A, The right temporal lobe has been elevated. The middle incisural space, located between the lateral surface of the midbrain and the tentorial edge, opens upward into the ambient cistern where the PCA and basal vein course. The internal carotid artery is exposed in front of the midbrain in the anterior incisural space. B, Enlarged view of the junction of the anterior and middle incisural space. The internal carotid artery, optic nerves, and basilar bifurcation are located in the anterior incisural space. The oculomotor nerve passes forward between the PCA and SCA. C, The inferior temporal and fusiform gyri have been removed to expose the lateral edge of the parahippocampal gyrus above the middle incisural space. The opening into the temporal horn exposes the choroid plexus attached along the choroidal fissure. The veins draining the roof of the temporal horn empty into the basal vein. D, The choroidal fissure has been opened by detaching the choroid plexus from the fimbria of the fornix. Opening the fissure exposes the upper part of the ambient cistern and the branches of the PCA and basal vein. (Images courtesy of AL Rhoton, Jr.)