Discussion and Conclusions

Abstract

The transformation of the nasal placode via nasal groove into nasal tube, which leads to changes in the shape of the embryonic facial region, is caused by three swellings separated from each other by grooves. These swellings are indicated either as processes or as prominences. The former term implies, or at least suggests, the existence of individual separate formations that fuse secondarily; the latter term (used by Patten, 1961, and Andersen and Matthiessen, 1967) implies a continuous mesenchymal area giving rise only externally to “prominences” separated by grooves. We shall return to this point later on, but wish to deal first with the problem concerning the participation of the respective processes in the formation of the nasal groove and tube, as well as of Hochstetter’s plate, the primitive palate and the naso-lacrimal duct, to mention the main structures involved. The divergent opinions found in the literature may be briefly summarized here.