DEVELOPMENT OF THE THORACIC DUCT 69 



to the immediate neighborhood of the thoracic duct approach. 

 Fig. 63 shows the sections of the internal jugular vein (25) and 

 jugulo-cephalic trunk (29), approaching their point of union in 

 the common jugular confluence. A large process of the jugular 

 lymph sac (13) extends, as the jugular approach, into the interval 

 between the main veins. Along the mesal aspect of the internal 

 jugular vein (25). are placed the sympathetic (1), the vagus (22), 

 the left common carotid artery (28), and, further ventrad, the 

 thymus (21 ) . The dorsal portion of the sac is about to form the 

 subclavian approach (11, 14). 



In fig. 64, the jugular approach (13) has entered more deeply 

 into the narrowing interval between the internal jugular (25) 

 and jugulo-cephalic trunks (29), and the sharply marked con- 

 striction between it and the remainder of the sac (subclavian 

 approach, 14) foreshadows its coming separation from the latter. 

 A protrusion of the dorso-medial angle of the jugular approach, 

 adjacent to the internal jugular vein, indicates the beginning 

 derivation of the thoracic duct approach (12). 



In the succeeding section (fig. 65) the jugular approach (13) 

 has separated from the subclavian approach (14) of the jugular 

 lymph sac and thus cleared the path for the passage of the thyro- 

 cervical artery (24) between the two cardinal divisions of the 

 lymph sac, whose caudal terminations are represented by the 

 jugular and subclavian approaches. The origin of the thoracic 

 duct approach (12) from the dorso-medial angle of the jugular 

 approach is now defined. 



In the succeeding section (fig. 66) the triple termination of the 

 jugular lymph sac, in the subclavian (14), jugular (13) and tho- 

 racic duct approaches (12), is accomplished, and the latter is begin- 

 ning to extend mesad across the dorsal surface of the internal 

 jugular vein. The main thyro-cervical artery is approaching 

 the junction with its secondary dorsal branches. 



In fig. 67 the jugular approach (13) has divided into the inter- 

 mediate part between the internal (25) and jugulo-cephalic (29) 

 veins, which is to establish the tap at the common jugular angle, 

 and a ventral process which extends from the tap caudad over 

 the ventral surface of the common jugular angle and vein. 



