Structure and Function of the Skeleton in Dogs
By: Virginia Wells
Read By: Pet Lovers
Appendicular skeleton – the bones of the limbs
What Is the Skeleton?
The skeleton is the bony framework of the body that is present in all vertebrate animals. It consists of bones, ligaments, and cartilage. The skeleton is composed of the hard tissues of the body, and its primary functions are to support the body, to provide a system of levers used in locomotion, to protect the soft organs of the body, and to produce red blood cells (hematopoiesis).
A dog's skeleton is formed so the dog can run fast, hunt and chase. For example, a dog's shoulder blades are not tightly connected to its skeleton, so the dog has potential for greater motion and flexibility. The dog skeleton has an average of 319 bones.
Where Is the Skeleton Located?
The skeleton is located throughout the entire head and body.
What Is the General Structure of the Skeleton?
The skeleton is composed of three skeletal subunits:
Axial skeleton – the bones of the skull, spine, ribs and sternum
Visceral skeleton – bone that forms part of an organ (such as the middle ear ossicles)
Bones are organs composed of hard, mineralized tissue that provide structural support to the body. Not all dogs have the exact same size and shape to their bones. Since people have been breeding dogs for hundreds of years, bones vary greatly in their length and thickness depending on the specific breed. Even though the tiny Chihuahua has the same number and type of bones as the Great Dane, the size and shape of their bones are very different. Dogs have the greatest variety in the size and configuration of their skeletons of any species of animal.
The skeleton consists of bones that may be classified according to shape:
Long bones are found in the limbs.
Short bones are confined to the wrist (carpus, metacarpus) and ankle (tarsus, metatarsus) regions.
Sesamoid bones are present near freely moving joints, such as the wrist and the knee (stifle).
Flat bones are found in the pelvis where they provide for the attachment of muscles and long bones, and in the head where they surround and protect the eye, ear, sinuses, and brain.
Irregular bones include the vertebral column, all bones of the skull that are not of the flat type, and three parts of the hip bone.
Bones contain several layers of tissue. The periosteum, a fibrous membrane, covers the outside of bone. This membrane is rich in small blood vessels called capillaries, which are responsible for nourishing bone.
The firm, dense, outer layer of bone is called cortical bone. Eighty percent of skeletal bone mass is cortical bone. Cortical bone assumes much of the weight bearing of the body. Cancellous bone (also called trabecular bone) is an inner spongy structure that resembles honeycomb. Cancellous bone accounts for 20 percent of bone mass. This spongy mesh-like bone is specially designed for strength, with the meshwork behaving similar to the steel rebar rods that are buried within concrete.
Bones also contain bone marrow within the hollow center shaft of bone (medullary cavity). Marrow is yellow when it is made up of mostly fat, and it is red in areas where red and white blood cells are produced. Red marrow is present in certain bones, like the leg (femur), upper arm (humerus), pelvis (ilium), and ribs.
What Are the Functions of the Skeleton?
The skeleton serves four functions:
Bones support and protect the body.
Bones serve as levers for muscular action.
Bones serve as a storehouse for calcium and phosphorus, and many other elements.
Bones serve as a factory for red blood cells and for several kinds of white blood cells. In the normal adult dog, it also stores fat.