A 6-month-old boy was born with hypospadias. This condition is due to failure in the development of which of the following:

The edge of the cloacal membrane forms the urogenital fold and by the process of invagination forms the urethral groove and finally the penile urethra. The severity of hypospadias depends on the location of the anomalous opening onto the penile urethra. The mildest degree is where the opening is on the glans and the most severe form at the peno-scrotal junction.