Oblique Posterior View of Right Temporal Bone. The sigmoid sinus descends along the posterior surface of the mastoid portion in the sigmoid sulcus and turns upward along the lower surface of the petrous part to form the jugular bulb, which sits in the jugular fossa. The internal acoustic meatus opens onto the central portion of the posterior surface of the petrous part. The trigeminal impression and arcuate eminence are located on the upper surface of the petrous part. The porus of the internal acoustic meatus is positioned below the shallow depression, the meatal depression, positioned between the lateral edge of the trigeminal prominence and the arcuate eminence. The endolymphatic duct connects the vestibule in the petrous part with the endolymphatic sac, which sits on the posterior surface inferolateral to the internal acoustic meatus. (Image courtesy of AL Rhoton, Jr.)