Synonym for yolk sac ... <embryology, ornithology> One of the set of extra embryonic membranes, growing out from the gut over the yolk surface, in birds formed from the splanchnopleure, an outer layer of splanchnic mesoderm and an inner layer of endoderm. ... (18 Nov 1997) ... 
the pear-shaped expansion of the mammalian yolk sac growing out into the cavity of the chorion, joined to the midgut by the yolk stalk.
Type: Term Synonyms: yolk sac