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The earliest known samples of writing on the circulatory system can be dated to the sixteenth century BCE, to a collection of ancient Egyptian papyri. The ancient Egyptians believed that air travelled from the mouth to the lungs and heart, and from there to the arteries. By the fourth century BCE arteries and valves had been discovered, but most physicians still believed they were filled with air, because these circulatory structures appear empty after death. By the second century AD, Roman physicians had identified vessels as carrying the liquid known as blood, but it was assumed that blood was "used up" in the body's extremities, and wasn't recirculated.
Is your knowledge of the circulatory system akin to that of the ancient Egyptians or the Romans of the second century, or are your facts a little more up-to-date? Take the quiz and see how you rank!
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Circulatory System Quiz