Vitelline circulation refers to the system of blood flowing from the embryo to the yolk sac and back again.
The yolk-sac is situated on the ventral aspect of the embryo; it is lined by endoderm, outside of which is a layer of mesoderm. It is filled with fluid, the vitelline fluid, which possibly may be utilized for the nourishment of the embryo during the earlier stages of its existence. Blood is conveyed to the wall of the sac by the primitive aortæ, and after circulating through a wide-meshed capillary plexus, is returned by the vitelline veins to the tubular heart of the embryo. This constitutes the vitelline circulation, and by means of it nutritive material is absorbed from the yolk-sac and conveyed to the embryo.
Famous quotes containing the word circulation:
“There is probably not more than one hundred dollars in cash in circulation today. That is, if you were to call in all the bills and silver and gold in the country at noon tomorrow and pile them on the table, you would find that you had just about one hundred dollars, with perhaps several Canadian pennies and a few peppermint Life Savers.”
—Robert Benchley (1889–1945)