Around the ureteric orifices, the muscular coat of each ureter also fans out into the bladder. Some of these muscle fibers cross the midline to unite with strands from the opposite side, raising an interureteric crest.

The sides of the trigone are outlined by yet another group of submucosal fibers, known as Bell muscle, which connect the ureteral muscles with the wall of the urethra. Tension across these bands, especially when combined with pressure from the neighboring middle lobe of the prostate (in males), leads to a small elevation above the bladder neck known as the uvula.

The innermost layer of the bladder is the mucosa. When the bladder is empty, the mucosa is corrugated by numerous folds. As the bladder distends, however, the folds are obliterated. The mucosa of the trigone is anatomically distinct, however, because it is firmly attached to the muscularis, consequently appearing smooth even when the bladder is empty.