FLEXOR LONGUS POLLICIS PRONATOR <4lJADHATUS. 213 



wrist-joint. By its radial border with the flexor longus pollicis, the 

 anterior interosseous artery and nerve being interposed. By its 

 ulnar border with the flexor carpi ulnaris. In the hand : its tendons 

 are in relation superficially with the tendons of the superficial flexor ; 

 and deeply with the interossei muscles, adductor pollicis, and deep 

 palmar arch. In the fingers : the tendons of the deep flexor are 

 interposed between the tendons of the superficial flexor and the 

 phalanges. 



The Flexor longus pollicis arises from the upper two-thirds of the 

 radius, and part of the interosseous membrane. Its tendon passes 

 beneath the annular ligament, to be inserted into the base of the last 

 phalanx of the thumb. 



Relations. By its anterior surface with the flexor sublimis digito- 

 rum, flexor carpi radialis, supinator longus, and radial artery and 

 veins. By its posterior surface with the radius, interosseous mem- 

 brane, proriator quadratus and wrist-joint. By its ulnar border it is 

 separated from the flexor profundus digitorum by the anterior inter- 

 osseous artery and nerve. In the hand : after passing beneath the 

 annular ligament, it is lodged in the interspace between the two por- 

 tions of the flexor brevis pollicis, and afterwards in the tendinous 

 theca of the phalanges. 



If the tendons of the two last muscles be drawn aside or divided, 

 the third muscle of this group will be brought into view, lying across 

 the lower part of the two bones. 



The Pronator quadratus arises from the ulna, and is inserted into 

 the lower fourth of the oblique line, on the outer side of the radius. 

 This muscle occupies about the lower fourth of the .two bones, is 

 broad at its origin, and narrower at its insertion. 



Relations. By its anterior surface with the tendons of the supina- 

 tor longus, flexor carpi radialis, flexor longus pollicis, flexor profun- 

 dus digitorum, and flexor carpi ulnaris, radial artery and veins, and 

 ulnar artery, veins, and nerve. By its posterior surface with the 

 radius, ulna, and interosseous membrane. 



Actions. The pronator radii teres and pronator quadratus muscles 

 rotate the radius upon the ulna, and render the hand prone. The 

 remaining muscles are flexors: two flexors of the wrist, flexor 

 carpi radialis and ulnaris ; two of the fingers, flexor sublimis and 

 profundus, the former flexing the second phalanges, the latter the 

 last ; one flexor of the last phalanx of the thumb, flexor longus pol- 

 licis. The palmaris longus is a tensor of the palmar fascia. 



Posterior brachial Region. 



Superficial layer. 

 Supinator longus, 

 Extensor carpi radialis longior, 

 Extensor carpi radialis brevior, 

 Extensor communis digitorum, 

 Extensor minimi digiti, 

 Extensor carpi ulnaris, 

 Anconeus. 



