Which bone is an example of a sesamoid bone?

The correct choice, the kneecap, is a clear example of a sesamoid bone. Sesamoid bones develop within tendons and serve to protect those tendons from stress and wear, as well as improving the mechanical advantage of muscles. The kneecap, or patella, specifically plays a crucial role in knee movement, allowing for more efficient leverage when the muscles around the knee joint contract.

In contrast, the humerus, femur, and radius are all long bones that serve different functions in the skeletal system, such as providing support and facilitating movement at joints, but they do not have the specific characteristics that define sesamoid bones. This distinction is essential for understanding the diversity of bone types and their functions in the body.