Julia King
New York, United States

Leonardo da Vinci was a “Renaissance man” in the truest sense, contributing his inexhaustible talent to many fields, including anatomy. In a time when medicine was still rudimentary and dissection was viewed with disdain, Leonardo plowed through with his keen intellectual curiosity and honed draughtsman skills. His work on anatomy can grossly be divided into two stages: his earlier artistic pieces and his later analytical studies.¹ Leonardo’s earliest studies focused on illustrating ancient texts and indulging in anatomical explanations of metaphysics; he was concerned with the soul and the eye as a means to both localize the soul and better understand artistic perspective. His later scientific blossoming drove his interest in observational description of the human body, its function, and its relation to the world. Leonardo’s growth from metaphysics toward a more empirical science informed not only his drawing style, but also the content and presentation of his anatomical works.

The earliest sheet of Leonardo’s anatomical work dates “a di 2 d’aprile 1489,” marking his early anatomy exploration through imaginative comparative anatomical structures and illustration of ancient anatomical literature.² It is well known that Leonardo dissected many animals in addition to men, and many of his drawings are deliberately composed of different parts from different animals, an approach he reinforced with his writings: “You know that you cannot make any animal which does not have parts each of which is itself like that of ‘some other animal.’”³ He also devised rules for the composition of human figures: “you should not mix limbs of the young with those of the old, nor those of the stout with those of the lean . . . you should not make men with feminine limbs, nor mix graceful limbs with clumsy ones.”⁴ He used his imaginative faculties even when working from observation: most of these drawings were less about direct representations than artificial demonstrations of his partial knowledge of debased traditional notions and medical legends.^2,5 Leonardo’s first visualization of the “conception of man” came from ideas of Plato and Hippocrates, primarily concerning the soul’s origin:

From the passage of egress for the drink where it receives and joins in discharging the fluid which has come past the lungs and the kidneys below into the bladder, they [the gods] bored a hole into the condensed marrow which comes from the head down through the neck along the spine, which marrow we termed ‘seed.’ And inasmuch as it is animate and has been granted an outlet, it has endowed the part where its outlet lies with a love for generating by implanting therein a lively desire for emission.

These are words from Plato’s Timaeus, but could have easily been those of Leonardo writing about his drawing of coitus.³ Similarly, on 19057v, he notes a passage “through which the visual power passes to the sensorium” and another by which “tears well up from the heart to the eye, passing via the canal of the nose,” thus connecting the “lacrimator” with the Platonic center of emotion (the heart).² Furthermore, his drawing technique is often indicative of his tenuous grasp on physiology: the original silverpoint studies are hesitant and have been adjusted by tentative outlines of brown and black ink.²

Leonardo’s neurology is equally kowtowing to the ancients, particularly Galen: his nerves are cord-like structures serving their traditional functions as hollow vessels for transmitting animal spirits across undifferentiated nerves, tendons, ligaments, and muscles. Sensibility is carried from brain to muscle: from the pia and dura mater via the lateral canals to the nerves, where the “purpose of the soul” causes muscle movement. The two cannot be divorced and so an artist must use physiology to visually communicate the figure’s inner mind.² This concept pervades his early work:

The good painter has to paint two principal things, that is to say, man and the intention of his mind. The first is easy and the second difficult, because the latter has to be represented through gestures and movements of the limbs—which can be learned from the dumb, who exhibit gestures better than any other kind of man.⁴

Here the scientific basis for art and the anatomical explanation of metaphysics mesh. For Leonardo, the soul was a physically localized entity functioning to comprehend the natural world²; he could use it to explain the artistic “perspective,”  the cornerstone of Renaissance art.

The 1489 skull studies are artistic masterpieces and exemplify his pseudo-scientific approach to anatomy. The striking sectioning of the skull and its accompanying annotations speak to his concern with architectural theory (at a time when he was involved with architectural problems in Milan and Pavia) and its application to geometrically localize the sensus communis—the common sense, the seat of the soul—an idea derived from a misinterpretation of Aristotle’s De anima.^2,3 It is thus named because Leonardo followed the optic nerve back into the brain to elucidate where vision occurs.³ His quirky diagrams on 12627r and 12626 show the cranial nerves and their terminations in the brain’s various ventricles, exalting vision as the only sense to pass directly to the intellect; for him it was not only the “window of the soul, [it] is the chief means of understanding the infinite works of nature,” as well as the “prince of mathematics,” stemming from his reverence for the mathematical “certainty” of optics.² Since Leonardo called perspective a “function of the eye”¹ —and optical impressions travel according to infallible optical laws directly to the intellect² —it makes sense that the primacy of vision in the brain and in understanding the natural world lends itself to a “scientific” justification of perspective.

Leonardo used the (fictitious) convergence of the senses to assert that the intellect-soul is localized; he argued from (imagined) structure toward a theory of function.² The second phase of his anatomies embraced a more empirical approach. Between the first and second stages of Leonardo’s anatomical inquiries, some twenty years apart, three major events influenced his outlook: his physics experiments, his work with mathematician Luca Pacioli, and the 1493 translation of Mondino’s dissection manual from Latin to Italian.³ Armed with more rigorous tools, Leonardo took his work in a new direction.

Leonardo’s early 16^th century anatomies can be divided in two: his 1500–1506 Florentine work, which coincided with his shift from art serving science to anatomy as a subject for rigorous scientific inquiry; and his 1506–1512 Milanese work, where he sought to understand the interplay between the microcosm of the body and the macrocosm of the universe.¹ He moved away from fitting forms to preconceived functions and towards understanding function as a result of observed form.⁵ His approach reshaped the anatomy book he had in mind: whereas his early anatomies combined form, function and theory without room for text, his later anatomies embraced the importance of both—illustration to detail visual information and description to discuss function in the context of natural laws.⁵

Leonardo saw the body as a microcosm of complex dynamics, an instrument governed by the laws of Nature.⁵ In his 16^th century research, he allows his encounters with the physical world to reshape his earlier notions: “I intend to say the same about animals and plants universally, reducing or increasing them proportionately according to their diminution or increase in size.”⁴ The 1508–1509 studies of the vascular and pulmonary systems are particularly obvious examples. Leonardo’s windpipe branches were regular, equal bifurcations, a scheme shared by plants:

the total amount of air which enters the trachea is equal to the total number of stages generated from its branches, like . . . a plant in which each year the total estimated size of its branches when added together equals the size of the trunk of the plant.⁵

He described the trachea with disunited rings that individually contact each other for different voices and the larynx for compressing wind turbulence in the bronchi “for the creation of the various types of voices and also to compress and dilate the ventricles of the brain.”⁵

In the del vecchio series, he compared a germinating seed to the vascular system: both have repetitive, equal branching; this is an argument, in his mind, for the unity of the macro and micro worlds, as well as an argument for the heart as the focal point of the venous network. Again, we hear echoes of his earlier days, reminiscent of the philosophical debate over the status of heart and liver—and where that leaves the soul.⁵ However, his highly practical language is in marked contrast to the tone of his 1480s anatomies, which were characterized by “confluence of the senses” and the trafficking of “animal spirits.”⁶ A similar movement away from the metaphysical is found in Paris Manuscript D in a small section on optics: the eye is now described as receptive, not as a pro-active radiator of rays as before, a machine that can be disassembled and understood like the rest of the body.⁶

His 1510 drawings increase in complexity and include extensive notes on the function of each form.⁵ Leonardo’s skeleton and muscle studies are described by principles of the lever, and the body as a whole is described in various states of balance and unbalance.³ He treated the body as a complex instrument governed by mechanical laws, including the expression of deepest emotion, since it is intimately connected with physical motion.¹ For example, Leonardo argued that the three-part arrangement of cardiac cusps is Nature’s “Necessity” at work and should be followed also by human engineers.⁵

Leonardo continued on this trajectory, resulting in an almost ascetic approach to his anatomies. On 19017r, he makes a conscious attempt to evoke the detailed appearance of the specimen, describing its actual structure rather than attempting to explain its function.⁵ He developed a technique of multiple representations, from all-around views to cross-section to sfumatura; he is grimly empirical, using his skill for the investigation of truth, even at the expense of beauty.⁶ He invented a technique of “explosion” to accurately expose the inter-relationships between body structures.⁵ In the 1512–1513 heart and thorax studies, he revised his bifurcation scheme for vessels and bronchi: “the vessels are always larger internal to the bifurcation of their trunks than outside,” reconciling observed complexity with his insistence upon their mathematical basis.⁵ In Anatomical Manuscripts A and B, Leonardo is primarily concerned with muscles and he warns the painter against abusing anatomical knowledge:

It is necessary . . . to know in diverse motions and forces which chord or muscle is the cause of such motion and only to make these evident and swollen, and not the others, like many who, in order to appear as great draughtsmen, make their nudes wooden and without grace, so that they seem to look like a sack of nuts rather than the surface of a human being, or, indeed, a bundle of radishes rather than muscular nudes.⁴

The irony is that we “see his system of shading following form carried almost to the point of mannerism. The line is dry and wiry, seldom betraying any feeling or vivacity, a sad, scientific style, compared to the beautiful anatomical drawings of 1489.”⁷

Thus we have seen Leonardo progress in his mental faculties, his uses for anatomy, and his artistic and didactic style—from metaphysical and architectural inquiries in a hesitant, loose style to a functional and empirical approach in a clean, meticulous style. Though his anatomy book was never compiled and published, his Treatise on Painting is revealing because it unites his early and late approaches, while also serving as a painter’s guide. The anatomical information is scattered throughout the book, under various headings about gestures, movement, proportion, and description¹; all are topics he investigated in his early and late anatomies, including the involvement of the mind, the balance and mathematics of the body, and the use of science for improved art.

References

1. Keele, Kenneth D. Leonardo da Vinci’s Influence on Renaissance Anatomy. Medical History. 1964; 8: 360-370.
2. Kemp, Martin. Il Concetto Dell’Anima in Leonardo’s Early Skull Drawings. Journal of the Warburg and Courtauld Institutes. 1971; 34:115-134.
3. Keele, Kenneth D. Leonardo da Vinci’s ‘Anatomia Naturale.’ The Yale Journal of Biology and Medicine. 1979; 52: 369-409
4. Kemp, Martin (ed., trans.) Leonardo on Painting. New Haven, CT: Yale University Press; 1989.
5. Kemp, Martin. Dissection and Divinity in Leonardo’s Late Anatomies. Journal of the Warburg and Courtauld Institutes. 1972; 35:200-225.
6. Nicholl, Charles. Leonardo da Vinci: Flights of the Mind. New York, NY: Penguin Books; 2004.
7. Clark, Kenneth. Leonardo da Vinci. New York, NY: Penguin Books; 1988.