THE LATERAL PHARYNGEAL LYMPHATIC 41 



The above observations, as illustrated by sections of injected' 

 embryos and by reconstructions, fairly represent the average con- 

 ditions presented by all of the anlagen of the lateral pharyngeal 

 lymphatic at a time before, during, and after their confluence 

 to form a continuous vessel by means of which the subocular 

 lymph sac drains into the veins. We have already considered 

 in detail the development of the more anterior anlagen of the lat- 

 eral pharyngeal lymphatic, and it now remains for us to consider 

 more closely the relations which the otic and cardino-Cuvierian 

 lymph sacs bear to the veins. 



From what has been said concerning the variable relations 

 which the otic and cardino-Cuvierian lymph sacs bear to the 

 veins, it is evident that direct and positive proof is wanting 

 either in favor of or against their being of venous origin; 

 this being so for the reason that, amongst the earliest stages 

 examined, some of these sacs were found to be independent of the 

 veins while others were connected with the veins at the typical 

 points of lymphatico-venous entry. In view of the circumstance 

 that in certain instances these sacs were found to connect with 

 the veins one might infer, in the case of those sacs which did not 

 connect with the veins, either that they had been derived from 

 the veins and had secondarily severed their connection with them, 

 or, that they had developed in situ in the mesenchyme and had 

 not yet established a connection with the veins at the typical 

 points of lymphatico-venous communication. In order to prove 

 that the otic and cardino-Cuvierian lymph sacs have been de- 

 rived from the veins, it would be necessary to show that a primary 

 continuity invariably exists between the cells which form the walls 

 of these sacs and the endothelium of the veins. This, we have 

 seen, has not been found to be the case. 



It has already been stated that a definite endothelium which 

 can be distinguished from mesenchyme is wanting in the subocular 

 lymph sacs and in the independent anlagen of the more anterior 

 portion of the lateral pharyngeal lymphatic, at the time of their 

 inception. I may also state that what one might regard as a 

 definite endothelium, similar to that of the veins, is also wanting 



