The oral cavity is the initial part of the digestive tract. It can be defined as a space extending between the lips and oral fissure anteriorly and faucial pillars and oropharyngeal isthmus posteriorly. It connects the external environment with the pharynx. Overall, the oral cavity receives food, produces saliva and initiates digestion. Besides the function related to digestion, the oral cavity also provides such functions as speech formation and respiration.

The oral cavity is located anteriorly in the lower aspect of the face and head right under the nasal cavity. It begins at the border between the facial skin and the lips. It has two parts, two openings and four walls. Overall, the oral cavity is formed by the following structures:

• Lips
• Cheeks
• Gingiva (gums)
• Teeth
• Soft and hard palate
• Salivary glands
• Muscles of the oral diaphragm (mylohyoid)

The oral cavity houses the tongue.

Parts

The oral cavity is composed of the following parts:

• Oral vestibule - horseshoe-shaped anterior portion; it can be described as an area bounded by the lips and cheeks anteriorly and laterally and by the teeth and gingiva posteriorly; it connects with the outer environment via the oral fissure;
• Oral cavity proper - the second or posterior part located behind the oral vestibule; it can be described as an area behind the teeth; it extends between the alveolar arches of the maxilla and mandible anteriorly and laterally and the oropharyngeal isthmus posteriorly; the oral cavity proper is formed by the soft palate and hard palate and minor and major salivary glands; it is occupied by the tongue.

Overall, both parts are separated by the teeth, gingiva and alveolar arches of the mandible and maxilla. If the mouth is open, the oral cavity proper and oral vestibule connects through the gap that forms between the maxillary and mandibular teeth. If the maxillary and mandibular teeth are in contact, the connection happens via a small gap behind the last molar teeth.

Openings

As mentioned above, the oral cavity has two openings:

• Oral fissure - orifice of the mouth; anterior opening that connects the oral vestibule with the external environment;
• Oropharyngeal isthmus - posterior opening that connects the oral cavity proper with the pharynx; it leads into the oropharynx, which is the middle portion of the pharynx. 

Walls

The oral cavity has four walls:

• Roof - formed by the hard palate anteriorly and soft palate posteriorly; it separates the nasal cavity from the oral cavity;
• Lateral wall (2) - formed by the soft tissue of the cheeks, mastication and facial muscles (mainly by the buccinator);
• Floor - mostly formed by the mylohyoid and geniohyoid muscles; the sublingual and submandibular salivary glands lie within the floor.