se
of that pipe which is called the Whistle, by which the breath enters.
And the great artery, which proceeding from the heart, disperseth its
branches thorow all the body. I would also that they would carefully
observe the eleven little skins, which, as so many little doors, open
and shut the four openings which are in these two concavities; to wit,
three at the entry of the _vena cava_, where they are so disposed, that
they can no wayes hinder the bloud which it contains from running into
the right concavity of the heart; and yet altogether hinder it from
coming out. Three at the entry of the arterious vein; which being
disposed quite contrary, permit only the bloud which is in that
concavity to pass to the lungs; but not that which is in the lungs to
return thither. And then two others at the entry of the veinous artery,
which permits the bloud to run to the left concavity of the heart, but
opposeth its return. And three at the entry of the great artery, which
permit it to go from the heart, but hinder its return thither. Neither
need we seek any other reason for the number of these skins, save only
that the opening of the veinous artery, being oval-wise, by reason of
its situation, may be fitly shut with two; whereas the other, being
round, may the better be clos'd with three. Besides, I would have them
consider, that the great artery and the arterious vein are of a
composition much stronger then the veinous artery or the _vena cava_.
And that these two later grow larger before they enter into the heart,
and make (as it were) two purses, call'd the ears of the heart, which
are composed of a flesh like it; and that there is always more heat in
the heart then in any other part of the body. And in fine, that if any
drop of bloud enter into these concavities, this heat is able to make it
presently swell and dilate it self, as generally all liquors do, when
drop by drop we let them fall into a very hot vessel.

For after this I need say no more for to unfold the motion of the
heart, but that when these concavities are not full of bloud,
necessarily there runs some from the _vena cava_ into the right, and
from the veinous artery into the left; for that these two vessels are
always full of it, and that their openings which are towards the heart
cannot then be shut: But that assoon as there is thus but two drops of
bloud entred, one in either of these concavities, these drops, which
cannot but be very big, by reason that th