Changes

==Proximal Phalanx==

==Proximal Phalanx==

The proximal phalanx is shaped like an hourglass and is wider proximally than distally. Proximally, it has two shallow articular surfaces separated by a small '''sagittal groove'''; the medial cavity is larger than the lateral cavity.  The saggital groove accepts the saggital ridge of the distal third metacarpal (cannon) bone.  Distally there are two convex areas separated by a sagittal groove to accept the proximal articulation of the middle phalanx. The proximal phalanx is approximately twice the length of the middle phalanx.

The proximal phalanx is shaped like an hourglass and is wider proximally than distally. Proximally, it has two shallow articular surfaces separated by a small '''sagittal groove'''; the medial cavity is larger than the lateral cavity.  The saggital groove accepts the saggital ridge of the distal [[Limb Bones and Cartilages - Horse Anatomy#Metacarpals and Metatarsals|third metacarpal ]](cannon) bone.  Distally there are two convex areas separated by a sagittal groove to accept the proximal articulation of the middle phalanx. The proximal phalanx is approximately twice the length of the middle phalanx.

==Middle Phalanx==

==Middle Phalanx==

The distal phalanx is rounded to a point distally; articulating with another bone only at the proximal end.  It does not have a cortex or medullary cavity, but has three surfaces: articular surface, parietal surface and solar surface.

The distal phalanx is rounded to a point distally; articulating with another bone only at the proximal end.  It does not have a cortex or medullary cavity, but has three surfaces: articular surface, parietal surface and solar surface.

:The proximal '''articular surface''' has two concavities separated by a ridge. The palmar border meets with the distal sesamoid (navicular) bone. The dorsal aspect has a marked '''extensor process''', where the common digital extensor attaches.  

:The proximal '''articular surface''' has two concavities separated by a ridge. The palmar border meets with the distal sesamoid (navicular) bone. The dorsal aspect has a marked '''extensor process''', where the [[Tendons - Horse Anatomy#Thoracic Limb|common digital extensor]] attaches.  

:The '''solar surface''' has two distinct areas, the more palmar area is the roughened flexor surface and the remainder is smooth, concave and crescent-shaped. There is a '''solar groove''' on each side of the flexor surface, which leads to the '''solar canal'''. The palmar aspect extends either side to form the medial and lateral '''palmar processes''', which each have a foramen.  The juction between the solar surface and the parietal surface forms the solar border. There is a notch in the dorsal solar border, known as the '''crena marginis solearis'''.

:The '''solar surface''' has two distinct areas, the more palmar area is the roughened flexor surface and the remainder is smooth, concave and crescent-shaped. There is a '''solar groove''' on each side of the flexor surface, which leads to the '''solar canal'''. The palmar aspect extends either side to form the medial and lateral '''palmar processes''', which each have a foramen.  The junction between the solar surface and the parietal surface forms the solar border. There is a notch in the dorsal solar border, known as the '''crena marginis solearis'''.

:The '''parietal surface''' of the distal phalanx is that which conforms to the hoof wall. It is convex, rough, porous and has processes on each side heading in a palmar direction. There are many foramina and grooves on this surface for vasculature and nerves to pass.  The '''ungual (collateral) cartilages''' attach to these processes, they are squarish plates which are palpable above the level of the hoof. They become more fibrous in life and may ossify.

:The '''parietal surface''' of the distal phalanx is that which conforms to the hoof wall. It is convex, rough, porous and has processes on each side heading in a palmar direction. There are many foramina and grooves on this surface for vasculature and nerves to pass.  The [[Hoof - Horse Anatomy#Deeper Structures of the Hoof|'''ungual (collateral) cartilages''']] attach to these processes, they are squarish plates which are palpable above the level of the hoof. They become more fibrous in life and may ossify.

==Distal Sesamoid (Navicular) Bone==

==Distal Sesamoid (Navicular) Bone==

The distal sesamoid in horses is known as the navicular bone. It is elongated transversely and articulates with both the distal and middle phalanx, lying palmar to the distal interphalangeal joint. Dorsally, the articular surface is covered by hyaline cartilage. It articulates with the palmar aspect of the middle phalanx.  The palmar flexor surface is characterised by a prominent '''sagittal ridge''' and is covered by fibrocartilage; providing a smooth surface for the deep digital flexor tendon to glide during weightbearing.  The distal border contains a small articular facet of hyaline cartilage for articulation with the distal phalanx. The distal border contains numerous, synovium-lined, nutrient foraminae.

The distal sesamoid in horses is known as the navicular bone. It is elongated transversely and articulates with both the distal and middle phalanx, lying palmar to the [[Joints and Ligaments - Horse Anatomy#Thoracic Limb|distal interphalangeal joint]]. Dorsally, the articular surface is covered by hyaline cartilage. It articulates with the palmar aspect of the middle phalanx.  The palmar flexor surface is characterised by a prominent '''sagittal ridge''' and is covered by fibrocartilage; providing a smooth surface for the [[Tendons - Horse Anatomy#Thoracic Limb|deep digital flexor tendon ]] to glide during weightbearing.  The distal border contains a small articular facet of hyaline cartilage for articulation with the distal phalanx. The distal border contains numerous, synovium-lined, nutrient foraminae.

===Ligamentous Support===

===Ligamentous Support===

*The '''distal sesamoidean (impar) ligament''' originates from the distal margin of the navicular bone and deep digital flexor tendon. It extends from the navicular bone proximally for 1.0-1.5cm and distally to the insertion of the deep digital flexor tendon on the distal phalanx (pedal bone).   

*The '''distal sesamoidean (impar) ligament''' originates from the distal margin of the navicular bone and deep digital flexor tendon. It extends from the navicular bone proximally for 1.0-1.5cm and distally to the insertion of the deep digital flexor tendon on the distal phalanx (pedal bone).   

The navicular bone is separated from the deep digital flexor tendon by the '''navicular bursa'''.  There is no communication between the navicular bursa and the distal interphalangeal (coffin) joint.

The navicular bone is separated from the [[Tendons - Horse Anatomy#Thoracic Limb|deep digital flexor tendon ]] by the '''navicular bursa'''.  There is no communication between the navicular bursa and the [[Joints and Ligaments - Horse Anatomy#Thoracic Limb|distal interphalangeal (coffin) joint]].  

===Innervation===

===Innervation===

Sensory innervation to the navicular bone is supplied by the '''digital nerves'''. Nerves run distally through the collateral sesamoidean ligaments and within the distal sesamoidean (impar) ligament. Sensory innervation to the navicular bursa is also via digital nerves.

Sensory innervation to the navicular bone is supplied by the '''digital nerves'''. Nerves run distally through the collateral sesamoidean ligaments and within the distal sesamoidean (impar) ligament. Sensory innervation to the navicular bursa is also via digital nerves.

===Vasculature===

===[[Limb Vasculature - Horse Anatomy|Vasculature]]===

Arterial supply to the navicular bone is via anastomoses between '''medial and lateral palmar digital arteries'''. Proximally, a '''transverse plexus''' joins these arteries and gives rise to several small arteries that enter the formania of the navicular bone along its proximal border.  Distally, branches connecting the medial and lateral palmar digital arteries form a '''distal navicular plexus'''; which give off additional small arteries that enter foramina along the distal border. These digital arteries supply most of the blood to the navicular bone.  Anastamoses between the proximal and distal blood supplies occurs in the adult horse.  

Arterial supply to the navicular bone is via anastomoses between '''medial and lateral palmar digital arteries'''. Proximally, a '''transverse plexus''' joins these arteries and gives rise to several small arteries that enter the formania of the navicular bone along its proximal border.  Distally, branches connecting the medial and lateral palmar digital arteries form a '''distal navicular plexus'''; which give off additional small arteries that enter foramina along the distal border. These digital arteries supply most of the blood to the navicular bone.  Anastamoses between the proximal and distal blood supplies occurs in the adult horse.  

*Pasquini, C, Spurgeon, T.L., An Anatomy of Domestic Animals: A Systemic and Regional Approach, 10th Edition (2003), Bowker

*Pasquini, C, Spurgeon, T.L., An Anatomy of Domestic Animals: A Systemic and Regional Approach, 10th Edition (2003), Bowker

*Parks, A., Form and Function of the Equine Digit, Veterinary Clinics of North  America: Equine Practice 19 (2003) 285-307

*Parks, A., Form and Function of the Equine Digit, Veterinary Clinics of North  America: Equine Practice 19 (2003) 285-307