EXTERNAL ORGANS OP FISHES. 



FIG. 345. BEARDED MULLET, showing position of 

 fins ; p, pectoral fin ; v, ventral fin ; d>, first dorsal ; 

 d 8 , second dorsal ; c, caudal; a, anal; o, opening of 

 gill-covers. 



The anterior members, which correspond with the arms of Man 

 and the wings of Birds, are fixed on each side of the trunk, 

 immediately behind the 

 head, and are called pec- 

 toral fins. The abdo- 

 minal members are less 

 separated from each 

 other, and are generally 

 found on the lower side 

 of the body ; they may 

 be situated more or less 

 forwards or backwards, 

 from the under part of 

 the throat to the com- 

 mencement of the tail ; these are called ventral fins. The single 

 fins occupy, as we have already said, the central line of the 

 body ; and are divided into dorsal fins, anal fins, and caudal fins, 

 according as they are placed along the back, under the tail, or 

 at its extremity. They have all very nearly the same structure, 

 and consist almost always of a fold of skin, supported by bony 

 or cartilaginous rays ; very nearly in the same manner as tho 

 wings of bats and dragons are sustained by the fingers or by the 

 ribs, of the animals. 



537. On the external surface of the body, large openings are 

 seen on each side ; which are placed immediately behind the 

 head, and which serve as an outlet for the water that has passed 

 through the gills. In general there is only one on each side ; 

 and its anterior edge is moveable, and resembles a flap or 

 valve. 



538. The skin is sometimes almost entirely bare, but it is 

 generally covered with scales. Occasionally these scales have 

 the appearance of coarse grains, at other times they exist as 

 large tubercles or plates of considerable thickness; but in 

 general they present the aspect of very thin laminae or plates, 

 arranged in the manner of tiles upon a roof, and held together in 

 the folds of the skin. We may compare them to our nails ; but 

 they contain a much larger quantity of calcareous salts. The 



