In the human embryo, the vitelline duct, also known as the omphalomesenteric duct, is a long narrow tube that joins the yolk sac

Yolk sac

The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...

 to the midgut lumen of the developing fetus. It appears at the end of the fourth week, when the yolk sac presents the appearance of a small pear-shaped vesicle (the umbilical vesicle).

Obliteration

Generally, the duct fully obliterates (narrows and disappears) during the 7th week of fertilization age (9th week of gestational age

Gestational age

Gestational age relates to the age of an embryo or fetus . There is some ambiguity in how it is defined:*In embryology, gestational age is the time elapsed since conception. This interval is also termed fertilisation age....

), but a failure of the duct to close is termed a vitelline fistula. This results in discharge of meconium

Meconium

Meconium is the earliest stools of an infant. Unlike later feces, meconium is composed of materials ingested during the time the infant spends in the uterus: intestinal epithelial cells, lanugo, mucus, amniotic fluid, bile, and water. Meconium is almost sterile, unlike later feces, is viscous and...

 from the umbilicus. About two per cent of fetuses exhibit a type of vitelline fistula characterized by persistence of the proximal part of the vitelline duct as a diverticulum

Diverticulum

A diverticulum is medical or biological term for an outpouching of a hollow structure in the body. Depending upon which layers of the structure are involved, they are described as being either true or false....

 protruding from the small intestine

Small intestine

The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...

, Meckel's diverticulum

Meckel's diverticulum

A Meckel's diverticulum, a true congenital diverticulum, is a small bulge in the small intestine present at birth. It is a vestigial remnant of the omphalomesenteric duct , and is the most frequent malformation of the gastrointestinal tract...

, which is situated about two feet above the ileocecal junction and may be attached by a fibrous cord to the abdominal wall at the umbilicus

Navel

The navel is a scar on the abdomen caused when the umbilical cord is removed from a newborn baby...

.

Afterbirth

The vesicle can be seen in the afterbirth as a small, somewhat oval-shaped body, the diameter of which varies from 1 mm to 5 mm. It is situated between the amnion

Amnion

The amnion is a membrane building the amniotic sac that surrounds and protects an embryo. It is developed in reptiles, birds, and mammals, which are hence called “Amniota”; but not in amphibians and fish , which are consequently termed “Anamniota”. The primary role of this is the protection of the...

 and the chorion

Chorion

The chorion is one of the membranes that exist during pregnancy between the developing fetus and mother. It is formed by extraembryonic mesoderm and the two layers of trophoblast and surrounds the embryo and other membranes...

 and may lie on or at a varying distance from the placenta

Placenta

The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...

.

Sometimes a narrowing of the lumen

Lumen (anatomy)

A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...

 of the ileum

Ileum

The ileum is the final section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms posterior intestine or distal intestine may be used instead of ileum.The ileum follows the duodenum...

is seen opposite the site of attachment of the duct.

Mnemonic

A mnemonic used to recall details of a Meckel's diverticulum is as follows: "2 inches long, 2 feet from ileocecal valve, 2% of population, 2% symptomatic, 2 types of ectopic tissue: gastric and pancreatic."