Metaphor and analogy in Vesalian anatomy

I. Architecture (The Edifice Complex)
Ancient and early modern anatomy was deeply influenced by the conviction that nature was created by design. This idea was perhaps best expressed by Aristotle, who often remarked that "Nature does nothing in vain." At least as early as Plato, such teleology — the belief that everything in nature was put there to fulfill a telos or purpose — sometimes took the form of an architectural metaphor when applied to anatomy.

Appeal to this metaphor starts on the first page of Book I of the Fabrica: "What walls and beams provide in houses, poles in tents, and keels and ribs in ships, the substance of bones provides in the fabric of man." The first chapter of Book II makes a similar claim for the muscles and ligaments: "these parts of the body are placed beneath all the others as foundations and bases." A shallow glenoid depression (such as the one in the scapula that admits the humerus) is hollowed out "no differently than if two flat, planed roof timbers were placed against each other." The presence of sutures in the skull is explained by comparing it to a loosely constructed roof of the type (thatch, wooden shingles, tile, etc.) then common in Europe:
Because the head resembles the roof of a warm house, receiving whatever smoky and vaporous wastes of the parts below that ascend upwards, and consequently the head itself needs a more plentiful means of evacuation, the wise Parent of things shaped a helmet for the brain that is not solid everywhere but full of hollows and laced with sutures.Vesalius did not invent this metaphor for the skull: he took it, like most of his metaphors, from Galen. The ginglymus or hinge joint (such as the elbow or knee) took its name as early as the Hippocratics from the hinge in a door or window, and is illustrated as such in the Fabrica. It is what you would see, he remarks, "if you compared this species of joint with the hinges of doors in which the iron driven into the wall receives that which is attached to the door, and the iron from the wall enters up into that of the door. The present species of articulation got its name from this model." The septum in the sphenoid bone of the skull strengthens it "like a wall in the middle of a house." The cartilages of the larynx

shape the larynx just as we see the houses of rustics are made of beams before thatching, tiles, and clay are applied to them. In fact, if you stripped bones and cartilages of their flesh and then joined them together, you would compare them to nothing more closely than the structure of huts when they are first erected and not yet covered with branches and earth.

Sometimes this powerful metaphor drives the anatomy of the Fabrica. In describing the vertebrae, Vesalius points out that the twelfth thoracic vertebra has a superior articular process resembling that of the thoracic vertebrae above, and an inferior articular process like that of the lumbar vertebrae beneath it. This made him think of the keystone in an arch, and he remembered that Galen had compared the spine to avault in On the Use of the Parts and had explained "just as this vertebra has a special position ... so its articulations are special too; for in order that the whole spine might bend uniformly it was of course necessary for the middle vertebra to remain in place while all the others withdrew gradually from one another and from it, the upper ones retiring upward and the lower ones down." Galen had based his description on the Barbary apes he dissected, which because they do not hold an erect posture have only a single curvature in their spine. Vesalius worked on human specimens, but the idea of an architectural component and the elegance of design it suggested so caught his imagination that he made the human spine conform to the paradigm. He therefore praise

the signal craft of Nature, which fashioned a vertebra in the midst of the back, stable and supported on both ends just as we see builders place one stone between two others in vaulted and arched buildings, which is supported on each side though it supports no stone itself, while all the others support one stone and are received and supported by another

and illustrated the spine slightly rotated (a practice he often employed in other illustrations), thereby minimizing the cervical and lumbar curvatures. The triple curvature of the human spine had been well known long before Galen (see for example the Hippocratic De articulis 45.24 ff.), but once in the grip of the metaphor Vesalius was loth to surrender it. He reminded his readers that the title page illustration contained two keystone arches (one them shown at the head of this page), and when giving instructions at the end of Book I for the articulation of a skeleton he warns the student that "the greatest care should be taken with the iron rod [inside the vertebrae] that it not be ineptly bent backward and forward and hold the body upright in an unbecoming way." The two skeletons viewed in profile at the end of Book I are posed in slightly stooped postures, eliminating the cervical and lumbar curves that would properly show if they were fully erect.

II. Vegetation (the body as a plant)
Though "vegetable" has come to imply a comatose and morbid condition, "vegetative" retains something of its original force, connoting the opposite condition of growth and vitality. This metaphor too survives in nomenclature through the brain stem and the various trunks, branches, and twigs by which the veins, arteries, and nerves are distributed through the body. Teeth, nails, and hairs have roots; the spinal nerve is one of several with a root. The aorta, the clitoris, and the lung also have a root.

In the Renaissance when woodcuts and metal engravings propelled anatomical illustration into prominence, pictorial representation of the systems and parts of the body took on a distinctly botanical character.The mixture of architectural and vegetative metaphors is nowhere better illustrated than in the full-page muscle men with which Vesalius famously had the second book of his Fabrica illustrated. The landscapes in which most of these écorchés stand feature vegetation in the foreground and middle distance, with buildings in the background. Though these landscapes have been shown to be based on an actual area close to Padua, their symbolic content is no less important than their local allusiveness. Even when represented in isolation (as most are) body systems in Vesalius' book are sometimes given a decidedly plantlike aspect. This is best illustrated by the illustration of the portal vein system in Book 3 (left) where the lower viens are rootlike and the distribution of veins in the kidney is both floral and branchlike in appearance. Another plantlike structure is the heart and its surrounding tissues, in some renderings looking like nothing so much as a cauliflower with its surrounding leaves (right).

These resemblances occur in the context of another kind of illustration that flourished during the sixteenth century, the botanical handbooks which were important to the people who searched out, harvested, processed, and marketed the plants sold in pharmacies. It is no surprise that some of the foreground plants in the illustrations of Vesalius' muscle men are represented in striking detail.

Vesalius' terminology keeps reminding readers of the Fabrica of the plantlike nature of the body's parts: muscles and ligaments are implanted (we now say "inserted") in the parts to which they are attached.
The origins of this metaphor lie in the language used by the Greeks and Romans: Latin coma, for example, means hair or foliage, as does its cognate Greek kome, as early as Homer. Greek blastano means to bud, sprout, or grow, properly of plants, but In the Hippocratic treatise On Joints (45.17), tendons sprout from cartilaginous epiphyses in an apoblastesis. In Aristotle (HA564a-b), animate nature imitates vegetative: peafowl moult when the trees shed their leaves and growing new feathers when the trees break into leaf. Nature (physis) is everything that grows (phyo), making the animal and plant kingdoms parallel aspects of the living world. Phyteuo is to plant a tree (for example) or to beget a child.

In the Timaeus (90a6), Plato describes humankind as a "heavenly plant," distinguished from the earthly kind. The more earthbound Aristotle was not interested in this metaphor, however: the vegetative does not share in the rational principle, being the instinctual part of nature common to plants and animals. Worse yet, Aristotle distinguished plants from animals by whether they produced excretion.