The philtrum (Latin philtrum, Greek φίλτρον philtron), is a vertical groove in the middle area of the upper lip, common to many mammals, extending from the nose to the upper lip. Technically referred to as the medial cleft, together with a glandular rhinarium and slit-like nostrils, is believed to constitute the primitive condition for mammals in general. The philtrum in most mammals is a narrow groove, and may carry moisture from the mouth to the rhinarium or nose pad to keep it wet through capillary action. A wet nose pad is able to trap odor particles better than a dry one, thus it greatly enhances the olfactory system. For humans and most primates, the philtrum survives only as a vestigial medial depression between the nose and upper lip. The human philtrum, bordered by ridges, is also known as the infranasal depression, but has no apparent function. That may be because most higher primates rely more on vision than on smell and so no longer need a wet nose pad or a philtrum to keep the nose pad wet. Strepsirrhine primates, such as lemurs, still retain the philtrum and the rhinarium, unlike monkeys and apes.
In humans 
In humans, the philtrum is formed where the nasomedial and maxillary processes meet during embryonic development (colloquially known as Hulse lines).
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.
A study of boys with diagnosed autism spectrum disorders found that a broader than average philtrum is one of a cluster of physical abnormalities associated with autism.
In religion and folklore 
In Jewish mythology, an angel strikes a newborn on the upper lip right before birth to create the philtrum, so he forgets all he saw and knew as a soul. A version of this legend was depicted in the 1947 film "Key Largo", in a scene with Lauren Bacall and Lionel Barrymore, where Humphrey Bogart recounts the story to them, as told to him by his fellow soldier friend.
See also 
- ^ Orders PRIMATES & SCANDENTIA
- ^ Philip Hershkovitz,Living New World monkeys (Platyrrhini): with an introduction to Primates, University of Chicago Press, 1977, Vol. I, p. 16
- ^ Ankel-Simons, F. (2007). Primate Anatomy (3rd ed.). Academic Press. p. 394. ISBN 978-0-12-372576-9.
- ^ hednk-032 — Embryo Images at University of North Carolina
- ^ FAS Clinical
- ^ Aldridge, Kristina; George, Ian D.; Cole, Kimberly K.; Austin, Jordan R.; Takahashi, T. Nicole; Duan, Ye; Miles, Judith H. (2011). "Facial phenotypes in subgroups of pre-pubertal boys with autism spectrum disorders are correlated with clinical phenotypes". Molecular Autism 2 (15). doi:10.1186/2040-2392-2-15.
- ^ Gabriel's Palace: Jewish Mystical Tales p57
- ^ Babylonian Talmud; Niddah 30b