Fig. 3.

Three models of morphogenesis of early primary palate in the chicken embryo based on undirected, regionalized cell proliferation. (A) In the model from Wu et al (2006) morphogenetic movements are directed by differential proliferation at the tip of the facial primordium. At HH26 regionalized proliferative zones (brown dots) in the globular processes of the FNP lead to outgrowth. Subsequently, at HH28-29, these proliferative zones merge to form a single growth center in the FNP (based on Wu et al. 2006) (B) In the model from Szabo-Rogers et al. (2008), in addition to the differential proliferation in the globular processes (brown dots), proliferating cells located more cranially (orange dots) exert a “pushing” force that directs outgrowth during this period. (C) In the model by Fritz et al. (2014) a single growth center is proposed to direct outgrowth. The shape changes of this growth zone determines the contour of the beak (adapted from Fritz et al. 2014).