Thoracic Duct
Collier's New Encyclopedia (1921)
the name applied to the tubular structure in which the absorbent system of vessels may be said to terminate, and into which the lacteals of the intestine ultimately pour their contained fluid. It thus receives (1) the products of digestion or chyle from the lacteal vessels of the intestine, and (2) the lymph or fluid, brought as the elaborated waste-matters of the body from the tissues by the absorbent system of vessels or lymphatics. Being poured into the thoracic duct, these products, which are destined to replenish the blood, and thus renovate the tissues, are in due course poured into the circulation. The thoracic duct of man exists as a tubular structure attaining a length of about 18 inches. It extends from the second lumbar vertebra to the root of the neck, where it ends in the angle formed by the junction of the left internal jugular and subclavian veins, into which vessels its contents are therefore poured. At its commencement in the abdomen it exhibits a dilatation, termed the receptaculum chyli, which receives the lymphatics of the lower extremities. The thoracic duct has a flexuous course, and exhibits an irregular or contracted appearance. It is provided internally with valves, preventing the backflow of its Occasionally it divides contained fluid. above into two branches; and a right thoracic duct is normally found as a short trunk attaining about an inch in length, and devoted to the reception of the lymph from the right side of the head and neck, from the right side of the chest and heart, and from other regions on that side of the body. In birds, the right thoracic duct may be equally developed with the left.
What Has Changed in the Last Century
The anatomy Collier's set down in 1921 is still what medical students learn: a duct of roughly 38-45 cm running from the abdomen to the junction of the left internal jugular and subclavian veins, valved against backflow, fed by a dilatation at its base (now usually called the cisterna chyli rather than the receptaculum chyli). What has moved is what can be done with it. Since the 1990s interventional radiologists have routinely catheterised and embolised the thoracic duct through the skin to treat chylothorax, a leak of chyle into the chest that was once often fatal, and the duct's chyle is now known to carry fats as chylomicrons and to be a major route by which some drugs and immune cells enter the bloodstream. The vessel itself is also recognised as one of the most anatomically variable structures in the body, a hazard in neck and chest surgery that the old account only hints at with its "occasionally it divides above into two branches."
Written for this edition, 2026.