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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.

===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 perioplic corium, proximal to the coronary band and continuous with the skin, it produces the thin, shiny layer (stratum externa) of the hoof wall.

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 it 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.

==Deeper structures of the foot==

==Deeper structures of the foot==

[[File:Horse_hoof_wild_bare_sagittal.jpg|thumb|200px|right|Saggital section through horse hoof.]]

[[File:Horse_hoof_wild_bare_sagittal.jpg|thumb|200px|right|Sagittal section through horse hoof.]]

Enclosed within the hoof capsule are the bony structures – the distal phalanx, distal end of the middle phalanx, the distal interphalangeal joint, and the distal sesamoid bone (navicular).  There are also soft tissue structures including ligaments, cartilage, the digital cushion and the insertions of the common digital extensor tendon and the deep digital flexor tendon.

Enclosed within the hoof capsule are the bony structures – the [[Phalanges_-_Horse_Anatomy#Distal_Phalanx|distal phalanx]], distal end of the [[Phalanges_-_Horse_Anatomy#Middle_Phalanx|middle phalanx]], the [[Joints_and_Ligaments_-_Horse_Anatomy#Distal_Interphalangeal_.28Coffin.29_Joint|distal interphalangeal joint]], and the [[Phalanges_-_Horse_Anatomy#Distal_Sesamoid_.28Navicular.29_Bone|distal sesamoid bone (navicular)]].  There are also soft tissue structures including ligaments, cartilage, the digital cushion and the insertions of the [[Tendons_-_Horse_Anatomy#Thoracic_Limb|common digital extensor tendon]] and the [[Tendons_-_Horse_Anatomy#Flexorsdeep|digital flexor tendon]].

 

 

 

 

 

 

 

 

The [[Phalanges_-_Horse_Anatomy#Distal_Sesamoid_.28Navicular.29_Bone|distal sesamoid bone (navicular)]] lies between the middle and distal phalanges and the deep digital flexor tendon. Associated with it is a fluid-filled sac that reduces friction between the bone and the [[Tendons_-_Horse_Anatomy#Flexorsdeep|digital flexor tendon]] that lies over the top of it— the navicular bursa.  Inflammation in the region is involved in navicular disease which is a common cause of lameness.

 

==Structure and Function==

===Digital Cushion===

===Equine Hoof===

===Blood supply to the digit===  

The main vessels supplying the digit in the forelimb are the medial and lateral palmar digital aa, both of which arise from the median a.  In the digit of the hind limb the medial and lateral digital aa. are a continuation of the metatarsal a. and are also contributed to by the medial and lateral plantar aa. which branch from the sapheneous a.  

[[image: Plantar hoof aspect.jpg|thumb|175px|left|A view of the solar surface of an equine hoof.  The wall has been removed on the right to show the underlying dermis.  ©Rachael Wallace2008]]

The digital arteries give rise to numerous branches forming rich networks for the vascular tissues. Many anastomoses occur. The terminal branches of the main vessels finally enter a bony canal in the distal phalanx. Venous drainage is similar with the most distal vessels being the medial and lateral palmar/plantar digital veins. The compressive action of the hoof on the soft tissues within during locomotion generates an important function promoting venous return.

As outlined above, the equine hoof can be divided into three topographical regions; the '''wall''', the '''frog''' and the '''sole'''. 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 '''frog''' 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 '''sole''' is the area distal to the bars and apex of the frog enclosed by the hoof wall. The area where the bars and wall enclose it is known as the '''angle of the sole'''.  

 

5. Heel perfusion.

Loss of perfusion to the lamella vessels, circumflex vessels, and terminal arch indicates a poor prognosis without aggressive therapy.

The dermis of the distal phalanx is arranged in hundreds of leaves or '''laminae''', each of which has microscopic '''secondary laminae'''. The coronary region has a germinative layer associated with papillae that is responsible for producing the horn tubules that make up the hoof wall. This wall glides distally at a rate of 5-6mm a month and by forming epidermal laminae itself it interdigitates with the underlying dermal laminae. Neither of these laminae are pigmented so when the epidermal laminae appear on the solar surface, a non-pigmented region known as the '''white line''' appears. The white line is used as important landmark in farriery as structures central to the line will be dermal and so vascular and sensitive.  

===Microcirculation in the dermal laminae===

Numerous arteriovenous anastomoses occur which are of a somewhat unusual type. Under normal circumstances these are closed and as a result circulation within the capillary beds of the dermal laminae occurs. Certain systemic pathologies may result in opening of these AV anastomoses resulting in ischaemia of the laminae. This in turn results in the hoof wall separating from the distal phalanx producing the disease termed “laminitis”, which can be either acute or chronic.

The dermis in the frog is also arranged in papillae and produces incompletely keratinised flexuous horn tubules resulting in a soft, elastic horn. The hypodermis of the region of the frog forms the '''digital cushion'''. This lies between the ungual cartilages and is collagenous, elastic tissue infiltrated by adipose tissue. At the bulbs of the heel, it is subcutaneous and is soft and loose in texture. The sole area also has papillae that produces superficially flakey horn. The coronary part of the wall is surrounded by a bony prominence called the '''periople'''. This soft, lightly coloured area is restricted to this proximal area and is produced by the germative layer covering the papillae. The rest of the hoof is covered by the '''tectorial layer''', this is a very thin layer of horn that is covered distally by the growth of the horn.

===Innervation of the equine digit===

The digit of the forelimb is innervated by the medial and lateral digital nerves. The medial digital n. is a continuation of the median n. and the lateral digital n. is derived from both median and ulnar nerves. These run on the palmar aspect of the digit in close proximity to the main arteries and veins. They give rise to several dorsal branches which supply dorsally located areas.  

A well-trimmed foot should weight bear on its walls, bars and frog. This occurs as the weight applied to the distal phalanx is then transferred across the interdigitating laminae to the hoof wall. Thus an injury resulting in damage to the laminae is of extreme importance to the horse.  

The pelvic limb digit is innervated on the dorsal aspect by the common digital nn. Derived from the fibular n.  The plantar aspect is innervated by the medial and lateral digital nn which originate from the tibial n.

In addition to their normal importance in supplying innervation to the sensitive tissues of the equine digit these nerves are also of considerable clinical importance as they are utilized for the procedure termed diagnostic nerve blocks.

===Ruminant Hoof===

===Ruminant Hoof===

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[[Category:Integumentary System - Anatomy & Physiology]]

[[Category:Integumentary System - Anatomy & Physiology]]

[[Category:A&P Done]]

[[Category:A&P Done]]