G. ST. H1LA1RE ON THE FAHAKA OF THE NILE. 117 



separating them from a third,, more external and more slender, 

 numbered O, leads us to think that this last does not belong to the 

 abdominal muscles, but that it is analogous to the fleshy wattle 

 (panicule charnue) ; it extends considerably beyond the region of the 

 stomach, is continued to the head, and furnishes branches which 

 spread themselves over the muscles of the breast fins : the direction 

 of the fibres is across, and some are seen as well above as below. 



It always concurs, with the two other muscles L and M, in the 

 expulsion of the air from the pouch, and of course in diminishing its 

 capacity : it folds the skin across L obliquely, and M lengthwise -, 

 forming three powers, the concurrence of which diminishes the sur- 

 face of it. 



We now know then the nature of this great air pouch of the 

 fahaka : let us next show by what agents the air is kept in it while 

 distended. 



The Swim Bladder. 



The most remarkable of these agents is the swim-bladder, which 

 only acts by impulsion and in a passive manner. It will excite 

 surprise, I dare say, that it should figure here, when its functions 

 are transferred to the stomach. It is known that, in many fishes, 

 its use is to communicate with the fauces (arrilre-boucke), and to 

 receive air from it. This is not the case with that of the fahaka, 

 which does not communicate with the mouth by any air-tube or 

 opening j but is a sac closed in every part, of the form of a horse- 

 shoe, the circular margin of which is directed forward, and the ter- 

 minating branches backwards. Fig. 2 represents it of the natural 

 size.* 



Its surface, visible in the design, is adherent, but by a very loose 

 cellular tissue to the part of the stomach which is above it ; the 

 other surface adheres in a similar manner to the spine, so that it is 

 there only suspended in a manner, and may be carried both forward 

 and backward. 



The opening marked G, which is seen above the swim-bladder, is 

 the section of the gullet or intermediate canal, which is between the 

 fauces and the stomach. 



* This is diminished two thirds in our copy of the figure. EDITOR. 



