Fibroblasts of the transseptal fiber region of the periodontal ligament contain well developed bundles of microfilaments or stress fibers. The stress fibers are made up of numerous parallel and closely packed cytoplasmic filaments approximately 6 nm wide. These intra‐cellular stress fibers appear to be connected to and colinear with extracellular non‐striated microfibrils. The junction occurs at a juxta‐membrane dense patch called the fibronexus (Singer 1979).Similar associations of cytoplasmic microfilament bundles and the attachment protein fibronectin have been shown by other investigators to be necessary for cell attachment to substrata and oriented cell migration in fibroblasts culturedin