Single bone is a bone with small bones and thin bones; Double bones are bones with large bones and high bone density. Single bone and double bone can distinguish the thickness of human bones. Bone tissue is a mixture of living cells and minerals (mainly calcium and phosphorus). It has different shapes and sizes, such as long arm bone, short wrist bone, flat sternum and skull and irregular vertebrae. Adult bones are mainly composed of two kinds of tissues, namely, hard dense bone and porous cancellous bone.

Bone function:

1, protection function: bones can protect internal organs, such as the skull to protect the brain; Ribs protect the chest.

2, support function: bones form a skeleton and maintain body posture.

3. Hematopoietic function: Bone marrow produces blood cells through hematopoiesis in the bone marrow cavity space between long bone and sponge bone.

4, storage function: bones store important minerals of the body, such as calcium, phosphorus and so on.

5, sports function: bones, skeletal muscles, tendons, ligaments and joints jointly produce and transmit strength to make the body move.