636 THE VASCULAR SYSTEMS 



The base, directed downward, is formed by the integument and a thick layer of 

 fascia, the axillary fascia (fascia axillaris) (Fig. 348), extending between the lower 

 border of the Pectoral is major in front and the lower border of the Latissimus 

 dorsi behind (page 407). The axilla is broad internally at the thorax, but narrow 

 and pointed externally at the arm. The anterior wall is formed by the Pectoralis 

 major and minor muscles, the former covering the whole of the anterior wall of 

 the axilla, the latter covering only its central part, the costocoracoid membrane, 

 the clavicle, and the Subclavius muscle. The posterior boundary, which extends 

 somewhat lower than the anterior, is formed by the Subscapularis above, the Teres 

 major and Latissimus dorsi below. On the inner side are the first four ribs with 

 their corresponding Intercostal muscles, and part of the Serratus magnus. On 

 the outer side, where the anterior and posterior boundaries converge, the space is 

 narrow, and bounded by the humerus, the Coracobrachialis and Biceps muscles. 



Contents. It contains the axillary yes? els, and the brachial plexus of nerves, 

 with their branches, some branches of the intercostal nerves, and a large number 

 of lymph nodes, all connected by a quantity of fat and loose areolar tissue" 



Position of the Contents. The axillary artery and vein, with the brachial plexus 

 of nerves, extend obliquely along the outer boundary of the axilla, from its apex 

 to its base, and are placed much nearer the anterior than the posterior wall, the 

 vein lying to the inner or thoracic side of the artery and partially concealing 

 it. At the fore part of the axilla, in contact with the Pectoral muscles, and along 

 the anterior margin are the thoracic branches of the axillary artery, and along 

 the lower margin of the Pectoralis minor the long thoracic artery extends to the 

 side of the thorax. At the back part, in contact with the lower margin of the Sub- 

 scapularis muscle, are the subscapular vessels and nerves; winding around the 

 outer border of this muscle is the dorsalis scapulae artery and veins: and, close 

 to the neck of the humerus, the posterior circumflex vessels and the circumflex 

 nerve are seen curving backward to the shoulder. 



Along the inner or thoracic side no vessel of any importance exists, the upper 

 part of the space being crossed merely by a few small branches from the superior 

 thoracic artery. There are some important nerves, however, in this situation 

 viz., the long thoracic or external respiratory nerve, descending on the surface 

 of the Serratus magnus, to which it is distributed; and perforating the upper 

 and anterior part of this wall, the intercostohumeral nerve or nerves, passing 

 across the axilla to the inner side of the arm. 



The cavity of the axilla is filled by a quantity of loose areolar tissue and a large 

 number of small arteries and veins, all of which are, however, of inconsiderable 

 size, and numerous lymph nodes, the position and arrangement of which are 

 described on a subsequent page. 



Applied Anatomy. The axilla is a space of considerable surgical importance. It trans- 

 mits the large vessels and nerves to the upper extremity, and these may be the seat of injury or 

 disease; it contains numerous lymph nodes which may require removal when diseased; in 

 it is a quantity of loose connective and adipose tissue which may be readily infiltrated with blood 

 or pus. The axilla may be the seat of rapidly growing tumors. Moreover, it is covered at its 

 base by thin skin, largely supplied with sebaceous and sweat glands, which is frequently the 

 seat of small cutaneous abscesses and boils, and of eruptions due to irritation. 



In suppuration in the axilla the arrangement of the fasciae plays a very important part in the 

 direction which the pus takes. As described on p. 457, the costocoracoid membrane, after 

 covering in the space between the clavicle and the upper border of the Pectoralis minor, splits 

 to enclose this muscle, and, reblending at its lower border, becomes incorporated with the axillary 

 fascia at the anterior fold of the axilla. Suppuration may take place either superficial to or 

 beneath tnis layer of fascia; that is, either between the Pectorals or beneath the Pectoralis minor; 

 in the former case the pus would point either at the anterior border of the axillary fold or in 

 the groove between the Deltoid and the Pectoralis major; in the latter, the pus would have a 

 tendency to surround the vessels and nerves and ascend into the neck, that being the direction 

 in which there is least resistance. Its progress toward the skin is prevented by the axillary 



