535 



LEFT INT 

 JUGULAR V 



LEFT JUGULAR 

 LYMPH SAC 



not shown in the figure. On tracing the thoracic duct caudad of the 

 jugular lymph sac it at first lies upon the dorsal surface of the common 

 jugular vein, lateral to the sympathetic nerve and between the latter 

 and the A. thyro-cervicalis. Near the origin of the A. thyro-cervicalis 

 and the A. vertebralis from the left subclavian, the thoracic duct lies 

 on the medial side of the sympathetic nerve, having reached this 

 position , by passing 

 ventral to the nerve, 

 although in some em- 

 bryos it passes dorsal 

 to the same. From 

 this point on to the 

 innominate cross -ana- 

 stomosis, the thoracic 

 duct lies along the 

 dorso-medial surface 

 of the left innominate 

 vein. Then, after cross- 

 ing the left subclavian 

 artery on its dorsal 

 surface, it follows the 

 ventro-medial and ven- 

 tral surface of the left 

 azygos vein to the 

 caudal end of the 

 thorax where it be- 

 comes continuous with 

 the lymphatics of the 

 lumbar region. These 

 are not extensively 

 developed as yet in 

 the 16 mm embryo 

 and will not be further 

 considered in the pre- 

 sent paper. The tho- 

 racic possesses a slight- 

 ly larger caliber than 

 the right lymphatic 



duct and is easier to follow in sections, although no great difficulty 

 is involved in following either of these ducts in the 16 mm embryo 

 along their entire course. 



RIGHT INNOMINATE ' 



INNOMINATE 

 CROSS ANASTOMOSIS 



RIGHT DUCT 

 OF CUVIER 



Fig. 7 



RIGHT A2YG0S V 



RIGHT LyWPHATIC 

 DUCT 



Fig. 1. Dorsal view of a wax reconstruction of a 

 16 mm cat embryo showing the left jugular lymph sac and 

 thoracic duct and their relations to contiguous structures. 



