Douglas Q. Adams:The Distribution of Retracted Sibilants in Medieval Europe. In: Language. Band51, Nr.2, 1975, ISSN0097-8507, S.282–292, doi:10.2307/412855.
Helmut Esau:The Medieval German Sibilants /S/ and /ʐ/. In: The Journal of English and Germanic Philology. Band75, Nr.1/2, 1976, ISSN0363-6941, S.188–197.
Douglas Q. Adams:The Distribution of Retracted Sibilants in Medieval Europe. In: Language. Band51, Nr.2, 1975, ISSN0097-8507, S.282–292, doi:10.2307/412855.