|Internal urethral orifice
|ostium urethrae internum
The internal urethral orifice is the opening of the urinary bladder into the urethra. It is placed at the apex of the trigonum vesicae, in the most dependent part of the bladder. It is usually somewhat crescent-shaped; the mucous membrane immediately behind it presents a slight elevation in males, the uvula vesicae, caused by the middle lobe of the prostate.