Cross-section of the thorax showing the position of the mediastinum.
Lateral view of the mediastinum.
The mediastinum contains the thymus gland, the pericardial sac, the heart, the trachea, and the major arteries and veins.
The middle mediastinum is centrally located in the thoracic cavity. It contains the pericardium, heart, origins of the great vessels, various nerves, and smaller vessels.
Sagittal section of the pericardium.
The fibrous pericardium is a tough connective tissue outer layer that defines the boundaries of the middle mediastinum. The serous pericardium is thin and consists of two parts:
▪The parietal layer of serous pericardium lines the inner surface of the fibrous pericardium.
▪The visceral layer ( epicardium) of serous pericardium adheres to the heart and forms its outer covering.
The parietal and visceral layers of serous pericardium are continuous at the roots of the great vessels. The narrow space created between the two layers of serous pericardium, containing a small amount of fluid, is the pericardial cavity. This potential space allows for the relatively uninhibited movement of the heart.