Why Do Dogs Have a Split on Their Top Lip?


Dogs have a split on their top lip for a good reason. That line is just not there for decoration. Discover the purpose of that split on the dog's top lip along with some other interesting facts about this little-known body part.

Why Do Dogs Have a Split on Their Top Lip? You may have noticed how your dog has a split at the top of his upper lip, right under his nose, and may be wondering if that vertical groove has some function. As with other body parts, most likely it does, so here at "Why do Dogs" we decided to once again put on our investigative hats and fetch some good old answers. The search has sure yielded some interesting findings about that mysterious indentation that are worthy of sharing.

A Shared Feature

If you look at your dog's split right under his nose and then look at yourself in the mirror, you will notice how you also have a similar split. 

Turns out, this indentation is common to many mammals and goes by the name of "philtrum" or "medial cleft." According to the National Human Genome Research Institute, the term derives from the Greek word "philtron" which means love potion, possibly because this area back in time was considered by the ancient Greeks as one of the most erogenous parts of the body. 

Ancient Romans also found the area quite erotic, which is why they often referred to this little dip in the upper lip as “Cupid’s Bow.”

A Sensory Purpose

A dog's philtrum has really no romantic feature other than perhaps for Lady and the Tramp's spaghetti-eating kiss. There is some speculation on its role though that's worth sharing. 

According to the"e-Study Guide Illustrated Anatomy of the Head and Neck" in mammals the philtrum may carry moisture from the mouth to the rhinarium, the moist surface around the nostrils, so to keep the area wet through capillary action. 

A wet nose is is essential to a dog's keen sense of smell as it helps absorb tiny water droplets that carry scent. It appears that in humans, the philtrum doesn't carry a function and is therefore considered a vestigial structure.

Formation in the Womb

Both in animals and humans, the philtrum appears exactly where the nose and lips fuse during development in the embryo. In order to fuse correctly, it's important that these body parts grow and fuse at the exact same time.

 Failure to do so, may lead to the baby or puppy to develop what is known as a "cleft palate," a deforming birth defect that requires surgery to correct. 

According to the Veterinary Surgery Small Animal Textbook, in order to fix the issue, the pup's philtrum, nasal planum and oronasal barrier will need reestablished

Did you know? According to veterinarian Allen M. Shoen, in veterinary acupuncture, the nasal philtrum houses the GV-26 point, which is one of the most commonly used points for treating shock and cardiovascular collapse.