Fibroblast networks that form collagen and connect the two ends of bone develop in the haematoma after corticotomy. This regenerative tissue is vascularized and distracted. Even during the lengthening, mineralization starts. This starts at the ends created by the osteotomy, in the form of conical bony columns 200 microns thick, which grows towards each other in a manner reminiscent of stalagmites and stalactites, until the central, fibrous inner zone (growth zone) formed during distraction is completely mineralized. Connective tissue and bony bars are arranged lengthwise. As a rule, intramembranous callus formation takes place during distraction osteogenesis with no intermediate cartilaginous step.