Why do we have bones?

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Across
  1. 2. Hard, strong tissue that protect organs
  2. 4. a group of bones, joints and ligaments
  3. 6. The shortest bones we have
Down
  1. 1. The place where two bones meet
  2. 3. The picture to examine bones
  3. 4. The tissue that covers the body, soft and flexible
  4. 5. Organ protected by the cranium