Quote from the Official Standard

"Smooth-coated, thick set, rather low in stature, broad, powerful and compact.  Head fairly large in proportion to size, but at no point so much in excess of others as to destroy the general symmetry, or make the dog appear deformed, or interfere with its powers of motion.  Face short, muzzle broad, blunt and inclined upwards.  Dogs showing respiratory distress highly undesirable.  Body short, well knit, limbs stout, well muscled and in hard condition with no tendency towards obesity.   Bitches not so grand or well-developed as dogs."

Example of dog

Example of  bitch