Axial perspective of perimesencephalic cisterns. For perspective, the midbrain has been sectioned at the level of the cerebral peduncles, and this view is from below. The interpeduncular cisterns lie anterior (ventral) to the midbrain and contain perforating arteries from the basilar apex and P1 segments of the PCA, along with the oculomotor nerves. The crural cisterns lie anterolateral to the cerebral peduncles and contain the P2 segments of the posterior cerebral arteries (PCA), the quadrigeminal and medial posterior choroidal arteries, and the basal veins of Rosenthal (BVR). The ambient cisterns lie posterior to the cerebral peduncles and contain the BVR, the P2p segment of the PCAs, and medial posterior choroidal arteries. The quadrigeminal cistern lies dorsal to the midbrain and contains both basal veins of Rosenthal and both internal cerebral veins as they form the great cerebral vein of Galen. (Image courtesy of AL Rhoton, Jr.)