The document discusses the structure and composition of bone. It notes that bone is composed of collagen fibers and hydroxyapatite crystals. It describes two types of bone tissue: cortical bone forming the hard outer layer and cancellous bone comprising the inner layer. Cortical bone contains osteons (Haversian systems), which are cylindrical structures containing blood vessels and nerves. Cancellous bone has a sponge-like structure. The document also mentions osteocytes, osteons, lamellae, lacunae and canals in bone. It provides details on the composition of cortical and cancellous bone and concludes by wishing the reader good luck.