DEVELOPMENT OF THE THORACIC DUCT 81 



general systemic lymphatic channels. These have in the mean- 

 while formed along and around the temporary embryonic veins, 

 as the result of the confluence of large numbers of extraintimal 

 perivenous spaces in the sense previously defined in detail. 

 Their line of further growth, extension and union with each other 

 is altogether centripetal, from the outlying regions toward the 

 jugular lymph sacs, and their union with the latter's processes 

 is the last and final step in the definite organization of the lym- 

 phatic system. 



