MUSCULO-SPIRAL PiERVE. 4)9 



distributed, one to the ulnar side of the little finger, one to the adjoining 

 borders of the little and ring fingers, and a communicating branch to joiu 

 Ihe median nerve. 



The Deep palmar branch passes between the abductor and flexor 

 minimi digiti, to the deep palmar arch, supplying the muscles of the little 

 finger, and the interossei and other deep structures in the palm of the 

 hand. 



The MUSCULO-SPIRAL NERVE, the largest branch of the brachial plexus, 

 arises from the posterior part of the plexus by a common trunk with the 

 circumflex nerve. It passes downwards from its origin in front of the 

 tendons of the latissimus dorsi and teres major muscle, and winds around 

 the humerus in the spiral groove, accompanied by the superior profunda 

 artery, to the space between the brachialis anticus and supinator longus, 

 and thence onwards to the bend of the elbow, where it divides into two 

 branches, the posterior interosseous and radial nerve. 



The Branches of the musculo-spiral nerve are 



Muscular, Spiral cutaneous, 



Radial, Posterior interosseous. 



The Muscular branches are distributed to the triceps, to the supinator 

 longus, and to the extensor carpi radialis longior. 



The Spiral cutaneous nerve pierces the deep fascia immediately below 

 the insertion of the deltoid muscle, and passes down the outer side of the 

 fore-arm as far as the wrist. It is distributed to the integument. 



The Radial nerve runs along the radial side of the fore-arm to the com- 

 mencement of its lower third ; it then passes beneath the tendon of the 

 supinator longus, and at about two inches above the wrist joint pierces 

 the deep fascia, and divides into an external and an internal branch. 

 The external branch, the smaller of the two, is distributed to the outer 

 border of the hand and thumb, and communicates with the posterior 

 branch of the external cutaneous nerve. The internal branch crosses the 

 direction of the extensor tendons of the thumb, and divides into several 

 filaments for the supply of the ulnar border of the thumb, the radial border 

 of the index finger, and the adjoining borders of the index and middle 

 fingers. It communicates on the back of the hand with the dorsal branch 

 of the ulnar nerve. 



In the upper third of the fore-arm 1 the radial nerve lies beneath the 

 border of the supinator longus muscle. In the middle third it is in rela- 

 tion with the radial artery lying to its outer side. It then quits the artery, 

 and passes beneath the tendon of the supinator longus, to reach the back 

 of the hand. 



The Posterior interosseous nerve, somewhat larger than the radial, sepa- 

 rates from the latter at the bend of the elbow, pierces the supinator brevis 

 muscle, and emerges from its lower border on the posterior aspect of the 

 fore-arm, where it divides into branches which supply the whole of the 

 muscles on the posterior aspect of the fore-arm. One branch, longer than 

 the rest, descends to the posterior part of the wrist, and forms a large 

 gangliform swelling (the common character of nerves which supply joints) 

 from which numerous branches are distributed to the wrist joint 



