The =pericardium= is the fibro-serous sac which surrounds the heart, and
also the great vessels in connection with it to a greater or less
extent. Its form is in general similar to that of the heart. The
=fibrous layer= is relatively thin, but strong and inelastic. It is
attached dorsally to the large vessels at the base of the heart, and is
continued in part up to the longus colli muscle. Ventrally it is firmly
attached to the middle of the posterior half of the thoracic surface of
the sternum. The =serous layer= is a closed sac, surrounded by the
fibrous pericardium, and invaginated by the heart. It is smooth and
glistening, and contains a small amount of clear serous fluid, the
=liquor pericardii=. Like other serous membranes, it may be regarded as
consisting of two parts, parietal and visceral. The =parietal part=
lines the fibrous layer, to which it is closely attached. The =visceral
layer= covers the heart and parts of the great vessels, and is therefore
also termed the =epicardium=. The serous pericardium is composed of a
connective-tissue membrane, rich in elastic fibers, and covered on its
free surface by a layer of flat endothelial cells.
The pericardium is covered by the mediastinal pleura (Pleura
pericardica) and is crossed laterally by the phrenic nerves. Its lateral
surfaces are related chiefly to the lungs, but the lower part is in
partial contact with the chest-wall. On the left side the area of
contact is from the third to the fifth intercostal space inclusive. On
the right side the contact is smaller and is at the third and fourth
ribs. The anterior border of the base is opposite to the second
intercostal space, and the posterior border is opposite to the sixth rib
or space. The base is related to the great vessels, the trachea and its
bifurcation, the bronchial lymph glands, the œsophagus, and the vagus,
left recurrent, and cardiac nerves.
The two parts of the serous pericardium are, of course, continuous
with each other at the line of reflection on to the great vessels. The
latter are covered in varying degree by the visceral layer. The aorta
and pulmonary artery are inclosed in a complete common sheath as far
as the bifurcation of the latter. A pouch passes inward between the
pulmonary artery and the left auricle, and is connected with another
pouch which passes backward between the right auricle and the aorta,
thus forming the great transverse sinus of the pericardium. The
posterior vena cava is covered on the right and below for a distance
of an inch or a little more (ca. 3 cm.). The pulmonary veins receive
practically no serous covering. The epicardium is closely adherent to
the muscular tissue of the heart, but is attached to the vessels by
loose tissue and fat, and hence is easily dissected off them.