Parts of a Horse's Skeleton

Skeletal System

• The horse's skeletal system, composed of bones and cartilage, gives the body its rigid framework and protects its internal organs. Made of one part organic matter and two parts minerals -- mostly lime salt -- bones are covered with the periosteum, a dense, vascular, connective tissue that nourishes the bone and protects its surface from damage, according to Dr. Rick Parker in "Equine Science." Tendons, ligaments and fibrous capsules provide stability to the joints, the areas where the bones meet, and attach tissues and organs to the skeleton.

  Scientists classify bones by their shape as flat, long, short and irregular. Flat bones enclose cavities containing vital organs and include the ribs, some of the skull bones and the scapula, or shoulder blades. Long bones, found in the horse's limbs, support body weight and propel the horse's movement. Short bones cushion the shock of impact and occur chiefly in the hock and knee. Irregular bones are called "unpaired", meaning they are not jointed with other bones in the body. These include some of the bones of the skull and all of the vertebrae, or bones of the spine.

Axial Skeleton

• The horse's axial skeleton consists of the skull, the ribs and sternum -- also called the breastbone -- the vertebral column, the pelvis and the tail.

  The bones of the horse's skull surround the cranial cavity that houses the animal's brain. Composed of both flat and irregular bones, the skull joins with the facial bones to form the eye and nasal cavities in the front, and melds in the back with the spinal column. Facial bones include the maxilla, or upper jaw, and the mandible, the lower jaw. The mandible attaches to the horse's skull on either side by a freely movable joint below the base of the ear. Both jaws contain openings for the horse's teeth.

  A flexible column of small bones, the horse's spine from the skull toward the tail consists of 7 cervical vertebrae, 18 thoracic vertebrae, and typically 6 lumbar vertebrae. The Arabian breed of horse, the only exception, has only five lumbar vertebrae, according to Lowes Luard in "The Anatomy and Action of the Horse." Five sacral vertebrae fuse together to form the sacrum and 15 to 21 coccygeal vertebrae make up the horse's tail.

  Eighteen pairs of ribs, joined to the thoracic vertebrae on the top and the sternum, or breastbone, on the bottom, form a cavity containing the heart, the lungs, part of the trachea and esophagus, and major blood vessels and nerves.

  Two large flat hip bones shape the pelvis and enclose the pelvic cavity. Each hip bone contains the joint where the femur, the large, upper bone of the hind leg, rotates to provide movement. The upper part of the pelvis forms the point of the horse's croup; the back angle is the point of the rump.

Appendicular Skeleton

• The appendicular skeleton refers to the horse's forelegs and hind legs and is used for movement, grooming, feeding and defense, according to Dr. Ronald Riegel and Susan Hakola in "Illustrated Atlas of Clinical Equine Anatomy and Common Disorders of the Horse."

  Connected only by muscles to the horse's axial skeleton, the forelimbs consist of the scapula, or shoulder blades, the humerus (the long, upper bone), the radius and ulna, the carpal bones, splint bones, and the cannon bone -- the long bone of the lower limb. Bones of the feet include the sesamoids, the first and second phalanx, and the coffin bone.

  The hind limbs attach to the pelvis at the hip joint and include, from the top down, the femur, the patella (or kneecap), the tibia and fibula, tarsals, splint bones and the cannon bone. The bones of the hind feet are the same as those of the fore feet.