xiv GIANT FISHES, WHALES AND DOLPHINS 



fish, are supported by structures known as fin-rays, and are 

 further strengthened at their bases by special parts of the 

 internal skeleton. The fins are of two kinds : median or 

 unpaired, and paired. The median fins consist of a dorsal in 

 the middle line of the back, an anal on the middle line of the 

 belly behind the vent, and a caudal or tail-fin at the hinder 

 end of the fish. The fleshy part of the tail behind the dorsal 

 and anal fins is known as the caudal peduncle. The paired fins 

 are of two kinds only, the pectorals and pelvics, corresponding 



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Topography of a Fish. 



respectively to the fore- and hind-limbs of land Vertebrates. 

 The pectorals are nearly always placed just behind the head, 

 but the position of the pelvics varies in different fishes, some- 

 times being well back on the belly, sometimes more or less 

 below the pectorals, and sometimes in front of the pectorals. 

 The form and position of the various fins present considerable 

 diversity in the different groups of fishes, and are of some 

 importance in classification (Fig. i). 



We have seen that the fins are supported by structures 

 known as fin-rays, which are usually joined to one another by 

 fine membrane. In the Selachians the rays are all covered 

 over with a thick skin and are quite invisible. In many Bony 

 Fishes all the fin-rays have the form of flexible jointed rods 

 (soft-rays), which may be simple or branched and brush-like 



