EXTERNAL CUTANEOUS NERVE. 461 



its costal surface. In its course it sends one or two twigs to the 

 deltoid muscle and gives off a branch which forms a loop of com- 

 munication with the posterior branch. The posterior branch passes 

 forward beneath the axillary artery and unites with the communicating 

 branch of the preceding to form a loop, from which numerous branches 

 are given off to the pectoralis major and pectoralis minor. 



The Long thoracic nerve (posterior thoracic, external respiratory of 

 Bell) is a long and remarkable branch arising from the fourth and 

 fifth cervical nerves, immediately after their escape from the inter- 

 vertebral foramina. It passes down behind the plexus and axillary 

 vessels, resting on the scalenus posticus muscle ; it then descends 

 along the side of the chest upon the serratus magnus muscle to its 

 lowest serration. It sends numerous filaments to this muscle in its 

 course. 



The Supra-scapular nerve arises above the clavicle from the fifth 

 cervical nerve and descends obliquely outwards to the supra-scapular 

 notch ; it then passes through the notch, crosses the supra-spinous 

 fossa beneath the supra-spinatus muscle, and passing in front of the 

 concave margin of the spine of the scapula enters the infra-spinous 

 fossa. It is distributed to the supra-spinatus and infra-spinatus muscle. 



The Subscapular nerves are two in number ; of which one arises 

 from the brachial plexus above the clavicle, the others from the poste- 

 rior aspect of the plexus within the axilla. They are distributed to 

 the subscapularis muscle. 



The Inferior muscular nerves are two or three branches which pro- 

 ceed from the lower and back part of the brachial plexus, and are 

 distributed to the latissimus dorsi and teres major. The former of 

 these is the longer, and follows the course of the subscapular artery. 



The terminal branches of the plexus are arranged in the following 

 order : the external cutaneous, and one head of the median to the 

 outer side of the artery ; the other head of the median, internal cuta- 

 neous, lesser internal cutaneous, and ulnar, upon its inner side ; and 

 the circumflex and musculo-spiral behind. 



The EXTERNAL CUTANEOUS NERVE (musculo-cutaneous, perforans 

 Casserii) arises from the brachial plexus in common with the external 

 head of the median ; it pierces the coraco-brachialis muscle and passes 

 between the biceps and brachialis anticus, to the outer side of the 

 bend of the elbow, where it perforates the fascia, and divides into an 

 external and internal branch. The branches pass behind the median 

 cephalic vein, the external, the larger of the two, taking the course of 

 the radial vein and communicating with the branches of the radial 

 nerve on the back of the hand ; the internal and smaller following the 

 direction of the supinator longus, communicating with the internal 

 cutaneous, and at the lower third of the fore-arm sending off a twig, 

 which accompanies the radial artery to the wrist, and distributes 

 filaments to the synovial membranes of the joint. 



The external cutaneous nerve supplies the coraco-brachialis, biceps 



