In HA2, the inner (bottom) and outer (top) circumferential lamellae (bone layers) are arranged around the inner and outer regions of the compact bone, like growth rings of a tree. These layers formed by appositional growth. Haversian systems or osteons can be seen between the inner and outer circumferential lamellae. Most of the Haversian systems or osteons in HA2 have 2 to 3 concentric lamellae of osteocytes around them. Haversian canals contain vessels, nerves, and resting osteoblasts.