Anatomy of the Horse Leg Skeletal System

horse leg skeleton

The horse’s light-weight, strong, shock-absorbing legs are a key part of their amazing speed. As horses evolved from forest-dwellers into grazing grassland creatures, their leg bones grew longer. But it was the bones of the foot that became most long, giving horses a long, sturdy stride and the ability to quickly move their body weight forward. The hind legs also became shorter, with the ankle bone moving higher up on the leg. This allows the horse to balance its weight more evenly over both feet.

The keratinous hoof is made of a layer of keratin that is deposited in small clusters on the bottom of the foot. These keratin layers are known as lamellae. The frog, the soft connective tissue located at the base of the hoof, is softer than and distinct from the hoof proper and has its own keratin-generating structure.

As the hoof grows, the keratinous structures merge together as the horn of the hoof is formed. A cross section of the adult hoof (NS 297) shows that the frog and keratinous hoof have merged distally, but still retain their separate structure in the centre. The keratinous hoof is heavily supplied with blood through two arteries which run down the back of the leg and into the foot. This blood flow is important for allowing growth of new horn, absorbing impact, and damping shock.

Anatomy of the horse

The forelimbs of modern horses are organized into the stylopod (humerus and ulna) and the autopod segments (carpals and metacarpals). As horses evolved, the development of these distal autopod segments was more variable than the proximal stylopod and zeugopod elements. This is likely because these segments were less adapted to the changing conditions of the environment and were subject to the influence of other equid species that had already developed a more stable distal forelimb anatomy.

These changes were most pronounced in the metacarpals of the hind limb. The metacarpals of the horse are isometrically smaller than those of other tetrapods, but have a more robust proximal area that tapers to a ridge distally. The ridge is made up of a textured area on the dorsal surface of the metacarpal which extends distally to a ridge that narrows to a point.

The metacarpals of the horse are relatively strong, but can be fractured if struck by a heavy object. Engineers have studied how the bones of the horse metacarpal are able to resist such forces and have found that the textured surface of the bone has a special feature, an elliptical hole in the middle of the plate. This elliptical shape allows stresses to be concentrated away from the hole and toward stronger regions of the bone, increasing its strength. This helps to explain why the horse metacarpal does not fracture as often as it might in other animals.