Fig. 2

Transverse sections (a, b, d, f and f’) through the snout and 3D reconstructions (c and e) of the vomeronasal organ and associated structures of the grass snake embryos at different developmental stages. a The vomeronasal organ at the end of developmental stage II. b The vomeronasal organ at the end of developmental stage II. The dashed line indicates the connection of the VNO with the nasal cavity. c The medial aspect of the vomeronasal organ (blue) and its relation to the nasal cavity (green) and the lacrimal duct (orange) at the beginning developmental stage IV. The star indicates the area of the future fusion between the maxillary process and the frontonasal mass. d The connection between the primordium of the vomeronasal organ and the developing nasopharyngeal duct at the beginning of developmental stage IV. e The medial aspect of the vomeronasal organ and its relation to the nasal cavity and the lacrimal duct at developmental stage V. The colours of the structures are the same as in the c. f The embryonic vomeronasal organ and its duct (blue dashed line) at developmental stage V. f’ The choanal groove (green dashed line) at developmental stage V. Seven sections posterior to f. Abbreviations: C concha of the nasal cavity, CH choana, CHG choanal groove, CHNG Choanengang, DNP nasopharyngeal duct, DV duct of the vomeronasal organ FNM frontonasal mass, LV lumen of the vomeronasal organ, MB mushroom body, MNC main nasal cavity, MXP maxillary process, NC nasal cavity, NVN vomeronasal nerve, OC oral cavity, SE sensory epithelium of the vomeronasal organ, VES vestibulum. Scale bars 100 μm (a, b); 50 μm (d, f and f’). 3D reconstructions are not scaled