Development of the cribriform plate and of the lamina mediana.

The development of the cribriform plate and lamina mediana was studied in macerated isolated ethmoid bones in specimens from late fetal life to the stage of its final shape (60 specimens). From fetal life to the first year of age, the ethmoid bone consisted of two separate symmetrical halves which had joined together by the end of the first year. Each half of the future ethmoid bone incorporated the superior, middle and occasionally also the supreme nasal concha. The ossification of the cribriform plate started in the new-born where it initially displayed a vertical position but became horizontal in the course of the first year. At the end of the first year both halves of the ethmoid bone had been united by the formation of the crista galli, lamina mediana and complete ossification of the cribriform plate. The lamina mediana reached its final shape by ten years of age. Each half of the ethmoid bone displayed furrows for the fila olfactoria in the region of the superior and occasionally also of the anterior part of the middle nasal concha. The furrows run in a postero-anterior direction. In the course of our investigations we found three cases where all three nasal conchae formed a unique block thus proving the common origin of these structures from the cartilaginous nasal capsule.