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Structure and Function of the Tail in Dogs

By: Virginia Wells

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What Is the Tail?

The tail is the most posterior or caudal terminal appendage of the vertebral column. It extends beyond the trunk or main part of the body.

Where Is the Tail Located?

The tail is located at the end of the vertebral column. It is the hind-most part of the backbone.

Not all dogs have a tail. Some dogs are born with short, rudimentary tails. Other dogs have their tails docked short soon after birth. Dogs without tails and those whose tails are commonly docked often belong to the herding and working breeds of dogs. In these breeds, a long tail is considered a disadvantage or a hazard, depending upon the dog's intended usage or line of work.

What Is the General Structure of the Tail?

The canine tail usually consists of between six and 23 highly mobile vertebrae. These vertebrae are enclosed by a versatile musculature that make the various segments, especially the tip, capable of finely graded movements that lift the tail, move it from side to side, or draw it down toward the anus or between the hind legs. The caudal muscles lie on the lumbar vertebrae, sacrum (in the lower back region) and tail vertebrae. The muscles insert on the tail/caudal vertebrae exclusively. The muscles are attached to the tail vertebrae by tendons. The most posterior tendons attach to the last tail vertebrae.

Part of the musculature is formed from muscles associated with the rectum, the anus and the pelvic diaphragm. Four to seven paired nerves serve the tail muscles. These muscles have many tendons that insert from the fifth or sixth caudal vertebra, then onto the next vertebra, and so on to the end of the tail.

What are the Functions of the Tail?

You can tell a lot about what dogs are feeling by watching their tails. Dogs use their tails for communicating. They express happiness, aggression, stress and many other emotions with their tail. By looking at the position and movement of the tail, you can often tell what dogs are thinking. When a dog wags his tail high and wags it back and forth, he's usually feeling pretty good. When he is interested in something, his tail is usually horizontal to the ground. A tucked tail indicates the dog is frightened or submissive. When the tail goes from horizontal to upright and becomes rigid, he is feeling threatened or challenged. A tail that is low and wagging indicates the dog is worried or insecure.

The tail has another vital role in communicating. Every time your dog moves his tail, it acts like a fan and spreads his natural scent around him. One of his most important odors comes from the anal glands, two sacs under the tail that contain a smelly liquid that is as unique among dogs as fingerprints are to us. Every time the dog wags his tail, the muscles around the anus contract and press on the glands, causing a release of the scent. A dominant dog that carries his tail high will release much more scent than a dog that holds his tail lower. Likewise, a frightened dog holds his tail between his legs to keep others from sniffing him, and in that way does not draw attention to himself.

The tail is important as a means of counterbalance when the dog is carrying out complicated movements such as leaping, walking along narrow structures or climbing. Dogs that run at great speeds often have thin tails that are very long in proportion to the rest of their body, and they use their tails as a counterbalance when making turns. Their tails may increase their agility and ability to turn quickly, so they can keep up with their prey. Tail muscles are also important in stabilizing the vertebral column and supporting the action of the extensor muscles of the back, as well as those of the croup and buttocks.

Some dogs use their tails as rudders when swimming. Dogs bred for swimming frequently have tails that are thick, strong and very flexible, which helps them to move easily through the water and make quick turns.

Some dogs use their tails for insulation. Nordic and Arctic breeds have bushy or plumed tails with long dense fur. When lying down they may pull their tails over their faces to keep out the cold. They also use their tails as rudders when pulling a sled across the ice.

What are the Common Diseases of the Tail?

  • Congenital malformation or absence of the tail
  • Trauma – with fractures or dislocations of the vertebrae, wounds to the soft tissues, and possibly paralysis of the tail
  • Cauda equina syndrome – an instability of the vertebrae over the pelvis where the tail attaches
  • Alopecia – loss of hair on the tail
  • Dermatitis around the base of the tail. This is particularly common in breeds with screw type tails (English bulldog, Boston terrier)
  • Tumors of the tail – both benign and cancerous

    What Types of Diagnostic Tests are Used to Evaluate the Tail?

    Various tests are used to diagnose disorders of the tail. These include:

  • X-rays
  • Epidurography
  • Possibly CT scan or MRI of the lower back
  • Electrodiagnostic testing on the muscles and nerves of the tail
  • Trichogram (microscopic exam of the hair)
  • Skin scrapings
  • Fungal culture
  • Skin biopsy or biopsy of masses

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