**Core Concept:** Epiplocele is a herniation of the inner lining of the abdomen, known as the peritoneum, through a weak point in the abdominal wall.

**Why the Correct Answer is Right:** An epiplocele occurs when the peritoneum, which forms the inner lining of the abdominal cavity, herniates through a weak point in the abdominal wall. In this case, the correct answer is **D**, which refers to the "Peritoneum".

Peritoneum is a thin, semi-transparent, serous membrane lining the inner surface of the abdominal and pelvic cavity, covering and separating the organs within these cavities. When a peritoneal sac herniates through a weakness in the abdominal wall, it presents as an epiplocele.

**Why Each Wrong Option is Incorrect:**

A. **Option A (Peritoneum):** This is the correct answer, as the content of an epiplocele is the peritoneum, which lines the inner surface of the abdominal and pelvic cavities.

B. **Option B (Subcutaneous tissue):** The subcutaneous tissue lies beneath the skin and is not the content of an epiplocele.

C. **Option C (Muscle fibers):** Muscle fibers are part of the abdominal wall musculature and do not form the content of an epiplocele.

D. **Option D (Peritoneum):** Although this option is correct, it should be combined with Option A (Peritoneum) as the correct answer to avoid confusion.

**Clinical Pearl:** An epiplocele is a relatively common clinical condition, usually asymptomatic and does not require surgical intervention unless it becomes inflamed or causes symptoms. Understanding the anatomy and content of an epiplocele is essential for differential diagnosis and proper patient management.