512 NERVES OF THE ARM. 



The seventh cervical is joined by the first dorsal, which pro- 

 ceeds iijjwards, and unites with it at a short distance from the 

 spine. The cord produced by their junction soon unites with 

 one of the cords above described. As these different cords pro- 

 ceed downwards, they divide, and their branches again unite. 

 The axillary artery, which passes in the same direction, is sur- 

 rounded by them. In this manner the axillary plexus is com- 

 monly formed. 



The muscles about the shoulder, both before and behind are 

 supplied by the axillary plexus. Thus, it sends two branches 

 called the Short Thoracic to the Suh-scapularis, Teres Major, 

 and Latissimiis Dorsi, behind ; and to the Pectoralis Major 

 and Minor and the Mammary Gland. It also sends off a branch 

 called the Supra-Scapular or Scapularis, which commonly arises 

 from the upper part of the plexus, and proceeds through the 

 notch in the upper costa of the scapula to the supra and infra 

 spinatus, teres minor, he. 



— Three or four small branches called Sub-Scapular, go to the 

 muscle of that name. An important branch called the Long 

 thoracic, or external respiratory of Sir Charles Bell, arises high 

 up in the plexus from the fourth and fifth cervical nerves and 

 descends along the side of the chest over the serratus major 

 amicus muscle to which it is distributed. — 



Nerves of the Arm. 



All the great nerves of the arm are derived from the axillary 

 plexus. There are six of them, which are denominated The 

 Musculo- Cutaneus ; The Median;* The Cubital, or Ulnar; 



the superficial palmar. 15. The ulnar nerve giving off several muscular 

 branches to the triceps which have received no name. IG. The point at which 

 it passes between the two heads of the flexor carpi ulnaris. 17. Its dorsal 

 branch. 18. The termination of the nerve dividing into a superficial and deep 

 palmar branch. 19. The musculo-spiral nerve. 20. Muscular branches of 

 this nerve. 21. Spiral cutaneous nerve. 22. Posterior interosseous nerve, 

 piercing the supinator brevis muscle. 23. The radial nerve. The two last 

 nerves are the terminal branches of the musculo-spiral. 24. The point at 

 which the radial nerve pierces the deep fascia. 25. The circumflex nerve of 

 the shoulder joint. 



* Sometimes called Brachial. 



