A, Superolateral view. The tentorium, except the edge, has been removed. The dura has been removed from the middle fossa floor and cavernous sinus wall to expose the greater petrosal nerve, middle meningeal artery, and the nerves in the sinus wall. B, The middle fossa floor has been opened to expose the cochlea, semicircular canals, petrous carotid artery, and the facial, cochlear, and superior vestibular nerves in the meatus. The superior canal bulges upward into the middle fossa below the arcuate eminence. The cochlear nerve passes below the facial nerve to enter the cochlea, which is located above the lateral genu of the petrous carotid in the angle between the pregeniculate facial and greater petrosal nerves. C, Another temporal bone drilled to expose the internal acoustic meatus, cochlea, vestibule, semicircular canals, tympanic cavity, and external meatus. The vestibule is located posterolateral and the cochlea is anteromedial to the fundus of the internal meatus. The vestibule communicates below the meatal fundus with the cochlea. The tensor tympani muscle and eustachian tube are layered along, but are separated from, the anterior surface of the petrous carotid by a thin layer of bone. The tegmen has been opened to expose the head of the incus and malleus in the epitympanic area. The internal acoustic meatus lies directly medial to, but is separated from, the external meatus by the tympanic cavity and the labyrinth. D, The nerves in the meatus have been separated to expose the superior and inferior vestibular, facial, and cochlear nerves. (Images courtesy of AL Rhoton, Jr.)