106 



situated on the inside of the thoracic ribs : into 

 these the water passes from the gullet, and is 

 afterwards forced out again, in the myxine, by 

 one common tube leading again to the gullet, 

 but in the lamprey, by an equal number of open- 

 ings on the sides of the neck. Perhaps also the 

 air-bladder, of which I have already spoken, is, 

 in those fishes that have one, a second respira- 

 tory organ ; but its chief use is probably that of 

 enabling the animal to rise at pleasure in the 

 water. 



The respiration of reptiles, though more simi- 

 lar to that of birds and mammiferous animals, 

 still differs from it in some remarkable particu- 

 lars. The former are indeed furnished, like the 

 two latter, with a kind of lungs ; but, unlike 

 them, they have membranous, and not fleshy 

 lungs, that is to say, the cells which they contain 

 are so much larger, as to give them a membra- 

 ous and not a fleshy appearance nay, in many 

 reptiles, the lungs consist of one membranous 

 bag very similar to the air-bladder of fishes. 

 These lungs, or bags, are situated in the abdo- 

 men for reptiles having no diaphragm or mid- 

 riff, have no chest properly so called and are 

 loose arid floating among the entrails ; and they 

 receive their supply of air in general, not, as in 

 birds and mammiferous animals, in consequence 

 of the formation of a vacuum around them, but by 

 a process very similar to that of swallowing. In 

 this process the broad lingual bone is first drawn 

 down by its proper muscles, and the air of the 



