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The heart, pericardium, lung roots and adjoining parts of the great ves-
thoracic arteries.
sels constitute the middle mediastinum (Figs 3.1 and 7.1).
• Nerve supply: the fibrous pericardium and the parietal layer of
The pericardium • Blood supply: from the pericardiacophrenic branches of the internal
serous pericardium are supplied by the phrenic nerve.
The pericardium comprises fibrous and serous components. The Following thoracic trauma blood can collect in the pericardial
fibrous pericardium is a strong layer which covers the heart. It fuses space (haemopericardium) which may, in turn, lead to cardiac tam-
with the roots of the great vessels above and with the central tendon of ponade. This manifests itself clinically as shock, distended neck veins
the diaphragm below. The serous pericardium lines the fibrous peri- and muffled/absent heart sounds (Beck’s triad). This condition is fatal
cardium (parietal layer) and is reflected at the vessel roots to cover the unless pericardial decompression is effected immediately.
heart surface (visceral layer). The serous pericardium provides smooth
surfaces for the heart to move against. Two important sinuses are The heart surfaces
located between the parietal and visceral layers. These are the: •The anterior (sternocostal) surface comprises the: right atrium, atri-
• Transverse sinusalocated between the superior vena cava and left oventricular groove, right ventricle, a small strip of left ventricle and
atrium posteriorly and the pulmonary trunk and aorta anteriorly the auricle of the left atrium.
(Fig. 7.2). •The inferior (diaphragmatic) surface comprises the: right atrium,
• Oblique sinusabehind the left atrium, the sinus is bounded by the atrioventricular groove and both ventricles separated by the interven-
inferior vena cava and the pulmonary veins (Fig. 7.2). tricular groove.
•The posterior surface (base) comprises the left atrium receiving the
four pulmonary veins.

The heart I 19