32 THE SUPERIOR EXTREMITY 



right angle (p. 14), and, when the scapula is fixed by the 

 trapezius and the rhomboids, it acts as an elevator of the ribs. 



The lateral cutaneous branches of the second and third intercostal 

 nerves pierce the medial wall and run laterally across the axilla. 

 They supply the skin over the floor of the axilla and the medial 

 aspect of the arm ; the uppermost is termed the intercosto- 

 brachial (intercosto-humeral) nerve, and it communicates with 

 the medial cutaneous nerve of the arm (lesser internal cutaneous). 

 In malignant disease of the breast intermittent pain may be 

 referred to the medial side of the arm, in the area supplied by 

 these two nerves. It is suggested that this is due to pressure 

 on the intercosto-brachial nerve by enlarged axillary lymph 

 glands ; but the pain is very frequently referred from the 

 irritated sympathetic branches supplying the mammary gland 

 itself. 



The Lateral Wall of the Axilla, to which the 

 important vessels and nerves are closely related, is narrow and 

 is formed by the biceps, the coraco-brachialis, and the proximal 

 part of the humeral shaft. 



The Axillary Sheath is a prolongation of the prevertebral 

 fascia (p. 112) from the neck. It encloses the vessels and 

 nerves (and some of the apical lymph glands), and gradually 

 becomes lost upon them as they pass through the axilla. In 

 malignant disease of the breast, the apical lymph glands are 

 removed, and they may be exposed by resecting a part of the 

 sheath and separating the artery from the vein. 



AXILLARY ARTERY. The course of the axillary artery may 

 be mapped out on the surface by drawing a line from the middle 

 of the clavicle to the medial side of the elevation formed by the 

 coraco-brachialis (p. 38), the limb being abducted to a right 

 angle. The vessel is about six inches long and extends from 

 the outer border of the first rib to the lower border of the 

 teres major. It is conveniently divided into three parts by 

 the pectoralis minor. The First Part lies above the muscle ; 

 the Second, behind the muscle ; the Third, below the muscle. 



The First Part of the axillary artery lies behind the 

 costo-coracoid membrane and the clavicular head of the pectoralis 

 major, and it is crossed by the cephalic and thoraco-acromial 

 veins. Posteriorly, the artery rests on the first intercostal space 

 and the first digitation of the serratus anterior, but it is separated 

 from them by the long thoracic nerve (of Bell), and, usually, 

 the medial cord of the brachial plexus. To the lateral side are 



