The Couinaud's segmental nomenclature of the liver is based on the position of which of the following structures?

According to the nomenclature of Couinaud classification, liver is divided into 4 sectors and 8 segments. Each segment has independent aery, bile duct, tributary of hepatic vein and poal tributary. Liver is divided into 8 couinaud's segments depending on the position of 3 main hepatic vein and poal vein. Hepatic veins lie between segments. The left hepatic vein divides the left side of the liver into medial and lateral segments. Middle hepatic vein divides the liver into left and right lobes. The right hepatic vein divides the right side of the liver into anterior and posterior segments. Horizontal line through the left and right main poal vein branches divide hepatic lobes into superior and inferior segments.