406 



THE MUSCULATURE 



Structure and insertion. — The fibre-bundles diverge, the proximal short and horizontal, the 

 distal long and oblique, and are inserted on the whole of the ulnar border and on a part of the 

 head of the fifth metacarpal. Often the^muscle is divisible into two portions between which the 

 ulnar nerve runs. 



Nerve-supply. — Before the deep palmar branch passes through the muscle it gives rise to 

 a twig which enters its volar surface in the middle third near the ulnar margin. The nerve 

 fibres arise from the (seventh and) eighth cervical and first thoracic nerves. 



Action. — To flex, adduct, and slightly rotate the fifth metacarpal; as, for example, in 'cup- 

 ping' the hand to drink from it. 



Relations. — The opponens lies beneath the abductor and flexor brevis muscles. The deep 

 branches of the ulnar nerve and artery pass through the opponens near its carpal origin and 

 then under it extend into the palm. 



Fig. 376. — The Deeper Muscles op the Palm of the Hand. 



Flexor carpi 

 ulnaris 



Flexor digitorum 

 sublimis 



Flexor digitorum 

 profundus 



Abductor pollicis longus 

 Flexor carpi radialis 

 Extensor pollicis brevis 



Abductor pollicis brevis 

 Opponens pollicis 



Abductor pollicis 



brevis 

 Flexor pollicis 

 brevis 



Adductor pollicis 



Variations. — It may be fused with neighbouring muscles or receive accessory slips. 



The tensor capsularis articulationis metacarpo-phalangei digiti quinti is a slender muscle 

 which ari.se.s from tlio ligaments which unite the pisiform to the hamatum, and is inserted into 

 the volar surface of the metacarpo-phalangeal joint of the little finger. 



(c) Muscles of the Thumb 



(Fig.s. 375, 376, 377) 



In the thcrar region tluirG are four muscles. Of these, the abductor pollicis 

 brevis is the most superficial. Then come the opponens pollicis and the short 

 flexor, and beneath the last the adductor pollicis. All are triangular in form. 

 The abductor pollicis brevis arises from the radial side of the volar surface of the 



