Right lateral view of midbrain at level of tentorial notch.  The medial edge of the tentorium cerebelli is seen near the lower and right border of the image. The cerebral peduncles are prominent structures on the anterior midbrain. The right oculomotor nerve can be seen leaving the midbrain within the interpeduncular fossa passing between the superior cerebellar and terminal posterior cerebral arteries, branches of the basilar artery. It passes forward just lateral to the posterior clinoid process (not labeled) to pierce the dura covering the roof of the cavernous sinus. The trochlear nerve originates from the dorsal surface of the midbrain near the midline cerebral aqueduct and wraps around the cerebral peduncles within the subarachnoid space and pierces dura slightly inferolateral to the oculomotor nerve.  Anteriorly, the intradural portion of the internal carotid artery (ICA) is exposed. It gives rise to the posterior communicating arteries to the posterior cerebral arteries and, slightly more distally, to the anterior choroidal arteries. The latter vessels usually course along the lateral aspect of the optic tracts to the lateral geniculate bodies. The ICA divides into its terminal anterior and middle cerebral arteries. The anterior cerebral artery courses medially around the optic nerve to enter the longitudinal interhemispheric fissure. The larger middle cerebral artery enters the Sylvian (lateral) fissure. (Image courtesy of PA Rubino)