It is from the " labia," or lips, that the Brocchi[1] have received the surname of Labeo. All animals that are viviparous have a mouth that is either well-formed, or harshly defined, as the case may be. Instead of lips and mouth, the birds have a beak that is horny and sharp at the end. With birds that live by rapine, the beak is hooked inwards, but with those which gather and peck only, it is straight: those animals, again, which root up grass or puddle in the mud, have the muzzle broad, like swine. The beasts of burden employ the mouth in place of hands in gathering their food, while those which live by rapine and slaughter have it wider than the rest. No animal, with the exception of man, has either chin or cheek-bones. The crocodile is the only animal that has the upper jaw-bone[2] moveable; among the land quadrupeds it is the same as with other animals, except that they can move it obliquely.