Bone growth that is periosteal (aka appositional) is via thickening (widening).
Bone Growth: Periosteal (Appositional)
Endosteum (which delineates the marrow cavity, itself) comprises the inner circumferential lamellae, which distinguishes this inner bony layer from the compact bone external to it.
- Osteoprogenitor cells line the endosteum and form the lamellae that derive the spongy bone that form the trabecular meshwork of the primary ossification center.
External to the endosteum, lies layer of compact bone, which, namely, comprises osteons that encompasses circular layers of lamellae around a Haversian (aka central) canal.
Periosteum divides into an outer, collagenous layer, and inner, osteogenic layer.
- Osteoblasts from the periosteum create new osteons along the longitudinal grooves and ridges within what is referred to as the outer circumferential lamellae: it forms concentric osteons (with Haversian canals), and it also forms interstitial lamellae, which fill the spaces between osteons.
- The inner circumferential lamellae thickens, as well.