A and B are from one specimen, and C is from another. A, The basal cisterns in the region of the tentorial incisura have been exposed by removing the thalamus and all of the left cerebral hemisphere except the occipital and temporal lobes. The roof of the temporal horn has been removed. The structures related to the anterior incisural space, located between the tuberculum sellae anteriorly, the midbrain posteriorly, and the anterior tentorial edge laterally, includes the optic nerve and chiasm, and the internal carotid, basilar, superior cerebellar, and PCAs. The anterior incisural space opens posteriorly into the middle incisural space, which extends into the crural and ambient cisterns. The crural cistern is located between the cerebral peduncle and the uncus, and the ambient cistern is located between the lateral midbrain and the medial surface of the temporal lobe. The ambient cistern opens posteriorly into the posterior incisural space, which contains the quadrigeminal cistern. The basal vein and the PCA and SCA pass around the midbrain in the middle incisural space to reach the posterior incisural space and quadrigeminal cistern. B, Enlarged view. The preserved tentorial edge is exposed between the basal vein and trochlear nerve. C, Superior view of the middle and posterior incisural space in another specimen. The basal vein courses through the crural and ambient cisterns. The upper lip of the calcarine sulcus has been removed but the lower lip of the sulcus has been preserved. The calcarine branch of the PCA loops laterally into the calcarine sulcus, which extends so deeply into the medial part of the hemisphere that it forms a prominence, the calcar avis, in the lower part of the medial wall of the atrium. (Images courtesy of AL Rhoton, Jr.)