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
Trigger Twins appears in The Multiversity Guidebook #1. The Trigger Twins are Justice Riders' members. In the second part of Arrowverse's "Elseworlds" crossover, John Deegan rewrites reality, turning Barry Allen and Oliver Queen into the Trigger Twins. Trigger Twins The Trigger Twins are the names of two sets of fictional Western themed comic book characters published by DC Comics. The Trigger Twins first appear in "All-Star Western" #58 (May 1951), the first issue of that title under its new name (previously known as "All Star Comics"), and was one of the features that replaced the previous stars, the Justice Society of America.