The equine forelimb
of the horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
is attached to the trunk of the animal by purely muscular connections (the serratus ventralis, trapezius, rhomboideus, latissimus dorsi, brachiocephalicus, subclavius and pectoralis muscles). This is in contrast to the forelimbs of several other vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s, including humans, who have skeletal attachments (the coracoid
In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally...
During locomotion, the forelimb functions primarily for weight-bearing rather than propulsion and supports the forehand
- Balance :A horse's "motor" is located in his hindquarters, and a horse that is heavy on the forehand is not able to properly move forward with impulsion...
of the horse. In the standing horse, the forelimbs together support approximately 60% of the weight of the horse, and this pattern is carried over to locomotion, where the forelimb props the weight of the horse, while forward momentum is generated by the hind limbs (Merkens et al., 1993; Merkens and Schamhardt, 1994). As the horse moves, increasing impulsion
Impulsion is the pushing power of a horse, which comes from its desire to move powerfully forward with energy. However, speed does not create impulsion, and a rushing horse is more likely to be "flat" than impulsive...
shifts the horse's weight to the hindquarters.
The equine forelimb contains three metacarpal bones. These are analogous to the bones within the human palm. The large third metacarpal (informally the cannon bone
bone) provides the major support of the body weight. The smaller second and fourth metacarpals are positioned medially and laterally respectively, toward the palmar side of the third metacarpal. These smaller metacarpals are often called splint bones
. The second and fourth metacarpals terminate distally in small residual swellings, (buttons
) which can be palpated on a living horse. The second and fourth metacarpals are joined to the third metacarpal by fibrous tissue, and occasionally by ossified bridges of bone, which often form after trauma to the region.
The proximal sesamoids are paired bones which lie palmar to the metacarpophalangeal joint (the fetlock joint
Fetlock is the common name for the metacarpophalangeal and metatarsophalangeal joints of horses, large animals, and sometimes dogs. It is formed by the junction of the third metacarpal or metatarsal bones proximad and the proximal phalanx distad...
). These bones are joined to each other by a strong intersesamoidean ligament. These bones are sesamoids
In anatomy, a sesamoid bone is a bone embedded within a tendon.Sesamoids are found in locations where a tendon passes over a joint, such as the hand, knee, and foot. Functionally, they act to protect the tendon and to increase its mechanical effect. The presence of the sesamoid bone holds the...
of the interosseous ligament (the suspensory ligament
) of the forelimb.
The proximal phalanx or long pastern bone lies immediately distal to the third metacarpal bone, with which it articulates to form the condylar metacarpophalangeal joint (fetlock joint
). This joint undergoes large motion in extension (this motion is sometimes called dorsiflexion
) during fast locomotion.
The middle phalanx or short pastern bone lies distal to the proximal phalanx, forming the proximal interphalangeal joint (the pastern joint
). This joint undergoes relatively little movement during locomotion (Degueurce et al., 2001; Crevier-Denoix et al., 2001), although there is evidence to suggest that what little motion it does experience is of quite large importance (Wilson et al., 2001; Ratzlaff and White, 1989).
The distal phalanx or third phalanx (coffin bone
), is the most distal bone of the forelimb, and lies completely within the hoof
A horse hoof is a structure surrounding the distal phalanx of the 3rd digit of each of the four limbs of Equus species, which is covered by complex soft tissue and keratinised structures...
capsule. The distal phalanx articulates with both the middle phalanx and the distal sesamoid, forming the distal interphalangeal joint (the coffin joint
The distal sesamoid, or navicular bone
The navicular bone is a small bone found in the feet of both humans and horses.- Human anatomy :The navicular bone is one of the tarsal bones, found in the foot. Its name derives from the bone's resemblance to a small boat, caused by the strongly concave proximal articular surface...
(note that "navicular bone" is acceptable in a veterinary context), articulates closely with the distal phalanx, to which it is connected by the impar ligament of the navicular bone. The impar ligament is very strong and permits relatively little motion between the navicular bone and the distal phalanx.
- Skeletal system of the horse
The skeletal system of the horse has three major functions in the body. It protects vital organs, provides framework, and supports soft parts of the body. Horses typically have 205 bones...
- Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
- Equine anatomy