36(j 



THE MECHANICAL FUNCTIONS. 



nor even for the cellular or cancellated structure 

 which we have noticed in the more perfect bones.* 

 The general disposition of the bones which com- 

 pose the entire skeleton will be understood from 

 Fig. 184, which represents that of the Ci/prinus 



carpio, or carp. The muscular flesh of fishes is 

 likewise softer than that of the higher classes; 

 and the cellular substance more attenuated and 

 more gelatinous ; so that the membranes which it 

 forms are of a looser and more pulpy texture. 



Progressive motion in fishes is effected by the 

 simplest means, the principal instrument employed 

 for this purpose being the tail ; for the fins, as we 

 shall presently find, are merely auxiliary organs, 

 serving chiefly to balance the body, while it re- 

 ceives its propulsion from the tail. A fish moves 

 in the water on the same principle as a boat is 

 impelled in paddling ; for the action of the tail on 

 the water is lateral, like that of an oar, which it 

 resembles in the vertical position of its plane ; and 

 the effect is transferred by the resistance of the 

 water to the body whence the impulse originates. 



* Cuvier, sur les Poissons. Tom. i. p. 218. 



