S, The basilar artery can be seen through the opticocarotid triangle, but the basilar bifurcation is so high that it cannot be seen. T, The optic tract has been gently elevated and the carotid bifurcation depressed to expose the basilar apex. U, The right temporal lobe has been elevated to expose the optic, oculomotor, and trochlear nerves above the tentorial edge. The posterior communicating artery passes backward superomedial to the oculomotor nerve. The basilar bifurcation is located behind the dorsum sellae, just below the tentorial edge. V, The tentorial edge has been divided just behind where the trochlear nerve joins the tentorium to expose the basilar bifurcation located in back of the dorsum sellae. Elevating the posterior cerebral artery exposes the thalamoperforating arteries. W, Another exposure. The bifurcation is located behind the dorsum. The P1 extends upward on the medial side of the oculomotor nerve. X, The tentorium has been divided while preserving the trochlear nerve to expose the upper part of the basilar artery and the bifurcation. The posterior cerebral artery passes above and the superior cerebellar artery below the oculomotor nerve. (Images courtesy of AL Rhoton, Jr.)