Which lamellae wrap around the entire bone and are sometimes called circumferential lamellae?

• A. Circumferential
• B. Concentric
• C. Interstitial
• D. Perforating

Answer: (A)

Circumferential lamellae are the layers that encircle the entire bone. They line the outer surface beneath the periosteum (outer circumferential lamellae) and the inner surface next to the endosteum (inner circumferential lamellae). These lamellae run around the bone’s circumference, increasing the bone’s diameter and helping resist torsion and bending across the whole bone, not just within a single osteon.

In contrast, concentric lamellae form around the central Haversian canal to create an osteon, so they wrap around a micro-unit inside the bone rather than the entire bone. Interstitial lamellae are remnants between osteons, and perforating canals connect vascular channels rather than wrapping lamellae around the bone. So the description fits circumferential laminating around the whole bone.