If you like dogs with squished-in faces, you're a fan of the brachycephalic breeds. Brachycephalic or "short head" canines come in various sizes. Their head shape make them prone to respiratory issues, and many airlines won't allow them on board.
Many of the brachycephalic breeds are relatively small and portable, weighing under 20 pounds. These include the Pekingese, the pug, the Boston terrier, the Cavalier King Charles spaniel, the Japanese Chin, the Brussels griffon, the Shih Tzu, the Lhasa apso and the French bulldog.
Brachycephalic breeds are better represented among the smaller and larger canine spectrum, only a couple purebreds falling in the midsize dog range. If you're in the market for a dog maturing between 20 and 50 pounds, brachycephalic breeds fitting the bill include the English bulldog and the American bulldog.
Big brachycephalic dog breeds include some of the largest of all dogs: mastiffs. These giant canines, some of which can top the scales at 200 pounds and up, include the English mastiff, Neapolitan mastiff and bull mastiff. Boxers, large but not huge, are also brachycephalic. So are the extremely wrinkled Chinese Shar-Peis.