Notes and Drawings on the Thorax and Abdomen (1901) - Page 72

⚠The manuscript shows significant staining and some fading of the ink, particularly in the marginal notes.

The lung is the instrument Leonardo uses the word "instrument" to describe a biological organ's mechanical function. that draws in the air and sends it through the arterial veins original: "vee artiali"; Leonardo often used the term "arterial veins" to describe the pulmonary vessels, as the distinction between arteries and veins was still being refined in his era. to the heart to refresh it, to purify the blood, and to consume the excessive humidity of the blood. The vessels of the soul original: "vasi d'essa ania [anima]"; Leonardo frequently explored the physical location of the "soul" or "vital spirit" within the vascular system. because it moves away from the limbs, it moves away from the motion of the limbs.

polmone (lung) — The primary organ of respiration.
sangue (blood) — The vital fluid Leonardo believed was cooled by the lungs.
cuore (heart) — The central engine of the body's heat and life.
anima (soul/vital spirit) — In Renaissance anatomy, the "soul" was often thought to reside in the blood or the cavities of the brain and heart.
vasi (vessels) — The tubes (veins and arteries) that transport fluids.
vasi arteriali (arterial vessels) — Specifically referring to the pulmonary circulation.
anatomia (anatomy) — The study of the structure of living things.
rinfrescarlo (to refresh/cool it) — Leonardo believed a primary function of breathing was to prevent the heart from overheating.

The central diagram on this page is one of Leonardo's most sophisticated anatomical drawings. It illustrates the "bronchial tree" and the heart's internal chambers. He was among the first to realize that the heart is a muscle and to accurately depict the valves, though he still adhered to some traditional theories, such as the idea that the lungs' main purpose was to "cool" the heart's heat.