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STRUCTURE OF FISHES. 20V 



between each flake, the branches of which seem to enter Particular dc«- 

 without ramifying there. Another small nerve passing ^JP^l^offishef 

 from the head, and running deep-seated, and close to the 

 dorsal spines, crosses and unites with each of the spinal 

 fibrils, and at the junction a remarkable body appears : 

 it is a loose transparent vesicle, about the size of a millet- 

 seed, containing a white substance like the carbonate of 

 lime found in the intercostal ganglions of frogs. This 

 vesicle is included within the sheath of the nerve. 



The coats of the blood-vessels are of a delicate texture, 

 and easily ruptured. In order, therefore, to secure them 

 from being injured by the violent and sudden actions of 

 the muscles, the principal trunks both of the arteries and 

 veins are inclosed in osseous canals, formed by the bases 

 of the superior and inferior spinous processes ; and their 

 first ramifications lie vrithin grooves in the spines. As 

 they pass out to supply the muscles, their branches are 

 immediately subdivided, so that a considerabfe vessel soon 

 becomes extremely minute. 



The rate, at which many fishes move through a medium Fish movewlth 

 so dense as water, is very remarkable ; their velocity loc^y f n^ariv" 

 being scarcely surpassed by the flight of the swiftest birds ; equal to that 

 and although the large proportion of muscles, and their °^^^^*^'' 

 advantageous application, may partly account for the phe- 

 nomenon, yet the power would be inadequate to the eflect, 

 if it were not suddenly enforced; as is evident from the 

 glow progress of eels, and such fishes as are incapable 

 from their length and flexibility, of giving a sudden late- 

 ral stroke. 



But the quickness and for.ce of action in the muscles of This extreme 

 fishes are counterpoised by the short duration of their ^^^'^^ ^* ^^^'^ 

 powers. Those accustomed to the diversion of angling, 

 are aware how speedily the strength of a fish is ex- 

 hausted, for if, when hooked, it be kept in constant 

 action, it soon loses even the ability to preserve its ba- 

 lance, and turns upon its side, fatigued and incapable of 

 motion. This has been vulgularly attributed to drown- 

 ing, in consequence of the mouth being closed upon the 

 hook ; but the same eflfects take place when the hook 

 is fastened to the side, or tail. This prostration of 

 strength n^ay depend partly on fear, and partly on iu^ 



terrupted 



