The Oral Cavity

Divisions of the Oral Cavity

The oral cavity extends from the oral fissure anteriorly (the opening between the lips) to the oropharyngeal isthmus posteriorly (the entrance to the oropharynx).

It is divided into two regions by the upper and lower dental arches – the vestibule and oral cavity proper.

Vestibule

The horseshoe-shaped vestibule is situated anteriorly. It is the space between the lips/cheeks, and the gums/teeth.

The vestibule communicates with the mouth proper via the space behind the third molar tooth, and with the exterior through the oral fissure. The diameter of the oral fissure is controlled by the muscles of facial expression – principally the orbicularis oris.

Opposite the upper second molar tooth, the duct of the parotid gland opens out into the vestibule, secreting salivatory juices.

By TeachMeSeries Ltd (2025)

Fig 1
The two divisions of the oral cavity are the vestibule and oral cavity proper.

Mouth Proper

The mouth proper lies posteriorly to the vestibule. It is bordered by a roof, a floor, and the cheeks. The tongue fills a large proportion of the cavity of the mouth proper.

Roof

The roof of the mouth proper consists of the hard and soft palates.

The hard palate is found anteriorly. It is a bony plate that separates the nasal cavity from the oral cavity. It is covered superiorly by respiratory mucosa (ciliated pseudostratified columnar epithelium) and inferiorly by oral mucosa (stratified squamous epithelium).

The soft palate is a posterior continuation of the hard palate. In contrast to the hard palate, it is a muscular structure. It acts as a valve that can lower to close the oropharyngeal isthmus, and elevate to separate the nasopharynx from the oropharynx.

Cheeks

The cheeks are formed by the buccinator muscle, which is lined internally by the oral mucous membrane.

The buccinator muscle contracts to keep food between the teeth when chewing, and is innervated by the buccal branches of the facial nerve (CN VII).

Floor

The floor of the oral cavity consists of several structures:

• Muscular diaphragm – comprised of the bilateral mylohyoid muscles. It provides structural support to the floor of the mouth, and pulls the larynx forward during swallowing.
• Geniohyoid muscles – pull the larynx forward during swallowing.
• Tongue – connected to the floor by the frenulum of the tongue, a fold of oral mucosa.
• Salivary glands and ducts.

By TeachMeSeries Ltd (2025)

Fig 2
Structures of the oral cavity floor.