42 FISHES. 



traced. Sometimes the dorsal fin of Malacopterygian fishes is 

 very long, extending from the head to the end of the tail, some- 

 times it is reduced to a few rays only, and in a few cases it is 



Fig. 5. — Saurus undosquamis, a Malacopterygian with anterior 

 soft dorsal, and additional adipose fin. 



entirely absent. In addition to the rayed dorsal fin, many 

 Malacopterygian fishes (as the Salmonoids, many Siluroids, 

 Scopeloids, etc.) have another of greater or lesser extent, with- 

 out any rays ; and as always fat is deposited within this fold, 

 it is called a. fatty fin {pinna adiposa). 



The anal fin is built on the same plan as the dorsal, and 

 may be single or plural, long or short, or entirely absent ; in 

 Acanthopterygians its foremost rays are frequently simple and 

 spinous. 



The horizontal or paired fins consist of two pairs : the 

 pectorals and ventrals. 



The pectoral fins (with their osseous supports) are the 

 homologues of the anterior limbs of the higher Vertebrata. 

 They are always inserted immediately behind the gill-opening ; 

 either symmetrical with a rounded posterior margin, or asym- 

 metrical, with the upper rays longest and strongest ; in Mala- 

 copterygians with a dorsal spine the upper pectoral ray is 

 frequently developed into a similar defensive weapon. 



The ventral fins are the homologues of the hmd-limbs, and 

 inserted on the abdominal surface, either behind the pectorals 

 {Pisces s. Pinnm abdominales), or below them {Pisces s. Pinnm 

 tJioracicce), or in advance of them {Pisces s. Pinnm jtigulares). 

 They are generally narrow, composed of a small number of 



