[Origin of osteoclasts].

The haematogenous origin of osteoclasts has been demonstrated in recent years by the use of cellular markers in experiments in early bone grafts in bird embryos and the transfer of haematopoietic cells in the osteoporotic mammals. The nature of the mononuclear precursor(s) of the osteoclasts has not been determined. Studies currently underway demonstrate that relatively immature cells present in the bone marrow of adults and in various embryonic haematopoietic organs, as well as blood monocytes are capable of participating in osteoclastic differentiation in various animal models.