SUPRASCAPULAR NERVE — AXILLARY NERVE 697 



dips into the interstice between that muscle and the long and internal heads of 

 the trice])s. 



8. The axillary or circumflex nerve (N. axillaris) arises behind the musculo- 

 cutaneous. It passes downward and backward on the inner face of the subscapu- 

 laris and disappears between that muscle and the subscapular artery. 



9. Tlu^ long thoracic nerve (X. thoracalis longus) is wide and thin. It passes 

 l)a('kward across the surface of the serratus magnus, to which it is distriluited. 

 The branches which enter the muscle are given off both upward and downward in 

 fairly regular fashion. 



10. The thoraco-dorsal nerve (X. thoracodorsalis) passes upward and back- 

 ward across the subscai)ularis nniscle to ramify in the teres major and the latissimus 

 dorsi. 



11. The external (or sujjcutaneous) thoracic nerve arises by a common trunk 

 with the ulnar. It runs backward and downward across the inner face of the tensor 

 fasciae antibrachii, communicates with the anterior pectoral branches, and gives 

 twigs to the tleep pectoral nniscle. It then runs backward in company with the 

 external thoracic or "spur" vein, gives branches to the latissimus dorsi and the 

 deep pectoral, and ramifies in the panniculus and the skin of the abdominal wall. 

 It communicates with perforating branches of the intercostal nerves. A branch 

 from it, accomjxuiied by a large perforating intercostal l^ranch, winds around 

 the lower border of the latissinms dorsi and ramifies in the panniculus on the outer 

 surface of the arm. 



The term posterior thoracic or pectoral nerves (Xn. pectorales caudales) maj^ be used to 

 include S, 9, and 10. 



Suprascapular Nerve 



The suprascapular (Fig. 441 j is a large nerve derived chiefly, if not exclusively, 



from the sixth and seventh cervical components of the brachial plexus. It passes 



between the suj^raspinatus and subscapularis nmscles and turns around the distal 



fourth of the anterior border of the scapula to reach the supraspinous fossa. It 



gives branches to the supraspinatus and continues backward and upward into the 



infraspinous fossa, where it supplies the infraspinatus, deltoid, and teres minor 



muscles. 



The direct relation of this nerve to the scapula renders it liable to injury, the result of wliieh 

 maj' be paralysis and atrophy of the muscles suppHed by it. 



HUSCULO-CUTANEOUS NeRVE 



The musculo-cutaneous nerve (Fig. 441) arises close behind the suprascapular, 

 and is derived chiefly from the part of the brachial plexus which is supplied by the 

 seventh and eighth cervical nerves. It descends across the outer surface of the 

 brachial artery, below which a great part of the nerve unites with the median to 

 form the loop previously mentioned. It gives off a branch which enters the upper 

 part of the belly of the coraco-brachialis, passes downward and forward between the 

 two parts of that muscle or between the muscle and the bone, and divides into 

 branches which enter the biceps brachii. It contributes one of the nerves to the 

 pectoral muscles. In some cases this nerve sends a branch to join the cutaneous 

 branch of the median. 



Axillary Nerve 



The axillary nerve (Figs. 441, 520), also termed the circumflex, derives its 

 fibers from the eighth cervical and first thoracic roots of the brachial plexus. It 

 runs downward and backward across the lower part of the subscapularis and dips 

 in between that muscle and the subscapular artery at the level of the shoulder joint. 

 Continuing outward in the interval between the teres minor and the long and ex- 

 ternal heads of the triceps, it reaches the deep face of the deltoid and divides into 



