Figure 1.

CT reconstruction of some of the left middle ear structures of the gerbil Gerbillurus setzeri, seen from rostrally and medially. The auditory ossicles (malleus, incus and stapes) are shaded yellow, the pars tensa of the tympanic membrane is brown and the pars flaccida is pink. The anatomical area ratio is defined as the area of the pars tensa divided by the area of the stapes footplate. The anatomical axis of rotation of the ossicles is indicated, running between the tips of the anterior process of the malleus and the short process of the incus. The malleus lever arm (ML) is the perpendicular distance between the tip of the manubrium and this axis; the incus lever arm (IL) is the perpendicular distance between the centre of the lenticular apophysis of the incus (which articulates with the stapes) and the same axis.