280 George 8. Huntington and Charles F. W. McClure. 
nerves to the veins and veno-lymphatics of the right side suggest 
that here the terminal of tributary 1 has been retained, while 
tributaries 2 and 3 have lost their precardinal connections. Thus 
on the left side the common trunk of the first and second cervical 
nerves comes to lie cephalad of all veno-lymphatic terminals into 
the precardinal, while on the right side this trunk is placed caudad 
of the first veno-lymphatie precardinal tap. 
3. On the left side (fig. 49) the extension cephalad of the dorsal 
plexus involves both the portion derived from the promontory 
and that furnished by the primitive ulnar arch, both components 
uniting in the plexiform network of the dorsal veno-lymphatic 
arch. On the right side (fig. 50) the primitive ulnar arch yields a 
relatively small plexiform veno-lymphatic cephalic prolongation, 
which, while undoubtedly destined to unite eventually with the 
other components of the dorsal veno-lymphatic arch to form its 
caudal extension is, in this stage, still separate and discrete. The 
arch is in this instance evidently produced by cephalic extension 
of that portion of the dorsal plexus, which was originally derived 
from the promontory, but which, in establishing a secondary ante- 
rior connection with one of the veno-lymphatic compounds of the 
cephalic division of the ventral plexus, has given up its original 
promontorial connection in the area of Tap C (cf. fig. 44). 
4. On the right side (fig. 50) the promontorial portion of the 
dorsal plexus has given up its original connection with the prom- 
ontory, still present on the left side, and now ends in this region 
in a caudal blind prolongation which lies dorsal to the thyro- 
cervical artery, and constitutes that portion of the future lymph 
sac which we have termed the subclavian approach. 
5. This right side of this embryo (fig. 50) illustrates an impor- 
tant phase in veno-lymphatic development, which, in a more 
advanced condition, is found in series 78 (fig. 57). In embryos 
ranging between 10 and 12.5 mm. the dorsal veno-lymphatic 
plexus makes a secondary, although temporary, connection with 
the anterior part of the straight segment of the precardinal, and 
in doing so, often gives up its original promontorial connection 
(series 78, fig. 57). The secondarily acquired anterior connection 
with the preecardinal vein apparently serves for the evacuation of 
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