262 George 8S. Huntington and Charles F. W. McClure. 
The anterior part of the straight precardinal segment, in the area 
corresponding to the dorsal tributaries 1, 2 and 3, carries on its 
dorso-lateral aspect a large diverticular sac, which extends caudad 
in the direction of the promontory. This sac, produced by conden- 
sation of the peri-precardinal capillary network. forms the anterior 
or cephalic division of the ventral veno-lymphatic plexus (cj. fig. 9). 
On the right side of this embryo (fig. 41) this structure is in the pro- 
cess of differentiating from the main vein. In the later stages it 
will fuse with the dorsal plexus derived from the promontory, and 
with the caudal division of the ventral plexus, and will then form 
the anterior portion of the continuous veno-lymphatic sac (fig. 42, 
area of 1,2and3). Atits anterior end it is still in wide-open communi- 
cation with the precardinal and it terminates caudally in a blind 
and deeply bifurcated extremity which overlaps the dorso-lateral 
aspect of the straight precardinal. When the cephalic division of 
the ventral plexus is formed in this manner the precardinal tribu- 
taries 1, 2 and 3 appear to be taken up as a whole in the veno-lym- 
phatie organization and do not divide into veno-lymphatic and 
somatic components as far as we can determine. 
The left side of this embryo apparently represents an instance in 
which primary dorsal tributary 4 of the precardinal has been trans- 
formed in its entirety into a dorsal somatic promontorial branch (48) and 
has not contributed a component to the ventral veno-lymphatic 
plexus. 
It may be possible that the more dorsal of the two processes 
(4VL’) which, form the bifurcated extremity of the anterior veno- 
lymphatic sac has been derived from tributary 4 and has been sec- 
ondarily joined to the’sac. If such is the case, we are not in a 
position to prove it, and must, therefore, abide by our original 
contention that tributary 4 per se, in this particular instance, 
does not furnish a veno-lymphatic component. 
The dorsal somatic tributary 4 (4S, fig. 42) is formed by two 
confluent branches which enter the dorso-medial aspect of the pro- 
montory at the promontorio-precardinal angle. The vessel is 
expanded and fenestrated near its promontorial connection and les 
in line with a series of promontorial and postcardinal dorsal somatic 
tributaries (5S, 6S, 7S and 8S, fig. 42), of which it forms the first 
or most anterior member of the series. 
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