Urethral sphincters
In mammals, the Urethral sphincters are two muscles that control the exit of urine from the bladder through the urethra. If either of them contracts, the urethra is sealed shut. In male mammals, one of the muscles is placed around the urethra. In female mammals, it is placed on the side of the vagina. In male mammals, the muscles are also used to transport the sperm, when an erection happens.