Developmert of the Jugular Lymph Sacs. 283 
of common occurrence, and is well illustrated by series 102 (fig. 
45) and by series 112 (fig. 47) in which two such channels are 
met with opening into the lateral surface of the promontory at 
Tap B. In the latter series, if these two channels were to separ- 
rate completely from each other and from the remaining portion 
of the ventral plexus, they would oecupy the same relative 
position with respect to each other and to the precardinal vein 
and promontory as do the two closed sacs in series 101 (fig. 50). 
Series 77 mbryo 
S ie EB b y 
Reconstruction of left side, 
Lateral aspect, fig. 51 and 
) aD 
Reconstruction of right side, 
Lateral aspect, fig. 52 
This 11 mm. embryo offers an exceedingly interesting and sug- 
gestive comparison with the 10 mm. embryo just considered (figs. 
49 and 50), since it further emphasizes two principal features of 
development first noted in the latter:—(1) the forward extension of 
the dorsal veno-lymphatic plexus and the establishment of an 
anterior tap of evacuation and (2) the beginning of the amalgama- 
tion of the three primary divisions of the veno-lymphatic plexus 
to form a common single veno-lymphatic sac. 
On both sides of the embryo, (figs. 51 and 52) an anterior tap 
of evacuation has been established at the level of the cephalic arch, 
between the anterior end of the dorsal veno-lymphatic arch and 
the straight segment of the precardinal. As mentioned above, we 
have every reason to believe that this communication, secondarily 
established, between the dorsal arch and the precardinal, repre- 
sents a normal phase of development and serves as the main, if 
not the only exit, in some cases, by which the blood is evacuated 
from the veno-lymphatic sac into the systemic veins. 
Further, on both sides of thisembryo (figs. 51 and 52), the cephalic 
division of the ventral veno-lymphatic plexus has become incorpor- 
ated by fusion with the anterior end of the dorsal plexus so that 
this portion of the ventral plexus no longer appears as a separate 
structure. 
On the left side (fig. 51) the dorsal veno-lymphatic plexus com- 
