A 1-year-old infant is admitted to the pediatric clinic because he is passing urine on the underside of the penis as shown. Which embryologic structure failed to fuse?

(c) Source: GAS 444-453; GA 219, 222Hypospadias is a developmental defect in the urethra resulting in urine being expelled from the ventral side of the penis. This ectopic malformation may present when the urethral folds fail to completely fuse. Failure of fusion of the spongy urethra would result in epispadias. A failure of the labioscrotal folds to fuse will cause the external urethral orifice to be situated between the two scrotal halves. This is referred to as penile hypospadias. Failure of the urogenital folds to fuse would lead to agenesis of the external urethral folds.