Editing Amphibian (section)

=== Skeletal system and locomotion ===
[[File:Xenotosuchus skull roof.svg|thumb|Skull diagram of ''[[Xenotosuchus]],'' a temnospondyl]]
Amphibians have a skeletal system that is structurally [[Homology (biology)|homologous]] to other tetrapods, though with a number of variations. They all have four limbs except for the legless caecilians and a few species of salamander with reduced or no limbs. The bones are hollow and lightweight. The musculoskeletal system is strong to enable it to support the head and body. The bones are fully [[ossification|ossified]] and the vertebrae interlock with each other by means of overlapping processes. The [[pectoral girdle]] is supported by muscle, and the well-developed [[pelvic girdle]] is attached to the backbone by a pair of sacral ribs. The [[ilium (bone)|ilium]] slopes forward and the body is held closer to the ground than is the case in mammals.{{sfn | Dorit | Walker | Barnes | 1991 | p=846 }}

[[File:Ceratophrys cornuta skeleton front.jpg|thumb|alt=Frog skeleton|Skeleton of the [[Surinam horned frog]]<br/>(''Ceratophrys cornuta'')]]
In most amphibians, there are four digits on the fore foot and five on the hind foot, but no claws on either. Some salamanders have fewer digits and the [[amphiuma]]s are eel-like in appearance with tiny, stubby legs. The [[Siren (genus)|sirens]] are aquatic salamanders with stumpy forelimbs and no hind limbs. The caecilians are limbless. They burrow in the manner of earthworms with zones of muscle contractions moving along the body. On the surface of the ground or in water they move by undulating their body from side to side.{{sfn | Stebbins | Cohen | 1995 | pp=26–36 }}

In frogs, the hind legs are larger than the fore legs, especially so in those species that principally move by jumping or swimming. In the walkers and runners the hind limbs are not so large, and the burrowers mostly have short limbs and broad bodies. The feet have adaptations for the way of life, with webbing between the toes for swimming, broad adhesive toe pads for climbing, and keratinised tubercles on the hind feet for digging (frogs usually dig backwards into the soil). In most salamanders, the limbs are short and more or less the same length and project at right angles from the body. Locomotion on land is by walking and the tail often swings from side to side or is used as a prop, particularly when climbing. In their normal gait, only one leg is advanced at a time in the manner adopted by their ancestors, the lobe-finned fish.{{sfn | Dorit | Walker | Barnes | 1991 | p=846 }} Some salamanders in the genus ''[[Aneides]]'' and certain [[lungless salamander|plethodontids]] climb trees and have long limbs, large toepads and prehensile tails.<ref name="BritCaudata" /> In aquatic salamanders and in frog tadpoles, the tail has [[dorsal fin|dorsal]] and [[ventral fin|ventral]] fins and is moved from side to side as a means of propulsion. Adult frogs do not have tails and caecilians have only very short ones.{{sfn | Stebbins | Cohen | 1995 | pp=26–36 }}
[[File:Didactic model of an amphibian heart-FMVZ USP-14.jpg|thumb|left|upright=0.65|[[Educational toy|Didactic model]] of an amphibian heart.]]
Salamanders use their tails in defence and some are prepared to jettison them to save their lives in a process known as [[autotomy]]. Certain species in the Plethodontidae have a weak zone at the base of the tail and use this strategy readily. The tail often continues to twitch after separation which may distract the attacker and allow the salamander to escape. Both tails and limbs can be regenerated.<ref name="Beneski">{{cite journal | author=Beneski, John T. Jr. | date=September 1989 | title=Adaptive significance of tail autotomy in the salamander, ''Ensatina'' | journal=Journal of Herpetology | volume=23 | issue=3 | pages=322–324 | doi=10.2307/1564465 | jstor=1564465 }}</ref> Adult frogs are unable to regrow limbs but tadpoles can do so.{{sfn | Stebbins | Cohen | 1995 | pp=26–36 }}