The artist and science

Excerpt from the book 'Leonardo da Vinci - The Complete Paintings and Drawings' by Frank Zöllner

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In his representation of sexual intercourse, Leonardo draws upon contemporary thinking and the physiology enshrined in the Corpus Hippocraticum in depicting the ways in which the internal organs of the human body interconnect. Thus a tubelike duct leads from the woman's breasts to her womb, while the male organ is directly linked not only to the testicles but also to the lungs and the spinal cord, and hence to the brain. The sketches at the bottom of the sheet, showing a cross section and a longitudinal section of the penis, accordingly portray two channels, the lower for the sperm from the testes and the upper for the spiritual powers transported from the brain along the spinal cord. In his later anatomical drawings, which were based on extensive studies of dissected corpses, Leonardo increasingly questioned these antiquated notions of the human anatomy and how it functions.

Leonardo's conviction that the inner organs of the human being were closely interconnected reflects a highly complex understanding of human nature. The two channels in the penis, for example, illustrate the view that there were two ingredients necessary for procreation: in addition to sperm, a spiritual substance was also required. This spiritual substance, which ultimately came from the very seat of the soul, was thought to carry higher intellectual and spiritual qualities, while the sperm from the testicles, with its own specific make-up, was responsible for baser urges, although also for such properties as courage in battle. Similar notions of the effect and function of bodily substances also informed Leonardo's thinking on tears, which he believed came directly from the heart as the seat of all feeling (RL19057v).

In order to appreciate the full significance of the physiological notions encountered so far, we must take a closer look at just how Leonardo thought the brain, and in particular the senso comune, actually worked. At the heart of this physiology, which presupposes that the processes of the soul exert a direct mechanical influence upon the body and its functions, lie Leonardo's views on the functioning of the brain (Cat. 353/ill. p. 129). To Leonardo's understanding, the things perceived by the five senses are sent first to the imprensiva, which is no more than a temporary holding centre. The impressions received here are then transferred to the senso comune for correlation and evaluation, before finally being stored in the memoria, where they "are more or less retained according to the importance or force of the impression" (RLW § 836).
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Anatomical Study of the Muscles of the Leg, c. 1490