Histological sections of the head of Sibon nebulatus. Sagittal section of the head of Sibon nebulatus (MZUSP 9316); Paraffin, Hematoxylin-eosin staining (A). Mandibular region showing infralabial gland constituted by mucous (m) and seromucous cells (sm); Paraffin, Hematoxylin-eosin staining (B). Detail of the duct from infralabial gland opening in the oral cavity; Paraffin, Hematoxylin-eosin (C). Epithelium of the infralabial gland constitute by mucous (m) and seromucos cells (sm); Paraffin, Hematoxylin-eosin staining (D). Histochemical reaction of the bromofenol blue showing positivity for the posteriormost cells of the infralabial glands; Paraffin (E). Transversal section of the head at the level of the eyes showing infralabial gland (il) and its association with the muscle levator anguli oris (lao); Paraffin, Hematoxylin-eosin staining (F). Transversal section of the head at the level of the snout showing infralabial glands with its tubules (tu) and ducts (du) distended to the anterior portion of the mouth; Paraffin, Hematoxylin-eosin staining (G). Abbreviations: cp, compound bone; d, dentary; d-il, ducts of the infralabial gland; dslg, ducts of the sublingual gland; e, eye; f, frontal; Hg, Harderian gland; ils, infralabial scales; Jo, Jocobson’s organ; lao, muscle levator anguli oris; mx, maxillary; n, nasal bone; nc, nasal cavity; ng, nasal gland; oc, oral cavity; oe, oral epithelium; sl, supralabial gland; slg, sublingual gland. Scale bar = 1 mm (A, F and G); 500 μm (B); 200 μm (C and E); 50 μm (D). Panels at the upper right corner denote position of the section in A, F, G.