240 POSTERIOR BRACHIAL REGION. 



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 ra- 

 dius. 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 profundus 

 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 pollicis. The palmaris 

 longus is primarily a tensor of the palmar fascia, and secondarily a 

 flexor of the wrist and fore-arm. 



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. 



Dissection. The integument is to be divided and turned aside, 

 and the fasciae removed in the same manner as for the anterior brachial 

 region. 



The SUPINATOR LONGUS muscle is placed along the radial border of 

 the fore-arm. It arises from the external condyloid ridge of the hu- 

 merus, nearly as high as the insertion of the deltoid, and is inserted 

 into the base of the styloid process of the radius. 



Relations. By its superficial surface with the extensor ossis meta- 

 carpi pollicis, extensor primi internodii pollicis, and fascia of the fore- 

 arm. By its deep surface with the brachialis anticus, extensor carpi 

 radialis longior, tendon of the biceps, supinator brevis, pronator radii 

 teres, flexor carpi radialis, flexor sublimis digitorum, flexor longus 

 pollicis, pronator quadratus, radius, musculo-spiral nerve, radial and 

 posterior interosseous nerve, and radial artery and veins. 



This muscle must be divided through the middle, and the two ends 

 turned to either side to expose the next muscle. 



