Each ramus of lower jaw or mandible in mammals is formed of a single large membrane bone, called as dentary. The dentary is broad and flat behind but narrow and conical in front. The front end bears a single incisor tooth. The lower jaw in frog is toothless and movable up and down. Each ramus of the lower jaw is slender and slightly a curved skeletal rod. It is formed of two membrane bones?the dentary on outer and angulosplenian on inner side.