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In anatomy, a sesamoid bone (〔''OED'' 2nd edition, 1989 as .〕〔(Entry "sesamoid" ) in ''(Merriam-Webster Online Dictionary )''.〕) 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.〔Kenneth S. Saladin, ''Anatomy and Physiology'', 6th edition (New York:McGraw Hill, 2012), 234.〕 Sesamoids act like pulleys, providing a smooth surface for tendons to slide over increasing the tendon's ability to transmit muscular forces.〔 ==Structure== Sesamoid bones can be found on joints throughout the body, including: * In the knee — the patella (within the quadriceps tendon). This is the largest sesamoid bone.〔 * In the hand — two sesamoid bones are commonly found in the distal portions of the first metacarpal bone (within the tendons of adductor pollicis and flexor pollicis brevis). There is also commonly a sesamoid bone in distal portions of the second metacarpal bone. * In the wrist - The pisiform of the wrist is a sesamoid bone (within the tendon of flexor carpi ulnaris).〔Tim D. White, ''Human Osteology'', 2nd edition (San Diego: Academic Press, 2000), 199, 205.〕 It is not present at birth and generally develops in children ages 9–12.〔Kenneth S. Saladin, ''Anatomy and Physiology'', 6th edition (New York:McGraw Hill, 2012), 263.〕 * In the foot - the first metatarsal bone usually has two sesamoid bones at its connection to the big toe (both within the tendon of flexor hallucis brevis).〔White, ''Human Osteology'', 2nd edition, 257-261.〕 One is found on the lateral side of the first metatarsal while the other is found on the medial side. In some people, only a single sesamoid is found on the first MTP. * In the neck - Although the hyoid bone is free floating, it is not technically a sesamoid bone. All sesamoid bones form directly from the connective tissue found in tendons and ligaments. By contrast, the hyoid bone forms from a cartilaginous precursor like most other bones in the body. * In the ear - the lenticular process of incus is a sesamoid bone and therefore is considered the fourth ossicle of middle ear 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sesamoid bone」の詳細全文を読む スポンサード リンク
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