A – D Histological staining nuclear red/light green/orange G. Note that A – D are depicted at the same magnification and that all zones contain OSNs (based on results from semi- and ultrathin sections). A Olfactory epithelium in zone 1 close to the naris. B Ventrolateral olfactory epithelium in zone 2. The height of the epithelium is variable. Bowman glands (bg) are present. bv – blood vessel. C Olfactory epithelium in zone 4 (anterior turbinate). bv – blood vessel. D Olfactory epithelium in zone 4 (anterior turbinate) in a different region than shown in C. bg – Bowman gland. E – F Semithin (1 μm) sections stained with toluidin blue. Both E and F depict zone 3. Bowman glands are numerous (bg). Note in F how few OSNs are present (arrows). Sc shows a nucleus in the layer of nuclei of the supporting cells. osn shows the layer of nuclei of the olfactory neurons and bc the layer of basal cells. bg – Bowman gland, bv – blood vessel, ms – muscle.