Women, and men without moustaches, try this experiment. Move your index finger across the space between your nose and your upper lip. You'll probably feel a little groove in the center, a depression caused by the thinness of the underlying tissue there.

You've touched one of the most enigmatic parts of your body: the philtrum. Its function, if any, remains obscure. The ancient Greeks considered it an erogenous zone. Some researchers say it allows a greater range of lip movements than otherwise be possible, helpful in giving visual cues to expressing emotion.

Anatomically, the philtrum is a reminder of our very early life as an embryo. It's the juncture of two regions of growth in the face, the upper jaw and the nose. A similar juncture is found at the point of the chin, which sometimes shows a dimple in that place.

When embryonic development is disrupted, the philtrum may not form. When the philtrum incompletely fuses, the result is a cleft lip, which is correctable by surgery.

A missing philtrum is one of the identifying characteristics of fetal alcohol syndrome, caused when the mother drinks too much during pregnancy. (While some studies have shown that drinking small amounts of alcohol does not pose a risk to the baby, doctors say it is safest for pregnant mothers to totally abstain).

When present, variations in the shape of the philtrum may be an indicator of a congenital disease. For example, a wide, deeply grooved philtrum is one of the facial characteristics of Ackerman syndrome, a rare condition identified in two generations of a family. Other characteristics include sparse body hair, oddly shaped teeth and, in some cases, deafness.

Normal philtrums vary in size and prominence. Celebrities such as Cindy Crawford and Mickey Rourke are noted for having very visible philtrums. According to folklore, a wide philtrum is supposedly indicative of sexual desire.

But sight is far inferior to touch in identifying the philtrum. Depending on whose philtrum is being touched, you may find the ancient Greeks knew what they were talking about.

Contact staff writer Bradley J. Fikes at (760) 739-6641 or bfikes@nctimes.com.