THORACIC DUCT. 



355 



Fig. 123 * 



phagus and behind the perpendicular portion of the left subclavian 

 artery to the root of the neck opposite the seventh cervical vertebra, 

 where it makes a sudden curve forwards and downwards, and ter- 

 minates at the point of junction of the left subclavian with the left 

 internal jugular vein. 



The thoracic duct is equal in size to the diameter of a goose- 

 quill at its commencement from the 

 receptaculum chyli, diminishes consi- 

 derably in diameter towards the middle 

 of the posterior mediastinum, and again 

 becomes dilated near its termination. 

 At about the middle of its course it fre- 

 quently divides into two branches of 

 equal size, which reunite after a short 

 course ; and sometimes it gives off se- 

 veral branches, which assume a plexi- 

 form arrangement in this situation. Oc- 

 casionally the thoracic duct bifurcates 

 at the upper part of the thorax into two 

 branches, one of which opens into the 

 point of junction between the right sub- 

 clavian and jugular veins, while the 

 other proceeds to the normal termina- 

 tion of the duct on the left side. In rare 

 instances the duct has been found to 

 terminate in the vena azygos which is 

 .its normal destination in some Mam- 

 malia. 



The thoracic duct presents fewer 

 valves in its course than lymphatic 

 vessels generally ; at its termination it 

 is provided with a pair of semilunar 

 valves which prevent the admission of 

 venous blood into its cylinder. 



Branches. The thoracic duct re- 

 ceives at its commencement four or 

 five large lymphatic trunks which unite 

 to form the receptaculum chyli ; it next receives the trunks of the 



* The course and termination of the thoracic duct. 1. The arch of the aorta. 2. 

 The thoracic aorta. 3. The abdominal aorta ; showing its principal branches divided 

 near their origin. 4. The arteria innominata, dividing into the right carotid and right 

 subclavian arteries. 5. The left carotid. 6. The left subclavian. 7. The superior 

 cava, formed by the union of 8, the two vense innominate ; and these by the junction 

 9, of the internal jugular and subclavian vein at each side. 10. The greater vena 

 azygos. 11. The termination of the lesser in the greater vena azygos. 12. The re- 

 ceptaculum chyli; several lymphatic trunks are seen opening into it. 13. The tho- 

 racic duet, dividing opposite the middle of the dorsal vertebra into two branches 

 which soon reunite ; the course of the duct behind the arch of the aorta and left sub- 

 clavian artery is shown by a dotted line. 14. The duct making its turn at the root of 

 the neck and receiving several lymphatic trunks previously to terminating in the pos- 

 terior aspect of the junction of the internal jugular and subclavian vein. 15. The 

 termination of the trunk of the ductus lymphaticus dexter. 



