Which statement best defines an osteon (Haversian system)?

• A. Cylindrical unit of bone
• B. A central canal that contains the neurovascular bundle supplying the osteon
• C. Hairlike canals connecting lacunae
• D. The facial skeleton

Answer: (A)

The osteon is the cylindrical, repeating unit of mature compact bone. Each osteon consists of concentric lamellae arranged around a central Haversian canal that houses the blood vessels and nerves supplying the osteon. Osteocytes lie in lacunae between the lamellae and communicate with each other through tiny channels called canaliculi. The central canal connects with perforating (Volkmann) canals, linking the osteon to the periosteum and the marrow so nutrients and waste can move efficiently. The cylindrical arrangement of lamellae around the central canal gives strength to bone and helps it resist bending and twisting. While the central canal is a crucial feature, the whole osteon is more than just that canal, and canaliculi are the small networks that connect the lacunae. The facial skeleton is unrelated to what an osteon is.