The ureters develop from the caudal portion of the ureteric bud. The urinary bladder and urethra are derived from the primitive urogenital sinus (a ventral part of the cloaca) and adjacent splanchnic mesenchyme. The cloaca, the terminal portion of the hindgut is divided into the dorsal primitive rectum and ventral primitive urogenital sinus by the growth of the urorectal septum. The same septum also divides cloacal membrane into the urogenital membrane anteriorly, and the anal membrane posteriorly.

1. Urogenital ridge
2. Genital ridge
3. Mesonephric duct
4. Mesonephros
5. Gonad
6. Metanephric tissue
7. Ureter
8. Cloacal membrane
9. Cloaca
10. Allantois
11. Urorectal septum
12. Tail

1. Mesonephric duct
2. Mesonephros
3. Gonad
4. Metanephros
5. Ureter
6. Cloacal membrane
7. Cloaca
8. Urorectal septum
9. Urogenital sinus
10. Anorectal canal
11. Tail

1 . Ureter
2 . Metanephros
3 . Gonad
4 . Mesonephric duct
5 . Anal membrane
6 . Urogenital membrane
7 . Perineal body
8 . Bladder
9 . Rectum

The urogenital sinus gives rise to the urinary bladder, which is cranially continuous with allantois (later urachus) and caudally with the urethra. During division of the cloaca the caudal portins of the mesonephric ducts are incorporated into the wall of the urinary bladder thus forming the trigone of the bladder. The ureters and mesonephric ducts with time obtain the separate entrances into the urinary bladder.
In the male, the pelvic part of the urogenital sinus gives rise to the prostatic and membranous part of the urethra. The penile urethra is partly formed by the closure of urethral folds, while its most distal portion is formed by an inward penetration of ectodermal cells on the tip of the glans.

1. Ureter
2. Mesonephric duct
3. Urinary bladder

1. Ureter
2. Mesonephric duct
3. Urinary bladder