A. M. Miller 295 
In Fig. 7 a pair of important vessels are shown which have not been 
present in the preceding illustrations. These are the Vv. renales 
magnae (V.r. m.d ands), the efferent veins of the permanent kidney. 
There are also two other smaller vessels which appear for the first time 
in this figure—the Vv. intervertebrales lumbales (V. 1. 1. d ands). 
Before the permanent kidney appears the anterior ends of the post- 
cardinal veins have atrophied and disappeared. ‘The kidney begins to 
develop about the 6th day of incubation and is situated dorsal to the 
mesonephros and lateral to the aorta and chorda. As soon as the head 
end develops the V. intervertebralis lumbalis appears as a small vein 
enclosed among the tubules, which empties into the postcardinal at the 
same level as the external iliac vein. As the head end of the kidney 
enlarges this vessel becomes larger and in Fig. 7 (V. i. 1. d and s) is 
seen to be a vein of considerable importance. Moreover, the segmental 
(vertebral) veins which previously emptied into the enterior end of the 
postcardinal now open into this new vessel. It functions as the efferent 
vein of the head end of the kidney (Fig. 9, V. i. 1. s.). 
After the kidney has attained 
a considerable size still another 
vessel, the V. renalis magna, is 
developed on each side as a 
branch of the subcardinal system 
at the level of the large anasto- 
mosis; but it is not included in 
tne subeardinal system. This vein 
runs laterad from the anasto- 
‘mosis till it reaches the dorsal 
side of the mesonephros, that is, 
it reaches a position on the me- 
dian side of the kidney. As the 
kidney develops the above vein “SS ah Sian UNOS 
becomes more or less enclosed 
KS 
Seacqea : Ky : . Fig. 9. Region of the bifurcation of the 
within its ventral side (Fig. 8) postcava in the adult domestic fowl, showing 
Pa AL a Gee the part of the postcava which is formed 
and 2Towlng caudad, finally €X- from the subcardinal system, and the rela- 
: tions of the common iliac and great renal 
tends to the level of the umbil- veins. The right V. intervertebralis lumbalis 
s m s Ty= is omitted and instead the small efferent renal 
ical artery. While the mesone-  yeinsareshown. Ventral view. Natural size. 
phros persists ‘t receives a small (Explanation of lettering on page 284.) 
amount of blood from this organ; but its more important func- 
tion is to carry blood from the kidney to the postcava: it is the large 
efferent vein of the kidney. When the great renal veins have reached 
an advanced stage of development, as in Fig. 7, they anastomose with 
