Modern amphibians occupy a pivotal point in the understanding of important evolutionary events such as the change from anamniotic to amniotic eggs, realization of air-breathing, and the transition from aquatic to terrestrial life. Contemporary amphibians fall into 3 orders. These are: Apoda, Anura, and Urodela. During the larval stages of development, amphibians have transient external and internal gills. The morphological heterogeneity and multiplicity of the amphibian gas exchangers correspond to the remarkable diversity of habitats and environments they occupy, the lifestyle they pursue, and their pattern of interrupted development. Amphibian lungs are best-developed in Anura where septa intensely subdivide the lung, converting the large central air space into small, stratified air cells. The lungs of most amphibian species, such as Amphiuma means, Bufo marinus, Boulengerula taitanus and Chiromantis petersi, have a preponderance of smooth muscle tissue that may explain their high compliance.