ON THE RESPIRATION OF FI9IIE3. 355 



other; all the hinder part of the head is enlarged by the 

 raising of the opercula; the bony arches, that support the 

 bronchial laminae, are acted upon by the hyoides, which is ' 

 depressed as in the act of swallowing; these arches separate 

 from each other, and the water immediately enters into the 

 spaces between them ; but, at the moment these operculi 

 are raised and separated from the body, the hyoides and all 

 the bronchial laminae connected with it rise against th^e 

 arch of the palate, and drive before them all the water con* 

 tained in the cavity of the mouth, which passes entirely 

 round the bronchiae, and is commonly discharged by th6 

 esterior apertures. 



1 Thus we see the respiration of water by fishes is a real 

 deglutition, but incomplete, because the mouth is perfo- 

 rated at bottom, and suffers the liquid, which necessarily 

 enters with all its food, to escape. ; 



This explains how fishes can swallow air in pretty large Fishes can 

 quantity*, because the specific gravity of gaseous fluids ^^^^^"^^^'^' 

 carries them to the highest part of the mouth, which is 

 seldom perforated : this being the reverse of what happens 

 in animals that respire air, which cannot naturally swallow- 

 it, because this fluid escapes by the posterior opening of the 

 nostrils ; while they can all swallow water without any 

 difficulty. 



The cetaceae, which from their nature are obliged toCetaccr^ 

 reside in water, are circumstanced precisely the same 'as 

 fishes. Every time these animals open their mouths to seize 

 their prey, they are under the necessity of expelling the 

 fluid introduced into them ; and accordingly they are fur- 

 nished with a peculiar organ, analogous in its effects to 

 that of fishes. By the help of this organ they expel the 

 water through their nostrils. > 



V All the muscles, that serve in fish to expel the water Muscles of re. 



from the cavity of the mouth into that of the ffills, are the^P['^'^°""* 

 •^ & ? fishes. 



same as those that produce deglutition in other species of 

 animals: only the apparatus is much more complex, as will 



* This commonly happens in the balistes and tetrodontes, wliich 

 come to the surface of the water to suck in air, and thus puff 

 themselves up considerably. . m ■..-.« r.i 



A a 2 readily 



