Hepatic portal system occurs in all vertebrates and is meant for taking blood from digestive tract, pancreas and spleen into liver. It is formed by four veins ie,
(i) Splenic vein-takes blood from spleen
(ii) Inferior mesentric-from different parts of alimentary canal
(iii) Superior mesentric from different parts of alimentary canal
(iv) Gastroepiploic-from stomach and pancreas