THORACIC DUCT 659 



In early life they are of a ])iiikish coLmr, but as life advaiiees tlit-v heconie 

 bluish, and later aluKtst hlaek, from the deposit of })ignient arrt'st<'d in thciu in its 

 passage from the lungs. 



THE THORACIC DUCT 



The thoracic duct l)egins in the abdomen at the rcceptaciilum chyli opposite 

 the first or second lunil»ar vertebra, enters the thorax through the aortic o}>ening 

 of the diaphragm, runs up the posterior mediastinum to the right of the aorta, 

 crosses behind the aortic arch, and, leaving the thorax at the su}»erior opening, 

 ascends on the left side of the neck as high as the seventh cervical vertel)ra, and, 

 finally curving over the a})ex of the left pleura and suljclavian artery, ends in the 

 confluence of the left internal jugular and subclavian veins. 



The duct is about eigliteen inches long, and i)ursues a tortuous course. It de- 

 tains many double valves which, when the duct is dilated, cause it to be constricted 

 at intervals, and give it somewhat the appearance of a string of beads. The valves 

 are more numerous in the upper than in the lower part of the duct. At its entrance 

 into the innominate vein there are two perfect valves, which effectually prevent any 

 regurgitation of lymph or entrance (;f blood. The calibre of the duct usually 

 decreases as it ascends through the thorax, l)ut increases again at its upper part. 

 It is least at or al)Out the fifth thoracic vertebra. The thoracic duct conveys the 

 lymph iroxw the lower extremities, the lymph and chyle from the abdomen (except 

 some of the lymph from the convex surface of the liver), the lyn)})h from the left 

 side of the thorax, and some of that from the right side, and the lymph from the 

 left upper extremity and the left side of the head and neck. 



The relations of the thoracic duct in the abdomen, thetliorax, and at the 

 root of the neck, may be considered separately. 



1. The abdominal portion of the thoracic duct lies deeply placed behind 

 and between the aorta and the right crus of the diaphragm on tlie front of the body 

 of the second lumbar vertel)ra. This part of the duct is dilated into an irregular, 

 sacculated, and fusiform sac, known as the receptaculum chyli, or cistern of 

 Pecquet. It receives the efferent vessels of the lumbar glands, the intestinal 

 lymi)hatic trunk, and sometimes some of the hepatic and gastric lymphatics. It is 

 thin- walled and contains no valves, and is about an inch and a half long (38 mm.) 

 and about a quarter of an inch in diameter at its widest part (7 mm.). As the duct 

 passes through the aortic opening of the diaphragm, it still lies to the right of the 

 aorta, and has the vena azygos major to its right side. 



2. The thoracic portion of the thoracic duct lies at first in the posterior 

 mediastinum between the aorta and the vena azygos major, in front of the seven 

 lower thoracic vertebra'; Init at the level of the fifth thoracic vertebra it ])asses to the 

 left behind the cesophagus and aortic arch, and enters the superior mediastinum, 

 whence it escapes through the upper a])erture of the thorax into the root of the 

 neck. This portion of the duct is not of equal calibre throughout; as a rule, it is 

 contracted in some places and dilated at others. The constrictions indicate the 

 situation of the valves. 



In the posterior mediastinum it has in front of it, from below upwards, the 

 jtericardium, the u'sophagus, and the arch of the aorta; behind it, the seven lower 

 thoracic vertebra?, the anterior connnon ligament, the lower right intercostal arteries, 

 the vena azygos minor, and at times one or moi'e of the mid left intercostal veins, 

 and the vena azygos tertia. To its left is the thoracic aorta, and to its right the 

 vena azygos major and the right ])U'Ura. In the superior mediastinum it a.^cends, 

 between the O'sophagus and left pleura, to the posterior and left side of the superior 

 tlioracic opening. It here has in front of it the first jwrtion of the left subclavian 

 artery, behind it the upper thoracic vertel)ra\ to its left the i)leura. and to its right 

 the cesophagus. 



Opening into the thoracic portion of the duct are: — tlie lymjihatics from the 

 left half of the thoracic walls; the efferent vessels from the left anterior mediastinal 

 and intercostal glands; the lymphatics of the left lung and the left side of the 

 heart; the lymphatics of the trachea and a^sophagus, and the right lower internal 

 mannnary lymphatics. 



