Vesalius's Fabrica and the Everyday Machines Inside the Body

The title of Andreas Vesalius’s great anatomy is usually rendered in English as On the Fabric of the Human Body. Printed in Basel by Johannes Oporinus in 1543, its seven books were the work of a Brussels-born physician who had moved to Padua in 1537 to teach anatomy, and who used his own dissections to test, and often to correct, the Galenic anatomy he had been trained on.¹ Its woodcuts are famous. Less often discussed is the way its Latin prose keeps reaching outside the body for help: to the carpenter’s beam, the pulley, the charioteer’s reins, the cheesemaker’s basket and the winepress.

Read in the original, those comparisons are not decoration. Vesalius uses them as teaching tools, as arguments about function, and in one striking case as the boundary of what anatomy could claim to know.

A body built like a house, a tent and a ship

Vesalius sets the tone on the first page of Book I. Bone, he writes, is the hardest, driest and most earthy part of the body, and the supreme Maker (he calls God rerum Opifex, the craftsman of things) gave it that nature so that it could be laid under the whole body as a foundation. What walls and beams do in houses, what poles do in tents, and what keels and ribs do in ships, the substance of bone does in the human fabrica.² The same word in his title thus carries both senses at once: the body as a made thing, and the body as a structure that stands up because of how its parts are joined.

The comparisons become more exact as the book narrows to particular joints. Describing the lower end of the upper arm bone, where the ulna articulates, Vesalius tells the reader to picture the wheel of a pulley around which ropes are wound. The wheel is round at its rim and flat at its sides, and the groove cut in its rim, with raised edges on either side, keeps the rope from slipping off. That, he says, is the shape of the humerus at this point.² The image does two jobs. It gives a student without a skeleton to hand a picture of a shape that is hard to describe in words, and it hints at what the shape is for: something has to run in that channel and stay there.

Strings, reins and the ankle

The most hands-on comparison in the book comes in Book II, in the discussion of the ligaments that hold the long tendons of the foot in place at the front of the ankle. Vesalius proposes an experiment a reader can try. Tie a cord to one toe, run it up the shin to the knee, and pull: the cord lifts the toe, but it also bows away from the leg. Now pass the cord under a band tied across the bottom of the shin and pull again. The cord stays straight against the leg and still raises the toe.²

Without such ligaments, he explains, the tendons that extend the toes would spring forward from the front of the ankle every time the toes were straightened. Nature here imitates charioteers, who fix rings to the yokes of their horses so that the reins, passed through them, can steer animals the driver is not sitting on.² The comparison is mechanical in the plain sense. A tendon pulling around a corner needs a guide, and the guide works the same way whether it is made of leather and bronze or of fibrous tissue.

Vesalius applied the same practical imagination to his own tools. In the chapter on the instruments a dissector should have, he recommends probes of silver or bronze wire, a siphon that the student might pass into the bladder through the penis to gain practice, and probes hollowed into a half-channel, the way surgeons’ tools for removing bladder stones are made, or like the blades that weavers of pile silk use to cut the pile, so that a membrane can be slit lengthwise without injuring what lies beneath it.² For him the craftsman’s workshop and the dissecting table were not separate worlds.

Cheese baskets and garden channels

Not every comparison in the Fabrica came from machinery, and not every one was new. Explaining what fills the spaces between the fibers of a muscle, Vesalius turns to dairy work. The flesh of a muscle, he says, sits among its fibers much as curd sits in the wicker baskets in which people skilled in such matters set their cheese. Imagine the fibers that spread from nerve and ligament as the rushes, the blood as the milk and the flesh as the cheese, since flesh is made from blood as cheese is made from milk. The picture improves, he adds, if one imagines many little cords and hooks stretched right through the cheese. Then, so that the flesh would not be left without nourishment and its heat would not fail, veins and arteries had to be mixed into the muscle like little streams.² He reuses the dairy image in Book VII, where the thin inner membrane of the brain holds and shapes the brain’s substance the way cheese forms hold milk that has just been curdled.²

Both images had ancient roots. Galen, whose works Vesalius knew in the humanist editions of the 1520s and 1540s,³ used cheesemaking in On the Natural Faculties to argue about the kidneys: “the example of milk being made into cheese will show clearly what I mean,” he writes, before explaining that whey drains through wicker strainers while the curd stays behind, and that the kidneys cannot work like such a sieve because the whole of the blood does not pass into them.⁴ Later in the same work, Galen compares the distribution of blood to irrigation: “Numerous conduits distributed through the various limbs bring them pure blood, much like the garden water-supply,” with small channels cut from the large one so that every part can draw what it needs.⁴

The overlap matters for how we read Vesalius. He corrected Galen on many points of structure, but he worked inside a long tradition in which explaining the body by comparison to familiar crafts was ordinary scholarly practice. His streams of blood and his baskets of curd are part of that inheritance, sharpened by his own dissections.

A winepress and a funnel inside the skull

Some of the most durable comparisons attached themselves to the head. In Book III, while describing the venous sinuses of the dura mater, Vesalius stops to address a name he expects readers to ask about: the region the Greeks named after a winepress, rendered in Latin as torcular. He admits that he cannot say for certain which part Galen meant. It might be the meeting place of the first and second sinuses, from which the third and fourth sinuses arise, or it might be the end of the fourth sinus, which faces the part of the brain called the testes and reaches toward the ventricles. Galen, he observes, seems to give the name now to one, now to the other, and nothing prevents calling either a torcular, since the meeting place sends blood into the third and fourth sinuses tanquam uinum e torculari, like wine from a winepress, and the end of the fourth sinus distributes blood to every branch it sends out.² He adds that this was also the region where the Arabic authors supposed blood stood outside the veins.²

Vesalius was not alone in using the term. In 1536, in a short illustrated book on the anatomy of the head, Johannes Dryander of Marburg labeled a space in the dura where part of the blood is pressed out “the torcular of Avicenna.”⁵ Anatomical vocabulary is full of such borrowed images. Many terms for brain structures are metaphors, among them architectural ones such as the pons (bridge), the tectum (roof), the septum (wall) and the fornix (vault).³ Vesalius himself describes a part of the brain built in the manner of a vault or arched chamber.²

A second container image governed his account of the brain’s drainage. In Book IV he describes the ventricles ending in a basin, the pelvis, which receives the brain’s phlegm and carries it like a funnel down to the gland that sits at the base of the brain.² Here the comparison is doing physiological work: it encodes the period’s belief that the brain produced waste fluid that had to be led away, and it gives that belief a shape a reader could see.

The machine he would not take apart

If the Fabrica treated the body as a structure with beams, pulleys and channels, it might seem a short step to treating the brain as a mechanism that produces thought. Vesalius refused to take that step, and his reasons are the most interesting part of the story.

In Book VII he lays out what he thought dissection could show. Vital spirit, carried to the brain in the arteries, was refined in the ventricles into animal spirit and passed into the spinal cord and the nerves. He declined to argue anxiously about whether that spirit ran through passages in the nerves, as vital spirit ran through arteries, or spread along their sides like light along a column, or whether the brain’s power reached the body simply through the continuity of the nerves.² So far, he says, the functions of the brain can be followed with reasonable probability in the dissection of living animals. But how the brain performs imagination, reasoning, thought and memory he does not understand.²

He then turns on those who claimed to understand it. He asks who will not marvel at the philosophers and theologians of his day who detract from “the divine and most admirable machine of the human brain” (diuinae ac summe admirabili hominis cerebri machinae), inventing, as if they were Prometheus, a structure of the brain out of their own dreams.² He recalls his student years at Louvain, where a teacher who was a theologian, lecturing on Aristotle’s On the Soul, taught that the brain had three ventricles: the first for common sense, the second for imagination and reasoning, the third for memory, which pressed impressions into itself as into wax or stone. The students copied into their notes a diagram taken from the Margarita philosophica, believing it showed not only three ventricles but every part of the head.² The decisive objection was comparative. The brains of the sheep, goat, ox, cat, monkey and dog, and of the birds he had dissected, came very close to the human brain in their parts and above all in their ventricles, although theology denied these animals a rational soul.² As one modern study of anatomical terminology puts it, for Vesalius the ventricles had no role in the faculties of the soul, even though he still held that they produced animal spirits.³

He made the same kind of admission about the ear. Describing the tiny bones of the middle ear, he likens one to a molar tooth or an anvil and says the arrangement looks as if a hammer were loosely tied to an anvil. Yet he will not claim that they work as hammer and anvil, since he does not grasp how hearing happens. The Maker, he writes, contrives far more divine things here with the most cunning art; he can show their structure clearly in the classroom, but their use and manner of working escape him no less than those of the eye. Readers who want to see them, he advises, should lay the head of a calf or lamb on the table and divide the temporal bone, examining a raw head rather than a cooked one, and better still a human head.²

This is the clearest lesson of the Fabrica’s comparisons. A pulley explains a groove; reins explain a ligament; a winepress names a meeting of veins. Each image is tied to something a dissector could see and test. When the subject became thought itself, Vesalius kept the word machina as a term of admiration and declined to invent the parts.

Others, before and after him, went further. Arabic-language authors had already described the motor and sensory systems by analogy with hydraulic automata, according to a recent review of Renaissance brain anatomy.⁶ In the next century René Descartes, in L’Homme, written between 1629 and 1633 and published only after his death (in Latin in 1662, in French in 1664), treated the body as a machine comparable to clocks, fountains and mills, and the brain as a hydraulic device in which animal spirits flowed through tubes.⁷ Measured against that program, the Fabrica is a more cautious book. Its machines are everywhere in the bones and tendons, and they stop at the edge of what Vesalius could see.

Footnotes

1. NLM, Historical Anatomies on the Web, “Vesalius: Author & Title Description.” ↩

2. Vesalius 1543 (Latin, NLM copy, OCR): bk. I ch. 1 (bones); bk. I c. p. 105 (pulley); bk. I c. p. 35 (ossicles); bk. II c. pp. 215-216 (ankle ligaments, reins); bk. II c. pp. 220-221 (cheese, rivulets); bk. II c. pp. 236-237 (instruments); bk. III c. p. 309 (torcular); bk. VII c. p. 622 (vaulted body); bk. IV pp. 323-324 (pelvis and funnel); bk. VII pp. 623-624 (ventricles, “machine,” Louvain); bk. VII c. p. 628 (pia mater). ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷

3. García-Cabezas, Pérez-Santos and Cavada 2021, sections “Metaphors in Brain Structure” and “Early Renaissance: The Galenic Hollow Thalamus Was Translated to Latin from Galen’s Originals, but It Is Not Found in Pre-Vesalian and Vesalian Anatomy.” ↩ ↩² ↩³

4. Galen, On the Natural Faculties, trans. Brock 1916, bk. I ch. 15 (cheese); bk. III ch. 15 (garden conduits). ↩ ↩²

5. Voogd and De Zeeuw 2020, discussion of Dryander, Fig. 8 legend. ↩

6. Parent 2019, section “Pre-vesalian Anatomists.” ↩

7. Engelhardt 2021, on L’Homme. ↩