The development of the lymphatic system is closely associated with the circulatory system. The primordial circulatory system begins oxygenating tissues at week 3, while the initial lymphatic sacs begin communicating with venous structures at week 5. By the end of week 8, there are six primary lymphatic sacs in the developing fetus including the cisterna chyli, two jugular lymph sacs, two iliac lymph sacs, and a retroperitoneal lymph sac. Vessels begin to connect the lymphatics sacs, forming the early lymphatic system.