The rugae are located in the ________ layer of urinary bladder.

The innermost layer of the wall of the urinary bladder is the mucous membrane (also called the mucosa), which contains transitional epithelium tissue that can stretch. The ability of this tissue to stretch is important because it contains variable volumes of liquid - as the bladder is filled and emptied several times per day. Because it is only loosely attached to the (strong and substantial) muscular layer, the mucosa falls into many folds known as rugae when the bladder is empty or is only filled to a small extent.