As in the case of abcaudal duplication, so here, one of the halves may develop fully, while the other is dwarfed, and remains as an appendage or parasite.

(A) Epigastrius (Smaller Part Appended In Front Of Larger)

This form is much rarer than the corresponding one in abcaudal duplication. There is a head and part of the body appended to the thorax and abdomen of a fully developed foetus, but the parasitic portion is dwarfed. The monstrosity is quite consistent with life.

(B) Inclusio FœTalis

To what extent the occasional occurrence of teratoma inside the skull or in the mediastinum may be due to abcranial duplication with imperfect development of one half is not known.