Right posterolateral view of the bony labyrinth following mastoidectomy. Projections of the semicircular canals (lateral, superior, and posterior) can be seen, along with the tympanic and mastoid segments of the facial nerve. The chorda tympani branch arises from the mastoid segment of the nerve and arches anteriorly to enter and traverse the middle ear cavity. The facial nerve exits the stylomastoid foramen. The endolymphatic sac is a blind-ended pouch containing endolymph from the inner ear that emerges on the posterior surface of the petrous portion of the temporal bone. (Image courtesy of AL Rhoton, Jr.)