Inferolateral view of the dorsal brainstem with fiber tracts dissected. The tentorium is visible on the left side of the image. Portions of the cerebellum have been removed to visualize the posterior midbrain and pons. The superior and inferior colliculi are visible on the posterior aspect of the midbrain. The trochlear nerve (CN IV) emerges from the dorsal aspect of the midbrain below the inferior colliculus and courses around the lateral aspect of the brainstem and penetrates the dura below the free edge of the tentorium cerebelli to enter the cavernous sinus. The lateral lemniscus is a fiber bundle connecting the cochlear nucleus with the contralateral inferior colliculus. The trigeminal nerve (CN V) emerges from the lateral side of the pons. The superior cerebellar peduncle is a fiber bundle that connects the cerebellum to the midbrain and forms the superior portion of the roof of the fourth ventricle. (Image courtesy of AL Rhoton, Jr.)