226 DESCRIPTION of a 
in the minute beginnings of the umbilical vein, to complete 
the circle in which the feetal blood was moved. 
Tuus, 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 veflel 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 Caufes 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- 
{cribed, no red blood was found in any of the veflels ; and 
therefore we muft conclude, that none of the red arteries of 
the mother anaftomofed with the umbilical veins; and even 
where there is the ordinary ftructure, it is fo far from being 
certain, that the veffels of the uterus, which convey red blood, 
anaftomofe with thofe of the umbilical cord, that the contrary 
is the moft probable opinion. 
Ir 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 anaftomofed 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 veflel 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 mother, and beginnings of the umbilical veins. 
WE 
