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Conjoined twins are three times more likely to be female than male. Some are successfully separated through surgeries. Other live connected together throughout their lives. Some hypothesize the condition is caused by a fertilized egg not completely separating. Others believe the fertilized egg completely separates but that stem cells from one twin find similar cells on the other twin, fusing them together. Most conjoined twins are fused from the upper chest to the lower chest although some are joined via other body parts.
The earliest known depiction of conjoined twins dates back to ceramics from the Moche culture in Peru from around the year 300 AD. St. Augustine of Hippo also wrote about conjoined twins in 450 AD in his book, City of God. It is unclear, however, if these descriptions and depictions were fictional or not. The earliest known documented case of conjoined twins dates to 942 AD when a pair was brought from Armenia for medical evaluation in Constantinople.
Some other early descriptions of conjoined twins exist, such as from Arabia and England but the vast majority of case have been documented in the 20th century and beyond. This includes Chang and Eng Bunker (1811-1874) who were born in Siam (now Thailand) and thus became known as “Siamese twins.”
|The Famous Siamese Twins|
One of the most interesting descriptions is the title, “A Relation of a Monstrous Birth.” Such a description, while likely apt to the doctor who delivered the baby, would never be allowed in medical journals today because it would be considered offensive and pejorative. Because English was written and spelled differently back in the 1600s, I will offer a modern translation of some parts of the article.
The first thing the author noted is that “It had two heads,” which sounds more like a sci-fi movie title to describe a monster (e.g., “It Came From Beneath the Sea”) rather than the opening line of a medical article. Modern journals would stick to using the gender, which in this case was female. Also interesting is that the name of the mother (Joan Peto) is listed, which would never be allowed today due to confidentiality protections. She is also described as the wife of a butcher.
Both of the heads were described as very well-shaped, which is not unusual if this was a full-term delivery. The left face looked swarthy (dark-skinned) and did not breath. The right head was perceived to breathe but not cry. Thus, one side appeared to be a stillbirth with the other side surviving to birth. The left head was bigger. This type of discordance between the left and the right is not uncommon in conjoined twins, likely due to genetic, environmental, and abnormalities in the placenta and/or in the circulation of the fetus.
The author says that between the heads was a protruberance, like another shoulder. The clavicles and breast were very large, about seven inches wide. The conjoined twins were of the parapagus variety, meaning they were fused side by side with a shared pelvis. There were two hands and two feet, although other conjoined twins are known to be born with four hands and feet. The brain in each head was described as very large, indicating that the heads must have also been quite large, perhaps macrocephaly (abnormally large head), which is a known malformation in some conjoined twins. There were also two spinal cords, two pairs of lungs, and two hearts (on each side of the chest, the left heart being bigger). The lungs on the left were blackish and the other lungs looked well.
The esophagus was divided into two branches, with one branch projecting to each throat. There was one aorta (the main artery in the human body) and vena cava (two large veins that bring blood to the heart). The aorta and vena cava were divided into two parts, bringing blood to both hearts in the shape of a Y.
There were also two stomachs. One was shaped naturally but the other was shaped like a “great bag,” resembling what would be found in a cow or sheep. The intestines contained a substance like meconium (early feces), similar to newborns. The intestines were also large, as was the liver, spleen, uterus, and left kidney. Overall birth weight was 8 pounds. It is unknown what happened to the conjoined twin who was breathing.
Reference: Morris, S. (1677). A Relation of a Monstrous Birth, Made by Dr. S. Morris of Petworth in Suffex, from His Own Observation: And by Him Sent to Dr. Charles Goodall of London; Both of the Colledge of Physicians, London, Philosophical Transactions, 138, 961-62.