294 The Development of the Postcaval Vein in Birds 
While the glands are in their earlier stages of development they may 
give blood to the subeardinals through several small branches. As the 
glands become shorter, approaching the adult condition, some of these 
small branches disappear, and finally one or two remain on each side 
which ultimately persist as the spermatic or ovarian veins emptying 
into the pars subcardinalis of the posteava just cranial to the bifurca- 
tion. In Fig. 7 the genital veins (Vv. g.) are seen as branches of the 
small remaining part of the posterior ends of the subcardinals. 
Hochstetter (88, 93) advanced the idea that the spermatic or ovarian 
veins in birds were formed froin the subcardinals (efferent veins of the 
primitive kidney), though he did not make a positive statement and 
gave no illustrations. here certainly can be no doubt that the genital 
and at least the left suprarenal veins are derived directly from the sub- 
cardinals. 
Fic. 8. Outline sketch of a cross-section through a sparrow embryo, 
corresponding to a chick of 14 days; taken a short distance caudal to the 
bifureation of the postecava. Showing relative position of the great renal 
veins. X about 20. (Hxplanation of lettering on page 284.) 
Fig. 8 shows the adult conditions in the postcaval vein. It is rather 
difficult to state with certainty to just what extent the subcardinal system 
persists. The writer has carefully considered the matter and has indi- 
cated by crosses a small portion proximal to the bifurcation into which 
empty the suprarenal (V. sr. s) and the spermatic veins (Vv. g.). Jt 
may be safely stated, however, that the subcardinal system persists at 
least as a small portion of the postcava proximal to the bifurcation, 
which portion, as stated above, is marked by crosses. Furthermore the 
genital and left suprarenal veins are true subcardinal derwatives and: 
empty into the subcardinal portion of the postcava. 
