What is the axilla?

What it is

• The axilla is a pyramidal space, situated between the upper lateral part of the chest and the medial side of the arm. Boundaries. —The apex, which is directed upward toward the root of the neck, corresponds to the interval between the outer border of the first rib, the superior border of the scapula, and the posterior surface of the clavicle, and through it the axillary vessels and nerves pass.
• The base, directed downward, is broad at the chest but narrow and pointed at the arm; it is formed by the integument and a thick layer of fascia, the axillary fascia, extending between the lower border of the Pectoralis major in front, and the lower border of the Latissimus dorsi behind. The anterior wall is formed by the Pectorales major and minor, the former covering the whole of this wall, the latter only its central part.
• The space between the upper border of the Pectoralis minor and the clavicle is occupied by the coracoclavicular fascia. The posterior wall, which extends somewhat lower than the anterior, is formed by the Subscapularis above, the Teres major and Latissimus dorsi below. On the medial side are the first four ribs with their corresponding Intercostales, and part of the Serratus anterior.
• On the lateral side, where the anterior and posterior walls converge, the space is narrow, and bounded by the humerus, the Coracobrachialis, and the Biceps brachii. Contents. —It contains the axillary vessels, and the brachial plexus of nerves, with their branches, some branches of the intercostal nerves, and a large number of lymph glands, together with a quantity of fat and loose areolar tissue.
• The axillary artery and vein, with the brachial plexus of nerves, extend obliquely along the lateral boundary of the axilla, from its apex to its base, and are placed much nearer to the anterior than to the posterior wall, the vein lying to the thoracic side of the artery and partially concealing it.
• At the forepart of the axilla, in contact with the Pectorales, are the thoracic branches of the axillary artery, and along the lower margin of the Pectoralis minor the lateral thoracic artery extends to the side of the chest.