646 SPINAL NERVES. 



The muscular branches supply the Triceps, Anconeus, Supinator Longus, Ex. 

 tensor Carpi Eadialis Longior, and Brachialis Anticus. These branches are 

 derived from the nerve, at the inner side, back part, and outer side of the arm. 



The internal muscular branches supply the inner and middle heads of the 

 Triceps muscle. That to the inner head of the Triceps, is a long, slender fila- 

 ment, which lies close to the ulnar nerve, as far as the lower third of the arm. 



The posterior muscular branch, of large size, arises from the nerve in the 

 groove between the Triceps and the humerus. It divides into branches which 

 supply the outer head of the Triceps and Anconeus muscles. The branch for 

 the latter muscle is a long, slender filament, which descends in the substance of 

 the Triceps to the Anconeus in the same course with the posterior articular 

 branch from the superior profunda artery. 



The external muscular branches supply the Supinator Longus, Extensor Carpi 

 Radialis Longior, and, usually, the Brachialis Anticus. 



The cutaneous branches are three in number, one internal and two external. 



The internal cutaneous branch arises in the axillary space, with the inner 

 muscular branch. It is of small size, and passes across the axilla to the inner 

 side of the arm, supplying the integument on its posterior aspect nearly as far 

 as the olecranon. 



The two external cutaneous branches perforate the outer head of the Triceps, 

 at its attachment to the humerus. The upper and smaller one follows the course 

 of the cephalic vein to the front of the elbow, supplying the integument of the 

 lower half of the upper arm on its anterior aspect. The lower branch pierces 

 the deep fascia below the insertion of the Deltoid, and passes down along the 

 outer side of the arm and elbow, and along the back part of the radial side of 

 the forearm to the wrist, supplying the integument in its course, and joining, 

 near its termination, with a branch of the external cutaneous nerve. 



The radial nerve passes along the front of the radial side of the forearm, to 

 the commencement of its lower third. It lies at first a little to the outer side 

 of the radial artery, concealed beneath the Supinator Longus. In the middle 

 third of the forearm, it lies beneath the same muscle, in close relation with the 

 outer side of the artery. It quits the artery about three inches above the wrist, 

 passes beneath the tendon of the Supinator Longus, and, piercing the deep fascia 

 at the outer border of the forearm, divides into two branches. 



The external branch, the smaller of the two, supplies the integument of the 

 radial side and ball of the thumb, joining with the posterior branch of the 

 external cutaneous nerve. 



The internal branch communicates, above the wrist, with a branch from the 

 external cutaneous, and, on the back of the hand, forms an arch with the dorsal 

 branch of the ulnar nerve. It then divides into four digital nerves, which are 

 distributed as follows: The first supplies the ulnar side of the thumb ; the second, 

 the radial side of the index finger; the third, the adjoining sides of the index 

 and middle fingers ; and the fourth, the adjacent borders of the middle and ring 

 fingers. The latter nerve communicates with a filament from the dorsal branch 

 of the ulnar nerve. 



The posterior interosseous nerve pierces the Supinator Brevis, winds to the back 

 of the forearm, in the substance of that muscle, and, emerging from its lower 

 border, passes down between the superficial and deep layer of muscles, to the 

 middle of the forearm. Considerably diminished in size, it descends on the 

 interosseous membrane, beneath the Extensor Secundi Internodii Pollicis, to 

 the back of the carpus, where it presents a gangliform enlargement, from which 

 filaments are distributed to the ligaments and articulations of the carpus. It 

 supplies all the muscles of the radial and posterior brachial regions, excepting 

 the Anconeus, Supinator Longus, and Extensor Carpi Radialis Longior. 



