Assertion: vein's structure | /r/HasProperty | the pericardium
Facets:
Source sentences:
text: The outer layer of cells is called the epicardium, the second layer of which is a membranous layered structure (the pericardium) that surrounds and protects the heart; it allows enough room for vigorous pumping, but also keeps the heart in place, reducing friction between the heart and other structures.