Left lateral transmastoid view of bony labyrinth and sigmoid sinus after mastoidectomy. Mastoidectomy reveals the sigmoid sinus, which continues as the jugular bulb. The superior petrosal sinus is just out-of-view at the top of the image. Trautmann's triangle is bounded by the bony labyrinth anteriorly, the sigmoid sinus posteriorly, and the superior petrosal sinus superiorly. The labyrinth has been opened to visualize the posterior, superior, and lateral semicircular canals. Just inferior to the lateral semicircular canal is the mastoid portion of the facial nerve. (Image courtesy of AL Rhoton, Jr.)