Development of Oral and Facial Motor Mechanisms in Human Fetuses and Their Relation to Craniofacial Growth

During a recent investigation to correlate transposition of the palatal shelves in hu-man fetuses with reflexes that include active mouth opening by mandibular depression,' an increase in size of the mandible was noted immediately after the change in position of the palatal shelves and tongue. In that paper, ' an explanation was offered for the rapid change in size of the mandible at this period of development. Because these preliminary observations are not en-tirely in agreement with some of the con-clusions in the literature,2 including those based on morphologic cephalometric meth-ods of investigation,3-5 a greater number and wider age span of human fetuses were studied to provide a more comprehensive series of photographs showing craniofacial growth changes. To make correlations be-tween activity in the oral and facial regions and the morphologic changes in these r-gions, summaries of the types of orofacial activity will be provided from previous publications.6-'3 Likewise, the data on movements of the mandible will be cor-related with the development of the tem-poromandibular joint as described in the literature.'4 Materials and Methods The motion picture negatives from the investigations on human fetal activity by This investigation was supported by USPHS research career program award 5-K6-NS-16716 from the Na-