Ventrolateral view, left internal thoracic artery

Ventral view, left internal thoracic artery

Ventral view, right internal thoracic artery

The internal thoracic (mammary) artery is usually the first branch of the subclavian artery on both sides.  It serves the ventral (anterior) thoracic wall.  There is one on the left and one on the right.   They normally run along both sides of the sternum.