Why Do Dogs Have Slits on the Sides of Their Nose?

Dogs have slits on the sides of their nose for a very good reason: to help them sniff the world around them. Mother Nature wasn't certainly stingy when it came to dog noses, blessing them with some powerful capabilities that us humans can only dream of. Let's take a closer look then into a dog's almighty nose and why dogs have those mysterious slits on each side of their nose.

Ever wondered why do dogs have slits on the sides of their nose? If you take a closer look at your dog, you'll likely notice those slits and wonder what's their purpose. Interestingly, everything seems to have a purpose in this world when it comes to anatomy. 

And if something doesn't have much of a purpose, shrinkage and possibly atrophy of the body part will take place sometime during evolution. Hence, the term vestigial, which is used to depict any organs or body parts remaining in a rudimentary form. For sure, dog noses are quite the opposite, even though they are no longer used much for the purpose of hunting or scavenging for food, one thing is for sure: they are here for good.

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 Anatomy of the Dog's Nose

If we look at our dog's nose we will identify several anatomical features. The first thing we notice is the dog's nose in general. Whether it's black or liver colored, the furless skin surface of the dog's nose is called rhinarium or planum nasale. Some dog owners simply refer to it as nose or snout, while breeders may prefer to call it "nose leather. "

Interestingly, the skin on the dog's nose is sort of pebbled in texture rather than smooth. There is belief that the topography of this surface varies between one dog and another in the same way as human fingerprints.  

On a more utilitarian side, this surface is crammed with pressure and temperature sensors, explains John Bradshaw, in the book: "Dog Sense: How the New Science of Dog Behavior Can Make You A Better Friend to Your Pet."  

In dogs, the rhinarium is characteristically wet. This wetness has also a purpose: to absorb more odors and detect temperature changes that can direct dogs towards a cooling breeze that might carry odors, explains Alexandra Horowitz in the book "Being a Dog, Following the Dog Into a World of Smell."

If we look closer, we may also notice that the nose has a midline groove that goes from the nose down to the dog's upper lip. This small indentation is known as philtrum and it too has a purpose: it carries moisture from the mouth to the rhinarium.

And then you have the nostrils, also known as nares. Let's take a closer look at the conformation of the dog's nostrils, shall we?

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Those Interesting Dog Nostrils 

A dog's nostrils are the two openings that are commonly comma-shaped. The two nostrils are divided by a cartilaginous and bony septum. 

The main purposes of a dog's nostrils are to allow dogs to breath in air (inhale), exhale and carefully analyze smells lingering around the world surrounding them. 

Dog nostrils are also known for having the unique capability of being moved independently, one at a time. Interestingly, according to a study conducted by Siniscalchi, M., et al, dogs show a preference for using first their right nostril for smelling things considered non-threatening, neutral or enjoyable. And then right afterward they tend to switch to using their left nostril. 

When dogs, on the other hand, are sniffing instead things associated with threat such as adrenaline or veterinary sweat, they exclusively use their right nostril. 

At a closer evaluation, this finding makes sense considering that the olfactory system in dogs is displayed ipsilaterally (which means affecting the same side of the body), and therefore, their right nostril connects with the right side of the brain, while their left nostril connects to the right.

From previous research, we know that the right hemisphere of the brain is meant to deal with novelty and emotions associated with the fight or flight response, while the left side of the brain is known to deal with routine investigations, approach behavior, and attractiveness.

And then we have those interesting slits at the sides of the dog's nostrils...

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Why Do Dogs Have Slits on the Side of Their Nose?

So why do dogs have slits on the sides of their nostrils? As mentioned, every anatomical feature seems to have a purpose in life, only that the purpose of some parts may not be yet well understood.

When it comes to those slits though, we have some interesting explanations and they have to do with the dog's intake or air and predisposition for sniffing and analyzing smells. 

While the interior part of the dog's nostrils is meant to take in air, those exterior slits on both sides of the dog's nostrils are meant to allow air to escape every time the dog exhales. But there is more to that...

In us, humans, when we exhale, that air is gone for good. Gone with the wind. This is of course a good thing when dealing with unpleasant odors that make us cringe. In dogs instead, when they exhale, the air flows out of those slits creating a swirl of air.

These small currents of air, seemingly exiting from the side of the dog's nostrils, are not gone for good, but rather lift more particles of odor off the sniffed surfaces which are then once again suctioned for further investigation.

"It is the sniff without punctuation, allowing dogs to get a continuous read of the world—just in the way that we see the world without pauses while we blink," explains Horowitz.

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Heat Sensors in Puppy Noses 

Interestingly, there's another reason why dogs have slits on the sides of their nose, and this time, it dates back to when dogs are days-old puppies in the litter with their moms and siblings.

Functionally born blind, deaf and unable to regulate their own temperatures, puppies are pretty much in a helpless state when they are delivered into this world. However, their noses are already functional at birth (actually, their noses were already functional while in the womb, prior to birth according to some studies). 

The next question, is therefore, how can young puppies crawl back to mom should they find themselves at a distance? The answer is: they can crawl back and it is thanks to their sense of touch and smell. 

Yngve Zotterman, of the Swedish Research Council, discovered another fascinating perk. Basically, puppies comes equipped with special heat sensors that are strategically located just around those slits at the side of the nose and the opening to their nasal passages. The goal of these heat sensors is to help puppies locate energy that's radiated from warm objects.  How fascinating is that?

Interestingly, this function is only there for a limited time. Mature dogs lack these special heat-detecting sensors which suggests that they must disappear or become nonfunctional as the dogs mature and develops other senses, explains Stanley Coren in the book "How Dogs Think: Understanding the Canine Mind."

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