EXTERNAL ANATOMY OF FISHES. FINS. 15 



are viviparous, the young being protruded through a 

 very short canal. 



(18.) On the external anatomy of fishes, and of 

 their natural history, we shall he less concise. Next to 

 the structure of the bones, the fins claim our greatest 

 attention ; since itis an acknowledged fact, that the organs 

 of locomotion are those which have furnished the best 

 characters, above all others, for distinguishing the various 

 subdivisions, not only of vertebrated, but of annulose 

 animals. We shall first describe their number and 

 position, and then point out several interesting con- 

 clusions resulting therefrom. 



(19.) There are five sorts of fins possessed by the 

 typical groups ; which are named pectoral, ventral, anal, 

 dorsal, and caudal : the two first of these are in pairs, and 

 are the most important, inasmuch as they represent those 

 members in the higher organised Vertebrata, that are 

 called legs and wings. The pectoral fins, in fact, are 

 only the anterior feet of quadrupeds, and the wings of 

 birds, presented under a new and strikingly different 

 form : the three other fins are single, or, in other words, 

 they are not in symmetrical pairs. Each of these will 

 require a separate consideration, more especially as they 

 have hitherto been regarded with little attention. 



(20.) The pectorals are, obviously, the most im- 

 portant to fishes in general ; because we find them in 

 groups, where several of the other fins are wanting, and 

 it is only among the lampreys, and a very few genera, so 

 low in the scale as to form a passage to the worms, that 

 they disappear. In the majority of fishes they are of the 

 same moderate size as the ventrals, but in particular fa- 

 milies they become much m ore developed : they are alway s 

 composed of flexible*, and, generally, branched rays, 

 so as to yield to every stroke on the water made by fishes 

 in the act of swimming. When the shape is pointed 

 or triangular, the first ray is either very strong or spinous. 

 This spine, in the silure family, is not only remarkably 



* The only exception we are aware of at this moment, is a small species of 

 blenny, the B. variabilis of Rafinesque, whose psctoralrays are all spinous. 



