FOREARM AND HAND 141 



with the radial recurrent. On the medial side of the joint the 

 anterior and posterior ulnar recurrent arteries ascend respectively 

 in front of and behind the medial epicondyle, the former 

 anastomoses with the anterior branch of the inferior ulnar 

 collateral artery, and the latter with the posterior branch of 

 the same artery and with the superior ulnar collateral artery. 



In this sketch of the anastomosis around the elbow-joint 

 only the leading inosculations are mentioned. Rich networks 

 of fine vessels are formed over the olecranon and the two 

 epicondyles of the humerus. One very distinct and tolerably 

 constant arch requires special mention. It is formed by a 

 branch which crosses the posterior aspect of the humerus, 

 immediately above the olecranon fossa, and connects the 

 posterior branch of the profunda brachii artery with the 

 posterior branch of the inferior ulnar collateral artery. 



Nervus Interosseus Dorsalis (O.T. Posterior Interosseous 

 Nerve). This is the continuation of the profunda 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 supina- 

 tor a short distance proximal to the distal border of the muscle, 

 and is carried distally between the superficial and deep muscles 

 on the back of the forearm. Reaching the proximal border of 

 the extensor pollicis longus, it leaves the dorsal interosseous 

 artery, dips anterior to the extensor pollicis longus, and -joins 

 the volar interosseous artery on the dorsal aspect of the inter- 

 osseous membrane. It will afterwards be traced to the dorsum 

 of the carpus, where it ends, under cover of the- tendons of the 

 extensor digitorum communis, in a gangliform enlargement. 



The branches which spring from the dorsal interosseous 

 nerve in the forearm are given entirely to muscles. Before 

 the profunda branch pierces the supinator and becomes the 

 dorsal interosseous nerve, it gives branches both to it and to the 

 extensor carpi radialis brevis. After it appears on the dorsum 

 of the forearm as the dorsal interosseous nerve it supplies the 

 extensor digitorum communis, the extensor digiti quinti pro- 

 prius, the extensor carpi ulnaris, the abductor pollicis longus, 

 two extensors of the thumb, and the extensor indicis proprius. 

 It therefore supplies all the muscles on the lateral and dorsal 

 aspects of the forearm, with the exception of the brachio-radialis 

 and the extensor carpi radialis longus, which derive their nerve- 



