Final answer:
The thoracic duct, along with the cisterna chyli, drains the lymph from the lower limbs, external genitalia, lower abdomen, and buttocks into the left subclavian vein.
Step-by-step explanation:
The lymph nodes that drain the legs, external genitalia, lower abdomen, and buttocks are primarily associated with the thoracic duct and the cisterna chyli. The cisterna chyli is a sac-like chamber that begins just beneath the diaphragm, receiving lymph from the lower abdomen, pelvis, lower limbs, and the left and right lumbar trunks as well as the intestinal trunk. The thoracic duct, which is an extension of the cisterna chyli, then drains this lymph into the left subclavian vein. The thoracic duct is the large duct responsible for draining lymph from the lower limbs, left thorax, left upper limb, and the left side of the head.