Heart anatomy. Diagram of a dissected heart by the Italian artist and scientist Leonardo da Vinci (1452-1519). The four chambers of the heart: the two atria and the two larger ventricles below them are clearly seen. The belief at that time, first proposed by the Roman anatomist Galen, was that there were only two chambers. However, another of Galen's mistaken beliefs, the existence of pores in the heart's central wall, the septum, is shown. Da Vinci studied the heart by dissecting oxen and human cadavers. His notes were in mirror writing which he is thought to have used, along with abbreviations and a lack of punctuation, to protect himself from claims of heresy.
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