Anatomy and Physiology Part 5: The Equine Foot

The equine lexicon is filled with clichés about the equine foot. Most horse owners have heard them all. "No foot, no horse...The foot is the horse's foundation...For want of a shoe..." The list goes on. Without sound feet, a horse can't move freely, and a horse whose movement is hindered becomes a predator's meal in the wild and a liability to its owner in a domestic setting.

A quick outward glance at a horse's foot gives little clue as to its complex nature. On the surface, we see a hard, horny substance called the hoof wall and nothing more. Beneath that hard exterior, however, is a sophisticated arrangement of bones, tendons, ligaments, nerves, blood vessels, and sensitive tissue. When this amalgamation of parts is properly assembled and functioning well, it is one of Nature's masterpieces. When something goes awry, however, the effect can be akin to an explosion in a closed room.

That hard, horny hoof wall is not malleable. When an injury or systemic insult causes blood vessels to expand or tissues to swell, there is no room to accommodate enlargement of any kind and something must give.

We will examine the anatomy of the foot in this article. Once again, we use a variety of sources, but two deserve additional mention. They are Doug Butler, PhD, Certified Journeyman Farrier, Fellow of the Worshipful Company of Farriers, of Colorado, a lecturer, author, and consultant; and David Hood, DVM, PhD, a professor at Texas A&M University who has been involved in that institution's Hoof Project. Information from these researchers comes from past interviews and papers they have authored. Other information comes from a variety of papers and textbooks.

It should be noted that hoof and foot are not synonymous. The hoof or hoof wall, generally speaking, is the three-layered outer surface of the foot. The foot, on the other hand, includes the hoof and all the bones, blood vessels, ligaments, tendons, and nerves therein.

The Outer Hoof

We begin with that rather innocuous-appearing exterior hoof wall. It plays a complicated role to house and protect the sensitive inner foot, support weight, resist wear, conduct moisture, and absorb shock.

In order to accomplish these tasks, the hoof wall and the foot must be healthy. It is at this point that the owner or caretaker plays a role. Because we have the horse in an environment of our choosing, the natural selection process does not come into play. In the wild, a horse with poor feet didn't survive and its genes were not passed on. Not so today. Some horses with horrid feet are included in breeding programs because of their talent and capabilities in the show ring or on the racetrack. As a result, special care sometimes becomes the norm in order to keep these hooves and feet functional.

The hoof wall is composed of three distinct layers. The outer layer is the periople (like the human cuticle) and stratum tectorium. The periople extends about three-fourths of an inch below the coronet, except at the heels, where it caps the bulbs of the heels. The coronet encircles the upper area of the hoof and is the point of demarcation between the skin and the beginning of the hoof wall. The stratum tectorium, much like the human fingernail, extends down to the bottom of the foot. It is a thin layer of horny scales--hardened cells--that provides the hard, glossy-appearing surface below the periople. It is composed of keratinized epithelial cells that are solidly cemented together with keratin. One of its tasks is to protect the hoof wall from drying out. The hoof wall should be approximately 25% water.

The middle layer of the hoof wall comprises the bulk of the wall and is the densest portion. The inner layer is the laminar layer. It is concave from side to side and bears a multitude of primary and secondary leaf-like laminae, which attach the coffin bone to the inside of the hoof wall, similar to Velcro. There are some 600 primary laminae, each of which bears 100 or more secondary laminae on its surface. These combined laminae bear much of the weight of the horse.

The junction between the laminae of the wall and the tubules of the sole is known as the white line.

Let's pause for a review of terms. The external surface at the front of the foot is its dorsal surface, and the surface facing the ground is the solar surface. On the front leg, the caudal (rear) aspect of the foot is its palmar surface. In the rear leg this is referred to as the plantar surface. Medial (inside) is the term for the portion of the foot nearest the foot on the opposite side. Lateral (outside) is the term for the portion of the foot farthest away.

On all surfaces of the hoof wall are small, thin, generally parallel lines that reach from the coronet to the solar surface. These lines are the tubules of the wall. The tubules are constructed in such a way that they resist compression of the hoof wall when the horse's foot bears weight.

Beneath the surface of the coronet is the coronary band. It is the primary growth and nutritional source for the hoof wall. Within this structure lies a massive supply of blood vessels that feed the hoof. These blood vessels, combined with nerves, form a sensitive layer that is attached to the inside of the hoof wall and the third phalanx (coffin bone).

Injury to the coronary band can have a serious negative effect on hoof growth and development. If the injury to the coronary band is serious, it can result in permanent disfigurement of the hoof and, in some cases, disrupt proper hoof growth to the point where the horse is no longer usable.

Time to learn another term--corium. Understanding its role helps to understand how the foot is nourished. The corium is a modified vascular (supplied with blood vessels) tissue that is divided into five parts. First is the perioplic corium, which is a narrow band lying in the perioplic groove above the coronary border of the wall. Its job is to distribute nourishment around the top of the hoof wall. Second is the coronary corium, which, with the perioplic corium, helps to form the coronary band. It furnishes the bulk of nutrition to the hoof wall and is responsible for growth of the wall. Third is the laminar corium that is attached to the coffin bone and nourishes the dermal laminae, the epidermal laminae of the wall, and the inter-laminar horn of the white line. Fourth is the sole corium, which is composed of fine hair-like papillae over the entire inner surface of the sole. These papillae furnish nourishment and growth to the sole. Fifth is the frog corium, which is similar in structure to the sole corium and furnishes nourishment and growth to the frog.

Back to the parts of the foot that are readily visible. On the solar surface is the sole. The structure of the sole is similar to that of the wall, with tubules running vertically as formed by the papillae of the sole corium. These tubules curl near the ground surface, which accounts for the self-limiting growth of the sole and causes shedding. The sole is not designed to constantly bear weight from the ground surface, but it is designed to bear internal weight.

An integral part of the foot is the frog, a wedge-shaped mass that occupies angles bounded by the bars and the sole. The frog is divided into the apex, which is the forward-most point; the base, which is the rear portion; and the frog stay, which is the central ridge. The frog is about 50% water and is quite soft.

The frog serves as a shock absorber in two ways. First, it helps absorb concussive force from the ground and, second, it acts as a stop that redirects concussive force coming down from the bony column through the lateral cartilages and the hoof.

The heels of the hoof form the most caudal part of the bearing surface of the hoof wall. There the wall makes an acute change in direction, turning back toward the toe. The portions that turn toward the toe are the bars of the foot.

The Skeletal System

The bones of the foot provide framework and facilitate locomotion. Nature did an excellent job in designing the bones. They had to be light enough to facilitate easy movement, yet strong enough to sustain the rigors of weight-bearing and concussion. When all goes well, they fulfill their roles admirably. However, when something goes awry with the bones, the result can be devastating lameness that is difficult to treat because of their location inside the horny hoof wall.

The three bones of the foot are the distal end of the short pastern bone, also known as second phalanx (P2) or middle phalanx (which extends distally from its connection with the pastern bone or first phalanx (P1); the coffin bone, also known as the third phalanx  (P3) or distal phalanx (which extends distally from the short pastern bone); and the navicular bone, also known as the distal sesamoid bone, located behind and distal to the short pastern bone and behind and proximal to the coffin bone. The bones of the foot and leg are connected by joints and ligaments, so an injury to one can have a negative effect on the others.

Soft Tissues

There are two key tendons within the foot. The extensor tendon attaches to the front of the coffin bone and the deep digital flexor tendon attaches to the bottom of the coffin bone.

The navicular bursa is positioned between the deep digital flexor tendon and the flexor surface of the navicular bone and helps reduce concussion on the bone. Another inner foot structure that helps absorb concussion is the digital cushion located between the distal coffin bone and the sole. The digital cushion is a wedge-shaped structure with a fibro-fatty composition. It is very elastic and has very few blood vessels or nerves. When the digital cushion is compressed by the pastern bones and frog with weight bearing, it absorbs shock, cushions the bones, and is divided by the frog's exterior spine so that it is forced outward and obliquely upward against the lateral cartilages. The lateral cartilages are part fibrous tissue and part hyaline cartilage. They slope upward and backward from the wings of the coffin bone and reach above the margin of the coronary band.

The coronary cushion is the elastic portion of the coronary band. It is a fibro-fatty cushion that is thickest in the center and thinnest at the quarters where it attaches to the lateral cartilage. It then widens out and thickens to form the base of the bulbs of the heel, where it blends in with the digital cushion. The coronary cushion helps in the reduction and transfer of compression between the hoof wall and the coffin bone as well as other internal foot parts.

The inner foot is serviced by a blood supply that is pumped by the heart through the arteries to the foot and is assisted in its return to the heart by a pumping mechanism within the foot facilitated by compression involving a complex network of veins whenever the horse bears weight on the foot. They lymphatic system of the limbs also requires this pumping action to move fluids. This is one reason that a horse standing still for a long time will "stock up" because fluids in the legs are not being pumped back up the limbs by cycles of foot loading and unloading.

Take-Home Message

Because the foot plays such a key role in the horse's ability to survive and function, we will end this dissertation on the anatomy of the foot with the oldest of clichés: "No foot, no horse."

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at or by calling 800/582-5604.

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