Da Vinci's Ghost (23 page)

Like Aristotle, Augustine had argued that the soul and the
body were one. Near the end of
The City of God
he made that case and then left his readers with some remarkable final thoughts on the subject.

This would be more apparent
to us if we were aware of the precise proportions in which the components [of the body] are combined and fitted together; and it may be that human wit, if it sets itself to the task, can discover these proportions in the exterior parts, which are clearly visible. As for the parts which are hidden from view, like the complex system of veins, sinews, and internal organs, the secrets of the vital parts: the proportions of these are beyond discovery. Even though some surgeons, anatomists they are called, have ruthlessly applied themselves to the carving up of dead bodies, even though they have cut into the bodies of dying men to make their examinations and have probed into all the secrets of the human body … even after all that, no man could ever find—no man has ever dared to try to find—those proportions of which I am speaking, by which the whole body, within and without, is arranged as a system of mutual adaptation. The Greeks call this adaptation
harmony
, on the analogy of a musical instrument; and if we were aware of it, we should find in the internal organs also, which make no display of beauty, a rational loveliness so delightful as to be preferred to all that gives pleasure to the eyes in the outward form—preferred, that is, in the judgement of the mind, of which the eyes are instruments.

Given the widespread popularity of Augustine’s work and
the nature of Leonardo’s interests, it’s quite possible that he would have encountered this passage in his program of self-education. If indeed he did, he would have found it at once fascinating, misguided, and provocative—especially that remark about the body’s secret internal proportions being “beyond discovery.”

Leonardo begged to differ. To make his case, in early 1489, he sawed open a human head.

I
T WAS A
grisly task.

As he began, Leonardo surely found himself assaulted by competing emotions: curiosity, revulsion, excitement, wonder, fear. Not that any of those feelings would have surprised him. In a way, he had anticipated this very moment several years earlier. Perhaps after waking from a powerful dream, he had jotted down an allegory of imminent discovery in which he had described that precise nexus of feelings.
“Driven by an ardent desire
and anxious to view the abundance of varied and strange forms created by nature the artificer,” he wrote,

having traveled a certain distance through overhanging rocks, I came to the entrance to a large cave and stopped for a moment, struck with amazement, for I had not suspected its existence. Stooping down, my left hand around my knee, while with the right I shaded my frowning eyes to peer in, I leaned this way and that, trying to see if there was anything inside, despite the darkness that reigned there. After I had remained thus for a moment, two emotions suddenly awoke
in me: fear and desire. Fear of the dark, threatening cave; and desire to see if it contained some miraculous thing.

In 1489, at least, desire won out over fear—and the result, based on the dissections Leonardo then undertook, was a magnificent set of skull studies the likes of which had never been seen before in the history of art or science. Executed in a profoundly new and imaginative visual idiom, deriving from the cutaway views that he and others were producing to illustrate architectural and engineering treatises, the skulls leap off the page with a clarity, precision, and grace that appeal powerfully to the modern eye—and that in significant ways anticipate the work of today’s anatomical illustrators and even imaging radiologists.

Studying the skulls in sequence, you can watch Leonardo as he goes in. He starts with a frontal view, reminiscent of many of his proportional studies of the face, that illustrates the throbbing veins that lie just under the skin of the forehead (
Figure 39
). Then he strips the flesh away entirely to expose the skull, which he renders in a split view that allows him to illustrate, with an eerie beauty, the structures of the face at two different depths: a technique, groundbreaking for its time, that is still in use today (
Figure 40
).

Many of these anatomical features had never before been drawn or described. In that respect, they certainly represent a fundamental break with the past. As fresh and modern as they look, however, Leonardo’s skull studies in fact illustrate a profoundly medieval idea: that somewhere inside the brain exists the locatable seat of the human soul.
“The cavity of the orbit
and the cavity of the bone that supports the cheek,” he wrote
alongside his split skull, “and that of the nose and of the mouth, are of equal depth, and terminate in a perpendicular line below the
sensus communis
.”

Below the …
what
?

Today we consider common sense a quality of mind, an intangible faculty of judgement. To Leonardo, however it was the
sensus communis
, or Common Sense: an actual part of the human anatomy. Philosophers and medical authorities in his day subscribed to an age-old theory known as the cell doctrine, in which the powers of the human mind were said to reside in three or more interconnected cells at the center of the brain. Such cells, now known as ventricles, do indeed exist, and for centuries they seemed the natural place to locate mental activity. It surely couldn’t take place in all of that mushy, useless gray matter that surrounded the ventricles.

Figures 39 and 40.
Studies of the human head and skull (1489), by Leonardo.

European and Arab writers had proposed a number of variations on this theme over the centuries, but the basic version, summarized by Mundinus in the
Anatomy
, went something like this. The
sensus communis
, residing in the foremost ventricle, was a kind of central processing unit linked to the body’s various sense organs.
“The parts pertaining to sensation
end here,” Mundinus explained, “as do streams at a fountain.” It also housed the powers of fantasy and the imagination, which allowed it not only to receive sensory information but also to create ideas based on that information. Then came the middle ventricle, devoted to cogitation on whatever perceptions and ideas the
sensus communis
might pass along. Finally, at the back lay the third ventricle, in which memory was created and stored.

Leonardo knew the cell doctrine well. He read and owned all sorts of texts in which the theory was laid out, often with the help of rudimentary illustrations (
Figures 41
and
42
).

But Leonardo didn’t just read about the idea. Appalled by the crudity of the illustrations he came across, he decided to draw his own. In 1490, for example, he laid out both a plan and an elevation of the human head—cutaway views, similar to architectural drawings he was making at the time, that showed, with fanciful precision, the interior location of the ventricles (
Figure 43
).

When he began his studies of the human skull in 1489, he had these ideas powerfully in mind. “
The soul
,” he speculated, “seems to reside in the judgment; and the judgment would seem to be seated in that part where all the senses meet; and this is called the
sensus communis
.” Philosophers and physicians alike had been spouting vaporously about the nature of body and soul for centuries, but Leonardo decided he could do better. Just two
years earlier, after all, in exploring the simple anatomy of a frog, he had managed to locate the source of all movement and life. So why shouldn’t he be able to go a step further and locate the seat of the human soul? Here, at last, was a way he could
prove
that artists could be natural philosophers of the first order—a point he desperately wanted to get across to the scholars who condescended to him at the court of Milan.

Figures 41, 42, and 43. Top left:
The cell theory of the brain as illustrated in 1489, the year Leonardo began his own skull studies.
Top right:
A more detailed diagram from 1503, showing connections from the eyes, nose, tongue, and ears to the
sensus communis
, near the front of the head.
Bottom:
The theory as illustrated by Leonardo in 1490. The image at the bottom right of the drawing represents the skull sawed open and viewed from above, with the top half folded over and faintly visible to the right.

And so in he went, sawing into the top of the skull, flipping it open, and removing the brain. He left no record in his notes of what he did next, but Mundinus showed him the way.
“Now, cut carefully
through the midst,” Mundinus wrote, guiding his readers toward the
sensus communis
, “until you come upon the great fore ventricle.” The rest was easy. By simply cutting toward the rear of the brain, he explained, dutifully citing the authority of Avicenna, Aristotle, and Galen, you could then expose and carefully examine its other two ventricles.

This was hogwash—as Leonardo already knew from his dissection of animals. When taken out of its housing and cut open, the brain, which has roughly the consistency of Jell-O, loses its structural integrity. The ventricles become as easy to see as the five lobes on a human liver.