Article
Article
Yolk sac
Article By:
Oppenheimer, Steven B. Department of Biology, California State University, Northridge, California.
Last reviewed:August 2020
DOI:https://doi.org/10.1036/1097-8542.753600
An extraembryonic membrane which extends through the umbilicus in vertebrates. In some elasmobranchs, birds, and reptiles, it is laden with yolk which serves as the nutritive source of embryonic development. Developed in the splanchnopleure, it is composed of an endodermal layer and a mesodermal layer in which blood vessels are formed. See also: Germ layers
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