A horse’s skeleton serves three key functions: protecting essential organs, supporting soft tissues and providing a framework for movement. Bones are held together by ligaments and tendons, and they’re coated in a tough membrane called periosteum. The skeletal system also contains joint capsules that contain synovial fluid to lubricate the joints.
A broken bone in a horse’s leg is serious business, because the legs bear most of the animal’s weight. A typical adult horse has 80 bones in each leg, and if a leg is fractured it can be debilitating for the animal and difficult to repair. Horses are also prone to developing pressure ulcers on their legs, especially if they’re left standing for long periods of time.
Horses are built for speed and long distance running, so their skeletal structure has evolved to make this possible. The skeletal system has gone through major changes over the last 55 million years, including elongating the front and back legs and losing several toes. These changes helped the horse’s ancestors to run faster, as they could cover more ground with each step.
The axial skeleton contains the skull, vertebral column, and ribs. The skull is formed of a series of bones connected to each other: the frontal bone, parietal bone, temporal bone, occipital bone, sphenoid bone and the palatine bone. The vertebral column is made of 7 cervical, 18 thoracic, 6 lumbar, and 5 sacral vertebrae. The sternum is formed from multiple sternebrae that fuse together to connect the 8 “true” pairs of ribs (out of a total of 18).
In the forelimbs, horses have 4 metacarpals. The 1st metacarpal is the one closest to the hoof, and the 4th metacarpal is the one that supports the weight of the head. The metacarpals are attached to phalanges, which are the long bones that make up the fingers and wrist. In humans, each finger has five phalanges and the wrist has four metacarpals.
The radius and humerus are the two main long bones in a horse’s arms. The radius sculpts the forearm, while the humerus creates an angle of around 55 degrees at the elbow joint. The radius is also attached to the carpus (knee) bone, which can flex up to 60 degrees when the horse jumps or does something strenuous.
The hind legs of the horse are supported by a complex structure in the back called the laminar arch. The laminar arch is a strong support for the back, allowing the horse to reach forward with its back legs when running. It also allows the horse to change directions quickly when a rider asks it to, without the hind legs collapsing or becoming injured.