Bones come in many shapes and sizes. Bones are tough and hard, but they are alive. Bones get bigger as an animal grows. They make themselves stronger when they get stressed or strained, and they can repair themselves if they get broken.
Together, the bones in an animal’s body form its skeleton. An animal’s bones support its body. They protect its heart, brain, and other internal organs. By working with muscles and tendons, bones enable an animal to move. By doing all these things, bones have allowed animals to get bigger, smarter, and faster.