What is the pericardial sac? what type of tissue makes up the sac?

Pericardial sac also known as pericardium is a cone-shaped sac made of fibrous tissue surrounding the heart and the blood vessels. It has two parts: the inner coat which is double-layered supporting the heart; and the outer coat which is solid and heavily built attached to the diaphragm and the rear part of the breastbone.

primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs