membranous sac attached to an embryo, formed by cells of the hypoblast adjacent to the embryonic disk
via Wikipedia infobox
The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though yolk sac is far more widely used. The yolk sac is one of the fetal membranes and is important in early embryonic blood supply. In humans much of it is incorporated into the primordial gut during the fourth week of embryonic development.
In humans
via PubMed
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).