THE FOREARM. 83 



interosseous membrane. They consist of four muscles which may be subdivided at the middle 

 of the forearm into an ulnar and a radial pair of muscles. The ulnar pair is composed of the 

 extensor indicis, passing to the terminal phalanx of the index-finger (both the index and little 

 fingers consequently having two extensor tendons), and of the extensor longus pollicis, which is 

 inserted into the terminal phalanx of the thumb. The radial pair is composed of the extensor 

 brevis pollicis, which is inserted into the base of the first phalanx of the thumb, and of the ex- 

 tensor ossis metacarpi pollicis, which is attached to the base of the metacarpal bone of the thumb. 

 The muscles should also be reviewed in transverse section (see Fig. 36) and the different groups in 

 the illustration may be outlined by variously colored pencils. 



Arteries. The radial artery, the more superficial of the two main arteries of the forearm, 

 passes over the tendon of the pronator radii teres muscle and is covered at first by the supinator 

 longus muscle. The radial nerve runs to the radial side of the radial artery, though at sorm? 

 distance from the vessel, and is also covered by the supinator longus muscle (see page 84). Above 

 the wrist the radial artery is so superficial that in ligating the vessel it is frequently sought for at 

 too great a depth. Below the middle of the forearm the artery appears from beneath the border 

 of the supinator longus and runs downward between the tendons of the supinator longus and 

 flexor carpi radialis muscles. Just above the wrist the vessel passes to the radial side of the hand 

 (see Fig. 37). With the exception of the radial recurrent (see page 80), the radial artery gives off 

 no large branches in the forearm. 



The ulnar artery becomes deeply situated immediately after its origin; it passes beneath the 

 pronator radii teres and runs upon the flexor profundus digitorum in a line corresponding to the 

 continuation of the brachial. Above the wrist the vessel lies beneath the border of the flexor 

 carpi ulnaris muscle and is covered by two layers of deep fascia which must be divided before 

 ligating the vessel. The ulnar nerve is situated immediately to the ulnar side of the vessel. In 

 contrast with the radial artery, the ulnar always remains upon the flexor side of the forearm and 

 passes into the hand at the radial side of the pisiform bone, where it may also be exposed and 

 ligated with comparative ease. The main branch is the common interosseous artery, which divides 

 immediately after its origin into the anterior and posterior interosseous. The anterior interosse- 

 ous artery runs downward upon the anterior surface of the interosseous membrane to the upper 

 margin of the pronator quadratus, where it passes to the dorsal surface to the arterial anastomosis 

 at the back of the wrist (rete carpi dorsale). The posterior interosseous artery passes through 

 the interosseous membrane to the extensor surface, is smaller than the anterior interosseous, and 

 also ends in the rete carpi dorsalis. 



Nerves. The relations of the three great nerves of the arm in this situation must also be 

 considered. The median nerve perforates the pronator radii teres, runs between the flexor sub- 

 limis and flexor profundus digitorum, supplying the neighboring muscles, and escapes from 

 beneath the flexor sublimis digitorum above the wrist (see Fig. 35), where it may easily be ex- 

 posed, to the radial side of the tendon of the palmaris longus [or is found directly beneath this 

 tendon. ED.]. In this situation the nerve is occasionally injured in suicidal attempts, in wounds of 

 the vessels, or by sabre-cuts. Such injuries are followed by paralysis of the opponens pollicis muscle 

 and by a loss of sensation upon the radial side of the palm (see page 87). The branch supplying 

 the deep flexors ends in the anterior interosseous nerve, which runs upon the interosseous mem- 



