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2. I have already faid, that the mouths, h. of the 
umbilical vein, and, e. of the aorta inferior , were 
exadtly of the fame diameter, of the fame white 
color, and of the fame ftrength ; and that the other 
veffel, d. was much weaker, of a laxer texture, and of 
a fomewhat livid color, like the coats of the veins. 
3. The umbilical vein is, with refpedt to the mo- 
ther, or to the placeiita , which tranfmits the blood 
to the foetus, a real artery, going from the center to 
the circumference, or from the principal body, which 
is the mother, to an adjoining organ, which is the 
child ; and the umbilical arteries are properly veins, 
which return the blood from that adjoining body to 
the common center of the grand circulation. The 
blood from the umbilical vein then is truly an arterial 
blood to the foetus. In the ufual ftrudlure of the 
e?nbryo , nature has fhortened all the ways, to bring 
the arterial blood of the mother more fpeedily into 
the heart, into the very aorta mferior of her foetus. 
Therefore, in a fubjedt, where there is no heart, or 
even liver, that vein ought to communicate imme- 
diately with the aorta mferior. In this manner one 
conceives how this fubjedt could do without a heart, 
the umbilical blood being a continuation of that from 
the arteries of the placenta , the uterus , and in Ihort 
of the mother ; the impulfion of the maternal blood 
was propagated by that aorta through all its ramifica- 
tions both above and below. In one word, the heart 
of the mother fupplied that of the fcetus, and the 
circulation in this was a continuation of that of the 
mother. Thefe are the reafons inclining me towards 
that fir ft opinion ; and here are thofe that fufpendcd 
my judgment for fome time in favor of the fuppolition 
