Drawing of the Boy of Bengal, affected by<unk> .<unk>  is an extremely rare type of parasitic twinning occurring in about 2 to 3 of 5,000,000 births. In<unk> , a parasitic twin head with an undeveloped body is attached to the head of a developed twin. Fewer than a dozen cases of this type of conjoined twin have been documented in literature.
Craniopagus parasiticus
Gnathostoma spinigerum
Ancylostoma tubaeforme
Gongylonema pulchrum
Echinostoma revolutum
Dracunculus medinensis
Fannyhessea vaginae
Brachyspira pilosicoli