What do amphibians breathe when on land?

Since adult amphibians live both on land and in water, many develop lungs in addition to absorbing oxygen from their aquatic environment. Water is rich in oxygen and therefore diffuses easily through the skin surface and into oxygenated blood vessels close to the surface. On land, many amphibians breathe through the lungs and also through the skin, while some – like the four-toed salamanders – breathe only through the skin. Amphibian lungs are essentially empty balloons, much less complex than human lungs.