THE THORACIC DUCT. 



547 



THORACIC DUCT. 



The thoracic duct is the common trunk which receives the absorbents from both 

 the lower limbs, from the abdominal viscera (except part of the upper surface of the 



Fig. 418. SKETCH OF THE THORACIC DUCT WITH THE PRINCIPAL 

 SYSTEMIC VEINS. (Allen Thomson. ) | 



The full description of this figure will be found at p. 511. 



10, 10, thoracic duct ; the lower number is close to the 

 receptaculum chyli ; 6, on the left subclavian vein, marks the 

 termination of the duct in the angle of union of the subclavian 

 and internal jugular veins ; 5, on the right subclavian vein, 

 indicates the similar termination of the right lymphatic duct. 



liver), and from the walls of the abdomen, from the 

 left side of the thorax, left lung, left side of the 

 heart, and left upper limb, and from the left side 

 of the head and neck. It is from fifteen to eighteen 

 inches long in the adult, and extends usually from 

 the second lumbar vertebra to the root of the neck. 

 Its commencement, however, is often as low as the 

 third lumbar vertebra ; and in some cases as high 

 as the first lumbar, or even the last dorsal vertebra. 

 Here there is usually a dilatation of the duct, of 

 variable size, which is called receptaculum chyli 

 (Pecquet), and is the common place of junction of 

 the lymphatics from the lower limb with the trunks 

 of the lacteal vessels. 



The lower part of the thoracic duct is generally 

 wider than the rest, being from 6 to 8 mm. in dia- 

 meter ; it lies at its commencement to the right 

 side of or behind the aorta, and then ascends be- 

 tween that vessel and the right crus of the dia- 

 phragm to the thorax, where it is placed at first 

 upon the front of the dorsal vertebrae, between the 

 aorta and the large azygos vein. The duct runs 

 upwards, gradually inclining to the left, and at the 

 same time diminishing slightly in size, until it v 

 reaches the fourth dorsal vertebra, where, passing 

 behind the arch of the aorta, it becomes applied to 

 the left side of the oesophagus, lying between that 

 tube and the left subclavian artery. Continuing 

 its course into the neck to the level of the seventh 

 cervical vertebra, it changes its direction and turns 

 outwards, at the same time arching downwards and 

 forwards so as to describe a curve over the apex of 

 the pleura, and then terminates on the outer side of 

 the internal jugular vein, in the angle formed by 

 the union of that vein with the subclavian. The 

 diminution in the size of the duct as it ascends is 



such that at the fifth dorsal vertebra it is often only 3 or 4 mm. in diameter, but 

 above this point it again enlarges. The duct is generally waving and tortuous in 

 its course, and is often alternately contracted and enlarged at irregular intervals. 



The thoracic duct has valves at intervals throughout its course, the constrictions 



VOL. II. 



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