The third branch of the subclavian artery is the internal thoracic artery (Fig. 8.191). This artery branches from the inferior edge of the subclavian artery and descends.
It passes posterior to the clavicle and the large veins in the region and anterior to the pleural cavity. It enters the thoracic cavity posterior to the ribs and anterior to the transversus thoracis muscle and continues to descend giving off numerous branches.