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, 



r.y. 



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. CEs., (Esophagus. PC., 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. 



