Transmastoid view of left lateral labyrinth and Trautmann's triangle. Removal of temporal (mastoid and petrous portions) and occipital bone reveals the bony labyrinth and the posterior, superior, and lateral semicircular canals. Trautmann's triangle is bounded superiorly by the superior petrosal sinus, posteriorly by the sigmoid sinus, and anteriorly by the bony labyrinth. It serves as a surgical pathway to the posterior fossa from the mastoid cavity. The tympanic segment of the facial (CNVII) nerve courses inferior to the lateral semicircular canal before bending and descending as the mastoid segment. From this latter segment arises the chorda tympani nerve, which enters the middle ear cavity through the posterior canaliculus and courses between the malleus (on its medial surface) and the incus. The superior petrosal sinus, located within the attachment of the tentorium cerebelli to the petrous ridge, drains the cavernous sinus and receives tributaries of the inferior cerebral veins before emptying into the junction of the transverse and sigmoid sinuses. The jugular bulb, located at the jugular foramen, is the continuation of the sigmoid sinus. (Image courtesy of M Nunez)