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
Jean Riolan the Younger through the blood vessels to the body's extremities and returned to the heart only two or three times a day. He also postulated that blood often ebbed and flowed in the veins and that it was taken in as nourishment by different parts of the body. Riolan also did not believe that the heart propelled the blood, instead he proposed that the blood kept the heart in motion, analogous to a stream moving the wheel of a water mill. Riolan had other disagreements with Harvey, such as the role of the liver as a blood-manufacturing organ. Riolan was an opponent