SUPRASCAPULAR NERVE—MUSCULO-CUTANEOUS NERVE 815 
trunk. It descends behind the brachial artery and is accompanied a short distance 
by the radial nerve, from which it can be distinguished by its smaller size. 
7. The radial nerve (N. radialis) arises from the posterior part of the plexus 
and is sometimes the largest branch. It descends with the ulnar nerve over the 
medial face of the origin of the subscapular artery and the lower part of the teres 
major and dips into the interstice between that muscle and the long and 
medial heads of the triceps. 
8. The axillary nerve (N. axillaris) arises behind the musculo-cutaneous. It 
passes downward and backward on the medial face of the subscapularis and dis- 
appears between that muscle and the subscapular artery. 
9. The long thoracic nerve (N. thoracalis longus) is wide and thin. It arises 
from the anterior end of the plexus, gives off (usually) three branches to the ser- 
ratus ventralis at the Junction of its cervical and thoracic parts, and passes back- 
ward across the surface of the serratus thoracis, 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 (N. thoracodorsalis) passes upward and back- 
ward across the subscapularis muscle to ramify in the latissimus dorsi. 
11. The external thoracic nerve (N. thoracalis lateralis) arises by a common 
trunk with the ulnar. It passes backward and ventrally across the medial surface of 
the humeral tendon of the cutaneus muscle, and continues backward in company with 
the external thoracic vein. Its terminal branches ramify in the cutaneus and the 
skin of the abdominal wall as far back as the flank. It gives collateral branches 
to the deep pectoral muscle and others which anastomose with perforating branches 
of intercostal nerves. A branch from it, accompanied by a large perforating inter- 
costal branch, winds around the ventral border of the latissimus dorsi and ramifies 
in the cutaneus on the lateral surface of the arm. 
The term posterior thoracic or pectoral nerves (Nn. pectorales caudales) may be used to 
include 9, 10, and 11. 
SUPRASCAPULAR NERVE 
The suprascapular nerve (Fig. 566), short but large, is usually 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 supra- 
spinous fossa. It gives branches to the supraspinatus and continues backward 
and upward into the infraspinous fossa, and terminates in several branches which 
innervate the infraspinatus. 
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. There is, however, a small tendinous 
band which extends over the nerve as it turns around the edge of the scapula. 
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MUSCULO-CUTANEOUS NERVE 
The musculo-cutaneous nerve (Fig. 566) 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 lateral 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 proxi- 
mal part of the belly of the coraco-brachialis, passes downward and forward in 
company with the anterior circumflex vessels 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. 
