The earliest written account of actual conjoined twins dates from 945, when conjoined twin brothers from Armenia were brought to Constantinople for exhibition. They were reported to be well formed and healthy but were banished from the court until the reign of Constantine VII. One took sick and died. Surgeons, attempting the first separation in recorded history failed to save the twin – he joined his brother in death three days later.
The subject of conjoined twins was a popular one in the old monster texts. Pare describe thirteen individual cases including two sisters joined back to back, two sisters joined at the head and a pair of boys who shared a single heart. In 1560, Pierre Boaistuau’s histoires prodigieuses features a plate illustrated a pair of women – joined at the waist and sharing a single set of legs –depicted in an almost Botticelli flair.
There are several types of conjoined twins and they are classified by the point at which they are joined. Greek suffix ‘pagus’ (fixed) follows each classification.
Cephalopagus is a rear union of the upper half of the body with two faces on opposite sides of a conjoined head. It is extremely rare and it is sometimes called Janus Syndrome. Craniopagus is a cranial union only and constitutes about 2% of all conjoined twins .Craniothoracopagus is a union of head and chest. There is only one brain, and the hearts and gastrointestinal tracts are fused. It is also known as epholothoracopagus. Dicephalus is a term that refers to one body with two heads and it is likely the rarest form. The ischopagus and omphalogagus unions are unions of the lower half of the body and constitute about 12% of all conjoined twins. Papapagus is a lateral union of the lower half, extending variable distances upward and constitutes about 5% of all conjoined twins. There is the pygopagus union – a joining at the rump (19% and also know as Illeopagus) and finally the thoracopagus which is a union at the upper half of the trunk and the most common (35%).
Just to throw some more numbers at you, conjoined twins occur in once out of every two hundred thousand pregnancies and seems to be female dominant – with about 77% of all recorded conjoined twins being female. Furthermore, there has never been a documented case of conjoined triplets among human beings – but it has occurred in amphibians.
The cause of conjoined twining and what exactly happens inside the womb is still a big medical mystery. Aristotle, in his The Generation of Animals, argued that conjoined twins came from two embryos based on an observation he made of conjoined chickens – which had four legs and four wings, by the way. The creation of deformed chickens was quite common in ancient and even Victorian times. A simple vigorous shaking of an egg often resulted in abnormal births. Later, he amended his argument to the idea that conjoined twins formed from one embryo split into two. These two theories are referred to as the fission and fusion theories.
There are a lot of unusual question surrounding conjoined twins. Unlike traditional twins, conjoined twins share a placenta and a single amniotic sac but also each have one of their own.
The most recent theory surrounding conjoined twins is the most shocking of all. Some researches now theorize that conjoined twins are not twins at all. Rather, via a malfunctioning organizer gene –nicknamed Noggin, conjoined twins are one being in which multiple appendages are duplicated. Instead of growing a single head, for example, the gene sends a signal to grow two. Two bodies, two brains equals one human marvel of medicine.
For more information on medical marvels I highly recommend Mutants by Armand Marie. Leroi.