474 



ON THE ORIGIN AND EARLY DEVELOPMENT 



around the stump (fig. 10) . The anterior portion of this plexus was entirely normal, 

 as was also the posterior portion, except for the absence of large channels over the 

 posterior tip of the pelvis and the presence in their place of a more primitive plexus 

 with fine delicate endings. 



On the right side there was a very large gap which bordered dorsally on the 

 spinal column and left the entire Wolffian body and most of the liver exposed. The 

 lymphatic injection showed a normal plexus dorsal to the shoulder, connected 

 anteriorly, as on the left side, with the deep cervical plexus, and posteriorly with 

 the side lymphatics. This plexus was not extensive, owing to the large size of the 

 gap. It connected anteriorly through the axilla with the deep jugular plexus, and 

 posteriorly ended blindly in numerous fine points at the edge of the gap. On the 

 anterior border of the pelvis (in the region just 

 posterior to the gap), as in the younger chicks 

 just described, no lymphatics were injected. 

 Farther posteriorly on the pelvis, however, a large 

 plexus of lymphatic capillaries was injected. This 

 was normal in appearance and more extensive 

 than that shown in fig. 9. It extended over the tip 

 of the pelvis, ending, like the plexus of the opposite 

 side, near the middle of the stump in numerous 

 finely-pointed, blind tips (figs. 11 and 12). 



A still older stage is shown in figure 13, a 

 chick of 7 days. The lymphatics of the left side 

 resembled those shown in figure 10, except for 

 the presence of some larger ducts in the side 

 region between the limbs. On the right side the 

 lymphatics of the shoulder region, and of the 

 side region anterior to the gap, were normal for 

 chicks of this stage. Over the pelvis, from the 

 region just posterior to the gap and extending 

 well around the stump, was a luxuriant plexus 

 of lymphatics resembling those of the opposite 

 side in character and extent. No connections 

 between this posterior lymphatic plexus and the 

 veins could be found in any specimen after this 

 type of operation. It should be emphasized, 

 however, that no microscopic studies were made on the operated chicks at the 

 younger stages in which probable venous connections were found in this region 

 in normal chicks. 



This series of specimens shows that there is apparently still another point of 

 origin for the superficial lymphatics of chick embryos i. e., a region over the 

 posterior part of the pelvis. The lymphatics which develop here make their appear- 

 ance somewhat later than those in the jugular region, the side region anterior to 

 the leg, or those which differentiate in the posterior lymph-heart region of the tail. 



FIG. 13. Riaht side of an operated embryo of 6 

 days 18 hours, showing a later stage of devel- 

 opment of the superficial lymphatics after 

 operation 3. Operative procedure same as 

 that described under figure 12. Injected 

 lymphatics in the suprascapular and axillary 

 regions normal in appearance. The lym- 

 phatics posterior to the gap, in this specimen, 

 cover the whole pelvis and stump just as on 

 the left (unoperated) side. X 12. 



