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 two per cent of cases its proximal part persists as a diverticulum from the
small intestine,
Meckel's diverticulum, which is situated about two feet above the
ileocolic junction, and may be attached by a fibrous cord to the abdominal wall at the
umbilicus.
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