THE LATERAL PHARYNGEAL LYMPHATIC 33 



anlagen of the lateral pharyngeal lymphatic ever establish with 

 the precardinal vein. 



If the lateral pharyngeal lymphatic sprouts centrifugally, 

 continuously and uninterruptedly from the endothelium of the 

 veins, the supporters of the ' centrifugal' theory would neces- 

 sarily maintain that it should do so only from the primary and 

 typical points at which it can be observed to connect with the 

 veins. Such being the case, they would also maintain that that 

 portion of the lateral pharyngeal lymphatic which lies anterior 

 to the points at which communications are established with the 

 veins (between 13 and 1 in fig. 10), should be formed as the re- 

 sult of the forward extension of the more caudally situated an- 

 lagen of the lateral pharyngeal lymphatic which do connect with 

 the veins. Also, in accordance with the 'tests' they have made, 

 Sabin ('11) and E. R. Clark ('11 a) would necessarily agree that 

 this anterior portion of the lateral pharyngeal lymphatic should 

 always remain in continuity with the veins and that it should be 

 potentially capable of being injected from the veins. 



Let us see to what extent these conditions are fulfilled as 

 shown by a study of injected trout embryos. We will first con- 

 sider the development of that portion of the lateral pharyngeal 

 lymphatic which lies anterior to the points at which primary 

 communications are established between it and the veins; and 

 second, that portion of the vessel which arises contiguous to and 

 which communicates with the precardinal vein. 



1. The development of that portion of the lateral pharyngeal lym- 

 phatic which lies anterior to the points at which primary com- 

 munications are established between it and the precardinal vein 



This portion of the lateral pharyngeal lymphatic, as stated 

 above, extends between the otic communication and the sub- 

 ocular lymph sac (between 13 and 1 in fig. 10), and develops 

 slightly later than the more caudally situated portion of the 

 vessel which establishes typical communications with the pre- 

 cardinal vein. A study of injected trout embryos shows that 

 this anterior portion of the lateral pharyngeal lymphatic makes 



