Haversian canals, lamellae, lacunae and canaliculi are collectively called Haversian canals or osteons. The structure of pure bone or osteon is described below-
1. Haversian Duct: The duct located in the unstable center is called Haversian duct. It contains veins, arteries and lymphatics. The Haversian ducts are connected to each other by the ducts of Vochmans.
2. Lamellae: 5-15 layers surround the Haversian canal. Each layer is called lamellae. It contains calcium, phosphorus and collagen.
3. Lacuna: Each lamella has small cavities. Each cavity is called a lacuna. Each lacuna contains bone cells called osteocytes or osteoblasts or osteoclasts.
4. Canaliculi: Each lacuna is surrounded by several fine canals. These ducts are called canaliculi. Lacunae are connected to each other by canaliculi. It transports nutrients and waste materials.
5. Medullary cavity: The cavity in the unstable center is called the medullary cavity. It is filled with red or yellow pulp