Chick frontonasal process excision significantly affects mid-facial development.

The midfacial region in vertebrates may be considered as developing from five separate processes, namely the central frontonasal process (FNP) and the paired maxillary and lateral nasal processes. Relatively little is known about the mechanisms whereby these processes interact to produce structures of the neonatal/adult face. This study was undertaken to gain some insights into the events involved in this process, and involved observing the effects on facial development in the chick of surgical excision of the FNP, prior to its fusion with the other facial processes. In the absence of the FNP, outgrowth of the upper beak was dramatically reduced, agenesis of the primary palate occurred, and development of the maxillary processes and palatal shelves was impaired. Thus, in the chick, the frontonasal process plays a major role in midfacial morphogenesis. Not only does the FNP provide the primary palate and a contribution to the development of the nasal septum, it is also important in the ordered development of the maxillary processes and of the definitive secondary palate--contributions which have not emerged clearly from in vitro and teratogenic studies.