8 FISHES. 



membrane, more or less transparent, stretched 

 over parallel or radiating rays. These rays are 

 slender bones, sometimes consisting of a single 

 piece, stiff and spinous ; at other times composed 

 of several pieces jointed together, and therefore 

 flexible ; the latter are frequently divided each 

 into two or more branches at the tip. These cha- 

 racters of the fin-rays afford a ground for the 

 division of one of the Sub-classes into Orders. 



The fins of Fishes are of five kinds, and are 

 designated according to their position, as pectoral , 

 or breast-fins ; ventral, or belly-fins ; dorsal, or 

 back-fins ; anal, or vent-fins ; and caudal, or 

 tail-fins. The pectorals and ventrals are arranged 

 in pairs, and correspond to the fore and hind 

 limbs in other vertebrate animals ; the pectorals, 

 for instance, representing the wings of birds, 

 the ventrals the feet. The other kinds have 

 nothing corresponding to them in the other 

 Classes, except it be the web-like expansion of 

 skin that fringes the Newts, &c., or the carti- 

 laginous dorsal in some of the Cetacea. The dorsal 

 runs along the medial line of the back ; it w^as 

 formerly supposed to preserve the body in a per- 

 pendicular position in the water, but recent ex- 

 periments have shown that it is not necessary for 

 that object, though it may be accessory to it. 

 Almost all fishes have this fin, and many have 

 two ; while a few, as the Haddock and Cod, have 

 three dorsals. The anal fin corresponds to the 

 dorsal, but is placed beneath the body, just be- 

 hind the vent. The caudal is the most important 

 fin of all, being the great organ of motion. It is 

 the termination of the body, being expanded 

 around the postejior extremity. In those fishes 



