240 George 8. Huntington and Charles F. W. McClure. 
Series 2, 7" Embryo 
Reconstruction of right side, 
Lateral aspect, fig. 31 and 
Reconstruction of left side, 
Lateral aspect, fig. 3% 
~ 
t 
This embryo, although of the same crown-rump measurement 
as the following series 138 (figs. 33 to 36), is less developed than 
the latter in so far as its veno-lymphatic elements are concerned. 
There is also considerable variation present upon opposite sides 
of the embryo, the right side having progressed to a lesser extent 
than the left. 
On the right side the dorsal precardinal tributaries 1 and 2 
(fig. 31), are expanded and plexiform at their terminals, and repre- 
sent a stage preparatory to their final separation into dorsal 
somatic and veno-lymphatic components, as seen in series 138 
(figs. 38 and 36). (Also compare with schematic diagram, fig. 10, 
which corresponds in this respect to the condition presented by 
this embryo). 
Precardinal tributary 3 is not represented on the right side 
by any well-defined vessel. It may have become incorporated in 
the funnel-shaped expanded terminal of 2, as in series 109 (fig. 29), 
or subsequently detached from the same, as in fig. 28, in which 
case it may be represented on the right side in series 2 by the 
detached element labelled 3VL(fiz. 31). 
Precardinal tributary 4 presents essentially the same condi- 
tions as on the left side of the 6.2 mm. embryo (series 109, fig. 27). 
It opens cephalad into the precardinal vein at X and caudad into 
the promontory. The former connection (fig. 31, X) represents 
its original junction with the precardinal vein (compare series 
30 and 31, figs. 22, 283 and 24). Its connection with the promon- 
tory has been secondarily acquired by the condensation of the 
precardinal plexus into a para-precardinal channel, which, separ- 
ated from the main vein by the fenestra Y (fig. 31, Y), spans 
the interval! between the promontory and the primary terminal 
of 4 (fig. 31, X), and now drains the greater part of the blood cur- 
rent of 4 directly caudad into the promontory. 
