The Bull Terrier Breed Standard
A breed standard is the guideline which describes the ideal characteristics, temperament, and appearance of a breed and ensures that the breed is fit for function with soundness essential...
Soundness as it refers to dogs has never been precisely defined.
In Bull Terriers it refers to the general skeletal and muscular perfection as laid down in the Breed Standard...
The Bull Terrier Club of America - The Bull Terrier Illustrated Standard, 1991