Craniopagus twins conjoined twins develop inutero remains unclear. Embryologists have traditionally attributed identical twinning as "splitting or fission" of either the inner cell mass of pleuripotential cells or early embryonic disc at 13–14 days of gestation just before the primitive streak. Some theorists suggested that conjoined twins develop as a result of the failed fusion of a single fertilized ovum. However a new hypothesis suggests that cranial fusion occurs between two separate embryos before the end of the 4th week of gestation. This can happen because the cranial neuropore is still open, which is responsible for the ultimate fusion and formation of
Twins in mythology Twins in mythology Twins appear in the mythologies of many cultures around the world. In some they are seen as ominous and in others they are seen as auspicious. Twins in mythology are often cast as two halves of the same whole, sharing a bond deeper than that of ordinary siblings, or seen as fierce rivals. They can represent another aspect of the self, a doppelgänger, or a shadow. However, twins can also reflect a complete opposition of the other, such as the "civilized" Gilgamesh, and the "wild" Enkidu; or in the commonly known instance of good and evil twin