Terminal branches of the left internal carotid artery. The intradural portion of the left internal carotid artery is in view in this dissection. Prior to its termination it gives rise to the posterior communicating artery to the posterior cerebral artery and slightly more distally the anterior choroidal artery. The latter vessel usually courses along the lateral aspect of the optic tract to the lateral geniculate body. The left middle cerebral artery, the larger of the two terminal branches of the internal carotid artery, is shown entering the Sylvian (lateral) fissure where it progressively divides into four M segments. The anterolateral central arteries are small arteries that arise near the origin of the middle cerebral artery. They supply the basal ganglia. The anterior cerebral artery, the smaller terminal branch of the ICA, courses medially into the longitudinal fissure where it supplies the medial aspect of the frontal lobes and the superior part of the parietal lobes. In its proximal segment it gives rise to small anterior perforating arteries (provided also from anterior choroidal and middle cerebral arteries) that enter the anterior perforating substance to supply the internal capsule, caudate nucleus, putamen, and globes pallidus. The optic nerve system is exposed with the optic nerves, chiasm, and tracts revealed. Mobilization of the temporal lobe exposes the basilar artery and its superior cerebellar and terminal posterior cerebral arteries. The oculomotor nerve is seen emerging from the anterior midbrain and coursing forward in the subarachnoid space between these two vessels. The olfactory tract is seen on the inferior surface of the frontal lobe. (Image courtesy of PA Rubino)