The fibrous pericardium is the most superficial layer of the pericardium. It is made up of dense, and loose connective tissue which acts to protect the heart, anchoring it to the surrounding walls, and preventing it from overfilling with blood. It is continuous with the outer adventitial layer of the neighboring great blood vessels.
The fibrous pericardium forms a flask-shaped bag, the neck of which is closed by its fusion with the external coats of the great vessels, while its base is attached to the central tendon and to the muscular fibers of the left side of the diaphragm. In some of the lower mammals the base is either completely separated from the diaphragm or joined to it by some loose areolar tissue; in man much of its diaphragmatic attachment consists of loose fibrous tissue which can be readily broken down, but over a small area the central tendon of the diaphragm and the pericardium are completely fused. Above, the fibrous pericardium not only blends with the external coats of the great vessels, but is continuous with the pretracheal layer of the deep cervical fascia. By means of these upper and lower connections it is securely anchored within the thoracic cavity.
It is also attached to the posterior surface of the sternum by the superior and inferior sternopericardiac ligaments; the upper passing to the manubrium, and the lower to the xiphoid process.
The vessels receiving fibrous prolongations from this membrane are: the aorta, the superior vena cava, the right and left pulmonary arteries, and the four pulmonary veins. The inferior vena cava enters the pericardium through the central tendon of the diaphragm, and receives no covering from the fibrous layer.