Formation of marrow cavity and ossification in mouse limb buds grown in vitro.

Explanted mouse limb buds aged 12, 13 or 14 days cultured for 9 days in vitro failed to develop a marrow cavity or show endochondral ossification. Explants aged 15 days developed a marrow cavity and showed signs of endochondral ossification. The periosteum in these limbs was perforated and laminated and cells appeared to be passing between the laminae to populate the marrow cavity. This suggests that there is a periosteal contribution to the bone marrow even in the absence of a blood supply.