Which tunic is normally the thickest layer in the wall of a vein?

1. Arteries and veins both carry three tunics: intima, media and externa. 2. In an artery the tunica media, packed with smooth muscle and elastic fibers, is the thickest layer. 3. In a vein that pattern inverts: the collagen rich tunica externa is normally the thickest tunic. 4. The tunica intima in a vein is thinner than the externa, so it cannot be the answer. 5. The basement membrane is a component inside the intima, not a tunic in its own right. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 20 "The Cardiovascular System: Blood Vessels and Circulation", section 20.1 Structure and Function of Blood Vessels_