246 PISCES. 



in the latter genus it always consists of a single piece, but in Diodon 

 and Tetrodon of two ; in all these genera, as in Uranoscopus and 

 Cyclopterus, the copula is wanting. The piece supporting the 

 tongue is absent in Tetrodon, Diodon, Balistes, Muraenophis, and 

 others. The branchiostegous rays are very rarely wanting, as in 

 Syngnathus. Polypterus has only one of these rays, while three are 

 found in Cyprinus, Cobitis, and others ; seven in Muraena anguilla, 

 twenty-five in M. colubrina, and upward of thirty in Elops. The 

 passage from the Osseous to the Cartilaginous Fishes is made by the 

 Sturgeon, in which the hyoid arch consists of three pieces instead of 

 four, and both copula and branchiostegous rays are entirely wanting. 

 In the Sharks a cartilaginous arch is found upon either side, sup- 

 porting some cartilaginous rays, divided simply in a digitate manner. 

 In the Rays similar arches are found, supporting a pair of pseudo- 

 branchiae. 



Behind the hyoid bone is situated a system of bones or cartilages 

 called the Branchial arches, very generally four in number, and 

 which support the vascular fringes or leaflets of the gills. Each 

 arch consists of several pieces, varying in number according to the 

 species of fish and the several arches themselves. There are, how- 

 ever, never more than four pieces, mostly three, and rarely two ; 

 upon their convex side they are channeled out for the lodgement of 

 the branchial vessels, while on their concave side, or that turned 

 toward the cavity of the mouth, they are mostly beset with teeth, 

 and the upper segments of the posterior arches are usually so strong, 

 that they have been distinguished by the special name of ossa pha- 

 rytigea superiora ; the postero-inferior pharyngeal jaws are also in- 

 timately related, both by form and position, to the last and rudi- 

 mentary branchial arches. In the direction downward the branchial 

 arches are usually attached, like ribs to a sternum, to an interme- 

 diate chain of bones or cartilages, two to four in number, which are 

 articulated in front with the copula of the hyoid bone ; the posterior 

 arches are frequently united to this central chain by fibrous liga- 

 ments only, for it is seldom that all the arches are directly con- 

 tinued and connected to it by bone. Superiorly the branchial arches 

 are generally attached by muscles and cellular tissue, or by true 

 ligaments, to the basal surface of the skull, or sometimes further 

 backward to the first vertebrae. The teeth are usually disposed 

 in two rows upon the inner side of the branchial arches, and are 

 rarely absent, as in Cyprinus, Muraena, Mursenophis, Lophius, Fis- 

 tularia, and others. The median chain of ossicles uniting the 



