Frogs breath with their mouths closed. Their throat
movements pulls air through the nostrils to the lungs.
Then breathe out with body contractions.
The activity and temperature of an animal determine
how important breathing is. Anurans have much more complex
lungs then other amphibians, such as salamanders, because
they're more active and have higher body temperature.
Lungs can also help in water. Filling the lungs with
air gives a frog a better buoyancy, making it float
Frogs can also breath through their skin, with tiny
blood vessels, capillaries, under the outer skin layers.
The African 'Hairy' frog, Trichobatrachus robustus,
has small lungs and during breeding seasons the males
get hair like projections on their back legs. This is
because of the high oxygen needs at this time.