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→Deeper Structures of the Hoof
== Deeper Structures of the Hoof==
== Deeper Structures of the Hoof==
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.
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.
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.
The dermis in the frog is also arranged in papillae and produces incompletely keratinised flexuous horn tubules resulting in a soft, elastic horn. 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.
===Digital Cushion===
The digital cushion 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 flexible material that forms the digital cushion is produced from the hypodermis of the frog. It acts as one of the major shock absorbers of the foot. It is connected dorsoproximally with the digital annular ligament and attached at the apex to the deep digital flexor tendon at its point of insertion on the distal phalanx.
===Ungual Cartilages===
The medial and lateral cartilages of the distal phalanx (ungual cartilages) extend from the palmar processes of the bone to the coronary region of the hoof. They can be palpated proximally. The axial surface is concave and their abaxial surface convex. They curve towards each other in the heel region and become thicker distally. The cartilages contain several foraminae through which veins pass from the palmar venous plexus to the coronary venous plexus.
The ungual cartilages have a series of five ligaments going to the medial/lateral surfaces of the three phalanges and distal sesamoid (navicular) bone. A short ligament extends from the dorsal aspect to the dorsal surface of the middle phalanx. A thin elastic fibre extends from the proximal aspect to the proximal phalanx. Several short fibres attach from the distal part of the cartilages to the distal phalanx. Another ligament extends from the dorsal region of the cartilages to the insertion point of the deep digital flexor tendon. Finally, an extension of the collateral sesamoidean ligament attaches them to the navicular bone.
[[image: X-section through hoof.jpg|thumb|200px|right|A X-section through a typical hoof. ©Rachael Wallace2008]]
[[image: X-section through hoof.jpg|thumb|200px|right|A X-section through a typical hoof. ©Rachael Wallace2008]]