Development of the Jugular Lymph Sacs. 263 
The para-precardinal channel, so prominently developed on the 
right side in connection with the veno-lymphatic component. of 
tributary 4 (fig.41),is represented on the left side by a small diver- 
ticular process of the promontory which is connected with the dorso- 
lateral circumference of the latter (para-precardinal channel, fig. 
42). An examination of the actual reconstruction of the left side 
shows more clearly than is indicated in the figure that this short 
stump-like para-precardinal element was probably continuous at 
one time with the more ventrally situated of the two processes which 
form the posterior extremity of the cephalic division of the veno- 
lymphatic plexus or sac, and that it has separated from the latter, 
during the course of development. Such as it is,however, it repre- 
sents in its entirety, on the left side of this embryo, all that is present 
of the caudal division of the ventral veno-lymphatic plexus, which is 
well developed on the right side (fig. 41), as well as in certain embryos 
of the earlier stages (fig. 82). (Cf. also fig. 21). 
The dorsal! veno-lymphatic plexus of the left side (fig. 42) is 
extensively developed. It has given up its connection with the 
anterior end of the primitive ulnar anlage and lies further from the 
promontory than in earlier stages (fig. 31), as the result of an en- 
largement and elongation of the fenestree which lie between its 
promontorial connections. The dorsal veno-lymphatic plexus, as 
already described, has been separated by fenestration from the dorso- 
lateral circumference of the promontory and primitive ulnar segment 
of the posteardinal, and its general phases of development can now 
be easily followed by comparing the preceding figures. 
The anlage common to the primitive ulnar vein and the primitive 
ulnar veno-lymphatic is fully established and opens into the dorso- 
lateral circumference of the promontory about opposite the latter’s 
point of confluence with the seventh dorsal somatic tributary (7S, fig. 
42). The anlage of the primitive ulnar veno-lymphatic has not 
yet begun to separate from the anlage common to it and the primitive 
ulnar vein. 
The anlage of the cephalic vein has made its appearance on the 
left side of this embryo as a small vessel which opens laterally into 
the promontory, dorsal to the anlage of the permanent external 
jugular vein. 
