The urinary bladder and urethra develop from the cloaca during weeks 4 to 7 of development. A urorectal septum divides the cloaca into the primitive urogenital sinus ventrally and the anorectal canal dorsally. The primitive urogenital sinus then divides into three parts - a cranial vesical part that forms most of the bladder, a middle pelvic part that forms the main part of the male urethra and entire female urethra, and a caudal phallic part that grows toward the genital tubercle.