NERVES OF THE ARM. 513 



The Internal Cutaneiis ; The Radial or Muscular S])iral ; 

 and ihe Circumjlex or Articular. 



The Musculo- Cutaneous, 



External Cutaneous, or Perforating Nerve of Casserius, 

 passes obliquely through the upper part of the coraco-brachialis 

 muscle. Before it enters the muscle, it sends a branch to it. 

 After leaving the muscle it passes down the arm between the 

 biceps and the brachialis internus, to which it also gives 

 branches. It proceeds to the outside of the biceps, and con- 

 tinues under the median cephalic vein to the anterior and ex- 

 ternal part of the fore-arm ; along which it passes under the 

 integuments. — It perforates the fascia so as to become sub- 

 cutaneous at the outer part of the bend of the elbow. — On the 

 lower part of the fore-arm it divides into many branches, 

 which extend to the root of the thumb and back of the head, 

 and terminate in the integuments. 



The Median Nerve, 



Which is one of the largest of the arm, often proceeds from 

 the axillary plexus next to the musculo-cutaneus ; it passes 

 down the arm, very near the humeral artery, within the edge 

 of the biceps flexor muscle, and, during this course, gives off 

 no branches of any importance. — It comes off from the plexus 

 by two roots which embrace between them the axillary artery ; 

 a fact which it is injportant to recollect in ligature of this 

 vessel in the axilla. — After passing the bend of the elbow, it 

 proceeds under the aponeurosis of the biceps, between the 

 brachialis internus and the pronator teres, and continues down 

 near the middle of the fore-arm, between the flexor sublimis 

 and the flexor profundus. At the elbow it sends branches to 

 , several nmscles on the anterior side of the fore-arm, and to the 

 integuments. Among these branches is one, called the Ante- 

 rior Interosseal Nerve, which passes down on the anterior 

 surface of the interosseal ligament, with the artery of that name. 

 This nerve sends branches, in its course, to the long flexor of 

 the thumb, and the deep flexor of the fingers. When it arrives 



