Editing Amphiuma (section)

=== Lungs ===
Amphiuma possess relatively ancestral forms of lungs compared to some of the other groups of [[salamander]]s that live terrestrially today.<ref name=":33">{{Cite journal |last1=Toews|first1=Daniel P.|last2=McRae|first2=Ann|date=1974|title=Respiratory mechanisms in the aquatic salamander, ''Amphiuma tridactylum'' |jstor=1442591|journal=Copeia|volume=1974|issue=4|pages=917–920|doi=10.2307/1442591}}</ref><ref name=":44">{{Cite journal|last1=Martin|first1=Karen M.|last2=Hutchison|first2=Victor H.|date=1979|title=Ventilatory activity in ''Amphiuma tridactylum'' and ''Siren lacertina'' (Amphibia, Caudata)|jstor=1563477|journal=Journal of Herpetology|volume=13|issue=4|pages=427–434|doi=10.2307/1563477}}</ref> Their lungs are long organs, extending over half of the body length, with dense capillary networks and large surface area that suggest the utilization of the entire lung for respiration while the animal is in water or on land.<ref name=":44"/> Although it is common for amphibia to respire out of their skin, also known as [[cutaneous respiration]], it was found that amphiuma primarily respire through their lungs, despite their aquatic lifestyle.<ref name=":5">{{Cite journal|last=Szarski|first=Henryk|date=1964|title=The structure of respiratory organs in relation to body size in Amphibia |jstor=2406426|journal=Evolution|volume=18|issue=1|pages=118–126|doi=10.2307/2406426}}</ref> This is suggested by the high lung to respiratory capillary density compared to the relatively low skin to respiratory capillary density.<ref name=":44"/><ref name=":5" />
[[File:Zoomed in and Annotated Amphiuma Lung with Body Orientation.jpg|thumb|Amphiuma lung with a magnified portion of the lung to show the amphiuma vascular tissue.]]

==== Respiration ====
Pressure gradients for respiration occur in two different locations, the buccal cavity/nares (mouth and nostril) region, and in the lungs of the amphiuma. The first system for respiration occurs in the buccal cavity/nares through a two-cycle pressure-induced buccal cavity/nares process.<ref name=":33"/><ref name=":62">{{Cite journal |last1=Brainerd |first1=Elizabeth |last2=Ditelberg |first2=Jeremy |date=1993 |title=Lung ventilation in salamanders and the evolution of vertebrate air-breathing mechanisms |doi=10.1006/bijl.1993.1028 |journal=Biological Journal of the Linnean Society|volume=49|issue=2 |pages=163–183|doi-access= }}</ref><ref name=":44"/> In the first system, the amphiuma performs one full cycle of body expansion and compression in order to inhale and another full cycle to exhale, a unique process that utilizes both the [[Mouth|buccal cavity]] and the nares (openings of nostrils).<ref name=":33" /><ref name=":62" /> The buccal cavity creates pressure that aids in driving the cycles of expansion and compression required for respiration, although it was found that the buccal pressure gradient alone was not enough to drive respiration in the ''[[Amphiuma tridactylum]]''.<ref name=":33" /> Rather, the buccal cavity allows for small pressure changes that are thought to have an [[Olfaction|olfactory]] purpose.<ref name=":33" />  This buccal cavity/nares component to the amphiuma respiratory process supplements the contribution performed by the lung. It is the pressure control performed in the lungs that drive the inhalation and exhalation forces through the flexing of [[Smooth muscle tissue|smooth muscle]] in the lung.<ref name=":44" /> In order to exhale, amphiuma push air from their lungs into their buccal cavity, distending the cavity, before releasing the air. Without inhaling, amphiuma repeat the process, exhaling a second volume of air that allows them to completely empty their lungs.<ref name=":44" /> Only after both exhales can they then inhale, using a negative pressure gradient made by the smooth muscles in their lungs to take in air.<ref name=":44" /> [[File:Amphiumadig.jpg|thumb|Amphiuma digestive tract. Specimen from the Pacific Lutheran University Natural History collection, dissection and photos by Misty Lang and Nina Thach.]]