FISHES. 



231 



fins (figs. 165, 166, v), and are not only often wanting altogether, 

 but when present are less developed than the pectorals and less fixed 

 in their position. They ai-e united to an imperfect bony arch, which 

 represents the innominate bones, or pelvic arch, of the higher Verte- 

 brates, but which is never joined to the spinal column. In some 

 fishes the ventral fins are placed far back, and in these the bony 

 arch which supports them is freely suspended in the muscles. In 

 others the ventral fins are altogether out of position, and are placed 

 beneath or even in front of the pectoral fins ; and in these cases the 

 pelvic arch is attached to part of the pectoral arch. The pectoral 

 and ventral fins represent, as just said, the fore and hind limbs, and 

 consequently there are always two of each, when they are present at 

 all. They are therefore spoken of as the " paired " fins. Besides 



r. 166. — Outline of a Fish (Ferca granvlatii), showing the " paired " and " median " 

 fins, p Pectoral tin; v Ventral tin; d First dorsal fin; cV Second dorsal fin; c 

 Caudal fin ; a Anal lin. 



these, however, or in the absence of one or both of these, there is 

 also a series of what are called " median '' fins ; that is to say, fins 

 which are placed in the middle line of the body, and which are un- 

 paired, having no fellows. These median fins agree with the paired 

 fins in being expansions of the integument, supported by bony or 

 gristly supports or " rays," and they are carried by the heads of the 

 " interspinous " bones, already described (fig. 165, i i). They are 

 variable in number, and in some cases there is only a single fringe 

 running round the hinder extremity of the body. Commonly, how- 

 ever, the median fins consist of one, two, or three expansions of the 

 dorsal integument, called the " dorsal " fins (fig. 165, d d') ; one or 

 two on the ventral or lower surface near the vent, called the " anal " 

 fins (a) ; and a broad fin at the extremity of the vertebral column, 

 constituting the '' caudal " fin or tail (c). 



