On the presence of a ductus venosus in the fetal pig in late gestation.

Evidence is presented to show that there is a functional bypass in the liver of the fetal piglet between the umbilical vein and the posterior vena cava. Injections of labelled microspheres (14 micrometer) into the umbilical vein in six fetuses in late gestation resulted in the appearance of radioactivity in the arterial blood and throughout the tissues of all piglets. About 60% of the umbilical venous blood bypassed the liver whereas in a fetal foal, injection in a similar manner, no evidence for a shunt was found. Radiographic studies confirmed the presence of a large vascular connection, equivalent to the ductus venosus, between the umbilical vein and posterior vena cava in the fetal piglet.