232 ~=George 8. Huntington and Charles F. W. McClure. 
the dorsolateral aspect of the umbilical vein and receives a 
number of serially arranged branches, which open into it dorsally. 
Caudal to the last of these tributaries indicated in the figure the 
posteardinal appears dilated and fenestrated and then rapidly 
diminishes in caliber. 
Series 47, 5°” Embryo 
. Reconstruction of right side, 
Lateral aspect, fig. 26 
The junction of the pre- and postcardinal veins is, relatively, 
of narrow caliber and perforated by a fenestra, agreeing with the 
peculiar slender and irregular formation exhibited by the Cuvier- 
ian confluence in series 134 and 30, figs. 25, 22 and 23. The om- 
phalo-mesenteric and umbilical veins have shifted their terminals 
caudad and now obtain an opening into the sinus venosus inde- 
pendently of the duct of Cuvier proper. A branch from the 
body wall entering the umbilical at the sinus venosus seems to 
correspond to the primitive drainage of the external jugular terri- 
tory. The umbilical vein also receives further caudad a number 
of somatic tributaries and branches from the anterior limb bud. 
This drainage area, compared with series 134 (fig. 25) appears 
reduced and in the process of transferal to the path of the postcar- 
dinal whose somatic branches are more fully developed. 
The greatest interest attaches to the neighborhood of the pre- 
and posteardinal confluence. In both embryos (134 and 47) con- 
ditions are presented in this region which directly lead up to those 
found in the succeeding stages (embryos 30 and 31). Two points 
are here involved: 
(a) Precardinal 
The dorsal precardinal tributary 4 (4 in fig. 26), which is 
destined to play so important a réle in the subsequent venous and 
veno-lymphatic development, appears to be laid down at a very 
early stage. In series 134 (4, fig. 25), it is represented by the two 
large dilated and tortuous branches which enter the dorsal cir- 
