Masculinization of the indifferent external genitalia occurs under the influence of androgens produced by the fetal testes. The genital tubercle enlarges and elongates rapidly to form the phallus, which is the primordium of penis. The elongating phallus pulls the urethral folds, so that the urethral groove comes to lie on ventral (ie, inferior) surface of the developing penis. A coronary sulcus around the distal part of the penis defines the glans. The urethral groove does not extend into the glans penis. The epithelial lining of the urethral groove becomes thickened to form the urethral plate. During the 7th and 8th weeks the urethral folds fuse in the median plane. The urethral groove is thus converted into an endoderm-lined canal, which lies within the penis and is known as spongy or penile urethra. Because the urethral groove does not extend to the tip of the penis, the penile urethra is initially blindended. The terminal part of the urethra is ectodermal in origin and is formed during the 4th month in the following manner. A sold cord of ectodermal cells grows inwards from the apex of the glans penis. This rod meets and fuses with the endodermal penile urethra. Complete canalization of the ectodermal cord occurs during the 5th month. This results in completion of the terminal part of the urethra and carries the external urethral meatus to the tip of the glans penis.
The genital (labioscrotal) swellings grow in a caudal direction and also move toward each other. Finally, they fuse in the midline to form the scrotum. Externally the line of fusion of the genital swellings persist as scrota/ raphe, whereas infernally the two halves of the scrotum are separated by the scrotal septum.