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Skeletal System

What are the four basic shapes of bones?

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October 25, 2014 12:42AM

There are actually five basic shapes for bones:

1. Long bones - examples: humerus or femur. Long bones are characterized by a shaft, the diaphysis, that is much greater in length than width. They are comprised mostly of compact bone and lesser amounts of marrow, which is located within the medullary cavity, and spongy bone. Most bones of the limbs, including those of the fingers and toes, are long bones. The exceptions are those of the wrist, ankle and kneecap.

2. Short bones - examples: carpels and tarsals (wrist and ankles bones). Short bones are roughly cube-shaped, and have only a thin layer of compact bone surrounding a spongy interior. The bones of the wrist and ankle are short bones, as are the sesamoid bones.

3. Flat bones - example: sternum. Flat bones are thin and generally curved, with two parallel layers of compact bones sandwiching a layer of spongy bone. Most of the bones of the skull are flat bones, as is the sternum.

4. Irregular bones - example:: vertebra in the spine. Irregular bones do not fit into the above categories. They consist of thin layers of compact bone surrounding a spongy interior. As implied by the name, their shapes are irregular and complicated. The bones of the spine and hips are irregular bones.

5. Sesamoid bones - example: patella