180 
THOUGHTS CONCERNING THE 
such seeming negligence; nor is this matter important to 
the subject of my present paper, — which concerns the heart, 
of course including the tubes opening into and leading from 
it. 
We all know how the circulation is described. The blood 
enters one cavity, and by the contraction of that one is forced 
into another cavity; the tricuspid and mitral valves serving 
to keep each cavity separate and distinct. 
Now, when the auricles first dilate, the ventricles are con- 
tracted or pressed close together. The auricle being the 
uppermost, the contracted ventricle must form the floor of 
the dilated cavity. Now, when the floor gives way, no force 
is required to compel a fluid to fall down the opening below. 
This is self-evident. But what becomes of the impulse 
derived from the contraction of the auricle in those cases in 
which the walls of the last-mentioned cavity are ossified ? 
How can we, according to our present theory, account for the 
circulation being carried on in those instances, when the 
pericardium covering the ventricles has been changed to 
bone. Mr. Gowing, of Camden Town, possesses a very fine 
specimen of this last-mentioned kind, for the formation of 
which the animal must have lived long enough to allow the 
deposition of bone, and I dare say of a vast quantity of 
resistant cartilage being deposited besides. 
Post-mortems, however, convince us that the circulation is 
properly conducted, even during violent exercise, for years, 
with one or either of the cavities of the heart converted into 
bone. How is this to be reconciled ? How are we to explain 
the ventricle which contains more than the auricle being 
filled with the contents of the lesser cavity ? 
This, according to our present theory, cannot be explained ; 
but supposing the veins contract with the auricle, (and they, 
both the cavas and the pulmonaries, have a perceptible 
coating of red contractile fibre,) then the whole is easily ex- 
plained. The viens contracting with the auricles empty 
their contents into the ventricle, and thus make up the 
deficiency. 
The auricles contract with the veins, i. e. they shut them- 
selves up into the smallest possible space. The auricles, thus 
compressed, then become the ceilings or topmost parts of the 
ventricles. What then becomes of the tricuspid and mitral 
valves which were to keep the cavities distinct, seeing that 
when the ventricles exist as cavities, the auricles are ob- 
literated? The heart may have four cavities. That is per- 
fectly true. But it has only two cavities open at one time, 
since as one expands the other closes. 
