214 HENRY K. DAVIS 



branches to join the duct of the left side. A single trunk would 

 be thus formed which would empty into the venous system of 

 the left side. The cephalic portion of the right duct would fail 

 to connect with the thoracic duct and would remain as the right 

 lymphatic duct (fig. 2). 



Type 3. In this type of thoracic duct we would have caudad 

 the persistence of the original double thoracic duct of the embryo. 

 There would be a right and a left duct, which starting in the 

 abdominal cavity, would pass cephalad through the thorax and 

 the left duct would cross by persistence of one of the embryonic 

 cross anastomosing branches to join the duct of the right side. 

 A single trunk would thus be formed which would empty into 

 the venous system of the right side. The cephalic portion of the 

 left duct would fail to connect with the thoracic duct and would 

 remain as a left lymphatic duct which would be comparable to 

 the usual right lymphatic duct (fig. 3). 



Type 4-- In this type of thoracic duct, we would have cephalad 

 the persistence of the original double thoracic duct of the embrj^o. 

 There would be complete atrophy of the caudal portion of the 

 left duct and the cephalic portion of the left duct would join 

 the right duct through the persistence of one of the embryonic 

 cross anastomosing branches (fig. 4). 



Type 5. In this type of thoracic duct, we would have cephalad 

 the persistence of the original double thoracic duct of the embryo. 

 The caudal portion of the right duct would be completely atro- 

 phied and the cephalic portion of the right duct would join the 

 left duct through the persistence of one of the embryonic cross 

 anastomosing branches (fig. 5). 



Type 6. In this type of thoracic duct, we would have the 

 persistence of the cephalic portion of the left duct and the caudal 

 portion of the right duct. These two segments would be joined 

 together by the persistence of one of the embryonic cross anas- 

 tomosing branches. The caudal portion of the left duct would 

 be completely atrophied and the cephalic portion of the right 

 duct would persist as the right lymphatic duct (fig. 6). 



Type 7. In this type of thoracic duct, we would have the 

 persistence of the cephalic portion of the right duct and the 



