Jacobson's Organ (Vomeronasal Organ)

The Jacobson’s organ, also termed as vomeronasal organ, is a sensory receptor for detecting special smells. This is located on the roof of the mouth of reptiles, amphibians, and mammals. Since the Jacobson’s organ is an extension of the olfactory system, it enables animals to detect scents which humans could not. Unlike typical olfaction this organ senses stimuli through humidity, specifically moisture-borne particles which are traces of chemicals like pheromones. Through their tongues, reptiles flick such stimuli into their Jacobson’s organ. As for mammals, they often manifest the Flehmen reaction which is the curling of the upper lip to expose the organs to better sense chemical traces. For instance, a dog is Flehmening when he is sensing the territory of another dog who just urinated on a wall. Humans have this organ but it is merely vestigial.

This was initially discovered in the 1700s by Frederick Ruysch, a Dutch botanist and anatomist; however, this was named after Ludwig Lewin Jacobson, a Danish surgeon, as he brought it to public attention in the 1800s.