Andreas Vesalius (1514–1564) was a Flemish anatomist, born in Brussels into a family of imperial-Habsburg court physicians. He trained at Louvain and Paris before being appointed in 1537, at age 23, as professor of surgery and anatomy at the University of Padua — the leading European medical school of the period and the only major one where direct human dissection was a permitted part of the undergraduate curriculum.

For three years from 1540 to 1542 Vesalius personally dissected approximately thirty human cadavers — provided by the Paduan magistrate’s court, who supplied the bodies of executed criminals — in front of his medical-student audiences. The standard 16th-century anatomical lecture procedure had been for the named anatomist to read aloud from Galen while a barber-surgeon performed the actual dissection on the table below. Vesalius reversed the practice. He dissected the body himself, with his own hands, and lectured directly from what he was uncovering.

What he was uncovering did not match what Galen had written.

The Galenic problem

Claudius Galen (c. 129 – c. 216 CE) was the senior physician of the late Roman Empire. His approximately 100 surviving medical works had been the foundation of European medical-school anatomy for thirteen centuries, transmitted through Arabic intermediaries (including Ibn Sina’s Canon) and direct Greek-to-Latin Renaissance translations.

Galen had worked in 2nd-century Rome under a strict legal prohibition on human dissection. His detailed anatomical descriptions were drawn from the dissection of Barbary apes, dogs, and pigs — animals he believed sufficiently similar to humans to substitute for them in anatomical study. Some Galenic descriptions were correct as far as the apes were concerned and wrong as far as humans were concerned.

Vesalius discovered approximately 200 such mismatches during the 1540–1542 dissections.

The most-cited examples include:

— The rete mirabile, a vascular plexus at the base of the brain that Galen had described as the seat of the pneuma psychikon (the animal spirit). The rete mirabile exists in pigs and cattle. It does not exist in humans. — The human sternum, which Galen had described as seven-segmented. The human sternum is three-segmented. The seven-segmented sternum is a Barbary ape feature. — The human liver, which Galen had described as five-lobed. The human liver is four-lobed. The five-lobed liver is a dog feature. — The lower jaw, which Galen had described as two-boned. The human lower jaw is a single bone. The two-bone configuration is found in apes.

The Fabrica

Vesalius published the resulting anatomical atlas — De humani corporis fabrica libri septem (“On the Fabric of the Human Body in Seven Books”) — at Basel in June 1543. The book runs to over 700 pages of folio text plus approximately 200 large woodcut illustrations. The illustrations were executed by a Venetian workshop traditionally identified with the Titian student Jan Stephan van Calcar, though modern art-historical attribution is debated.

The Fabrica is technically magnificent — the illustrations and the printing are the highest quality 16th-century Basel book production could deliver — and intellectually devastating. Every Galenic anatomical error is identified by chapter and verse from Galen and refuted from the cadaveric evidence.

The medical-faculty response was furious. Vesalius’s former Paris teacher Jacques Dubois (Jacobus Sylvius) published a 1551 defence of Galen on the grounds that human anatomy must have changed since Galen’s time — that the discrepancies were the result of degenerative modern-European bodily decline rather than Galenic error. The position was an extreme defensive posture; it implied that no observation could ever disprove Galen, because any observed mismatch could be attributed to post-Galenic biological change.

What Vesalius did next

Vesalius did not write a second anatomical treatise. He left Padua in 1544 to become court physician to the Holy Roman Emperor Charles V, then to Charles’s son Philip II of Spain. He spent the rest of his career as an imperial physician at the Habsburg courts of Brussels, Madrid, and the Netherlands.

In 1564 he undertook a pilgrimage to Jerusalem. His reasons are unclear; one Catholic-source account says he had been condemned by the Spanish Inquisition for performing an autopsy on a living patient (a story modern historians regard as a fabrication). The return voyage shipwrecked on the Greek island of Zante. Vesalius died there in October 1564, aged 50.

The Fabrica entered its second edition (1555), then its third (1604), then approximately twenty further European editions through the 17th century. The conventional periodisation of Western medical history dates the end of the Galenic era and the beginning of the modern anatomical-empirical era from June 1543 — the publication of the first edition.