Bulldogs have brachycephalic skulls, meaning that their faces are pushed in. That usually results in the upper jaw being shorter than the lower -- underbite. Some bulldogs have little underbite, while others have the condition so excessively that they cannot eat without difficulty. The severity of the condition depends a lot on the type of bulldog and the breeding standards of that type.
Bulldog's Squashed Face
Bulldogs have flat faces with short muzzles, and they also have deformed nostrils, and much too narrow tracheae. The only part of the dog's face that sticks out is his lower jaw, which gives him the appearance that his lower jaw rolls up over the upper one. Since there are only 20 teeth in the upper jaw and 22 in the lower one, there needs to be more room in the lower jaw for all those teeth.
Breeding the Bulldog
Breeders and pet owners alike admire the appearance of the bulldog's flat face, which includes an undershot jaw. The dogs are bred with that jaw because it is considered an attractive look. Bulldogs often have slobbering issues due to this condition, as their airways are compromised by the skull deformities, and they have to breathe with their mouths open all the time.
Origins of the Bulldog
Bulldogs were originally bred to fight bulls; their undershot jaw helped them hang on to a bull during a fight. The dogs had tenacious grip and were stubborn to a fault, simply refusing to let go of the bull right to death. Without the undershot jaw, these dogs would probably have a different name today, as they would not be able to hang on to a bull as well.
Bulldogs and other short-faced dogs are prone to a bone condition known as achondroplasia, which is characterized by the bones being smaller than normal or bent into unusual shapes. Dogs with this bone condition have short, slightly or severely bent legs, flat faces and short muzzles. Dwarfism is common with achondroplasia. An undershot jaw is a symptom in dogs with this condition. Achondroplasia is a form of osteochondrodysplasia, which is bone and cartilage abnormality.