miodidymus

mi·o·did·y·mus

, miodymus (mī'ō-did'i-mŭs, mī-od'i-mŭs),
Unequal conjoined twins with the head of the smaller twin joined to the occipital region of the head of the larger twin. See: conjoined twins.
[mio- + G. didymos, twin]

miodidymus

(mī″ō-dĭd′ĭ-mŭs) [″ + didymos, twin]
A fetus with two heads joined at the occiput.