Axillary artery: the artery in the armpit, its three parts and six branches

What it is

The axillary artery is the main artery of the armpit, continuing the subclavian artery.

Location

It begins at the lateral border of the first rib and ends at the lower border of teres major, where it becomes the brachial artery. It is divided into three parts by pectoralis minor, and its branches are the superior thoracic, thoracoacromial, lateral thoracic, subscapular and the anterior and posterior circumflex humeral arteries.

Function

It supplies the shoulder, chest wall and upper arm.

Body system

Cardiovascular · paired (left and right)

FMA ID

FMA22656 (Foundational Model of Anatomy)

Key facts

• Its branches give the scapular and shoulder anastomoses.
• Its first part has one branch, its second part two and its third part three (superior thoracic; thoraco-acromial and lateral thoracic; subscapular and the two circumflex humeral arteries).

Clinical relevance

Injury or blockage near the shoulder can threaten blood flow to the whole arm.

The subclavian artery is renamed the axillary artery at the lateral (outer) border of the first rib, as it passes behind the middle of the clavicle into the axilla. (Radiopaedia: Axillary artery.)

From there it descends through the axilla behind the axillary vein, behind pectoralis minor and in front of teres major. It ends at the lower border of teres major, where it becomes the brachial artery. (Radiopaedia: Axillary artery.)

It lies inside a sleeve of fascia called the axillary sheath, deep to pectoralis minor, and it is the main artery supplying the upper limb. (TeachMeAnatomy: Arterial Supply to the Upper Limb.)

The subclavian artery that leads into it comes from the brachiocephalic trunk on the right and straight from the arch of the aorta on the left, so the two axillary arteries have different origins but the same course. (Radiopaedia: Subclavian artery.)

The axilla is a pyramid-shaped space between the upper arm and the chest wall. Its apex, the axillary inlet, is bounded by the clavicle in front, the first rib medially and the upper border of the scapula behind; the axillary artery enters through this opening. (TeachMeAnatomy: The Axilla.)

The anterior wall is formed by pectoralis major, pectoralis minor and subclavius. The posterior wall is subscapularis, teres major and latissimus dorsi. The medial wall is serratus anterior over the ribs, and the narrow lateral wall is the intertubercular groove of the humerus with coracobrachialis and the short head of biceps. (TeachMeAnatomy: The Axilla.)

The axillary vein, the main vein of the limb, runs through the same space. It forms at the lower border of teres major from the brachial and basilic veins and climbs through the axilla on the medial side of the artery to become the subclavian vein at the first rib. (Radiopaedia: Axillary vein.)

Pectoralis minor crosses in front of the artery and is used to divide it into three parts. The first (suprapectoral) part runs from the lateral border of the first rib to the upper border of pectoralis minor. The second (retropectoral) part lies behind pectoralis minor. The third (infrapectoral) part runs from the lower border of pectoralis minor to the lower border of teres major. (Radiopaedia: Axillary artery.)

A useful rule is that the number of the part equals the number of its branches: the first part gives one branch, the second two and the third three. Real arteries often break this rule, as described under variants below. (Radiopaedia: Axillary artery.)

The cords of the brachial plexus are named after their position around the second part of the axillary artery: the lateral cord lies lateral to it, the medial cord medial to it and the posterior cord behind it. (Radiopaedia: Axillary artery.)

Around the first part the lateral and posterior cords lie above and lateral to the artery and the medial cord lies behind it, with a nerve loop joining the medial and lateral pectoral nerves in front. Around the third part the cords have already divided into the nerves of the limb. (Radiopaedia: Axillary artery.)

This close packing explains why disease of the artery affects the nerves. An axillary artery aneurysm, a dilatation to more than twice the normal width, can press on the brachial plexus and cause pins and needles and weakness in the arm; it is treated surgically by removing the dilated segment and inserting a graft. (TeachMeAnatomy: Arterial Supply to the Upper Limb.)

The brachial plexus and the nerves of the arm, forearm and hand. Nerves of the upper limb.

First part: the superior thoracic artery, a small branch that runs forwards to the two pectoral muscles. (Radiopaedia: Axillary artery.)

Second part: the thoraco-acromial artery runs over pectoralis minor, pierces the clavipectoral fascia and splits into four terminal branches that supply the clavicle, the acromion, deltoid and the pectoral muscles. The lateral thoracic artery follows the lower border of pectoralis minor and supplies serratus anterior and the pectoral muscles; in women it is an important blood supply to the breast. (Radiopaedia: Axillary artery.)

Third part: the subscapular artery is the largest branch of the axillary artery. It divides into the thoracodorsal artery, which travels with the thoracodorsal nerve to latissimus dorsi, and the circumflex scapular artery, which joins the anastomosis around the scapula. (Radiopaedia: Axillary artery.)

Third part, continued: the anterior circumflex humeral artery winds round the front of the surgical neck of the humerus and sends an ascending branch to the humeral head. The posterior circumflex humeral artery passes backwards through the posterior wall of the axilla with the axillary nerve, supplies deltoid, triceps and the shoulder joint, and is the dominant supply to the humeral head. (Radiopaedia: Axillary artery.)

The posterior circumflex humeral artery leaves the axilla through the quadrangular space, a gap in the posterior wall of the axilla. (TeachMeAnatomy: The Axilla.)

The two circumflex humeral arteries join around the surgical neck of the humerus, and a fracture there can damage them. (TeachMeAnatomy: Arterial Supply to the Upper Limb.)

Radiopaedia describes the branching of the axillary artery as highly variable. Recorded patterns include a common trunk for the lateral thoracic and subscapular arteries, for the subscapular and posterior circumflex humeral arteries, for the two circumflex humeral arteries, or for the thoraco-acromial and lateral thoracic arteries. (Radiopaedia: Axillary artery.)

Other variants are a subscapular artery arising from the second part, a lateral thoracic artery that is absent and replaced by branches of the intercostal arteries, an extra alar thoracic artery to the fat, skin and lymph nodes of the axilla, and an early division into radial and ulnar arteries within the axilla. (Radiopaedia: Axillary artery.)

The search term "axis artery" belongs to embryology. Each upper limb of the embryo is supplied by an axis artery derived from the seventh intersegmental (subclavian) artery; its main trunk becomes the axillary and brachial arteries, and parts persist as the anterior interosseous artery and the deep palmar arch. (Tsoucalas G et al. High Bifurcation of the Brachial Artery: An Embryological Overview. Cureus. 2020.)

At the apex of the axilla the artery, vein and nerves pass between the clavicle, the first rib and the scapula. They can be squeezed there, after a clavicle fracture, with repetitive arm movements or with a cervical rib, causing thoracic outlet syndrome: pain, tingling, weakness and colour change in the arm. Holding the arm overhead can narrow these passages in susceptible people. (TeachMeAnatomy: The Axilla.)

The axilla also contains the lymph nodes that receive about 75% of the lymph from the breast. These nodes may be biopsied or removed (axillary clearance) in breast cancer, and the operation can injure the long thoracic nerve and cause a winged scapula. (TeachMeAnatomy: The Axilla.)

Double axillary veins occur in about 14% of people, and the lower vein of the pair can be injured during axillary dissection for breast cancer. (Radiopaedia: Axillary vein.)

OpenStax places the axillary artery in the main arterial route to the arm: subclavian, axillary, brachial, then radial and ulnar arteries. Every artery further down the limb depends on it. (OpenStax Anatomy and Physiology 2e, 20.5: Circulatory Pathways.)

The nearest named structures in the 3D model, measured from the centre of each part:

• Axillary vein · cardiovascular
• Clavicular part of pectoralis major · muscular
• Subscapular artery · cardiovascular
• Acromial branch of thoraco-acromial artery · cardiovascular
• Deltoid branch of thoraco-acromial artery · cardiovascular
• Trunk of thoraco-acromial artery · cardiovascular
• Circumflex scapular artery · cardiovascular
• Clavicular part of deltoid · muscular
• Suprascapular artery · cardiovascular
• Pectoral branch of thoraco-acromial artery · cardiovascular