THORACIC DUCT DEVELOPMENT IN THE PIG 



419 



Fig. 1 Transverse section through the left jugular lymph sac region in a 19 mm. 

 pig embryo (series 168, slide 16, section 16), X 100. 1, lymph sac; 2, thoracic 

 duct approach; 6a, precardinal veno-lymphatic; 8, root of a precardinal segmental 

 tributary; 9, internal jugular vein; 13c, carotid artery; 14, sympathetic nerve 

 trunk; 15, vagus; 16, recurrent laryngeal nerve; 17, oesophagus; 18, trachea. 

 (Reconstruction, fig. 28.) 



ritory lateral and dorsal to the sympathetic trunk. In figure 

 28, which represents a reconstruction of a 19 mm. embryo, these 

 two kinds of tributaries (6a, 8) and their relations to the neigh- 

 boring structures can be clearly distinguished. 



Continued back from the terminals of the precardinal veno- 

 lymphatics (6a, fig. 28) is a vessel which passes obliquely over the 

 aorta and oesophagus to enter the right postcardinal vein at the 

 level of the Cuvierian ducts (7, fig. 28). Although it is morpho- 

 logically a part of the precardinal veno-lymphatics, it will often 

 be treated separately and called the ' oblique vessel' on account of 

 its diagonal course. The simplicity and size of this vessel varies 

 with the individual, but it is a constant factor in all of the early 



