PISCES FISHES. 



503 



will have little diffi- Fig- 225. 



culty in comparing 



the different pieces 



of the skeleton of the 



Flounder (Pleuro- 



nectes flesus) with 



the corresponding 



bones of the Perch 



already described. 



(540.) The ske- 

 letons of the Car- 

 tilaginous Fishes 

 (Chondropterygii *) 

 will require a dis- 

 tinct notice, inas- 

 much as they pre- 

 sent very remarkable 

 peculiarities of no 

 inconsiderable inter- 

 est. In the Sharks, 

 Skates, and other 

 genera belonging to 

 this important divi- 

 sion of the great 

 class we are now con- 

 sidering, the interior 

 of the bones remains 

 permanently cartila- 

 ginous, but the ske- 

 leton is in some re- 

 gions encrusted, as it were, with osseous granules. No centres of 

 ossification, from which radiating fibres of bony matter progressively 

 extend themselves, as is the case in the osseous fishes, are ever de- 

 veloped ; and consequently the skull, although it presents exter- 

 nally the same regions, eminences, and apertures that are usually 

 met with, is never divided into separate bones, but is formed of a 

 single mass of cartilage, in which no sutures or lines of division are 

 ever distinguishable. 



The face is likewise much more simple in its structure ; for, 

 instead of the numerous pieces composing the palato-temporal 

 region of the Perch (j 532), two bones only are met with, one of 



* ^avSga;, cartilage ; x-Ttpuyiav, a fin. 



