Ontogenetic modelling of the petrous part of the temporal bone in man.

The inner and the outer layers of the petrous part of the temporal bone (p.p.t.b.) become definitive until the sixth intrauterine month. Therefore, the growth and modelling of the p.p.t.b. are subsequently achieved by apposition of the periosteal outer layer. Periosteal apposition takes place in the form of plates appearing successively. The author identified seven such plates concentrated around the canals passing through the p.p.t.b. and describes them in fetuses, premature infants and adults. Periosteal ossification may cause compression of nerves passing through the p.p.t.b. thus inducing the onset of Ménière's disease. The anatomical peculiarities determined by the periosteal bone must be thoroughly known to permit high-accuracy surgical interventions at the p.p.t.b. level.