Conjoined twins. Name generally applied to twins congenitally united in a manner not incompatible with life or activity. The name derived from the well-known twins Eng and Chang (1811-74), born of Chinese parents in Siam. Eng and Chan were joined together at the sternum by a thick, muscular ligament. Conjoined, or Siamese twins may be connected at the hips, buttocks, or other parts of their bodies and may have one or more organs in common. In some cases each separate organ in one twin is the mirror image of the same organ in the other. Joined twins are always of the same sex. Surgical separation is sometimes possible, but the operation is usually fatal to one of the twins. An operation was successfully performed in the 50's on twins who were joined near the base of the spine and shared the lower intestinal tract.
A exceptional phenomenon, the occurrence is estimated to range from 1 in 50,000 births to 1 in 100,000 births, with a somewhat higher incidence in Southwest Asia and Africa.
