Anterior view of right lateral pons, medulla, and cerebellum. The vertebral arteries ascend on the ventrolateral surface of the medulla and unite near the pontomedullary junction to form the midline basilar artery. The posterior inferior cerebellar artery arises from the vertebral artery near the olive and wraps around to the posterior surface of the medulla and then the cerebellum. The anterior inferior cerebellar artery arises from the proximal portion of the basilar artery and often loops between the facial and vestibulocochlear nerves enroute to the anterior surface of the cerebellum. The anterior and posterior lobes of the cerebellum are separated by the primary fissure (not labeled). The vertebral and basilar arteries and their branches course superficial to the veins. The veins on the anterior surface of the pons (transverse pontine), medulla (medullary veins), and the petrosal surface of the cerebellum (anterior hemispheric vein) drain predominantly into the superior petrosal veins, which empty into the superior petrosal sinuses. The trigeminal nerve is shown with its larger sensory and smaller motor root emerging from the anterolateral surface of the pons. The abducens nerve exits the pons near the midline of the pontomedullary junction, while the facial and vestibulocochlear nerves emerge laterally near the cerebellopontine angle. The flocculus projects just inferior to these nerves. Arising as a series of rootlets from the postolivary sulcus on the medulla are the glossopharyngeal, vagus, and cranial root of the spinal accessory nerves in a cranio-caudal sequence. Rootlets of the hypoglossal nerve emerge from the preolivary sulcus. (Image courtesy of AL Rhoton, Jr.)