Part of the reason why we love animals so much is the fact that they have so many unique features that we don’t. We’re fascinated by the dolphin’s rubbery skin and blowhole, and we’re wowed by the elephant’s prehensile trunk and enormous ears. Our amazement isn’t limited to wild animals, either: we’re curious about cats’ whiskers and giddy for guinea pigs’ teeth.
The dogs we know and love have plenty of interesting anatomical features as well. Even within the species, dog bodies vary wildly from breed to breed. Though we’re able to identify many of their body parts and intuitively understand their purposes, sometimes observing a dog’s anatomy leaves us with more questions than answers.
If you’ve ever wondered how many toes a dog has, how a dog’s tail works or how good a dog’s senses are, read on – we’re about to discover the answers to these questions!
How Many Toes Does a Dog Have?
One of the first things we learn as children is how many toes we have. We use them, along with our fingers, to learn how to count, and they’re perfectly numbered for this purpose: five fingers to a hand and five toes to a foot. This symmetry may work out well for us, but what about dogs?
Take a look at your dog’s paws and you’ll see that they’re divided into four toes each. While our toes are long and adorned with nails on their tips, the dog’s toes look completely different. They’re short, packed so closely together that sometimes you can barely tell that they’re separated, and the nails curve into thick claws that protrude from the spaces in between the toes.
The Dewclaw Debacle
The four toes on a dog’s paw are located where you’d expect them to be: at the front of the foot, just like ours. But look to the side or back of your dog’s front foot and you’ll probably see a small nub with a claw protruding from it. Some dogs, such at St. Bernards and Portuguese sheepdogs, have this feature on their back legs as well; in fact, many of them have two!
Though it’s not obvious at first glance, this little anatomical oddity is actually a toe as well. It’s called the dewclaw, and at first glance it doesn’t really seem like it should count as a toe; it usually doesn’t touch the ground when the dog walks, and many times it appears only loosely attached to the foot. So what exactly is the dewclaw and what’s the point of it?
The dewclaw used to be a fully functional toe like its four footmates, but over many generations it became less and less useful, eventually atrophying and getting relegated to the back of the foot. Extra digits are useful for handling objects, but since dogs didn’t need to hold things they didn’t really gain any extra functionality from their “thumbs.” Dogs were built for endurance and speed, and though the weight of a single toe may seem negligible, evolution determined that it was preferable to save a few grams and ditch the toe.
So the toe became vestigial, a remnant of anatomies past, present but not really necessary for anything. Over the years it shrunk and relocated to the back of the foot. Some dogs still have bones in their rear dewclaws, but many don’t – another casualty of evolutionary streamlining.
A Functional Fifth Toe?
Because many people don’t perceive the dewclaws, especially the rear ones, as having any purpose, they choose to have them removed from their dogs during early puppyhood. Some do so for aesthetic reasons while others see the removal as precautionary; a boneless dewclaw can flop around, getting caught on things and causing painful injuries. But some dogs are able to take advantage of their dewclaws; in fact, a few are able to actively use them!
Although dewclaws don’t touch the ground while the dog is walking, it’s a different story at higher speeds. Running causes more of the dog’s leg to contact the ground, and when the dewclaw meets the earth it acts just like a regular claw, providing traction and grip. Herding dogs in particular make excellent use of their dewclaws as they regularly make tight turns at high speeds; the extra stability provided by the dewclaw can make all the difference in these situations.
Some dogs are actually able to move their front dewclaws enough to use them as very rudimentary thumbs, helping the dog grip toys and bones. Their unique position on the foot makes them useful for scratching tough-to-reach places like the ears and nostrils. And some breeds such as the Catahoula leopard dog use their dewclaws to help them climb trees!
How Does a Dog’s Tail Work?
Anatomy of a Tail
Not all dogs have tails – some are naturally tailless while others have their removed, or docked, at a young age – but for those that do, tails are a vital part of their lives. These flexible, expressive appendages are used for communication, balance, movement and, as anyone who’s seen a dog chasing its tail can attest, fun.
The tail is actually an extension of the spine and is made up of six to 23 bones depending on length. These bones are called caudal vertebrae, a name you might partially recognize since the spinal bones are also called vertebrae. Cushioning disks in between the caudal vertebrae stop the bones from grinding against each other, lending the tail some extra protection and flexibility.
Surrounding the caudal vertebrae are scores of muscles that can be expanded and contracted with high precision. These muscles give the dog the ability to fine-tune the position of its tail and perform a variety of complex movements including that most famous of motions: the wag.
Tail Me About It!
If dogs could talk, or write, or draw pictures, there would be far fewer misunderstandings between us. As it is, though, the best way our two species can communicate with one another is by using body language. For a dog, a good portion of body language is performed with the tail.
A wagging tail is widely understood to indicate happiness and excitement. When you get home after being gone all day or reach towards the treat jar, you’ll probably be met with a wildly wagging tail. But you may not know that wagging isn’t always a sign of a good mood; in fact, sometimes it can mean just the opposite.
Tail wagging generally indicates some kind of intense mood, be it positive or negative. Agitated dogs sometimes wag their tails as well, which can be confusing. You’ll have to read the rest of the dog’s body language to determine its mood; happy dogs will have relaxed faces while annoyed dogs may have dilated pupils, pinned ears and clenched jaws.
Frightened dogs will hold their tails down and tuck them in between their legs. This is a defensive measure intended to protect the tail from potential harm but it’s also a great indicator of a dog’s sense of safety and security. If your dog’s tail is tucked down, something is making it very uncomfortable.
Balance and Movement
When a dog reaches high speeds, even the slightest mistake could send it tumbling to the ground, putting it at risk of injury. Keeping your balance on uneven terrain is tricky even when you’re not at top speed, so what’s a dog to do? Use its tail, that’s what!
Thanks to the precise control it has over its tail, a dog doesn’t need to worry about weight distribution or the effects of gravity as it rounds tight corners and dashes down hills. The tail serves as a counterbalance, allowing the dog to make reflexive split-second adjustments to its momentum and center of gravity. Tailless dogs can adapt and learn to balance as well, but there’s simply nothing quite like the built-in balancing bar that is the canine tail.
How Good Are a Dog’s Senses?
We share the five basic senses with dogs: sight, hearing, smell, taste and touch. But how does your dog experience these senses and how do they compare to yours? Let’s have a sensory showdown and find out whose senses are more powerful – and why.
The widely-believed myth that dogs see only in shades of gray is simply untrue, although humans do have them beat as far as color vision goes. Eyes contain special cells called “cones” that allow various wavelengths of light through. Each color has its own wavelength, so it can’t be perceived if an eye lacks the corresponding cone.
Humans with full color vision have three types of cones: red, green and blue. All the colors we see are some combination of these three colors – pretty amazing if you think about it!
On the other hand, dogs only have two cones: yellow and blue. All the other colors we see appear as some shade of yellow or blue to dogs. It may seem like dogs drew the short straw here, but they do have an upper hand in one type of vision: night vision.
Dogs have far higher concentrations of rod cells than we do. Rod cells detect shades of black, white and gray as well as movement. At night, when everything becomes monochromatic and details start to get fuzzy to our eyes, dogs are at the top of their vision game, barely bothered by the lack of light – or the lack of color.
Dogs don’t start out with good hearing; in fact, they’re born deaf and remain that way for the first three weeks of their lives. But don’t let these puppies fool you, because before long they’ll be using those ears like masters, hearing sounds from over a quarter of a mile away. With 18 muscles in each ear to fine-tune the position and amplification, dogs would be auditory superstars even if they couldn’t move their ears at all: they can hear frequencies that range from 67 to 45,000 Hz.
By comparison, humans are basically… well, puppies. We can hear sounds between 64 and 23,000 Hz, lacking nearly half of the high end perception that dogs have. This is why we use dog whistles to train our pups – we can’t hear those squeaky tones, but our dogs sure can!
Touch is a tough sense to quantify, but humans and dogs experience it very similarly. It’s the very first sensory input a newborn puppy receives – unable to see or hear, the puppy relies solely on its instinct to seek out its mother’s warm touch. A mother dog will spend much of her time licking and cuddling her babies, forming a connection and communicating with them through touch.
Many of the same touches feel nice to both humans and dogs. Who doesn’t enjoy a firm but gentle back rub or head scratch? Physical closeness to loved ones seems to be equally important to both of our species; nothing says “I love you” like a hug and a cuddle, no matter what kind of animal you are.
As you may have noticed from your dog’s questionable dining choices, taste is a dog’s least developed sense. With around 1,700 taste buds located mainly on the tip of the tongue, dogs do experience the same tastes that we do, but they perceive them much differently. They don’t like salt near as much as we do and they’re able to taste water – not just pick up hints of flavor in it, but really taste it!
We’ve got over 9,000 taste buds on our tongues, so it’s easy for us to claim that we have more refined palates. All those fancy dog food flavor descriptions are probably irrelevant to dogs, but if we tried a bowl of kibble we’d probably be able to distinguish the chicken from the carrots. Given our reluctance to do so, perhaps we should be thankful that our dogs don’t have very discerning taste buds – rather than getting bogged down in the nuances of flavor, they just dig in!
If you’ve ever watched a dog sniff out a toy, a treat or a squirrel, you’ll already know who wins this round of the sensory showdown. A dog’s wet nose is like a magnet for scents, containing between 125 million and 300 million scent receptors. Once a scent is picked up it’s straight to the olfactory bulb, a special scent processor that occupies up to one eighth of the brain!
So how do we stack up? Well, for starters, our noses contain around five million scent receptors, so at best we’re 25 times worse at smelling than dogs; compared to a bloodhound, the breed with the most powerful nose, we’re 60 times worse. Our olfactory bulbs are 40 times smaller proportionally than dogs’ – even if we had more scent receptors, we wouldn’t be anywhere near as sophisticated at processing and retaining smells as dogs are.