i 3 8 THE NERVOUS SYSTEM 



The cutaneous branches of the axillary nerve supply the skin 

 over the distal two-thirds of the deltoid. They are slightly 

 overlapped, proximally by the posterior supra-clavicular (supra- 

 acromial) nerves (C. 3 and 4) and distally by the dorsal 

 cutaneous branch of the radial nerve (upper external cutaneous 

 branch of the musculo-spiral nerve) (Fig. 63). In complete 

 paralysis of the axillary nerve, the skin over the distal two- 

 thirds of the deltoid shows loss of both epicritic and protopathic 

 sensibility. The combination of the motor and sensory pheno- 

 mena renders paralysis of this nerve easy to determine. 



The Radial (Musculo-spiral) Nerve arises from the posterior 

 cord in the axilla and descends behind the artery. In this 

 part of its course it lies medial to the proximal part of the 

 shaft of the humerus, against which it is compressed in " crutch " 

 and " Saturday night " paralyses. A short distance beyond 

 the posterior fold of the axilla, it passes distally and laterally 

 across the posterior aspect of the humerus in the radial groove. 

 At the distal extremity of the groove, the nerve re-enters the 

 anterior compartment of the arm and, in front of the lateral epi- 

 condyle of the humerus, it ends by dividing into superficial 'and 

 deep branches (O.T. radial and posterior interosseous nerves]. 



The radial nerve can be rolled against the lateral aspect of 

 the humerus as it pierces the lateral intermuscular septum. 

 This point corresponds to the junction of the middle and 

 proximal thirds of the line joining the insertion of the deltoid 

 to the tip of the lateral epicondyle. Proximal to that point, 

 the radial nerve may be rolled against the floor of the radial 

 groove on deep pressure through the triceps. 



As the radial (musculo-spiral) nerve passes through the axilla, 

 it gives off a cutaneous branch, which supplies the skin on the 

 dorsum of the arm (Fig. 64), and motor branches to the long 

 and medial heads of the triceps. In the radial groove, the 

 nerve supplies branches to all three heads of the triceps and 1 to 

 the anconaeus. At the distal extremity of the groove it gives 

 off the dorsal cutaneous nerve of the forearm. This branch 

 breaks up into proximal and distal divisions (upper and lower 



