Development of the Jugular Lymph Saces. 285 
ventrally situated elongated portion which lies along the lateral 
surface of the precardinal and promontory and of an expanded, 
oval dorsal portion which is flexed mesad so that it lies directly 
upon the dorsal surface of the precardinal, just in front of the 
promontory (figs. 14 and 20). The promontory, however, does 
not form a prominent swelling of the main venous channel on the 
left side of this embryo. 
On the right side of this embryo (fig. 52), in addition to the an- 
terior tap of evacuation, the dorsal veno-lymphatie plexus com- 
municates with the systemic veins at three points, all of which are 
situated on the dorso-lateral surface of the promontory. The 
most anterior of these three points of communication (Tap C), 
made through the subclavian approach, lies dorsal to the cephalic 
vein and caudal to the thyro-cervical artery and in this respect 
corresponds to the Tap C observed on the opposite side of the 
embryo (Tap C, fig. 51). The two points of communication caudal 
to Tap C on the right side (fig. 52) represent a condition in which 
the process of separation of the dorsal plexus from the promon- 
tory is less complete, owing to the establishment of secondary 
connections representing the anlage of the subclavian vein ter- 
minal. The primitive ulnar veno-lymphatic is fully established 
on the right side but, as it was not reconstructed, has not been 
indicated in the figure. 
In addition to its connection with the systemic veins, the dorsal 
veno-lymphatic plexus also communicates, by two narrow trans- 
verse channels, with the caudal division of the ventral plexus. 
These two connections, as well as the single one of the opposite side, 
must be regarded as secondary communications which have been 
established between the dorsal and ventral plexus preliminary to 
a complete fusion between the two. The composition of the cau- 
dal division of the ventral plexus is essentially the same as on the 
left side. It consists of an elongated portion, which lies along the 
lateral surface of the precardinal and promontory, and communi- 
cates with the latter (Tap B) near the entrance into the promon- 
tory of the cephalic vein,and of a dorsal oval, expanded portion 
which is flexed mesad so that it lies upon the dorsal surface of the 
precardinal, just in front of the promontory. The promontory is 
