62 ACTION OF THE FINS IN FISHES. 



by a special prolongation of tlie carpal joint of the pec- 

 toral fin, which projects in these " frog fishes," as they 

 have been termed, like the limb of a land quadruped, and 

 presents two distinct segments clear of the trunk. 



The sharks, whose form of body and strength of tail 

 enable them to swim near the surface of the ocean, are 

 further adapted for this sphere of activity, and compen- 

 sated, for the absence of an air-bladder, by the large pro- 

 portional size of their pectoral fins, which take a greater 

 share in their active and varied evolutions than in ordi- 

 nary fishes ; more especially in producing that half turn 

 or roll of the body required to bring the mouth, which is 

 on the under part of the head, in contact with their prey. 

 The maximum of development of the many-fingered 

 hands is attained in the rays, and in those fishes — e. g.^ 

 .Exoccetus and Dactylopterus — called "flying fishes," in con- 

 sequence of the pectorals being long enough, and their 

 webs broad enough to sustain them in the air, in their 

 long " flying leaps" out of the water. 



With regard to the ventral fins — the rudiments of hind- 

 limbs — these combine merely with the pectorals in raising 

 the fish, and in preventing, as outriggers, the rolling of 

 the body during progression. In the long-bodied and 

 small-headed abdominal fishes the ventrals are situated 

 near the vent, where they best subserve the office of ac- 

 cessory balancers ; in the large-headed thoracic and jugu- 

 lar fishes they are transferred forwards, to aid the pectorals 

 in supporting and raising the head. If the pectoral and 

 ventral fins in one of these fishes be cut off, the head 

 sinks to the bottom ; if the right pectoral fin only be cut 

 ofF, the fish leans to that side ; if the ventral fin on the 

 same side be cut away, then it loses its equilibrium en- 

 \ tirely ; if the dorsal and anal fins be cut ofij the fish reels 



