Each primitive aorta
receives anteriorly a vein—the vitelline vein
—from the yolk-sac
, and is prolonged backward on the lateral aspect of the notochord
under the name of the dorsal aorta
The dorsal aortæ give branches to the yolk-sac, and are continued backward through the body-stalk as the umbilical arteries to the villi of the chorion.
The two dorsal aortae combine to become the descending aorta in later development.