In anatomy, a sesamoid bone (/ˈsɛsəmɔɪd/) is a bone embedded within a tendon or a muscle. It is derived from the Latin word "sesamum" (sesame seed), due to the small size of most sesamoids. Often, these bones form in response to strain. Sesamoids act like pulleys, providing a smooth surface for tendons to slide over increasing the tendon's ability to transmit muscular forces.