THORACIC DUCT DEVELOPMENT IN THE PIG 



441 



11d 



6b 

 X 



vr«.. «?». ft , 







Fig. 15 Transverse section taken shortly beyond the right Cuvierian duct 

 in a 23 mm. pig embryo (series 23a, J.H.E.C., slide 26, section 10), X 200. 4d, 

 anterior tip of the long fusiform lymphatic space in the right thoracic duct line; 

 X, position of extravasated particles from the injected portion of the right thora- 

 cic duct anlage; 6b, postcardinal veno-lymphatic ; lid, right postcardinal; 13, 

 aorta; 17, oesophagus; 25, venules or branches of the postcardinal. The more deli- 

 cate lining of the lymphatic space as compared with that of the veins and venules 

 can be clearly distinguished in the figure. (Reconstruction, fig. 30.) 



of its wall can be distinguished without the least difficulty. 

 Figure 17, again, illustrates the occasional circumclusion of the 

 precardinal veno-lymphatics (6b) by this space and draws more 

 plainly, perhaps, the distinction between lymphatics and venous 

 channels, where the latter are replete with blood and possess 

 sharply defined boundaries as compared with the often ill-defined 

 outlines of the lymphatic space. Caudally this long space after 

 a course which can be easily pursued through thirty-seven sec- 

 tions, as already stated, becomes more indistinct until it vanishes 

 by the loss of its cavity in the confusion of the interstices of the 

 tissue reticulum, but after a number of sections it is followed by a 

 second space, which, though shorter and simpler (figs. 13 and 31), 



