The official AKC description is the Chihuahua is a small dog that comes in two varieties or coat types. The difference in coat type (the Long Coat or the Smooth Coat) is the only official description used to identify a difference within this breed. Our Standard does not categorize the Chihuahua by size.

For the purpose of showing and record keeping, the American Kennel Club includes the Chihuahua (along with 19 other breeds)in the Toy Group. Therefore, irrespective of their weight or physical stature, ALL Chihuahuas registered with A.K.C. are considered to be a toy breed of dog.
 
As with all living things, there will be a size variance between individual dogs within this breed. Look within the human family - brothers and sisters will differ in height and in weight, as well as other physical attributes. They are described as humans, male or female, and there is seldom if ever a need to break the description down further. The same holds true in regard to the Chihuahua; they are Chihuahuas-Long Coat/Smooth Coat, Male/Female.

Unfortunately, the additional adjectives used to describe the size difference and physical appearances are many; and have been misused for so long they now seem legitimate. Tea-cup, Pocket Size, Tiny Toy, Miniature or Standard - are just a few of the many tags and labels that have been attached to this breed over the years. The Chihuahua Club of America is concerned that these terms may be used to entice perspective buyers into thinking that puppies described in this way are of greater monetary value. They are not and the use of these terms is incorrect and misleading.

Occasionally, within a litter, there may be a puppy that is unusually small. That puppy is a small Chihuahua and any other breakdown in description is not correct. To attach any of these additional labels to a particular pup is to misrepresent that animal as something that is rare or exceptional and causes a great deal of confusion among those fanciers who are looking for a Chihuahua.

The Chihuahua Club of America does not endorse or condone the use of these terms and would caution the perspective puppy buyer not to be misled by them.

We recognize that many Chihuahua fanciers do want the very small puppy. While they are adorable and can be perfectly healthy, the buyer should be cautioned as to the extra care that may be required with regard to their general health and well-being.

*Sponsored by The Chihuahua Club of America

I

THE CHIHUAHUA STANDARD

A.K.C. Chihuahua Standard

General Appearance
A graceful, alert, swift-moving little dog with saucy expression, compact, and with terrier-like qualities of temperament.

Size, Proportion, Substance Weight-A well balanced little dog not to exceed 6 pounds. Proportion-The body is off-square; hence, slightly longer when measured from point of shoulder to point of buttocks, than height at the withers. Somewhat shorter bodies are preferred in males. Disqualifications-Any dog over 6 pounds in weight.

Head
A well rounded "apple dome" skull, with or without molera. Expression-Saucy. Eyes-Full, but not protruding, balanced, set well apart-luminous dark or luminous ruby. (Light eyes in blond or white-colored dogs permissible.) Ears-Large, erect type ears, held more upright when alert, but flaring to the sides at a 45 degree angle when in repose, giving breadth between the ears. Muzzle-Moderately short, slightly pointed. Cheeks and jaws lean. Nose-Self-colored in blond types, or black. In moles, blues and chocolates, they are self-colored. In blond types, pink nose permissible. Bite-Level or scissors. Overshot or undershot bite, or any distortion of the bite or jaw, should be penalized as a serious fault. Disqualifications-Broken down or cropped ears.

Neck, Topline, Body
Neck-Slightly arched, gracefully sloping into lean shoulders. Topline-Level. Body-Ribs rounded and well sprung (but not too much "barrel-shaped"). Tail-Moderately long, carried sickle either up or out, or in a loop over the back, with tip just touching the back. (Never tucked between legs.) Disqualifications-Cropped tail, bobtail.

Forequarters
Shoulders-Lean, sloping into a slightly broadening support above straight forelegs that set well under, giving a free play at the elbows. Shoulders should be well up, giving balance and soundness, sloping into a level back. (Never down or low.) This gives a chestiness, and strength of forequarters, yet not of the "Bulldog" chest. Feet-A small, dainty foot with toes well split up but not spread, pads cushioned. (Neither the hare nor the cat foot.) Pasterns-Fine.

Hindquarters
Muscular, with hocks well apart, neither out nor in, well let down, firm and sturdy. The feet are as in front.

Coat
In the Smooth Coats, the coat should be of a soft texture, close and glossy. (Heavier coats with undercoats permissible.) Coat placed well over body with the ruff on neck preferred, and more scanty on head and ears. Hair on tail preferred furry. In Long Coats, the coat should be of a soft texture, either flat or slightly curly, with undercoat preferred. Ears-Fringed. (Heavy fringed ears may be tipped slightly if due to the fringes and not to weak ear leather, never down.) Tail-Full and long (as a plume). Feathering on feet and legs, pants on hind legs and large ruff on the neck desired and preferred. Disqualifications-In Long Coats, too thin coat that resembles bareness.

Color
Any color-Solid, marked or splashed.

Gait
The Chihuahua should move swiftly with a firm, sturdy action, with good reach in front equal to the drive from the rear. From the rear, the hocks remain parallel to each other, and the foot fall of the rear legs follows directly behind that of the forelegs. The legs, both front and rear, will tend to converge slightly toward a central line of gravity as speed increases. The side view shows good, strong drive in the rear and plenty of reach in the front, with head carried high. The topline should remain firm and the back line level as the dog moves.

Temperament
Alert, with terrier-like qualities.

DISQUALIFICATIONS
Any dog over 6 pounds in weight. Broken down or cropped ears. Cropped tail, bobtail. In Long Coats, too thin coat that resembles bareness.
 
* Approved September 11, 1990 Effective October 30, 1990

Helpful items to keep on hand.

I found this to be very informative.. so i added it to my website.. i got it off of a veterinarian's site.

           THE CHIHUAHUA

                A CLOSER LOOK

     The skull of the chihuahua is of most unusual shape. The skull of 'basic dog' is like an elongated cube, with a bony occipital peak and a slight bony ridge along the center line of the skull, where the plates of the cranium knit together. The chihuahua, as a legacy of the dwarfing of the breed, has a large rounded baby-like skull. Mammalian babies tend to be born with disproportionately large heads (and eyes) which grow on more slowly than the rest of the animal. In the chi this largeness of head and eye is never completely lost. The large head of a whelp requires that the many bones which knit together to form the skull must be capable of movement at birth to allow the bitch to pass the head. In chis these bones do not always grow together as the head develops and changes shape during puppyhood. A small gap (molera) is left atop the skull where the bones fail to meet. Provided this gap is not large, and that there are not several gaps, the presence of a molera is of little significance. In many chihuahuas the cranial plates do knit together, they should not however form a crest or ridge where they meet.
 

     In shape the skull should resemble an apple (a cooking apple is generally thought most descriptive), it should not be a perfect round (ball) shape. A round skull would lose breadth between the ears, and less room within the cranium. The eye sockets should be well protected with a bony surround. It is this protection of the eye sockets which lifts the front lobes of the skull and creates greater width at eye level. This protection also forms the basis for the required distinct stop. A round skull lacking this protection will either have small eyes, or 'frog' eyes which stick out.

     Jaws and cheeks are supposed to be lean, muzzle 'moderately short, slightly pointed' and the stop 'definite'. Coarse dogs have too broad a muzzle and broad cheeks. There is not enough distinction between muzzle and skull. Snipy dogs have cheeks pinched in beneath the eyes, and narrow muzzles; their jaw muscles are of poor substance.

     The muzzle itself is fairly short; the chihuahua is a member of the brachycephalic group (large heads and short muzzles). Ultra short muzzles are not desirable. They can lead to respiratory problems. Long muzzles are untypical---they spoil the balance of the head, lead to 'foxy' faces with insufficient cheek and stop, often allied to flattened, plain heads. The muzzle is slightly pointed---flattened muzzles tend to be coarse, or too short (even perhaps with a turned up nose). The flat muzzle often accompanies an undershot mouth, if too pointed it may indicate an overshot mouth.

     The 'definite' stop does not mean the skull is at right angles (90 degrees) to the muzzle. Given that the muzzle is the horizontal (sloping neither up nor down), then the skull should describe an angle of approx. 100 degrees. A very short muzzle may appear to be set in the skull, describing an angle less than 90 degrees; a legacy of the flat-faced breeds introduced into chi ancestry to shorten the muzzle (Pugs, Pekes, etc.). It is potentially a source of breathing problems.

     A correct scissors bite is such that, side view, the top incisors just overlap, in front of the bottom ones, but the bottom canine fits neatly in front of the  top one. If the incisors meet edge to edge, this is a 'level' mouth, not scissors. "Set square to the jaws", it must be noted, means that the teeth are set at approx. 90 degrees to the gums. It does NOT mean that the incisors should be lined up neatly in a straight line like guardsmen; the dental arch (arcade) should curve gently forward from the canines.

     Given that the head and muzzle are the result of dwarfing, it is not too surprising that the upper and lower mandibles are not evenly shortened; the result is an over- or under-shot bite. If overshot, the upper incisors protrude beyond the lower, in severe cases the bottom incisors may be level with the top canines. If undershot, the bottom incisors stick out beyond the top ones.

     Ideally the incisors should be even in size, strong and white, with six top and bottom. In shorter muzzles this is sometimes difficult to achieve---there may be insufficient room, so the dog may have only 4 bottom incisors (acceptable in U.K. if the teeth are of even size with no large gaps); the teeth may be uneven in size, or the bottom incisors may be set in a straight line. How serious these mouth faults are is a difficult point. Unless severe, a poor bite will probably have no significant effect of the dog, but successive generations may show deteriorating mouths. Uneven teeth, or the odd gap are considered by some to be unavoidable in the best heads, although there is no reason why the best of heads should not carry a perfect mouth.

     Although large, a chihuahuas eyes should not protrude, as this would increase the risk of injury. Bulging, frog eyes are not attractive, and are particularly prone to weeping and damage. Weeping of the eyes is quite a common problem in chihuahuas, the most serious cause is ingrowing lashes, but draughts, dust and the moulting of the fine short hair around the eyes are also causes. When injured the eyeball often turns cloudy blue, either in whole or just around the injury. This should not be confused with the staring, light blue 'wall eyes' (common in merle collies) which look uncanny and unattractive, and are not the light eyes permitted by the standard. The ruby eye is associated with pale pigmentation of the nose, in light colored chihuahuas, and reflects a most attractive color in the dark.
 
 

     Chihuahuas ears are set on the side of the head rather than the top, and are carried erect, flaring out at an angle, often wrongly described as being at 'ten to two'. Particularly alert, or dozy, chis will naturally use their ears, pricking them higher, or laying them flat to the skull, but in repose should revert to the 45 degree angle. The ears are large, with rounded ends to the pointed tips, not to be confused with the rounded ends of the 'bat ears' of such as the French Bulldog. Because they are so large, chihuahuas ears sometimes take a while to become fully erect. The ears of teething pups are often soft at the tips, bending forward or back. Truly soft ears, those which fail to stand up, flop down beside the head and are both a serious fault in the show ring and are more likely victim of problems such as canker. Small, kitten ears set high on the head produce an alien, foxy, pommy expression and are sometimes difficult to weed out of breeding lines.

      The neck is 'slightly arched, medium length' for strength, as it both carries the weight of the head and is part of the fore-quarters assembly. If the neck is long and whippy the whole dog will probably be built along racy, whippet-like lines with long spindly legs. Extension of the vertebrae of the neck generally accompanies a pro rata extension of the rest of the spinal column, giving long, weak backs, slab sides and long, ratty tails. This so called 'deer-type' is no longer as common in chihuahuas. More common is the chi with a stuffy neck---too short a neck leaves too little room for the muscles, and is associated with heavy, overbuilt forequarters. The head, in such a chi, often looks as if it has been stuck straight on to the body, especially in longcoats where the ruff hides the true lines of the neck. When felt the neck, measured from base of skull to the shoulder should be approx. one-third of the length of the back.
 
 

      The arch of the neck is required for strength, to be effective it must carry the head forward, and not up (star-gazing). If the arch of the neck is inverted the dog's movement suffers, being less smooth and rhythmic, choppy and without reach and drive.

      It should be noted in passing that a chihuahua should have no loose folds or flaps of skin on the neck. The chi should offer clean bodylines to the eye.

      The forequarters of the dog may not always receive as much attention as the hindquarters, but they are equally important. The hindquarters provide the drive, the forequarters propel on the turn, absorb the impact of each stride or jump, ensure travel in a straight line, assist in maintaining the stability of the center of gravity and carry weight. Faults in the forequarters assembly can therefore have serious consequences. Note that the foreleg does not end at the elbow, although its structure is harder to see than that of the hindquarters.

      The shoulder, as the foundation upon which the forequarters are based, should be correctly laid, the most efficient arrangement is generally accepted to be 45 degree from the horizontal (side view). An upright shoulder (an angle significantly greater than 45 degrees) tends to shorten the shoulder blade, thereby also shortening the muscles anchored to it, reducing their efficiency. There is also a loss of reach, as the foreleg cannot straighten beyond the angle of the shoulder, and this reduces drive and is the root of a number of serious gaiting faults.

     If the hindquarters are better angulated than the front and provide more drive than the front can accommodate, problems occur. Unless a corrective remedy is found the dog  'Pounds'---the front legs hit the ground before the hind legs have completed their forward push, the resultant excessive strain may cause the dog to 'break down' in front, especially at the pasterns. Excessive rising and falling at the withers often betray this condition. To avoid pounding the dog may flick up its front pads just prior to impact. This reduces the shock of impact, the dog lands on the heel pads, which act as buffers. 'Padding", as this fault is known, often looks most smart to the casual observer, but it is only the dog's natural compensation for its structural deficiencies, and a trap for the unwary!

     Overreaching is another problem caused by an imbalance of drive, the hind feet interfering with the front. To avoid tripping on its own feet the dog may then have to 'Crab', swinging the hindquarters out to one side so it appears to walk sideways. When walking directly toward you the hind legs of the 'crabbing' dog are visible beside the forelegs (a), those of the correctly moving dog are masked (b).
 
 

      An alternative method of avoiding contact is to throw the front legs high in the air, the 'Hackney' gait. This is specifically described in the standard as a fault, in part because, for just a few specific toy breeds this is, for differing reasons, the required gait.

      Shoulders are also required to be 'lean, sloping into slightly broadening support'. This refers to the view from the front of the dog. The shoulders lay along the ribs; too much muscle on the shoulder pushes the tops of the shoulder blades apart. These 'loaded shoulders' are heavy, rather than lean, and result in a lack of balance. The shoulder point is tied in closer to the ribcage and the elbow is forced out of line, which is an ugly fault. A dog with loaded shoulders may also appear overbuilt at the front, tailing off to weaker hindquarters.
 
 

     Balance is determined in two situations; on the move (kinetic balance) and standing still (static balance). Static balance is achieved if the dogs structure allows standing on all fours with the minimum of effort. For this to be possible the base of the support (the heel pad) must be vertically beneath the center of gravity of the shoulder, although the support is not a solid vertical 'pole'.
"Forelegs set well under" means that the humerus must be long enough to set the legs under the shoulder, the best arrangement being the humerus set at 90 degrees to the shoulder blade, and of the same length. The ultra straight  'terrier front' is the result of a shortening of the humerus with a resultant shorter, more upright shoulder. This may look extremely smart, but it is most definitely incorrect in a chihuahua. The foot is set too far forward, rather than being well under. The leg appears to be a continuation  of the neck, with no brisket visible in front of it.
 

The straightness throws the foot forward of the center of gravity and straightens the pasterns until they tend to knuckle over. This is not the straight front the standard refers to. A short humerus would bring the elbow above the brisket line. To give freedom of movement the elbow is lower. This of course, is freedom of movement front to back, 'looseness' refers to side to side movement and is not wanted.

     To get the heel pad beneath the center of the shoulder requires a slight bend at the pastern joint. If the pasterns are too upright weight will be thrown forward on to the toes, risking damage to the foot. The standards 'straight forelegs'  refers to the legs as seen from the front. if completely straight (side view) from elbow to heel the leg muscles are constantly at work equalizing the pull forwards and back, so that the leg tends to quiver. If the muscles are weak the pastern will knuckle over. If the pastern bends forward too much there is constant strain on the muscles of foot and leg, and displace certain small bones in the foot.
 
 

     Viewed from the front the foreleg should be straight from point of shoulder to the pad. However to be in complete balance the foot may incline inwards slightly from the vertical, to ensure that the foot is vertically beneath the center of gravity of the shoulder blade.

      Once on the move, kinetic balance requires maximum work for minimum effort, to increase stamina and reduce fatigue. Viewed from the side the radius and ulna should be parallel with a line drawn from foot to center of the shoulder, when the foot is in contact with the ground.

      From the front the foreleg should still be straight, but it must be noted that the faster a dog moves, the greater the tendency to place the feet near the center line beneath the body. This is not a fault, it helps prevent body roll, which would be unduly tiring. However, the speed a chihuahua is normally gaited at in the ring should not require anything approaching single-tracking. The opposite of single-tracking, 'paddling' can also be a problem. Tied in elbows are restricted in their movement, as a result the legs are thrown wide of the body, which rocks from side to side because the feet fall so wide apart.

     Other gaiting faults combine various features of a front that is not straight, the leg bending at elbow, pastern or even just the foot. Movement is most efficient when the leg, from point of shoulder to foot, is a straight  column of bones. Loose elbows which 'flap in the wind' wide of the body throw the leg inwards. Weak
 
 

pastern joints throw the pastern out, or turn the feet both in and out. 'Weaving' is the result of the elbow problem, 'winging' that of the pasterns.
     Each forelimb is an entirely separate structure, only anchored to the main frame of the dogs skeletal structure by muscle and ligaments. Therefore weak musculature will compound the problems of poor bone structure, or it may force sound structure into unnatural situations. Faults of both bone and muscle must therefore both be considered important. Equally problems evidenced in puppyhood may resolve as the adult dogs develop and harden the necessary muscle, roadwork is often the prescribed remedy for loose elbows in a young dog.
Age is not always a benefit however. Continued muscle development on upright shoulders often results in the fully mature dog, at 2 or 3 years old, becoming overbuilt in front, characteristically 'stuffy' in neck.

     The hindquarters, from the croup to the feet, are more involved in the provision of drive than in the maintenance of stability. Thus the dictates of stable balance are modified to cope with the not entirely compatible requirements for providing drive. The hip joint is therefore a more straightforward ball and socket joint, with the hip securely anchored to the spine, creating fewer mechanical constraints to the delivery of push.  It should also be noted that the hock is a joint, not to be confused with the hind pastern.

     Static balance is achieved when, viewed from the rear, the hind feet are equally spaced either side of the center of gravity (an imaginary vertical line drawn through the center of the pelvis, usually the root of the tail). For perfect balance the leg should form a straight, vertical column of bones from pad to hip joint. A modified balance is achieved by spreading the hind legs apart and back slightly,
 

usually to display alertness or aggression, or to lower the croup and straighten the topline. Free-standing chihuahuas should not show more than a minor amount of stretch, and never stand artificially stretched like a gundog.
      Balance, modified or not, will be lost if the hind legs are not straight, i.e. if the hocks are turned in or out. Turned out hocks are the less common, they turn the feet in, 'Pigeon-toed'. Turned-in hocks, 'Cowhocks', are a well-known and more prevalent fault. Lack of room forces the stifle out, which in turn forces in the hocks and splays out the feet. In cows this allows room for the udder but in dogs it is a fault as it seriously weakens drive. Drive is provided at an angle to the desired line of movement.

     When the dog moves away these faults and more may be revealed. Hocks "well apart" refers to the fault of moving close (brushing hocks). This fault has to be distinguished from single-tracking, which is the natural tendency of most breeds as their speed increases. The reason and extent of this tendency are the same, front and back. When a dog is 'moving close' behind, the hind pasterns brush past each other and may even touch. The stifles usually break the hip-foot line as well. Drive is lost as a result. The condition is often attributable to weak rearing muscles.
 

     The differing requirements for hindquarters mean that the pelvis thought most efficient at 30 degrees to the horizontal (not the 45 degrees of the shoulder). If the pelvis (& thus croup) is steeper, forward reach is gained, but push and follow through are restricted. If the pelvis is flat, forward reach is reduced, but the length of muscle from pelvis to hock shows an apparent increase. This however is not so as the femur, which tends to lie at 90 degrees to the pelvis, is nearer the vertical, straightening the stifle joint and decreasing that joints ability to operate  as a pulley for the rearing muscles and ligaments. A shallow croup gives hind movement that is stilted, in Spitz breed style, whilst a steep croup shows up as slack hind movement and a "Goose-rump".
 

     Angulation of the hindquarters (good turn of stifle) is required for extra speed. Increasing the turn of stifle proportionately increases the length of both the thigh and second thigh, thereby also lengthening the rearing muscles. These muscles, particularly of the second thigh, provide the drive. Weak hind muscles lead to poor hind action, hence 'Muscular' in the standard.

     The natural result of lengthening the second thigh, by developing a good turn of stifle, is that the hind pastern shortens, giving hocks that are 'well let down'-i.e. close to the ground. A shorter hind pastern gives greater endurance. Ideally the hind pastern should incline slightly forward---foot slightly behind the hock, but a vertical hock is the norm in the showing. The hind pastern should not incline backwards, foot in front of the hock, since these 'sickle hocks' imply that the achilles tendon is unable to fully extend the leg. In more severe cases the dog may look as though it bounces up and down on its hind feet. Rather than being directly under the pelvis, the hind foot should stand so that the hind pastern is beneath the point of buttock.
 

     The stifle joint is most unusual in construction. The patella runs between grooves on the end of the femur, to prevent overstraightening and act as a pulley for the rear muscles. If the muscles and ligaments are slack the patella may jump the groove. In a dwarfed breed like the chihuahua it is more likely that the groove may not develop in proportion to the joint, shallow grooves therefore tend to be more common. This fragile joint is particularly susceptible to external damage. Enthusiastic pulling and tweaking of the hind leg can have serious results. The judge may find this patella luxation (slipping stifle) evidenced by hopping, locking the leg straight when standing, or by feeling (& sometimes hearing) the patella move when gently handled. The problem is another that age tends to amplify, and the unnatural wear on the joint may lead to arthritis.

     Hip dysplasia also regularly leads to arthritis, and is not confined to big dogs, it is known in chihuahuas. HD can be debilitating in its severest form. HD occurs where the ball joint of the femur does not fit snugly in the socket of the pelvis. The result is uneven wear on both surfaces, and strain on the muscles. Subclinical HD (showing no external symptoms) is tested for by X-Rays in the most susceptible breeds, which tend to be the larger and heavier ones. Like all other structural faults HD must usually be assumed to be hereditary and breeding programs planned accordingly to discard, rather than store up problems for future generations.

     Good conformation does not begin and end with the structure of the limbs, nor does soundness relate only to movement. The spinal column, from neck to tail, has an important role to fulfill. The vertebrae are more than just protection for the spinal cord. They anchor the limb muscles which allow movement, they are the foundation of the dogs skeleton. Differing stresses along the length of the spine mean that this strength must be combined with a degree of flexibility. The spine is not just a hollow tube. The thoracic vertebrae and the neck anchor the muscles of the forelimbs, the former also support the ribcage; the vertebrae of loin and croup anchor muscles of the hindquarters and tail. The bony protrusions  at the top of each vertebrae do not all face the same way, those anchoring the forelimb are angled to the rear, for the hindquarters they angle forward, and between are some with less pronounced, more upright ridges. Where these ridged vertebrae meet the neck, at the withers, there should be a slight dip, just before the withers.

     The spine is naturally curved--there should be a slight rise at the withers and also over the loin, although the latter is often disguised under muscle, fat and coat, even in Smooths. The spine should not curve from side to side (viewed from above), nor should there be any pronounced dip or rise in the topline. Weakness of the spine results in faults such as a 'Sway back' - a pronounced sag in the spine between withers and pelvis, or a 'Roach or Camel back'--a pronounced rise behind the withers. A level back should not be billiard table flat, but it should not slope, height at withers should be the same as at the croup.

     Length of body is now specified clearly in the standard and the definition of 'back' (not entirely agreed upon in canine circles) need no longer worry anyone wishing to understand the Chihuahua standard. It should be noted in passing however, that there is no resorting to the standard to justify personal preferences for long bitches and short, 'cobby' dogs, the chihuahua standard is totally unisex in all its requirements (except the obvious of course!).

     The ribcage is an important structure, determining the room available for heart and lungs. There are 13 pairs of ribs, pivoting where they join the spine, and connected to the sternum by cartilage. The first 9 pairs connect by cartilage directly to the sternum,, the next 3 pairs are connected by cartilage to the cartilage of the rib in front, whilst the final pair are 'floating ribs' with no connection to the cartilage of the other ribs. These joints (bone/cartilage or cartilage/cartilage) allow the ribcage to expand outward with each breath, increasing lung capacity. The heart rests between the lungs on the sternum between the 3rd and 8th ribs. The ribs are set against the ribs and against the diaphragm--the muscle which runs diagonally from the loin vertebrae, down the rib walls, to the 7th rib and the sternum, separating thorax from abdomen. The action of the diaphragm creates a vacuum behind the lungs, greatly assisting breathing.
 

     The standard recognizes the need for plenty of heart room by requiring 'well spring ribs, deep brisket'. The ribs should spring out in their initial curve away from the spine, but then flatten and lengthen slightly to deepen the chest, the length of rib and depth of chest best increases heart and lung room. If slab-sided, with little or no spring of rib from the spine and flat sides to the ribcage room is restricted. Rounded, "Barrel ribs" offer an illusion of room, but adequate depth of brisket could only be obtained with a disproportionately large ribcage. As well as depth and width, the ribcage should also be sufficiently long, so the brisket line should not cut up before the 7th or 8th rib. If the brisket line rises immediately behind the elbows, at the 3rd or 4th rib, the heart is pressed upwards, reducing lung room. Depth of brisket should be measured through the tip of the sternum, not merely between the forelegs.

     The tail completes the body's structure, the tail bones are a direct continuation of the spinal column, becoming progressively smaller and tapering to the rear. Control is by three quite powerful muscles, two above and one below. The set of the tail should be fairly high, to allow the tail to be carried up and over the back.
A low set tail is likely to accompany a 'goose-rump', with steep croup and movement problems. If the tail is set too high, laying flat across the back like a Pom's, the pelvis is likely to be laid too flat, with a resultant short, stilted hind action. A twist or kink in the tail is a fault that may be more serious than it appears, since unnatural twists in the tail vertebrae may be symptomatic of further weaknesses along the spinal column. The curly 'pig' tail, and the long tail twisted to one side, the results of muscular imbalance may also signal further weaknesses in muscular development. The typical Chihuahua tail is the result of a slight flattening of the vertebrae combined with strong muscles, modifications which slightly reduce tail length. A long, round bony, 'whippy' or 'rats' tail is a deviation from type.