The Jack Russell is frequently confused with the Parson Russell terrier (see the American Kennel Club) and the Russell terrier, which is a shorter-legged, stockier variety. (Within the Fédération Cynologique Internationale, the 'Russell terrier' is also known as 'Jack Russell terrier'.) Each breed has different physical proportions according to the standards of their national breed clubs. The head should be of moderate width at the ears, narrowing to the eyes, and slightly flat between the ears.