A MORPHOMETRIC ANALYSIS OF HUMAN EMBRYONIC CRANIOFACIAL GROWTH IN THEMEDIAN PLANE DURING PRIMARY PALATE FORMATION

As the human primary palate develops between embryonic stages 15 and 1 8, the facial prominences are part of a rapidly growing craniofacial c omplex that undergoes extensive morphogenetic change. The purpose of t his study was to analyze growth in the medial plane in order to identi fy regional changes that occur during changes in craniofacial morpholo gy. Photographs of midsagittal sections of 35 human embryos of stages 15 to 19 from the Carnegie Embryology Collection were enlarged, and la ndmarks were digitized for angular and linear measurements and for fin ite element modeling (FEM) analysis. The results showed magnitudes and directions of growth required to change average stage 15 morphology t o later stages. As the facial and cranial components increased in size , shape change was most pronounced in the posterior cranial and orofac ial 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 by 21-degrees and the orofac ial angle increased by 22-degrees, but the anterior and middle cranial angles remained unchanged. As the posterior cranial angle decreased, the forebrain and midbrain rotated superiorly toward the hindbrain, th e orofacial angle increased, and the face grew above the thorax. The r esults suggest that morphogenetic growth changes in the cranial region s are closely associated with facial regions during primary palate for mation.