We have described the basic development of the urethra including the two-zipper hypothesis of urethral development. The human male urethra appears to form by two mechanisms: (1) An initial “opening zipper” that facilitates distal canalization of the solid urethral plate to form the urethral groove, (androgen independent) and (2) A “closing zipper” facilitating fusion of the two epithelial surfaces of the urethral groove, and thus extending the penile urethra distally (androgen dependent).
