PISCES. 



209 



attached to a bony arch which is attached either to the back 

 of the skull or to the spinal column (Fig. 101,^5, and 10|,^). 

 The hind-limbs in fishes are known as the ventral fins (Figs. 

 101, 103, v), and are not only often wanting altogether, but 

 when present are less developed than the pectorals and less 

 fixed in their position. They are united to an imperfect bony 



Fig. 102. — Outline of a Fish (P&rca gratmlata), showing the "paired" and "median" fins, 

 p Pectoral fln; r Ventral fin; (2 First dorsal fin; d' Second dorsal fin; c Caudal fin; 

 a Anal fin. 



arch, which represents the innominate bones, or pelvic arch, 

 of the higher Vertebrates, 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 alto- 

 gether 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 ven- 

 tral 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 these, however, or in the absence of one or 

 other of these, there is also a series of what are called " me- 

 dian " fins ; that is to say, fins which are placed in the middle 

 line of the body, and which are unpaired, having no fellows. 

 These median fins agree with the paired fins in being expan- 

 sions of the integument, supported by bony or gristly supports 

 or " rays," and they are carried by the heads of the " inter- 

 spinous" bones, abeady described (Fig. 101, ii). They are 



