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Horses are '''perissodactyl''' '''unguligrade''' animals. Unguligrade means that horses bear their weight on a horny covering (hoof) that surrounds their distal phalanx, perissodactyl means that they have only one weightbearing digit. They are virtually identical in their structure in the hindlimb and forelimb. The main differences are that in the forelimb they have metacarpals and the metacarpophalangeal joint, the hindlimb equivalents are the metatarsals and the metatarsophalangeal joint. Also in anatomical planes we use the term palmar for forelimb and plantar for hindlimb. These terms are all interchangable in the below article depending on whether you are referring to the fore or hindlimb.

Horses are '''perissodactyl''' '''unguligrade''' animals. Unguligrade means that horses bear their weight on a horny covering (hoof) that surrounds their distal phalanx, perissodactyl means that they have only one weightbearing digit. They are virtually identical in their structure in the hindlimb and forelimb. The main differences are that in the forelimb they have metacarpals and the metacarpophalangeal joint, the hindlimb equivalents are the metatarsals and the metatarsophalangeal joint. Also in anatomical planes we use the term palmar for forelimb and plantar for hindlimb. These terms are all interchangable in the below article depending on whether you are referring to the fore or hindlimb.

Only the third metacarpal ('''cannon''') bone remains complete whilst the second and fourth metacarpals are greatly reduced and are known as the '''splint bones'''. Metacarpal III has a distal articular surface with two condylar areas separated by a '''sagittal ridge'''. This separates the two sesamoids on the palmar aspect of the joint and ensures only sagittal movement of the fetlock. There is also a transverse ridge leading to two radii of curvature. The proximal part has articulating facets on its palmar side where the splint bones articulate. It has a '''metacarpal tuberosity''' on the dorsomedial surface of the proximal end. The splint bones are held to metacarpal III by strong ligaments which are usually ossified and can lead to lameness if there is excessive bone production. They curve away distally from the main shaft and end in palpable nodules 2/3rds to 3/4s the way down the cannon bone.

Only the third metacarpal ('''cannon''') bone remains complete whilst the second and fourth metacarpals are greatly reduced and are known as the '''splint bones'''; metacarpal II is the medial splint and metacarpal IV the lateral splint. Metacarpal I and V are completely absent in the horse.  The splint bones are approximately a third shorter than the metacarpal III. Proximally, the metacarpals articulate with carpal bones. Metacarpal II and III articulate with the second carpal bone and metacarpal IV with the fourth carpal bone.

 

Metacarpal III is robust and well developed, as it has to bear the entire weight transfered through the limb. The distal end of the bone has an articular surface comprised of two condylar areas seperated by a '''saggital ridge''', which engages with a groove in the proximal phalanx. This ensures only sagittal movement of the fetlock. There is also a '''transverse ridge''' leading to two radii of curvature. The proximal aspect of metacarpal III has articulating facets on its palmar side, where the splint bones articulate. It has a '''metacarpal tuberosity''' on the dorsomedial surface of the proximal end.  

 

The splint bones are held to metacarpal III by strong ligaments which are usually ossified and can lead to lameness if there is excessive bone production. They bones curve away distally from the main shaft and end in rounded nodules, which are important palpable landmarks ('''buttons of the splint'''), approximately a 1/3 to 3/4 of the way down metacarpal III.

===[[Equine - Anatomy & Physiology#Phalanges|Phalanges]]===

===[[Equine - Anatomy & Physiology#Phalanges|Phalanges]]===