Right anterolateral view of structures following transoccipital bone removal. Bone of the right lower clivus and adjacent parts of the petrous temporal bone were removed to expose the rostral medulla and its associated neurovasculature. The right vertebral artery is shown joining the left artery to form the basilar artery at the pontomedullary junction. A portion of the posterior inferior cerebellar artery is in view on the right side and is commonly a branch of the ipsilateral vertebral artery. Along the rostral lateral medulla emerge in sequence (rostral to caudal) the glossopharyngeal (CNIX), vagus (CNX), and spinal accessory (CNXI) nerves. These nerves converge on the jugular foramen. The hypoglossal (CNXII) nerve exits the sulcus between the medullary pyramid and olive and passes toward and through the hypoglossal canal. At the left border of the image is the internal jugular vein and internal carotid artery. The former exits the jugular foramen while the latter enters the carotid canal. The petroclival fissure has been drilled to expose the inferior petrosal sinus that passes through the pars nervosa of the jugular foramen to enter the internal jugular vein. The ascending pharyngeal artery, a small diameter branch of the external carotid artery, is shown here dividing into jugular and hypoglossal divisions. Each passes through corresponding foramina to supply associated cranial nerves and intracranial dura mater. (Image courtesy of AL Rhoton, Jr.)