CHONDROPTERYGII BRANCHIIS FIXIS. 227 



ORDER II. 



CHONDROPTERYGII BRANCHIIS FIXIS, 



OR the Chondropterygii with Jixed bronchia, instead of having those organs 

 free on the external edge, and opening all their intervals into a large common 

 orifice, as is the case in all the fishes of which we have hitherto spoken, have 

 them adhering by this external edge in such a manner that they permit the 

 water to escape through as many holes pierced in the skin as there are intervals 

 between them, or, at least, that these holes may terminate in a common duct, 

 through which the water is ejected. Another circumstance peculiar to these 

 fishes is the presence of little cartilaginous bows, frequently suspended in the 

 muscles opposite to the external edges of the branchiae, and which may be 

 termed branchial ribs. 



FAMILY I. 



SELACHII. 



THIS family, hitherto comprised under two genera, SQUALUS and RAIA, has 

 many common characters. The palatines and post- 

 mandibularies, alone armed with teeth, supply the 

 place of jaws, the usual bones of which are reduced to 

 mere vestiges ; one single bone suspends these apparent 

 jaws to the cranium, representing at once the tympanal, 

 jugal, and temporal bones, and the preoperculum. The hyoid bone is attached 

 to the single pedicle just mentioned, and supports branchiostegal rays, as in 

 ordinary fishes, although they are not so very visible externally ; it is followed 

 by the brancliial arches, as usual, but neither of the three pieces compose the 

 operculum. These fishes have both pectorals and ventrals: the latter are 

 situated behind the abdomen. Their membranous labyrinth is inclosed by 

 the cartilaginous substance of the cranium ; the sac, which constitutes part of 

 it, contains mere amylaceous masses, and not stones. 



SQUALUS, Linnceus. 



The Sharks form a first great genus, distinguished by an elongated body, a 

 thick fleshy tail, and moderate pectorals, so that the general figure approaches 

 that of ordinary fishes ; the branchial openings correspond with the sides of 

 the neck, and not with the under surface of the body, as we shah 1 see is the 

 case with the Rays ; the eyes also are on the sides of the head. The snout 

 is supported by three cartilaginous branches connected with the anterior 

 part of the cranium, and the rudiments of the maxillaries, intermaxillaries, 

 and premandibularies are evident in the skeleton. 



Several are viviparous. The others produce ova invested with a yellow and 

 transparent horn, the angles of which are prolonged into horny cords. The 



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