The major objective of this research project is to further elucidate the function of tissue interactions during morphogenesis and histogenesis of organ systems within the cranio-facial region. Ultrastructural studies in combination with light-microscopic studies are being made to reveal the developmental sequence of tissue differentiation, and experimental in vitro studies are being made to determine the flexibility and the precise requirements of differentiating tissues within the cranio-facial region. The specific aims of the project are the following: 1) A detailed study of membrane bone formation within the cranio-facial region is being made (using primarily the membrane bones of the mandibular, maxillary, palatal, and cranial regions) in order to determine the specificity and the extent of epithelial requirements for membrane bone formation. 2) A study of morphogenesis and histogenesis of epithelium primarily from the palatal region is being made to determine more precisely the factors which control the parameters of epithelial differentiation.