The anatomy of dogs
varies tremendously from breed
to breed, more than in any other animal species, wild or domesticated. And yet there are basic physical characteristics that are identical among all dogs, from the tiny Chihuahua
to the giant Irish Wolfhound
Like most predatory mammals, the dog has powerful muscles, a cardiovascular system that supports both sprinting and endurance, and teeth for catching, holding, and tearing.
The dog's ancestral skeleton provided the ability to run and leap. Their legs are designed to propel them forward rapidly, leaping as necessary, to chase and overcome prey. Consequently, they have small, tight feet, walking on their toes; their rear legs are fairly rigid and sturdy; the front legs are loose and flexible, with only muscle attaching them to the torso.
Although selective breeding has changed the appearance of many breeds, all dogs retain the basic ingredients from their distant ancestors. Dogs have disconnected shoulder bones (lacking the collar bone of the human skeleton) that allow a greater stride length for running and leaping. They walk on four toes, front and back, and have vestigial dewclaws (dog thumbs) on their front legs and sometimes on their rear legs. In some cases, these claws are missing due to surgery, the rear dewclaws sometimes being removed to prevent the possibility of their being ripped off, or catching on something and breaking, especially in dogs with loose dewclaws. This practice is illegal in some countries.
The dog's ancestor was about the size of a Dingo, and its skeleton took about 10 months to mature. Today's toy breeds have skeletons that mature in only a few months, while giant breeds such as the Mastiffs take 16 to 18 months for the skeleton to mature. Dwarfism has affected the proportions of some breeds' skeletons, as in the Basset Hound.
These characteristics and basic structure also help when competing in dog shows or contests.
Researchers have identified a particular piece of DNA
that is common to every small-dog breed and, in turn, is probably responsible for making them tiny. The discovery, reported in the journal Science, helps explain the vast diversity in dogs, from the pug
to the massive mastiff
Coat colors range from pure white to solid black and many other variations.
- For a complete detailed list of dog colors and patterns, see Coat (dog).
Dogs exhibit a diverse array of fur coats. They range from different coat textures, colors, and markings, and a specialized vocabulary has evolved to describe them.
Originally, dogs all had dense fur with an undercoat and long muzzles and heads, although both of these features have been altered in some of the more extremely modified breeds, such as the Mexican Hairless Dog and the Bulldog.
One often refers to a specific dog first by coat color rather than by breed; for example, "a blue merle Aussie
" or "a chocolate Lab
". Coat colors include:
- Black: Usually pure black but sometimes grizzled.
- Brown: From mahogany through very dark brown.
- Red: Reminiscent of reddish woods such as cherry or mahogany; also tawny, chestnut, orange, rusty, liver, and red-gold.
- Yellow: From pale cream to a deep yellowish-gold tan.
- Gold: From pale apricot to rich reddish-yellow.
- Gray: Pale to dark gray, including silver; can be mixed with other colors or various shades to create sandy pepper, pepper, grizzle, blue-black gray, or silver-fawn.
- Blue: A dark metallic gray, often as a blue merle or speckled (with black).
- Sable: Black-tipped hairs; the background color can be gold, silver, gray, or tan.
- White: Distinct from albino dogs.
Coat patterns include:
- Two-color coats: such as Black and tan, red and white. The coat has both colors but in clearly defined and separated areas; usually the top and sides are darker and lower legs and underside are the lighter color.
- Tricolor: Consisting of three colors, usually black, tan, and white or liver, tan, and white.
- Brindle: A mixture of black with brown, tan, or gold, usually in a "tiger stripe" pattern.
- Harlequin: "Torn" patches of black on white.
- Merle: Marbled coat with darker patches and spots of the specified color.
- Particolor: Two-colored coat with the colors appearing in patches in roughly equal quantities.
- Tuxedo: Solid (usually black) with a white patch (shirt front) on the chest, and white on some or all of the feet (spats.) This pattern is sometimes called Irish Spotting, Flashy, or Boston.
Coat textures vary tremendously. Some coats make the dogs more cuddly and others make them impervious to cold water. Densely furred breeds such as most sled dogs
types can have up to 600 hairs per inch, while fine-haired breeds such as the Yorkshire Terrier
can have as few as 100, and the "hairless" breeds such as the Mexican Hairless
have none on parts of their bodies. The texture of the coat often depends on the distribution and the length of the two parts of a dog's coat, its thick, warm undercoat
) and its rougher, somewhat weather-resistant outer coat (topcoat
, also referred to as guard hairs
). Breeds with soft coats often have more or longer undercoat hairs than guard hairs; rough-textured coats often have more or longer guard hairs. Textures include:
- Double-coated: Having a thick, warm, short undercoat (or down) that is usually dense enough to resist penetration by water and a stronger, rougher weather-resistant outer coat (topcoat), also referred to as guard hairs. Most other coat types are also double-coated.
- Single-coated: Lacking an undercoat.
- Smooth-coated: "Smooth" to the eye and touch.
- Wire-haired: Also called broken-coated. The harsh outer guard hairs are prominent, providing excellent weather protection for hunting dogs such as the Border Terrier or Wirehaired Pointing Griffon.
- Long-haired: Hair longer than an inch or so.
- Short-haired: Hair around an inch or so long.
- Corded coat: for example, see Puli
Parts of the body
A special vocabulary has been developed to describe the shapes of various body parts including the ears and tail.
Dogs' ears come in a variety of sizes, shapes, lengths, positions on the head, and amounts and types of droop. Every variation has a term, including:
- Bat ear: Erect, broad next to the head and rounded at the tip, such as the ears on a Chihuahua.
- Button ear: A smaller ear where the tip folds forward nearly to the skull, forming a V, as in the Jack Russell Terrier.
- Cropped ear: Shaped by cutting; see docking.
- Drop ear: An ear that folds and droops close to the head, such as most scent hounds'and the little known Blue Lacy. Also called a pendant ear.
- Natural: Like a wolf's.
- Prick ear: Erect and pointed; also called pricked or erect.
- Rose ear: A very small drop ear that folds back; as in the greyhound or bulldog.
- Semiprick ear: A prick ear where the tip just begins to fold forward, as in the Rough Collie.
- Hound ear: A floppy ear that is long and droopy. It is common to all hound-type breeds as in the Beagle, Basset Hound, and Foxhound.
Like ears, tails come in a tremendous variety of shapes, lengths, amounts of fur, and tailsets (positions). Among them:
- Bob: Short or non-existent tail, such as an Australian Shepherd or Pembroke Welsh Corgi.
- Corkscrew: Short and twisted, such as a Pug's
- Docked: Shortened by surgery or other method, usually two or three days after birth; see docking
- Odd: Twisted, but not short. Uncommon. Tibetan Terriers have odd tails.
- Saber: Carried in a slight curve like a saber
- Sickle: Carried out and up in a semicircle like a sickle
- Squirrel: Carried high and towards the head, often with the tip curving even further towards the head.
- Wheel: Carried up and over the back in a broad curve, resembling a wheel.
Puppies often have characteristics that do not last beyond early puppyhood. Eye color often changes from blue to its adult color as the puppy matures. The coat color may change: Kerry Blue Terrier
puppies have black coats at birth and change to blue with maturity, and Dalmatians
are white and gain their spots with age. The ear shape will also often change, especially with erect-eared breeds such as the German Shepherd Dog
which have soft ears at birth, but the cartilage strengthens with age. Blue Lacy
Dogs and Labrador Retrievers
, however, stay very much the same through life.
It is not uncommon for puppies to have their ears cropped or straightened, tails docked, or in the case of the Chow Chow, to have their eyefolds stitched back so that they can see. Many of these are done in accordance with breed standards for many Kennel Clubs. Some countries like Italy have banned this practice as an act of animal cruelty.
A common misconception is that dogs do not sweat
. Primarily, dogs regulate their body temperature in a completely different way, through panting. That is why after a dog has been running or on a hot day, its mouth will be seen wide open with the tongue hanging out. This form of cooling maximizes heat loss while conserving moisture, because it carries heat from the hottest part of the body, the interior core of the thorax
. Perspiration cools the body by the evaporation of moisture from the skin. This is much less efficient, because the skin is already the coolest part of the body—or in more scientific terms, this higher efficiency of thermal loss relative to moisture conservation arises because heat flow is proportional to temperature gradient
. Dogs sweat through the pads of their feet, since they are not furred. On a warm day and after exercise, a dog's naturally wet footprints might be visible on a smooth floor.
Dogs possess a rete mirabile, a complex of intermingled small arteries and veins, in the carotid sinus at the base of their neck. This acts as a heat exchanger to thermally isolate the head, containing the brain, the most temperature-sensitive organ, from the body, containing the muscles, where most of the heat is generated. The result is that dogs can sustain intense physical exertion over a prolonged time in a hot environment, compared to animals which lack this apparatus; thus, a dog chasing a jackrabbit through the desert may not be able to outrun the rabbit, but it can continue the chase until the rabbit literally drops dead from overheating.
Information and facts on dog anatomy