The Dog’s Body and How It Functions

A general knowledge of your dog's body and how it functions will prove helpful in his daily care. It will also be useful in giving the location of wounds or symptoms to the veteri­narian over the telephone.

First, let us consider the nature of the dog. He is a hunter and scavenger. He comes from a long line of carnivorous animals, tracing back more than 40 million years to the Eocene epoch. His earliest ancestor was a civetlike animal named Miacis, a meat eater that lived in the prehistoric forests. The dog is related to the wolf, coyote, fox, jackal, dingo, raccoon, dhole and fennec. All of these, including the domestic dog, are geared for the hunt. They are all predators and scavengers and all show the same wolf- or dog-like appearance.

Nature has endowed the dog with a body to help him perform his role of a hunter. His nervous and muscular sys­tems are designed to make him tops in his trade of hunter. He has adequate nervous energy, speed and muscular control —all vital assets to the hunting animal.

In developing the dog, Nature practiced "natural" selec­tion, producing an animal that is adaptable to a variety of climates and conditions. Among all the animals, the dog is the most cosmopolitan in this respect. There is hardly an area on earth that does not have some member of the dog family.

Man, however, has taken a hand in the development of the dog. He has practiced what is known as "selective breed­ing." For centuries, men have developed dogs for specialized purposes, for hunting, herding livestock, police work and as draft animals. But so far, nobody has been able to radically change the basic nature of the dog or his body. The dog is still a dog. And despite all the fancy coiffures—the custom-made sweaters and blankets—the dog remains a hunter and scavenger.

Even though the dog is a specialized animal, there is not a wide variation between his body and that of other mam­mals. Or man, for that matter. Your dog has all the vital organs found in other mammals: heart, lungs, liver, pancreas, spleen, stomach, intestines, kidneys, bladder, etc. He does have some variations in the functions of these organs. And he differs somewhat in his skeletal and muscular structure. But, in general, we can make many comparisons between the dog's body and organs and those of other animals and man.

HAIR AND SKIN

Hair

The dog's hair and its condition is very important to his well-being. It serves as an insulator against both heat and cold. If the dog's hair is in poor condition—thin, patchy or dry—it cannot perform its function as insulator. Therefore, it's imperative that you keep your dog's hair in top condi­tion. A fancy trim, while it may be stylish, is of no value to the dog if his hair is sparse and unthrifty, exposing him to cold or heat.
Normally, the dog sheds his hair twice a year, in the spring and fall. During shedding, the old hair is replaced with new.

Nature does this to keep the dog in a more or less standard coat, protecting him at all times. Excessive shedding of hair, caused by disease, parasites or faulty diet, defeats this pur­pose. The result is the dog is uncomfortable.

The dog's hair has another protective function besides serving as an insulator. When angry or aroused, the dog's hair "stands on end." This rising of the hair or feathers is a very common reaction in animals and birds. It's also found in certain reptiles. The puff adder snake, for instance, will puff up or elate when aroused. It's all done to scare or im­press the enemy. Watch your dog the next time he's aroused or frightened. His reaction to being startled or sensing a strange person or animal is to growl and raise the hairs along his back. The reaction is controlled by many small muscles along the dog's back. Human beings sometimes experience a. similar reaction when faced with the unknown or eerie.

Skin

There is a wide variation in the color of the skin among dogs. Some dogs have pink skin, some dark and others mottled. But the color of the dog's skin has no bearing on its function.

The dog's skin can be visualized as a binder or wrapper to cover the skeleton, muscles, nerves, viscera, etc. It has more or less the same glands as human skin. But the dog's skin glands do not function the same as those of human beings. Take, for example, the dog's sweat glands. At one time we were told the dog perspired only through the pads of his feet and his tongue. He does use these outlets for cooling, but his skin also helps out. His sweat glands help to some extent, but not as much as those of human beings. Instead of regulating the internal body temperature—as our sweat glands do—the dog's cooling system regulates only his skin or surface temperature.

When heat builds up in the human body, the sweat glands go to work and cool the body by evaporating the perspira­tion given off by the sweat glands. Not so with the dog; he cools off by radiation, without any evaporation. Thus, only the surface of the dog's skin is cooled. This is a big reason why the dog often has difficulty adjusting to overly hot days. It's also a reason why dogs become heat-exhaustion victims when locked up in automobiles with little or no ventilation on a hot day. In a hot car, there is simply no place for the dog's heat to go—and without any evaporation, he is in trouble.

Dog skin has great powers of regeneration. It can quickly repair damage to tissues. Minor cuts, tears or abrasions usu­ally heal with little trouble. The dog has an additional heal­ing aid in his saliva. The saliva contains a "built-in" germicide. If the dog has an opportunity to lick his cuts or wounds, he speeds up the healing process. But there is always the possibility of infection and it's best to apply an antiseptic, especially to deep or large wounds.

THE SKELETON

The dog is a quadruped. He can stand on his hind legs, but he does so with difficulty. His normal position is on all fours. His whole skeletal formation is constructed with that end in view. And while circus or other trick dogs seem to be very nimble and at home on their hind legs, the average dog prefers to stand on all fours.

There is not much difference between the dog's skeleton and that of other mammals. Nature has made some changes here and there, depending upon the animal's mode of life. But, except for these minor changes, most mammals, includ­ing man, have a common skeleton. When the prehistoric forerunner of man walked on all fours, his skeleton approxi­mated that of the dog. And even though we walk upright today, that similarity of skeleton still exists.

What variations do exist between our skeleton and that of the dog are minor. The dog, for example, has more caudal or tail bones than we do. We have collarbones or clavicles; the dog does not. His shoulder blades are fastened directly to his skeleton. We also have opposable thumbs. These are lacking in the dog and most mammals.

While we don't need to know every bone in the dog's skeleton, we should be familiar with the main bones or sec­tions of the skeleton. The "body" part of the dog's skeleton consists of the skull, ribs and spinal column (atlas, axis, cer­vical vertebrae, thoracic vertebrae, lumbar vertebrae and the caudal vertebrae). The skull is attached to the spinal cord at the atlas. The front or fore legs consist of the shoulder blade or scapula, humerus, radius, carpus (knee) and the metacarpus or pastern. The hind quarters consist of the pelvis, femur, tibia, fibula, tarsus (hock) and the metatarsus.

The dog's skeleton is a strong framework and under nor­mal conditions offers good protection to the vital organs. Unfortunately, domestic dogs don't live under normal condi­tions. Too many dog skeletons are cracked by automobiles. Automobile injuries account for the majority of dog bone fractures or breaks. The bones most frequently broken are the ribs, bones of the fore and hind legs, and the pelvis. Frac­tures of the pelvis are far more common that you would suppose. A large number of dogs hit by cars manage to get the front part of their bodies clear of the car, but are struck in the hindquarters or pelvis. (See Chapter 17, under

CAR AND TRUCK ACCIDENTS)

THE MUSCULAR SYSTEM

In keeping with his role as a hunter, the dog has a well-muscled body. His muscles are tough and well coordinated. In some dogs, certain muscles are highly developed. Draft dogs, such as the Husky and Newfoundland, have powerful chest and back muscles. But all dogs have good muscles that help them run, jump and spring.

As with human muscles, those of the dog can be strained, stretched and otherwise injured. This is a point to keep in mind when you try to get your dog to jump too high or drag something that may be too heavy. He can get a charley horse just as easily as you can.

THE NERVOUS SYSTEM

Like all mammalian nervous systems, that of the dog is complex. Basically, the dog's nervous system is composed of the peripheral and central nervous systems. The peripheral system consists in part of sensory fibers and motor neurons. These are gathered together in bundles and are called nerves. The central system has segregated neurons and lies within the skull and spinal cavities. The central nervous system is divided into two main parts: the brain and the spinal cord. The brain has an important role in complex behavior, since it governs learning, motivation, perception, etc. The func­tion of the spinal cord is twofold: it acts as a conductor to and from the brain and it effects reflex actions.

All of the above are true for other mammals, including man. It is in the area of reflex action that the dog's nervous system differs from man. The dog has a highly developed reflex-action mechanism. His reflexes are very important to his daily life. They play a major part in his everyday beha­vior. For example, reflexes are responsible for the dog's blink­ing when something strikes his eye, for scratching when he has an itch, for making his hair stand up on end when he sights or smells something strange, and for making his ears twitch when he hears various sounds. These and many other reflexes are well developed in the dog.

The dog's reflexes have been the subject of study for many years. Much of the information obtained from studying the dog's reflexes can be applied to man. Perhaps one of the most publicized experiments involving the reflexes of the dog was that done by the Russian scientist Ivan P. Pavlov (1849-1936). Pavlov introduced the concept of the conditioned reflex. The conditioned reflex involves a simple response to a particular action or stimulus.

In a very simplified version, Pavlov's experiment went something like this: He set a pan of food in front of a dog. At the sight of the food, the dog's saliva began to flow. This act of salivating at the sight of food, Pavlov called an uncon­ditioned response or reflex. He next varied the experiment by ringing a bell before setting down the pan of food. After a time, the dog salivated when he heard the bell ring and without seeing the food. Pavlov called the ringing of the bell a conditioned stimulus and the dog's flow of saliva at hearing the bell, a conditioned response or reflex.

The dog's nervous system can be damaged by disease. Distemper and rabies are diseases that involve the central nervous system. The majority of dogs that recover from dis­temper are usually left with an impairment of the central nervous system. In the case of rabies, there are no survivors.

THE DIGESTIVE SYSTEM

None of the dog's digestion takes place in the mouth, as it does in human beings. It starts in his stomach. But the main process of digestion occurs in the dog's small intestine.

The dog's digestive apparatus consists of the mouth (merely a passageway for food), esophagus, stomach, pylorus, small intestine, large intestine and the rectum. The liver and pan­creas are also involved in the digestive process.

Very often, the dog's manner of eating surprises and startles a new dog owner. The dog is not what you would call a dainty eater. He bolts or wolfs his food, swallowing whole chunks or masses. This bolting down of food is a hangover from the wild state, the days when the dog's ancestors had to eat their food fast or else have it taken away. It was purely a question of the wild dog getting his food "while the getting was good."

As a prevention against acute indigestion, Nature has sup­plied the dog's stomach with strong juices. He also has a good reverse action and can regurgitate food that may be too large. The stomach juices are capable of dissolving large chunks of food and bones. By the time the food reaches the small intes­tine, the juices have broken it down to a state where it can be easily processed and assimilated.

At one time it was believed that the dog's digestive system could not handle starches. Dog owners were cautioned not to feed dogs starchy food in any form. Today, we know that this is not true, that dogs can tolerate starch in their diet. Dogs having a disease or malfunctioning of the pancreas, however, have difficulty in utilizing starch and must be put on a special diet. It was also a common belief that fat should not be fed to dogs. This, too, has been disproved. The no-starch, no-fat dictum forced dogs into being strictly protein eaters. As a result, many dogs were suffering from malnu­trition.

THE URINARY SYSTEM

The dog's urinary system is similar to that of other mam­mals. Its purpose is to process and get rid of liquid wastes. The main parts of the urinary tract are the kidneys (used to excrete urea, uric acid and other wastes), the bladder (a re­ceptacle for fluid), and the urethra (the canal that carries the urine from the bladder).

Urinary-tract ailments are more common in older dogs, although puppies may have urinary-tract infections. These infections may exist as part of a major disease, such as leptospirosis, or as a primary condition. (For the symptoms of urinary tract ailments, see Chapter 13.)

THE REPRODUCTIVE SYSTEM

The male dog reaches sexual maturity at between 6 to 8 months. He can then mate at any time of the year and for a large part of his life. Some males seem to be more sexually active in the late winter and early spring. This could be a throwback to his wild ancestors and the modern wolves and coyotes that breed in late winter and early spring.
The reproductive organs of the male include the penis, testicles and the prostate gland. Males, to be efficient breeders, must be in good health and not overly fat. Adequate exercise is very important in keeping the male sexually potent.

Females can mate and produce offspring twice a year. Suc­cessive matings are not usually recommended. Also, a female entering her heat period or estrus cycle for the first time should not be bred. Rather, she should be permitted to reach maximum growth. When bred on the second heat period and thereafter, the bitch will produce healthier and more vigor­ous puppies.

The reproductive organs of the female include the vagina, ovaries and uterus. The bitch has a reproductive cycle that is divided into four phases: 1) a nine-day period in which the external genitals are enlarged, swollen and emitting a bloody discharge; 2) another nine-day period during which ovulation occurs and the bitch has a strong desire to mate (she can be mated during this stage); 3) the anestrum period lasting 2 months; and 4) the metestrum period lasting 3 months. The anestrum and metestrum periods are post-heat periods dur­ing which the female cannot be mated. The average female reaches sexual maturity or the first heat period at 6 to 8 months of age. Some individuals and breeds vary from this rule, not coming into heat for as long as 12 months.

Domestic dogs will mate with wolves and coyotes and pro­duce hybrids. They will also breed with jackals. The repro­ductive similarity between the dog, wolf and jackal has re­ceived considerable study. The duration of pregnancy in the dog and wolf is the same—60 to 63 days, and the wolf-dog puppies are fertile. Coyotes are small wolves and the same breeding similarities exist between them and dogs.

A more detailed coverage of the dog's reproductive cycle, whelping and rearing the puppies will be found in Chapters 19 and so.

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