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the system of skeletal elements of the pharynx in cyclostomes and fish. Each gill arch embraces the pharynx in a half-ring. The majority of present-day fish have five gill arches; cyclostomes and some sharks have up to seven. In bony fish the number of gill arches may be reduced to three with the reduction of the posterior ones. Cyclostomes, cartilaginous fish, sturgeon, and dipnoans have cartilaginous gill arches; bony fish have bony gill arches.
Fully developed gill arches offish consist of four movably united segments. In bony fish the fifth gill arch, which is called the subpharyngeal bone, is usually rudimentary, but sometimes (in cyprinoids) bears teeth and is very powerful. In terrestrial vertebrates, the superior segments of the gill arches are reduced; the inferior ones participate in the formation of the subglossal apparatus and become the laryngeal cartilage.
REFERENCESSevertsov, A. N. “Morfologiia vistseral’nogo apparata elasmobrankhii.” Sobr. soch., vol. 4. Moscow-Leningrad, 1948.
Gimmerreikh, G. A. “Vistseral’nyi apparat osetroobraznykh kak organ priema pishchi.” In Voprosy evoliutsionnoi morfologii pozvonochnykh. Moscow, 1963.