434 



OTTO F. KAMPMEIER 



Fig. 11 Transverse section through the left lower cervical region in a 20 mm. 

 pig embryo (series 193, slide 14, section 20), X 200. This figure shows the anterior 

 lymphatic plexus (3) of the thoracic duct not developed from extra-intimal spaces, 

 but formed in the mesenchyme independently of the precardinal veno-lymphatics 

 (6a); 9, internal jugular; 14, sympathetic nerve trunk; 15, vagus; 17, oesophagus. 

 (Compare with fig. 8.) 



ous channel undergoing atrophy almost constantly contain 

 numerous blood corpuscles, or the deeply staining debris of cel- 

 lular material (figs. 6, 7, 8 and 10), and without exception possess 

 a sharply defined endothelium. 



To strengthen the evidence of figures 0, 7 and 10, illustrating 

 the formation of lymphatic spaces without the features of extra- 

 intimal replacement, figure 11 from series 193, another 20 mm. 

 embryo, may be introduced here as a very definite specific case 

 to show conclusively that such replacement of venous channels 

 is not inevitably a requisite in the genesis of lymphatics, and that 

 its absence is quite as common as its occurrence. In this embryo 

 the most anterior portion of the thoracic duct anlage (3) has not 

 been modelled, so to speak, upon the anterior precardinal veno- 



