E, Anterior and middle incisural space, enlarged view. The opening through the choroidal fissure exposes the basal vein and branches of the PCA in the upper part of the ambient cistern. The PCA gives off numerous branches to the choroid plexus, including a large lateral posterior choroidal artery. F, The hippocampus and the medial part of the temporal lobe, including the parahippocampal gyrus, have been removed to expose the upper part of the middle incisural space. The PCA and basal vein course through the middle incisural space on the medial side of the parahippocampal gyrus, which has been removed. The choroid plexus remains attached along the choroidal fissure located between the fimbria and the lower surface of the thalamus. The inferior ventricular veins drain the roof of the temporal horn and empty into the basal vein. G, The branches of the PCA have been removed to expose the basal vein, which originates below the anterior perforated substance and courses posteriorly through the middle incisural space to gain access to the posterior incisural space and the quadrigeminal cistern. The pulvinar and lower surface of the thalamus, including the geniculate bodies, are in the upper margin of the exposure. H, The basal vein has been removed. This exposes the lateral aspect of the cerebral peduncle and the tegmental part of the midbrain, which are separated by the lateral mesencephalic sulcus. The medial and lateral geniculate bodies protrude downward from the lower surface of the thalamus. (Images courtesy of AL Rhoton, Jr.)