CHAP. II.] ACTION OF THE LUNGS. 107 



a state of supineness, those of the horse are about 

 three or four inches thick at the conjunction with 

 the wind-pipe, and ten or thirteen inches from thence 

 to each extremity, according to the size of the sub- 

 ject ; but, when fully inflated with air, they to- 

 gether fill up the whole cavity of the chest, obstruct- 

 ing in a trivial degree the vibration of the heart : 

 then do they reach to the enormous difference of 

 twelve or thirteen inches in thickness, and somewhat 

 more than double in length. At least such were the 

 dimensions of this organ in a horse which was opened 

 by us in May, 1820 : he was of the cart-horse breed, 

 under sixteen hands, and healthy in other respects 

 than having been blown by eating too much corn ; 

 whereby nature was compelled to leave the lungs 

 quite full at the moment of his death. The same 

 subject is alluded to in the 26th section, where we 

 intended to illustrate the formation and functions 

 of the cellular membrane. 



" No part of the animal has been formed in vain," 

 as we before observed (section 23) : quadrupeds 

 and bipeds both press the earth which gave them 

 birth, and which affords them the means of pro- 

 longing life ; accordingly, this order of beings is 

 furnished with a midriff, but fishes and insects, 

 having no such occasion for this organ, are without 

 it: neither have birds a midriff; but Mr. John 

 Hunter was of opinion, that the want of it is sup- 

 plied by the hollowness of the bones, which not 

 only increases their buoyancy, but that the air con- 



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