Conjoined twins, defined by Stedman's Medical Dictionary, is:
"Identical twins born with their bodies at some point and having varying degrees of residual duplication, a result of the incomplete division of the ovum from which twins developed."
Simply put, conjoined twins are twins whose bodies are joined together at birth.
There are many different names for conjoined twins, however the two most common are conjoined and Siamese. The word Siamese most likely originated from the twins Chang and Eng who were from modern day Thailand. Both words however refer to twins who are a form of monozygotic twins. Monozygotic twins are formed when a single fertilized egg splits into two embryos. Or perhaps in an easier to understand way, conjoined twins are formed when the zygote (a cell that is the result of fertilization) of identical twins fails to completely separate. This failure of the zygote to completely separate is not affected by heredity, infertility treatments, maternal age, or any other factors. The cause of the birth of conjoined twins is really unknown, and at this point completely random.
There are several conjoined twins now present in the world, most of which have been featured in some kind of news article or TV show. Some of the most