Anterior view of proximal cervical segment of the spinal cord. The occipital condyles and clivus (partially removed in this specimen) indicate the level and location of the foramen magnum. Anterior portions of the atlas and axis have been removed to expose the spinal cord. Along the anterior surface of the spinal cord, within the anterior median fissure, is the anterior spinal artery. Anterior spinal arteries arise from the vertebral arteries and then anastomose into a single vessel at the level of the foramen magnum. This artery is reinforced by other branches distally that enter the spinal canal through intervertebral foramina. The artery spinal artery supplies the anterior two-thirds of the spinal cord. Paired posterior spinal arteries (not visible here) supply the posterior one-third. The anterior spinal vein accompanies the artery. Arising from the anterolateral surface of the cord are anterior rootlets and roots of cervical spinal nerves. The spinal portion of the spinal accessory nerve can be seen as a single trunk that ascends through the foramen magnum to unite with its cranial portion, which arises from the medulla. The spinal portion arises from fibers from ventral horn cells between C1 and C5 segments. These fibers emerge from the cord between the anterior and posterior spinal nerve roots before joining to form a single trunk. Also, the denticulate ligaments, seen here as glistening white structures along the lateral border of the cord, are likewise positioned between anterior and posterior nerve roots. These are longitudinal condensations of pia mater that attach as focal adhesions to the spinal dura to stabilize the spinal cord within the dural sac. (Image courtesy of AL Rhoton, Jr.)