atlodidymus

at·lan·to·did·y·mus

(at-lan'tō-did'ē-mŭs),
Conjoined twins with two heads on one neck and a single body.
Synonym(s): atlodidymus
[atlanto- + G. didymos, twin]

atlodidymus

(at′lō-did′ĭ-mŭs) [ atlas + didymos]
Conjoined twins with one body and two heads.