This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The axillary artery and vein are both important. The avoidance of hemorrhage in operations in this locality requires skill and knowledge, and venous bleeding is more apt to be troublesome than arterial. Wounds of the vessels, whether artery or vein, of those portions of the body like the axillae, groins, or base of the neck are particularly dangerous; the blood current is both large and rapid.
The axillary vein drains the whole upper extremity and part of the chest, while the axillary artery carries all the blood going to those parts. The veins being so much weaker and thinner walled than the arteries is the reason of their being more frequently injured. Ligation of the artery, or vein, or both, may cause gangrene of the extremity and require amputation.
The axillary artery begins at the lower border of the first rib and ends opposite the lower border of the folds of the axilla (teres major). If the arm is lying by the side of the body the artery describes a curve with its 17 convexity outward. If the arm is placed straight out away from the body, the artery is straight. If the arm is abducted above the level of the shoulder, the artery again becomes curved but with its convexity downward.
The line of the artery is straight only when the arm is out from the body, when its course is represented by a line drawn from the middle of the clavicle to the anterior surface of the elbow, midway between the two condyles. It passes down along the inner side of the coracoid process and the coracobrachialis muscle about at the junction of the anterior and middle thirds of the axilla. It is divided into three parts by the pectoralis minor muscle (Fig. 270).
The first portion of the axillary is usually stated to be 2.5 cm. (1 in.) in length, and for surgical purposes we may accept this as a working basis.
A. H. Young has pointed out that, with the arm out from the body, the upper border of the pectoralis minor is nearly or quite level with the lower border of the first rib, but the muscle leaves the side of the chest to go to the coracoid process and that makes an interspace, more than 2.5 cm. long, above its upper edge and between it and the lower edge of the subclavius muscle, in which the artery can be ligated. In the first portion the axillary artery above the pectoralis minor lies too deep to be compressed, being on a lower level than the pectoralis major, therefore it is better to compress the subclavian above the clavicle.
Fig. 270. - Line indicating the course of the axillary artery.
The first portion of the axillary gives off two branches, the superior thoracic and the acromiothoracic (thoraco-acromialis) (Fig. 271).
The superior thoracic comes off posteriorly and winds around behind the axillary vein to supply the under surface of the pectoralis minor, intercostal muscles, serratus anterior, and side of the chest. It is a small vessel.
The acromiothoracic (thoraco-acromialis) is a short large trunk which comes off anteriorly, winding around the edge of the pectoralis minor and piercing the costo-coracoid membrane to divide into four branches: an acromial, to the acromion process; a humeral, which follows the cephalic vein between the deltoid and pectoralis major; a pectoral, which supplies the under surface of the pectoralis major and gives branches to the mammary gland; and a clavicular, to supply the subclavius muscle.