From FCI standard:
BRIEF HISTORICAL SUMMARY : The Jack Russell Terrier originated in England in the 1800’s due to the efforts of the Reverend John Russell. He developed a strain of Fox Terriers to suit his needs for a dog to run with his foxhounds and go to ground to bolt the fox and other quarry from their dens. Two varieties evolved with basically similar Standards except for differences, mainly in height and proportions. The taller, more squarely built dog is now known as the Parson Russell Terrier and the shorter, slightly longer proportioned dog, is known as the Jack Russell Terrier.
