A morphometric analysis of human embryonic craniofacial growth in the median plane during primary palate formation

As the human primary palate develops between embryonic stages 15 and 18, the facial prominences are part of a rapidly growing craniofacial complex that undergoes extensive morphogenetic change. The purpose of this study was to analyze growth in the medial plane in order to identify regional changes that occur during changes in craniofacial morphology. Photographs of midsagittal sections of 35 human embryos of stages 15 to 19 from the Carnegie Embryology Collection were enlarged, and landmarks were digitized for angular and linear measurements and for finite element modeling (FEM) analysis. The results showed magnitudes and directions of growth required to change average stage 15 morphology to later stages. As the facial and cranial components increased in size, shape change was most pronounced in the posterior cranial and orofacial regions. Increases in cranial linear dimensions were significantly larger than those in the cranial base regions. Between stages 15 and 18, the posterior cranial angle decreased, the forebrain and midbrain rotated superiorly toward the hindbrain, the orofacial angle increased, and the face grew above the thorax. The results suggest that morphogenetic growth changes in the cranial regions are closely associated with facial regions during primary palate formation.