All are true about trigone of bladder except

The wall of the urinary bladder consists of an outer serous layer,a thick coat of smooth muscle and a mucous membrane.The mucous membrane is lined by transitional epithelium.The trigone is a smooth triangular region of the internal urinary bladder formed by the two ureteral orifices and the internal urethral orifice.Here the mucous membrane is always smooth even when the bladder is empty, when mucous membrane of the rest of the pa is thrown into folds. Smoothness of mucosa over trigone is because of the firm adherence to underlying muscular coat (Detrusor muscle).The bladder is derived from two sources, the cloaca and mesonephric ducts. Ref: Cooper C.S., Joudi F.N., Williams R.D. (2010). Chapter 38. Urology. In Dohey G.M. (Eds), CURRENT Diagnosis & Treatment: Surgery, 13e.