Mr. Wilson's Description , &c, 347 
recorded such cases, but I have not been able to meet with a 
description of any which have been at all similar. 
It is well known to most of the Members of this Society, 
that the circulation of the blood throughout the body, and ex- 
posure of it to the atmospheric air in respiration, seem, in most 
animals, to be necessarily connected ; but are not equally so in 
all. They are so much connected in the human subject, and in 
most quadrupeds, that after birth there is a double heart ; viz. 
one for the circulation of the blood throughout the body, to be 
subservient to the various purposes of life and growth; the 
other for its circulation through the lungs, where it undergoes 
a change which is essential to its general circulation through 
the body : these two circulations, in the natural state, bear an 
exact proportion to each other. Instances, however, have oc- 
curred, even in the human subject, where this exact proportion 
has not been preserved ; yet life has been prolonged for some 
years, but in a feeble and imperfect state. In some of these 
instances, the pulmonary artery has been smaller than usual, 
so that much less than the natural quantity of blood was ex- 
posed to the influence of the air in the lungs ; in others, the 
foramen ovale has not been closed, but a considerable commu- 
nication has remained between the two auricles ; and, in others, 
there has been a communication between the two ventricles, 
from a deficiency in the septum. The effect of all these devia- 
tions is the same, upon the blood in the general circulation, viz. 
that a part of the blood is not exposed to the air in the lungs ; 
so that it is less pure as it circulates over the body. A more 
remarkable deviation in the structure of the heart, than any to 
which I have just alluded, has been lately published by Dr, 
Baillie, in his Morbid Anatomy. In this heart, the aorta 
Yy 2 
