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mutually conjoined, and serving both systems of vessels indiffer- 

 ently. But the circulation which I discovered teaches clearly 

 that there is a necessary outward and backward flow of the blood, 

 and this at different times and places, and through other and 

 yet other channels and passages ; that this flow is determinate 

 also, and for the sake of a certain end, and is accomplished in 

 virtue of parts contrived for the purpose with consummate 

 forecast and most admirable art. So that the doctrine of the 

 motion of the blood from the veins into the arteries, which 

 antiquity only understood in the way of conjecture, and which 

 it also spoke of in confused and indefinite terms, was laid down 

 by me with its assured and necessary causes, and presents itself 

 to the understanding as a thing extremely clear, perfectly well 

 arranged, and of approved verity. And then, when I perceived 

 that the blood was transferred from the veins into the arteries 

 through the medium of the heart with singular art, and with 

 the aid of an admirable apparatus of valves, I imagined that 

 the transference from the extremities of the arteries into those 

 of the veins could not be effected without some other admirable 

 artifice, at least wherever there was no transudation through 

 the pores of the flesh. I therefore held the anastomoses of 

 the ancients as fairly open to suspicion, both as they nowhere 

 presented themselves to our eyes, and as no sufficient reason 

 was alleged for anything of the kind. 



Since, then, I find a transit from the arteries into the veins 

 in the three places which I have above mentioned, equivalent 

 to the anastomoses of the ancients, and even affording the 

 farther security against any regurgitation into the arteries of 

 the blood once delivered to the veins, and as a mechanism 

 of such a kind is more elaborate and better suited to the 

 circulation of the blood, I have therefore thought that the 

 anastomoses imagined by the ancients were to be rejected. 

 But you will ask, what is this artifice? what these ducts? 

 viz. the small arteries, which are always much smaller 

 twice, even three times smaller than the veins which they 

 accompany, which they approach continually more and more, 

 and within the tunics of which they are finally lost. I 

 have been therefore led to conceive that the blood brought 

 thus between the coats of the veins advanced for a certain 

 way along them, and that the same thing took place here 



