1, bone pinyin: [gǔtou]. Bone tissue is composed of living cells and minerals (mainly calcium and phosphorus), which makes bones have solid physical properties.

2. Bones come in different shapes and sizes. For example, the arm bone is long, the wrist bone is short, the sternum and skull are flat, and the vertebrae are irregular. Adult bones are mainly composed of two kinds of tissues: hard and dense bones on the outside and porous cancellous bones on the inside. The thigh bone in the long bone or femur is filled with fat called yellow bone marrow.