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==Introduction==  

==Introduction==  

For general skeletal anatomy, follow links in blue. The following section will concentrate on anatomy specific to the horse.

The following section will concentrate on anatomy specific to the horse. For general skeletal anatomy, follow links in blue. In anatomical planes we use the term palmar for forelimb and plantar for hindlimb. These terms are all interchangable depending on whether you are referring to the fore or hindlimb.

==Thoracic Limb==

==[[Forelimb - Anatomy & Physiology|Thoracic Limb]]==

===[[Forelimb - Anatomy & Physiology#Scapula|Scapula]]===

===[[Forelimb - Anatomy & Physiology#Scapula|Scapula]]===

The scapula is roughly triangular in shape and flat. It lies against the thoracic wall in a cranioventral direction. It does not form a true articulation with the trunk, instead forming a '''synsarcosis'''; meaning it is attached by only muscle. The dorsal border points towards the spinal column and joins the scapular cartilage. The '''scapular cartilage''' is crescent shaped, enlarging the area of attachment for muscles of the scapula as well as acting as a shock absorber.  This cartilage ossifies, thus becomes more brittle, with age. In the horse, the cartilage extends caudally to the level of the withers; which is extensive compared with other species.

The scapula is roughly triangular in shape and flat. It lies against the thoracic wall in a cranioventral direction. It does not form a true articulation with the trunk, instead forming a '''synsarcosis'''; meaning it is attached by only muscle. The dorsal border points towards the spinal column and joins the scapular cartilage. The '''scapular cartilage''' is crescent shaped, enlarging the area of attachment for muscles of the scapula as well as acting as a shock absorber.  This cartilage ossifies, thus becomes more brittle, with age. In the horse, the cartilage extends caudally to the level of the withers; which is extensive compared with other species.

The spine of the scapular ends in a bony prominence ventrally, known as the '''acromion'''. In the horse, this structure becomes smaller distally. A second bony prominence, the '''tuberosity''', exists dorsal to the middle of the scapular spine.

The spine of the scapula ends in a bony prominence ventrally, known as the '''acromion'''. In the horse, this structure becomes smaller distally. A second bony prominence, the '''tuberosity''', exists dorsal to the middle of the scapular spine.

===[[Forelimb - Anatomy & Physiology#Humerus|Humerus]]===

===[[Forelimb - Anatomy & Physiology#Humerus|Humerus]]===

The '''lesser and greater tubercles''' on the lateral and medial sides of the proximal humerus, respectively, are nearly equally well developed. Both tubercles divided into two parts (cranial and caudal). The tubercles are separated by an '''intertubercular groove''', which is wide and has a central saggital ridge ('''intermediate tubercle'''). This ridge fits into a depression on the deep surface of the biceps tendon and restricts movement of the tendon relative to the humerus in the standing horse.

The '''lesser and greater tubercles''' on the lateral and medial sides of the proximal humerus, respectively, are almost equally well developed. Both tubercles divided into two parts (cranial and caudal). The tubercles are separated by an '''intertubercular groove''', which is wide and has a central saggital ridge ('''intermediate tubercle'''). This ridge fits into a depression on the deep surface of the [[Elbow Muscles - Horse Anatomy#Flexors|biceps tendon]] and restricts movement of the tendon relative to the humerus in the standing horse.

The body of the bone bears the '''teres major tuberosity''' on its medial surface and the '''deltoid tuberosity''', which is opposite, on the lateral surface.

The body of the bone bears the '''teres major tuberosity''' on its medial surface and the '''deltoid tuberosity''', which is opposite, on the lateral surface.

The distal end forms a cylindrical '''condyle''' that transfers weight to the radius. On the lateral aspect of the condyle there is a small '''saggital ridge''' with grooves to allow articulation with the radius and ulna. The medial and lateral '''epicondlyes''' and '''lateral supracondylar crest''' are palpable landmarks. A shallow '''radial fossa''' is just proximal to the condyle on the cranial surface. The deeper '''olecranon fossa''', between the two epicondyles, lies opposite the radial fossa on the caudal surface. There is no supratrochlear foramen between the two fossae in horses.

The distal end forms a cylindrical '''condyle''' that transfers weight to the radius. On the lateral aspect of the condyle there is a small '''saggital ridge''' with grooves to allow articulation with the radius and ulna. The medial and lateral '''epicondyles''' and '''lateral supracondylar crest''' are palpable landmarks. A shallow '''radial fossa''' is just proximal to the condyle on the cranial surface. The deeper '''olecranon fossa''', between the two epicondyles, lies opposite the radial fossa on the caudal surface. There is no supratrochlear foramen between the two fossae in horses.

===[[Forelimb - Anatomy & Physiology#Radius and Ulna|Radius and Ulna]]===

===[[Forelimb - Anatomy & Physiology#Radius and Ulna|Radius and Ulna]]===

====Radius====

====Radius====

On the proximocranial aspect of the radius is the '''radial tuberosity''', the point of insertion of the biceps tendon.  At the distal end of the radius are the medial and lateral ''''styloid processes'''. The lateral styloid process of the radius is in fact, developmentally, the distal end of the ulna.

On the proximocranial aspect of the radius is the '''radial tuberosity''', the point of insertion of the biceps tendon.  At the distal end of the radius are the medial and lateral '''styloid processes'''. The lateral styloid process of the radius is in fact, developmentally, the distal end of the ulna.

====Ulna====

====Ulna====

===[[Forelimb - Anatomy & Physiology#Metacarpals and Metatarsals|Metacarpals and Metatarsals]]===

===[[Forelimb - Anatomy & Physiology#Metacarpals and Metatarsals|Metacarpals and Metatarsals]]===

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 - Horse Anatomy|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.  

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.  

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.  

Metacarpal III is robust and well developed, as it has to bear the entire weight transferred through the limb. The distal end of the bone has an articular surface comprised of two condylar areas separated 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.

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. The 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.

===[[Phalanges - Horse Anatomy|Phalanges]]===

===[[Phalanges - Horse Anatomy|Phalanges]]===

==Pelvic Limb==

 

==[[Hindlimb - Anatomy & Physiology|Pelvic Limb]]==

===Pelvic Girdle and Hip===

===Pelvic Girdle and Hip===

The pelvic girdle is formed by two hip bones which are joined ventrally at the cartilagenous '''pelvic symphysis''' and articulate dorsally with the sacrum. The three components of each hip bone are the [[Hindlimb - Anatomy & Physiology#Ilium|ilium]], [[Hindlimb - Anatomy & Physiology#Pubis|pubis]] and [[Hindlimb - Anatomy & Physiology#Ischium|ischium]]. The bone that articulates with the hip bones to form the hip joint is the [[Hindlimb - Anatomy & Physiology#Femur|femur]].

The pelvic girdle is formed by two hip bones which are joined ventrally at the cartilagenous '''pelvic symphysis''' and articulate dorsally with the sacrum. The three components of each hip bone are the [[Hindlimb - Anatomy & Physiology#Ilium|ilium]], [[Hindlimb - Anatomy & Physiology#Pubis|pubis]] and [[Hindlimb - Anatomy & Physiology#Ischium|ischium]]. The bone that articulates with the hip bones to form the hip joint is the [[Hindlimb - Anatomy & Physiology#Femur|femur]].

===Femur===

===Femur===

The '''[[Hindlimb - Anatomy & Physiology#Femur|femur]]''' has a notched femoral head that is wedge-shaped and opens towards the medial side of the head. The apex of the '''fovea''' on the femoral head serves as the point of attachmentfor the '''ligament of the head of the femur'''. At the base of the fovea  is the '''accessory ligament''' from the prepubic tendon; which has most of its fibres originating from tendon of insertion of the ''rectus abdominis'' muscle. The femoral neck is indistinct in the horse, continuous laterally with '''greater trochanter'''; which is divided into a smaller cranial and larger caudal part. The caudal part of the greater trochanter extends beyond the the dorsal limit of the femoral head and ventrally contributes to lateral border of '''trochanteric fossa'''. The medial border of trochanteric fossa is formed by the '''lesser trochanter'''. The horse has an extra process called the '''third trochanter''' that is situated on the lateral aspect of the proximal third of the femoral shaft and allows the ''superficial gluteal'' muscle to insert here. The third trochanter is also the origin of the ''superficial digital flexor'' muscle. The trochanteric fossa has a raised lateral edge known as the '''lateral supracondylar tuberosity''', where the lateral head of the ''gastrocnemius'' arises. The medial and lateral '''condyles''' at the distal ends of the femur are separated by the '''intercondylar fossa'''. Both condyles extend to form trochlea, the medial ridge of which is larger than lateral ridge and provides a tubercle projecting proximally. This large medial protuberance is critical in the '''patellar locking mechanism''' of the stifle. The trochlea also provides a gliding surface for articulation with the patella.

The '''[[Hindlimb - Anatomy & Physiology#Femur|femur]]''' has a notched femoral head that is wedge-shaped and opens towards the medial side of the head. The apex of the '''fovea''' on the femoral head serves as the point of attachmentfor the '''ligament of the head of the femur'''. At the base of the fovea  is the '''accessory ligament''' from the prepubic tendon; which has most of its fibres originating from tendon of insertion of the ''rectus abdominis'' muscle. The femoral neck is indistinct in the horse, continuous laterally with '''greater trochanter'''; which is divided into a smaller cranial and larger caudal part. The caudal part of the greater trochanter extends beyond the the dorsal limit of the femoral head and ventrally contributes to lateral border of '''trochanteric fossa'''. The medial border of trochanteric fossa is formed by the '''lesser trochanter'''. The horse has an extra process called the '''third trochanter''' that is situated on the lateral aspect of the proximal third of the femoral shaft and allows the [[Rump Muscles - Horse Anatomy|''superficial gluteal'']] muscle to insert here. The third trochanter is also the origin of the [[Carpal and Digital Muscles - Horse Anatomy#Flexors|''superficial digital flexor'']] muscle. The trochanteric fossa has a raised lateral edge known as the '''lateral supracondylar tuberosity''', where the lateral head of the ''gastrocnemius'' arises. The medial and lateral '''condyles''' at the distal ends of the femur are separated by the '''intercondylar fossa'''. Both condyles extend to form trochlea, the medial ridge of which is larger than lateral ridge and provides a tubercle projecting proximally. This large medial protuberance is critical in the [[Stay Apparatus - Horse Anatomy#Pelvic Limb|'''patellar locking mechanism''']] of the stifle. The trochlea also provides a gliding surface for articulation with the patella.

===Patella===

===Patella===

The tarsal bones are arranged in three rows: proximal, middle and distal.  

The tarsal bones are arranged in three rows: proximal, middle and distal.  

*'''Proximal''' row: talus and calcaneus

*'''Proximal''' row: talus and calcaneus

**The calcaneus is punctuated by the '''calcaneal tuberosity''' and the '''sustentaculum tali''', which supports the deep digital flexor tendon. It articulates distally with the fourth tarsal bone.

**The calcaneus is punctuated by the '''calcaneal tuberosity''' and the '''sustentaculum tali''', which supports the [[Tendons - Horse Anatomy#Pelvic Limb|deep digital flexor tendon]]. It articulates distally with the fourth tarsal bone.

**The talus bears a trochlea, which consists of two deep ridges to articulate with the cochlea of the tibia.

**The talus bears a trochlea, which consists of two deep ridges to articulate with the cochlea of the tibia.

*'''Middle''' row: central tarsal bone

*'''Middle''' row: central tarsal bone

{{Learning

{{Learning

|dragster = [[Equine Skeletal Anatomy Dragster resource|Equine Skeleton]]<br>[[:Category:Equine Pelvic Limb Dragster|Equine Hindlimb Resources]]

|dragster = [[Equine Skeletal Anatomy Dragster resource|Equine Skeleton]]<br>[[:Category:Equine Thoracic Limb Dragster|Equine Forelimb Resources]]<br>[[:Category:Equine Pelvic Limb Dragster|Equine Hindlimb Resources]]

|OVAM = [http://www.onlineveterinaryanatomy.net/content/skeletal-structure-equine-forelimb PowerPoint presentation on the skeletal structure of the equine forelimb.]

}}

}}