The axillary artery is the direct continuation of the subclavian artery. It begins at the lateral border of the 1st rib and ends at the inferior border of teres major, where it continues as the brachial artery. The pectoralis minor divides the axillary artery into three parts.
First Part
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The First Part of the Axillary Artery is located between the lateral border of the first rib and the superomedial border of the pectoralis minor. This segment is enclosed in the axillary sheath along with the cords of the brachial plexus. The axillary vein lies anteromedial and superficial to the sheath.
The first part of the axillary artery has one branch, the superior (or supreme) thoracic artery, which helps supply the first and second intercostal spaces and the superior part of the serratus anterior. It is small and variable in appearance.
The Second Part of the Axillary Artery lies deep to the pectoralis minor and has two branches: the thoracoacromial trunk and lateral thoracic artery. Its origin is variable, but often from the 2nd part of the axillary artery.
The thoracoacromial artery divides into four branches: acromial, deltoid, pectoral, and clavicular. The lateral thoracic artery supplies the lateral pectoral region, serratus anterior, and lateral breast*. The lateral thoracic artery typically runs along the superficial surface of the serratus anterior muscle with the long thoracic nerve.
The Third Part of the Axillary Artery rests lateral to the pectoralis minor and medial to the teres major. This segment has three branches: subscapular, anterior circumflex humeral (smaller), and posterior circumflex humeral (larger) arteries.
The subscapular artery ends by bifurcating into the circumflex scapular and thoracodorsal arteries. The circumflex scapular artery passes around the lateral border of the scapula to supply muscles on the dorsum of the scapula. The thoracodorsal artery supplies the latissimus dorsi muscle.
The anterior and posterior circumflex humeral arteries pass around the surgical neck of the humerus. The posterior circumflex humeral artery passes through the posterior wall of the axilla via the quadrangular space with the axillary nerve to supply the deltoid and glenohumeral (shoulder) joint. Clinical pearl: the posterior circumflex humeral artery is the key vessel in surgical neck fractures and quadrangular space pathology.
The Branches of Axillary Artery are named according to their distribution rather than their somewhat variable origin. There are extensive arterial anastomoses around the scapula. The surgical importance of the collateral circulation becomes apparent during ligation of an injured axillary or subclavian artery.
If the axillary artery is ligated proximal to the subscapular artery, collateral channels can perfuse the distal segment. Note that the subscapular artery receives blood via several anastomoses with the suprascapular artery, dorsal scapular artery (or deep transverse cervical artery), and intercostal arteries. Ligation of the axillary artery distal to the subscapular artery risks ischemia to the arm.
