[Evolution of the functional axes of the middle ear in mammals]

In 44 mammalian species, the auditory ossicles have been studied in situ in the tympanic cavity and in vestibular orientation. After the lateral semicircular canal's direction and dimensions have been put in common, measurements have been undertaken leading to a comparison of 4 phylogenic stages. Thus we have observed a rotation of the stapes, of the incus and of the malleus head, a receding of the manubrium of the malleus ending in an inversion of the bone's concavity, an extension of the supposed unfolded chain, a parallelization of the malleolus handle and of the lower incudal apophysis, a slope of the functional axes towards the back, a diminution of the distance between the two lever arms due to a receding of the anterior arm and a diminution of the ratio between these lever arms. These varied changes are linked to the occipital rotation and to the receding of the jaws following humanization.