Transverse view of midbrain at level of sella turcica. The edges of the tentorium cerebelli are in view as these extend from the superior ridge of the petrous temporal bone to the anterior and posterior clinoid processes of the sphenoid bone. The midbrain is enclosed by the tentorial notch and a window cut out of the tentorium exposes the superior surface of the cerebellum. Anterior to the midbrain is the dorsum sellae. Between it and the tuberculum sellae is the pituitary gland with its stalk emerging through an aperture in the diaphragma sellae. Just medial to each anterior clinoid process is the opening of the optic canal for the optic nerve and ophthalmic artery. Here also, the intradural portion of the internal carotid artery (ICA) emerges before branching into its terminal anterior and middle cerebral arteries. The cerebral peduncles are prominent on the anterior midbrain. Dorsal to these are the darkly pigmented substantia nigra, the largest nuclei in the midbrain. The oculomotor nerves 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. The nerves pierce the dura at the roof of the cavernous sinus. The trochlear nerves originate from the dorsal surface of the midbrain near the midline cerebral aqueduct and wrap around the cerebral peduncles within the subarachnoid space toward the lateral wall of the cavernous sinus. The trigeminal nerves can be seen ascending from the anterolateral pons before entering Meckel's cave near the petrous apex. Posterior communicating arteries from the ICA join the posterior cerebral arteries as part of the circle of Willis arterial anastomoses.  The anterior cerebral arteries course medially around the optic nerves to enter the longitudinal interhemispheric fissure. The larger middle cerebral arteries enter the Sylvian (lateral) fissures and begin dividing into M segments. Perforating arteries of the interpeduncular fossa arise from the distal basilar artery and proximal portions of the superior cerebellar and posterior cerebral arteries. (Image courtesy of PA Rubino)