REGION OF (UPPER) ARM 41 



nerve lies on the lateral border of the brachialis (b. anticus), 

 and is covered in front by the brachio-radialis (supinator longus) 

 proximally and the extensor carpi radialis longus distally. It 

 ends in front of the lateral epicondyle of the humerus by dividing 

 into superficial (radial) and deep (posterior interosseous) branches. 

 Callus following a fracture of the shaft of the humerus 

 sometimes implicates the radial (musculo - spiral) nerve, 

 necessitating operative interference. The nerve can be 

 conveniently found as it pierces the lateral intermuscular 

 septum, and it can then be traced upwards by cutting through 

 the musculo - tendinous roof of the radial groove, until the 

 damaged portion is found. In the usual procedure the nerve 

 is sought for in the anterior compartment by separating the 

 brachio-radialis from the brachialis (b. anticus). Owing to the 

 absence of a well-marked septum, the groove between these 

 muscles, which are closely applied to one another, is not easy 

 to determine. The interval between the brachialis and the 

 biceps may inadvertently be opened, in which case the musculo- 

 cutaneous nerve is exposed (vide infra). Injury to the radial 

 (musculo-spiral) nerve is dealt with on p. 101. 



Muscles of the anterior compartment. The coraco - brachialis 

 is inserted into the middle of the shaft of the humerus on the medial side, 

 and helps in flexion and adduction of the arm. Its nerve -supply from 

 the musculo-cutaneous nerve is derived entirely from C. 7. 



The biceps brachii arises by a long head (p. 18) and by a short head from 

 the tip of the coracoid process. It is inserted into the posterior part of the 

 tuberosity of the radius and is separated from the anterior part by a bursa. 

 Primarily, it is a flexor and supinator of the forearm ; secondarily, it helps 

 to produce flexion and adduction at the shoulder. The musculo-cutaneous 

 nerve (C. 5 and 6) supplies both heads. 



The biceps occupies the greater part of the anterior compartment of the 

 arm, and its medial border is the surgical guide to the brachial artery. The 

 belly or either head of the muscle may be ruptured during violent movements, 

 and, as a result, flexion of the elbow and forcible supination are much 

 weakened. 



The brachialis (b. anticus) covers the distal half of the anterior surface 

 of the humerus and passes in front of the anterior ligament of the elbow to 

 be inserted into the front of the coronoid process of the ulna. It is a powerful 

 flexor of the elbow, and it derives its nerve-supply from the musculo-cutaneous 

 (C. 5 and 6) and the radial (musculo-spiral) nerves (C. 5 and 6). 



In fracture of the distal part of the shaft of the humerus a portion of 

 the brachialis may become interposed between the two fragments causing 

 non-union. 



The shaft of the humerus should be examined along the 

 lines of the intermuscular septa (p. 38), as the anterior and 

 posterior surfaces of the bone are obscured by muscles. At 

 its distal end, however, it may be examined by deep pressure 



