6o8 HUMAN ANATOMY. 



2. Abductor Pollicis (Fig. 577). 



Attachments. — The abductor of the thumb (m. abductor pollicis brevis) is the 

 most superficial muscle of the thenar eminence. It arises from the anterior annular 

 ligament and from the scaphoid bone or the trapezium and passes distally to be in- 

 serted along with the flexor brevis pollicis into the radial side of the base of the first 

 phalanx of the thumb and into the sheath of the tendon of the extensor longus pollicis. 



Nerve-Supply. — By the median nerve from the sixth and seventh cervical 

 nerves. 



Action. — To flex and abduct the thumb. 



Variations. — The portion of the muscle arising from the carpus is sometimes separate from 

 that taking origin from the transverse carpal ligament. Slips are occasionally sent to the abduc- 

 tor from the extensores carpi radiales, the extensor ossis metacarpi pollicis, the opponens pol- 

 licis, and the flexor brevis pollicis. 



3. Opponens Pollicis (Figs. 578, 588). 



Attachments. — The opponens pollicis is almost completely covered by the 

 abductor pollicis. It arises from the anterior annular ligament and from the trape- 

 zium, and is inserted into the whole length of the radial border of the first metacarpal. 



Nerve-Supply. — By the median nerve from the sixth and seventh cervical 

 nerves. 



Action. — To flex and adduct the thumb, opposing it to the other fingers. 



4. Flexor Brevis Pollicis (Figs. 578, 588). 



Attachments. — The flexor brevis pollicis lies along the lower (ulnar) border 

 of the opponens pollicis. It arises from the lower border of the anterior annular 

 ligament and is iyiserted, along with the abductor pollicis, into the radial side of the 

 base of the first phalanx of the thumb. 



The muscle above described is usually regarded by English anatomists as representing the 

 outer or radial head of the flexor brevis, a second inner or ulnar head being included as part of 

 that muscle. Concerning the inner head three views are held : {a) no inner head is recognized, 

 the small slip arising from the ulnar side of the base of the first metacarpal bone and passing 

 downward to be inserted with the adductor pollicis into the base of the first phalanx, which by 

 many English anatomists is regarded as a small inner head of the flexor brevis, being described 

 as an additional (first) palmar interosseus (page 612) ; {b) the small slip just noted is the inner 

 or ulnar head of the flexor brevis ; {c) the small slip and all the fibres described as forming the 

 adductor obliquus (page 610) are regarded as the inner head of the flexor brevis. The first 

 view, adopted by German anatomists, is here followed. 



Nerve-Supply. — By the median nerve from the sixth and seventh cervical 

 nerves. 



Action. — To flex the first phalanx of the thumb. 



Variations. — The muscle is sometimes intimately connected with the abductor pollicis and 

 opponens pollicis. 



5. Abductor Minimi Digiti (Fig. 577). 



Attachments. — The abductor of the litde finger (m. abductor digiti quinti) 

 occupies the ulnar border of the hand. It arises from the anterior annular ligament 

 and from the pisiform bone and is inserted into the ulnar side of the base of the first 

 phalanx of the little finger. 



Nerve-Supply. — By the deep division of the ulnar nerve from the eighth cer- 

 vical and first thoracic nerves. 



Action.— To abduct the fifth finger. 



6. Opponens Minimi Digiti (Fig. 578). 



Attachments. — This muscle (m. opponens digiti quinti) is almost completely 

 covered by the abductor and short flexor of the litde finger. It arises from the 

 anterior annular ligament and the uncinate process of the unciform bone and is in- 

 serted into the whole of the ulnar border of the fifth metacarpal bone. 



