Right posterior view of medulla, spinal cord, and posterior fossa. The posterior aspects of cervical vertebrae and the occipital bone have been removed (as have the meningeal coverings) to show posterior cranial fossa contents and the medulla passing through the foramen magnum. The third segment of the vertebral artery is shown coursing around the lateral mass of the atlas before passing through the spinal dura to ascend into the posterior fossa as the fourth segment. It gives rise to the posterior inferior cerebellar artery, which passes upward on the posterior surface of the medulla between the origins of the spinal accessory and vagus nerves to the undersurface of the cerebellum. The glossopharyngeal, vagus, and spinal accessory nerves are shown converging on the opening of the jugular foramen and the vestibular nerve can be seen coursing toward the opening of the internal auditory canal. (Image courtesy of AL Rhoton, Jr.)