3 6^ Dr. Clarke's Account of a Tumour 
vations upon the structure and functions of the placenta, in 
order to shew that the principal use of it is to transmit, and 
apply respectively to each other, the blood of the foetus, and 
that of its mother. No other action is carried on by the ves- 
sels of the foetal portion of the placenta, as far as is yet known, 
than what has been described, unless so much as may be ne- 
cessary for their own growth and nourishment. 
The tumour which gave occasion to this Paper is, however, 
an instance to prove, that these vessels are capable, like those 
in other parts, of forming solid organized matter ; and that very 
considerable deviations from the ordinary structure of the pla- 
centa may exist, and be perfectly compatible with the life and 
health of the foetus. 
Previously to the birth of a healthy child, an amazing quan- 
tity of liquor amnii was evacuated, which was by accident re- 
ceived in a vessel, and, being afterwards measured, was found 
to amount to two gallons, Winchester measure. 
When the placenta came away, a hard solid body was found 
in its substance. It was preserved by Mr. Mainwaring, under 
whose care the case occurred, and was by him obligingly pre- 
sented to me. 
Fine injection was thrown into the arteries and vein of the 
funis umbilicalis : when they were filled, they appeared to be 
enlarged thrice beyond their natural size. 
The placenta, thus prepared, was subjected to examination. 
Its anterior surface was found to be covered with the amnion, 
behind which lay the chorion, as usual. Some branches, both 
of the arteries and veins, coming from the funis, ramified in the 
common manner, forming the foetal portion of the placenta. 
Others, of a very large size, not less than a swan's quill, were 
