There are about 205 bones in a horse’s body, and muscles have to attach to them for movement. The structure of bones is supported by ligaments, tendons and a tough membrane called the periosteum. The joints in the skeleton are lubricated by synovial fluid. A horse’s heart is also supported by structures including a pair of large atria, and the scaphoid bone of the pelvis.
These bones form a rigid framework which supports the limbs, back and other organs. Proper nutrition during pregnancy and the foals’ early years is essential for the development of healthy bone structure. Inadequate diet can stunt bone growth in foals and lead to skeletal disorders.
A horse’s head is shaped like a human’s, but has a much longer neck and larger eyes. The nose is shorter and deeper, and there is a layer of hair on top called the mane and forelock.
The limbs of the horse are similar to those of humans, but have a longer back and a larger tail. There is also a longer scapula, or shoulder blade, which has a rounded area of cartilage at the front that helps form the withers.
There are two main muscle groups in the horse’s back – the flexor and extensor chain. The flexor chain is responsible for forward movement, while the extensor chain moves the neck and back. A well-conditioned flexor and extensor chain create powerful movements such as the extended trot or piaffe.
During rest, a horse’s heart beats about 30 times a minute. During exercise, the rate increases to 250 beats per minute. This is because of the need to supply blood for the muscles and other parts of the body. The heart is regulated by a pacemaker known as the sinoatrial node, which fires rhythmic electrical impulses that make the muscle fibers in the heart contract.
The lower legs are characterized by long, straight bones. The femur joins with the pelvis in a ball-and-socket joint called the hip, and connects to the tibia and patella in the stifle. A shin bone (tibia) connects the foot to the hoof, and there are also a pair of small bones embedded within the tendon called the digital sesamoids. A sac, or bursa, is situated between the third phalanx and the deep flexor tendon. It reduces friction between the bones and tendons.
There are a number of different joints in the horse’s feet, and there is an important balance between the flexion and extension muscles. The flexors and extensors need to be well conditioned to support the weight of the horse and prevent them from becoming too tense and causing injury.