**Core Concept**
The Phrygian cap is a congenital anomaly of the gallbladder characterized by an abnormal, curved, or folded configuration of the gallbladder fundus. This condition is often identified during imaging studies or surgical exploration. The Phrygian cap is a result of an abnormal development of the embryonic liver and gallbladder.

**Why the Correct Answer is Right**
The Phrygian cap is a benign congenital anomaly that typically does not cause any symptoms. It is thought to result from an abnormal rotation of the liver during embryonic development, leading to an abnormal shape of the gallbladder fundus. The name "Phrygian cap" is derived from the shape of the anomaly, which resembles the ancient Phrygian cap worn by warriors. The Phrygian cap is usually an incidental finding and does not require treatment.

**Why Each Wrong Option is Incorrect**
**Option A:** A septum is a wall of tissue that separates two structures, whereas the Phrygian cap is a curved or folded configuration of the gallbladder fundus, not a wall of tissue. This option is incorrect because it does not accurately describe the Phrygian cap anomaly.

**Option B:** A diverticulum is an outpouching of a hollow organ, whereas the Phrygian cap is an abnormal shape of the gallbladder fundus, not an outpouching. This option is incorrect because it does not accurately describe the Phrygian cap anomaly.

**Option C:** The normal gallbladder is a pear-shaped organ, whereas the Phrygian cap is an abnormal, curved, or folded configuration of the gallbladder fundus. This option is incorrect because it does not accurately describe the Phrygian cap anomaly.

**Clinical Pearl / High-Yield Fact**
The Phrygian cap is a benign congenital anomaly that is often identified incidentally during imaging studies or surgical exploration. It is essential to recognize the Phrygian cap to avoid misdiagnosis and unnecessary treatment.

**✓ Correct Answer: D. Phrygian cap**