SUPRASCAPULAR NERVE — AXILLARY NERVE 697 



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

 the triceps. 



8. The axillary or circumflex nerve (N. axiharis) arises beliind the nnisculo- 

 cutaneoiis. It jiasses downward and l)ackward on the inner face of the suljscapu- 

 laris and disappears Ijetween that muscle and the subscapular artery. 



9. The long thoracic nerve (N. thoracalis longus) is wide and thin. It passes 

 backward across the surface of the serratus magnus, to which it is distributed. 

 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 u]:>ward and back- 

 ward across the suliscapularis muscle to ramify in the teres major and the latissimus 

 dorsi. 



11. The external (or subcutaneous) thoracic nerve arises by a conunon trunk 

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

 fascia? antibrachii, communicates with the anterior pectoral Ijranches, and gives 

 twigs to the deep pectoral muscle. 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, accompanied l^y a large perforating intercostal branch, winds around 

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

 surface of the arm. 



The term posterior thorarie or pectoral rer-^Ts (Xn. pectorales caudales) may be used to 

 include 8, 9, and 10. 



Suprascapular Kerve 



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



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



between the supraspinatus and subscapularis muscles 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 upAvard 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 which 

 may be paralysis and atrophy of the muscles supplied 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 doAvnward 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 clips 

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

 Continuing outward in tlu^ 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 



