A. M. Miller 287 
to the union of the latter vessel with the ducts of Cuvier (indicated by 
an asterisk in Fig. 3). 
A marked difference 
is seen here between the 
relations of the proximal 
end of the postcava in 
reptiles, birds and mam- 
mals. While in birds it 
arises as a branch of the 
ductus venosus (Hoch- 
stetter, 88, 93), in rep- 
tiles it arises either as a 
branch of the right 
omphalomesenteric vein silts Haan, from, sumnz neconetruction of the ves 
L same specimen as Fig. 4. Outline of liver dotted. Dorsal 
(Lacerta) or as a branch view. x about 55. ‘(£xplanation of lettering on page 284.) 
of the union of the latter 
vein with the right umbilical (Tropidonotus) (Hochstetter, 92). In 
Echidna (Hochstetter, 96) the right V. hepatica revehens forms the com- 
mon stem of the posteava and the ductus venosus Aranzii. In the higher 
mammals thus far observed it arises from the V. hepatica revehens com- 
munis (Hochstetter, 93, Lewis, 02). 
The postcaval vein in the chick first appears about the 90th hour of ineu- 
bation, as Hochstetter has observed, though the writer has noticed it in 
the initial stages somewhat earlier. The liver at this time is composed 
of merely a few tubules surrounding the ductus venosus. Among the 
tubules are to be seen a number of small venous islands, or hepatic sinu- 
soids, as Minot has called them. The hepatic portion of the posteava is 
the result of a fusion of some of these sinusoids lving dorsal to the ductus 
venosus, that is, in the dorsal part of the right lobe of the liver. At this 
stage there is also found a series of venous islands extending through the 
caval mesentery, and ending on the median side of the right mesonephros 
a short distance anterior to the origin of the A. omphalomesenterica. 
These islands are in the direct line of the future continuous postcaval 
vein, and by their fusion, which takes place soon after their first appear- 
ance, the portion of the postcava between the liver and the mesonephros 
is formed. 
In his description of the development of the postcava in the chick 
Hochstetter (88, 93) does not state the fact that it is derived through a 
fusion of islands in the caval mesentery and through the fusion of a num- 
ber of hepatic sinusoids. In his work on the mammals, however, he indi- 
cates that the postcava arises in some such manner (“ durch Erweiterung 
