Most people are at least somewhat familiar with the Medieval Wound Man, but I expect Zodiac Man is not as well known. Physicians had to consult a lunar calendar, to make sure they didn’t bleed someone in the wrong part of the body, as it was thought the zodiac also ruled over the physical body.

Zodiac Man, 1522 Courtesy of The New York Academy of Medicine Library.

In medieval Europe, bleeding was thought to be the most effective cure around. Medical practitioners believed no disease could withstand a nick in the neck from a small blade, otherwise known as a fleam. Have smallpox? No problem. Epilepsy? Easy. Gout? Cured.

But there was a catch.

Before operating on a patient, medieval physicians needed to consult the stars. The success of the procedure depended on it.

A foundational tenet of medieval medicine was the connection between astrology and human anatomy. The idea—which originated in Ancient Babylonian mythology—was that humans are microcosms of the Ptolemaic universe; the human body was divided into specific regions governed by Zodiac signs, analogous to the way the Earth was divided and ruled by planets.

The moon lay at the center of this theory. The moon’s alignment with a certain constellation signaled that a Zodiac sign was active—Libra, for instance, occurred when the moon blocked out the constellation Libra. Unlike their solar counterparts, lunar signs last only two or three days, rather than an entire month. (If you’re curious, you can find your moon sign here.)

Heh, I hold no hidden mysteries. Sign is scorpio, and so is my moon sign. Guess I’m scorpions all the way down. :D

[…]

When a Zodiac sign was active, it was considered dangerous to operate on the associated body parts. Cutting into the neck during Taurus, for instance, could spell death. Because of these dangers, medieval physicians needed to pay special attention the stars.

To determine whether a Zodiac sign was active, they consulted volvelles, or rotating lunar calendars.

They then cross-referenced the active Zodiac sign with its corresponding body parts. To do this, they turned to the Zodiac Man.

The Zodiac Man is an illustration of the human body divided into twelve sections based on astrological signs. It guides physicians as to which body parts present a danger in which months. Before bleeding their patients—or performing any kind of medical operation—physicians relied on the Zodiac Man to tell them whether a body part could be safely cut.

[…]

The moon even helped physicians make diagnoses. Diseases, it was believed, appeared cyclically with the alignment of the moon and the planets. The moon’s positioning with Jupiter often signaled the presence of liver disorders, while its alignment Venus usually triggered urinary problems.

You can see a version of the Fasciculus medicinae in its entirety here, and you can determine—per the Zodiac Man—which body parts your lunar sign puts at risk here.

You can read more and see more, too, at Atlas Obscura. Never thought I’d be quite so grateful to be stuffed into an MRI as often as I am.