part of part of lymphatic part of lymphoid system jugular lymph sac UBERON:0011765 Lymphatic vessels develop from lymph sacs that arise from developing veins, which are derived from mesoderm. The first lymph sacs to appear are the paired jugular lymph sacs at the junction of the internal jugular and subclavian veins. [Wikipedia:Lymphatic_system][VHOG] EMAPA:18249 VHOG:0001000 NCIT:C34196 An embryonic lymph sac that forms at the junction of the future internal jugular/anterior cardinals and subclavian veins. embryonic lymph sac