G, The superior vestibular and facial nerves have been retracted to expose the superior and inferior vestibular nerves posteriorly and the facial and cochlear nerves anteriorly within the meatus. The anteroinferior cerebellar artery loops into the meatus. The nervus intermedius courses with the VIIIth nerve near the brainstem and jumps to the facial nerve, either in the cerebellopontine angle or internal acoustic meatus. H, The petrous apex has been drilled downward to the level of the inferior petrosal sinus and medially to the lateral edge of Dorello’s canal. This exposure includes the anteroinferior cerebellar artery bifurcation and extends down to the level of the vertebral artery. I, The facial nerve has been retracted backward to expose the nervous intermedius and the superior and inferior vestibular and cochlear nerves. The rostral trunk of the anteroinferior cerebellar artery loops into the internal acoustic meatus, and the caudal trunk passes downward to the inferolateral part of the cerebellum. J, The roof of the cavernous sinus is located medial to the tentorial edge and includes the oculomotor triangle, through which the oculomotor nerve passes, and the dura lining the lower margin of the anterior clinoid. The optic nerve has been elevated to expose the origin of the ophthalmic artery, which enters the optic canal and penetrates the optic sheath to enter the orbit on the lateral side of the optic nerve. K, The roof and lateral wall of the orbit have been removed to expose the orbital contents. L, Enlarged view of the structures in the upper part of the orbit. The levator and superior rectus muscles have been elevated and the lateral rectus muscle has been depressed. The superior ophthalmic vein passes backward and empties into the cavernous sinus after passing downward along the lower margin of the ophthalmic nerve. The nasociliary nerve, ophthalmic artery, and superior ophthalmic vein course above the optic nerve and are located on the lateral side of the optic nerve at the orbital apex. (Images courtesy of AL Rhoton, Jr.)