Siamese or conjoined twins

Twins congenitally joined at a part of their body (parastic ectopy). Xiphopages are joined at the side or sternum, Pygopages at the pelvis, Ischiopages at the pelves and Craniopages at the head.

Conjoined twins occur in about one in 100,000 pregnancies and only about 19 sets have been dealt with at British hospitals since 1984. Around 40% of conjoined twins are joined at the chest.

Conjoined twins can share a variety of organs. It is rare to have only a single heart, but there are frequently heart problems in conjoined twins.

The case of conjoined twins has caused many artistic, physical and metaphysical implications throughout history. The two-as-one body (similar in some ways to the hermaphroditic one), inevitably evokes a sense of transgressive sexuality, both in its creation (through unsplit ovum/ova) and in its daily physiology. Sexual privacy necessarily dissolves in the shared world of conjoined twins. In seventeenth century Europe, the Italian conjoined twin Lazarus-Johannes presented theological conundrums of great import for a civilization still trying to come to terms with the repercussions of the Reformation: did they possess one soul or two? (Pender 144).

After the wedding of the famous Cheng-Chang with the sisters, the private practices of the twins came under public scrutiny. "the sexuality of either man, because witnessed-and thus to some extent participated in-by the other, represented prospects transgressive to the Victorian American culture in which they lived: homosexuality (because both were male), incest (because they were brothers), and adultery (because each would, in a sense, be sleeping with a woman not his wife" (Pingell 105-106).

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Other classification

• Union of several fetuses.
• Union of two distinct fetuses by a connecting band.
• Union of two distinct fetuses by an osseous juction of the cranial bones.
• Union of two distinct fetuses in which one or more parts are eliminated by the junction.
• Fusion of two fetuses by a bony union of the ischii.
• Fusion of two fetuses below the umbilicus into a common lower extremity