Bone: intramembranous formation
The spongy bone (left) and a forming Haversian system in a long bone (right) are each lined by endosteum. Any lamellae deposited by this layer, such as additional lamellae to the spongy bone or to the osteon, are formed by intramembranous bone formation. 200x, 400x
Spongy, lamellar bone >
When this trabeculum was being formed, the surface cells were osteoblasts that deposited laminae of spongy lamellar bone onto the surface of existing bone, conforming to the original shape that was present. Such bone deposition is called intramembranous bone formation. As this spicule is no longer growing, the surface osteoblasts have been replaced by flattened lining cells.
Forming osteon >
Osteoblasts lining an internal bony space deposit concentric lamellae centripetally by intramembranous ossification, forming an osteon.
Canaliculi can be seen radiating from some of the osteocyte lacunae.