Feline Anatomy – Bones and Joints

Cats are Built for Speed

Three Kinds of Joint Allow for Superb Flexibility

 picture of cat skeleton

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Feline Anatomy: Skeleton.The feline skeleton evolved for a lifestyle of speed and agility. A cat’s slender but robust legs support a narrow ribcage and a highly supple spine. Its shoulder blades are unattached to the main skeleton, permitting superb flexibility at any speed. The entire structure is held together by strong but elastic ligaments. The hard structure of the skeleton protects the internal organs, provides points of attachment for muscles, and acts as a system of levers and joints necessary for fluid movement.

Feline anatomy: The structure and growth of bone

Bones grow continuously during kittenhood. The skull begins as separate bones, to permit birth, and then fuses along suture lines. The long bones of the limbs and ribcage begin as hollow cartilage tubes; they calcify in infancy, becoming bone. Bones increase in length by production of bone at the growth plates, or epiphyses, at their ends. Epiphyses are nourished by a rich supply of tiny arteries. Growth is also influenced by growth and sex hormones. Curiously, the latter seems to inhibit activity: cats neutered very early grow slightly longer leg bones. If a bone breaks, bone cells produce new bone to bridge the gap. The cat’s skeleton is a tiny replica of that of the big cats. The vertebrae give great mobility and the forelegs provide superb flexibility. The structure of the wrists allows dexterity in actions such as walking along narrow ledges.

Feline anatomy: Joints

Cats have three different kinds of joints: fibrous, cartilaginous, and synovial. Each has a different level of flexibility and a different function.

  • Fibrous joints: This type of joint has no flexibility at all. The mandible (jawbone), for example, is really made up of two bones with a fibrous joint at the midline. If a cat lands heavily on its jawbone in a fall, this joint may split; so, although the cat may seem to have broken its jaw, it has, in fact, torn this fibrous joint.
  • Cartilaginous joints: Some joints, like the thick discs between the spinal vertebrae, are made from tough cartilage. In cats, these are looser and more supple than similar joints in other species, providing a greater degree of flexibility in the torso. During infancy, the growth plates at the ends of the long bones are temporarily cartilaginous joints, and as such they are less sturdy and more prone to damage than in adulthood.
  • Synovial joints: These are found where the most movement is needed, such as in the legs. They are hinged or ball-and-socket joints, with smooth, articulating cartilage on their contact surfaces, and are surrounded by a joint capsule filled with lubricating synovial fluid. These joints may suffer from excess production of synovial fluid or inflammation due to arthritis or synovitis through injury, disease, or allergy.

Feline anatomy: Ligaments

The tough bands that hold bones together, ligaments, are important in all joints, but vital in synovial joints, which are inherently unstable. The hip joint, in particular, is prone to dislocation.

Skeletal variations and problems

Environmental pressures create natural variations in the cat’s skeleton. In hot climates, cats are naturally small, with a higher surface-area-to-weight ratio, which helps cooling. Cats in cold climates have larger, heavier skeletons. In the wild, severe skeletal anomalies disappear, usually because lethal problems are associated with them. In recent times, active selection for breed standards has led to more dramatic skeletal variations. This has perpetuated the most considerable, and worrying, skeletal problems.

Retractable claws

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Claws grow from the last bone of the toe and are , anchored by tendons. They consist of modified skin: an outer cuticle of hard protein (keratin) protects the dermis, or quick. Cats’ claws are kept sheathed for protection on the move. At rest, ligaments naturally sheath the claws. A cat exposes its claws by contracting digital flexor muscles in its legs, pulling taut the flexor tendons under the paw.

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