Polycephaly
condition of having more than one head
Polycephaly is the condition of having more than one head. The term is derived from the Greek stems poly (Greek: "πολύ") meaning "many" and kephalē (Greek: "κεφαλή") meaning "head". A polycephalic organism may be thought of as one being with a supernumerary body part, or as two or more beings with a shared body.
Two-headed animals (called bicephalic or dicephalic) and three-headed (tricephalic) animals are formed by the same process as conjoined twins from monozygotic twin embryos.
In humans, there are two forms of twinning that can lead to two heads being supported by a single torso. In dicephalus parapagus dipus, the two heads are side by side. In craniopagus parasiticus, the two heads are joined directly to each other, but only one head has a functional torso—in most cases, this manifests as an underdeveloped twin head joined to the head of a developed twin. Documented survival into childhood is extremely rare. Survival to adulthood is rare, but does occur in some forms of dicephalus parapagus dipus, as was reported in a case of dicephalic twin born at 36 weeks of gestation to a multigravida mother in central India.
There are many occurrences of multi-headed animals in mythology.
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This entry incorporates text from “Polycephaly” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.