438 OTTO F. KAMPMEIER 



nates just below the level of the right Cuvierian duct at X. There 

 is also a long and spindle-shaped space which lies lateral to it 

 and in the pathway of a tributary of the anterior lymphatic 

 plexus were it prolonged downward, as suggested in figures 13 

 and 30 



Passing to the postcardinal division (B, fig. 30) of this embryo, 

 we meet with the most decisive evidence in favor of the non- venous 

 origin of the thoracic duct, namely, a clear case of discontinuity 

 in its anlage than which nothing could be more conclusive. Im- 

 mediately following the injected portion of the right duct (5d) is a 

 long fusiform mesenchymal space (4-d), but in no way connected 

 with it, as exemplified by the drawings, figures 13, 30 and 31 

 (ventral view), and the microphotographs, figures 15, 16 and 17 

 which represent transverse sections taken at this level. Espe- 

 cially the ventral view of the reconstruction (fig. 31) illustrates the 

 abrupt break (X) in the duct anlage, the position of the terminal 

 portion of the injected channel (5d), and the independent fusi- 

 form space (4d) and its longitudinal extent. The injected channel 

 ends obscurely in a ' mossy' area produced by slight extravasa- 

 tions, the position of which is indicated at X in figure 15 just 

 ventral to the broad lumen of the anterior tip of the independent 

 space (4-d). That there is absolutely no open communication 

 between these two segments of the duct-anlage is strikingly con- 

 firmed by both observation and experiment. In the first place 

 the most critical examination with the high powers of the micro- 

 scope was not able to detect continuity, and secondly, not a 

 particle of the injection mass was found to have entered the cavity 

 of the blind fusiform space (4-d), although the pressure of the 

 injection was sufficiently great to produce the extravasations 

 referred to above. 



Fig. 13 A simplified or schematic drawing of an accurate reconstruction of 

 the thoracic duct region in series 23a (Johns Hopkins University Embryological 

 Collection) represented in figure 33. The lymph sac and the injected portion of 

 the thoracic duct anlage were drawn in black; the uninjected lymph spaces are 

 discontinuous but are located in the axes of the injected channels and consequently 

 in the paths of the future complete thoracic ducts. The cross lines indicate the 

 levels at which figures 14, 15, 16 and 17 were taken. 



