Roof of the right internal auditory canal has been removed to show the compartmentalization of the nervous structures within. This canal is divided distally into superior and inferior compartments by the transverse crest (falciform crest), a thin horizontal crest of bone. The superior compartment is subdivided into an anterior superior quadrant and posterior superior quadrant by a vertically directed bony partition, the vertical crest or Bill’s bar. The facial nerve and nervus intermedius occupy the anterior superior quadrant, and the superior division of the vestibular nerve is located in the posterior superior quadrant. Although there are three osseous canals, this area is conceptually divided into four quadrant areas. Thus, the anterior inferior quadrant contains the auditory or cochlear nerve and the posterior inferior quadrant contains the inferior vestibular nerve. Note also, the cochlea is located anterior to the canal, while the semicircular canals lie posterior to it. (Image courtesy of AL Rhoton, Jr.)