Final answer:
The purpose of the ductus venosus in fetal circulation is to allow umbilical vein blood to bypass the liver.
Step-by-step explanation:
The purpose of the ductus venosus in fetal circulation is to allow umbilical vein blood to bypass the liver. The ductus venosus is a temporary blood vessel that branches from the umbilical vein, allowing freshly oxygenated blood from the placenta to go directly to the fetal heart without passing through the liver. It closes slowly after birth and becomes the ligamentum venosum.