THE AXILLARY ARTERY. 529 



the dorsal is 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 feAv small branches from the superior 

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

 viz. the posterior thoracic or external respiratory nerve, descending on the sur- 

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

 and anterior part of this wall, the intercosto-humeral 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 lymphatic glands, the position and arrangement of which are 

 described on a subsequent page. 



Surgical 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 lymphatic glands 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 inflammatory exudation, and it 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 fre- 

 quently 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 page 379, the costo-coracoid 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. This is known as the clavi-pectoral fascia. Suppura- 

 tion may take place either superficial to or beneath this layer of fascia; that is, either between 

 the Pectorals or below the Pectoralis minor : in the former case, it would point either at the ante- 

 rior border of the axillary fold or in the groove between the Deltoid and the Pectoralis major ; 

 iu 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 fascia; its progress backward, by the Serratus magnus ; forward, 

 by the clavi-pectoral fascia ; inward, by the wall of the thorax ; and outward, by the upper limb. 

 The pus in these cases, after extending into the neck, has been known to spread through the 

 superior opening of the thorax into the mediastinum. 



In opening an axillary abscess the knife should be entered in the floor of the axilla, midway 

 between the anterior and posterior margins and near the thoracic side of the space. It is well 

 to use a director and dressing forceps after an incision has been made through the skin and 

 fascia in the manner directed by the late Mr. Hilton. 



The student should attentively consider the relation of the vessels and nerves in the several 

 parts of the axilla, for it is the almost universal plan, in the present day, to remove the glands 

 from the axilla in operating for cancer of the breast. In performing such an operation it will be 

 necessary to proceed with much caution in the direction of the outer wall and apex of the space, 

 as here the axillary vessels will be in danger of being wounded. Toward the posterior wall it 

 will be necessary to avoid the subscapular, dorsalis scapulae, and posterior circumflex vessels. 

 Along the anterior wall it will be necessary to avoid the thoracic branches. In clearing out the 

 axilla the axillary vein should be first defined and cleared by the fingers and an elevator up to 

 the apex of the axilla, the Pectoralis major being pulled up by an assistant with a retractor. 

 When the apex of the space is reached, all fat and glands must be carefully removed and the 

 whole axilla cleared by separating the tissues along the inner and posterior walls, so that when 

 the proceeding is completed, the axilla is cleared of all its contents except the main vessels and 

 nerves. 



THE AXILLARY ARTERY. 



The Axillary Artery, the continuation of the subclavian, commences at the 

 outer border of the first rib, and terminates at the lower border of the tendon of 

 the Teres major muscle, where it takes the name of brachial. Its direction varies 

 with the position of the limb : when the arm lies by the side of the chest, the 

 vessel forms a gentle curve, the convexity being upward and outward ; when it is 

 directed at right angles with the trunk, the vessel is nearly straight ; and when 

 it is elevated still higher, the artery describes a curve the concavity of which is 

 directed upward. At its commencement the artery is very deeply situated, but 

 near its termination is superficial, being covered only by the skin and fascia. The 

 description of the relations of this vessel is facilitated by its division into three 



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