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Woodcut from William Harvey's book Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus (On the Motions of the Heart and Blood), published in 1628. Harvey (English physician 1578- 1657), discovered the circulation of the blood. The above book was an expression of the theory. The one way system of valves in the veins (seen here) alerted Harvey to their role in the general circulation of blood. The left illustration shows the valves in the superficial veins of the forearm, from a living subject. The finger has been passed along the vein from O to H (away from the heart).
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