Posterior view through right petrous portion of temporal following drilling. The posterior wall of the petrous bone has been removed to visualize the internal carotid artery passing through the carotid canal (petrous segment of the artery) medially toward the foramen lacerum. The superior petrosal sinus can been seen on the superior ridge of the petrous bone and the inferior petrosal sinus descends along the petroclival groove before draining into the internal jugular vein through the jugular foramen. Both petrosal sinuses drain the cavernous sinus. The sigmoid sinus continues as the jugular bulb to the jugular foramen. Facial (CN VII), nervus intermedius, and vestibulocochlear (CN VIII) nerves can be seen passing into the internal auditory meatus in company with the labyrinthine artery. The trigeminal nerve (CN V) travels within a split of the dura where the trigeminal ganglion occupies Meckel’s cave at the apex of the petrous bone. Abducens nerve (CN VI) exits at the pontomedullary junction and travels along the clivus where it pierces the dura mater to run within the cavernous sinus. The trochlear nerve (CN IV) is shown entering dura along the lateral wall of the cavernous sinus. The labyrinth has also been drilled to expose the superior and posterior semicircular canals and the common crus, which they share.  Intraosseous and extraosseous portions of the endolymphatic sac are also shown. (Image courtesy of AL Rhoton, Jr.)