THE DORSAL ANTIBRACHIAL MUSCLES 



455 



Lateral epicondyle 



Radial collaierallig. 

 - Annular ligament 



Deep branch of radial 

 nerve 



Interosseous recurrent 

 art. 



Deep "branch of radial 



nerve 

 Dorsal interosseous 



art. 







form a sling-like fasciculus, which encircles the neck of the radius above the tuber- 

 osity and is attached to the back part of its medial surface; the greater part of 

 this portion of the muscle is inserted into the dorsal and lateral surfaces of the 

 body of the radius, midway between the oblique line and the head of the bone. 



The Abductor pollicis longus (Ex- 

 tensor oss. metacarpi pollicis) lies im- 

 mediately below the Supinator and 

 is sometimes united with it. It 

 arises from the lateral part of the 

 dorsal surface of the body of the ulna 

 below the insertion of the Anco- 

 nseus, from the interosseous mem- 

 brane, and from the middle third of 

 the dorsal surface of the body of the 

 radius. Passing obliquely downward 

 and lateralward, it ends in a tendon, 

 which runs through a groove on the 

 lateral side of the lower end of the 

 radius, accompanied by the tendon 

 of the Extensor pollicis brevis, and 

 is inserted into the radial side of the 

 base of the first metacarpal bone. 

 It occasionally gives off two slips 

 near its insertion : one to the greater 

 multangular bone and the other to 

 blend with the origin of the Abduc- 

 tor pollicis brevis. 



Variations. More or less doubling of 

 muscle and tendon with insertion of the 

 extra tendon into the first metacarpal, the 

 greater multangular, or into the Abductor 

 pollicis brevis or Opponens pollicis. 



The Extensor pollicis brevis (Ex- 

 tensor primi internodii pollicis) lies 

 on the medial side of, and is closely 

 connected with, the Abductor pollicis 

 longus. It arises from the dorsal surface of the body of the radius below that 

 muscle, and from the interosseous membrane. Its direction is similar to that of 

 the Abductor pollicis longus, its tendon passing through the same groove on the 

 lateral side of the lower end of the radius, to be inserted into the base of the first 

 phalanx of the thumb. 



Variations. Absence; fusion of tendon with that of the Extensor pollicis longus. 



The Extensor pollicis longus (Extensor secundi internodii pollicis) is much larger 

 than the preceding muscle, the origin of which it partly covers. It arises from 

 the lateral part of the middle third of the dorsal surface of the body of the ulna 

 below the origin of the Abductor pollicis longus, and from the interosseous mem- 

 brane. It ends in a tendon, which passes through a separate compartment in the 

 dorsal carpal ligament, lying in a narrow, oblique groove on the back of the lower 

 end of the radius. It then crosses obliquely the tendons of the Extensores carpi 

 radialis longus and brevis, and is separated from the Extensor brevis pollicis by a 

 triangular interval, in which the radial artery is found; and is finally inserted into 

 the base of the last phalanx of the thumb. The radial artery is crossed by the 



FIG. 420. The Supinator. 





