Oblique Enlarged Inferior View of the Right Temporal, Sphenoid, and Occipital Bones. The tympanic part of the temporal bone is positioned between the squamosal part anteriorly and the petrous and mastoid parts posteriorly. The petrous part of the trigeminal bone is wedged between the sphenoid and occipital bones. The petrous apex faces the foramen lacerum and is separated from the clival part of the occipital bone by the petroclival fissure. The dome of the jugular fossa, in which the jugular bulb sits, is on the lower surface of the petrous part. The carotid canal is positioned anterior to the jugular foramen. The tympanic canaliculus, located between the jugular fossa and carotid canal, is the opening through which Jacobson’s branch of the glossopharyngeal nerve passes to reach the tympanic cavity and, finally, the middle fossa, where it becomes the lesser petrosal nerve. (Image courtesy of AL Rhoton, Jr.)