Development of the Jugular Lymph Saes. Dae 
=| . 
Series 18, 7.25" Embryo 
Reconstruction of left side, 
Lateral aspect, fig. 39 
The two salient features of this embryo which distinguish 
the left side (fig. 39) from the right (fig. 38) are that on the left 
side the dorsal precardinal tributaries, with the exception of 
tributary 1, are either rudimentary or are practically wanting as 
such, and that the promontorial end of the straight segment of the 
precardinal consists of two parallel channels, subequal in caliber, 
which are separated from each other by an elongated fenestra 
Ce tie 39). 
The dorsal precardinal tributary 1 (fig. 39) is a vessel of fairly 
large size. It opens dorso-medially into the precardinal ard as 
yet shows no sign of fenestration. 
Preeardinal tributary 2 is represented by a veno-lymphatic 
element, which opens dorso-laterally into the precardinal (2VL, 
fig. 39) and probably by the detached element which lies contig- 
uous to the latter. 
Precardinal tributaries 3 and 4, as distinct branches of the pre- 
cardinal, are wanting, as no trace of any tributaries opening into 
the precardinal could be found in the territory usually occupied 
by them. In their place, however, and occupying a dorso-lateral 
position with respect to the para-precardinal channel and in line 
with the dorsal veno-lymphatic plexus, are situated a number of 
independent veno-lymphatics (3, 4VL, fig. 39) which probably 
represent these tributaries, and which in further development 
would probably contribute to the formation of the continuous 
veno-lymphatic arch of later stages, which lies dorso-lateral to the 
straight segment of the precardinal. 
The separation of the promontorial end of the straight segment 
of the precardinal into two parallel channels is a feature of develop- 
ment which has already been described in connection with series 
109 (fig. 28) and series 2 (fig. 31). Usually, however, the more 
dorsal of the two channels, which we have termed the para-pre- 
cardinal channel, is the smaller of the two and serves, at a cer- 
tain period of development, as the main pathway through which 
the precardinal tributary 4 drains into the promontory. In the 
