This free iPhone app shows you extensive views of the muscle systems. You can tap to enlarge, rotate, and "cut away" a layer of muscle and see muscles underneath. Zoom in for a close-up of a specific muscle group; the app lets you go deeper and deeper. When you rotate an image, you get a side view of the muscle system, as well as a posterior view and front view. The app provides information such as what the muscle is innervated by. It also will quiz you and tell you what each muscle is, the origin and insertion of the muscle, the action (what it does), and the nerve supply. 3D4Medical.com has several other iPhone apps, including the iMuscle app for the iPhone that lets users zoom in and identify muscles, and then shows the exercises associated with building up a specific muscle or muscle group. It also has iPhone apps for the cardiovascular system, the urogenital system, the skeletal system, the nervous system, the digestive system, and other muscle systems. iPad versions are available for several systems, including nervous, cardiovascular, and digestive. Some of 3D4Medical's apps are free but more specialized ones must be purchased.