296 The Development of the Postcaval Vein in Birds 
the postcardinals at the level of the external iliac veins. They approach 
so near the posteardinals that the walls break through and there then 
exists a direct channel on each side from the postcardinal to the post- 
cava. 'Thus the renal portal system is destroyed. It is interesting to 
note, as Hochstetter has done, that a renal portal system of the perman- 
ent kidney also exists before the anastomosis between the great renal 
veins and the postcardinals; for more or less blood is given to the kid- 
neys by the postcardinals which in turn is carried to the postcava by the 
great renal veins. But as soon as the above anastomosis takes place 
this renal portal system is destroyed, as well as that in the mesonephroi. 
In Fig. 7, on the right side, the anastomosis between the great renal 
vein and the postcardinal is shown; the one on the left has not yet taken 
place. As a general rule they occur about the 14th or 15th day of incu- 
bation in the chick and at a corresponding stage of development in the 
sparrow. After these anastomoses the adult condition is practically 
reached and it only remains for a few changes in relative position to 
take place. In Fig. 7 the anastomosis is seen to be very short; but dur- 
ing further development it lengthens out to a considerable extent so that 
in the adult condition it forms about the distal half of the common iliac 
vein. What was originally the proximal end of the great renal vein 
forms the proximal half of the common iliac vein. (Compare Fig. 9). 
There remain to be described two important changes which take place 
in the region of the posterior portion of the postcardinal veins: (1) 
About the 6th day of incubation in the chick an anastomosis between 
the two postcardinals is found far back in the tail-region, which lies 
ventral to the caudal aorta. As the tail-region shortens up in the pro- 
cess of development the anastomosis is gradually pushed forward till it’ 
reaches the normal position just caudal to the posterior lobe of the kidney 
about the 11th day. In the meantime the V. coccygomesenterica has 
developed and on the 8th day it is seen as a small vessel coming from 
the dorsal surface of the hind gut. It joins either the anastomosis 
directly or the one or the other posteardinal anterior to the anastomosis ; 
but in the latter case it finally joins the anastomosis itself. In the adult 
it communicates directly with the hepatic portal system (vide Fig. 7, 
CeVieeye 
(2) The other change takes place in the postcardinal veins in rela- 
tion to the umbilical arteries. In the early stages of development the 
postcardinals are found lying ventral to the umbilical arteries (Figs. 
4 and 5), which condition is characteristic in reptiles. About the 5th 
day of incubation in the chick, and at a corresponding stage of devel- 
opment in the sparrow, a new venous channel is found dorsal to the 
