THE FOREARM. 329 



branch of the radial nerve. Following the nerve and edge of the brachioradialis 

 tendon would lead to the interspace between it and the extensor carpi radialis 

 muscle posteriorly. When the middle of the forearm was reached the insertion of 

 the pronator teres would be encountered, and from that point up the bone would 

 be covered by the supinator (brevis). 



Operations on the median nerve (page 319) and the ulnar nerve (page 320) 

 have already been alluded to. 



In operations involving the upper third of the radius the deep branch of the 

 radial (posterior interosseous) nerve is liable to be wounded as it passes through the 

 supinator (brevis) muscle. It is best avoided by elevating the muscle from the 

 bone and raising the nerve along with it, for it does not rest immediately on the 

 bone but has some muscular fibres intervening. 



The arteries have already been sufficiently described. 



PUS BENEATH THE DEEP FASCIA. 



The deep fascia of the forearm is continuous with that of the arm. It forms a 

 complete covering for the muscles and sends septa between them. It is especially 

 strong posteriorly. It is attached to the medial and lateral condyles of the humerus, 

 the sides of the olecranon process and the whole length of the ulna posteriorly. 

 Below the medial condyle anteriorly it is strengthened by the bicipital fascia. In 

 the antecubital fossa it is pierced by a large communicating vein which connects the 

 superficial and deep veins. Toward its lower end posteriorly, it is strengthened 

 by transverse fibres and becomes attached to the longitudinal ridges on the radius 

 and blends with the posterior annular ligament. 



Below anteriorly it is thin and forms a covering for the tendons of the palmaris 

 longus and flexor carpi radialis muscles and at the wrist blends with the annu- 

 lar ligament beneath. This latter, as pointed out by Davies Colley ("Morris's 

 Anatomy, ' ' page 3 1 1 ) , is a continuation of the layer of fascia covering the flexor 

 sublimis digitorum. 



When infection involves the deep tissues of the forearm the pus, being hindered 

 from going externally by the fibrous septa between the various layers of muscles as 

 well as the deep fascia itself, tends to burrow up and down the arm. If in the upper 

 portion of the forearm, it tends to point in the antecubital fossa. If lower down, it tends 

 to come to the surface on the radial side between the flexor carpi radialis and brachio- 

 radialis or toward the ulnar side between the palmaris longus and flexor carpi ulnaris. 



The three structures, the tendons of the palmaris longus and flexor carpi radialis 

 and the median nerve, form a solid barrier anteriorly which inclines the pus to one 

 side. Above posteriorly it may work its way upward behind the internal condyle, 

 following the ulnar nerve. 



The fibrous septa of the various muscles hinder the progress of pus laterally, and 

 the attachment of the deep fascia to the ulna prevents its passing around the arm at 

 that point. The many pockets formed by the pus in its burrowing between the 

 muscles render these abscesses difficult to drain and tedious in healing. 



Should infection from the thumb travel up the flexor longus pollicis tendon, 

 when it reaches above the wrist it is directly beneath the tendon of the flexor carpi 

 radialis. In such a case an incision should be made along the radial (outer) edge of 

 the tendon, taking care not to wound the radial artery still farther out. If pus infects 

 the forearm by following up the flexor tendons of the fingers beneath the anterior 

 annular ligament, it shows itself above the wrist between the palmaris longus and 

 flexor carpi ulnaris tendons and can here be incised. If it is desired to introduce a drain 

 beneath the flexor muscles, an incision may be made along the side of the ulna and a 

 forceps passed under the flexor tendons and made to project under the skin of the 

 radial side where a counter opening can be made and the drain inserted. (For a dis- 

 cussion of the treatment of purulent affections of the hand and forearm see A. B. 

 Kavanel : " Surgery, Gynecology, and Obstetrics," 1909, p. 125, vol. viii, No. 3.) 

 Suppuration around these tendons is very serious, as the effusion binds together the 

 tendons and irritates the nerves and produces disabling contractures which are exceed- 

 ingly difficult to remedy. 



