National Purebred Dog Day
The philtrum is the vertical groove between the base of the nose and the border of a dog's upper lip, and it has a purpose. Every time a dog licks his lips, a bit of saliva stays in this groove and is drawn upwards due to capillary action. This keeps the dog's nose moist, if not wet, which enables the dog to capture scent particles from the air. Pretty cool, eh?
Image from Wikicommons