4,503
edits
Changes
→Thoracic Limb
{{unfinished}}
{{unfinished}}
==Thoracic Limb==
==Thoracic Limb==
===Scapula===
The horse lacks an acromion, it has a '''tuber scapular''' half way along the spine. The scapular cartilage is reasonably extensive compared to other species.
The horse lacks an acromion, it has a '''tuber scapular''' half way along the spine. The scapular cartilage is reasonably extensive compared to other species.
<br>
<br>
===Humerus===
The intertubercular groove has a central sagittal ridge.
The intertubercular groove has a central sagittal ridge.
<br>
<br>
===Radius and Ulna===
The two bones are fused, so all movement is in a sagittal plane, with very little pronation and supination. The ulna tapers out distally at the middle of the radius shaft. For the proximal quarter of the radius, the bones are joined by ligaments. There is an '''interosseous space''' for the passage of blood vessels and distal to this the bones are fused. The lateral '''styloid process''' of the radius is in fact, developmentally, the distal end of the ulna. It appears as a separate ossification centre in a foal until it fuses at about a year old.
The two bones are fused, so all movement is in a sagittal plane, with very little pronation and supination. The ulna tapers out distally at the middle of the radius shaft. For the proximal quarter of the radius, the bones are joined by ligaments. There is an '''interosseous space''' for the passage of blood vessels and distal to this the bones are fused. The lateral '''styloid process''' of the radius is in fact, developmentally, the distal end of the ulna. It appears as a separate ossification centre in a foal until it fuses at about a year old.
<br>
<br>
===Carpal bones===
Carpal bones comprise two rows:
Carpal bones comprise two rows:
#Proximally (mediolaterally):radial, intermediate, ulnar and accessory bones.
#Proximally (mediolaterally):radial, intermediate, ulnar and accessory bones.
#Distally: 1st carpal bone is small or absent, II-IV are all present.
#Distally: 1st carpal bone is small or absent, II-IV are all present.
<br>
<br>
===Metacarpals and Metatarsals===
Horses are '''perissodactyl''' '''unguligrade''' animals. Unguligrade means that horse's bear their weight on a horny covering (hoof) that surrounds their distal phalanx, perissodactyl means that they have only one weight-bearing digit. They are virtually identical in their structure in the hindlimb and forelimb. The main differences are in the forelimb we 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 want to talk about the fore or hindlimb.
Only Metacarpal III ('''cannon bone''') remains complete whilst metacarpals II and IV 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.
<br>
<br>
===Phalanges===
'''Proximal Phalanx'''
'''Proximal Phalanx'''