84 TOPOGRAPHIC AND APPLIED ANATOMY. 



FlG. 35. The anterior aspect of the forearm above the wrist. The ulnar artery and nerve have been made 

 visible by displacing the tendon of the flexor carpi ulnaris. 



FIG. 36. A cross-section through the middle of the forearm. 



brane with the anterior interosseous artery to the pronator quadratus muscle. A small palmar 

 branch passes alongside of the tendon of the flexor carpi radialis to the skin of the palm. Par- 

 alysis of the median nerve is followed by a loss of radial flexion (flexor carpi radialis) and of 

 flexion of the fingers (flexor sublimis and profundus digitorum); the thumb is extended and 

 adducted (the adductor pollicis is supplied by the ulnar nerve). The ulnar nerve, after reaching 

 the deep surface of the flexor carpi ulnaris, gradually approaches the ulnar artery and comes in 

 relation with its ulnar side at about the middle of the forearm. It lies between the flexor pro- 

 fundus digitorum and the flexor carpi ulnaris and; below the middle of the forearm, divides into 

 a large anterior branch, which follows the ulnar artery (see page 83), and a smaller posterior 

 branch, which reaches the back of the hand by passing beneath the flexor carpi ulnaris. Paralysis 

 of the ulnar nerve is followed by a loss of ulnar flexion of the hand (flexor carpi ulnaris) and 

 by an impairment of motion of the terminal phalanges of the fingers upon the ulnar side (flexor 

 profundus digitorum). The musculos piral nerve, while still in the region of the bend of the 

 elbow, divides into the motor posterior interosseous nerve and the sensory radial nerve. The 

 posterior interosseous nerve pierces the supinator brevis, and at the lower border of this muscle 

 (upon the extensor side of the forearm) gives off numerous branches which ramify between the 

 superficial and deep groups of muscles and supply all of the extensors in the forearm. The 

 radial group of muscles is supplied by the nerve before its entrance into the supinator brevis. 

 The continuation of the nerve runs upon the interosseous membrane as a small branch which 

 reaches the back of the wrist. The radial nerve is at first covered by the supinator longus; 

 about a handbreadth above the wrist it passes beneath the tendon of the supinator longus to the 

 extensor side and to the dorsal surface of the hand. If the musculospiral nerve is injured (for 

 example, by an injury of the soft parts of the upper arm or by a fracture of the humerus), there is, 

 in addition to the loss of motion of the extensors and of the muscles of the radial group, a loss of 

 sensation upon the extensor surfaces of .the upper arm, of the forearm, and of the radial half of 

 the back of the hand (see page 78). 



THE HAM). 



The dividing-line between the forearm and the hand is easily determined in the living subject 

 by locating the styloid processes of the radius and ulna. The line connecting these two processes 

 corresponds to the wrist-joint, and if it is desired to disarticulate the hand or excise the wrist- 

 joint, the knife must be introduced immediately to the distal side of these processes. 



Upon the palmar surface of the base of the hand may be seen and felt the hand prominences 

 produced by the eminentice carpi radialis and ulnaris. The eminentia carpi radialis is formed 

 by the tubercle of the scaphoid and by the ridge of the trapezium; the eminentia carpi ulnaris is 

 formed by the pisiform bone and by the unciform process of the unciform bone. These eminences 

 are united by the anterior annular ligament which converts the deep groove lying between them 

 into the important carpal canal. When the thumb is abducted, a marked prominence appears 



