 where the olecranon and the posterior border meet, and passes down the posterior border of the 

 ulna on the flexor carpi ulnaris ; at the wrist it divides into two tendons — one is inserted into the 

 skin over the palmar surface of the 5th metacarpal bone, the other is bound to the sheath and 

 the deep fascia along the ulnar side of the 5th metacarpal, and ends opposite the ulnar side of the 

 head of the 1st phalanx into which it is inserted. It is both an abductor and flexor of the manus, 

 the flexing action commencing after the abduction is complete. It is supplied by the ulnar nerve. 



The Manus. — The inner or palmar region consists of three groups of muscles. The First 

 Group is composed of two adductors, found only in Arctocephalus : — 



The Adductor of the 2nd digit, named superficial interosseous in Otaria and Trichcchus, arises 

 from the base of the 3rd metacarpal between the two heads of the flexor brevis of the same digit. 

 It is inserted into the proximal extremity of the ulnar side of the 1st phalanx of the 2nd digit, 

 and is superficial to the flexores breves which it crosses. 



The Adductor minimi digiti is the adductor minimi digiti in Otaria and is absent in Trichcchus. 

 It arises from the middle of the ulnar side of the 4th metacarpal and from the deep fascia 

 between the 4th and 5th metacarpals ; after passing downwards and backwards it is inserted into 

 the outer half of the shaft and head of the 5th metacarpal and base of the 1st phalanx. 



The Second Group contains the flexores breves, which are the deep interossei in Otaria and 

 Trichcchus. In the Phocinre the first arises from the ulnar side of the metacarpal of the pollex ; 

 and is inserted into the ulnar side of the 1st phalanx of the 1st digit. In Arctocephalus it is disposed 

 as in the Phocinae. The 2nd interrosseus in the Phocina? is double and arises from the radial and 

 ulnar sides of the 2nd metacarpal. The radial head is inserted into the radial side of the base of 

 the 1st phalanx of the 2nd digit ; the ulnar head into the ulnar side of the same digit. It has the 

 same relations in Arctocephalus. The 3rd and 4th muscles in the Phocinse and Arctocephalus resemble 

 the last named. The 5th in the Phocina? is single and arises from the radial side of the 5th digit, 

 and is inserted into the same side of the base of the 1st phalanx of the same digit. In Arctocephalus 

 I did not observe any muscle for the 5th digit. In Otaria these muscles are in pairs for all the 

 digits but the 1st, which has only one. In Trichcchus the 1st and 5th digits have only one each, 

 the other digits two. 



The Third Group embraces the following : — 



The Abductor brevis jwllicis is the M. flexor pollicis of Lucae, and is wanting in Otaria and 

 Trichcchus. In the Phocinse it arises from the lower side of the process on the outer side of the 

 scapholunar bone, and from the lower border of this bone to the outer side of the tendon of the flexor 

 carpi radialis ; and is inserted into the front of the radial side of the base of the 1st phalanx of 

 the thumb. There is a sesamoid bone beneath its tendon. 



In Arctocephalus it arises from the trapezium, from the upper and internal half of the 1st 

 metacarpal, from the radial side of the base of the 2nd metacarpal, and from the carpo-metacarpal 

 ligament. The greater portion is inserted into the ulnar side of the distal end of the 1st metacarpal, 

 and the remainder into the distal extremity of the radial side of the 2nd metacarpal. Humphry 

 does not mention this muscle, but Lucae describes it. 



The Abductor minimi digiti is the flexor brevis minimi digiti in Otaria and is absent in 

 Trichcchus ; in the Phocinse it arises from the pisiform bone, and from the tendon of the flexor carpi 



