The roof of the oral cavity consists of the hard and soft palates. The floor is formed mainly of soft tissues, which include a muscular diaphragm and the tongue. The lateral walls (cheeks) are muscular and merge anteriorly with the lips surrounding the oral fissure (the anterior opening of the oral cavity).
The posterior aperture of the oral cavity is the oropharyngeal isthmus, which opens into the oral part of the pharynx.