90 DISSECTION OF THE BACK OF THE FOREAEM. 



substance of the muscle the posterior interosseous nerve ( 3 ) winds to 

 the back of the limb. 



use. Action. When the radius has been moved over the ulna in 



pronation, the short supinator comes into play to bring that bone 

 again to the outer side of the ulna. 



Posterior The POSTERIOR INTEROSSEOUS ARTERY (fig. 37, rt) IS an offset 



artery SSe US ^ rom tne common interosseous trunk (p. 66), and reaches the back 



of the forearm above the membrane between the bones. Appearing 



between the contiguous borders of the supinator brevis and extensor 



between the oss * 8 metacar pi pollicis, the artery descends at first between the 



layers of superficial and deep layers of muscles ; and afterwards with u 



muscles, superficial position in the lower third of the forearm, along the 



and super- tendon of the extensor carpi ulnaris as far as the wrist, where it 



ends by anastomosing with the carpal and anterior interosseous 



arteries. It furnishes muscular offsets to the surrounding muscles, 



and the following recurrent branch : 



its recur- The recurrent branch (b) springs from the artery near the beginning, 



rent branch. an( j ascen( j s on or through the fibres of the supinator, but beneath 



the anconeus, to supply both those muscles and the elbow-joint ; 



it anastomoses with the superior profunda artery and the recurrent 



radial (fig. 19, p. 46). 



Posterior The POSTERIOR INTEROSSEOUS NERVE ( 3 ) is derived from the 



nerve*? 860 IS niusculo-spiral trunk (p. 53), and winds backwards through the 



fibres of the supinator brevis. Issuing from the supinator, the nerve 



position to is placed between the superficial and deep layers of muscles as far 



muscles ; as tne j^dcQe O f the forearm. Much reduced in size at that spot, it 



sinks beneath the extensor of the second phalanx of the thumb, and 



runs on the interosseous membrane to the back of the carpus. 



termination Finally, the nerve enlarges beneath the tendons of the extensor 



on back of J . . . . 



the carpus ; commums digitorum, and terminates in filaments to the articulations 



of the carpus. 

 its muscular Branches. It furnishes offsets to all the muscles of the deep layer, 



and to those of the superficial layer with the exception of the three 



following, viz., anconeus, supinator longus, and extensor carpi radial is 



longior. 



arter^at RADIAL ARTERY AT THE WRIST (fig. 37). The radial artery (//), 



wrist: with its vense comites, winds below the radius to the back of the 



carpus, and enters the palm of the hand at the first interosseous 



space, between the heads of the first dorsal interosseous muscle. At 

 parts 10 " 8 10 fi rst tne vesse l I* 68 deeply on the external lateral ligament of the 

 around, wrist-joint, and beneath the tendons of the extensors of the meta- 



carpal bone and the first phalanx of the thumb ; but afterwards it is 



more superficial, and is crossed by the tendon of the extensor of the 



second phalanx of the thumb. 



and nerves. Offsets of the niusculo-cutaneous nerve entwine around the artery 

 Branches (p. 56), and branches of the radial nerve are superficial to it. Its 



small : ^ fmc /j, es are numerous but inconsiderable in size : 

 to back of 1. The dorsal carpal branch (/) passes transversely beneath the 

 carpus ; extensor tendons, and forms an arch (the dorsal, or posterior, carpal 



arch}, with a corresponding offset of the ulnar artery ; this arch is 



