78 OUTLINES OF NATURAL HISTORY. 



two pairs. The front pair (fig. ^^, p) represents the fore- 

 legs, and is termed the "pectoral fins" (Latin, pectus, the 

 breast). They are placed on the side of the body, just 

 behind the head. The hinder pair (fig. 33, v) represents 

 the hind-legs, and is termed the "ventral fins" (Latin, 

 venter, the belly), being placed on the lower surface of the 

 fish, behind and below the pectorals. Both the pectoral 

 and ventral fins of the fish are employed chiefly in steering 

 the animal, and more especially in ascending and descend- 

 ing in the water. All the "rays," lastly, of the pectoral 

 'fins are "soft" and jointed ; and all those of the ventral 

 fins have the same character, with the exception of the 

 first ray, which is " spinous." 



The "uni^aired" fins are divided into three sets : one 

 placed above or on the back, one placed at the end of the 

 body, and one placed below. The unpaired fins along the 

 back are two in number (fig. 33, d, d'), and are known as 

 the first and second "dorsal fins" (Latin, dorsum, the 

 back). The first dorsal is supported by fifteen "spinous" 

 rays, the second dorsal by rays of which all but the first 

 are "soft." The function of the dorsal fins is chiefly to 

 enable the fish to maintain its equilibrium and vertical 

 position in the water. The unpaired fin at the end of the 

 body is commonly called the " tail," but is technically 

 known as the "caudal fin" (Latin, cauda, the tail). It is 

 entirely supported by "soft" rays, and is symmetrical in 

 form, consisting of two equal lobes (fig. 33, c). The posi- 

 tion of the tail is vertical, so that it strikes the water from 

 side to side. Along with the whole flexible hinder end of 

 the body, it constitutes the main organ of progression of 

 the fish, its powerful strokes driving the animal forwards, 

 much as a boat can be propelled by a single oar placed 

 over the stern. Lastly, a single unpaired fin (fig. 33, a) is 

 placed upon the lower surface of the body in front of the 

 tail, and is known as the "anal fin" (Latin, anus, the 

 vent), because it is placed near the vent. All its rays are 

 "soft," except the first two, which are rigid spines. 



The skeleton of the Perch (fig. 35) is very complicated, 

 and can only be briefly alluded to. Its most important 



