A small, rounded bone that is embedded in a tendon or joint capsule. Sesamoid bones are typically found where a tendon works over a ridge of underlying bone, as in the case of the patella (kneecap). In addition to the knee joint, sesamoid bones are found in the hand (for example, at the base of the first metacarpal and also in the wrist) and foot (where the first metatarsal connects to the big toe). Sesamoid bones help to protect and increase the mechanical effect of tendons, and also to prevent the tendons from pressing into the joint. Compare with meniscus.