page_title: Polycephaly
section_title: Mythological occurrences
hierarchical_section_title: Polycephaly / Mythological occurrences
context_page_description: Polycephaly is the condition of having more than one head. The term is derived from the Greek stems poly meaning "many" and kephalē 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 and three-headed animals are the only type of multi-headed creatures seen in the real world, and form 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. Survival to adulthood is rare, but does occur in some forms of dicephalus parapagus dipus.
  There are many occurrences of multi-headed animals in mythology. In heraldry and vexillology, the double-headed eagle is a common symbol, though no such animal is known to have ever existed.
caption: The 16th-century German zoologist Conrad Gesner has been influenced by the Beast of Revelation in his depiction of the Hydra in volume four of Historiae Animalium.
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