Differences in embryogenesis of epispadias, exstrophy-epispadias complex and hypospadias

The tail may briefly compress and separate the merging second sacral pair of mesodermal streams that sever the cloacal-allantoic connection and form part of the phallus. These streams then come together to form the phallus behind the allantoic connection which then lies on the dorsal slope of the epispadiac penis. If the compression by the tail occurs after the first paired streams have met and formed the penis, the next pair that form the inner genital folds and penile urethra may be held apart by compression of the tail creating extreme forms of hypospadias on the ventral slope of the penis. This tail compression theory may explain the rarity of epispadias compared to the relatively more common exstrophy-epispadias complex.