ss.

In examining the heart itself it is necessary to recall that it lies in
the anterior portion of the chest slightly to the left of the median
line and that it extends from the third to the sixth rib. It extends
almost to the breastbone, and a little more than half of the distance
between the breastbone and the backbone. In contracting, it rotates
slightly on its axis, so that the point of the heart, which lies below,
is pressed against the left chest wall at a place immediately above the
point of the elbow. The heart has in it four chambers--two in the left
and two in the right side. The upper chamber of the left side (left
auricle) receives the blood as it comes from the lungs, passes it to the
lower chamber of the left side (left ventricle), and from here it is
sent with great force (for this chamber has very strong, thick walls)
through the aorta and its branches (the arteries) to all parts of the
body. The blood returns through the veins to the upper chamber of the
right side (right auricle), passes then to the lower chamber of the
right side (right ventricle), and from this chamber is forced into the
lungs to be oxidized. The openings between the chambers of each side and
into the aorta are guarded by valves.

If the horse is not too fat, one may feel the impact of the apex of the
heart against the chest wall with each contraction of the heart by
placing the hand on the left side back of the fifth rib and above the
point of the elbow. The thinner and the better bred the horse is the
more distinctly this impact is felt. If the animal is excited, or if he
has just been exercised, the impact is stronger than when the horse is
at rest. If the horse is weak, the impact is reduced in force.

The examination of the heart with the ear is an important matter in this
connection. Certain sounds are produced by each contraction of the
normal heart. It is customary to divide these into two, and to call them
the first and second sounds. These two sounds are heard during each
pulsation, and any deviation of the normal indicates some alteration in
the structure or the functions of the heart. In making this examination,
one may apply the left ear over the heavy muscles of the shoulder back
of the shoulder joint, and just above the point of the elbow, or, if the
sounds are not heard distinctly, the left fore leg may be drawn forward
by an assistant and the right ear placed against the lower portion of
the chest wall that is ex