Steppin' Out: Hooves From An Artistic Perspective Part III: Structure Cont'd

Hello again! We're now at Part III of an twelve-part series exploring the equine foot as it relates to sculpture. We've explored its evolution and general biology as well as its structure, which we're continuing with this installment. Next we'll move onto its mechanics in Part IV. So let's continue, shall we?…

Bars

Part of the hoof capsule, the bars are formed by that portion of the wall that inflects backward at the buttress of the heel and which grows along on either side of the frog. They should be tough and widely spaced apart to allow for a broad, a well-developed frog. 

Traditionally perceived as villains responsible for a host of destructive effects, such as crushing of the corium, causing navicular, or creating a contracted foot, bars were often aggressively trimmed away. However, new data from varied sources is finding this perception is wrong, by clearly demonstrating that the bars actually are essential in the foot’s circulatory, weight-bearing, and energy management mechanisms. Indeed, the bars (and the heel buttresses) are located right beneath the lateral cartilages, with the frog between them, in the perfect position to help with the expansion and contraction cycle of the foot. They’re structured of wall material to effectively increase the wall’s surface area, providing further vertical support when the foot is loaded. In fact, some assert that it’s the bars (in conjunction with the heel buttresses) that may be the primary weight-bearing structure in the rear portion of the foot (Ramey, 2006). However, there’s debate as to whether the bars should always have ground contact in stance or whether they should lie at the bottom of the “vault” of the sole, along with the frog. Incidentally, the bars on an average horse will usually self-regulate either level with the sole (usually on rocky ground), or within a range of about 1/16 inch to 1/8 inches above the sole, or sometimes by as much as 1/4 inch above the sole (often on flat terrain) or even longer than the walls (often on soft terrain, like sand) (Ramey, 2006). So it seems that the appropriate amount of bar is a function of the horse’s lifestyle since they find equilibrium with the footing in a natural setting. There also is disagreement regarding the proper angle of the bars, with some stating they should be entirely upright, and others claiming they should be 45˚ to the ground, while still others contending the bars should be about 60˚ to the ground. 

New data implies that most keratinized sole growth actually comes from the bar lamellae and grows forward toward the toe and white line (Bowker, Ramey). And farriers have noted that the sole in the bar area and alongside the frog appear to produce sole material the fastest, especially if there’s been an injury to the sole, a laminitic attack, or if the sole is too thin (Ramey, 2006). Accordingly, it may be that the sole’s corium only produces enough material to help this bar-produced sole move towards the toe, like a fleshy conveyor belt. This suggests that paring down the bars actually compromises the foot’s ability to produce adequate sole or to repair itself, which has a cascade of detrimental and long-term effects (Ramey, 2006). Hopefully, research will clarify the bar’s structure and function so we can better manage domestic populations.

Sole

Normally about 30%-33% water, the sole forms the largest surface area on the distal foot and consists of two parts, the sensitive sole of the foot (internal sole) and the insensitive cornified sole of the hoof (external sole), which naturally sloughs off to maintain optimum thickness consistent with the horse’s lifestyle in natural conditions. 

Perhaps bearing the greatest brunt of indifference in traditional podiatry, the sole has been perceived largely as an incidental element of the foot. In the belief that a thick sole inhibited foot mechanics, caused bruising, or actually crushed the sole’s corium, it historically was pared down as a matter of course, creating soles far thinner than what nature probably intended. In fact, in nearly every conformational or anatomical text, thicknesses described for a “good sole” typically reflect those that are unnaturally too thin, usually offering only 3/8 inch to 1/4 inch at the heel and perhaps only 3/16 inch at the toe, demonstrating how entrenched this perspective has been. Even today, it’s still common practice to pare down the sole to “clean it up” with each trim. There’re also current theories that claim the sole on a deformed foot must aggressively be pared down to permit hoof mechanics to function properly for rehabilitation, yet this perspective is subject to ongoing debate (Strasser).

Yet new data indicates that all the ills a “too thick” sole was accused of creating weren’t only untrue, but most likely were caused by other factors. Indeed, if the myriad dissected feral and wild hooves had thick soles, but no bruising, crushing, or inhibition of foot function (Jackson, Ramey), then sole thickness isn’t the problem. What may have been happening were conventional practices of trimming and shoeing that were producing the observed damage and impaired foot mechanics. For example, an inhibition of hoof expansion caused by improper trimming or a rigid shoe disables the sole’s ability to expand at impact, thereby inhibiting the hoof capsule from making enough room for the descending coffin bone, which causes the pinching and bruising of the solar corium. Likewise, another cause may have been the habitual thinning inherent in conventional trimming that caused bruising to the solar corium from the ground. Couple this with the underdeveloped interior foot characteristic of domestic horses, and it’s no wonder why so many horses suffer mysterious foot pain. 

Indeed, new data suggests that the sole actually may have a very different role than what traditional theory has maintained and may be pivotal in our new understanding of foot function and soundness. To begin with, studies have suggested the sole corium itself may participate in the shock absorption mechanisms of the foot since it contains rich plexuses of microvessels and may even contain large amounts of proteoglycans (Bowker). Proteoglycans are a kind of protein designed to provide resiliency and resistance to compression, and typically comprise the gel matrix into which collagen fibers are encased to form cartilage. The sole also forms the largest feature on the distal foot, and incoming data is suggesting that it should be made of dense, tough, firm, thick cornified tissue, with a particularly dense callous under the coffin bone (not directly under the bone, but as a slanted extension of it) and a supportive callus all around the inner perimeter of the white line, from bar to bar (Ramey, 2005). This suggests the sole may be of a far better construction and in a far better position for weight-bearing and support of the internal foot than the frog, walls, or lamellae alone. In fact, the optimum sole thickness is now thought to be 1/2 inch to 3/4 inch, and even up to 1 full inch (in rocky terrain) to protect the internal structures, to facilitate the proper function, and to elevate the coffin bone within the hoof capsule (Ramey). Moreover, the thick sole adjacent to the bars, the thickest part of the sole often referred to as the “sole ridge,” also may help to support the coffin bone, as well (Ramey). Interestingly, the sole never becomes too thick only because it finds the optimum thickness and density, and then becomes self-maintaining so as not to pull the hoof capsule off the coffin bone. This further suggests the new data is pointed in the right direction. 

A handy way to determine the thickness of the sole (or in other words, how far the coffin bone is elevated within the hoof capsule), is to use the collateral grooves as a gauge. Happily, this method is also applicable to sculpture. Okay then…dissections of feet have shown consistently that the deepest part of the collateral grooves is typically about 7/16 inch to 1/2 inch away from the laminar corium on the bottom of the coffin bone. In turn, a healthy foot with proper sole thickness and concavity seems to have the anterior depth (around the apex of the frog) of these collateral grooves lifted upwards 5/8 inch to 3/4 inch from the ground and a posterior depth (at the heels and along the bars) lifted about 1 inch off the ground by the outer rim of sole adjacent to the white line and wall (Ramey, 2005). The additional height in the posterior area is thought to allow the best necessary depression of the sole during peak loading and subsequent expansion of the foot. As more sole grows, especially around the perimeter of the white line, the more the collateral grooves are lifted off the ground. Conveniently, these relationships can be measured with a straight edge laid across the walls by measuring from the flat edge to the anterior and posterior depth of the collateral grooves. If the measurement is less than 5/8 inch, the sole is too thin and the degree of concavity is inadequate, whereas if the measurement is more than 3/4 inches, the sole can be trimmed safely (Ramey, 2005). This method is also handy in determining if the coffin bone has sunk within the hoof capsule because it would have collateral grooves that are far too shallow (sometimes as thin as 1/16 inch!), with a long hoof capsule and “crunched up” lateral cartilages (and often contraction is present as well). And then specifically for sculpture, a large measurement could be caused by a wall’s rim that's too long in relation to the sole and frog. And, of course, for sculpture, all these measurements would have to be scaled down. 

Thought to mirror the vault on the coffin bone, the sole should be vaulted as well, with the frog at the bottom of the arch about 1/4 inch deep from the walls, to provide traction, absorb shock through downward compression, to allow the apex of the frog to surrender under the descending navicular area, to allow the hoof to expand when loaded (the 1/4 inch vault is thought to allow the hoof to expand 1/4 inch at peak loading) and to increase weight-bearing ability through an arched design (Ramey. 2005). However, even if a foot is vaulted adequately, that concavity can be disguised through adaptation to certain terrain. For example, feral horses living in rocky habitat or yielding terrain tend to have visibly concave soles, whereas hard and flat terrain (such as concrete or packed clay) tends to create soles that are “filled in” along the perimeter, giving the palmar foot a flatter appearance (and in this case, the frog tends to become higher to compensate for the additional sole material) (Ramey, 2005). All the extra tissue actually supports the internal foot with continued impact on this kind of surface. But if the collateral grooves are lifted 5/8 inch to 3/4 inch from the ground, the sole is still considered concave. This means the soles of our sculptures should reflect their implied lifestyle as well.

Lastly, the sole between the heel walls and the bars is sometimes referred to as the “seat of the corn” and is used by farriers as a landmark to gauge heel length. What’s sometimes referred to as “live sole” in trimming doesn’t necessarily mean the actual living sensitive sole, but usually refers to the new waxy sole that’s less dense and hasn’t calloused yet.

Waterline (previously discussed in Part II)

White Line

A bit of a misnomer, the white line is really a tan color. Nonetheless, it’s the junction between the inner wall and the sole and is about 1/8 inch wide, encompassing the circumference of the sole and inverting to continue along the bars to almost the apex of the frog. It’s comprised of soft horn of about 50% water, making it softer than the sole or the wall and therefore wears faster than either, creating a subtle groove around the wall and bars, which often collects dirt that stains it dark in an unwashed foot. It thus creates an obvious feature for sculpture.

The white line grows with the wall, and when the wall is firmly attached to the coffin bone the entirety of its length (i.e. tight adhesion of the lamellae), the white line is distinct, regular and tight, lacking any stretching, distortion, or weakness and is thus highly resistant to infection. Functionally, it’s thought to act as a buffer zone for the necessary tiny give-and-take movements between the wall and sole, while also serving farriery as a means to evaluate wall thickness and serve as the zone shoe nails penetrate. 

Frog

The frog is comprised of the same kind of horn as the wall, but contains more glutinous intertubular horn and approximately 40%-50% water, plus special fat glands originating in the digital cushion to keep it rubbery, pliable and elastic. It consists of two parts, the internal sensitive frog and the external insensitive frog, the latter forming the familiar “V”-shape on the foot's underside. The collateral clefts on either side of the frog form deep crevices that separate it from the bars and the rest of the sole. The frog’s central ridge (or frog stay) has a groove called the central sulcus or central cleft, and the posterior bulbs of the frog (or heel bulbs) are rounded, prominent, and divided by a shallow indentation originating in the cleft of the frog, to continue upward between the lateral cartilages. Also, the frog on the forefoot is typically broader than that of the hindfoot.

Believe it or not, the function of the frog is still unclear and subject to debate (discussed later). For example, there’s little data on the frog’s (sensitive or insensitive) actual relationship with its neighbor, the digital cushion, even though these two structures are thought to participate actively in foot mechanics. Data also is inconclusive as to whether the frog’s abundance of propioceptors helps to determine stride length and limb coordination. Furthermore, the interpretation of the frog and digital cushion as the foot’s primary circulatory pump is uncertain since plenty of domestic feet with inadequate frogs engage in high performance activities with assumed soundness (La Pierre), though it’s unclear whether this is due to other mechanisms compensating to mask what’s actually happening. 

Generally speaking, however, the frog is thought to provide traction, disperse impact and pressures through expansion, and perhaps to stabilize the digital cushion against the rotating coffin bone during compression. Benefited most by constant impact-release stimulation, the frog also may play an important role in the blood-pumping action of the foot’s expansion and contraction cycle, by alternately helping to squeeze and release the internal blood supply with each footfall. The frog also offers counter-support for the loaded foot, to stabilize and support the inner structures against the descending bony column at impact. Indeed, observations show that in those feet with fully developed inner structures, the frogs are enormous and actively contribute to weight-bearing and energy management (Ramey, 2006). Consequently, it's generally believed the frog should be long, covering at least 2/3 the distance from heel to toe, and broad, being no less than 1/2 the width of the foot (at the widest part), and also make contact with the ground, though there’s debate as to whether is should have ground contact in stance or only when loaded. There’s also debate as to whether the frog should be bulbous and protruding beyond the heels.

Regardless, the frog is another foot tissue that has suffered from overzealous trimming dictated by traditional thought. Recent studies are finding that systematic frog trimming can seriously compromise performance and soundness by diminishing its role in foot mechanics and also by creating tenderness at the rear of the foot, which sets up a cycle that destroys foot function (discussed later). New information is showing that a healthy foot always should have at least 5/8 inch to 1/2 inch of dense, calloused frog tissue so that this feature of the foot can properly do its job (Ramey, 2006). However, it can take over a year for the foot to create this kind of tissue on the frog, and constant trimming prohibits this callous from ever forming. But like with the rest of the foot in natural conditions, the frog achieves equilibrium with the horse’s lifestyle to become self-maintaining, suggesting its active role in foot mechanics.

Tendons

All the tendons in the equine foot are the fibrous extensions of muscles high on the leg and body, above the hock and knee, and act as cables, to flex or extend the limb, or to stabilize the limb in stance or motion. However, for the purposes of this series, we’ll only regard the tendinous portions of the muscle bellies and their effect on the foot, and only consider those tendons that insert on the coffin bone or 2nd phalanx for both the foreleg and hindleg.

Foreleg 

• Deep digital flexor tendon (perforans, flexor pedis perforans, flexor digitorum profundus): Flexor and stabilizer of the forefoot. It originates from three bundles from the humerus, ulna and radius and flows down the back of the leg to insert on the semilunar crest and cartilage of the fore coffin bone.
• Superficial digital flexor tendon (perforantus, flexor pedis perforatus, flexor digitorum sublimes, flexor digitorum superficialis): This tendon flexes and stabilizes the front fetlock. It originates on the medial condyle of the humerus, on top of the origin of the deep digital flexor tendon and runs down the back of the leg outside of the deep digital flexor tendon. It then forks at the back of the 1st phalanx, with each portion inserting on either side of the lower rear rim of the 1st phalanx and upper rear rim of the 2nd phalanx.
• Common digital extensor tendon (extensor pedis, extensor communis digitorum). This long servo extends and stabilizes the forefoot. It arises from the front lower shaft of the humerus and from the external tuberosity of the radius, up by the elbow joint, and flows down the side of the leg, curving to the front over the knee to orient on the front of the forecannon and the 1st and 2nd phalanges to insert on the front point along the top rim of the fore coffin bone. 

Hindleg

• Deep digital flexor tendon (flexor pedis perforans, flexor digitorum profundi, flexor digitalis pedis profundus, flexor longus pollicis): Flexor and stabilizer of the hindfoot. It originates from three bundles, two from the rear upper portion of the tibia and one from a ligament between the tibia and femur, and runs down the back of the leg to curve around the point of hock on the inside, to the back of the fetlock and inserts on the semilunar crest and cartilage of the rear coffin bone.
• Superficial digital flexor tendon (perforatus, flexor digitorum superficialis, flexor digitalis pedis superficialis): Flexes and stabilizes the hindfoot. Mostly tendinous, it arises on the back lower part of the femur’s shaft and runs to the point of hock where it attaches, to continue down to the rear fetlock to the outside of the deep digital flexor tendon and forks at the back of the 1st phalanx with each portion inserting on either side of the back lower rim of the 1st phalanx and back upper rim of the 2nd phalanx.
• Long digital extensor tendon (extensor pedis, extensor digitalis longus, extensor longus digitorum): Extends and stabilizes the hindfoot. It arises on the front, bottom part of the outside aspect of the femur and runs down the front, outside of the tibia to shift to the front of the hock joint to run down the front of the hindcannon and 1st and 2nd phalanges to insert on the front point along the top rim of the hind coffin bone.
• Long digital flexor tendon (accesorius, extensor digitalis longus, flexor longus digitorium, and sometimes referred to as the medial head of the deep digital flexor). Assists the action of the deep digital flexor tendon. It arises on the back of the upper tibia and flows down that bone until it curves around the point of hock on the inside of the hock joint to curve back around to the back of the hock joint to join with the perforans tendon to run to the semilunar crest of the coffin bone.
• Lateral digital extensor tendon (extensor digitalis lateralis): Assists the long digital extensor tendon. It originates on the external lateral ligament of the stifle and the fibula, runs down the outside middle portion of the tibia to the outside of the hock where it curves to the front under the hock to join the long digital extensor tendon to run down the front of the hind cannon, 1st and 2nd phalanges to insert on the front point along the top rim of the hind coffin bone.

Ligaments

The equine leg is laced together with a network of ligaments, and for the purposes of this series, we’ll focus only those that entail just the coffin bone and 2nd phalanx for both the foreleg and hindleg (however, a mention must be made of the unique check ligaments in the equine, which are thought to mediate most of the horse’s weight and force loads, particularly at full speed). Also, since the ligaments are so similar on both the foreleg and hindleg, we can consider the following descriptions applicable to both, with any differences noted, as follows:

• Suspensory ligament (interosseous muscle, interosseous medius): It helps to passively support the phalanges and provides energy storage for lift off. For the foreleg it originates from the back of the 2nd layer of carpals and cannon and forks behind the fetlock to run alongside the 1st phalanx to insert at the front top rim of the coffin bone. For the hindleg, it originates from the back of the 2nd layer of metacarpals and the cannon.
• Collateral chondrocompedal ligaments: Lashes the posterior of the lateral cartilages to the 1st phalanx on the lateral and medial sides; they tend to be prominent in draft horses. 
• Collateral pastern ligaments: Lashes the 1st phalanx and the 2nd phalanx together on the lateral and medial sides, over the pastern joint.
• Suspensory navicular ligaments (collateral sesamoidean ligaments): Lashes the navicular bone from the front of the 1st phalanx, on both sides. 
• Collateral chondrocoronal ligaments: Lashes the anterior portion of the lateral cartilage to the bottom of the 2nd phalanx towards the front, on either side.
• Collateral coffin joint ligaments: Lashes the 2nd phalanx and the coffin together, on either side. 
• Straight distal sesamoidean ligament (superficial distal sesamoidean ligament, straight distal sesamoidean ligament): Lashes the sesamoid bones to the upper rear rim of the 2nd phalanx. The oblique distal sesamoidean ligaments (middle distal sesamoidean ligament, oblique distal sesamoidean ligaments) lie internally to the straight distal sesamoidean ligament.
• Abaxial palmar ligament of the pastern joint: Lashes the 1st phalanx to the 2nd phalanx, on the sides towards the rear.
• Collateral chondroungular ligaments: Lashes the bottom of the lateral cartilages to the coffin bone on either side. 
• Collateral chondrosesamoidean ligaments: Attaches the inside top rim of the posterior aspect of the lateral cartilages to the navicular bone. 
• Distal sesamoid impar ligament (distal navicular ligament): Connects the distal rim of the navicular bone to the coffin bone, lying between the deep digital flexor tendon and the coffin joint, and within the lateral cartilages. This is a fibrocartilaginous ligament that becomes bigger and stronger with proper exercise stimuli; otherwise it remains a thin, small ligament (and is therefore typically missed in dissection). When developed, this ligament is more robust on the forelimb than on the hindlimb, and larger in draft breeds (Bowker, 2003).
• Distal digital anular ligament: At the back of the pastern, it creates a sling for the deep digital flexor tendon. 
• Axial palmar ligament of the pastern joint: Lashes the bottom of the 1st phalanx to the top rim of the 2nd phalanx at the back of the bone.

Fluids

Like with all body structures, nutrients are essential to the foot, and a complex network of blood and lymphs systems lace throughout the internal structures. Most of the veins deep in the foot are valveless, though some valves are present on the more superficial veins (such as around the heel and coronary band) and in the digital veins and the veins at the back of the foot. Likewise, research suggests that these fluids within the foot are active participants in foot mechanics, primarily through the three major valveless venous plexuses in the foot, the solar plexus, laminal plexus, and the coronary plexuses. Accordingly, two compelling concepts have developed from this preliminary data, the hemodynamic theory and the Suspension Theory of Hoof Dynamics™ (discussed later).

Blood

• Digital artery (medial and lateral): On the forelimb, the Digital arteries arise from the Common digital artery of the leg (also called the Palmar artery, medial and lateral), and travel down the medial and lateral side of the 1st and 2nd phalanxes and down either side of the navicular bone to the bottom of the coffin bone, forming complex networks of arteries that feed the internal foot. On the hindlimb, the digital arteries arise from the Great metatarsal artery (also called the Lateral dorsal metacarpal artery, and are also infused with the union of the superficial and deep plantar arteries (both lateral and medial); however, their unified arrangement exhibits individual variation.
• Digital vein (medial and lateral, also called the medial metacarpal vein, the common digital vein or the proper digital vein): Mirroring the flow of the digital arteries, the digital veins drain the venous plexuses of the foot. On the foreleg, they arise from the Volar metacarpal vein (medial and lateral, also called the Palmar veins, medial and lateral). On the hindleg, they arise from the Medial dorsal metatarsal vein (or Dorsal common digital vein) and the Superficial plantar veins (medial and lateral, also called the Plantar veins (medial and lateral, or the Common plantar digital vein).
• Solar plexus (or volar plexus or palmar/plantar venous plexus): Valveless and associated with the sensitive sole and the inner surfaces of the lateral cartilages.
• Laminal plexus (or the dorsal venous plexus): Valveless and associated with the sensitive lamellae.
• Coronary plexuses: Two for each foot, they're also valveless and lie within the coronary cushion and the outer surfaces of the lateral cartilages.
• Intraosseous plexus: Contained within the coffin bone and drained by the deep vein of this bone.

Lymph

The foot’s lymph vessels form a rich network in the corium of the sole and frog, paired with a broader-meshed plexus at the bottom of the digital cushion. The attached edge of each lamellae has a lymph vessel, as well.

Sensory Bundles

Recent research has found rich sources of proteoglycans and proprioceptors in the rear part of the foot, sensory cells that not only may be transmitting stimuli and information to the nervous system, allowing the horse to better navigate his way across varied terrain, but also may be increasing resistance to compression and resiliency of the area. These structures have been found in the frog, heel region and in the area of the digital cushion and insertion sites of the distal sesamoideum impar ligament, the deep digital flexor tendon and the navicular bone. Studies also have discovered that while proteoglycans are minimal in young horses, they’re more abundant in adult horses stimulated with proper exercise, suggesting that even the foot’s chemical and molecular structures are improved with movement. Indeed, it seems the more the foot is used according to nature's intent, the better it becomes.

A bottleneck of complex systems for motion, circulation and sensitivity also lie in the insertion area of the distal sesamoideum impar ligament and the deep digital flexor tendon around the navicular bone. For example, thick bundles of collagen, dense nerve fibers, and thick balls of arterio-venous capillaries are situated in this region (Bowker, 2003). In particular, these nerves contain certain peptides that cause vasodilation when triggered by pressures or movement, making the capillary balls highly sensitive to pressures experienced by the foot (Bowker, 2003). Certainly, this area would be subjected to sudden intense pressures and forces upon impact that could cause fluid and blood flow restriction or circulatory crushing, but this area seems to have a system of fluid management that's synchronized with movement, providing adequate nutrients and protection. Some studies have documented that when these peptides are artificially stimulated to release their components, the result is edema, vasodilation and inflammation. All these features imply that this area may act as a neural sensor to detect pressure changes while simultaneously regulating the fluid supply to minimize pressure and high frequency oscillations caused by impact and loading, the latter which appears to be the most destructive to the limb. What’s more, this area seems to become more developed and efficient with increased stimulation, such as through regular exercise.

Two ideas that incorporate this biological system are the hemodynamic theory and Suspension Theory of Hoof Dynamics™ (discussed later). Curiously, other research claims that unsound feet have these systems damaged by motion rather than stimulated by motion when there is inadequate development of the internal foot systems intended to mediate these impact forces (Bowker, 2003). In particular, feet with navicular syndrome appear to have most of their peptide receptors disrupted or destroyed, suggesting that the fluid management system is impaired or damaged, causing an insufficient supply of nutrients and buffering to this delicate area (Bowker, 2003). This may explain the erosion or reforming of the navicular bone and the degeneration of other features around that area.

Additionally, all these systems may provide foot proprioception, an instant and automatic sensory system that relays information to the central nervous system about the location and situation of the feet, sending signals to the body on how to react in response to the forces on the foot (Bowker et al, 1993, 1995). In this way, it’s hypothesized that these systems may also initiate full extension of the limb and help to regulate gait and footfall (Bowker), though data is still incoming. Considering the speed at which the legs move at a gallop, and that the horse is probably looking ahead rather than at his feet, then coupled with the varied terrain and balance adjustments, there has to be more at work than simply his eyes or inner ear. Don't we unconsciously "feel" where we're going and how with our own proprioception in our feet? And doesn't that information lend itself to more efficient and safer motion?

Interestingly, observers claim that barefoot horses will alter their steps in response to feeling the terrain, such as shifting a hip or shoulder in response to the ground, whereas shod horses do not (Ramey) (though it’s unclear whether the protection afforded by shoes invalidates the need for these adjusting steps). This implies there may indeed be some sort of sensory mechanism within the foot that affects the body’s responses and the horse’s decisions. Some claim that this sensory feedback allows a barefoot horse to be far more sure-footed, nimble and stable (i.e. a safer, more confident ride) and that shod horses are more prone to stumbling, interference, slipping and clumsiness, especially on uneven, rocky terrain (Ramey). While much of this information is based on observation, if even some of it’s true, it poses some hard questions for equine podiatry, especially when considering that domestic feet may be too chronically underdeveloped for any significant proprioceptive abilities.

Sum Up

So there you have it…the equine foot. There's nothing else like it in the animal kingdom, being totally unique to equines. It's a marvel, isn't it? 65 million years of evolution have created a finely-tuned mechanism based on economy, interdependence, and resilience that functions as a whole unit. Nothing is there by accident, and each part functions holistically to create a cumulative effect. Truly, if the new data is suggesting anything, it's that nothing about the equine foot should be taken for granted. 

What's also curious is that each horse develops custom-fitted feet for his lifestyle and his physical peculiarities; one size doesn't fit all apparently. That means there's a spectrum in what can be considered "quality feet" rather than one universal example. This is important to consider for sculpture, and we'll explore it further later in the series.

It's also interesting to learn, as recent studies are suggesting, that the more the foot is used—according to nature's prerogatives—the better it becomes. So the more we manage the horse aligned to nature's evolutionary conditions, the sounder he becomes. This bodes a serious rethinking of equine management which is dominated by stabling and limiting movement, especially of foals and young horses when their feet are starting to lay the groundwork for a lifetime of soundness. 

Anyway, with all this structure under our belt, we'll delve into foot mechanics in Part IV, or how all this works together to create the lovely motion we so admire with this beast. So until next time, keep tappin' yer toes!

"Nature is the best instructor." ~ Paul Cezanne