What did William Harvey observe about the direction of valves in the jugular vein?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

William Harvey observed that the valves within the jugular vein are oriented to face downward. This orientation inhibits blood flow away from the heart, rather than preventing the pooling of blood caused by gravity as previously believed.1

By demonstrating that these valves are cardiocentrically oriented—meaning they are positioned in relation to the heart—Harvey provided critical evidence that blood flows in a single, continuous system throughout the body.1