Final answer:
The lining of the pericardial sac consists of the parietal and visceral pericardium layers, with a pericardial cavity between them.
Explanation:
The lining of the pericardial sac consists of two fused layers: the parietal pericardium and the visceral pericardium (also known as epicardium). The parietal pericardium forms the outermost layer of the sac, while the visceral pericardium is the thin layer covering the surface of the heart. These layers create the pericardial cavity, filled with lubricating serous fluid, separating them from the heart.
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