Hans Christen Anderson, The Little Mermaid, 1837.

Mermaids have teased our imagination for thousands of years. One of the earliest tales originated in ancient Assyria, where the goddess Atargatis transformed herself into a mermaid out of shame for accidentally killing her human lover. Homer called them sirens in the Odyssey, and described them as beautiful singing creatures who lure sailors to their deaths. Throughout history, these seductive beings have been associated with floods, storms, shipwrecks and drownings. They have been depicted in countless mediums: in Etrurian sculptures, in Greek jewelry, and in bas-relief on ancient Roman tombs. Christopher Columbus even reported seeing these mythical creatures on his voyage to the Caribbean in 1493.

But could our concept of what a mermaid looks like actually have originated from a real medical disorder?

Sirenomelia is a lethal condition characterised by rotation and fusion of the legs, resulting in what often looks like a fish tail (left). It occurs when the umbilical cord fails to form two arteries, thus preventing a sufficient blood supply from reaching the fetus. As a result, the single artery steals the blood and nutrition from the lower body and diverts it back up to the placenta. Due to malnutrition, the fetus fails to develop two separate limbs.

Sirenomelia, also known as ‘Mermaid Syndrome’, is extremely rare. It affects 1 in 100,000 babies and is 100 times more likely to occur in identical twins. Usually, those born with this condition die within days.

Over the course of my research, I’ve found very little about  the disorder’s history. There are snippets here and there which claim that fetuses born with sirenomelia were sometimes preserved in jars and put on display in ‘freak shows’ during the 19^th century—but these sources are frustratingly vague. There is brief mention of the condition in a four-volume atlas published in 1891 titled Human Monstrosities, but nothing that hints at how medical practitioners understood sirenomelia in earlier periods.

Perhaps because the disorder is so rare, it’s also been hard for me to locate specimens in anatomical collections. My search in the Hunterian Museum at the Royal College of Surgeons in London came up cold. I did, however, find an early 20^th-century example at the National Museum of Health & Medicine in Washington D.C. There are also three fetuses in the Anatomical Museum of the Second University of Naples, which have undergone 3D bone reconstructions (two pictured below).

By far the largest number of fetuses comes from the Vrolik Museum in Amsterdam, which consists of more than 5,000 specimens of human and animal anatomy, embryology, pathology and congenital anomalies. The collection was founded by Gerardus Crolik (1755 – 185) and his son, Willem Vrolik (1801 – 1863), who both wrote extensively on anatomical deformities in the 18th and 19th centuries. The Vrolik Museum has both wet preparations and skeletal remains, all of which are on display to the public today.

Unlike the first disorder I examined in this series—Harlequin Ichthyosis—sirenomelia is extremely fatal. There are no accounts of anyone with this condition surviving in the past. Most died within days of being born due to kidney and bladder failure. Even today, the odds are against those with sirenomelia, though there are a handful of examples of children living past infancy.

In 1988, Tiffany Yorks underwent surgery to separate her legs before her first birthday. She continues to suffer from mobility issues due to her fragile leg bones, and compensates by using crutches of a wheelchair to move around. At the age of 26, she is the longest-surviving sirenomelia patient to date.

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