Presence and structure of anal and vaginal tonsils in the laboratory shrew (Suncus murinus).

In all the laboratory shrews (Suncus murinus) examined, a pair of tonsil-like structures was found at the boundary between the anus and the ostium urogenitoanalis. Moreover, the same tissues were recognized between the vagina and the ostium urogenitoanalis in 9 of the 13 females examined. They indicated clear epitheliolymphocyte symbiosis around both mucosal crypts (anal and vaginal crypts) and outer lymph nodules including the germinal centers, and were demarcated from other tissues by the fibrous capsule. Two kinds of tonsil-like structures in this study were found to be homologous with some of the tonsils in the fauces of other mammals. These will be therefore referred to as the anal and vaginal tonsils.