Mediastinum . 153 



the left bronchus, the pneumogastric and the recurrent 

 larnygeal nerves, are grouped closely together, and, there- 

 fore, an aneurism affecting this portion of the aorta may, 

 at a very early stage, produce serious symptoms. This 

 grouping occurs in the neighborhood of the fourth dorsal 

 vertebra. 



5. The Thoracic Duct, eighteen inches long, be- 

 gins in front of the second lumbar as a dilatation the re- 

 ceptaculum chyli, which, receives lymph and chyle, by 

 means of three branches, one from the intestine and two 

 from the lower extremities. This duct carries the lymph 

 from the whole of the body with the exception of the right 

 side of the thorax, head and neck, the right arm and lung, 

 and the upper border of the liver. It perforates the dia- 

 phragm at the aortic opening and then passes up in the 

 posterior mediastinum, between the aorta and vena azy- 

 gos major, lying on the right side of the former until it 

 reaches the fourth dorsal vertebra, where it passes to the 

 left, behind the aortic arch, and then runs upwards in the 

 superior mediastinum, on the left side of the oesophagus, 

 to the seventh cervical vertebra, where it arches over the 

 left pleura and lung, to empty into the junction of the left 

 internal jugular and the left subclavian vein. Its diam- 

 eter is about that of a goose quill, although it gradually 

 narrows from below upwards until it reaches the lower 

 border of the fourth dorsal vertebra, above which it grad- 

 ually increases again. The thoracic duct has numerous 

 valves that give it a beaded appearance, while, at its 

 junction with the jugular and subclavian veins, there are 

 two perfect valves which are directed towards the blood 

 current. On reviewing the above we notice that the rela- 

 tive length of the trachea, oesophagus and thoracic duct is 

 four and a half inches, nine inches and eighteen inches, re- 

 spectively, and that the fourth dorsal vertebra corre- 



