**Core Concept**
Meckel's diverticulum is a congenital diverticulum of the small intestine, resulting from the incomplete closure of the vitelline duct. It is a remnant of the yolk sac, which connects the embryo to the placenta during fetal development.

**Why the Correct Answer is Right**
During embryonic development, the vitelline duct connects the yolk sac to the midgut. Normally, this duct obliterates and disappears by the 5th to 8th week of gestation. However, if the duct fails to close, it develops into a Meckel's diverticulum, which is a true diverticulum containing all the layers of the intestinal wall. The presence of ectopic gastric mucosa in Meckel's diverticulum can lead to complications such as bleeding, obstruction, or diverticulitis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Meckel's diverticulum is not derived from the omphalomesenteric duct, which is a different embryological structure.
**Option B:** This option is incorrect because Meckel's diverticulum is not derived from the appendix, which is a separate anatomical structure.
**Option C:** This option is incorrect because Meckel's diverticulum is not derived from the mesenteric ducts, which are involved in the development of the pancreas and biliary system.

**Clinical Pearl / High-Yield Fact**
Meckel's diverticulum is the most common congenital anomaly of the small intestine and is often associated with complications such as gastrointestinal bleeding, obstruction, or diverticulitis.

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