ic6 Mr. Abernethy’s Observations on 
9 
by the coronary arteries, and which must have lost, in a greater 
or less degree, the properties of arterial blood, should not be 
mixed with the arterial blood which is to be distributed to every 
part of the body, but ought rather to be sent again to the 
lungs, in order that it may re-acquire those properties ; we 
therefore perceive why, in a natural state of the heart, the 
principal foramina Thebesii are to be found in the right cavi- 
ties of that organ. However, as, even in a state of health, those 
cavities are liable to be uncommonly distended, in consequence 
of muscular exertion sometimes forcing the venous blood into 
the heart faster than it can be transmitted through the lungs, 
there seems to arise a necessity for similar openings on the left 
side ; but these, in their natural state, though capable of emit- 
ting blood, and of relieving the plethora of the coronary ves- 
sels, are not of sufficient size to give passage to common waxen 
injections. Yet, when there is a distended state of the right 
cavities of the heart, which is almost certainly occasioned by a 
diseased state of the lungs, these foramina leading into the left 
cavities then become enlarged, in the manner that has been 
already described ; and thus the plethoric state of the nutrient 
vessels of the heart, and the consequent disease of that impor- 
tant organ, are prevented. 
The preceding remarks will, I think, sufficiently explain the 
cause of the variety in the size and situation of these foramina, 
which also appear to belong both to the arteries and veins ; be- 
cause, the injection which was employed was too coarse to pass 
from one set of vessels to the other, and yet the different co- 
loured injections passed into the cavities of the heart unmixed. 
There is yet another mode by which diseases of the heart, 
that would otherwise so inevitably succeed to obstruction in the 
