E, The dural incision has been extended through Trautman’s triangle and across the superior petrosal sinus and tentorium, taking care to preserve the vein of Labbe´ and the trochlear nerve. The semicircular canals have been opened. F, Enlarged view. The posterior canal faces the posterior fossa lateral to the internal acoustic meatus. The superior canal projects upward, below the arcuate eminence, toward the floor of the middle fossa. The lateral canal is a useful landmark for identifying the tympanic segment of the facial nerve, which courses between the canal and the stapes sitting in the oval window. The epitympanic area opens through the aditus into the mastoid antrum. G, The labyrinthectomy has been completed and the dura lining the meatus opened to expose the cisternal, meatal, labyrinthine, tympanic, and mastoid segments of the facial nerve. The SCA courses above the trigeminal nerve. H, Enlarged view along the opened tentorial incisura. The oculomotor and trochlear nerves course between the PCA and SCA. The SCA rests against the upper surface of the trigeminal nerve. (Images courtesy of AL Rhoton, Jr.)