largest of the medullary arteries that supply the spinal cord by anastomosing with the anterior (longitudinal) spinal artery; it arises from a lower intercostal or upper lumbar artery (on the left side about 65% of the time) supplying most of the blood to the lower two thirds of the anterior spinal artery.medullary arteries of brain SYN: arteria radicularis magna, artery of Adamkiewicz, great anastomotic artery (3), great radicular artery.