Cross-section of the posterior fossa at the level of the pons. The brainstem has been transected at the caudal pons; for orientation, the bottom of the image is ventral and rostral. Cranial nerves VI (abducens), VII (facial), and VIII (vestibulocochlear) arise from the pontomedullary junction and are visible here as they course in the pontine cistern. The basilar artery is visible along with its major branches: the anterior inferior cerebellar artery (AICA), the posterior inferior cerebellar artery (PICA), and bilateral superior cerebellar arteries and posterior cerebral arteries. The pons has been sectioned caudal to the trigeminal nerve; in this image, the trigeminal nerve is only visible in the prepontine cistern entering Meckel’s cave. (Image courtesy of AL Rhoton, Jr.)