Left lateral view of petrous bone following mastoidectomy and posterior tympanotomy with exposure of the jugular foramen. For orientation, the top border of the image is anterior; the right border is superior. In this view, the left cerebellar hemisphere has been reflected to reveal the roots of the vestibulocochlear, glossopharyngeal, vagus, and spinal accessory nerves emerging from the brainstem. The latter three cranial nerves are shown coursing through the intrajugular portion of the jugular foramen into the neck, along with the internal carotid artery and internal jugular vein. Along the medial wall of the tympanic cavity the facial nerve has been raised out of its facial canal inferior to which is the stapes attached to the oval window. The round window is visible beneath the promontory. The probe is seen entering the cochlear aqueduct, which is a small bony canal that drains perilymph within the bony labyrinth into the cerebrospinal fluid near the lateral margin of the jugular foramen. (Image courtesy of AL Rhoton, Jr.)