OSTEOCLASTS: ORGANIZATION IN CHICK EMBRYO BONE.

A multinucleated endosteum was observed in the long bones of chick embryos aged 14 to 17 days. The endosteum appears to be responsible for extensive bone resorption; the bulk of the diaphyseal bone is almost completely replaced during this particular 3-day interval. Eventually, the endosteum appears to be transformed into numerous individual osteoclasts. Both the endosteum and the osteoclasts are found almost entirely on the medial surfaces of the innermost bone spicules and they seem to destroy collagen by extracellular proteolysis.