Gills

GILLS, aquatic respiratory organs, which in lower vertebrates are located in special gill slits. Gills represent complex folds of the mucous membrane, abundantly supplied with venous blood. They are supported by a skeleton consisting of gill arches (see). Periodic respiratory movements cause a flow of water passing between the G. through the gill slits to the outside. In addition to such internal (in position) G., in the larvae of some fish, as well as in amphibians, branched external G. sometimes develop, situated on the outer surface of the lateral walls of the head. (See also Respiratory organs). The origin of branchiogenic fistulas - see Gill arches, slits.