The Superior Epigastric Artery enters the Rectus sheath behind the 7th costal cartilage and anastomoses with the Inferior Epigastric Artery which enters the Rectus sheath in front of the arcuate line. Thus, vessels to the upper and lower limbs are brought into communication with each other—for the superior epigastric artery is one of the two terminal branches of the internal mammary branch of the subclavian artery, and the inferior epigastric artery is one of the two collateral branches of the external iliac artery. Being the only two arteries in this region, the two epigastric arteries have of necessity to supply everything in the region.
Surgical Anatomy. Arch Surg. 1996;131(4):381. doi:10.1001/archsurg.1996.01430160039006