One of of the pair of folds derived from the cloacal folds which give rise to a portion of the external genitalia; in male embryos they close over the urethral plate and fuse to form the spongy (penile) urethra and ventral aspect of the penis, not including the glans; failure of fusion of the urethral folds leads to hypospadias; in female embryos they fuse only anterior to the anus and form the labia minora[MP]. [ http://en.wikipedia.org/wiki/Urogenital_folds ]