Structure and Function of the Skeleton in Cats

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). The cat skeleton has an average of 250 bones.

The cat's skeletal design is very similar to ours, although there are two significant differences. First, a cat's spine or backbone contains more bones that ours, mainly because of the tail. Their vertebrae are not as tightly connected as ours, making the cat's spine extremely flexible. This feature enables the cat to arch his back and to twist or turn his body so that he can squeeze through the tiniest gaps. Second, the cat lacks a clavicle or collarbone.

A collarbone would broaden the chest, thus reducing the cat's ability to get through narrow spaces, and limiting the length of his stride.

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:

Appendicular skeleton – the bones of the limbs

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 cats have the exact same size and shape to their bones. Since people have been breeding cats for thousands of years, bones may vary in their length and thickness depending on the specific breed.

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 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 cat, it also stores fat.