**Core Concept**
The fibrous pericardium is a dense, fibrous layer of the pericardial sac that provides support and protection to the heart. It is the outermost layer of the pericardium and is composed of tough, fibrous tissue that anchors the heart to surrounding structures.

**Why the Correct Answer is Right**
The fibrous pericardium is attached to the diaphragm, the sternum, and the xiphoid process, as well as the great vessels exiting the heart. This attachment is crucial for maintaining the heart's position in the thoracic cavity and preventing excessive movement. The fibrous pericardium also serves as a barrier against infection and inflammation, protecting the heart from surrounding pathogens.

**Why Each Wrong Option is Incorrect**
**Option A:** The visceral pericardium, also known as the epicardium, is the innermost layer of the pericardium and is directly attached to the heart muscle. It does not serve as a supporting structure like the fibrous pericardium.
**Option B:** The parietal pericardium is the middle layer of the pericardium, which lines the fibrous pericardium and visceral pericardium. While it is involved in the pericardial sac, it is not directly attached to the same structures as the fibrous pericardium.
**Option C:** The myocardium is the middle layer of the heart wall, consisting of cardiac muscle cells. It is not a structure to which the fibrous pericardium is attached.

**Clinical Pearl / High-Yield Fact**
The fibrous pericardium is a crucial structure in pericardial disease, as inflammation or infection of this layer can lead to severe complications, including cardiac tamponade.

**Correct Answer:** D.