STRUCTURE OF CARTILAGINOUS FISHES. 119 



LESSON IX. ' 



DIVISION OF CARTILAGINOUS FISHES, OR CHONDROPTERYGIANS. 



Oiyanizntiou. 



ORDER OP STURIONSS. Sturgeons. Caviar. fish-glue. 

 ORDER OF SELACHII. Shark*. Satv-Jish. Rays. Torpedo. 

 ORDER OP CYCLOSTOMI. Lampreys. 



DIVISION OF CHONDROPTERYGII, OR CARTILAGINOUS 

 FISHES. 



The Chondropterygians differ in many respects from all the 

 fishes we have spoken of, and are less uniform in their structure. 

 Some of them have organs even more complicated than the last, 

 and approximate more to the reptiles, while others form a sort of 

 connecting link, between the vertebrata and inferior classes of 

 animals. 



1. Their skeleton is essentially cartilaginous: it is not formed 

 of bony fibres, anJ the calcareous matter that hardens on its 

 surface, is only deposited in small grains Sometimes the skeleton 

 is only membranous, and it is always more simple in its confor- 

 mation than that of the osseous rishes. It is also remarked, there 

 is a resemblance between it and the cartilaginous skeleton of the 

 tadpole. The cranium is not divided by sutures, and is composed 

 of a single piece, shaped in other respects very much like the 

 skull of an ordinary Hsh. The uppei jaw is formed of pieces 

 analogous to the palate bones and vorner ; the maxillary and 

 intermaxillary bones do not exist, or are found only in a rudi- 

 mentary state, concealed beneath the skin The lower jaw is 

 constituted of one piece on each side, and the opercular apparatus 

 is, in general, entirely wanting. The vertebral column is some- 

 times formed, in a great part, of a single tube, pierced on each 

 side for the passage of nerves, but not divided into distinct 

 vertebrae ; frequently too, the bodies of the vertebrae are pierced 

 through and through, so that the gelatinous substance, which tills 

 the spaces betwixt these bones, forms a continuous cord. The 

 disposition of the bones of the shoulder, of the pelvis, and fins, 

 varies The hyoid apparatus, which supports the branchiae, is, 

 in general, much the same as it is in ordinary fishes; but. 

 towards the termination of this series or division, the branchial 

 arches are wanting, and the branchiae are only attached, on the 



1. What are the characters of the skeleton of cartilaginous fishes? 

 there any thing peculiar in the arrangement of their branchiae ? 

 2Q* 



