The muscles in the oral group move the lips and cheek. They include the orbicularis oris and buccinator muscles, and other muscles that can be divided into a lower and an upper group of muscles. Many of these muscles intersect just lateral to the corner of the mouth on each side at a structure termed the modiolus. 
 

Orbicularis oris

The orbicularis oris is a facial muscle that is located in the thickness of the lip around the oral opening. The main function of the orbicularis oris is closing of the mouth. 

This muscle has two main parts: the marginal part consisting of longitudinal fibers and the labial part (also called the peripheral part) - composed of circular fibers.

Buccinator

The buccinator is a facial muscle that forms the anterior part of the cheek.

The buccinator originates from the alveolar processes of the maxilla and mandible at the region of the 1st and 2nd molar teeth, and the pterygomandibular raphe. The buccinator inserts into the angle of the mouth radiating into the fibers of the orbicularis oris muscle. The buccinator muscle participates in forming the lateral wall of the oral vestibule. 

Upon contraction, the buccinator pulls the angle of the mouth laterally, presses the cheeks to the teeth, thus decreasing the oral vestibule. Contractions of the buccinator muscle produce facial expressions presenting satisfaction, as well as laughing and crying.

Lower group of oral muscles

The lower group of oral muscles includes the following muscles:

• Depressor anguli oris
• Depressor labii inferioris
• Mentalis

Upper group of oral muscles

The upper group of oral muscles consists of the following muscles:

• Risorius
• Zygomaticus major
• Zygomaticus minor
• Levator labii superioris
• Levator labii superioris alaeque nasi
• Levator anguli oris