Like all brachycephalic dogs, bully breeds often suffer from brachycephalic airway obstructive syndrome. Brachycephalic dogs such as Boxers and Boston Terriers are most commonly affected. Several air carriers embargo certain brachycephalic dog breeds. Anatomical abnormalities associated with brachycephalic breeds can cause shortness of breath. Dog breeds such as the pug are sometimes classified as "Extreme Brachycephalic". It is seen in brachycephalic (short-nosed) dog breeds because of the shallow orbit. Being a brachycephalic breed, King Charles Spaniels can be sensitive to anesthesia. Muzzle length scales with the risks of brachycephalic syndrome. The risk of brachycephalic syndrome increases as the muzzle becomes shorter. This breed, along with other brachycephalic dogs (e.g., boxers, bulldogs), are also prone to hemivertebrae. Brachycephalic dogs may be prone to complications with general anesthesia. Because of its brachycephalic head, the Dogue can be affected by breathing problems. Metamynodonts were more brachycephalic and had a broader than longer snout. The modern brachycephalic Persian has a large rounded skull and shortened face and nose. Mesaticephalic skulls are not markedly brachycephalic or dolichocephalic.