(1) Expression muscles: There are many expression muscles between the skin and maxillofacial bones. Most of these expression muscles are thin bundles or cords, such as the quadratus labii superioris, zygomaticus, and smile muscles. , deltoid muscle and quadratus labii inferioris muscle are arranged radially around the lips, and the orbicularis oris muscle is arranged circularly around the lips. When the cranial nerve center transmits commands through the facial nerve to the expressive muscles to cause contraction, the circularly arranged orbicularis oris muscles contract, which can cause the upper and lower lips to close or the mouth shape to become smaller and tighter. The radial muscle bundles pull the corners of the mouth upward, downward or outward, changing the position or shape of the lips and corners of the mouth, and facial expressions such as smiling, laughing, sad or crying appear. When the quadratus labii inferioris and deltoid muscles contract, they pull the lower lip downward and the corners of the mouth outward and downward. When one side of the facial nerve is paralyzed, the facial expression muscles on one side of the face lose their function and become relaxed, causing the patient to have a distorted mouth and eyes. If a certain branch of the facial nerve is paralyzed, partial paralysis or distortion will occur at the corner of the mouth or eyelid. (2) Masticatory muscles: Human masticatory muscles are mainly two groups of muscles that grow and attach around the mandible: one group is the ascending mandibular muscle group that promotes the upward or sideways movement of the mandible, including the masticatory muscles, temporalis muscles, and medial pterygoid muscles. and lateral pterygoid muscles; the other group is the mandibular depressor muscle group, including the digastric, geniohyoid and mylohyoid muscles. When the ascending mandibular muscles contract in a coordinated and flexible manner, the mandible takes the mandibular joint as the axis, the front of the mandible rotates upward, the upper and lower teeth contact, and the sharp incisal edges and cusps of the teeth cut or crush food. If the mandible moves sideways or forward, the upper and lower molars come into contact and produce a grinding effect, thereby grinding and grinding the food. Due to the coordinated action of the mandibular lifting and lowering muscles, the mandible undergoes repeated opening and closing movements. The powerful chewing pressure continuously chews the food into pieces and mixes it with saliva. The lips, cheeks, tongue, and palate cooperate to complete the chewing function of the oral cavity. After the food is swallowed, it is digested and absorbed by the gastrointestinal tract, thus ensuring the nutritional needs of the human body.