Modelling the malleus vibration as a rigid body motion with one rotational and one translational degree of freedom.

Vibration of a set of points distributed along the manubrium of cat was measured with a heterodyne interferometer in response to sinusoidal acoustic signals. The observed motion did not fit pure rotation of the malleus around a fixed axis coinciding with the anterior mallar and posterior incudal ligament as is classically assumed. As a first approximation a model of motion consisting of a rotational and a translational component was used. At low frequencies the rotation is mostly predominant, but the situation may be entirely reversed at mid and high frequencies. The presence of a translation besides rotation was also found at some frequencies in the motion of the human malleus.