The philtrum (Latin philtrum, Greek φίλτρον philtron, 'love potion' [1]), is a medial cleft common to many mammals, extending from the nose to the upper lip, and, together with a glandular rhinarium and slit-like nostrils, is believed to constitute the primitive condition for mammals in general. [2] For humans and most primates, the philtrum survives only as a vestigial medial depression between the nose and upper lip. [3] The human philtrum, bordered by ridges, is also known as the infranasal depression, but has no apparent function.
[edit] In humans
In humans, the philtrum is formed where the nasomedial and maxillary processes meet during embryonic development. When these processes fail to fuse fully in humans, a cleft lip (sometimes called a "hare lip") can result. A flattened or smooth philtrum can be a symptom of Fetal alcohol syndrome or Prader-Willi syndrome.[5]
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