Posterior View of a Right Temporal Bone. The squamosal part forms part of the floor and lateral wall of the middle fossa. The sigmoid sulcus descends along the inner surface of the mastoid portion. The porus of the internal acoustic meatus opens onto the central portion of the posterior surface of the petrous part. The trigeminal impression, trigeminal prominence, meatal depression, and arcuate eminence are located on the upper surface of the petrous part. The endolymphatic duct connects the vestibule in the petrous part with the endolymphatic sac, which sits on the posterior petrous surface inferolateral to the internal acoustic meatus. The intrajugular process separates the petrosal and sigmoid parts of the jugular foramen. (Image courtesy of AL Rhoton, Jr.)