The planes of the skull and muzzle are parallel. The skull is flat and moderately broad, tapering slightly toward the muzzle. Cheeks are muscular, but not over-developed. The muzzle is strong with powerful, muscular jaws. There is a minimum of falling away under the eye, giving a moderately chiseled look.
Lips are tight and darkly pigmented.
The Jack Russell Terrier has a complete set of comparatively large, evenly spaced, white teeth. A scissors bite is preferred, but a level bite is acceptable. The nose is black and fully pigmented. Eyes are deep set, almond-shaped, dark in color, with a mischievous, intelligent expression. The Jack Russell Terrier has small, V-shaped, button ears of moderate thickness.