The structure indicated is the left subclavian artery.

The subclavian arteries are located under (“sub”) the clavicle (“clavian”) and receive blood from the aortic arch. The subclavian arteries supply the arms, with some branches that extend to supply the head.

The branches of the aortic arch are:

• Brachiocephalic artery
• Left common carotid artery
• Left subclavian artery

The left subclavian artery comes directly off the arch of the aorta, whereas on the right side of the body, the brachiocephalic artery splits, giving rise to the right subclavian artery, and the right common carotid artery.

The subclavian artery becomes the axillary artery at the lateral border of the first rib. It can be thought of in three parts, and gives rise to several branches:

• First part: vertebral artery, internal thoracic artery, thyrocervical trunk
• Second part: costocervical trunk
• Third part: dorsal scapular artery