Fetus of about eight weeks, enclosed in the amnion. (Vitelline duct labeled at lower right.)
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| colspan="2" |Sketches in profile of two stages in the development of the human digestive tube. (Vitelline duct labeled on bottom image.)
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|Latin
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|[[List of subjects in Gray's Anatomy:10#Gray.27s_page_.23|Gray's]]
|colspan="2"|[subject #10 ]
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|System
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|- class="hiddenStructure"
|Precursor
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|- class="hiddenStructure"
|MeSH
|colspan="2"|[A16.254.891]
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|Dorlands/Elsevier
|colspan="2"|[/]
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At the end of the fourth week the yolk-sac presents the appearance of a small pear-shaped vesicle (umbilical vesicle) opening into the digestive tube by a long narrow tube, the vitelline duct.
The vesicle can be seen in the after-birth as a small, somewhat oval-shaped body whose diameter varies from 1 mm. to 5 mm.; it is situated between the amnion and the chorion and may lie on or at a varying distance from the placenta.
As a rule the duct undergoes complete obliteration during the seventh week, but in about three per cent. of cases its proximal part persists as a diverticulum from the small intestine, Meckel's diverticulum, which is situated about three or four feet above the ileocolic junction, and may be attached by a fibrous cord to the abdominal wall at the umbilicus.
Sometimes a narrowing of the lumen of the ileum is seen opposite the site of attachment of the duct.
