The organ of Jacobson or vomeronasal gland is an almost forgotten body part. It is a sense organ with the ability to detect chemical signals. In humans, the external evidence consists of a pair of tiny pits, one on either side of the nasal septum, approximately 3mm above the nostril. In no mammal is the opening to the Jacobson’s organ obvious; it is tucked away somewhere on the edge of the air stream. In the elephant it is situated near the back of the palate, where the clearly visible marks of a pair of pits in the bone can be observed.
This organ communicates not only with the olfactory bulbs in the cortex of the brain (where we organise what we know and can remember about particular odours), but also with the limbic system in the back of the brain, where basic emotions involved with sex and aggression seem to be coordinated.
Elephants always put their trunks in their own and other elephants’ mouths. A bull will smell a pool of urine left by one of the females in a group, then lift his trunk to the roof of his opened mouth where he blows the inhaled smell to the pits in the palate. Chemicals and hormones in the urine then indicate to the bull when the female is ready to mate. This specific trunk to mouth behaviour is known as the Flehmen response.