Inferior transverse view of midbrain at level of tentorial notch. The midbrain has been sectioned transversely. Lateral to this are the temporal lobes. The cerebral peduncles are prominent on the anterior midbrain. Dorsal to this 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 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. The posteromedial central arteries are branches of the posterior cerebral arteries. These small vessels  penetrate the posterior perforated substance and supply portions of the internal capsule, thalamus and hypothalamus, mammillary bodies, and optic chiasm. The quadrigeminal or collicular artery is also a branch of the posterior cerebral and irrigates the tectal plate of the midbrain consisting of the superior and inferior colliculi. Anteriorly, the intradural portion of the internal carotid artery 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 arteries course medially around the optic nerves to enter the longitudinal interhemispheric fissure. The larger middle cerebral arteries enter the Sylvian (lateral) fissures. The anterolateral central arteries are small arteries that arise near the origin of the middle cerebral artery. They supply the basal ganglia. The pituitary stalk is located posterior to the optic chiasm and between the optic tracts. (Image courtesy of PA Rubino)