The early healing of circumscribed defects in albino rats.

Bourne (1944), describing the healing mechanism in tilt femoral defects, slated that initially they are filled by osteoid proliferation from the periosteum. Ma/.arow (I960) found that in the dog mandible the defect is tilled in from its cut surface and by bone trabeculae stemming chiefly from the periosteum. Mclchcr and Irving (1962) studied the healing mechanism in circumscribed defects in rat femora. They stated that .the initial callus formation is subperiosteal; it occurs some distance from the defect, and proliferates towards, but halts at its margins. Only then does endosteal callus formation begin which proliferates outwards to fill four-fifths of the defect; and the periosteal onc-lifth is then covered by subperiosteal callus and thus the defect is bridged. According to these authors, no callus arises from the cut surfaces of the defect.