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Feline Design

Evolution appears to have been particularly efficient in the design of the domestic cat. The cat remains as intended – an efficient, perfect carnivore of convenient size, still able to hunt and kill small animals.

The cat’s framework allows graceful, fluid and perfectly coordinated movement at all speeds. The sleekly muscled body and legs allow athletic leaps and bounds. Its retractable claws allow for swift running while sheathed, and for secure holding and gripping when extended. The cat’s well-developed brain allows for swift information of facts and fast reactions. Its adaptable eyes can cope with extremes of light conditions, allowing perfect vision on the brightest of days as well as in the dimmest of twilights. Its flexible ears can maneuver to catch the faintest rustling sound and its sensitive nose can identify the most subtle of scents. The cat is a practically perfect product of its early environment.

The Skelton
Light yet incredibly sturdy, the feline skeleton evolved for a lifestyle that called for sudden bursts of speed combined with dexterous agility. This substructure is the basis of the extraordinary grace of the cat’s movement.

Although the domestic cat is so much smaller than a human, its skeleton contains 230 bones, compared with the 206 bones of a human skeleton. But just like our skeleton, the feline skeleton is a bony framework supporting the body tissues. The bones of the limbs, spine, chest and pelvis provide a sophisticated system of levers manipulated by the cat’s powerful muscles, while other bony structures protect the vital organs; for instance, the arched ribcage and pelvis protect the heart, lungs and reproductive systems, and the rigid skull protects the delicate brain.

The cat’s skeleton is made from four distinct types of bones, known as long bones, short bone, irregular bones, and flat bones. The long bones are approximately cylindrical in shape with hollow shafts containing bone marrow, in which the red blood corpuscles are manufactured. These bones include the limb bones such as the femur, the humerus, the tibia, the fibula, the radius and the ulna. The short bones consist of a core of spongy material surrounded by compact bone, and are to be found in the cat’s toes and kneecaps. Irregular bones are similar to short bones in composition, and are the bones which form the spine. The flat bones consist of two layers of compact bone with a central layer of spongy bone, and they form the cat’s skull, pelvis and shoulder-blades.

The skull is formed from interlocking sections of flat bone, and in very young kittens the edges are not fused, so great care must be taken to avoid head injuries. The flat pieces of bone forming the skull are pierced by hundreds of tiny holes, through which pass blood vessels and nerves.

One end of the spine is attached to t he skull and the other end terminates in the tail tip. Some of the bones of the vertebral column are hollow and contain the spinal cord, while bony projections on each of the segments provide attachments points for the strong muscles of the back. Mobile, rather than rigid, connections from the spine to the pelvic girdle and the shoulder joints help to make the domestic cat one of the most agile and flexible of all mammals.

The arrangement of the cat’s collarbone means that it has a high degree of free movement in the shoulder region. The shoulder-blade, or scapula, is almost triangular in shape and is attached to the first long bone of the foreleg, the humerus, which in turn is attached to the two long bones of the forearm – the thick radius, behind which lies the thinner ulna. The forearm of the cat is easily discerned since it is the part of the foreleg which stands free from the body, while the part formed by the humerus runs down from the high point of the shoulder, along the line of the ribs, to the elbow. The forepaws correspond with the fingers of the human hand, being formed from sets of three small bones, each of which forms one digit. The final bones of each digit articulate, enabling the claws to be extended or retracted. The cat has no thumb, its position being taken by two small redundant bones forming the dew claw.

The pelvis provides an encircling structure to protect vital internal organs. A ball-and-socket joint connects the pelvis to the very long femur, or thigh bone, which connects at its lower end to yet another long bone, the tibia. Here is found the kneecap, or patella, which slides over the smooth end of the femur. From the kneecap down, the hind limb stands free from the cat’s body. The tibia is reinforced by a slimmer long bone, the fibula, down to the cat’s well developed hock. The bones of the hind foot are very similar to those of the forefoot, but the first toe is absent. The cat’s silent, swift gait is aided by its flexible leg joints and the fact that it walks and runs on tiptoe.

The cat’s ribcage is formed from elongated flattened bones. Thirteen pairs of ribs are attached by strong muscles, which can vary the volume of the chest cavity, enabling the lungs to expand and contract. Although the rib bones are not hollow, they do contain substantial amounts of bone marrow and are therefore able to produce a proportion of the body’s red blood cells.

All breeds of domestic cat have retained the same basic size, shape and structure as their ancestors, unlike dogs, which have been selectively bred to produce a wide range of heights and shapes. Cats are therefore fortunately free from many of the skeletal abnormalities that can afflict dogs.

The Muscular System
A complex network of muscles overlays the feline skeleton and is responsible for the general outline shape of the animal as well as for providing the power for movement. The muscles which straighten and extend a joint are known as extensor muscles, while flexor muscles bend and flex the joint. Abductor muscles move the limbs away from the body, while adductors draw the limbs towards the body. All muscles consist of specialized fibrous tissue designed to contract in response to stimuli received from the nerves. Three types of muscles are found in the cat’s body: striated, smooth and cardiac. Striated muscle operates all the limbs and other parts of the anima’s body that are under voluntary control. Smooth or unstriated muscle is connected to the parts of the body not under voluntary control, including the intestinal wall and the walls of the blood vessels. Cardiac muscle is unique in having the ability to contract and expand with rhythmic action without becoming fatigued, and is found only in the heart.

Circulation and Respiration
All parts of the cat’s body require oxygen and this is carried by the circulatory system. The cat’s heart beats at about 110 to 140 times each minute and its pump-like action first pushes the blood around part of the circuit to the lungs, where it is oxygenated. The blood then passes back through the heart and around the rest of the circuit, which includes all the other organs of the body. Certain arteries carry the blood at high pressure from the heart, forcing it through fine capillaries into the tissues, where exchanges of gases, nutrients and hormones take place. Blood at low pressure is collected by the veins ad returned to the heart for re-circulation. The lungs are a pair of spongy sacs providing the necessary link between the body’s blood system and the oxygen in the outside atmosphere. The muscular action of the ribcage draws air into the lungs where it eventually passes into tiny alveoli – special air sacs encased by thin-walled blood vessels that allow oxygen to pass into the bloodstream and carbon dioxide to pass out. The blood thus ‘picks up’ oxygen for use in the body and returns carbon dioxide to the lungs for expulsion as the cat breathes out.

As well as conveying oxygen and carbon dioxide, among the bloods other functions are the transport of food to the body cells and the removal of waste products. Nutrients are collected from the digestive system (including the intestines, the liver and the pancreas) once food is eaten by the cat has been broken down by the body’s digestive system into simpler chemical substances.

Cats evolved from animals that lived on the carcasses of other animals, and have digestive systems that reflect this history. Digestive processes start in the cat’s mouth, where food is first mixed with saliva. Then, after swallowing, the food passes into the stomach, where digestive juices and churning action of the stomach break the food down still further. From the stomach, the liquidized mixture passes a little at a time into the small intestine, where further digestive juices from the pancreas and the gut lining are added. Bile manufactured by the liver and stored in the gall bladder, aids the digestive process and nutrients from the liquid are absorbed by the blood through the intestinal wall. In the large intestine most of the water left in the liquid is removed, leaving semi-solid feces to be passed through the anus.

The kidneys are the principal waste-disposal organs of the body. They filter unwanted materials and excess water from the blood to form urine, which is stored in the bladder before being passed out of the body. The kidneys’ most important role is in maintaining the body’s critical water balance. In hot weather or if the cat is deprived of drinking water, the urine becomes very concentrated as the kidneys greatly reduce water excretion.

The bodily functions of the cat are controlled on two levels; by the nervous system and by the endocrine system. The cat’s nervous system is very precise. Its sensory preceptors are able to detect every event important to survival, while the brain initiates nerve messages to control the body’s responses. The endocrine system consists of a set of glands which secrete hormones. Hormones are basically chemical messengers deigned to travel through the blood stream and to cause certain organs to carry out specific functions. Each gland secretes specialized hormones; the thyroid hormone influences growth; the adrenal hormones influence kidney function, mobilize the cat’s body for flight or fight and help it to counteract stress; and sex hormones influence reproductive processes. The pituitary gland produces several hormones: one helps to regulate the blood pressure and others act on particular glands, stimulating production of their own hormones. The pituitary, often termed the ‘master’ gland, is under the direct control of the hypothalamus, the control center of the cat’s brain.

Skin and Fur
To the cat lover, the fur of the cat is often judged by its appealing color, pattern or texture. To the cat, the fur is important as a barrier between its body and the environment, maintaining its temperature and protecting against injury and excessive sunlight, wind and wet.

The skim of the cat is made up of two main layers. The outer layer is constantly being replaced as t he surface cells die and are sloughed off. Its function is mainly one of protection. The inner layer contains important specialized structures such as glands and pigments.

The condition of the cat’s skin can often give an indication of the animal’s state of health. In a fit, healthy cat the skin is loose, elastic and pliable. If the skin at the scruff of the neck is taken in hand, lifted ad then released, it immediately resumes its normal position. In the sick cat, the skin becomes stiff and unyielding. When the scruff is lifted, it remains in a pinched position and must be massaged back into place. The color of the skin, too, can be a barometer of the cat’s condition. A pallid appearance often points to a severe infestation by parasites, or to stress, trauma, shock or a lack of some vital dietary requirement. A blue tone to the skin might denote respiratory disease, heart failure or leukemia, while a reddish tone indicates an inflammatory condition of the skin itself or of the underlying tissues. A yellowing of the skin suggests jaundice: one symptom of several of the more serious feline diseases.

Sweat glands are contained in the cat’s skin, and these are found over the entire body with the exception of the nose. There are two types of sweat glands. Apocrine glands secrete a milky fluid which may become involved in attracting sexual partners. In some areas of the cat’s body groups of apocrine glands, along with sebaceous glands, certainly do produce scented secretions important in territorial marking and for leaving recognition markings on humans and other animals.

These groups of glands are situated on the chin, the lips, the temples and the base of the tail. The cat also has eccrine sweat glands. These are found in the pads of its feet and produce secretions which cause sets of damp footprints whenever the cat is hot or apprehensive. Usually, however, the sweat glands seem to play little part in temperature control in the cat, which may be seen to actively lose body heat by panting and by the cooling effect produced by saliva applied to the coat during self-grooming, which ten evaporates.

The hairless areas of the cat’s body, such as the nose, footpads and nipples, have a distinctive skin structure. The nose leather is extremely sensitive to touch and is kept damp by mucosal secretions from the nostrils. The skin of the footpads is thick and rough, and more sensitive to pressure than to touch. It provides a tough surface for walking and climbing, while allowing the distinctive, silent tread so characteristic of the cat.

The claws of the cat grow continuously from the base. They are formed of keratin, a horny protein layer that also forms the outer layer of the skin. The inner layer, or dermis, of the claw is known as the quick and is covered by a hard cuticle. The dermis is attached to the terminal bone of the toe and can be retracted under a fold of skin lying over the tip of the toe. The sharp tips of the claws with their hook-like curve and needle features are ideal for capturing and securing prey and because they retract, they do not make any noise when stalking prey.

Fur is derived from the outer layer of the skin and acts mainly as an insulating layer, keeping the cat warm in cold weather and cool in hot weather. The fur forms a complete pelt over the body and is modified in some areas for form whiskers, eyelashes and the sensitive carpal hairs on the back of the forelegs. Normal cat fur is made up of three different types of hair – guard hairs, bristle or awn hairs and wool or down hairs. The topcoat of a cat consists of guard hairs and awn hairs and acts as protective covering while the insulating undercoat is composed of the soft down hairs. Special muscles attached to large follicles enable the hairs to stand upright and erect whenever the cat is startled, angry or feeling cold. The shedding of dead hairs generally takes place during certain seasons of the year. Hair loss also follows some debilitating illnesses as well as infectious diseases such as eczema, mange and ringworm.

Whiskers are specialized hairs which grow in neat rows on either side of the cat’s upper lip. They are extremely sensitive and the slightest touch causes a message to be transmitted directly to the brain. Cat’s whiskers are used for touching and testing objects and obstacles, for sensing environmental changes and in registering certain emotions. Cats with poor vision may be seen to actively use their whiskers for testing their environment, walking cautiously and turning their head from side to side. Cats with normal vision also use their whiskers in dim light conditions to help feel their way about.

Although humans have better overall daylight vision than cats, it is in the twilight that the feline really comes into its own. While it obviously cannot see in total darkness, it has very good vision in the dimmest of lights. It is the ability of the cat’s pupil to expand and contract in response to the amount of light available that explains the variable appearance of the cat’s eye. In dim light the iris relaxes and the pupil dilates. Light passes through the curved cornea and lens to strike the retina at the back of the eye. The light is then reflected by a special layer of iridescent cells called the tapetum lucidium and this causes the strange glowing effect often seen when cats’ eyes are seen at night by lights. It is probable that the tapetum or even the retina itself may have a photo-multiplying effect on received light. The delicate mechanism of the feline eye must be protected from the effects of very strong light, however, and during such conditions the iris is able to contract, closing down to a mere slit.

The eyes of the cat face forward and the fields of vision overlap producing stereoscopic vision, enabling the cat to accurately judge distances when searching out and attacking its prey. Cats’ eyes are comparatively large and are set in deep pockets. They do not move freely and so often the cat has to turn its head and sometimes its whole body, in order to keep objects in sharp focus. Cats are said to be color blind but while they might not see colors as humans do, they certainly have sophisticated methods of distinguishing between colors. Tests have shown that the color-sensitive cone cells on their retinas are sensitive to blue and green, but not to red. In trials, cats differentiate between green, blue and yellow, but do not recognize red.

In addition to the upper and lower eyelids, the cat has a third eyelid known as the nicitating membrane or haw. This is a sheet of pale tissue normally tucked out of sight at the inner corner of each eye. As the eye moves within the socket, this membrane moves diagonally upwards over the front of the eyeball, removing dust and dirt and keeping the eye lubricated and moist. Whenever a cat is incubating an illness, out of condition or perhaps harboring internal parasites, the tiny pad of fat normally found behind the eyeball is inclined to shrink, causing the eyeball to retract slightly into the socket. This in turn causes the haw to partially extend across the eye. The cat is then said to ‘have its haws up’ and this condition is often taken as an early warning of illness.

Apart from the raised haws, the eyes of the cat can be used in other ways to diagnose illness, for a change in their general appearance is often the first sign that something is affecting the cat’s health. Weeping or discharging eyes point to the onset of diseases, while a distinct change in the color of the iris indicates jaundice. The eyes are also sensitive to foreign bodies such as grass seeds and awns which may lodge in the eyelids and they may be injured during fights and scuffles.

Sounds consist of vibrations and reach the cat’s ears as pressure waves. The vibrations of the waves trigger nerve signals to the cat’s brain. The cat has highly sensitive hearing: it is able to differentiate between a much wider range of sounds than a human, including ultrasonic sounds, to which we are totally oblivious.

The ear of the cat consists of three sections. Outwardly we see the mobile, cone-shaped pinna or earflap, naturally erect and forward-facing, but equipped with more than a dozen muscles, which enable it to move and accurately collect the slightest of sound vibrations, thus determining their source. The pinna acts as a funnel down which sound travels to the eardrum, stretched across the ear canal. The middle ear is made up of three small bones which act like a system of levers and convert the large, weak vibrations of the eardrum into small, strong vibrations of the cochlea of the inner ear. Here the sound waves are analyzed and converted into nerve impulses to be sent along the auditory nerve to the brain. Being of relatively high intelligence and with a sophisticated mammalian brain, the cat is capable of learning a wide range of special sounds, including its own name and a series of simple command words.

The cat’s ear is able to register frequencies approximately two octaves higher than the human ear but is les sensitive to the lower frequencies. Hearing acuity may diminish with the onset of old age and some elderly cats become totally deaf. Deafness can also result from ear disease or it may be hereditary when it is sometimes linked with white coat color in cats. Cats with normal hearing are able to accurately locate the source of the slightest sounds, a trait which as ensured the survival of the species and a boon for the animal that prefers to hunt at dawn and dusk.

Smelling and Tasting
Like most carnivores, the cat has a highly developed sense of smell. Very sensitive nerve endings in the form of fine olfactory hairs line the nasal cavities and these are linked with nerve cells connected to the brain. Here the olfactory region is much larger than would normally be expected in an animal as small as the domestic cat and this indicates just how vital to its survival is the sense of smell.

As well as performing a vital function in the hunt for food, this sense is important to the cat in its sexual life. A small pouch lined with receptor cells exists in the roof of the cat’s mouth; this is known as the vomeronasal sac or Jacobson’s organ, after its discoverer. When the cat receives an unusual or subtle scent, the minute particles of the scent are caught by the tongue and pressed against the roof of the mouth. The cat grimaces with a distinctive facial gesture called the flehmen reaction as the scent is transferred to the Jacobson’s organ for identification. The reaction can be stimulated when a tom cat smells another cat’s urine or scents a female in heat, and many cats exhibit this strange expression when given catnip.

The cat’s tongue is very specialized with a rough surface caused by the presence of large papillae. These are used for rasping and softening food, licking the meat from bones and grooming the fur. The papillae along the center of the tongue do not carry taste receptors but special mushroom-shaped papillae along the front and side edges of the tongue and several cup-shaped papillae at the back, do not carry taste buds. The cat shows no response to sweet tastes. It is remarkable, too, in its strong sensitivity to water tastes and its receptors for tasting water far outnumber the few sweet taste buds present in the animal’s mouth.

The tongue is long, strong and flexible, and its edge is capable of curling like the bowl of a spoon, enabling the cat to lap liquids. It generally laps three, four or five times to fill the mouth before swallowing. When eating prey, the cat may lick the carcass to soften it before starting to eat.

Teeth and Diet
The cat’s dentition is highly specialized, as befits a small, successful carnivorous animal. In the adult the mouth has twelve incisors, four canines, ten premolars and four molars, giving a full set of thirty teeth. Kittens are born with tiny teeth just visible in the pale gums and by six weeks of age these have erupted and are needle-sharp. Young kittens aid their own teething process by chewing on any hard material available and should be given long, thin strips of raw meat and suitable meaty bones, at this stage of their development. The baby teeth are generally shed quite painlessly as the permanent teeth come through but very occasionally double dentition occurs and the kitten stops eating.

Cats’ teeth are designed not for chewing but for tearing and biting. When prey is caught the cat first tears a piece from the carcass and swallows it whole. The salivary juices therefore have very little time to go into action while the food is in the cat’s mouth. Cats lack salivary amylase, the enzyme which initiates digestion of dietary starches and an increase in dietary carbohydrate does not stimulate an increase in enzyme activity. This adaptation reflects the nutritional composition of the typical prey animal. This also means that vegetable material present in the cat’s diet remain virtually unchanged by the time it reaches the small intestine. Conversely, the stomach of the cat contains much stronger digestive juices than that of a human’s and is able to reduce quite hard bone to soft matter. Small rodents and birds may be swallowed in chunks and nay parts not quickly broken down, such as feather and fur, may be regurgitated and either discarded or re-eaten by the animal.

The eating habits of cats are not always sensible or hygienic and as they also use their tongues for regular self-grooming sessions they inevitably ingest diet, dust, grease and hair. Cats like to drink almost stagnant water, given the opportunity. Confined cats, denied a full natural diet and the outdoors must be compensated. They need well-balanced meals with plenty of different textures, ensuring that their mouths and gums are sufficiently exercised and that their digestive systems are well maintained.


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The information on this website is not intended to replace Veterinary medical advice.