230 VERTEBRATE ANIMALS. 
the framework (rays) of the so-called “median” fins. Asa rule 
there is only one interspinous bone to each vertebra, but in the 
flat fishes (sole, turbot, &c.) there are two. The limbs of fishes 
may be wholly wanting, or one pair may be absent, but in no 
case is the number greater than the regular vertebrate type— 
namely, two pairs. When developed, however, the limbs of 
fishes are very different from those of other Vertebrates, con- 
sisting of expansions of the integument, furnished with bony or 
gristly supports or rays, and thus constituting what are called 
“fins” (fig. 124). The pair of limbs which correspond to the 
arms of man and to the fore-limbs of other Vertebrates are termed 
the Zectoral fins, and they are attached to a bony arch which is 
attached either to the back of the skull or to the spinal column 
(fig. 123, g, and 124, ). The hind-limbs in fishes are known 
Fig. 124-—Outline of a Fish (Perca granulata), showing the “paired” and 
‘‘median” fins. Pectoral fin; w Ventral. fin; @ First dorsal fin; ad Second 
dorsal fin ; ¢ Caudal fin ; @ Anal fin. 
as the ‘ventral fins (figs. 123, 124, 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 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 sup- 
ports them is freely suspended in the muscles. In others the 
ventral fins are aitogether out of position, and are placed be- 
neath or even in front of the pectoral fins; and in these cases 
the pelvic arch is attached to part of the pectoral arch. The 
