Contributions of differential growth of cartilages to changes in craniofacial morphology

During the late embryonic and early fetal periods of mammalian development, the cartilages of the chondrocranium and Meckel's cartilage form the major skeletal system in the craniofacial complex. Growth of craniofacial structures and changes in their spatial relations were morphometrically analyzed in normal human embryos and fetuses and in normal and abnormal rodent fetuses. The results showed that rodent and human specimens had similar patterns of differential facial growth which appeared to be related to regional growth of cartilages. Facial structures grew primarily in length with limited increases in height and in width. During the late embryonic period, the position of the head lifted rapidly relative to the body and the lower facial region became prominent. The predominantly sagittal direction of growth in Meckel's cartilage contributed to extension of the tongue and mandible beneath the primary palate at the time of secondary palatal closure. Growth of Meckel's cartilage was more rapid than other craniofacial cartilages and its growth appeared to be more sensitive to inhibition than other cartilages. The results of these studies suggest that differential growth of cartilages contributes significantly to changes in facial morphology and craniofacial relations during periods of development prior to extensive bone formation.