Cephalic glands of brazilian reptilia and amphibia .Iv. Histology of labial, premaxillary, and duvernoy's gland in the colubrid snake - Lopes, R A; Contrera, M G D; Costa, J R V; Campos, Geraldo Maia; Petenusci, Sérgio Olavo (Gegenbaurs Morphologisches Jahrbuch, 1987)