**Core Concept**
Meckel's diverticulum is a congenital anomaly resulting from the incomplete obliteration of the vitelline duct, a structure that connects the yolk sac to the intestinal tract during embryonic development. This remnant is a true diverticulum, containing all layers of the intestinal wall.

**Why the Correct Answer is Right**
The vitelline duct usually atrophies and disappears by the 6th week of gestation. However, when it fails to do so, it can form a Meckel's diverticulum, which is a bulge in the small intestine. This condition is often associated with gastrointestinal bleeding, intestinal obstruction, or diverticulitis. The presence of ectopic gastric or pancreatic tissue within the diverticulum can lead to complications.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as Meckel's diverticulum is not derived from the omphalomesenteric duct, although it is related to the vitelline duct.

**Option B:** This option is incorrect as Meckel's diverticulum is not a derivative of the umbilical cord.

**Option C:** This option is incorrect as Meckel's diverticulum is not a congenital anomaly of the appendix.

**Clinical Pearl / High-Yield Fact**
Meckel's diverticulum is the most common congenital anomaly of the small intestine and accounts for approximately 2-4% of all gastrointestinal anomalies.

**Correct Answer: D. Vitelline duct remnant.**