212 HENRY K. DAVIS 



the dissection of the abdomen, thorax, and base of the neck, I 

 supervised the students' work so that no injury would occur 

 to the duct and made the dissection of the duct myself. 



The thoracic duct in each case was injected with a carmine 

 gelatin mass (Lee '05). At first, I attempted to make the in- 

 jection from the cephalic portion of the duct but could not make 

 the injection mass flow caudad on account of the valves. By 

 experimenting, I found that by exposing the duct just cephalic 

 to where it pierces the diaphragm and making the injection 

 from this point, that the injecting mass flowed freely caudad as 

 well as cephalad. This seems to indicate that the valves are 

 much more efficient in the cephalic than in the caudal portion 

 of the duct. Before the injection, the innominate, vertebral, 

 subclavian, and internal jugular veins were clamped. This 

 insured a good filling of the duct. After the injecting mass had 

 been allowed to cool and gelatinize, a careful dissection and a 

 natural sized drawing of the duct was made. 



EMBRYOLOGY 



According to Sabin ('09) the thoracic duct in human embryos 

 begins in the abdominal cavity at the cisterna chyli as two ducts. 

 These pass cephalad through the thorax, the right duct crossing, 

 at about the level of the 4th thoracic vertebra, dorsal to the 

 aorta to join its fellow of the opposite side. There is thus formed 

 on the left side a single trunk that connects with the jugular 

 portion of the thoracic duct. The jugular portion of the thoracic 

 duct is a caudal outgrowth of the jugular lymph sac on the left 

 side. Sabin, however, has not been able to find the jugular 

 portion, that is, the caudal outgrowth of the right jugular lymph 

 sac, connecting with the thoracic duct. She was able to trace 

 it to the root of the lung but could find no connection of it with 

 the thoracic duct in this region. For this reason the duct as 

 described by Sabin is not a complete bilaterally symmetrical 

 duct. In the embryo there is a distinct right and left duct. 

 These two ducts are connected by numerous cross anastomoses 

 thus forming a plexus of lymphatic vessels along the course 



