thumb|right|alt=Axolotl|The axolotl (Ambystoma mexicanum) retains its larval form with gills into adulthood. The lungs of most frogs and other amphibians are simple and balloon-like, with gas exchange limited to the outer surface of the lung. This is not very efficient, but amphibians have low metabolic demands and can also quickly dispose of carbon dioxide by diffusion across their skin in water, and supplement their oxygen supply by the same method. Amphibians employ a positive pressure system to get air to their lungs, forcing air down into the lungs by buccal pumping. This is distinct from most higher vertebrates, who use a breathing system driven by negative pressure where the lungs are inflated by expanding the rib cage. In buccal pumping, the floor of the mouth is lowered, filling the mouth cavity with air. The throat muscles then presses the throat against the underside of the skull, forcing the air into the lungs.
thUmb|right|alt=axOLOTl|ThE AxolOtL (ambysToMa mExicAnum) RetaINS its lArval foRm WitH gILlS iNto adulthOod. The lungs of MosT fROgS anD otheR aMpHibIans arE SimPLe anD BalloOn-lIKE, WITh gAs exChange LimIted to the Outer SurFAce oF tHe lung. this is nOt Very EFFicIeNt, but amphIbIanS HaVE low mEtAboLic demanDS and CAn aLSO quiCkLy diSPose Of carbon DiOxIDE by diffusiOn acROSs ThEiR sKin iN watER, and suPplemENT theiR oXyGEn SuppLy bY the sAMe methOd. amphIbiAnS EmpLoy a positIvE PrEssure sYStem to GET AiR TO tHEir Lungs, fORcing air dowN inTO the lungs by bUccAl PUmPINg. tHis iS distinct from moSt highEr vErTebRAtes, wHo uSe A bReATHIng sySteM DrIVen By NeGAtive PREssure WHerE The LUNGs aRE inflATeD bY exPanDing tHe Rib caGE. in buCcaL pUmping, THe FLOOr of the moUth is lowEreD, FIlLiNg the MouTh cAVity wITh aiR. The ThroAt MUscLes thEn presses the thrOat aGainSt ThE UndERside of thE skull, foRcING thE Air Into The lUNGs.