G, The exposure has been extended to the opposite side by further elevation of the frontal lobe. The exposure includes both optic nerves and the ipsilateral and contralateral carotid and middle cerebral arteries. The lamina terminalis extends upward from the optic chiasm. The pituitary stalk is exposed below the optic chiasm. H, Further elevation of the frontal lobes exposes the opposite sylvian fissure to the level of the bifurcation of the contralateral middle cerebral artery. The pituitary stalk and contralateral oculomotor nerve are seen through the opticocarotid triangle. I, The left optic nerve has been elevated to expose the contralateral ophthalmic artery. J, The anterior clinoid process has been removed to expose the clinoid segment of the internal carotid artery. K, Pterional exposure of supra-and parasellar area in another specimen. The pituitary stalk and contralateral internal carotid artery are seen below the optic chiasm. L, The opticocarotid triangle has been opened by gently elevating the optic chiasm and displacing the carotid artery laterally to access the bifurcation of the basilar artery and the origin of both superior cerebellar and posterior cerebral arteries. The contralateral superior cerebellar artery arises as a duplicate artery. This exposure is adequate if the opticocarotid triangle is large, as occurs if both the internal carotid and anterior cerebral arteries are long, but is inadequate if the internal carotid and anterior cerebral arteries are short and the internal carotid artery courses tightly beside the optic nerve and chiasm. The basilar bifurcation cannot be exposed by this route if the bifurcation is especially high or is located below the dorsum sellae. (Images courtesy of AL Rhoton, Jr.)