Chap. III. The Anatomy of a WOKS^. 29 



pally the Pulmonary Artery and Vein : Thefe Veins and 

 Arteries have frequent Inofculations, or Communications 

 one with another, by which means they become curioufly 

 interwoven towards thofe VeficuU^ or Air-bladders above- 

 mention'd, which kind of Strudure is, by molt Anato- 

 mifts, believ'd to be, to the end that every minute Particle 

 of the Blood in thofe Parts may be impregnated with Air. 

 There are, befides thefe, abundance of Lymphaticks, 

 which attend on the Veins and Arteries thro' the whole 

 Surface of the Lungs, to receive the fuperfiuous Moifture 

 fcparated by the Glands, which they aftcrv/ards difcharge 

 into the Thoraick Dii^. The Lungs have alfo Nerves, 

 which fpring from the recurrent Branches of the wandring 

 Pair. Thefe accompany the Blood-veflels thro' their whole 

 Subftance, and are divided into innumerable Branches. 

 As to the Ufe of the Lungs, it is evident _, . jj^ 

 from what has been already faid, that they "'' •^^* 

 are the chief Organs of Refpiration, being in every refpeft 

 fuited to receive the Air, which is the proper Element for 

 all Quadrupeds, as well as Man, to breathe in : And as the 

 Windpipe, with all its Branches, is made up of cartilaginous 

 Rings, which adl in concert with its mufcular Coat ; it 

 thereby becomes endu'd with a fonof ElaJIicity or Spring, 

 by which it is extended as often as the Air is drawn in, and 

 in Expiration, becomes again contraded. This fort of Me- 

 chanifm is plainly vifible in the Windpipe of any Animal, 

 which being drawn out to its full Length, immediately 

 gathers itfelf up as foon as the Force whereby it was ftretch- 

 cd is remov'd. The Elevation and Depreflion of the Cheft 

 is in like manner occafion'd by the Extention and Contrac- 

 tion of the Lungs ; and as its Adion is thus fubfervient to 

 them in Refpiration, it feems alfo to be chieiiy derived from 

 them ; fo that the Air may be properly term'd the princi- 

 pal-, tho' not the immediate Caufe of that Action alfo. 



Now as we are fure the Air is the immediate and princi- 

 pal Caufe of that Refpiration, it would be to little purpofe 

 to fpend Time about the various Opinions concerning that 

 Motion of the Lungs, to wit, whether it be Natural or 

 Animal, as the Philofophers term it ; or whether, according 

 to fome, it be partly Natural and partly Animal : I fhall 

 only therefore obferve, that altho' it is fomewhat in our 

 Power to regulate that Adlion, by drawing in more or lefs 

 Air at pleafure, yet we are very well fatisfied no Creature 

 can Jmprifon ii in the Lungs, or keep it out two Minutes, 



with- 



