Internal thoracic a.

The internal thoracic artery (ITA), previously known as the internal mammary artery, is an artery that supplies the anterior chest wall and the breasts. It is a paired artery, with one on each side of the sternum accompanied by an internal thoracic vein.

The internal thoracic artery arises from the subclavian artery near its origin. It travels downward on the inside of the ribcage, approximately a centimeter from the sides of the sternum, and thus medial to the nipple. It runs deep to the internal intercostal muscles, but superficial to the transverse thoracic muscles.

It continues inferiorly until it divides into the musculophrenic artery and the superior epigastric artery around the sixth intercostal space.

Twelve anterior intercostal branches originate from the internal thoracic aa., one on the left side and one on the right side to each of the top six intercostal spaces. The lower five intercostal spaces are supplied anteriorly by branches of the musculophrenic arteries.

In a given space, the anterior intercostal artery has a main upper branch that travels laterally along the bottom of the upper rib bounding the space until it anastomoses with its corresponding posterior intercostal artery (a branch of the thoracic aorta). Each anterior intercostal artery also gives off a smaller lower branch, which anastomoses with a collateral branch of the corresponding posterior intercostal artery.