Right posteromedial view of the petrous portion of temporal bone following drilling. The superior petrosal sinus courses along its superomedial border within the attachment of the tentorium cerebelli toward the transverse sinus. Bone has been removed at the opening (porus) of the internal acoustic meatus. The nervus intermedius, facial (CN VII), and vestibulocochlear (CN VII) nerves and labyrinthine artery pass through the internal acoustic (auditory) meatus. Glossopharyngeal (CN IX) and vagus (CN X) nerves can be seen passing into the jugular foramen in company with the jugular bulb. The arcuate eminence is a bony elevation on the anterior surface of the petrous bone that marks the location of the superior semicircular canal.  Bone has been removed from this area to reveal the superior and posterior semicircular canals and the common crus, a limb shared by these two canals. The  endolymphatic sac, with its intraosseous and extraosseous portions, is also shown. It connects the endolymph compartment of the inner ear with the dura mater.  (Image courtesy of AL Rhoton, Jr.)