The cat’s skeleton is a lightweight but robust frame designed for speed and agility. The skull has characteristics of a hunting animal, and the limbs are adapted for pouncing and bursts of speed.
The highly flexible spine and maneuverable limbs allow a cat to reach most parts of its body when grooming with its paws, tongue, or teeth. Variances occur in body form among different breeds in cats but nowhere near the extent seen in dogs.
A cat skeleton, like that of all mammals, is a collection of bones connected by joints that allow different amounts of movement and are modified to suit its lifestyle as a carnivore. It provides a framework for the muscles that move the bones and also gives the cat its characteristic shape.
Other functions include the protection of delicate internal organs such as the heart and lungs. The skull contains the brain and houses the sense organs—eyes, ears, and nose—that, among other things, help the cat to detect prey effectively. The orbits are very large and often open posteriorly to allow for the powerful jaw muscles that attach to the skull just behind them.
The cat’s head can turn 180° to groom the back. The hyoid bone sits in the throat where it supports the tongue and voice box (larynx) and is thought to be involved in purring. A cat has seven neck, or cervical, vertebrae—the same number as is seen in nearly all mammals, but it has a long back for its size, with 13 thoracic vertebrae to which the ribs are attached.
The number of vertebrae and their structure increases spinal flexibility, as does the size of the intervertebral spaces, which are occupied with pads of gristly cartilage and allow some movement between adjacent bones.
The tail, an extension of the spine, is made up of about 23 bones in most cat breeds and aids balance when climbing. The rib cage, connected to the spine in the chest region, protects the heart, lungs, stomach, liver, and kidneys.
The cat’s forelimbs are “floating”: the clavicle is greatly reduced in size and the shoulder blade is supported only by muscles and ligaments. This arrangement gives the shoulders a great range of movements and allows a cat to squeeze effortlessly through gaps wide enough to accommodate its head.
Like all carnivores, three of the wrist bones are fused into what is known as the scapholunar bone. It is thought to be an adaptation for climbing that appeared in the early ancestors of the group. Powerful, long hind limbs are attached to the pelvis with ball-and-socket joints and provide drive when running and pouncing.
A domestic cat’s skull is broad with a short nose. It is made up of 29 bones that fuse together as a cat matures and stops growing. The eye sockets, or orbits, are very large and face forward, which allow hunters to judge distance accurately when pouncing on prey.
The lower jaw of the cat is relatively short compared to their wild relatives, especially big cats such as the leopard and lion. It is connected to the skull by a hinge joint that limits movement to the vertical plane and is controlled by strong masseter muscles that provide a powerful bite so that a cat can maintain its hold on struggling prey.
The body form of different types of cat is remarkably uniform when you consider the range of shapes and sizes in dogs. This is partly due to the fact that their function was solely pest control, whereas dogs were used for many different purposes, such as hunting and herding; and partly due to the fact that the genes that control size are not as easy to manipulate.
There are, however, some feline exceptions, such as the tailless Manx and the short-legged Munchkin. The smallest cats, such as the Singapura, reach an adult weight of 4–9lb (2–4kg) and the largest breeds, such as the Highlander, range from 10–25lb (4.5–11kg). The adult weight among dog breeds, on the other hand, can range from 3–175lb (1–79kg).
The relatively large size of some of the new hybrid breeds may be influenced by the genes from their wild cat ancestors. For example, the Savannah is derived from a serval-domestic cat cross and the Chausie from a jungle cat-domestic cat cross. Some variety does occur, however, within the head and body shapes of domestic cats. Oriental breeds, such as the Siamese, tend to have a slender, highly sinuous build, long, thin limbs and tail, and a wedge-shaped head.
Western breeds, such as the British Shorthair, have a stocky shape, with a compact, muscular body, relatively short legs, a thicker tail, and a rounder head. Of course, many breeds, such as the Ragdoll, fall between these two extremes of body shape, and the head and body forms can be combined in different ways by the different cat breeders. Body forms also tend to vary around the world, depending on the climate of a region.