Superior view of right orbital apex and tentorial incisura. The optic nerves are shown entering the optic canals where they are accompanied by the ophthalmic branches of the internal carotid arteries. The oculomotor and trochlear nerves exit, respectively, the anterior and posterior surfaces of the midbrain and course within the subarachnoid space. The oculomotor nerve enters the roof of the cavernous sinus. The trochlear nerve pierces the dura mater inferolateral to oculomotor to enter the lateral wall of the sinus. Between the brainstem and the tentorial notch one can see the basilar artery ascending on the anterior pons and its superior cerebellar artery coursing posteriorly in a subtentorial relationship. (Image courtesy of PA Rubino)