However, the most common and the most important of all the roles served is that of companion. Dogs crave close contact with their owners and people form loving bonds with their dogs. The companionship they offer helps ease the pain and isolation of the sick, the elderly and the physically handicapped. All dogs, regardless of breed, are essentially identical in anatomy. The skeleton of the domestic dog has about 321 bones, with variations in the number of bones in the tail and the presence of a dewclaw, an extra digit on the paw that not all breeds have.
Rear paws have four complete digits and front paws have four or five digits.
Most puppies have 28 temporary teeth, which are replaced with 42 permanent teeth at about six months of age. Differences in breeds evolved to help dogs survive in their native environment or occupation. Dogs that lived and worked outdoors needed a thick, weather-resistant coat to protect them from the elements and the biting teeth of predatory animals. Similarly a Labrador retriever developed an oily coat, webbed feet, and a rudder-like tail to help it perform better in recovering downed waterfowl. Just as distinct physical characteristics became trademarks in some breeds, unusual sensory abilities characterize others.