Leonardo da Vinci:Body as Machine and Machine as Body

3. Skull Bisected and Sectioned with the Four Types of Tooth, Windsor, Royal Library, 19058v.

4. Schematic Demonstration of the Nerves of the Neck and Shoulders , Windsor, Royal Library, 19040r.

Form and Function

Although human ingenuity makes various inventions, corrponding by various machines to the same end, it will never discover any inventions more beautiful, more appropriate or more direct than nature, because in her inventions nothing is lacking and nothing is superfluous.

The 1489 skulls series (fig.3), his earliest surviving set of anatomical demonstrations, immediately declares his ambitions. He believed that if a form was visible, it must have a function, since nature does nothing in vain. Thus, every bump and depression on the cranium must be respectfully recorded, whether or not Leonardo immediately knew what it did. When the skull is vertically sectioned, the frontal sinus (behind the eyebrows) became apparent for the first time and is duly recorded. Great design was both functional and beautiful. Thus he asks the skull to reveal the secrets of its proportions, one of which is that its geometrical centre corresponds to the point on which all the sensory impulses converge. Characteristically, he begins to think about the forms and functions of the teeth in relation to their position on the mechanical levers of the jaws – crunchers near the fulcrum (like cracking a nut) and cutters on the less powerful distal regions of the lever, as he later explained in full.

The major focus in his skull studies was not description but his location of the mental faculties in the light of what he was deducing about the paths of the cerebral nerves. He was seeking to understand the very centre of the intellectual, imaginative and communicative system that is man’s particular gift from god. It was a hierarchical system, like the courts in which he served: “the nerve branches with their muscles serve the nerve chords as soldiers serve the officers, and the nerve chords serve the sensus communis as their officers serve their captain, and the sensus communis serves the soul as the captain serves his lord”. The input mechanism from the senses was designed to transmit information, first and foremost visual, for analysis of the true state of affairs in the observable world. The painter was the supreme re-creator of this state. The output of voluntary action was also of great moment for the artist. A network of hollownerves (fig.4) transmitted il concetto dell’anima (the purpose of the mind) to the face and limbs in such a way that every element of expression, motion and posture speaks of the state of the person’s thoughts at any particular time. On his diagram of the brachial plexus (the net of nerves in the shoulders and upper back), he writes, “this demonstration is as necessary to good draftsmen as is the declension of latin vocabulary to good grammarians”.

Thus in the Last Supper, the innocent St. James the Greater registers spontaneous shock at Christ’s announcement of is forthcoming betrayal, as seen vividly in the preparatory drawing (fig.5), while the guilty Judas starts back, the whole of his posture rigidly locked in fear, like the corded tendons of his neck. In Leonardo’s parlance, the nerves were chorde, and their substance was continuous with the tendons and the fibre of the muscles. In this sense, the human being is literally a nervous machine.

5. Study for the Head of St James the Greater in the “Last Supper” and of a Domed Corner Pavilion for a Castle, Windsor, Royal Library, 12552.

The most sustained and brilliant of Leonardo’s surviving studies of the mechanism of the bones, muscles and tendons come from a series undertaken in 1510, when he wrote that he intended “to make an end of all this anatomy”. The bones and muscles of the shoulders, arms, hand and foot are particular focuses of attention (fig). Combining acute observation with brilliant mechanical visualisation in three dimensions, he shows the forms stripped down progressively to the bone, sometimes with flaps of muscles partially lifted away to disclose forms beneath. He works out that the turning of the lower arm is surprisingly effected by the biceps in the upper arm. In order to reveal the complex forms and articulations of the vertebrae of the neck, which produce compound motion in a “continuous quantity”, he shows them a little separated from each other, in the type of “exploded” demonstration that later became standard in manuals of machinery:
Show the bones separated and somewhat out of position so that it might be possible to distinguish better the shape of each bone by itself. And afterwards join them together in such a way that they do not diverge from the first demonstration except in the part which is concealed by their contact

He particularly delights in the supremely ingenious system of strings and stays（straps） in the hand, “the instrument of instruments” as it was termed in the Aristotelian tradition (fig.6). The interpenetration of the flexor tendons in the fingers, hailed by the ancient anatomist, Galen, as the perfect manifestation of divine design, receives the benefit of a separate, inset illustration between the two main drawings of dissected inner surface of the hand. The way that the tendons interpenetrate ensures that they can operate with power and economy within a self-contained system. As so often when he has to demonstrate the action of the muscles and the bones, he reduces the muscles to chords so that their spatial interaction along their lines of force can become more lucidly apparent. It is this page that provides the source of the quotation that stands at the head of the next section of this chapter.

6. Tendons and Ligaments of the Hand, Windsor, Royal Library, 19009.

The remarkable range of graphic techniques he was forging granted fresh cogency to his arguments about the superiority of the image over the word. The arguments were particularly pointed in the face of the widespread criticism and avoidance of illustration in traditional medicine.
With what words O writer will you describe with similar perfection the entire configuration which the drawing here does?… You who claim to demonstrate in words the shape of man from every aspect dismiss such an idea, because the more minutely you describe, the more you will lead away from the thing described.
Verbal description will be excessively “tiresome and confusing”. In essence, these claims for the superiority of visual representation in anatomy are those which elevate painting above poetry in conveying the wonders of the seen world.

But, in capturing the glory of the human machine, mere mechanics, however wondrous, were not enough. He keeps returning to the processes that stand at the heart of why we are living human beings - the process of generation, the dynamism of il concetto dell’anima, the motion of the “spirits” (“animal” in the medulla of the nerves, and “vital” in the blood) coursing through the vascular “trees” within the body, and the turbulent pulsing of blood in the heart itself. One of his greatest aspirations was to create a total, three-dimensional chart of the irrigation systems of the human body – the ramifying of the bronchi in the lungs, the pumping of the blood into ever smaller “branches” and “twigs” in the organs and limbs, the “roots” of the vessels in the liver and kidneys, the “seed” of the vascular system in the heart, the intricate “rivers” of the urinary and genital systems, and the infusion of life and soul within the womb. This vision of the body as a world in miniature will concern us in more detail in the next chapter.

The closest he comes to realising this complete map of the “lesser world” is in an astonishing composite of female anatomy (fig.7) in which even his graphic techniques collapse under the sheer weight of his ambition. Some forms are more or less solid, some sectioned, some transparent, some both sectioned and transparent. The notes crammed uncomfortably around the margins of the figure have typically been triggered by thoughts occurring during the act of drawing. They deal with rather scattered anatomical and physiological matters, including an argument with Mundinus’s text-book about the roles of the testes in generating sperm, and speculation about cycles of birth and decay in the human body. As always, Leonardo’s thoughts move laterally.

7. Principle Organs and Vascular and Urino-genital Systems of a Woman, Windsor, Royal Library, 12281.

Questions of life and death had been highlighted by his involvement with the “centenarian”, and many of the details are drawn from the results he synthesised from the dissection of his aged male subject. Although related to this major dissection, his characterisation of many of the key organs is still set in a traditional framework. The heart remains two-chambered (an idea he was shortly to abandon), and the womb has assumed a cellular structure within and is provided with external “horns”, in line with standard views. As always in his more developed drawings of the internal workings of human anatomy, there is a sense that the apparatus provided by nature should exhibit beauties of shape and proportion to no less a degree than the outer appearance of the body. The aim is not so much a raw picture of what is encountered in real life as a distillation of the ideal form that lies beneath the vagaries individual appearance. The totality of what lies inside this lady’s body is worthy of an antique Venus – or, more specifically, of Mona Lisa herself.

Undeterred by the optical density of this compound demonstration, he promises to repeat it from the side and from the rear. He has also pricked through the outlines of the body and main organs for transfer to another sheet. There is no indication that the full set of surveys was ever realised.

In the event, it was in the representation of the parts that his vision were most fully resolved. No drawing of an embryo in a womb (fig.8) ever came closer to capturing the very spirit of generation, as well as the foetus’s nested position - even if the exaggeratedly spherical womb displays the cotyledonous (multiple) placenta of a cow rather than the single placenta of a human. The whole page is a feast of visual exposition. A series of small sketches of the womb show the layers of its wall progressively opened, disclosing the germ of life within, like a chestnut within its protective seed-case. The interdigitations of the placenta and uterine wall are depicted in a solid section, drawn apart like a Velcro strip that is in the process of being peeled back. Typically, he speculates on why “the same soul governs these two bodies, and the desires and fears and sorrows are common to this creature as to all the other animal parts”. A mechanical diagram demonstrates how an asymmetrically weighted ball can stabilise itself on a slope – a mechanical meditation probably triggered by the question of the weight of the foetus’s head and the rotational motion that occurs before birth. Finally, in the lower right corner, he speculates as to why even the most fully realised representation of the three-dimensional from（form） will never appear to have the same “relief” as the same form seen simultaneously with two eyes. Even Leonardo’s brilliance in perspective and the modelling of forms in light and shade has to surrender in the face of the parallax that comes with binocular vision.

8. Foetus in the Womb, with Studies of Mechanics and Optics, Windsor, Royal Library, 12656.

In functional terms, the most fully satisfying of his anatomical expositions concerned the pulmonary aortic valve of the heart. A three-cusp structure located in the narrowing neck of the aorta, it is characterised by Leonardo as a piece of solid geometry in action, driven by the ionic volutes of the blood vortices as they recoil in the constricted diameter of the vessel (figs.9-10). Blood is thrust from below the valve, as the chambers of the heart - now four in number – contract. The three cusps collapse away from the centre to leave a triangular aperture, the geometry of which Leonardo inevitably strives to define. Subsequently, the spiral turbulence of the expelled blood in the neck of the aorta re-inflates the cusps and snaps the valve shut, so that the dilating chambers of the heart can draw in blood from other vessels. The trick is to make sure that when the blood was being forced into the pulmonary system, to reach the lungs, it should not be able to flow back into the heart, particularly as the chambers re-dilate to draw in blood from other vessels. He noted his intention to build a model of the valve in the neck of the aorta to demonstrate the truth of his theory.For once, he has been able completely to raise anatomical explanation to the level of maths. “Let no-one who is not a mathematician read my principles”, he wrote on one of his anatomical studies, paraphrasing Plato. “Necessity” rules, as always.

9. Heart of an Ox with the Coronary Vessels and Aortic Valves, Windsor, Royal Library, 19074v

10. Blood Flow in a Three-Cusp Heart Valve and Scheme to Build of Model of the Valve, Windsor, Royal Library, 19082r

He is so certain that he is right about the valves that he announces his intention to make a model of the set up in glass with artificial membranes. His pride was justified. Recent studies if the operation of the valve and imaging of the vortices within the neck of the aorta have revealed his extraordinary insight into the valve’s operation. Essentially Leonardo has learnt all that is needed to work out the mechanics of the kind of artificial heart valve that extended my mother’s life by a goodly span of years.