Contents of right internal auditory canal. The roof of the internal auditory canal or meatus, located within the petrous temporal bone, has been drilled to show the relationship of its contents. Anterior is toward the top of the image, posterior is toward the bottom. The facial nerve, nervus intermedius, and vestibulocochlear nerves traverse this canal. A loop of the anterior inferior cerebellar artery is shown here projecting into the proximal meatus as well as the acousticofacial cistern, an extension of the cerebellopontine cistern. A horizontal shelf of bone, the transverse or falciform crest, is located at the distal or fundic region of the canal and divides this space into a superior and inferior compartment. A vertical crest (not shown here) further subdivides the superior compartment. While there is no similar vertical partition in the inferior compartment, four quadrants can nevertheless be described conceptually. The anterosuperior quadrant is occupied by the facial nerve (to which the nervus intermedius has already joined); the superior vestibular nerve occupies the posterosuperior quadrant. Inferiorly, the cochlear nerve enters the anteroinferior quadrant while the inferior vestibular nerve enters the posteroinferior quadrant. (Image courtesy of AL Rhoton, Jr.)