I70 OUTLINES OF ICHTHYOLOGY. 



The numbers of fin-rays difier entirely In various 

 species, and, occasionally, in different individuals of 

 the same species. 



The names of the fins are derived from the parts 

 of the body to which they are most commonly 

 attached, as shown in the annexed diagram. They 

 are : — 



A. The pectoral or breast fins (so called from being placed 

 on the breast or shoulder of the fish). 



E E. The dorsal, or back fins. 



B. The ventral fins (named from their position on the belly). 



C. The anal fin (placed close behind the anal aperture). 



D. The caudal, or tail fin.' 



F marks the lateral or side line. 



This list includes the names of all the different 

 kinds of fins possessed by any fish, though the 

 numbers and arrangements of them vary in almost 

 every family, — some fish, such as the Salmon, for 

 instance, having two dorsal fins, and others, as the 

 Eels, lacking the ventrals altogether. The pec- 

 toral fins are considered to answer to arms or fore- 

 legs in other animals, and the ventrals to the 

 hinder legs ; and by means of the former several 



' These names are derived from the Latin — pectus, the 

 breast ; dorsum, the back ; venter, the belly ; anus, the anal 

 aperture; cauda, the tail. 



