part_of part of is part of part of bounding layer of develops from extraembryonic structure epithelium endoderm yolk sac yolk sac endoderm EMAPA:16086 UBERON:0003257 uberon The portion of the yolk sac that is derived from endoderm and lines the yolk sac. VHOG:0000626 EHDAA2:0002215 EHDAA:166 extraembryonic tissue endo-epithelium