Emptying internal urethral orifice
Ostium urethrae internum evacuans
Definition
The internal urethral orifice is placed at the apex of the trigonum vesicæ, in the most dependent part of the bladder, and is usually somewhat crescentic in form; the mucous membrane immediately behind it presents a slight elevation, the uvula vesicæ, caused by the middle lobe of the prostate.
When the urinary bladder fills, the orifice is closed and forms a flat sheet together with surrounding structure (Filling internal urethral orifice).
When the urinary bladderis emptying, the neck of bladder retracts like a funnel and the male urethra appears shortened (Emptying internal urethral orifice).
References
This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S. edition of Gray's Anatomy of the Human Body, published in 1918 – from http://www.bartleby.com/107/).
