H • /'. Sabin. 



In following th iralward from the level of fig. 9 



ii i- clear that the blood-filled lymphatics not only arch across the 

 midline dorsal to the aorta, but tbej follow the border of the Wolffian 

 be lateral to tl i. Above the adrenal bodies the Wolffian 



bodies approach very close to the aorta, and some of the lymphatic 

 buds curve around the ventral surface of the aorta. Thus in a sp 

 men 23 nun. long there is a plexus of blood-filled lymphatics surround- 

 ing Lhe aorta and extending into the lower thorax as Ear as I : >ral 



• ■ of the Wolffian bodies. At the cerebral end oi the Wolffian bodies 

 there are large veins which curve ventral to the aorta and conned 

 the veins of lhe capsule of the Wolffian bodies. Some of the lymphatics 

 are n< ar i dian veins. 



i Finding of the renal lymphatics in the blood-packed Btage makes 

 it quite certain that the thoracic duel arises in two places: First, 

 the jugular stem, which can lie injected from the left jugular sac ami 

 develops long after the jugular sacs arc entirely empty of blood; and. 



■ndlv. the renal plexus, which surrounds the aorta and forms a defi- 

 nite cisterna chyli. 



These two observations, namely, ( l ) the presence of hlood in one 



pail ami its absence in the other, and ('.') the fact that injections 

 prove a connection of the jugular -tern with the jugular sac. ami of 

 the abdominal plexus with the mesonephritic veins, make it quite cer- 

 tain that the two portions of the thoracic duct are distinct Erom each 

 other in embryo pig- measuring' 23 mm., and hence that the thoracic 

 dint begins in two places. Practically the entire question at issue 

 between those of us who think that the lymphatics grow by their own 

 endothelial wall and those who do not centers around the question 

 of how the thoracic duct develops, or, t.1 put it more specifically, how 

 these two lymphatic anlagen become connected. The discussion centers 

 around my specimen 23a, which Kampmeier studied and which be 

 - a- hi- mosl conclusive evidence of the theory of the growth of 

 lymphatics by the addition of tissue spaces. On the other hand, it 

 is my theory that the thoracic duct grows from these two anlagen Erom 

 the same method by which other lymphatic capillaries 



can be Been to grow in a living spei i n, namely, by the sprouting of 



their endothelial wall. It is time that 1 have nut yet sufficiently 

 mastered the difficulties of injecting the renal lymphatics to demon- 

 strate the progression of the thoracic duct and indeed it may not 

 pn.\e possible to gel as conclusive proof of the origin of the deep lym- 



