View through the choroidal fissure into the crural and ambient cisterns. The choroidal fissure of the right lateral ventricle’s temporal horn has been split. In this manner, the choroid plexus of the temporal horn is retracted superiorly and the hippocampus has been pulled downward. This reveals the crural and ambient cisterns. The major arterial structure in this region is the posterior cerebral artery’s P2a and P2p segments. The lateral posterior choroidal arteries of the PCA, along with the anterior choroidal artery (a branch of the ICA) enter the choroidal fissure to irrigate the choroid plexus of the lateral ventricle. The tentorial edge is prominent, as is the trochlear nerve and superior cerebellar artery running immediately medial to the edge of the tentorium. The basal vein is the vein formed by the deep middle cerebral vein and the anterior cerebral vein and courses posteriorly within the crural cistern. (Image courtesy of AL Rhoton, Jr.)