S, Enlarged view of the medial wall of the tympanic cavity before mobilizing the facial nerve. The stapedial muscle passes forward from the pyramidal eminence below the facial nerve and attaches on the neck of the stapes. The tensor tympani muscle passes backward and laterally, giving rise to a narrow tendon that makes a sharp turn around the trochleariform process at the lateral end of its semicanal to insert on the handle of the malleus. The basal turn of the cochlea is located deep to the promontory. The tympanic segment of the facial nerve courses above the stapes. T, Enlarged view of the labyrinth. The semicircular canals have been unroofed and the stapes has been removed from the oval window. The round window is located below and behind the oval window. U, The facial nerve has been reflected forward out of the facial canal and the vestibule has been opened. The ampullae of the superior and the lateral canal open into the vestibule anteriorly and are innervated by the superior vestibular nerve. Only the upper edge of the superior canal was preserved in opening the vestibule. The ampullae of the posterior canal is located at its lower end and is innervated by the singular branch of the inferior vestibular nerve. V, A probe is directed through the vestibule to the inner surface of the membrane covering the round window, which is located behind and below the oval window. W, Enlarged view of the labyrinth after opening the promontory to expose the cochlea. The jugular bulb is located below the vestibule and semicircular canals and the lateral genu of the internal carotid artery in position below the cochlea. The cochlea wraps around the modiolus through which the branches of the cochlear nerve are distributed to the cochlear duct. X, The temporal lobe has been elevated to expose the internal carotid, PCA, and SCA in the basal cisterns. The dura has been elevated from the lateral wall of the cavernous sinus. (Images courtesy of AL Rhoton, Jr.)