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==Introduction==

==Introduction==

The hoof is defined from a physiologic perspective as the modified skin [[Skin - Anatomy & Physiology#Epidermis|(epidermis)]] covering the tip of the digit and all enclosed structures. The hoof provides protection to the distal limb and is formed by keratinisation of the epithelial layer and modification of the underlying dermis. The keratin in the [[Skin - Anatomy & Physiology#Epidermis|epidermis]], when thickened and cornified, is referred to as [[Horn - Anatomy & Physiology|horn]].  Horn makes up the outer surface if the hoof and is particularly resistant to mechanical and chemical damage.

The hoof is defined from a physiologic perspective as the modified skin [[Skin - Anatomy & Physiology#Epidermis|(epidermis)]] covering the tip of the digit and all enclosed structures. The hoof provides protection to the distal limb and is formed by keratinisation of the epithelial layer and modification of the underlying dermis. The keratin in the [[Skin - Anatomy & Physiology#Epidermis|epidermis]], when thickened and cornified, is referred to as [[Horn - Anatomy & Physiology|horn]].  Horn makes up the outer surface if the hoof and is particularly resistant to mechanical and chemical damage.

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[[File:Lateral_view_horse_foot.jpg|thumb|right|150px|]]

[[File:Lateral_view_horse_foot.jpg|thumb|right|150px|]]

The wall of the hoof is the element of the hoof that is visible. The wall forms the medial, lateral and dorsal aspect of the hoof and it can be further divided into the toe, quarters and heels. At the heel the walls reflect back on themselves at a point called the angles and in doing so forms the bars. The bars, although moving cranially, gradually fade along the edge of the frog and never actually meet.

The wall of the hoof is the element of the hoof that is visible. The wall forms the medial, lateral and dorsal aspect of the hoof and it can be further divided into the toe, quarters and heels. At the heel the walls reflect back on themselves at a point called the angles and in doing so forms the bars. The bars, although moving cranially, gradually fade along the edge of the frog and never actually meet.

The wall of the hoof is widest at the distal aspect of the hoof, i.e. at the toe. The wall of the hoof decreases in width laterally and medially (around the quarters of the hoof). In most domestic species the wall of the hoof is between 5 - 10mm thick and consists of three layers. There is an outer layer of thin but dense horn that is shiny and acts to reduce evaporation from the horn and therefore prevent dehydration of the other layers of the horn – the periople. There is an intermediate layer which represents the main structure of the wall and is composed of amorphous horn reinforced with many tubular shaped horn rods. Finally, there is an inner laminar layer where there are interdigitating laminae of horn and dermal laminae which ensure the hoof itself is firmly anchored to the distal phalanx. The bond between the horn and the underlying dermis is a living bond that gradually allows the wall of the hoof to slide in a distal direction towards the ground where the distal border is worn away via contact with the ground.

The wall of the hoof is widest at the distal aspect of the hoof, i.e. at the toe. The wall of the hoof decreases in width laterally and medially (around the quarters of the hoof). In most domestic species the wall of the hoof is between 5 - 10mm thick and consists of three layers. There is an outer layer of thin but dense horn that is shiny and acts to reduce evaporation from the horn and therefore prevent dehydration of the other layers of the horn – the periople. There is an intermediate layer which represents the main structure of the wall and is composed of amorphous horn reinforced with many tubular shaped horn rods. Finally, there is an inner laminar layer where there are interdigitating laminae of horn and dermal laminae which ensure the hoof itself is firmly anchored to the distal phalanx. The bond between the horn and the underlying dermis is a living bond that gradually allows the wall of the hoof to slide in a distal direction towards the ground where the distal border is worn away via contact with the ground.  Attached by the subcutis to the periosteum of the distal phalanx, the laminar corium suspends the entire weight of the animal by the distal phalanx within the hoof capsule via microscopic interdigitations with the epidermal laminae of the hoof wall.  Damage to the vasculature of the laminar corium can result in compromises in the integrity of the interdigitations.  

The hooves in newborn foals are bilaterally symmetrical. Over a period of just a few months, forces exerted on the hoof during locomotion cause a visible difference between the right and left, as well as front and hind hooves. Thus, isolated specimens of equine feet can be distinguished as follows:

The hooves in newborn foals are bilaterally symmetrical. Over a period of just a few months, forces exerted on the hoof during locomotion cause a visible difference between the right and left, as well as front and hind hooves. Thus, isolated specimens of equine feet can be distinguished as follows:

===Periople===

===Periople===

The periople is a small band of soft tissue found over the proximal surface of the wall of the hoof. The periople represents the junction between the wall and the skin of the limb. The periople is responsible for the production of the outer layer of the wall (above). The periople segment extends around the proximal edge of the wall and in horses covers the bulb of the heel and part of the frog. In ruminants is forms part of the join between both hooves of the foot.

The periople is a small band of soft tissue found over the proximal surface of the wall of the hoof. The periople represents the junction between the wall and the skin of the limb. The periople is responsible for the production of the outer layer of the wall (above). The periople segment extends around the proximal edge of the wall and in horses covers the bulb of the heel and part of the frog. In ruminants is forms part of the join between both hooves of the foot. The perioplic corium, proximal to the coronary band and continuous with the skin, it produces the thin, shiny layer (stratum externa) of the hoof wall.

 

===Coronary Dermis Segment===

===Coronary Dermis Segment===

   

   

The pigmentation of the hoof is derived from melanocytes found in the coronary epidermis. Any pigmentation in the hoof will be most pronounced in the outer part of the hoof wall as the deeper layers of the hoof usually contain fewer melanocytes. It is this unpigmented element of the hoof that forms the 'white line' in the sole of hoofs and is particularly important in horses as a landmark for shoeing.

The pigmentation of the hoof is derived from melanocytes found in the coronary epidermis. Any pigmentation in the hoof will be most pronounced in the outer part of the hoof wall as the deeper layers of the hoof usually contain fewer melanocytes. It is this unpigmented element of the hoof that forms the 'white line' in the sole of hoofs and is particularly important in horses as a landmark for shoeing.

===Sole Segment===

===Sole Segment===

The sole represents the part of the foot in contact with the ground and its composition differs between species. The keratin found in the sole is formed from the epidermis on the underside of the third phalanx and can grow to a thickness of around 10mm in domestic species. The keratin found on the sole is much more easily worn down or abraded than that of the wall of the hoof. The equine sole has a central frog structure whilst ruminants and pigs have a bulb structure to the sole.

The sole represents the part of the foot in contact with the ground and its composition differs between species. The keratin found in the sole is formed from the epidermis on the underside of the third phalanx and can grow to a thickness of around 10mm in domestic species. The keratin found on the sole is much more easily worn down or abraded than that of the wall of the hoof. The equine sole has a central frog structure whilst ruminants and pigs have a bulb structure to the sole.

===Frog-Bulb Segment===

===Frog-Bulb Segment===

The frog is a wedge-shaped structure which sits between the bars and has an apex facing distally, with 2 crura flanking a central sulcus. Between the crus and bar of each half of the sole lies the collateral sulcus. Opposite the apex, the frog expands forming the bulbs of the heel. The frog is a mass of keratinized stratified squamous epithelium, which is softer than other parts of the hoof due to its increased water content. Usually, the frog contributes to the weightbearing surface where it functions as a shock absorber. Apocrine glands within the corium of the frog produce secretions on the surface.  The frog ensures that the wall of the hoof is forced outwards when weight is put on the limb thus ensuring that the 'hoof mechanism' functions correctly and ensuring circulatory flow around the hoof and back towards the heart.

The frog is a wedge-shaped structure which sits between the bars and has an apex facing distally, with 2 crura flanking a central sulcus. Between the crus and bar of each half of the sole lies the collateral sulcus. Opposite the apex, the frog expands forming the bulbs of the heel. The frog is a mass of keratinized stratified squamous epithelium, which is softer than other parts of the hoof due to its increased water content. Usually, the frog contributes to the weightbearing surface where it functions as a shock absorber. Apocrine glands within the corium of the frog produce secretions on the surface.  The frog ensures that the wall of the hoof is forced outwards when weight is put on the limb thus ensuring that the 'hoof mechanism' functions correctly and ensuring circulatory flow around the hoof and back towards the heart.

The ruminant/pig 'bulb' provides the hoof with the caudal and mid-hoof contact area with the ground and is chiefly involved in weight bearing. The bulb inserts into the V-shaped sole. The bulb is made of relatively soft material, mainly inter-tubular horn and is of a considerable thickness.

The ruminant/pig 'bulb' provides the hoof with the caudal and mid-hoof contact area with the ground and is chiefly involved in weight bearing. The bulb inserts into the V-shaped sole. The bulb is made of relatively soft material, mainly inter-tubular horn and is of a considerable thickness.

==Structure and Function==

==Structure and Function==