THE SHOULDER. 75 



3. The long thoracic, an inconstant branch, which arises above the subscapular (see page 

 95) and is situated in front of the thoracic dorsalis. 



4. The anterior circumflex, a small branch which runs outward over the anterior surface of 

 the neck of the humerus. 



5. The posterior circumflex, a large branch which arises beside the preceding one, passes 

 through the quadrangular space (see page 76) close to the bone to run posteriorly with the cir- 

 cumflex nerve and, like it, to particularly supply the deltoid muscle. As the vessel is closely 

 related to the neck of the humerus, it must be carefully treated in resection of the shoulder- joint. 

 If the operation is strictly subperiosteal, the elevator being always directed toward the bone, the 

 vessel will escape injury. 



The axillary vein, like the subclavian, is situated in front and to the inner side of the artery; 

 it consequently covers the artery to a varying extent, dependent upon the degree of its distention. 

 It is only in exceptional cases that the axillary vein is double. 



Brachial Plexus. Just beneath the clavicle the trunks of the brachial plexus, with the 

 exception of a few small branches, are situated to the outer side of the vessel. Beneath the 

 pectoralis minor muscle these trunks form three cords which are so arranged about this portion 

 of the artery that we may differentiate an outer, an inner, and a posterior cord. The outer and 

 inner cords supply chiefly the skin and muscles of the flexor surface, while the posterior cord 

 supplies the extensor surface. A more detailed study of the axilla shows that the outer cord 

 gives off the musculocutaneous nerve and the outer head of the median. From the inner cord 

 arises the inner head of the median which, together with the outer head, surrounds the axillary 

 artery like the prongs of a fork; the inner cord also gives off the ulnar, the internal cutaneous, and 

 the lesser internal cutaneous nerves. From the posterior cord arise the circumflex, the musculo- 

 spiral, and the subscapular nerves. 



Of the other branches of the brachial plexus there is one which is of particular importance 

 from a surgical standpoint; this is the long thoracic, the motor nerve of the serratus magnus 

 muscle. It lies directly upon the serratus magnus, in association with the thoracicodorsalis 

 artery, and is covered by the edge of the latissimus dorsi ; it is not particularly exposed to injury 

 in operations in the axillary cavity. The comparatively superficial long or middle subscapular 

 nerve running to the latissimus dorsi is more easily injured, and its division is followed by paralysis 

 of this muscle. [Note: The long thoracic nerve is related to the thoracico-dorsal artery only in 

 the lower part of its course; the long (middle) subscapular is in close relation to this vessel. ED.] 

 The other two subscapular nerves supply the teres major and the subscapularis muscles and are 

 more deeply situated. The suprascapular nerve, which runs through the suprascapular notch to 

 the dorsal surface of the scapula and supplies the supraspinatus and infraspinatus muscles, is 

 more rarely divided by the knife of the surgeon; the nerve filaments supplying the levator anguli 

 scapulae and the rhomboid muscles are also rarely injured. 



Posterior Region of the Shoulder. The arrangement of the muscles in this situation 

 forms a typical topographic picture which is of importance for the exposure of the deep vessels 

 and nerves of this region. The deltoid and teres major muscles have been previously described. 

 The supraspinatus muscle arises from the supraspinous fossa; it passes beneath the acromion 

 and the trapezius muscle and is attached to the greater tuberosity of the humerus. The infra- 



