Identical twins who are united bodily but are possessed of separate personalities. Their frequency is not known, but it has been estimated that throughout the world, six or more conjoined twins are born every year who are capable of separation. The earliest case on record is that of the ‘Biddendon Maids’ who were born in England in 1100. The ‘Scottish Brothers’ lived for 28 years at the court of James III of Scotland. Perhaps the most famous conjoined twins, however, were Chang and Eng, who were born of Chinese parents in Siam in 1811. It was they who were responsible for the introduction of the term, ‘Siamese twins’, which still remains the popular name for ‘conjoined twins’. They were joined together at the lower end of the chest bone, and achieved fame by being shown in Barnum’s circus in the United States. They subsequently married English sisters and settled as farmers in North Carolina. They died in 1874.
The earliest attempt at surgical separation is said to have been made by Dr Farius of Basle in 1689. The ﬁrst successful separation in Great Britain was in 1912: both twins survived the operation and one survived well into adult life. This is said to be the ﬁrst occasion on which both twins survived the operation. The success of the operation is largely dependent upon the degree of union between the twins. Thus, if this is only skin, subcutaneous tissue and cartilage, the prospects of survival for both twins are good; but if some vital organ such as the liver is shared, the operation is much more hazardous. (See MULTIPLE BIRTHS.)