The axillary artery is a major blood vessel that supplies oxygenated blood to the lateral aspect of the thorax, the axilla (armpit), as well as the upper limb. 

This artery lies deep to the pectoralis minor muscle. It is the direct continuation of the subclavian artery, as it passes between the first rib and the clavicle. And the axillary artery continues as the brachial artery below the teres major muscle.

Parts of axillary artery

The axillary artery may be divided into three parts based on its relation to the pectoralis minor muscle, which lies superficial to the artery:

• First part - the segment of the artery that is proximal (superior) to the pectoralis minor muscle;
• Second part - posterior to the pectoralis minor;
• Third part - distal (inferior) to the pectoralis minor.

Branches of axillary artery

On its course, the axillary artery gives off several branches arising from different parts of the artery.

• The first part gives rise to one branch:
  • Superior thoracic artery
• The second part gives off two branches:
  • Thoracoacromial artery
  • Lateral thoracic artery
• Finally, the third part of the axillary artery gives rise to three branches:
  • Subscapular artery
  • Posterior circumflex humeral artery
  • Anterior circumflex humeral artery

At the lower border of the teres major muscle, the axillary artery continues as the brachial artery. 

Relations with other structures

As mentioned, the axillary artery is related to the pectoralis minor muscle, as it travels deep to the muscle.

On its course, the artery is accompanied by the axillary vein, which travels on the medial side of the artery.  

Within the armpit, the axillary artery is surrounded by the brachial plexus.

The artery is enclosed within the axillary sheath, which is a fibrous layer covering the artery and three cords of the brachial plexus.