THE HORSE'S BACK
How did the horses back develop?

To appreciate how and why the horses back functions as it does, it is useful and interesting to look briefly at the history of the horse and recognise how and why the horses back developed as it did.

The horse's current skeletal structure is a result of a long process of evolution. Horses as we know them today began as life as a much different creature - the Hyracothercium, (also known as the eohippus) which first existed approximately 55 million years ago.

This small forest dwelling creature was a browser and survived on plant food such as berries and fruit. They looked very different, as shown by the artist's impression here - they had toes instead of hooves, different teeth and importantly for our interest, they had flexible spines.

As climate changes took place and the forests began to decline, these creatures were forced away from their usual habitat onto the outskirts and then onto the grassy planes. By necessity the early horse had to adapt to its new environment, over the course of time physical changes were evident and the horse as we know it today began to develop.

Along with other changes (i.e., teeth, toes / hooves, etc), the structure and shape of the horses body began to adapt, legs became longer and lighter, the neck lengthened to be able to reach the food now taken from the floor, and the spine rigid.

For this discussion of evolution it is the back that primarily concerns us. The horse was now vulnerable living on open Planes, the back was a means of communication seen easily from a distance, and they needed the speed and endurance to be able to escape their predictors and survive.

To achieve this, the structure of the horses back had to change to facilitate the forward propulsion required to outrun and escape its hunters. No longer did this animal scamper around the forest floor in and out of trees but run for long distances at high speed. Additionally the horse needed the ability and strength to take the weight behind to fight, protect itself or to procreate.

As the neck became longer powerful muscles were developed to be able to hold and control the heavy head, so as we can see each change in the horse was a response to the need to survive.

The back and the spine
The spine is made up of a series of vertebrae that are connected by ligaments. These ligaments provide the very slight flexibility to an otherwise rigid spine, however their function is to restrict movement rather than to allow it. As shown below, the vertebra acts as a tunnel for the spinal cord, each of the vertebras has an exit through which the nerves are threaded.


The vertebra varies in size and shape according to their placement, for example the vertebra in the neck are short and chunky, allowing the attachment of a system of layered muscles, this system allows the movement that we see in the horses neck. The Vertebra at the wither have long dorsal spinous processes which give the wither its shape and the bones under the saddle are much smaller and positioned closer together, all being practically vertical. The sacrum makes up the vertebra in the quarters; these five vertebras are fused together. Therefore the horses back is structured as shown in the diagram below:


The horses backbone consists of (on average) 54 bones and vertebrae, these bones are then divided into 5 sections:

  • The neck is made up of 7 Cervical bones
  • The mid back is made up of 18 Thoracic bones - to which the ribs are joined
  • The lumber area is made up of 6 bones
  • The sacrum consists of 5 bones - which are fused together
  • Finally the tail is made up of between 15 and 21 bones

    • Like the human spine the vertebrae are protected and cushioned from one another by intra-vertebral discs, although unlike humans there is no current evidence that horses suffer from slipped discs.


    The neck and tail have the most mobility in the top line, along with the area that joins C7 and T1, and it is the strong muscles in these areas that facilitate this range of movement. The muscles below and on each side of the spine are designed to support the spine, and assist the skeletons function of providing the framework of the horse, protecting the internal organs and supporting what is proportionally a huge gut.

    The supraspinous ligament is known as the nuchal ligament in the cervical area and extends from the poll to the wither, reaching down in a fan like manner to attach to the cervical vertebrae, it continues along the spine from the thoracic-lumber region ending at the sacrum.


    The position of the head is important in achieving the optimum position for the back, as the head lowers the ligament along the back tightens which represents greater traction force along the spine, as the head gets higher and the horse hollows, the ligament becomes looser and therefore there is less supporting traction for the thoracic-lumber regions. Hence the emphasis on riding our horses correctly, thus enabling them to be able to carry the rider more efficiently.

    The use of gadgets forcing the head down is of little use and is detrimental what we are trying to achieve.

    It can be noted in a horse that has been ridden in draw reins or some other restricting equipment that the neck will develop incorrectly at the top of the neck rather than at the bottom. The is a risk of straining or damaging the nuchal ligament, and once damaged this ligament will not repair. This will not facilitate engaging the hindquarters allowing the horse to work through, as is required for proper development of the muscle.

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