Right lateral view of drilled mastoid process, bony labyrinth, and epitympanum. The top of the image is anterior and the right side of the image is inferior. The outer table of the mastoid process and air cells have been removed to visualize the semicircular canals and dura of the posterior cranial fossa. The superior petrosal sinus empties at the transverse-sigmoid sinus junction. This intersection of sinuses is the sinodural angle. The sigmoid sinus is located within dura and is continuous with the jugular bulb inferiorly. Anteriorly, the facial nerve runs within the facial canal on its way to exit through the stylomastoid foramen. In this view, the tympanic segment of the nerve passes inferior to the lateral semicircular canal and becomes continuous with the mastoid segment. The incus and it's short limb (located in the fossa incudis) are seen in the epitympanum that opens posteriorly into the mastoid antrum. The facial recess, a small space on the posterior wall of the mesotympanum lateral to the pyramidal eminence, is located immediately anterior to the upper portion of the mastoid segment of the facial nerve.  (Image courtesy of AL Rhoton, Jr.)