CIRCUMFLEX NERVE DORSAL NERVES. 413 



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 separates from the radial 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. 



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 cuta- 

 neous. The Muscular branches are distributed to the subscapularis, 

 teres minor, teres major, latissimus dorsi, and deltoid. The cuta- 

 neous branches pierce the deltoid muscle and are distributed to the 

 integument of the shoulder. One of these cutaneous branches, 

 larger than the rest, winds around the posterior border of the del- 

 toid, 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 vertebra, and the last 

 between the twelfth dorsal and first lumbar. Each nerve, as soon 

 as it has escaped from the intervertebral foramen, divides into two 

 branches ; a dorsal branch and the true intercostal nerve. 



The Dorsal branches pass directly backwards between the trans- 

 verse processes of the vertebrae, lying internally to the anterior 

 costo-transverse ligament, where each nerve divides into a muscular 

 and a musculo-cutaneous branch. The muscular branch enters the 

 substance of the muscles in the direction of a line corresponding 

 with the interval of separation between the longissimus dorsi and 

 sacro-lumbalis, and is distributed to the muscles of the back. The 

 musculo-cutaneous branch passes inwards, crossing the semispinalis 



