Consists of the lateral abdominal veins, which receive blood from the iliac and subclavian veins. The anterior veins are derived from the cardinal system. The hepatic portal system is derived from the subintestinal system. The hepatic portal vein receives blood from the gut region. Inside the liver the vein breaks up into hepatic sinusoids, where the blood comes into contact with hepatic cells and phagocytic cells.
Harmful materials are detoxified and removed from the blood in the liver.
Posterior to the liver the blood is collected into the hepatic vein, which joins with the caudal vena cava. The renal portal system is derived from the posterior cardinal veins. Blood from the posterior part of the body flows into the renal portal veins, which passes into the caudal vena cava. The renal portal system is found only in fishes, amphibians, reptiles and birds. Thus, mammals have no renal portal system.