The Equine Skeleton
The skeleton has four principle functions in all species.
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It provides rigidity and form to the animal.
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It provides protection to vital organs, such as the brain being protected by the skull.
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It facilitates movement.
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It allows locomotion to take place, the limbs forming strong rigid levers for propulsion.
There are five different type of bones:
Long Bones - form the bulk of the limb bones, e.g. femur.
Flat Bones - fuse together to give a solid, rigid structure, e.g. skull.
Short Bones - make up the knee and hock
Irregular Bones - not the same as any other, e.g. spine vertebrae
Sesamoid Bones - formed within tendons and ligaments to reinforce where they change direction, e.g. fetlock joint.
Evolution of the Skeleton
All vertebrates have seven vertebrae in the neck (with the exception of the sloth), four limbs, and a spinal column supporting head, chest, abdomen, and limbs. The major skeletal differences are in the elongation of the distal limbs of the horse to give greater speed, but at the same time sacrificing manual dexterity.
The lower limbs have developed into long levers, to allow rapid flight from predators. The muscles are placed high up in the limbs, their actions being transmitted to the ends of the limbs via the long tendons. In this was the amount of weight that is moved with the limb is kept to a minimum, so using minimum energy, but the long limbs allow a long stride and maximum speed over distances.
The Head
The horse's brain is about the size of a fist, and lies between the ears and eyes. It is well protected from mechanical damage by the bones of the skull. The bulk of the head is the nasal chambers, air passages though to warm the air before it enters the lungs. The muscles used for eating and the lower jaw, make up another large proportion of the head, allowing the horse to graze continually.
The Distal Limbs
The lower portion of the limbs have been quite markedly adapted. The knee (carpus) in the foreleg is equivalent to our wrist, and the hock (tarsus) to our ankle. Below these joints, the cannon bones represent the bones on the palm of the hand, or instep of the foot. In both cases the cannon bone (metacarpus) is derived from the middle of the five bones. Below the fetlocks, the legs are a modification of the middle finger or toe, with the hoof being a modification of the nail.
