Lymphatic glands are found in great num bers in the axilla ; some are scattered over the internal wall, but there the majority of them will be found in a chain along with the external mammary, or thoracica longior artery. On the posterior wall they form a chain also, in the course of the subscapular vessels. Some will be seen above the lesser pectoral, and several along the axillary vein. Round this last vein we see numerous lymphatic vessels twining.
When the clavicle has been detached from its connexion with the trunk, and along with the scapula raised from the side, the serratus magnus may be seen to form the greater part of the internal wall, but extending far below it. This is a flat irregularly quadrilateral muscle ; one surface of it is in contact with the side of the thorax ; the other, looking externally, touches the subscapular muscle, the axillary vessels and nerves, the two pectorals, the latissimus dorsi, and the integuments. The anterior edge pre sents a convexity forwards, and consists of digi tations or fleshy slips which arise from the first eight or nine ribs. The fibres all run back to the posterior margin of the scapula, along the whole of which they are inserted.
The thoracic surface of the muscle, which may be seen by cutting through the trapezius and rhomboid muscles, and pulling out the base of the scapula from the ribs, rests on loose cellular tissue, which connects it with the ribs, intercostal muscles, and serratus pos ticus superior.
The posterior wall of the axilla is formed by the subscapular muscle, the tercs major and the Ltissimus dorsi, to which the long head of the triceps may be added. Along the inferior margin of the subscapular muscle, the subsca pular artery runs. This is a vessel of considerable size, and deserves the attention of the surgeon. It arises from the axillary artery at the tendon of the subscapular muscle, and passes all along the inferior or anterior edge of this muscle to the inferior angle of the scapula, where it ter minates by branches which supply the muscles connected with that point. The teres major is a long, flat muscle, strap-shaped, one inch and a half or two in breadth, extending from the inferior angle of the scapula, to the poste rior margin of the bicipital groove of the hu merus. Its lower edge is in part covered by the latissimus dorsi and then by the inte guments, and forms, principally, the poste rior fold of the axilla. The posterior surface is covered by the latissimus, nearer the arm by the integuments, and then by the long head of the triceps and the humerus. Its anterior sur
face corresponds to the subscapular, latissimus, coraco-brachialis, biceps, and the axillary ves sels and nerves.
The latissimus dorsi forms a very small part of the axilla ; we see it passing over the inferior angle of the scapula and twisting round the teres major, so that its posterior surface be comes anterior, and the tendon in which it ends gets internal to that of the teres. Its edge does not go quite so low as that of the teres major, but, except there, it prevents that muscle from touching the axillary vessels. It is some times connected to the great pectoral by a fleshy slip which passes across the axilla.
The axilla has all the conditions which ex pose a part to frequent disease ; a position which puts it in the way of many external injuries ; an important joint closely related to it; hones, liable to fracture ; arteries, veins, and nerves of great size ; numerous lymphatic glands, connected with the most delicate parts of the body, lying in it ; and then a quantity of cellular tissue, loose, vascular, and con stantly undergoing alterations.
To the observations made on these points in the course of the present article, we shall now make a few additions.
Wounds penetrating into the axilla endanger the nerves, artery, and vein, if inflicted near the humerus below, or close to the clavicle above. In the latter situation, as mentioned before, they may give rise to aneurismal varix. At the lower margin of the anterior wall the external mammary artery may be injured, and along the inferior border of the posterior wall the subscapular vessels lie exposed.
The shoulder-joint is more liable to disloca tion than any other in the body, and in most cases the head of the humerus comes into the axilla. The great vessels and nerves are dis placed inwards, the circumflex vessels and nerve often torn. The head Of the humerus lies just below the subscapular muscle, and forms a tumour in the axilla easily felt from below. (See ARTICULATIONS OF THE.) The neck of the humerus is often broken above the insertion of the arm-pit muscles. The lower fragment is drawn inwards by them and upwards by the deltoid, whilst the supra spinatus directs the upper fragment out. In this state of things the rough extremity of the lower piece irritates, perhaps lacerates the ves sels and nerves, and if not properly managed leaves a permanent osseous tumour in the axilla.