Differentiation of the urogenital sinus

The primitive urogenital sinus is in contact with the allantois. The upper part forms the future urinary bladder, while the middle and lower part forms the definitive urogenital sinus and, from it, the pelvic and phallic parts of the urethra.

The pelvic part of the definitive urogenital sinus forms the prostatic and membranous parts of the urethra, the phallic part of the definitive urogenital sinus, the spongy part of the urethra and the urethral vestibule. Around the 4th month an epithelial cord grows on the glans penis - into the depths - and binds it with the spongy part of the urethra.