The skeleton is a jointed structure of bones controlled by muscles. It supports the whole anatomy and contains the central nervous system. It also stores minerals and marrow for the body's use.
The bones are living organisms whose form, structure, and composition vary during the animal's life.
A dog has approximately 320 bones. The axial skeleton consists of 134 bones, including the skull, spinal column, breastbone, ribs, and hyoid bone.
The appendicular skeleton consists of 186 bones, including those of the limbs, and in male dogs the penile bone.
There are four types of bones:
- long bones such as the femur and tibia in the leg;
- flat bones such as the scapula (shoulder-blade) and cranium (skull);
- irregular bones such as the vertebrae;
- short bones such as the phalanges (bones of the paws); and
- the sesamoid bones, which are really ossified portions of tendons.
A dog's spinal column runs horizontally between the shoulders and the pelvis. It consists of 7 cervical, 13 thoracic, and 7 lumbar vertebrae, as well as 3 sacral vertebrae fused to form the sacrum.
There are also caudal vertebrae which vary in number according to the breed and the individual dog.
At the level of the thorax, the spinal column joins the ribs and the sternum (breastbone).
The skeleton of the head is made up of two sets of bones: the cranial bones, which protect the brain (cerebrum, cerebellum, and brain stem), and the facial bones around the mouth and nose cavities.
The proportions of these bones vary from one breed to another.
The limbs are connected to the axial skeleton by girdles. The shoulder girdle consists solely of two scapulae, one on each side of the body, since dogs, like other running animals, have no clavicles (collarbones).
The pelvic girdle links the hind legs to the spine. Together with the sacrum it forms the pelvis.
The bones of the limbs correspond to those in humans. In the foreleg (arm) the upper part is supported by the humerus; the lower part is supported by the radius and the ulna; the forepaw (hand) is supported by the carpus, the metacarpus, and five toes (fingers) of three phalanges each, except for the dew-claw (thumb), which has only two.
The hind leg consists of the thigh, supported by the femur; the leg, supported by the tibia and fibula; the foot, containing the tarsus and metatarsus; and four toes, each having three phalanges.