Superior view of left middle and inner ear. The roof of the petrous portion of temporal bone has been removed to visualize the bony labyrinth of the vestibule and semicircular canals. The bony labyrinth of the cochlea has been drilled to expose the membranous labyrinth. Sound waves enter the external acoustic meatus and are transmitted across the tympanic membrane to the ossicular chain. The handle of the malleus attaches to the tympanic membrane and vibrations pass though the incus and then stapes onto the oval window of the vestibule. Facial (CN VII) and vestibulocochlear (CN VIII) nerves enter the internal acoustic meatus. At the geniculate ganglion, the facial nerve gives off the greater superficial petrosal nerve that exits the petrous bone and travels in a groove deep to the trigeminal ganglion toward the foramen lacerum. The facial nerve continues posteroinferiorly through the facial canal where it will exit the skull through the stylomastoid foramen. (Image courtesy of AL Rhoton, Jr.)