## **Core Concept**
Meckel's diverticulum is a congenital diverticulum that arises from the incomplete closure of a specific embryonic structure during fetal development. It is a remnant of the **vitelline duct** (also known as the omphalomesenteric duct), which connects the midgut to the yolk sac.

## **Why the Correct Answer is Right**
The correct answer, , is right because Meckel's diverticulum is indeed a remnant of the **vitelline duct**. During embryonic development, the vitelline duct usually closes and obliterates by the 5th to 8th week of gestation. However, if it fails to close completely, it can leave behind a diverticulum that projects from the small intestine, specifically from the ileum. This diverticulum contains all layers of the intestinal wall and may contain ectopic tissue, most commonly gastric or pancreatic tissue.

## **Why Each Wrong Option is Incorrect**
- **Option A:** is incorrect because it does not specifically relate to Meckel's diverticulum.
- **Option B:** is incorrect because, although the urachus is another structure that may have remnants, Meckel's diverticulum is specifically related to the vitelline duct, not the urachus.
- **Option D:** is incorrect because Meckel's diverticulum is not a remnant of the cloaca or allantois; it is specifically associated with the vitelline duct.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl to remember is that Meckel's diverticulum can cause gastrointestinal bleeding, especially in children, due to the presence of ectopic gastric mucosa. The classic presentation is painless rectal bleeding. The "rule of twos" is often remembered: it occurs in 2% of the population, is located 2 feet from the ileocecal valve, and presents with complications in 2% of cases.

## **Correct Answer:** . Vitelline duct.