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Few people have ever heard of a filtrum, and yet it is usually as plain as the nose on one’s face. To be a bit more accurate, the filtrum is as plain as the area just under the nose on one’s face. It is no less than the name of the vertical groove found in the middle of the upper lip. More commonly it is known as a philtrum, or if you prefer to use the medical term, the infransal depression.

Other than being a very valuable piece of knowledge that can be displayed during trivia games, the filtrum serves no definite purpose. Some researchers think that it might help humans to form different sounds during speech, allowing the lips a certain freedom of movement. Having a filtrum is perfectly normal; the lack of this dimple is sometimes a sign of either fetal alcohol syndrome or mental retardation. The filtrum forms during embryonic development, and if the two sides of the upper lip fail to fully fuse, a person may be born with a cleft lip.

Dogs and cats also have filtrums. They are two of the few mammals in the animal kingdom, besides humans, that possess the feature. For the Lassie and Garfield set, however, the name applies to the meeting points of the two sides of the nose. The shallow groove serves no more purpose on these domesticated creatures than it does on humans.

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