Light and electron microscopy of the new born sagittal suture.

Morphogenesis and maturation of the sagittal suture in newborn C57B1/6J strain mice were studied using light and electron microscopy. Morphodifferentiation of the murine parietal bones progresses radially with the interposed sagittal suture, assuming a greater level of maturity at birth at a midpoint along its length. The presumptive suture develops in a sulcus, deeper posteriorly, more shallow anteriorly. Cells at the osteogenic front (OF) are distinguished from the surrounding fibrocytic cells by a number of distinctive characteristics: 1. increased cytoplasmic density; 2. extensive endoplasmic reticulum; 3. dispersed nuclear chromatin aggregates; 4. extensive surface projections; 5. close approximation. Mineralization of the developing parietal bone occurs extracellularly with the initial deposits of apatite crystals exhibiting no oriented relationship to either cellular or extracellular fibrillar elements. The majority of collagen fibers lie superior and inferior to the presumptive suture, oriented anteroposteriorly with their long axes parallel to the ectocranial surface. Other fiber bundles more intimately associated with the developing suture display a more random orientation.