Cells migrate from the neural crest of the mesencephalon rostrally and laterally into the space between the prosencephalon and the surface ectoderm. At S16, they form the impressive frontonasal process. The nasal placodes arise ventro-laterally on both sides and subdivide the frontonasal process into a medial and lateral nasal process (prominentia nasalis medialis, prominentia nasalis lateralis). The nasal placodes initially are thickenings of the surface ectoderm and are convex to the outside. As the nasal processes grow, the nasal placodes invaginate to become nasal pits. The nasal processes form elevations around the nasal pits (animation: facial development stage 12-13).