70 DEVELOPMENT OF THE SYSTEMIC LYMPHATIC VESSELS 



The thoracic duct approach has enlarged, is partially subdivided 

 (cf. p. 65, figs. 48 and 49, series 189) and its blind terminal 

 extremity is reaching ventro-mesad into the angle between internal 

 jugular vein and sympathetic (1). The thjTO-cervical artery (24) 

 lies between the subclavian and thoracic duct approaches, dorsal 

 to the jugulo-cephalic trunk {29). 



In fig. 68 the thoracic duct approach has further enlarged and 

 is still subdivided into two compartments the terminal of which 

 abuts directly against the sympathetic nerve. The jugular 

 approach (13) communicates in this section with the internal 

 jugular vein, while a narrower slit-like division continues further 

 caudad toward the common jugular angle. 



In fig. 69 the internal (25) and jugulo-cephalic (29) trunks are 

 only separated from each other by a narrow septum containing 

 the lumen of the slit-like prolongation of the jugular approach. 

 Both in this and in the preceding section the ventral process of 

 the jugular approach lies in the angle between the two veins, 

 closely applied to their ventral surface. 



The thoracic duct approach is a large sausage-shaped structure, 

 curved over the dorsal surface of the internal jugular vein. The 

 septum in its interior has disappeared and the process presents a 

 clear lumen. 



In fig. 70 (slide ix, section 2), the confluence of internal jugular 

 and jugulo-cephalic trunks has taken place (26). The thoracic 

 duct approach (12) has extended both ventro-mesad into an area 

 of indifferently defined mesodermal spaces, mesad to the syra- 

 pathetic nerve (1), and laterad toward the subclavian approach 

 of the jugular sac (14), passing between common jugular vein 

 (26) and thyro-cervical artery (24). 



In section 5 of slide ix (fig. 71) the thoracic duct approach 

 (12) appears as a long curved multilocular channel, which laterad 

 reaches the subclavian approach of the jugular lymph sac, between 

 the thryo-cervical artery (24) and common jugular vein (26), 

 while its l:»lind mesal extremity terminates just dorsal to the sym- 

 pathetic-vagus strand. In the following section (fig. 72) the 

 thoracic duct approach (12) connects with the subclavian approach 

 (14) of the jugular lymph sac affording an instance of the gene- 



