Emissary veins passing through the foramen ovale, jugular foramen, foramen lacerum, and hypoglossal canal. Because the emissary veins are valveless, they are an important part in selective brain cooling through bidirectional flow of cooler blood from the evaporating surface of the head. In general, blood flow is from external to internal but the flow can be altered by increased intracranial pressure. A type of emissary vein goes through the sphenoidal emissary foramen inferior to the zygomatic arch with the cavernous sinus on the inside of the skull. This is an important route for spread of infection because cranial nerve VI and the
Hepatic veins ultimately from numerous central veins of the liver lobules. None of the hepatic veins have valves. The hepatic veins are divided into an upper and a lower group. The upper three drain the central veins from the right, middle, and left regions of the liver and are larger than the lower group of veins. The lower group of from six to twenty smaller hepatic veins come from the right lobe and the caudate lobe, are in contact with the hepatic tissue, and are valveless. All the veins empty into the inferior vena cava at the back of the liver. Budd–Chiari