Craniopagus parasiticus
Overview
Parasitic twin
A parasitic twin is the result of the processes that produce vanishing twins and conjoined twins, and may represent a continuum between the two...
head with an undeveloped (or underdeveloped) body is attached to the head of a developed twin.
There have only been ten documented cases of this phenomenon, though to-date at least eighty cases of this phenomenon have been written about in various records http://www.forteantimes.com/features/articles/148/the_twoheaded_boy_of_bengal.html.
