Section 141: The chorda tympani (ct) crosses the middle ear space medial to the manubrium of the malleus (mm) and lateral the long process of the incus (i). The tendon of the tensor tympani (ttt) runs in a medial-lateral direction to insert into the medial side of the manubrium. Note that the tendon makes a 90° angle with the tensor tympani muscle (ttm). The utricular macula (mu) is still visible along with much of the non-sensory portion of the posterior semicircular canal. Two turns of the cochlear spiral (c1, c2) are seen medial to the tensor tympani. cc - common crus; lsc - lateral semicircular canal; psc - posterior semicircular canal. VIId - Tympanic segment of facial nerve.
Surgical perspective - The tympanic segment of the facial nerve anterior to the cochleariform process (cp) is in the epitympanum while posterior to the process, the tympanic segment is at the border of the epitympanum and mesotympanum.