LATER DEVELOPMENT OF VASCULAR SYSTEM 365 
a second venous ring is established around the alimentary canal, 
the lower portion of which is formed by the second anastomosis, 
Fig. 210. — Diagrams illustrating the development of the hepatic 
portal circulation. (After Hochstetter.) 
A. About the fifty-eighth hour. 
B. About the sixty-fifth hour; first venous ring formed around 
the intestine. 
C. About the seventy-fifth hour; the left limb of the first ve- 
nous ring has disappeared. 
D. About the eightieth hour; the second venous ring is estab- 
lished. 
E. About the one hundredth hour; the right limb of the second 
venous ring has disappeared. 
F. Hepatic circulation about the one hundred and _ thirtieth 
hour, immediately before the disappearance of the intermediate 
portion of the meatus venosus. 
a.i.p., Anterior intestinal portal. D.C., Duct of Cuvier.  int., 
Intestine. M. V., Meatus venosus. (Es., (Esophagus. Pe., Pan- 
creas. St., Stomach. S. v., Sinus venosus. V. c¢. i., Vena cava 
inferior. V.h., Hepatic veins. V.o.m., Omphalomesenteric vein. 
v. r. 1, First venous ring. v.r. 2, Second venous ring. V. u. d., 
Right umbilical vein. V. u. s., Left umbilical vein. 
