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Bones are made of a soft matrix which is then calcified with calcium hydroxyapatite, which gives it a rigid structure. The outermost layer is called the periosteum, and is a tough, fibrous layer to which ligaments and tendons attach. The next layer is the cortical bone, which is very rigid and hard. It provides the shape and structure of the bone. The next layer in is the cancellous bone layer, which is a bit softer, and provides space for vascular elements and marrow. The cancellous bone makes the bones lighter.

In humans, the cortical bone makes up about 80% of bone mass, while cancellous bone is about 20%.

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16y ago

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