DEVELOPMENT OF THE THORACIC DUCT 75 



In fig. 84 (series 142, slide x, section 16), the subclavian ap- 

 proach (14) has separated from the jugular approach (13) and 

 the thyro-cervical artery (24) is passing meso-laterad between 

 these two divisions. The origin of the thoracic duct approach 

 (12) from the dorso-medial circumference of the jugular approach 

 (IS) is well shown in the section. The concavity of the jugulo- 

 cephalic arch is expressed by the two cross-sections labelled 29. 



In fig. 85 (series 142, slide x, section 8) the thoracic duct 

 approach (12) has separated from the jugular approach (13). 

 The curve of the process, with the concavity directed meso- 

 caudad, gives the two cross sections of its lumen included in the 

 forked leader 12. The termination of the thoracic duct approach 

 has still further invaded the recess between sympathetic (1) and 

 vagus (22) and a slight interval has developed between the two 

 nerves. 



The lateral circumference of the vagus (22) covers practically 

 the entire mesal aspect of the internal jugular vein (25). 



In the following figure (fig. 86, series 142, slide x, section 20) 

 the termination of the thoracic duct process (12) is seen slipping 

 through the interval between sympathetic (1 ) dorsally and vagus 

 (22) ventrally. Instead of lying therefore dorso-lateral to the 

 sympathetic as in the preceding series 245 the end of the 

 thoracic duct approach in the present instance passes mesad on 

 the ventral aspect of this nerve, between the same and the vagus. 

 This relationship is also seen in the two succeeding figures, 87 

 and 88 (series 142, slide x, sections 22 and 24.) 



We are dealing therefore apparently with two potential paths 

 which the blind terminal of the thoracic duct approach may take 

 in its passage from the jugular lymph sac mesad beyond the vagus- 

 sympathetic line to the upper mediastinal region, where it estab- 

 lishes eventually its secondary connections with the preazygos 

 segment of the thoracic duct and with the broncho-mediastinal 

 trunk. In one type (illustrated by the sections and reconstruc- 

 tions of series 245 (figs. 79 to 82, fig. 90) the process dips, after 

 passing between the left superior intercostal and main jugular 

 vein at an acute angle, caudad on the lateral side of the sympa- 

 thetic strand (fig. 90). 



