If you've spent any time around horses, you probably know the basics: poll, withers, barrel, stifle, hock, fetlock.

But horse anatomy gets a lot more interesting once you get past simply memorizing the names.

Why do we measure horses at the withers? Is a horse's knee actually a knee? What exactly are those weird crusty things on their legs? And why can a horse breathe through its nose…but not its mouth?

Here are some of my favorite fun facts hiding behind the basic "parts of the horse."

A Horse's "Knee" Isn't Really a Knee

The joint we commonly call the horse's knee is actually the carpus—and anatomically, it's more comparable to our wrist.

The horse's actual equivalent of our knee is the stifle, located high on the hind leg.

And the hock? That's comparable to our ankle.

It sounds strange until you remember that horses essentially stand and move around on their toes. Their limb anatomy has evolved for efficient movement, which means the bones and joints don't line up quite the way our brains expect when we look at them.

There's Very Little Muscle in the Lower Legs

Look closely at a horse's legs below the knee and hock and you'll notice something interesting: there isn't much muscle down there.

Most of the muscles responsible for moving the lower limb are located higher up, with long tendons extending down the leg.

It's part of what gives horses those beautifully slender lower legs—and contributes to an incredibly efficient system for locomotion.

Horses Don't Have Collarbones

Unlike humans, horses have no clavicle, or collarbone, connecting the front legs to the skeleton.

Instead, the horse's body is suspended between the front limbs by muscles, tendons, ligaments and connective tissue. This arrangement is sometimes called the thoracic sling.

In other words, there's no traditional bony joint attaching the front leg to the rib cage.

That's one reason the muscles around the chest, shoulder and withers matter so much to the way a horse carries and moves its body.

The Withers Give Us a Consistent Place to Measure Height

We measure a horse from the ground to the top of the withers because they're a relatively fixed anatomical landmark.

The horse can raise, lower and stretch its head and neck dramatically, but the height of the withers stays essentially the same.

In the United States, horse height is traditionally measured in hands, with one hand equal to four inches.

So a 16-hand horse stands 64 inches at the withers.

A Horse's Tail Is an Extension of Its Spine

That flowing tail isn't just hair attached to the horse's backside.

Inside the dock are coccygeal (caudal) vertebrae that continue from the vertebral column. The long tail hairs grow from the skin surrounding this bony structure.

So yes—the tail really is an extension of the spine.

And that's one reason tail position and movement can tell us quite a bit about what's happening through the horse's body.

You Can Watch the Flank to Count Breaths

Want to check a resting horse's respiratory rate without putting your hand near their nose?

Watch the flank.

Each rise and fall associated with a complete breath can help you count the horse's respirations. A horse's breathing rate can give us useful information about exertion, heat, stress and overall condition.

It's one of those simple anatomy facts that becomes genuinely useful around the barn.

Horses Are Obligate Nasal Breathers

Humans can switch between breathing through our noses and mouths.

Horses can't.

A horse is an obligate nasal breather, meaning air normally travels through the nostrils rather than the mouth. The anatomy of the horse's soft palate separates the oral airway in a way that's very different from ours.

That's especially impressive when you think about the enormous amount of air a galloping horse needs to move.

Chestnuts Are Surprisingly Individual

Those rough, callus-like patches on the inside of a horse's legs are called chestnuts.

Every horse has its own distinctive chestnut shapes and patterns, and they can vary considerably from horse to horse—and even from leg to leg.

You'll sometimes hear much more dramatic stories about what chestnuts supposedly are, including the claim that they're scars from where a foal's legs were attached in the womb. That's a fun piece of horse-world folklore, but it isn't how equine development works.

Their exact evolutionary history is much more interesting: chestnuts are generally considered vestigial structures, remnants of anatomical features that changed as the ancestors of modern horses evolved.

And Then There Are Ergots

Chestnuts aren't the only strange little structures on a horse's legs.

The ergot is a small, often overlooked callus-like growth located near the back of the fetlock and partially hidden by the fetlock hair.

Like chestnuts, ergots are considered vestigial structures.

Some horses have obvious ergots. Others have tiny ones you might barely notice unless you go looking for them.

Once you know they're there, though, you'll probably start checking every horse you meet.

The Coronet Band Is Where the Hoof Begins

The coronet band, or coronary band, is the area where the hairline meets the top of the hoof.

It may look like a simple border, but it's incredibly important: specialized tissue in this region produces the hoof wall.

The hoof wall then grows downward from the coronary band—which is why damage in this area can sometimes create a visible defect that slowly travels down the hoof as it grows.

The Crest Is More Than a Pretty Neck

The crest follows the upper edge of the horse's neck, but underneath that beautiful topline is some important anatomy.

The nuchal ligament helps support the weight of the horse's head and neck, reducing the amount of muscular effort required to hold them up.

Considering how large and heavy a horse's head is, that's a pretty useful piece of engineering.

Learning the Parts Helps You Understand the Whole Horse

Knowing where the poll, loin, stifle or fetlock is isn't just about passing a horse anatomy quiz.

Anatomical language gives us a common way to talk about movement, conformation, injuries, grooming, tack fit, training and veterinary care.

And once you start understanding what lies underneath those familiar landmarks, the horse becomes even more fascinating.

The next time you're standing beside one, see how many parts you can identify—and then look a little closer.

There is a lot of interesting anatomy hiding under all that hair.