Thirty temporal bones of cadaver's skulls after fatal head injuries have been investigated. During explorations it has been ascertained that the transverse fractures of the pyramid involving the middle ear walls do not damage the ossicular chain, whereas the longitudinal fractures of the pyramid involving the middle ear walls are as a rule associated with the ossicular chain damage. The cases of the ossicular chain defect without any fracture of the pyramid were not rare. On the basis of the knowledge gained in experimentally induced fractures of the pyramid under different physical circumstances these facts are accounted for as a result of the differences in the solidity of the walls of the pyramid and in the mechanism of these fractures. In the longitudinal direction the pyramid is fractured by the mechanism of slide, while in the transverse direction the pyramid is fractured by the mechanism of drawing. The dislocation of the ossicles in the skull fractures not involving the pyramid is explained as a r...