324 THE VASCULAR SYSTEM 



At its bifurcation, the pulmonary artery is attached to the 

 lower surface of the aortic arch by the ligamentum arteriosum 

 (p. 306). 



The Thoracic Duct is the largest lymph vessel in the 

 body. It commences on the right side of the vertebral 

 column in a dilatation, termed the cisterna chyli, which is 

 situated in the epigastric region. From this origin the thoracic 

 duct ascends into the thorax, where it lies at first behind the 

 oesophagus. In the upper part of the thorax, however, it 

 crosses the median plane and ascends along the left margin of 

 the oesophagus in close contact with the left mediastinal pleura 

 (Fig. 113). In the neck the thoracic duct lies posterior to 

 the left lobe of the thyreoid gland, but, opposite the seventh 

 cervical vertebra, it passes laterally and then downwards and 

 terminates in the angle of union between the left internal 

 jugular and subclavian veins. 



The cisterna chyli receives the lymph vessels which drain 

 the alimentary canal, and it may, therefore, become infected 

 in cases of intestinal tuberculosis. Some cases of miliary 

 tuberculosis arise in this way. 



The Right Lymphatic Duct is a small vessel, which drains 

 the lymph from the right upper limb, the right side of the head 

 and neck, the right half of the thorax and its contents, and the 

 upper surface of the liver. It ends in the angle of union 

 between the right internal jugular and the right subclavian 

 veins. 



