Sometimes, people get shocked looking into the mouth of a chameleon, and scream: he has a cleft palate!
No panic. All chameleons do in a sense...
The vomeronasal organ, called also Jacobson's organ is a structure located on the hard palate and is as a chemoreceptory organ a part of the accessory olfactory system. It has been shown to play a role in the formation of social and sexual behavior in animals, thanks to its pheromone receptor cells and the stimulating effect on the secretion of gonadotropin-releasing hormone.
It is a patch of sensory cells within the main nasal chamber that detects heavy moisture-borne odour particles.
In reptiles, the forked tongue collects the odour particles and ring them to diversely deep fissures if the hard palate.
Despite the VNO was first described as a structure by the Dutch botanist and anatomist Frederik Ruysch in 1703, the description is more widely attributed to the Danish surgeon Ludwig Jacobson, whom the vomeronasal organ has been dedicated to wear also his name, because in 1803 he described the structure in a variety of mammals.
Jacobson's organ is present in many amphibians, reptiles, and mammals, including humans, although it does not occur in all tetrapod groups.
Chameleons possess the Jacobson's organ as well. Its functionality is discusses and not fully clear yet. It definitely serves analyzing the odors, collected by the tongue while exploring the environment - chameleons have been repeatedly reported to lick on unknown objects in their surroundings.
Pictures show the hard palate in Furcifer pardalis, Chamaeleo calyptratus and Furcifer oustaleti. Frucifer pardalis licking a branch.