The Structure of Bones

Bones are rigid organs made of a hard outer layer called compact bone, which provides strength, and an inner, spongy layer called cancellous bone that contains bone marrow—where blood cells are produced. The outer surface is covered by a membrane called the periosteum, which supplies nutrients and helps in repair. Bones have a central cavity called the medullary cavity, containing marrow. They are connected to muscles via tendons and to other bones by ligaments, allowing movement. Overall, bones support your body, protect organs, produce blood cells, and store minerals like calcium.