Right posterolateral view of the facial nerve following mastoidectomy. The lateral surface of the tympanic membrane can be seen for orientation; the left border of the image is superior. In this view, the labyrinthine segment of the nerve can be observed prior to its first genu at the geniculate ganglion. Here is the origin of the greater superficial petrosal nerve. The main trunk of the nerve subsequently courses posteriorly along the medial wall of the middle ear cavity as the tympanic segment and then descends in the posterior wall as the mastoid segment. Just before exiting through the stylomastoid foramen, the facial nerve gives rise to the chorda tympani branch, which takes a posterior to anterior course through the middle ear cavity along the medial aspect of the handle of the malleus. (Image courtesy of AL Rhoton, Jr.)