Final answer:
In ancient and medieval physiology, veins were believed to carry one of the four elemental bodily humors as part of the humoral theory. Arteries and veins in the modern understanding have different functions in the circulatory system. Thus, the option B is the correct answer.
Step-by-step explanation:
In old physiology, the vessels that were thought to convey one of the four elemental bodily humors were called veins. This concept was part of the ancient and medieval humoral theory, which proposed that the proper balance of the four humors (blood, phlegm, black bile, and yellow bile) in the human body was necessary for good health. The humors themselves were believed to be channeled through the body by a network of veins, which is distinct from the modern understanding of the circulatory system, where arteries carry blood away from the heart to the body's tissues, arterioles distribute blood to capillary beds, and veins return blood back to the heart.