One hundred trillion cells, more than 600 muscles, and over 200 bones--these are parts of the twelve major systems that make up the human body. Technological developments have given us a detailed glimpse within our bodies and led to a greater understanding of how we function. Starting with the integumentary system (that's your skin, nails, and hair) and finishing with the reproductive system, the human body covers everything about you--from the outside to the inside. Award-winning science writer Seymour Simon has teamed up with the Smithsonian Institution on this new book about the greatest wonder of the world: the human body.