Abstract
The vomeronasal organ of the rat fetuses at 10, 11, 12, 13, 14, 16 and 18 days of gestation was studied by light and scanning electron microscopy. The primordium of the vomeronasal organ was observed first on 11 days of gestation as a thickening of the ectodermal layer on the mediorostral wall of the olfactory pit, whereas the olfactory placode appeared on the 10th day. The ectodermal thickening, which was identified as the vomeronasal placode, was situated on the separate geometric territory lying apart from the olfactory epithelium, moreover the vomeronasal placode appeared one day later than the olfactory placode did. The vomeronasal nerves and intraepithelial capillaries were observed on 13 days of gestation and immature vomeronasal cartilage cells accumulated around the vomeronasal duct on 14-days. The vomeronasal complex appeared 1 or 2 days later than the structures in the olfactory organ. These findings were similar to those reported in other rodents such as mice and golden hamsters, however in the hamster the vomeronasal duct, cartilage and gland, and in the mouse the vomeronasal nerve, appeared earlier respectively than those in the rat.
