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 [[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.

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 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 [[Joints and Ligaments - Horse Anatomy#Thoracic Limb|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