Siamese twins /sī″əmēz/ [Chang and Eng, conjoined twins born in Siam (now Thailand) in 1811] , conjoined, equally developed twin fetuses produced from the same ovum. The severity of the condition ranges from superficial fusion, such as of the umbilical vessels, to that in which the heads or complete torsos are united and several internal organs are shared. With modern surgical techniques, most Siamese twins can be successfully separated. See also conjoined twins.
