The head should be clean-cut and free from fleshy cheeks; the bony structure of the skull chiseled beneath the eye with no prominence in the cheek. The skull may show some median line; the occipital bone is not conspicuous in mature dogs. Lips should not be squared off or pendulous, but fall away in a curve toward the throat. A wedge-shape head, or a head long and narrow in muzzle and back skull is incorrect as are massive, cheeky heads. The jaws are powerful and free from snippiness- the muzzle neither long and narrow nor short and stubby.
A vigorous dog may or may not be high-energy, but everything he does, he does with vigor: he strains on the leash (until you train him not to), tries to plow through obstacles, and even eats and drinks with great big gulps. These dynamos need lots of training to learn good manners, and may not be the best fit for a home with young kids or someone who's elderly or frail. A low-vigor dog, on the other hand, has a more subdued approach to life.