Conjoined twins as the Siamese twins. Chang and Eng were joined at the torso by a band of flesh, cartilage, and their fused livers. In modern times, they could have been easily separated. Due to the brothers' fame and the rarity of the condition, the term "Siamese twins" came to be used as a synonym for conjoined twins. Conjoined twins are typically classified by the point at which their bodies are joined. The most common types of conjoined twins are: Other, less common types of conjoined twins include: There are two theories about the development of conjoined twins. The first is that
Monoamniotic twins Monoamniotic twins Monoamniotic twins are identical twins that share the same amniotic sac within their mother’s uterus. Monoamniotic twins are always identical, always monochorionic and are usually termed Monoamniotic-Monochorionic ("MoMo" or "Mono Mono") twins. They also share the placenta, but have two separate umbilical cords. Monoamniotic twins develop when an embryo does not split until after formation of the amniotic sac, at about 9-13 days after fertilization. Monoamniotic triplets or other monoamniotic multiples are possible, but extremely rare. Other obscure possibilities include multiples sets where monoamniotic twins are part of a larger gestation such as triplets, quadruplets, or more. Monoamniotic