[A comparison of the morphology of mammalian and bird ear ossicles and reflections on the asymmetrical form of the human stapes arch].
BACKGROUND
The human middle ear presents some anatomical detail which can not be explained exclusively by sound transmission (joints, muscles). These details can be interpreted as an adaptation to environmental atmospheric pressure loads. In order to further investigate the influence of these non-acoustic loads on the geometry of the middle ear structures, the ossicles of animals from different environments were examined.


METHODS
In the first half of our century, the zoologist C. F. Werner collected the ossicles of 175 species, mostly mammals and birds. This collection was now cataloged and analysed with light and x-ray microscopy.


CONCLUSIONS
The diversity in size and design of the ossicles seems to be influenced not only by the acoustic environment of the animal--the ossicles of mammals living in the desert are relatively large, reflecting the better sensitivity of their middle ear for the far traveling low frequencies--but especially the bony structure of the ossicles can be related to the static loads of the environment of the animal. Ossicles of aquatic mammals are more solid and denser than in terrestrial forms. The bony structure aligns to the static load. This structural principle forms the basis of the skeleton and muscles and can also be found in the human stapes: the asymmetry of the stapedial arch can be explained as adaptation of the bony structure to the pull of the stapedius muscle.


CONCLUSIONS
The anatomical structure of the ossicles of human and animal origin is not only influenced by its function as sound transmitter, but it is also shaped by nonacoustic forces and static loads of the environment.
Hüttenbrink
K B
KB
Klinik und Poliklinik für Hals-Nasen- und Ohrenheilkunde am Universitätsklinikum Carl Gustav Carus Dresden.
D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000033:anatomy & histology*; D004429:Ear Ossicles / Q000033:anatomy & histology*; D006309:Hearing / Q000502:physiology*; D006801:Humans; D008322:Mammals / Q000033:anatomy & histology*; D010802:Phylogeny; D012931:Social Environment; D013045:Species Specificity; D013199:Stapes / Q000033:anatomy & histology*
Ein Vergleich der Morphologie von Säugetier- und Vogel-Gehörknöchelchen und Uberlegungen zur asymmetrischen Form des menschlichen Steigbügels.