Allantois

Allantois refers to one of the fetal membranes that contributes to umbilical cord formation. It takes part in waste material collection and gas exchange. 

During embryonic development, the allantois transforms into urachus, which in turn becomes the median umbilical ligament.

Related pathology

• allantoic cyst
• patent urachus

History and etymology

The allantois is a structure common in mammals. The word for the structure is derived from the Greek ἀλλαντοειδής (allantoeides) for sausage-shaped.