466 CIRCUMFLEX NERVE. DORSAL NERVES. 



commencement 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 the radial nerve lies beneath the 

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

 relation 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, 

 separates from the latter at the bend of the elbow, pierces the supina- 

 tor 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 distri- 

 buted to the wrist-joint. 



The CIRCUMFLEX NERVE arises from the posterior part of the 

 brachial plexus by a common trunk with the musculo-spiral nerve. It 

 passes downwards over the border of the subscapularis muscle, winds 

 around the neck of the humerus with the posterior circumflex artery, 

 and terminates by dividing into numerous branches which supply the 

 deltoid muscle. 



The Branches of the circumflex nerve are muscular and cutaneous. 

 The Muscular branches are distributed to the subscapularis, teres 

 minor, teres major, latissimus dorsi, and deltoid. The cutaneous 

 branches pierce the deltoid muscle and are distributed to the integu- 

 ment of the shoulder. One of these cutaneous branches (cutaneus 

 brachii superior), larger than the rest, winds around the posterior bor- 

 der of the deltoid, and divides into filaments which pass in a radiating 

 direction across the shoulder and are distributed to the integument. 



DORSAL NERVES. 



The dorsal nerves are twelve in number on each side; the first 

 appears between the first and second dorsal vertebrae, and the last 

 between the twelfth dorsal and first lumbar. They are smaller than 

 the lower cervical nerves, and diminish gradually in size from the first 



