The subcostal arteries are bilateral small arteries that arise of the distal descending aorta which courses laterally beneath the 12th rib. In part supplying the vertebra and spinal cord, they are considered one of the segmental arteries of the aorta.
The subcostal arteries are analogous to the posterior intercostal arteries, instead in the subcostal space rather than an intercostal space. They pass in front of the T12 vertebrae and behind the sympathetic trunk, pleura, and diaphragm. On the right, the subcostal artery also runs posterior to the thoracic duct and azygos vein, whereas the left runs posterior to the accessory hemiazygos vein.
The artery enters the abdomen along the inferior border of the twelfth rib, with the subcostal nerve and vein, passing between the lateral arcuate ligament, kidney and the quadratus lumborum.
After piercing the transversus abdominis aponeurosis it anastomoses with the superior epigastric, lower posterior intercostal and upper lumbar arteries.
The subcostal artery divides into the anterior and posterior rami like the posterior intercostal artery.
Along with the lower posterior intercostal arteries, the subcostal arteries supply the muscles and skin beneath the 12th rib of the anterolateral abdominal wall.