268 George 8. Huntington and Charles F. W. McClure. 
lymphatic plexus and thus contribute to the forward extension of 
the latter. If, in the meantime, it still retains its primary con- 
nection with the precardinal, this connection may serve*as a por- 
tal through which the blood is evacuated from the plexus into 
the systemic veins (Tap of evacuation). 
The distinctive element of the cephalic division of the ventral 
plexus in this region is represented by a capacious sac which has 
shifted to the lateral aspect of the precardinal and which com- 
municates with the same by a single opening (Tap A’). This sac 
occupies an area of the precardinal which formerly received the 
dorsal tributaries 2 and 3. The primary connection of one of 
these two tributaries (probably 2) with the precardinal has un- 
doubtedly persisted as the opening through which the sac now 
communicates with the vein, while the sac itself has probably 
been formed through a fusion of the veno-lymphatic components 
of these two tributaries, possibly in conjunction with an element 
derived from the plexiform dorso-lateral circumference of the main 
channel of the precardinal vein. 
The cephalic portion of the ventral division of the veno-lym- 
phatic plexus is not always developed to the extent shown in the 
present embryo but, when present, its origin can always be traced 
back to the veno-lymphatic components of the precardinal trib- 
utaries 1, 2 and 3, to the area of the precardinal which receives 
these tributaries, or, to both of these sources. 
2. Caudal Division. 
The caudal division of the ventral veno-lymphatic plexus, 
which has undoubtedly been derived from the veno-lymphatic 
component of precardinal dorsal tributary 4 and its related para- 
precardinal channel, forms an extensive sac with three elongated 
cephalic processes. The sac has shifted laterad and caudad on to 
the lateral aspect of the precardinal and promontory, a position 
which becomes more pronounced in later stages. It communicates 
laterally (fig. 46) with the precardinal near the promontorio- 
precardinal angle (Tap 6’) and with the promontory slightly cau- 
dal to this point (Tap B). 
7 
