216 HENRY K. DAVIS 



caudal portion of the left duct. These two segments would 

 be joined together through the persistence of one of the embryonic 

 cross anastomosing branches. The caudal portion of the right 

 duct would be completely atrophied and the cephalic portion 

 of the left duct would not connect with the thoracic duct and it 

 would persist as a left lymphatic duct (fig. 7). 



Type 8. In this type of thoracic duct, we would have the 

 complete persistence of the right embryonic duct. The caudal 

 portion of the left duct would be completely atrophied and the 

 cephalic portion of the left duct would not be connected with the 

 thoracic duct and would persist only as the left lymphatic duct 

 which would be comparable to the usual right lymphatic duct 

 (fig. 8). 



Type 9. In this type of thoracic duct, we would have the 

 complete persistence of the left embryonic duct. The caudal 

 portion of the right duct would be completely atrophied and the 

 cephalic portion of the right duct would not connect with the 

 thoracic duct and would persist only as the right lymphatic duct 

 (fig. 9). 



It should be noted that Types 2 and 3, 4 and 5, 6 and 7, 8 and 

 9 are respectively the reverse of one another in that those channels 

 which persist in one atrophy in the other and vice versa. 



Group I 



Winslow ('66), Cruickshank ('90), Sommering ('92), and 

 Hommel ('37) describe bilaterally symmetrical thoracic ducts. 

 The thoracic ducts start in the abdominal cavity as two ducts 

 which pass cephalad through the thorax, one opening into the 

 venous system of the left side and the other into the venous system 

 of the right side. The right duct lies to the right of the aorta and 

 the left duct on the left side of the aorta. These two ducts are 

 joined together by numerous cross anastomoses. I found no 

 ducts of this type. It is clearly evident that the thoracic ducts 

 described by the above investigators belong to Type 1 (fig. 1). 



