Off of the Aortic arch; The left sublclavian artery arises and is posterior to the left common carotid artery. It arches laterally toward the axilla in a manner similar to that of the right subclavian artery, where it continues as the left axillary artery. The right and left internal thoracic arteries arise from their respective subclavian arteries at the base of the neck. They run deep to the ribs, just lateral to the sternum to supply blood to the anterior portion of the thorax. The subclavian arteries also supply blood to the upper extremities.