Histologic study of the attachment of muscles to the rat mandible.

The relationship of muscle to periosteum, tendon and ultimately to bone was studied in histological sections of rat mandibles aged 19 days in utero to 56 days postnatal. The following stains were employed: Van Gieson, Masson trichrome, Couciero and Friere, Gomori, orcinol-new fuchsin and Fullmer. Three modes of muscle attachment to the growing rat mandible were described according to the arrangement of collagen and reticular fibres at the interface between the bone and muscles. The morphological characteristics of the three modes persisted even in 56-day-old rats. The structure of the muscle-bone interface suggested a single mechanism of adaptation of muscles to bone during growth. With maturation, the size, number and variety of cells decreased and the size and thickness of collagen fibres increased in the muscle attachments. Each muscle was attached to the mandible by one or more types of attachment defined in this study. A schematic map of the distribution of the different attachment modes associated with muscles of the rat mandible was constructed. Distinction between these modes of attachment may be important in relating the form of a bone to its function.