Section 321: The round-window membrane (rw) closes scala tympani at the posterior extreme of the hook. This membrane separates the inner ear from the middle ear space. The crista of the posterior semicircular canal (pc) is now visible along with the nerve to the posterior canal in the foramen singulare (fs). ct - Chorda tympani; sm - stapedius muscle; VIIf - Mastoid segment of facial nerve.
Surgical perspective - The nerve to the posterior crista innervates the end organ from an anterolateral position (same as superior division did in section 101). There is a narrow surgical course from the middle ear, past the proximate round window, to the nerve.
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