Janciceps are twins who are joined together with the
heads connected and the faces pointing in opposite
directions. The bodies and faces of the twins may be
completely formed. However, it is also possible for one
member of the twins to be only partially formed and act
as a parasite on the more fully developed twin (known
as janiceps parasiticus). A parasite is an organism that
lives in or on another organism to obtain nourishment.
There are two types of janiceps. Janiceps asymmetrus are janiceps in which one member
is completely developed and the other is very small with an incompletely developed face.
This is where the term "asymmetrus" comes in, since it means "asymmetry" or
Janiceps asymmetrus is also known as iniops and syncephalus asymmetros. Janiceps
parasiticus are janiceps in which one member of the twins is partially formed and acts as
a parasite on the more fully developed twin. A parasite is an organism that lives in or on
another organism to obtain nourishment. This is where the term "parasiticus" comes in,
since it means "parasite" in Latin.
Janiceps comes from the Latin word "Janus" who was a two-faced Roman god, and the
Latin word "caput" meaning "head."