The unstable cells which have more calcium and less marrow and are strong are called compact bone. Pure bones have the Haversian system. At the center of the Haversian system is the Haversian groove. Haversian ducts are surrounded by circular lamellae. The lamellae contain lacunae of tiny cavities. The lacunae are surrounded by tiny canaliculi. Lacunae communicate with each other by canaliculi. Haversian ducts are interconnected by transverse ducts. These transverse channels are called Volkmann’s canal. The unstable cavity is called the marrow cavity. The marrow cavity is filled with red or yellow marrow. Fixed bones like femur, tibia-fibula, humerus, radius-ulna etc. 80% of the total weight of the human body is bone.