Reptiles and amphibians both have lungs and exchange gases in the capillaries like mammals, but there are some differences in how they ventilate their respiratory systems. Reptiles do not typically breathe the same way as mammals since many reptiles lack a diaphragm. Without it they rely on muscles used in locomotion to ventilate their lungs.
Amphibians are capable of buccal pumping to push air into the lungs. This begins by muscles pulling air through the mouth or nose into a buccal cavity. Throat muscles then pump and move the floor of the mouth up in a way that Is visible from the outside. This forces air out of the mouth and into the lungs. Look at this frog's throat constantly moving.
Apart from their capillaries, amphibians can also perform gas exchange directly through their highly vascularized skin. This means that their skin has lots of blood vessels going through it. Since the blood vessels are close to their permeable skin surface, diffusion can take place right through the skin. In fact, some salamanders have no lungs at all, and they get all of their oxygen through their skin. The take home message is never get in a breath holding contest with a salamander. We wouldn't recommend a staring contest, either.
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