288 The Development of the Postcaval Vein in Birds 
und Zusammenfliessen schon vorhandener Venenbahnen,” 93, p. 568). 
Thus it appears that the early formation of the hepatic portion of the 
postcaya takes place on the same principle in both birds and mammals. 
SO es The above mentioned 
) ae islands of the postcava are 
shown in Fig. 4 (V. c.1.). The 
anterior island is of sinusoidal 
origin; the others are situated 
in the caval mesentery, ex- 
tending from the liver in front 
to the median side of the right 
mesonephros some distance 
anterior to the origin of the 
A. omphalomesenterica. At 
this stage the islands of 
the subeardinals have not yet 
undergone a complete longi- 
tudinal anastomosis. In Fig. 
5, which represents a slightly 
older stage than Fig. 4, the 
subeardinal on each side is a 
continuous vessel extending 
from a point just caudal to 
the duct of Cuvier almost to 
the level of the umbilical ar- 
teries—in other words the full 
length of the mesonephros. 
At their anterior ends both 
subeardinals join the postear- 
dinals; all other direct connec- 
tions between the former and 
latter veins have been broken 
up in the mesonephric circu- 
lation, with the exception of 
the vessels described above as 
situated in the ventral part of 
the mesonephros (Fig. 5, b). 
Fria. 4. Reconstruction of the venous system of Here the islands of the post- 
a sparrow embryo, corresponding to a chick of caval vein have also fused 
about 90 hours. Ventral view. x75. (Haplana- ? 
tion of lettering on page 284.) to form a continuous vessel 
(V. c. 1.), which, however, has not yet joined the ductus venosus, 
but ends in the hepatic sinusoids. This latter condition is short 
