Letters 181 



terms, was laid down by me with its assured and 

 necessary causes, and presents itself to the under- 

 standing 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 ad- 

 mirable artifice, at least wherever there was no trans - 

 udation 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 which we observe in the 

 conjunction between the ureters and the bladder, and 

 of the biliary duct with the duodenum. The ureters 

 insinuate themselves obliquely and tortuously between 

 the coats of the bladder, without anything in the 



