Allantois is a membranous sac in reptile, bird, and mammal embryos that serves in waste storage and gas exchange, forming part of the yolk sac in early development. In humans it is an extraembryonic structure contributing to the umbilical cord's development. The term also denotes the corresponding anatomical sac in Amphibia and other vertebrates. It’s primarily a technical, biological term used in embryology and anatomy.
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