vomeronasal organ (Jacobson's organ) A special ‘smell-taste’ organ in the hard palate of many mammals; it opens by ducts into the roof of the mouth behind the incisors. The facial gesture called Flehmen guides olfactory molecules into the vomeronasal organ, where odours, especially sexual ones, appear to be interpreted. In primates, the organ is functional in lemurs, tarsiers, and New World monkeys; in catarrhines, including humans, it begins to develop in embryos, but later degenerates. The vomeronasal organ is also present in amphibians, lizards, and snakes.

vomeronasal organ An organ of smell found in many terrestrial vertebrates, but not apparent in humans. Vomeronasal organs are typically paired blind-ending sacs opening into the oral or nasal cavities. They are lined with olfactory epithelium, whose cells express receptor proteins for airborne chemicals. The vomeronasal organs tend to respond especially to pheromones used in chemical signalling between members of the same species, and their receptor proteins belong to different protein families than those expressed by the nasal epithelium. Also, the axons of vomeronasal receptors project to a different site in the brain from the nasal olfactory axons.