Editing Lung (section)

=== Amphibians ===
{{Further|Frog#Respiration and circulation}}
[[File:Axolotl ganz.jpg|thumb|right|alt=Axolotl|The [[axolotl]] (''Ambystoma mexicanum'') retains its larval form with gills into adulthood.]]
The lungs of most [[frog]]s and other [[amphibian]]s 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 room pressure|negative pressure]] where the lungs are inflated by expanding the rib cage.<ref name=Breathing>{{cite journal |last1=Janis |first1=Christine M. |last2=Keller |first2=Julia C. |title=Modes of ventilation in early tetrapods: Costal aspiration as a key feature of amniotes  |journal=Acta Palaeontologica Polonica |date=2001 |volume=46 |issue=2 |pages=137–170 |url=https://www.app.pan.pl/article/item/app46-137.html }}</ref> 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.<ref name="review">{{cite journal |last1=Brainerd |first1=E. L. |title=New perspectives on the evolution of lung ventilation mechanisms in vertebrates |journal=Experimental Biology Online |date=December 1999 |volume=4 |issue=2 |pages=1–28 |doi=10.1007/s00898-999-0002-1 |bibcode=1999EvBO....4b...1B |s2cid=35368264 }}</ref>

Due to the possibility of respiration across the skin combined with small size, all known lungless [[tetrapod]]s are amphibians. The majority of salamander species are [[lungless salamander]]s, which respirate through their skin and tissues lining their mouth. This necessarily restricts their size: all are small and rather thread-like in appearance, maximising skin surface relative to body volume.<ref name=Duellman&Trueb>{{cite book|last1=Duellman|first1=W.E.|last2=Trueb|first2=L. |others=illustrated by L. Trueb |title=Biology of amphibians|year=1994|publisher=Johns Hopkins University Press|isbn=978-0-8018-4780-6}}</ref> Other known lungless tetrapods are the [[Bornean flat-headed frog]]<ref>{{cite news |last1=Bickford |first1=David |title=First Lungless Frog Discovered in Indonesia |url=https://www.scientificamerican.com/gallery/first-lungless-frog-discovered-in-indonesia/ |work=Scientific American |date=April 15, 2008 }}</ref> and ''[[Atretochoana eiselti]]'', a [[caecilian]].<ref>{{cite journal |last1=Wilkinson |first1=M. |last2=Sebben |first2=A. |last3=Schwartz |first3=E.N.F. |last4=Schwartz |first4=C.A. |title=The largest lungless tetrapod: report on a second specimen of (Amphibia: Gymnophiona: Typhlonectidae) from Brazil |journal=Journal of Natural History |date=April 1998 |volume=32 |issue=4 |pages=617–627 |doi=10.1080/00222939800770321 }}</ref>

The lungs of amphibians typically have a few narrow internal walls ([[:wikt:septum|septa]]) of soft tissue around the outer walls, increasing the respiratory surface area and giving the lung a honeycomb appearance. In some salamanders, even these are lacking, and the lung has a smooth wall. In caecilians, as in snakes, only the right lung attains any size or development.<ref name=VB />