The subcostal arteries (Latin: sg. arteria subcostalis) are blood vessels that travel below the last pair of ribs and are the lowest parietal branches arising from the descending thoracic aorta. The subcostal arteries mainly supply the flat muscles of the abdominal wall.
Each subcostal artery passes along the inferior border of the 12th rib behind the kidney and in front of the quadratus lumborum muscle. On its course, it is accompanied by the 12th thoracic nerve. The subcostal artery then pierces the aponeurosis of the transversus abdominis muscle. It passes forward between the transversus abdominis and the internal oblique muscles, where it anastomoses with several vessels, including the superior epigastric, lower intercostal, and lumbar arteries.
Each subcostal artery gives rise to a posterior branch that has a similar course as the posterior branches of the intercostal arteries. It also participates in supplying the spinal cord and soft tissue structures of the back.