ON THE RESPIRATION OF FISHES. SoX 



in fishes are altogether ditferent from what they are in other 

 vertebrate animals. 



In the mammalia and birds the whole of the venous blood Respiration of 

 is under the necessity of coming to place itself in contact as ^^^'t^'andbmb. 

 it were with the air, that penetrates their lungs. These 

 organs are enclosed, and capable of expanding, in the 

 thorax ; a cavity, the bony sides of which are capable of 

 various motions, and particularly of those that tend to 

 increase or diminish its diameters. ^ 



In the mammalia the thorax appears particularly intended Seat of the 

 to protect the principal organs of the circulation; and to ""^** 

 determiae the motions necessary to respiration. In all 

 other vetcbrate animals, that have lungs, theso parts are 

 contained in a less determinate space, with the organs of 

 digestion and other viscera. 



The ribs, or bony hoops, that surround this cavity, are Acting causes 

 evidently levers, that mechanically produce the expansion respiration. 

 or contraction of the space surrounding the lungs. The 

 powers that move the bones in these two directions, and 

 which are the muscles of the thorax and abdomen, and the 

 diaphragm, consequently determine the act of inspiration, 

 as well as that of expiration. It was* necessary to recapi- 

 tulate these general principles, to give a clearer notion of 

 "what follows. 



If it be true, as physiologists at present admit, that the Where ribs aw 

 ribs and, muscles inserted in them are the chief mechanical 7^"*!"^* i^'*^ 



rerent.mecha- 

 agents of respiration ; we must necessarily infer, that ver- nism necessaryj 



tebrate animals destitute of ribs, or in which these bones 



cannot be employed to produce those motions, must have 



some other mode of breathing : and this in fact is the case. 



The first example we have in certain reptiles, as frogs, as in cet tain , 



lizards, &c., during the first stage of their existence. These !^®^^''^^'"*^''^ 



. 1 . , . , first stags, &C. 



animals, previous to thvir metamorphosis, breathe in the 



manner of fishes, of which they have commonly the form, 



structure, and habitudes. They take in water at the 



mouth, and immediately expel it through a single bronchial 



aperture, or several holes in the side of the oepk. Thus 



tadpoles are similarly circumstanced with fishes of the genus 



sphagobronchiae of Bloch, or unibronchaperturae of Lac^. 



pcde; while the young lizards, protei, sirens, and other 



urodelas, 



