GROWTH AND MORPHOGENESIS OF THE HUMAN EMBRYONIC MIDFACE DURING PRIMARY PALATE FORMATION ANALYZED IN FRONTAL SECTIONS

Although it is recognized that morphology of the craniofacial complex changes during primary palate formation, little information is availab le about the sites and amounts of growth in different regions. The pur pose of this study was to analyze growth patterns of human embryonic h eads in frontal sections and to identify regional growth associated wi th changes in craniofacial morphology and formation of the primary pal ate. Photographs of frontal sections of 31 human embryos of stages 16 to 19 from the Carnegie Embryology Collection were selected at seven d ifferent planes through each head, enlarged and traced, and landmarks were located for computerized morphometric measurements and for finite element modeling (FEM) analyses. Anatomical form change from the init ial geometry of the average early stage 16 group to that of later stag es was shown by numerical values and graphic displays of regional grow th changes during midfacial morphogenesis. Between stages 16 and 19, e xtensive changes in midfacial morphology occurred as the frontonasal p rominence elongated vertically (height increased by seven times) and n arrowed to approximately half the width, with more pronounced changes in the anterior nasal region. The brain and the face became vertically separated, and the facial prominences became more frontally positione d relative to the brain. Changes in depth of the face were very limite d during this period. The area of the maxillary region increased exten sively, particularly in the anterior region, as the maxillary prominen ces grew forward, lateral to the nasal cavity, to contribute to the pr imary palate. The lateral nasal prominences increased in size with a p redominantly horizontal growth pattern. These patterns of vertical gro wth of the midfacial tissues, narrowing of the nasal pits and frontona sal prominence, forward growth of the maxilla, and relative separation of the brain and face were identified as predominant features of embr yonic craniofacial growth during primary palate development.