Left lateral view of tympanic cavity and bony labyrinth following mastoidectomy and posterior tympanotomy and exposure of the sigmoid sinus. For orientation, the top border of the image is anterior; the right border is superior. The profiles of the semicircular canals are in view and the facial nerve has been lifted out of the facial canal and reflected. The bony canal containing its tympanic segment has been opened just beneath the lateral semicircular canal. The sigmoid sinus becomes continuous with the jugular bulb that rests in the jugular fossa. In this view, an alternative description divides the jugular foramen into three parts: the petrous part is where the inferior petrosal sinus enters before terminating in the internal jugular vein; the intrajugular part is where the glossopharyngeal (CN IX), vagus (CN X), and spinal accessory nerves (CN XI) pass; the sigmoid part contains the terminal end of the sigmoid sinus. The occipital artery can be seen entering the field in the upper left border after crossing the internal carotid artery and internal jugular vein. It ascends between the transverse process of the atlas and mastoid process of the temporal bone deep to muscles not shown in this image enroute to the posterior scalp. (Image courtesy of AL Rhoton, Jr.)