M, The exposure is redirected to the area above the carotid bifurcation. N, The carotid bifurcation has been depressed and the optic tract elevated to expose the basilar bifurcation. A thalamoperforating artery arises from the basilar bifurcation. O, The posterior communicating artery passes in front of the basilar bifurcation. Gently depressing or elevating the posterior communicating artery, which crosses in front of the basilar artery, will increase access to the basilar apex. P, The posterior communicating artery has been elevated to expose the origin of the superior cerebellar arteries and the basilar bifurcation. Q, This oculomotor nerve arises from the medial surface of the cerebral peduncle and passes between the posterior cerebral and superior cerebellar artery to enter the roof of the cavernous sinus. R, The posterior communicating artery has been elevated to expose the basilar apex, both oculomotor nerves, and the junction of the right posterior communicating artery with the right posterior cerebral artery. (Images courtesy of AL Rhoton, Jr.)