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46 



PULMONARY ARTERIES 



Sect. IV. 11. 2. 



of aquatic animals, which confifts in the largenefs of their furface, 



F 



owing to their hair-like fubdivifions, and to their being terminated 

 with innumerable points. The gills of fifh confift of many folds of 

 blood-veffels lying over each other, each refembling a fringe, or the 

 downy part on one fide of a feather attached to the niiddle rib of it, 

 by which means they expofe a greater furface of blood to the water 

 than is expofed to the air by the internal membranes of the air-cells 

 of the lungs of other animals ; and undoubtedly for this final caufe, 

 becaufe water contains lefs oxygen in its uncombined flate, which is 

 the material neceffary to life, than air, though much more of it in its 

 combined ftate, is water confifts of eighty-five parts of oxygen to fif- 

 teen parts of hydrogen ; but it is the uncombined oxygen only dif- 

 folvcd in heat, and difFufed in water, which can fervc the purpofe df 

 animal or vegetable refpiration,, 



The apparatus for this purpofe, according to Duverney's Anatomy 

 of a Carp, is truly curious. He found 4386 bones in the gills, which 



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had fixty-nine mufcles to give them 



their due motions. See Bo- 



mare's Di6lionaire raifonee, Art Poiflbn. And Monro obfcrved by the 

 numerous divifions and folds of the membrane of the gills', that their 

 furface in a large Ikate was nearly equal to the furface of the human 

 body. Phyfiol. of Fifh, p. 15. He adds that in the whole gills there 



exifl 144,000 fubdivifions or folds, and that the whole extent of this 

 membrane may be feen by a microfcope to be covered with a net- 

 work of exceedingly minute veflels. 



2. In this refped the gills of fifh arc refembled by the fubaquatic 

 leaves of plants, which are flit into long wires terminated in points, as 



trapa, cenanthe, h 



the water-violet, and th 



cuius. 



Th 



laft plant;, and fome oth 



h 



frequently fome 



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erecl in the air, aad others immerfed in water, arifing from 



the fame fiem 

 nearly entire, 



nd it is curi( 

 divided only 



obferve that the aerial leaves are 

 I few lobes ; whilft the aquatic 



leaves 



flit into innumerable branches like a fringe, and have th 



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