Evolution

"The nasopalatine duct connects the organ of Jacobson in the nasal septum to the palate of many animals. Jacobson's organ is joined centrally to an accessory olfactory bulb. Cats, for instance, may sometimes be noticed to sense an interesting odour by inhaling through the mouth, and in most species Jacobson's organ is used to assess the state of sexual readiness of potential mates.

Disappointingly therefore, Jacobson's organ has disappoeared in man."

- R.A. Cawson, Oral Pathology and Oral Medicine (7th Edition)