Dog's anatomy

Parts of the dog

The anatomy of the dog is considerably different from a human being's. The fact that the dog moves on four limbs (a human being on two) and the dog is a toe stepper (it makes dog so fast) is the most considerable. The dogs' limbs and muscles have developed to stand quick and long running. The front limbs have developed for this for example to move only to the front and behind (unlike human's hands, which can move to any direction).

Skeleton

The skeleton of the dog consists total 300 individual bone. The muscles, ligaments and tendons are fastened on the bones. It indeed is the task of the bones to protect and to support the organs and to function as a part of the physical organism. The skeleton is almost the indicator of the physical education: the more your dog moves the better bones it has. Of course the genes and the correct diet (the bones requires calcium, phosphorus, proteins and D-vitamin) also have effect. The bones are a living tissue, which has consisted of bone cells and this is why the bones also develop through the dog's life. In other words you cannot affect the dog's bones by only moving with it when the dog is young. The work must be done through the dog's life. This way you can secure that your dog's bones also holds when it will be older. So the skeleton is a part of the dog's physical organism: if the bones are in bad condition, the moving of the dog suffers and in turn this weakens the bones further.

Usually the dog's knees, ankles, wrists and elbows are imagined being in different places in which reality they are. So the ankles and knees are higher than at first sight it would suppose as well as the elbows and wrists.

The individual bones of a skull, backbone, chest, hip and limbs form the skeleton. The connective tissues are partly a cartilage which is a material which is softer than the bone. There are many kinds of bones on the dog: among others long and round long bones, flat bones and ramified vertebraes. Some of the bones are fastened fixedly to each other (skull) and the part has fastened on each other with the help of vertebraes.

The front of the back below upper edge of the shoulder blade is called withers and dog's withers is is measured from this (the highest spot of the withers when dog is standing in natural position on the ground).

The chest and hip bones have become such that it is possible to bend the hip part strongly and to stretch hind limbs far front (these positions are found in when for example sleeping and running) . The dog walks on four feet from which you can conclude that its bones has become different from a human being's (different dimensions and corners).

The dog has 42 permanent teeth. Usually the puppies do not have teeth which have burst when whelped. The bursting of teeth begins when the puppy is 3-4 weeks old and continues to the age of 3-4 months. The deciduous teeth change 4-7 months old to permanent teeth. The first premolar tooth (P1) and the backmost molar teeth have no deciduous teeth (they burst directly as permanent teeth). The perfect permanent teeth will develop before the puberty. Usually the teeth change easily. Some individuals have a aptitude for the fastening of deciduous teeth which can lead to permanent wrong positions if the stucked deciduous teeth are not drawn away in time. Therefore you should watch the bursting of teeth. 

The diagram which indicates the number of the different teeth of the mammal is called as dental formula. Each tooth is corresponded to by a letter. In the dog's dental formula the front teeth are corresponded to by the letter I, canine teeth by the letter C, premolar teeth by the letter P  and molar teeth by the letter M. The top line informs the number of the teeth of the upper jaw and the bottom line the number of the teeth of the mandible.

The formula of the dog's deciduous teeth is:
    3I, 1C, 3P
    3I, 1C, 3P x 2
    =28 teeth

The formula of the dog's permanent teeth is:
    3I, 1C, 4P, 2M
    3I, 1C, 4P, 3M x 2
    =42 teeth

The dog's teeth are quite of different types among themselves and every tooth has its own purpose: with the canine teeth a catch is bitten, with the front teeth the meats are torn and with the molar teeth and premolar teeth are crushed.

Muscles and nervous system

The energy required for the operation of about 250 muscle groups the dog gets from the nourishment of the basic materials, in other words from carbohydrates, fat and protein. Big part of these materials however changes into heat which the dog needs for the maintaining of its body temperature. The dog has about 500 individual muscles of which about 300 muscles move limbs and others have the other tasks. The muscles require much energy and oxygen in order so to operate and these can be offered with physical education, nourishment and health.

The muscles are the most important part of the dog of the organs of motion (as also the human being's). The muscles bring about the movements, the bones keeps the body "in the pile". In addition to the movements, the muscles manage among others the continence in the bladder and intestines (the sphincters), produce heat, prevent movements and stabilise the joints (they support the joints so that they will not bend in vain). The muscles are regulated by the nerve impulses which can be either aware or automatic movements (reflex).

The muscles are fastened on the bones from their heads. The muscle consists of muscle fibres which have fastened on each other lengthwise. The muscle fibres consist of small muscle fibres which form a kind of bunches (fibres).

As with us the people also the dog's muscles often function in pairs. This means that when the other muscle contracts, the other stretches (the other has effect in the opposite direction as the other). Try this even with your own hand: when you bend your hand, your biceps will contract whereas at the same time the brachii (shoulder muscle) stretches. The same happens when a foot is bended (when the muscle of the second side contracts, it will stretch the muscle on the other side).

There are three types of muscles:

• through striped: voluntary, fast, moving for example the bones, ears and eyes
• smooth: operating from reflexes (not voluntary) for example in blood vessels and in alimentary canal
• heart muscle: pumps blood (as we surely know all)

As already earlier it was said, the muscles are directed by a nervous system. In addition to this work, the nervous system is directing for example operations of the internal organs and glands. The nervous system operates voluntary and automatic (reflexes). The brain produces the impulse which then the nervous system will transport to muscles. This is a kind of an order which the muscle has to follow. The good example is from the reflex operation is when the dog pushes its muzzle to the nettle. It hurts to the muzzle and the information starts its way to the brain. The brain transmits the impulse through the nervous system to the muscles that draw the muzzle out of the nettles right away and this happens. The the reflex impulses of this kind always go through the spinal cord.

The nervous system consists of two parts:

• from central nervous system (brain and a spinal cord)
• from peripheral nervous system (all the muscles, organs and sense organs are connected to the central nervous system by the nerves)
  • consists of two parts: from somatic, in other words from will from nervous system which is voluntary and autonomy (automatic, relflex)

Organs

From the internal organs the lungs and the heart have become extremely strong and the dog may thank them for its durability and speed. Thanks to its very expansive powered stomach the dog can enjoy a considerable amount of food at a time. Also the bladder is flexible and the dog can store to it the amount of urine which especially the males need for the marking of the territory.

Heart and the circulatory system

As already was told the heart is an individual strong muscle, which pumps blood in the body. When blood has given all its oxygen, it is carried back to the heart (the arteries) and to be oxidised that way to the lungs. When an oxidation has happened, the blood is carried back to the heart and that way to different parts of the body (the veins). Dog's, like all living's, heart is one of the most important parts of the body and it has an extremely complex institution.

The blood is liquid connective tissue in which there are red blood cells and white blood cells. The white blood cells are the armies of the organs against different bacteria. The task of red blood cells is to transport oxygen, carbon dioxide and nutritive substances.

The circulatory system contains not only a heart and blood, but also blood vessels which there are three different types: arteries, veins and capillaries. In the arteries the blood which should become oxidised goes to the heart and lungs. In the veins the blood is already oxidised and is on the way to the separate parts of the body. The capillaries connect veins and arteries among themselves. The arteries are stronger than the veins and they transport the blood faster. The walls of capillaries are extremely thin. Between blood and the tissues oxygen, carbon dioxide and nutritive substances are carried through the walls of blood vessels.

Respiratory organs

As all the mammals, dog also have two-piece lungs, in other words lungs are forming a pair (you even have right and left lung). When a dog breathes in, air will be carried through its nostril, nasal cavity, mouth and throat to the lungs. Oxygen goes to the circulation from the lungs. When the oxygen has become carbon dioxide in the organs, it is carried through the circulation to the lungs and from there to the tidal air going outside of the body.

Under the chest is located the midriff. The task of this muscle is to function as the adjuster of the volume of the lungs. When a midriff contracts, it will give room for the lungs.

Digestive organs

The nourishment will be first cut in the mouth to smaller pieces. Some dogs have a habit of gorging in which case they do not chew food but swallow it as such. It is good to give the dogs of this kind the food ready mashed. From the mouth the food leaves for the trip to the digestive organs where it degrades chemically to smaller parts than before after the chewing. The separated nutritive substances are used as the fuels of the organs and the part will come out as "waste" (the ones which the organs are not able to use). In addition to this, the part is stored in the organs (this is familiar especially with older dogs...). The dog has a considerably shorter intestine than a human being and this means that the food will come faster "through".

Here is the progress of the food in the dog's organs:

1. the food is chewed in the mouth (the spittle gives more slipperiness)
2. the food is swallowed in which case the food moves to the gullet
3. in the stomach the food is degraded further (normally a few hours)
4. in the duodenum fats, sugars and proteins are separated
5. in the small intestine the melting continues and nutritive substances are absorbed into the circulation through the walls
6. in the large intestine, water and some minerals are separated from the end (from the excrement)
7. to the rectum the rest is stored, which will disappear when the dog evacuates

Skin

The skin has a task to protect the dog's organs from drying and from different pathogens. Neither water nor bacteria is carried through the skin. Furthermore, the skin serves as the sense organ (a touch, temperature changing) and regulates the temperature of the body. The skin of the dog also produces hairs, tallow and sweat.

The skin is the bigger in relative size the smaller the dog is and the skin is also dog's biggest organ. Usually the dog's skin and other organs are doing fine, if the dog's skin and coat are in good condition, in other words the skin and the coat can be almost considered as the indicator of the dog's health. The skin diseases appear different types.

Dogs have sweat glands just like human beings, but they operate with dogs only in the muzzle and paws. When the dog is hot, it does not start to sweat, it just pants (to breathe thick and fast then normally = hyperventilation). In that case the inhalation and breathing out will not bring oxygen to the lungs but creates rather the constant stream of air which prevents the evaporating of the moisture from the tongue.

Urine organs

Many wastes accumulate in organs through the nourishment and tidal air. These wastes leave the body through the skin (sweat), digestive organs (an excrement) and respiratory organs (a tidal air), but also through the urine organs. Urine contains mainly water. About ten per cent of it is unnecessary waste products of the metabolism and surpluses of mineral salts and poisonous substances. Dog produces urine more than the human being and the urine is thicker. The producing and removal of urine from the organs are performed as follows:

1. producing of urine starts from the kidneys
2. from the kidneys urine moves to the ureters
3. along the urethras, urine moves to bladder to be stored
4. urine leaves the body and organs from the bladder

The removal of urine happens with the help of the sphincter which is a voluntary muscle. The small puppy may have problems using this muscle and it may urinate here and there. Adult dog can regulate urinating when it is healthy.

Genitals

The products of the genitals are gametes which the dog needs for the reproduction. The genitals of a bitch include in addition to the parts which produce increase cells also the organs of labour. So the bitch's and the male's genitals differ a little from each other. The parts of the genitals of the bitch are:

• ovaries (producing egg cells)
• Fallopian tubes
• womb (bifurcated, in the womb the puppies develop)
• vagina
• sex hole which are edged by the labiums
• lacteal glands
• teats

The sexual organs of the male consist of the following parts:

• testicles (producing spermatozoa)
• epididymides
• seminal ducts
• penis
• prostate (producing the secretion to the seminal fluid)

Bitches are sexually mature leaving from when they have the first heat. This takes place 6-12 months old (it depends on the size, race and parentage). From our homepage you also find the small guide about False pregnancy. The male will become sexually mature about 8-9 months old. After this it is ready whenever to mate the bitch whereas the bitch is ready to be mated only at a certain stage of the heat. The male's testicles descend normally 7-10 weeks old.

Internal secretion organs

To internal secretion organs means those organs which produce hormones. The hormones regulate the functions of the organs chemically. The internal secretion organs also are called the endocrine glands. The endocrine glands are not the only producers of the dog's hormones (for example the placenta is producing hormones). The hormones are many kinds of and every hormone has different effects on the organs where they are carried through the vascular system.

Endocrine glands and their tasks:

• the pituitary produces hormones which affect the operation of internal secretion organs, growth hormone and hormones affecting the excretion of urine, a labour and milk secretion
• the pancreas produces the insulin which affects the metabolism (too small forming of the insulin causes diabetes)
• the genitals, in other words the ovaries and testicles produce hormones which affect, among others, behaviour, heat circulation of bitches, to the operations of mammary glands and to the pregnancy, to the males' sexual drive, to operation of genitals and to bone and muscle mass
• thyroid gland and the parathyroid glands produce hormones for the metabolism, the bodily and sexual development and percentage of calsium and phosphate in the blood
• the adrenal glands produce adrenaline and other hormones which affect blood pressure, size of the pupils, to the percentage of the sugar of the blood, to the metabolism, a tolerance of stress and genitals

Senses

Smell

The most important sense organ of a dog is its extremely sensitive nose which serves as a kind of a scent compass. We, the people live mainly through our eyes whereas the dog experiences its environment in the first place on its advanced sense of smell. It also is difficult to us to understand the dogs' smell world sometimes; in their opinion, a smell may be especially interesting and good even if the smell did not please our noses.

So the dog's sense of smell is most clear-cut of the dog's senses and most important. The dog smells better than the majority of the mammals and it even moves with the help of its scent and its sense of smell (the dog's sense of smell is dozens of times, maybe even millions of times, better than that of the people). The trained dogs are able to filter and are able to distinguish certain smells among the others (for example the drug dogs).

As we know, the dogs mark their territory by spreading their own smell (either by urinating or stratching the ground when some secretion moves from the spaces of toes to the ground). Other dogs smell this and from the smell they can conclude the dog's sex, age, influence etc. The smell of the bitch in the heat is conveyed even as far as kilometres away to the males' nose, in other words also the mating partner is found with the help of the sense of smell as well as food.

The human being has begun quietly to use this incredible property of the dog. Drug dogs and search dogs are the most known from it at the moment. In addition to this, the dogs have been used to identificate the cancer (the dog smells the tumour from the skin of the human being). There is also dogs looking for of bodies, mushrooms and even for the perception of mould damage.

On which this is based? Dog has these epithelium cells in nasal cavity's mucous membrane total about 250 millions, when human has these only 5-10 millions and we must pay attention it is needed only some tens of these cells to produce sensation of smell (when the cells become sensitive). Smelling area (is depended on the length of the muzzle) dog has 150 cm² when human has only five. Dog also has in nasal cavity these nozzles of bone, which will blow all the breath air to smell epithelium (this is something human does not have). Dog is also able to sniff, which renders smell more effective (the nasal cavity will fills with air and this will sensitize the nerve cells for smell molecules). 

Hearing

The hearing is the dog's second most important sense. The human being hears about from 16 to 20000 hertz (vibrations per second). The dog's auditory cortex is from 70 to 100000 hertz. This means that the dog is able to perceive sounds which we do not hear (especially the high voices, such as dog pipe, which produces the voice of about 30000 hertz). The dogs' excellent guarding ability is also based on the sense of hearing.

In addition to the fact that the dogs' auditory cortex is wide, they are able to distinguish sounds from each other unbelievably detailed. For example the dog may hear the sound of the car already minutes before the home-coming of the family and it may go to the door or gate to wait (looking to the right direction). In other words the dogs may identify the car among other voices.

One reason to the dog's hearing is based on the big auricles. Also the lop-eared dogs have usually good hearing even if you might think that the auricles would stop some voices reaching a dog's ears.

Sight

The dog has relatively big eyes and its visual field is considerably wider than that of the human being but the plastic sight of the dog is weaker. The dog is by its nature farsighted and for this reason it has adapted itself to realize mainly the movements. This is the reason why the dog does not necessarily identify its master who stands far still. It is difficult for the dog to perceive objects in place because the stereoscopic vision is not the best side of dog's sense of sight. You might have noticed this when you have tried to show your dog for example the standing bird in place... the dog turns its head trying to look for movements without perceiving the bird. Because the visual fields of the dog's eyes not going crosswise as much as human being's, it is much more difficult for a dog to perceive the depth and the distance.

The dog sees colours in spite of an old belief (before it was thought that the dogs would be colour-blind). However, their colours separation is not the best possible. When you for example throw a red ball on a green grass, the dog has most probably to look for it on the basis of its sense of smell. However, the dogs have a much better dark sight than a human being (it sees better when it is dark).

There are big differences between the eyesight of individual dogs. For example the sighthounds have a considerably better sight than other dogs.

Taste

Also the taste is extremely exact and well developed with dogs. This of course is closely connected to a sensitive sense of smell. When there is a good sense of smell, one can already conclude from the smell of the food if it is suiting to be eaten. But ultimately the dog is able to conclude it also from the taste.

Touch

The dog has also a good sense of touch with which it feels the touch and temperament stimuli. The nose, lips, tongue and pads are the most sensitive to feel touches. Furthermore, the dog has tactile hairs which have fastened deep to the skin to support the senses (for example near the eyes and lips).

Other senses

The dog also becomes familiar with other dogs with the help of its senses. Usually the becoming familiar is started by sniffing the muzzle against the muzzle and after this they will sniff each others rumps, which shows how the dog should take an attitude in other dog.

In addition to the above mentioned senses, the dog has sensor cells in the muscles, tendons and joints. With the help of these cells the dog senses the position of the body. There is also a sense of balance (such as we have) with which the dog will perceive if the body is in horizontal or vertical position. The dog also senses cold, hot and other temperatures and also pain.

Source documents

Spaniels (Ullman Hans & Evamaria, 1981)
Dog show book (Rainer Vuorinen, 1999)
Own dog (U. Kokko, V-R Cajander, R. Nummisalo, 2000)
We dogs (Andreoli Giorgio, 1991)
Tiede 6/2002 magazine, pages 42-43 ("Mestarinuuskija jäljittää riistan ja syövän" by Jukka Ruukki)