Water-breathing fishes irrigate their gills with a dual pump mechanism
in which buccal and opercular cavities operate in tandem. Air-breathing fishes use a buccal pump mechanism, a modification of the dual
pump in which the buccal cavity is the major mechanical component. In adult amphibians, lung ventilation is based on a modified buccal
pump in which the opercular pump is lost entirely. However, the amphibian skull design is compromised because the buccal cavity must
function in feeding and in lung ventilation. One solution is found in plethodontid salamanders. Gas exchange is taken over entirely by
cutaneous respiration, and lungs are lost; therefore, the buccal cavity serves only feeding. In amniotes, the aspiration pump completely
separates feeding from lung ventilation, uncoupling demands on the jaws for service in both activities. The basic dual and buccal pumps
are specialized in many fishes. Bird respiration represents a specialization of the aspiration pump.