The Oral Cavity and Pharynx Quiz

See The Oral Cavity. Option A is correct because the teeth and their gums, arranged in the upper and lower dental arches (the curved rows of teeth held in the jaws), form the lateral boundaries of the oral cavity proper and separate it from the vestibule. The mouth opens at the oral fissure, the gap between the lips. Just inside it is the vestibule, a slit-like, horseshoe-shaped space with the lips and cheeks on the outside and the teeth and gums on the inside. Inside the dental arches lies the oral cavity proper, the main space of the mouth, which the tongue largely fills. The cheeks are often described as the side walls of the mouth, and that is true of the mouth as a whole. Formed by the buccinator muscle, they make up the outer walls of the vestibule, so they lie on the far side of the vestibule from the oral cavity proper and cannot separate the two spaces. Buccinator contracts to keep food between the teeth while you chew. A simple memory aid: the teeth are a fence, with the vestibule outside it and the oral cavity proper inside it. The boundaries of the oral cavity proper are:

• the teeth and gums of the dental arches, in front and at the sides
• the hard and soft palate above, forming the roof
• the tongue and mylohyoid muscles below, forming the floor
• the palatoglossal arches behind, where the mouth opens towards the oropharynx (the part of the throat behind the mouth)

• Boundary: the teeth and gums of the dental arches form the sides of the oral cavity proper.
• Vestibule: the slit-like space outside the teeth, with the lips and cheeks on its outer side.
• Cheeks: the buccinator forms the cheeks, which are the outer wall of the vestibule.

The buccinator muscles in C are the classic trap: they form the cheeks, which are the outer walls of the vestibule, so they lie outside the teeth rather than between the vestibule and the oral cavity proper. Buccinator would be right only if you were asked for the outer side wall of the vestibule. D names the paired mylohyoid muscles, which form a supporting muscular sheet (the muscular diaphragm) and, with the tongue, make up the floor of the mouth rather than its sides. The sublingual folds in B are mucosal ridges in the floor of the mouth, so they lie below the tongue and do not form the lateral boundary of the oral cavity proper. Finally, the palatoglossal arches in E are folds at the back of the mouth that mark where the oral cavity proper opens towards the oropharynx, so they form its posterior boundary rather than its sides.