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, and 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
- - "The Male Pelvis: The Urethra"