E, Inferior surface of both cerebral hemispheres showing the MCA coursing along the sylvian cistern and the PCAs coursing through the crural, ambient, and quadrigeminal cisterns. F, Enlarged view of the P2P coursing below the thalamus, which forms the roof of the ambient cistern. The left temporal horn has been opened by removing part of the floor. Some of the head of the hippocampus has been preserved. The P2P gives rise to a complex arborizing group of perforating arteries that enter the lower thalamus, some passing through the geniculate bodies, and constituting the thalamogeniculate arteries. G, Inferior view of another cerebral hemisphere. The medial part of the parahippocampal gyrus has been removed to expose the PCA coursing through the crural, ambient, and quadrigeminal cisterns. The AChA courses around the uncus. The uncus has an anterior segment that faces the carotid, middle cerebral, anterior choroidal, and posterior communicating arteries, and a posterior segment that faces the posterior cerebral and the terminal segment of the AChA. The choroidal fissure is located between fimbria of the fornix and the lower surface of the thalamus and has its lower end just behind the posterior uncal segment. The LPChA pass laterally through the choroidal fissure located between the fimbria and the thalamus. The dentate gyrus is located below the fimbria. A MPChA courses medial to the PCA. H, The dentate gyrus and adjacent part of the parahippocampal gyrus has been removed to expose the choroid plexus in the temporal horn. The LPChAs pass laterally between the fimbria and the lower margin of the thalamus, formed in part by the lateral geniculate body and pulvinar, to reach the choroid plexus in the temporal horn and atrium. (Images courtesy of AL Rhoton, Jr.)