Computer reconstructions of human embryonic craniofacial morphology showing changes in relations between the face and...

During early development of the human facial region, the craniofacial complex undergoes extensive morphogenetic change. The purpose of this study was to generate computer reconstructions of serially-sectioned embryos in order to illustrate major changes in spatial relations that occur between cranial and facial tissues. Five human embryos of stages 16 to 18 from the Carnegie Embryology Collection, which were used in the frontal morphometric study, were selected to illustrate phases of morphogenesis. Serial photographs of frontal sections were enlarged, traced, and digitized for computer reconstruction. The craniofacial complex was divided into components that were similar to those analyzed in a morphometric study [Diewert VM, Lozanoff S: J Craniofac Genet Dev Biol 1993: 13:162-183] to facilitate visualization of changes in regional components. The major changes observed included changes in form of the brain and its ventral contour above the face; enlargement, elongation, and more ventral positioning of the facial prominences relative to the brain; and forward positioning of the eyes and facial tissues relative to cranial components. As the brain became separated from the face at advancing stages of development, the frontonasal prominences narrowed and became vertically elongated, the lateral nasal prominences enlarged and became medially positioned, and the maxillary prominences enlarged and extended anteriorly. Changes in cranial flexion and lifting up and back of the forebrain [Diewert VM, Lozanoff S: J Craniofac Genet Dev Biol 1993:13:184-192.] appear to contribute to withdrawal of the brain from between the facial prominences during early midfacial development before cartilaginous tissues of the chondrocranium develop.