[TA] bilaminar smooth musculature of the trigone of the bladder. The cells of the deep trigonal muscle are indistinguishable from those of the detrusor; those of the superficial trigonal muscle are distinct, comprising small bundles continuous with the intramural part of the ureters, thickening around the periphery of the trigone and forming the substance of the interureteric crest, and continuing inferiorly with the muscular layer of the proximal urethro. SYN: musculi trigoni vesicae (superficialis et profunda) [TA].