U2 



THE MUSCLES 



Action. — Both heads -will flex the iiietacari)()-]>halanfroal joint of the thumb. 

 The outer head will flex also the earijo-metacarpal joint, while the inner head will 

 be an adductor as well as flexor of this joint. The former will act in association 

 with the abductor and opponens, and will draw the thumb forwards and inwards, 

 keepinp; it at some distance from the palm of the hand. The latter will act wdth 

 the adductor, and draw it more directly inwards in close proximity to the palm of 

 the hand. 



Relations. — The outer head lies beneath the abductor pollicis, and in contact 

 by its radial l)orderAvith the opponens pollicis. The inner head is partly separated 

 from it by the tendon of the flexor longus pollicis; upon its ulnar border it is in 



Fig. 284. — The Pronator Quadratus and Deep View of the Palm. 



>/" 





Pronator quadratus 



Abductor pollicis 



Outer head of flexor 

 brevis pollicis 



Inner head of flexor 



brevis pollicis i flrst 



division) 

 Opponens pollicis 

 Inner head of flexor 



brevis pollicis third 



division I 

 Inner head of flexor 

 brevis pollicis (second 

 division) 



Adductor pollicis 



Dorsal interosseous 



Third palmar 

 interosseous 



Fourth dorsal 

 interosseous 

 Second palmar interosseo 



Third dorsal interosseous 



First palmar interosseous 



Second dorsal interosseous 



contact with the adductor. In front of it lie the tendons of the flexor ]n-ofundus 

 with the outer lumbricalcs; behind, are the third part of the radial artery and the 

 interossei muscles of the flrst two spaces. 



4. ADDUCTOR POLLICIS 



The adductor pollicis, sometimes called tlie adductor pollicis transversus — 

 named from its action — is a thick trianjiular sheet. 



Origin. — The front border of the shaft of the third metacarpal bone. 



Insertion. — (1 ) The inner side of the base of the first phalanx of the thumb: 

 (2) the inner side of the aponeurosis of the extensor longus pollicis which covers 

 the first phalanx. 



