Tuesday, November 29, 2016

Equine Anatomy and Biomechanics: A Primer of Equine Engineering for Advanced Students Part XVI - Myths


Hello! This is part sixteen of this 17-part series on equine anatomy and biomechanics for the intermediate student. Refer back to Part 1 to start. Truly, we've covered a lot of material to get here and we have just a bit more to go. Specifically, we'll be discussing myths now, a subject that's just as important as the truths we've already discussed. Why? Well, because there exist many myths regarding the equine form and unless we're aware of them, we risk parroting them in our work...and that can compromise it.

Myths abound in the horse world largely because science hasn't really taken a hard, objective look at the animal until relatively recently. It's so odd that an animal so pivotal and ingrained in human civilization could be taken for granted so profoundly! Indeed, modern science is revealing just how much we didn't know about horses, and how much we've assumed quite wrongly. No wonder horses are notorious for going lame! It's a miracle any remain sound at all. It only proves what a sturdy, adaptable animal he truly is. But thanks to new thinking and new technology, we're starting to better understand this complex and fascinating animal we've worked with for so long. Who knows what future studies will reveal! Whatever it is, it will help us better preserve and foster the well-being of this incredible creature.

So without further adieu...let's get to it!


The Arabian "jibbah," or bulged forehead, is often claimed to be a function of a larger braincase, supposedly explaining the breed's keen intelligence. But we have to remember where the breed originated: the desert. And many desert mammals have domed foreheads from the donkey to the hemonids. Even foals often have domed foreheads. In other words, the jibbah isn't something unique to horses, or Arabians. It's simply a function of the sinus, an expanded cavern to add moisture and coolness to the incoming hot, dry air to protect the lungs. That's it. Nothing fancy. Simply a dry environment adaptation.

The jibbah also shouldn't be extreme, but at most only moderate. It also shouldn't be accompanied by a "crunched down" nasal bone, as we so often see with extreme, "classic" Arabian heads, or "seahorse heads," or "dolphin heads." Instead, the jibbah should only be a slight bulge of the forehead accompanied by that concave axis of the head, everything else being normal. This is because an "extreme" Arabian head causes pain, and seriously impairs performance by causing inflammation of those sinus tissues as well as causing bad dental and biting-up problems. These are things that severely compromise a breed renown for its vitality and endurance, so why exalt them? Remember how fast the air comes rushing into and out of the head at speed? Well, when that air hits the "ledge" caused by a strong dish, that causes the tissues to become painfully irritated and even bleed. This is why Arabians with "exotic" heads aren't typically seen doing anything but being "lawn ornaments" or at best, doing the "softer" types of performance like Western Pleasure rather than more energetic forms such as endurance racing, flat racing, and sporthorse discplines. It's also why the incidence of wheezing and gruntling has been on the rise, especially with Arabian halter horses, a sad testament to how far off-track Arabian ideals have become. This means validating such a head becomes an ethical question for sculpture, not an aesthetic one.

Arabians can show a great deal of "type" even with a straight profile, so a moderate or little bit of a dish is more than enough to get the point across yet still remain honest to this magnificent, athletic breed.

Bone Density

It’s a common misconception that certain light breeds don’t require a lot of "bone" since theirs is somehow intrinsically denser due to the historic, rougher conditions in which they were developed, such as the Arabian. As a result, these breeds are suffering from a diminishment of their bone in the belief they can "lose some" and still remain sound, creating legs that are too slender and fine. But the truth is that it’s not a good idea to have bone denser than normal since this is actually a disease that results in brittle bones prone to breakage or fracture. What we want is a normal bone density adequate for the animal's mass, right?

And that's where the confusion comes in...mistaking density for mass. Biologically speaking, nature designed the equine to be basically no larger than an Arabian, about 15hh. There are exceptions here and there during evolution, but overall, this is about the size that works best for the equine blueprint. Why? Well, because bone density decreases with each unit of mass in the equine. That's to say, the more massive the horse, the more bone density they need, so if it doesn't adequately increase as the horse becomes more massive, then bone density goes down in relation to the mass of the horse. And this is exactly what happens with the larger or taller breeds, which is why they have a tendency towards unsoundness in comparison to smaller-stature breeds. They simply need more bone to accommodate their greater mass. This is also why the Arabian and pony breeds are famous for their soundness...they have enough bone for their mass. They're exactly what nature intended for the equine blueprint. They don't have greater bone density then...they have normal bone density! They just have less mass. It's the larger breeds that have abnormal density, being too low for their increased mass.

In actuality, all breeds should have ample bone of normal density that’s proportional to the individual’s weight and height. That's about 8 inches of bone per 1,000 lbs. On the drafter in particular we see a great disparity between the required bone and their actual bone. Can you imagine 16 inches of bone for a 2,000 horse? Those are some huge legs, ones that we have yet to find in most drafters. This is one of the reasons why drafters are designed to walk to do their work. But it's also why it's so alarming to have inadequate bone on sport horses, especially those over 15hh. Bigger size doesn't necessarily mean better.

Small Dainty Muzzle

In Arabian breeding, the want of a small, delicate muzzle is a common standard. The idea is that the muzzle should fit inside a teacup, or the "teacup muzzle." However, the original meaning of the "teacup" idea was that the muzzle be delicate and dainty enough to sip from a teacup, not fit into one.

The horse requires a muzzle of adequate size to make room for all the big teeth he'll need to survive. He also needs large nostrils and large nasal passages to provide adequate air during exercise. Yet too many modern horses possess muzzles that are far too small, a particular fault with draft horses as breeders try to prettify their heads, or as artists misinterpret correct drafter construction. So artists should avoid sculpting tiny muzzles on their sculptures in order to validate correct biological structure. There's nothing coarse about a biologically sound muzzle.


Some folks confuse the crest with the cervical vertebrae column, as though the column laid beneath the crest, forming it. However, the equine neck, as we've learned, is an S-shaped curve starting deep within the neck about mid-shoulder and snaking its way through the neck up to the back of the skull. This gives the neck a tremendous ability to compress or stretch, something that wouldn't be possible with a cervical column laying beneath the crest.

With this understanding we can avoid many of the errors we see in equine sculpture regarding the neck. For example, we can avoid creating "crane necks," where the neck is unnaturally elongated in an arch more like a mechanical crane than an actual equine neck. Or when the neck starts at the tip of the wither rather than exhibiting that dip where it connects to the wither. We can also avoid the similar "rainbow neck," that common way to arch a neck that creates a rainbow-like even tube rather than the nuanced curves and angles correct for an actual arched neck. We can also avoid the "giraffe" neck that's far too long when we understand the nature of the S-shaped curve that elongates and compresses the neck depending on posture.

Long Toe-Low Heel (LT-LH)

When we understand how the horse moves and how his feet are supposed to be structured, we come to see that the many trimming philosophies are misguided. One of the most common is the idea of the LT-LH trim. Here the toe is left long and the heel is trimmed short, creating a "flipper-like" foot. The belief here is that this configuration creates a long and low "grass-clipper" stride, or that it increases speed for a race horse (the LT-LH trim is ubiquitous in racing, and also in the Quarter Horse and draft horse industry, even with halter horses).

However, as many studies done by Hillary Clayton have demonstrated, this trim does none of its purported benefits but actually causes unnatural stresses on the foot that eventually lead to lameness or gait or hoof problems. Tendon problems and contracted heels are common results, for example. It's also been strongly implicated in navicular syndrome. Instead, the toe should be short with enough heel to support the animal. With this type of foot, we actually achieve a longer, lower, freer stride, since the horse is allowed to move normally rather than wearing a pair of "flippers." It also improves the stride of a race horse. With this knowledge then, we can therefore avoid sculpting LT-LH feet on our sculptures to advocate healthy feet.

Mechanical Sinker

The pointed tip of the coffin bone (at the front) should be level or slightly above the coronet. This is the proper biologically-designed intention for a healthy foot. However, farriery has routinely carved the sole to be too thin when it actually should be quite thick (up to 1") to push the coffin bone upwards into this configuration and allow the hoof capsule to "sink," creating a short foot. When the sole is too thin, however, the coffin bone sinks into the foot because it has no support, its tip sinking below the coronet band, sometimes markedly so. This inhibits this joint from properly functioning inside the foot, and it causes lameness, bruising, and pain.

We can see a mechanical sinker by its long hoof capsule, and in X-rays. Many times the horse's foot will become "numb" and that interferes with proprioception, or the way the horse feels the ground and keeps track of where his feet are, which can cause the horse to become less nimble and light-footed.

Many sculptures have mechanical sinker feet, most commonly seen in their long hoof capsules with long heels. Keep the feet short, the toe short, and the heel of moderate length to help ensure sculpting a sound foot.

Hoof Size

It's often believed that hoof size is measured by the length of the hoof capsule, but science has proven this is an error. Instead, hoof size is measured by the circumference of the coronet band, i.e. the overall size of the hoof capsule, not its length. 

As for its length, generally speaking there should be a basic length (measured from coronet to toe) of the hoof capsule per pound of horse to maintain a healthy foot:

  • 3 inches for an 800-900 pound horse
  • 3.25 inches for a 950-1,050 pound horse
  • 3.5-4 inches for a 1150-1,250 pound horse

Also keep in mind that certain registries regulate hoof length. For example, the Arabian registry prohibits a toe that's longer than 4 1/2", including the show and pads.

As for size, science has provided a formula we can apply to our sculptures:

(12.56 x W) = R


The sum (R) is the ratio of the body size to foot size, described in pounds per square inch. (R) should amount to no more than 78, or 78 pounds per square inch, the maximum loading for an average performance horse. Statistically, ratios higher than 78, particularly those higher than 83, tend to develop lameness issues.

This is how we apply the equation:

  1. Measure the circumference of the hoof at the hairline, right below the coronet, in inches.
  2. Multiply the horse's weight in pounds by 12.56 and hit the "equals" sign.
  3. Divide this first number by the hairline measurement in inches, and hit the "equals" sign.
  4. Divide this number again by the hairline measurement (in inches) and hit the "equals" sign. 
The answer should be between 68 and 78. If the number is higher than this range, the horse's mass is too much for the feet. Scaled down, we can use this ratio by estimating how many inches our sculpted coronets are and then estimate the weight of our sculpted horse as if he were alive, and then plugging the numbers into the equation.

This means that hooves with long hoof capsules may not represent large hooves if their circumference is too small (as well as being a mechanical sinker). It also means that hooves that have short hoof capsules but with a sizable circumference to their coronets are good hooves, so we shouldn't let length throw us off. Indeed, a quality foot has a short hoof capsule, large circumference, and a short, rounded toe with adequate heel. The sole should be thick, vaulted, and smooth, and the frog large, wide, and extending to about 1" from the toe. For more information on quality hooves, please refer to my blog series, Steppin' Out: Hooves from an Artistic Perspective.

The Modern Horse

The horse of yesteryear, when he was a utilitarian animal as opposed to a sport, show, or recreational partner, was very different in build. Necks were shorter, heads were bigger, bone was more ample, hooves were bigger, and he was overall studier in build. In short, he was "coarser" by modern standards, but he was a "using" animal nonetheless.

It's been the pressures of art that has contributed to the shaping of modern standards of beauty. Indeed, we see the exact opposite of the everyday working horse exalted in many popular paintings and in the works of many popular artists. Long necks, small heads (sometimes markedly small), light bone, and small hooves are almost characteristic of art work in the past and present. The Victorian age, with its ideas of the eugenic "purebred" standards of beauty and social class put an inordinate amount of pressure in the modern age to adhere to these standards of beauty and purity, too. Indeed, it was a mark of "high blood" that a horse approach these troublesome ideals.

As a result, we've seen the results in the breeding shed. Necks have gotten longer, heads smaller, bone lighter, and hooves smaller, all of which compromise the working nature of these animals. It's no wonder so many are "lawn ornaments."

As artists we hold the grail in how this animal is portrayed. We shape the ideals many breeders aspire to as they shape their particular herds. Unless we understand biological functionality, we risk perpetuating problematic messages, and end up contributing to the ongoing problem of unusable horses. We have a responsibility. We can't just recreate what we see since what we see may be pathological, even if the animal has won great awards, is popular for breeding, or is regarded as an ideal standard. We need to know the difference between what's popular and what's functional. And there's nothing ugly about functionality!

Less Vertebrae

It's often believed that Arabians have one less vertebrae, as a point of breed uniqueness. However, many Arabians have a normal number of vertebrae despite being purebred. So this is a myth. And the truth is that many breeds derived heavily from Arabians, such as the Thoroughbred, can also have one less vertebrae, so it's not something unique to Arabians.

Wry Tail

We find in many conformation books the idea of a "wry tail," or a tail bone held off to the side, sometimes clenched to the buttock. The idea purported here is that this is a conformational fault, as though this posture was something bred into the animal.

However, in reality, a wry tail indicates bad posture brought on by poor riding technique. The animal is clenching his back and is moving crooked, and that manifests as a tail held and clenched to the side. It indicates bad riding, not bad conformation. And even when the animal is rehabilitated, he can still hold his tail this way, it having become habitual.

Big "Buggy" Eyes

We find in many Arabian circles the desire for a big, bulging eye, thinking this means the eye is bigger and more beautiful. However, while a big eye is desirable, it shouldn't "bug out." This indicates hypothyroidism, and it's no mistake then why this condition has been growing in the Arabian population as a result.

We want horses with a normal protrusion of their eyes despite size, so attending to this in sculpture helps to promote healthy visuals.

Pulled Manes and Tails

It's been a common belief that horses don't feel the process of "pulling" manes and tails to thin them out, such as we see when the mane is cropped short. However, modern studies have demonstrated that horses do, indeed, feel the entire process, and that it's quite painful. This might give us pause when we depict such types of manes and tails. It's also hoped that grooming practices switch to clippers and razor-cutting to achieve similar results and stop with the "pulling."

The Big Lick

Many in the Tennessee Walking Horse industry involved with Big Lick Showhorses try to convince us that the results they get are natural; that the resultant movement is a natural way of moving. However, recent court cases have revealed under oath that all horses demonstrating such movement have been "sored." This is something every equine anatomist already knew, knowing that equine biomechanics cannot produce such movement without coercion. And all those contraptions on their feet from chains to "packages" only serve to deliberately cause more pain by acting on the chemically burned skin to compel the horse to lift his feet even higher. Big Lick Showhorses often have big beefy chests, too, due to overdevelopment of the Shoulder Sling caused by the weight of those packages.

That means that every artistic representation of The Big Lick is a depiction of flagrant cruelty, and that may compel us to think twice before validating it in our work. It's not natural. It's not normal. It's not bred-in. It's flat-out abuse, plain and simple. If only horses reacted to hoof pain by dragging their feet instead of lifting them higher. *sigh*

Cat-Clock Eyes

The horse's eyes can move in unison (for example, eye whites at the front of both eyes), but contrary to common belief, they can also move like a "cat clock" (where eye white is at the front of one and and in the back of another). The horse is predominantly dependent on vision for survival, so it makes sense that his eyes could move in various ways. Yet this doesn't mean he can move them like a chameleon, but that they have a greater range of options than previously thought. 

Horses also have a special muscle connecting the orb to the back of the socket, which they contract when experiencing great fear or medical distress (like convulsions caused by tetanus). This muscle pulls the eye back further into the socket, creating a distinctive sunken-in look to the eye compared to the surrounding lids. So we need to be very careful when sculpting our eyes to make sure we aren't representing something we'd rather not.

Even Curve To The Spine

As we see in many horsemanship books, the horse is said to be able to bend evenly around a turn, as though his entire spine could curl around in an even half-circle. However, this isn't the case as the equine is mechanically incapable of such a bend as we've learned in this series.

Lateral bend of the torso occurs between T9 and T16, the front aspect of the spine. The loins aren't designed to laterally bend, but to coil, so minimal, if any, lateral bend occurs there. In turn, the horse shifts his ribcage to the outside of the bend, to "ride the rim" so to speak. We also learned that the pelvis cannot articulate with the spine laterally, but only as a hinge joint with the LS-joint. So all this, with the lateral bend to the neck, creates the illusion of an even curve. However, the horse actually bends as a series of kinks at the neck and the front of the torso, consistent to his structural biomechanics as we learned in the torso section of this series. 

Artists who sculpt a laterally bending rear thoracic section, loin, or pelvic sections, or even a bend at the LS-joint or sacrum, are actually creating a broken back, so we need to be careful when we sculpt our pieces to avoid this common mistake.

Sickle Hocks

Sickle Hocks aren't always genetic! Sometimes they're caused by poor riding technique that compels the animal to move with a hollow back. This can cause a misalignment in the hindlegs, causing them to assume sickle hock angles. With proper rehabilitation, those hocks can be made to straighten out to attain the natural, proper alignment of having the back of the metatarsal being plumb with the point of buttock.

A Good Foot

The adage, "no hoof, no horse" remains true today as it ever did. However, science is revealing just how much we've gotten wrong about it! It's imperative then for an equine artist to understand what constitutes a good foot in order to promote responsible visuals in artwork. 

Also, a horse's foot will customize itself to its lifestyle and natural habitat which is why the desert feet of Mustangs are different from the marsh feet of Camarque horses which are still different from the sandy feet of beach ponies. Or even more subtly, why the feet of horses worked on roads is different from the feet of horses worked on groomed footing. There isn't "one size fits all" foot, but a spectrum of possibilities. This means we need to take the imagined lifestyle and habitat of our sculptures into account in order to sculpt an accurate foot.

It's a complex subject, but one important to understand. For more detailed information then on what makes a good foot, please refer to the blog series, Steppin' Out: Hooves From An Artistic Perspective.

Close Hocks

Being "close hocked" isn't the same as being "cow-hocked." Being c
ow-hocked is where the metatarsals are oriented away from the median, when seen from the rear and standing square. In contrast, "close hocks" have metatarsals going straight down, in plumb and angled outward with the rest of the leg. In fact, many drafters, especially the Clydesdale, are expected to be close hocked to accommodate walking within the crop rows. Don't confuse the two.

"Straight Legs"

Many people confuse the issue of straight legs when it comes to evaluating the conformation of the horse. Indeed, some confuse them so much as to favor calf-knees and post-legs over correct ones.

For example, in the forelimb, the carpals should align to the metacarpal at 90˚, creating a look that appears "over at the knee" to many who don't understand this proper alignment. Likewise, the back of the metatarsal should be plumb with the point of buttock, regardless of standing stance, being neither post-legged or behind the plumb, or "camped out."

What's more, many believe "straight legs" has a literal connotation for the hindlimb, meaning that the entire limb from stifle to toe should be oriented straight forwards when standing, as seen from the back. Instead, the normal, correct orientation is an outward angle from stifle to toe, away from the median, to allow the stifle to pop around the wide barrel better. 

These flaws are quite common in equine art, so avoiding them promotes more responsible messages.

Growth Plates

In the immature horse, bones contain growth plates, zones of cartilaginous “bone” not yet ossified and still containing living osteoblasts. They’re located behind either end, between the diaphysis and the epiphysis of the bone. These are the only places where the bone can grow longer as the horse matures. The bone must also grow in diameter to maintain a strong proportion to the increasing length and this is achieved by the periosteum. Therefore, length is added by the growth plates and width by the periosteum in a lamellar fashion, like growth rings on a tree. 

A common fallacy is that only the radius has a growth plate, one that closes at about two years old, making the horse presumably ready to ride. But in reality, all the bones in the horse have growth plates that mature at rather predictable rates. In fact, the most important bones mature the last! Ultimately, this means that despite the rhetoric, there’s no horse of any breed at any time that's mature at two years old. All horses mature at six years except those who are very tall or have very long necks, maturing more around eight to nine years old. The closure schedule of the growth plates starts first on the lower limbs then ends in the spine. However, the coffin bone has full closure at birth and although it will gain width as the horse matures, it has all the height it will ever have as an adult. 

Anyway, the ossifying schedule is as follows:

  • Birth to six months: the top and bottom of the short pastern bone. 
  • Six months to one year: the top and bottom of the long pastern bone. 
  • Eight months to a year and a half: the top and bottom of the cannon bones.
  • One and a half to two and a half years: the carpus
  • Two to two and a half years: the bottom of the radius and ulna.
  • Two and a half to three years: the top of the radius and the top and bottom of the tibia.
  • Three to three and a half years: the top and bottom of the humerus.
  • Three and a half to four years: the bottom of the scapula.
  • Four years: the tarsals.
  • Three to three and a half years: the bottom of the femur.
  • Three and a half to four years: the neck of normal length. This can be up to eight years for long-necked types.
  • Three to four years: the growth plates in the pelvis.
  • Six to eight years (six months more for a male horse): the vertebral spine, with the last cervical vertebrae maturing the latest. 
Actually, the incremental growth in height in the limbs is only approximately 20% more between birth and age six. A horse will grow upwards until about three or four years old, but will continue to grow lengthwise until about six years, or even eight years with tall or long-necked types. So, really, foals aren’t long-legged, they're short backed!

The spine matures last, making its bones and plates vulnerable to slippage or disjoining if the youngster is ridden too young. The data with ridden two year olds or pre-two year olds (such as in futurities for racing, cutting, reining, etc.) doesn’t indicate much problem with the legs at that point (though it may show up when the horse is older since there isn’t much long-term follow-up data yet). But slipped vertebrae and growth plates can permanently injure the horse. Sometimes therapies can help the situation, such as with loin slippage, but slippage at the sternum is nearly impossible to fix. Yet only about 2%-4% of these ridden youngsters suffer from slippage, a relatively low number. In reality, the biggest problem with riding a horse too early is to teach him early on to automatically brace his back and neck muscles the instant he’s mounted because he'll instinctively protect his vulnerable spine. So there’s no good reason ever to ride a two year old horse. It’s much wiser to wait until after four and ideally six years when his spine has matured. And those preliminary four or six years are the ideal time to teach him all about manners, lounging, driving, therapeutic tricks, clipping, trailering, washing, and all those other things he’ll need to know. 

The location of the growth plates in mammals (and birds) is actually a revolutionary development that might have given mammals an evolutionary edge. Because the mushier growth plates are sandwiched in bone, the joints are precisely formed at birth, resulting in immediate motion, agility, and speed. However the trade-off is that growth is stopped after a period of time so the mammal cannot grow indefinitely. In contrast, the ends of dinosaur bones were mushier since their growth cartilage was immediately behind the hyaline cartilage of the joint. So while a dinosaur could grow almost indefinitely to tremendous statures, his joint design was imprecise. So it’s hypothesized by some that most dinosaurs really couldn’t move fast or be terribly agile, otherwise they would’ve crushed their joints under their own weight. 

Some bones in the horse may also fuse with wear or maturity such as the splint bones and some in the hock or lumbar. They may also fuse because of poor horsemanship, such as with "kissing spines" of the spinal column. Any which way, bones are rarely straight, but are typically curved to accommodate forces of mass, torque, and the mechanics of motion. A bone certainly isn't a cold, static piece of anatomy, but is organic, adaptive, and alive. It’s important to remember that every aspect of the bone has evolved for a functional reason whether for flesh attachment, protection, or support of fleshy structures or to act as lever-like mechanisms. It also changes shape and characteristics depending on the forces visited upon it. To understand the nature of his bones is to establish a good basic understanding of his motion, his evolution, and how it affects his lifestyle.

Conclusion to Part XVI

Understanding the nature of myths and misinformation surrounding horses arms us with knowledge that informs our art work. Informed art is powerful art...it's an advocate for this animal rather than just a superficial admiration. When our art has this kind of authority, it transcends simply being something "pretty" and becomes something provocative and meaningful. The horse is unable to speak for himself, and as artists, we can think of ourselves as his voice, his conduit for connection beyond superficiality. We can dig beneath the surface to get to the gist of the matter. Approach our work in this light, and we gain a new insight not only into our own motivations, but empower of our own sculptures.

In the next part, the final Part XVII, we'll wrap up this lengthy series with some additional observations. More than anything, it's hoped this series has given us pause to rethink what we know and assumed, and perhaps inspired us to take up the torch of pro-active education to learn even more. The horse is an unfolding mystery today thanks to renewed scientific research, and what science has been revealing is both fascinating and troubling. We artists stand in a unique position to spearhead these new discoveries freely and without hinderance of obsolete convention through out work, and so learning about them and infusing them into our clay becomes an exciting and enlightening proposition.

So until next time...bust those myths!

"It is better to have knowledge, even if the knowledge endures only for the moment that comes before destruction, than to gain eternal life at the price of a dull and swinish lack of comprehension of a universe that swirls unseen before us in all its wonder."

~ Isaac Asimov

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