96 DEVELOPMENT OF THE SYSTEMIC LYMPHATIC VESSELS 



surrounded by the extraintimal lymphatic space (5). On the 

 right side of the embryo the corresponding venous radicle (4) 

 and the perivenous lymphatic anlage (5) have been again cut 

 more at right angles, so that the envelopment of the former by 

 the latter can be clearly traced nearly throughout the entire cir- 

 cumference. 



Fig. Ill A shows the decadent vein and the replacing extrainti- 

 mal lymphatic on the left side of this section in a higher magnifi- 

 cation, ( X 300). The structure of the collapsed venous endothelial 

 tube, and the beginning development of endothelial character in 

 the mesodermal cells limiting the perivenous extraintimal lym- 

 phatic anlage, can be here clearly made out. 



Figs. 112 to 116 show the five succeeding sections of the same 

 embryo (series 189, slide viii, sections 37 to 41 inclusive) in a 

 magnification of 225 diameters. 



I publish this series of plates in order to prove on the one hand 

 that the extraintimal lymphatic anlages can be followed with 

 certainty and accuracy in their relation to the contained decadent 

 venule for longer or shorter distances, and that, on the other 

 hand, they are, in these earlier stages, still isolated and not yet 

 continuous with similar anlages in adjacent areas. The,y form, 

 in other words, in these earlier periods, detached links of a lym- 

 phatic chain, not yet united to each other to form the continuous 

 channel of the later stages. 



In figs. 112, 113 and 114 (sections 37, 38 and 39) beautiful and 

 clear pictures of the atrophying central venule (4) and the peri- 

 venous extra-intimal lymphatic space (5) are found on both sides 

 in the typical situation noted in the preceding sections, with 

 which they of course can easily be coordinated by simple com- 

 parison. 



Sections 38 and 39 (figs. 113 and 114) are particularly instruc- 

 tive inasmuch as the detached central vein (4) on the left side 

 still contains a few degenerating red blood cells, while its former 

 connection with the valid and functional venous plexus around 

 the left vagus nerve can still be faintly traced. 



In section 40 (fig. 115) the atrophying vein (4) and the sur- 

 rounding lymphatic (5) of the left side appear divided into two 



