A new theory of micturition and urinary continence based on histomorphological studies. 3. The two parts of the musculus sphincter urethrae: physiological importance for continence in rest and stress.

The urethral component of continence is the object of a lively discussion. A large number of the examiners interpret the external striated urethral muscle as part of the muscular pelvic diaphragm, formed partially or completely by the so-called musculus transversus perinei profundus. About 30,000 histological sections have been examined by light microscopy in a systematical manner. In contrast to numerous suggestions in the literature the musculus sphincter urethrae has been found to be an independent morphological unit in our investigation. It is separated from the surroundings by a segment of connective tissue. Furthermore, with the help of transversal, sagittal and frontal serial sections it was possible to show that the musculus transversus perinei profundus does not exist. In the female as well as in the male in the direction of the urethra the outer sphincter always borders on a layer of smooth muscle cells. In order to distinguish both parts the terms musculus sphincter urethrae transversostriatus and musculus sphincter urethrae glaber are introduced. In the context of a new continence theory three structures capable of occluding the urinary bladder will be discussed. It should be emphasized that the musculus sphincter urethrae glaber makes long-term continence possible.