1. Literature has been grouped in reference lists of several chapters in those cases where arguments are difficult to entangle or published over several articles or books. In cases of citation the article or book involved is indicated by the reference number together with a capital Arabic letter..
2. Kaye KW, Creed KE (1997) Anatomy and innervation of the external urethral sphincter. Dialogues in Ped Urol 20:3–4
3. Droës TTPM (1972) De musculatuur van blaas en urethra in de menselijke foetus. Thesis Leiden, The Netherlands
4. Patapoutian A, Wold BJ, Wagner RA (1995) Evidence for developmentally programmed transdifferentiation in mouse esophageal muscle. Science 270:1818–1820
5. Baskin LS, Borirakchanyvat S (1997) Studies on the origin of smooth and striated muscle cells in the intrinsic urethral sphincter. Dialogues in Ped Urol 20:2–3