The upper edge of the petrous ridge is the site of two shallow depressions, the trigeminal impression and the meatal depression, and two elevations, the trigeminal prominence and the arcuate eminence. The trigeminal impression, in which Meckel’s cave and the enclosed part of the trigeminal nerve sits, is located on the medial part of the upper surface. The trigeminal prominence is positioned at the lateral edge of the trigeminal impression. The area between the trigeminal prominence and the arcuate eminence is the site of another shallow depression, the meatal depression, which is positioned above the internal acoustic meatus. The tegmen, a paper-thin area of bone that roofs the external canal, mastoid antrum, and tympanic cavity, is positioned on the upper surface lateral to the arcuate eminence. The subarcuate fossa, through which the subarcuate branch of the anterior inferior cerebellar artery passes, is located superolateral to and the hiatus of the endolymphatic duct is positioned inferolateral to the internal acoustic meatus. (Image courtesy of AL Rhoton, Jr.)