In vertebrates other than fish, it refers to the large vein that guides blood from all parts of the body to the heart. It can be divided into anterior great vein and posterior great vein.
The precava (Vena Cavaanterior) is derived from the changes of the GV tube of the embryo. Amphibians, reptiles and birds each have one pair, which sends blood from the jugular vein and subclavian vein to the venous sinus. In mammals, there is also one pair of anterior great veins of monotremes, marsupials, denticles and insectivores, but generally only the right great vein remains, and the left Guvier's tube remains to form the coronary vein of the heart wall. Postcaval, vena cava posterior higher vertebrates It is a large vein that runs along the great dorsal artery. It mainly receives the blood from the tail, hind limbs and kidneys directly or through the renal portal system, and then flows upward to merge with the blood from the hepatic veins and enter the heart. 
