nt, and regular; it takes place upwards as well as downwards,
and overcomes numerous obstacles; it carries the blood from the
interior parts of the body to the surface, and from the surface back
again to the internal parts; it forces it from the left side of the
body to the right, and with such rapidity that not a particle of the
fluid remains an instant in the same place.

The principal organ concerned in the circulation of the blood, is the
heart; which is a hollow muscle, of a conical figure, with two
cavities, called ventricles; this organ is situated in the thorax or
chest; its apex or point is inclined downwards and to the left side,
where it is received in a cavity of the left lobe of the lungs.

At the basis of the heart on each side are situated two cavities,
called auricles, to receive the blood; and these contracting, force
the blood into the ventricles, which are two cavities in the heart,
separated from each other by a strong muscular partition. The cavity
which is situated on the right side of the heart, is called the right
ventricle, and that on the left the left ventricle. From the right
ventricle of the heart issues a large artery, called the pulmonary
artery, which goes to the lungs, and is there divided and subdivided
into a vast number of branches, the extremities of which are too
small to be visible. These ultimate ramifications unite again into
larger branches; these again into branches still larger, and so
continually, till at last they form four tubes, called the pulmonary
veins, which are inserted into the left auricle of the heart,

From the left ventricle of the heart there issues another large
artery, called the aorta, which, in its passage, sends off branches
to the heart, arms, legs, head, and every other part of the body.
These branches, in the course of their progress, are divided and
subdivided into innumerable minute ramifications, the last of which
are invisible. These small ramifications unite again into branches
continually larger and larger, till they form two great tubes, called
the venae cavae; which large veins are inserted into the right
auricle of the heart; where a vein, termed the coronary vein of the
heart, which returns the blood from the heart itself, also
terminates.

From what has been said, it will be evident, that strictly speaking,
there are only two arteries and seven veins in the body; one
pulmonary artery, which carries the blood from the right ventricle of
th