The trigone (also known as the vesical trigone) is a smooth triangular region of the internal urinary bladder formed by the two ureteric orifices and the internal urethral orifice. The area is very sensitive to expansion and once stretched to a certain degree, stretch receptors in the urinary bladder signal the brain of its need to empty. The signals become stronger as the bladder continues to fill. Embryologically, the trigone of the bladder is derived from the caudal end of mesonephric ducts, which is of mesodermal origin (the rest of the bladder is endodermal)...