Did you know the two largest bones in the body, the femur and the tibia, are both found in the legs? Bones make up about 20 percent of body weight. Discover more fascinating facts in Skeletal System, a title in the Body Systems series. Each title in Body Systems guides readers through the fascinating inner workings of the human body. The human body contains several complex systems that work closely together to support life and allow the body to function properly. Each book explores the characteristics and interactions of these systems, their makeup, and their importance. This is an AV2 media enhanced book. A unique book code printed on page 2 unlocks multimedia content that brings the book to life. This book comes alive with audio, video, weblinks, slideshows, activities quizzes, and much more.