THE THORACIC DUCT 



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multiple, or a single trunk may pass in front of the aorta instead"^of behind. In a few instances 

 it has been found emptying into the right instead of the left subclavian vein. There is also a 

 wide range of variation in the height to which the duct ascends in the neck before curving down- 

 ward to the vein. As regards the termination of the thoracic duct, variations are also frequent; 

 it may bifurcate and end as two ducts. It often connects with the lowermost part of the 

 internal jugular, or the beginning of the innominate. According to Henle, there is one un- 

 doubted case reported of a thoracic duct ending in the azygos vein near the sixth thoracic 

 vertebra, the duct being obliterated above this point. At the terminal bend the thoracic 

 duct receives the jugular trunk from the neck; it may also receive the subclavian and the broncho- 

 mediastinal trunks, but it is more usual for these last two to open either separately or together 

 into the subclavian. 



Variations are extremely numerous in the region of the receptaculum. Severa lobservers 

 state that, in the majority of cases in man, no definite receptaculum exists. Bartels found one 

 in only 25 per cent, of the cases studied. Instead, there is present a widening of each of the two 

 lumbar trunks, with several anastomoses between them (55 per cent., BartelsJ, or a widening 

 of these two stems without anastomosis (5 per cent.), or a much elongated widening arising 



( 



Fig. 571. — Abdominal Portion of the Thoracic Duct. (Poirier and Cuneo.) 



from the growing together of the two lumbar trunks (10 per cent.). In cases where the lumbar 

 trunks remain separate, the intestinal trunk joins the left one. 



Development. — While the exact mode of its development is still in dispute, enough is 

 agreed upon by the various investigators to explain most of the variations in the thoracic duct. 

 In brief, it is known that the lymphatics start in the neck as a variable number of outgrowths 

 from the veins in the region of the junction between the later internal jugular and subclavian 

 veins. A variable number of these connections disappear, while the various combinations of 

 one, two, thi-ee or four which are retained furnish the numerous variations in number and 

 position of the ducts which empty into the vein in the adult. Thus the thoracic duct may 

 have one, two or even three openings into the veins, while the jugular, subclavian and broncho- 

 mediastinal trunks may join the thoracic duct or may enter the veins separately or in various 

 combinations. 



It is also known that the upper part of the thoracic duct is at first bilateral, being formed 

 by outgrowths from the primary plexus, which meet in a common plexus around the aorta. 

 Normally the right portion of these connections disappears, so that the thoracic duct empties into 

 the left subclavian vein. In exceptional cases, where it opens into the right subclavian vein, 

 there have also been present variations in the large right arterial trunk. These conditions 

 in all probability at a certain stage in development produced a greater resistance to the lymph 

 stream in the left than in the right vessel causing it to become obliterated so that the right 

 instead of the left became the permanent ending of the duct. 



