书城教材教辅科学读本(英文原版)(套装1-6册)
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第377章 第四册(33)

How the Bones Move

Our lesson on the joints showed us the bones of the body in action-some moving with a simple backward and forward hinge-like movement, some swinging round in a circle by means of a ball and socket, and some, again, rotating on a peg or pivot. But have you asked yourselves why these bones do not slip out of their places with their work? Let me tell you the reason. At eachjoint there are strong gristly bands, called ligaments, which hold or bind the bones together, while at the same time they do not interfere with their freedom of movement.