 At the level of the conus medullaris, the posterior spinals are more frequently seen as distinct arteries, communicating with the anterior spinal artery to form a characteristic "basket" which angiographically defines the caudal extent of the spinal cord and its transition to the cauda equina.Branches from the posterior spinal arteries form a free anastomosis around the posterior roots of the spinal nerves, and communicate, by means of very tortuous transverse branches, with the vessels of the opposite side.Close to its origin each posterior spinal artery gives off an ascending branch, which ends ipsilaterally near the fourth ventricle.