Electron microscopy: attachment sites between connective tissue cells.

Regions of attachment have been observed between connective tissue cells from four different structures: fibroblasts in embryonic and fetal tendons, fibroblasts in fetal ligamentum nuchae, odontoblasts, and osteoblasts. Morpho logically these sites appear to be focal and to consist of an approximation of the plasma membranes of adjacent cells to within approximately 200 A. In the region of approximation both the extracellular space and the cytoplasm adjacent to the plasmalemma are increased in density. We have postulated a role for these sites in the maintenance of structural integrity.