The horse’s skeleton is complex, containing flat and long bones. Generally speaking, the flat bones are for protection and the long bones provide movement and support. The axial skeleton contains the skull, vertebrae, sternum and ribs. The appendicular skeleton is the fore and hindlimbs, and the phalangeal bones of the feet. The forelimbs are attached to the fetlock, and the back legs are connected to the pelvis.
The forelimbs are highly adapted for jumping and the gaits, as they don’t directly attach to the spine, but rather hang from muscles and ligaments. This allows the front limb to move freely, and is partially responsible for the horse’s ability to “fly” in the air during a gallop. The hind limbs, on the other hand, create most of the horse’s motion as they are attached to the pelvis and the spine.
Like other tetrapod vertebrates, the spine is made up of several segments called vertebrae that are connected by vertebral ligaments. These ligaments help the vertebrae stay together during movement and support the body’s weight.
From the side, the horse’s sacrum looks a little like an upside-down pyramid, with five oblong spines protruding upward from the bottom of the sacrum (figure 1). The spines get shorter as they go backward, and are positioned so that the back of the horse is toward the tailhead.
Metacarpals II and IV are full proximally and taper distally to a small ridge that is almost flat on the ventral surface. The ridge runs almost the entire length of the shaft. This is a feature that remains constant in equid evolution, as it also exists on the metacarpals of Mesohippus and Phenacodus.
The femur is the longest bone in the body. It forms a ball-and-socket joint with the pelvis to form the hip, and a joint with the tibia at the stifle. The femur also supports the patellar and meniscal ligaments of the knee, as well as the collateral and cruciate ligaments of the stifle.
The tibia runs from the stifle to the hock, and the shin is joined to it by the fibula. The tibia is very important for the horse’s motion, as it provides attachment points for the patellar and musculoskeletal system of the hock.