THE FOREARM. 321 



The deep and superficial branches are the continuation of the radial (musculo- 

 spiral) which divides in the groove between the brachioradialis (supinator longus) 

 and brachialis anticus muscles just above the elbow. 



The deep branch {posterior interosseous} is the larger and is a muscular nerve ; 

 the superficial branch (radial) is smaller and is solely sensory. The deep branch 

 passes down under the brachioradialis and extensor carpi radialis longior and brevior 

 muscles and then enters the substance of the supinator (brevis) through which it 

 passes to supply the extensor muscles on the back of the forearm and terminates in a 

 gangliform enlargement on the back of the wrist. It supplies all the muscles on the 

 back of the forearm except the anconeus, brachioradialis,* and extensor carpi radialis 

 longior, which are supplied directly from the radial (musculospiral) nerve. In 

 removing the head of the radius, in resection of the elbow, the supinator (brevis) is to 

 be carefully raised from the bone so as to carry the nerve with it and avoid injuring it. 

 Injury to this nerve causes paralysis of the extensors, and wrist-drop follows. 



The superficial branch (radial} is purely a nerve of sensation. It passes down 

 almost in a straight line and lies to the outer side of the radial artery at the junction 

 of its upper and middle thirds. It lies alongside of the artery to its outer side in its 

 middle third and then, about 7 or 8 cm. (3 in.) above the wrist, quits the artery, 

 passes beneath the tendon of the brachioradialis, and divides into two branches which 

 supply sensation to the dorsal (radial) side of the hand and fingers. 



In operating on the radial artery in the middle third of the forearm care should 

 be exercised not to include the nerve in the ligature with the artery. 



FRACTURES OF THE FOREARM. 



Fractures of the forearm may involve either the radius or ulna, or both. The 

 radius is the bone most often broken. The preservation of the interosseous space 

 and functions of pronation and supination are prominent points in treatment. 



Fractures of Both Bones. These fractures occur either from a direct blow 

 on the part or are due to violence in falling on the outstretched hand. They usually 

 occur in the middle or lower third. The character of the displacement depends 

 more on the manner in which the injury is produced than on the action of the 

 muscles, though in some cases they also have some influence. 



The main function of the forearm in addition to that of serving as a pedestal or 

 support for the hand is to perform the movements of pronation and supination. It 

 is these movements that are most apt to be impaired in cases of fracture. When 

 both bones are fractured the interosseous membrane still remains, running transversely 

 from one bone to that of the opposite side. Therefore, while it is common enough to 

 find the fractured ends displaced toward one another, thus narrowing or obliterating 

 the space between them, one never sees a displacement of the fragments produc- 

 ing a widening of the interosseous space. In fracture of both bones four types of 

 deformity or combinations of these types are found. 



1. The fractured ends of the distal or proximal fragments may preserve approx- 

 imately their normal position to one another but be displaced either anteriorly or 

 posteriorly or else to one side. When this is the case the displacement is one simply 

 of overlapping. If the fragments are displaced laterally from one another then the 

 tension of the muscles draws the fragments together and causes them to overlap. 

 There is no special direction which this displacement may take. The lower frag- 

 ments may be either in front or behind or to either side of the upper ones. The 

 position of the fragments varies according to the direction of the fracturing force. 



This displacement is to be remedied by traction on the hand to overcome the 

 muscles and bring the broken ends opposite one another, and then by direct pressure 

 pushing them as completely as possible back into their normal position. 



The shafts of both bones have muscles arising from them on both their anterior 

 and posterior surfaces and the sharp fractured ends of the bones not infrequently get 

 stuck in the muscular fibres and so prevent proper -approximation ; non-union may 

 be produced by this cause. 



2. The fractured ends of the distal or proximal fragments may be displaced 

 toward one another, thus lessening or even obliterating the interosseous space. When 



