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LOCATION AND PERICARDIAL MEMBRANES
The heart is located in the thoracic cavity between the lungs. This area is called the mediastinum. The base of the cone-shaped heart is uppermost, behind the sternum, and the great vessels enter or leave here. The apex (tip) of the heart points downward and is just above the diaphragm to the left of the midline. This is why we may think of the heart as being on the left side, because the strongest beat can be heard or felt here.
The heart is enclosed in the pericardial mem-branes, of which there are three layers (Fig. 12–1). The outermost is the fibrous pericardium, a loose-fitting sac of strong fibrous connective tissue that extends inferiorly over the diaphragm and superiorly over the bases of the large vessels that enter and leave the heart. The serous pericardium is a folded mem-brane; the fold gives it two layers, parietal and visceral. Lining the fibrous pericardium is the parietal peri-cardium. On the surface of the heart muscle is the visceral pericardium, often called the epicardium. Between the parietal and visceral pericardial membranes is serous fluid, which prevents friction as the heart beats.
Figure 12–1. Layers of the wall of the heart and the pericardial membranes. The endocardium is the lining of the chambers of the heart. The fibrous pericardium is the outermost layer.
QUESTION: What is found between the parietal and vis-ceral pericardial layers, and what is its function?
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