THE EMBRYONIC GROUND PLAN 7 



1. The lateral pharyngeal lymphatic (3 in figure 10, truncus lym-- 



phaticus pharyngeus lateralis) 



The lateral pharyngeal lymphatic occupies a superficial posi- 

 tion in the lateral wall of the pharynx and forms, on each side 

 of the body, a direct anterior continuation of the lymphatic of 

 the lateral line of the trunk (truncus lymphaticus longitudinalis 

 lateralis, 10 in fig. 10). The lateral pharyngeal lymphatic 

 drains the subocular lymph sac, the dorsal region of the head and 

 pharynx and, at a slightly later stage, the operculum and the 

 lower jaw. In fact, with the exception of one other channel 

 (medial pharyngeal lymphatic), the lateral pharyngeal lym- 

 phatic and its tributaries, together with the subocular lymph 

 sac, constitute, on each side of the body, the entire continuous 

 lymphatic system found in the regions of the head and pharynx 

 at this stage of development. The lymphatic of the lateral 

 line of the trunk (10, fig. 10) is also completely developed on the 

 twenty-second day and can be traced caudad into the tail 

 region. 



The points of communication established between the lateral 

 pharyngeal lymphatic (3) and the precardinal (jugular) vein (6) 

 are confined, at this period of development, to that portion of the 

 precardinal vein which extends between the caudal end of the 

 otocyst and the point where the pre- and postcardinal veins 

 (6, 11) unite to form the duct of Cuvier (24, cardino-Cuvierian 

 junction). A point of communication commonly occurs at the 

 cardino-Cuvierian junction (cardino-Cuvierian communication, 

 9 in fig. 10) where the lateral pharyngeal lymphatic (3) opens 

 into the veins in common with the lymphatic of the lateral line 

 of the trunk (10). This communication may be single or mul- 

 tiple in character, the latter being the case on both sides of the 

 embryo under consideration. Another point of communication 

 with the precardinal commonly occurs at about opposite the cau- 

 dal end of the otocyst (otic communication) and in the embryo 

 under consideration, was present only on the right side (13 in 

 fig. 10). The otic communication may be present on both sides 

 of the embryo, however, and, like that found at the cardino- 



