118 DEVELOPMENT OF THE THORACIC DUCT 



region, the cephalic end of the preaortic segment of the thoracic 

 duct (fig. 172, 35} is seen lateral to the oesophagus (8], between 

 the sympathetic nerve (1) dorsad and the subclavian artery (33) 

 and left innominate vein (40) ventrad. The cephalic end of the 

 broncho-mediastinal channel (37) lies in the angle between sub- 

 clavian artery and innominate vein, lateral to and at some dis- 

 tance from the trachea (9). The two lymphatic channels are 

 traced in the succeeding sections cephalad to their union and their 

 continuation with the thoracic duct approach of the jugular 

 lymph sac. 



In fig. 173 (series 143, slide xi, section 14) the lymphatic ducts 

 have approached each other and a third lymphatic cross-section 

 appears mesal to the subclavian artery in the interval between the 

 thoracic duct and the broncho-mediastinal channel, foreshadow- 

 ing their approaching fusion (38). In fig. 174 (series 143, slide xi, 

 section 12) this fusion has occurred (38 in fig. 174 representing 

 union of 35 and 37) 



In fig. 175 (series 143, slide xi, section 11) the connection is 

 interrupted, and in the succeeding sections (figs. 176, 177, 178 and 

 179) the two components of the area of confluence (38), viz, the 

 preaortic thoracic duct segment and the broncho-mediastinal 

 trunk, remain separated from each other. The latter assumes more 

 and more the typical character of the thoracic duct approach of 

 the jugular lymph sac, as previously described (cf. p. 60), 

 occupying the typical neuro-venous recess between sympathetic 

 nerve and innominate vein, as shown well in figs. 178 and 179 

 (series 143, slide xi, section 2, and slide x, section 32). 



In fig. 180 (series 143, slide q, section 28) the two lymphatic 

 components have again united (38), and they continue from this 

 point on as a single channel following the typical course of the 

 thoracic duct approach of the jugular lymph sac cephalad to union 

 with that structure. 



We have therefore in this stage a gradual approach of the cepha- 

 lic ends of the preaortic segment of the thoracic duct and of the 

 ventral broncho-mediastinal trunk, a preliminary anastomosis 

 between them (figs. 173, 174), followed further cephalad by a 

 final confluence and union with the thoracic duct approach of the 

 jugular lymph sac. 



