| pygopagus | Conjoined twins in which the two individuals are joined at the buttocks, most often back to back. See: conjoined twins. Origin: pygo-+ G. Pagos, something fixed (05 Mar 2000) |
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| craniopagus parasiticus | A variety of craniopagus in which one foetus is rudimentary in form and parasitic on the other. See: epicomus. (05 Mar 2000) |
| janiceps parasiticus | A janiceps in which one of the twins is a small and incompletely formed parasite attached to the more fully formed autosite. (05 Mar 2000) |