The skeletal system provides protection for vital organs, protects and supports soft parts of the body and allows movement. It consists of approximately 205 bones (this can vary as some bones fuse together) and can be divided into the Axial skeleton which is comprised of the skull, spinal cord, ribs and pelvic girdle and the Appendicular skeleton consisting of the two forelimbs and two hindlimbs.
The Appendicular skeleton is made up of the humerus, radius and ulna, carpal bones, metacarpal bones, phalanges and sesamoids. This skeleton is particularly important for the horse as it enables them to run fast by lengthening and straightening their forelimbs. The scapula connects the forelimb to the axial skeleton and the humerus supports the arm. The radius and ulna support the humerus, forming the elbow joint. The carpal bones and metacarpal bones form the wrist, and the phalanges and sesamoids are located in the feet.
These bones are joined to each other by ligaments and tendons which allow for movement. It is important that these muscles and tendons work in harmony to ensure that movement occurs. If the bones are misaligned it is more likely that there will be strain on the ligaments and tendons which could result in injury. The skeletal system also includes long bones which help with locomotion and store minerals. There are also flat bones which enclose body cavities such as the ribs and there are irregular or ‘funny’ bones.
An important function of the skeletal system is to provide support for soft parts of the body such as the muscles, skin and internal organs. This is essential for the survival of the animal as without it, the soft tissues would wither and wither away. The skeletal system also plays a role in the coordination of the activities of the various parts of the body and in absorbing energy generated during locomotion.
In the case of a horse, their limbs are highly adapted for fast running as they only take their weight on one lower leg bone (the central digit which is encased in a hoof). This reduction in weight and bulk allows the horse to move quickly by allowing the limb to be elongated and to be bent at the knee and hock.
As prey animals the horse has had to adapt to an environment in which they are hunted so they have to be able to turn quickly, hence the very reduced muscle below the knee and hock.
The fetlock and coffin joints are also unique to the horse as they feature a pair of sesamoids called the proximal and distal sesamoids. These act as a pulley for the flexor tendons and reduce the amount of friction that is created as the muscles are shortened during flexion, thus increasing efficiency of movement.