Right superior view into fundus of the internal auditory canal with exposure of the tympanic cavity. The roof of the distal end of the internal auditory canal and tympanic cavity have been removed to visualize structures internally. The fundus of the canal separates the cochlea anteriorly from the labyrinth posteriorly and is the location where the facial nerve and branches of the vestibulocochlear nerves separate to travel to target structures. Here, the labyrinthine segment of the facial nerve ends at the geniculate ganglion from which arises the greater superficial petrosal nerve. This nerves passes through bone before exiting its hiatus along the anterior surface of the petrous bone. It courses beneath the trigeminal nerve enroute to the foramen lacerum. The tympanic segment of the facial nerve curves sharply posteriorly from the ganglion within the facial canal and beneath the lateral semicircular canal located on the medial wall of the tympanic cavity. The superior petrosal sinus is seen within the attachment of the tentorium cerebelli to the superior border of the petrous bone. It drains the cavernous sinus to the transverse sinus. (Image courtesy of AL Rhoton, Jr.)