Mouth entrance to the digestive and respiratory tracts. The mouth, or oral cavity, is ordinarily a simple opening in lower animals; in vertebrates it is a more complex structure. In humans, the mouth is defined in front and at the sides by the lips, jawbone, teeth, and gums; in the rear it merges with the throat. The roof of the mouth is composed of the hard and soft palates and the floor of the mouth is formed by the tongue, a muscular structure that contains the organs of taste (taste buds).
An aphthous ulcer, also known as a canker sore, is a type of mouth ulcer that presents as a painful open sore inside the mouth or upper throat characterized by a break in the mucous membrane. Its cause is unknown, but they are not contagious. The condition is also known as aphthous stomatitis (stomatitis is inflammation of the mucous lining), and alternatively as Sutton's Disease, especially in the case of major, multiple, or recurring ulcers.