A new theory of micturition and urinary continence based on histomorphological studies. 4. The musculus dilator urethrae: force of micturition.

In an anatomical study of serial sections of the bladder neck taken from 65 cadavers of all age groups the ventral longitudinal muscle system is shown as a single unit. It is characterized by two origins and two insertions. A detailed description is given. It should be emphasized that there is no connection between this muscle system and any muscle layer of the urinary bladder. The muscle bundles of the upper part of the ventral longitudinal urethral muscle system cross in stages the whole ventral circumference of the trigonal sphincter muscle with functional consequences. The lower part is closely combined with the lumen of the urethra. During contraction the muscle could be able to open the musculus sphincter trigonalis and the musculus sphincter urethrae; we called them musculus dilator urethra. Summarizing all presented histomorphological results of parts 1-4 of these papers [Dorschner et al.; Urol Int 52;1994] a new theory of micturition and its initiation is presented.