The development of the tympanic cavity starts by the growth of the auditory tube and its subsequent division into four sacs: saccus anticus, medius, superior and posticus. The developmental process of the cavity is a complex phenomenon, it involves gradual disappearance of mesenchymal tissue, an increased volume of amniotic fluid, epithelization of the tympanic cavity and ossification of its walls. So far the mechanisms of disappearance of the mesenchyme were not elucidated. Although in the literature the term pneumatization of the tympanic cavity is used, we cannot agree with this term. Pneumatization should be associated with the presence of air in the cavity; the developing tympanic cavity is however before delivery filled with amniotic fluid. In the authors’ opinion it is better to decribe this process during the period of intranterine development of the foetus by the term „lumenization“ as the lumen of the tympanic cavity is created which is filled with amniotic fluid and not air. The process of prenatal lumenization depends on the presence of amniotic fluid, loss of mesenchymal tissue and the formation of the walls of the tympanic cavity which are at first made of cartilage and connective tissue and gradually ossify. During postnatal development the amniotic fluid is replaced by air, which penetrates into the tympanic cavity via the auditory tube or by diffusion of blood gases across the wall of small capillaries in the mucoperiosteum of the tympanic cavity.

        Key words: tympanic cavity, embryonic development, lumenization, pneumatization, temporal bone