226 DESCRIPTION of a 



in the minute beginnings of the umbilical vein, to complete 

 the circle in which the foetal blood was moved. 



Thus, we obferve the umbilical vein in the placenta and 

 umbilical cord performing the office of a vein, but its conti- 

 nuation within the body of the monfter, performing the office 

 of an artery. On the other hand, we find the vefTel we have 

 called aorta, performing the office of a vein within the mon- 

 fter, and that of an artery in the umbilical cord and pla- 

 centa. 



Of the Cai/fes of the Motion of the Blood in this Monfter. 



In the monfter examined by Winslow, which I have en- 

 deavoured to fhew agreed very nearly with that I have de- 

 fcribed, no red blood was found in any of the vefTels ; and 

 therefore we mud conclude, that none of the red arteries of 

 the mother anaflomofed with the umbilical veins ; and even 

 where there is the ordinary ftructure, it is fo far from being 

 certain, that the vefTels of the uterus, which convey red blood, 

 anaftomofe with thofe of the umbilical cord, that the contrary 

 is the moft probable opinion. 



It is therefore very improbable, that the blood in the umbi- 

 lical vein was pufhed on by the heart of the mother. 



Further, though we were to admit, that the arteries of the 

 mother anaflomofed with the umbilical veins, yet, as their com- 

 munications muft be fuppofed very minute, and the momen- 

 tum of the blood in them very much broken, we cannot con- 

 ceive, that it could have been fufficient to pufh the blood 

 through the terminations of all the branches of the umbilical 

 veins, in the feveral organs of its body, into the vefTel we call 

 aorta, and again from the aorta back to the placenta by the um- 

 bilical arteries, and through the minute branches of thefe to 

 the veins of the moiher r and beginnings of the umbilical veins. 



We 



