FOREARM AND HAND 185 



ceding muscle, from a limited area on the dorsal surface of 

 the ulna and from the adjacent part of the interosseous 

 membrane. Its tendon accompanies the tendons of the 

 extensor digitorum communis through the most medial 

 groove on the back of the radius, under cover of the dorsal 

 carpal ligament, and is enclosed in the same mucous sheath. 

 On the dorsum of the hand it lies along the medial side of 

 the most lateral tendon of the common extensor, and it 

 terminates in the expansion of that tendon on the dorsum 

 of the first phalanx of the index finger. It is supplied by 

 a branch of the dorsal interosseous nerve. It is an extensor 

 of all the joints of the index finger, and it takes part in the 

 production of extension of the wrist joint. 



Arteria Interossea Dorsalis. The dorsal interosseous 

 artery arises, in the front part of the forearm, from the 

 common interosseous branch of the ulnar artery. It at 

 once proceeds dorsally, between the two bones of the 

 forearm, in the interval between the oblique cord and the 

 proximal border of the interosseous membrane. It appears 

 in the back of the forearm between the contiguous borders 

 of the supinator and the abductor pollicis longus, and 

 then it extends distally between the superficial and deep 

 muscles on the dorsum of the forearm. It gives branches 

 to the adjacent muscles, and before it reaches the distal end 

 of the forearm it is greatly reduced in size. In a well- 

 injected limb it will be seen to end on the dorsum of the 

 carpus by anastomosing with the volar interosseous artery 

 and the dorsal carpal arteries. In addition to the branches 

 which it supplies to the muscles, it gives off one large branch 

 called the interosseous recurrent artery (Fig. 79). 



The arteria interossea recurrens takes origin from the parent 

 trunk as it appears between the supinator and the abductor 

 pollicis longus, and turns proximally, under cover of the 

 anconceus muscle, to reach the dorsal aspect of the lateral 

 epicondyle of the humerus. 



Nervus Interosseus Dorsalis. The dorsal interosseous 

 nerve is the continuation of the deep terminal branch of the 

 radial (musculo-spiral) nerve. It reaches the dorsum of the 

 forearm by traversing the substance of the supinator, and at 

 the same time winding round the lateral aspect of the body 

 of the radius. It emerges from the supinator a short distance 

 proximal to the distal border of the muscle, and passes 



