Define the borders of the oral cavity proper. It is bounded superiorly by both the hard palate and soft palate. The teeth and gums form the anterior and lateral boundaries. The palatoglossal folds (arches) , part of the isthmus facium, form the posterior boundaries of the oral cavity. Inferiorly, the floor of the oral cavity is principally formed by the tongue.
Lift the tip of the tongue and examine the inferior aspect of the tongue that is connected to the floor of the mouth by a midline mucosal fold, the frenulum (linguae). On either side of the frenulum, identify the sublingual fold of mucosa that is formed by the sublingual salivary gland and the small openings of the sublingual duct.