FLEXOR B RE VIS MIXIMI DIGITI 343 



Structure. — Ari^^ing by short tt-ndinous or fleshy fibres, the muscle converges 

 upon a short tendon, ^vhich blends on its outer side with the inner tendon of the 

 flexor lirevis pollieis, and sends a iibrous slip to the inner side of the aponeurosis 

 (jf the extensor loiigus pollieis. 



Nerve-supply. — From the lower cord of the brachial ])lexus (through the 

 eighth cervical nerve j, by the deep branch of the ulnar which sends filaments to 

 the upper border and deep surface near the origin. 



Action. — (1) To flex the first phalanx of the thumVj; (2) to adduct and flex 

 the carpo-metacarpal joint of the thumb; (oj to extend the second phalanx of the 

 thumb. This latter action of the adductor and abductor pollieis is useful in many 

 of the movements of the thumb, in which it will be found that the second phalanx 

 has to he kept extended, while its palmar aspect is being opposed to the tijjs of the 

 other digits. 



Relations. — Superficially, some of the tendons of the flexor profundus digi- 

 torum and the two outer lumbricales; deeply, the abductor indicis and the inter- 

 ossei of the space l»etween the second and third metacarpal bones. Part of the 

 lower border is subcutaneous. 



Variations. — The adductor pollieis is often difficult to separate from the inner head of the 

 flexor brevis pollieis. 



Muscles of the Hypothexar Eminence 



These are three in number — the abductor minimi digiti, the opponens minimi 

 digiti, and the flexor brevis minimi digiti. They lie under cover of the thin 

 internal division of the palmar fascia. 



1. ABDUCTOR MIXIMI DIGITI 



The abductor minimi digiti — named from its action — is fusiform and some- 

 what flattened. 



Origin. — ( 1) The lower half of the pisiform bone; (2) the continuation of the 

 tendon of the flexor carpi ulnaris below this bone. 



Insertion, — (1) The ulnar side of the base of the first phalanx of the little 

 finger; and (2) the adjacent portion of the aponeurosis of the extensor minimi 

 digiti. 



Structure. — Arising by short tendinous fibres, it soon forms a flat flesh}' mass 

 which contracts slightly below, and just before its insertion having again become 

 tendinous, it is for the most part attached to the first phalanx, but it also sends a 

 small slip backwards to the extensor aponeurosis. 



Nerve-supply. — From the ulnar nerve through the eighth cervical nerve. It 

 receives small filaments at the outer and deep aspect, usually from the deep palmar 

 division of the ulnar nerve. 



Action. — To abduct, and at the same time flex, the metacarpo-phalangeal joint 

 of the little finger; it will also assist, like an interosseous muscle, in the extension 

 of the second and third phalanges. 



Relations. — Superficially, the hypothenar part of the jxalmar fascia and the 

 palmaris brevis; deeply, the flexor brevis and opponens minimi digiti. Upon its 

 radial border are placed the deep palmar branches of the ulnar artery and nerve. 



2. FLEXOR BREVIS MIXIMI DIGITI 



Tlie flexor brevis minimi digiti — named from its action — is small and fusiform. 



Origin. — ( 1) The ulnar surface of the hook of the unciform bone; (2) the 

 adjacent part of the front of the anterior annular ligament. 



Insertion. — The ulnar side of the base of the first phalanx of the little finger. 



Structure. — Its origin and insertion are by short tendinous fibres, and the rest 

 of tlie nuiscle is fleshv. 



