The internal urethral orifice is the opening of the urinary bladder into the urethra.

[citation needed] It is formed by the neck of the urinary bladder.

It opens at the apex/inferior angle of the trigone of the bladder, some 2-3 cm anteromedial to either ureteral orifice.

[1] The mucous membrane immediately posterior to it presents a slight elevation in males - the uvula vesicae - caused by the middle lobe of the prostate.

[citation needed] This article incorporates text in the public domain from page 1232 of the 20th edition of Gray's Anatomy (1918)