The facial nerve exits the brain from the inferior edge of the middle peduncle of the cerebellum, enters the inner ear door, crosses the bottom of the inner ear canal into the facial nerve canal, exits the stem mammary foramen and enters the parotid gland. The facial nerve is intertwined in the parotid gland to form the parotid plexus, and radiates from the edge of the parotid gland in five branches to innervate the facial expression muscles. According to the anatomical location, there are the following branches in order from top to bottom. The temporal branch is often two branches, which go out from the upper edge of the parotid gland to the SMAS via the superficial or anterior edge of the mandibular condyle, and cross the superficial surface of the posterior part of the zygomatic arch to the frontalis and orbicularis oculi. Damage to this branch causes loss of ipsilateral frontal lines. The upper branch is thin and crosses the zygomatic bone and distributes to the orbicularis oculi of the upper and lower lids; the lower branch is thicker and runs parallel to the lower zygomatic arch and under the transverse facial artery, distributing to the zygomatic muscle and the deep surface of the superior labialis. Injury to the zygomatic branch can result in incomplete lid fissure closure. The buccal branch is often 3 to 5 branches. It is about 5.o to 5.5 cm away from the earlobe sulcus, penetrates from the anterior border of the parotid gland, lies on the deep surface of the chewing muscle fascia, and runs parallel to the parotid duct toward the corner of the mouth. The buccal branch is located above the parotid duct as the superior buccal branch, which is generally thicker and in a constant position, and its body projection is approximately above the line between the interauricular notch and the inferior nasal margin; the inferior buccal branch is located below the parotid duct and travels forward in the plane of the corner of the mouth or slightly above. Therefore, the parotid duct can be used as an important marker to find the buccal branch of the facial nerve (e.g., 7 in the figure is the parotid duct, and a 3 is the buccal branch of the facial nerve above and below 7). The buccal branch is distributed to the buccal muscle, orbicularis oris, smiling muscle, and upper lip square muscle. The upper and lower buccal branches often anastomose with each other to form a network during the stroke. If part of the buccal branch is inadvertently damaged during surgery, the other branches have some compensatory effect. Fourth, the lower collar margin branch After the mandibular margin expends the parotid gland, it travels along the mandibular margin at the deep surface of the occlusal fascia and crosses the facial artery at the anterior margin of the occlusal muscle to enter the muscles of the lower lip forward. Therefore, when freeing the SMAS on the surface of the occlusal muscle, as long as the deep surface of the latissimus dorsi muscle is separated closely without damaging the occlusal fascia, the mandibular margin branch of the facial nerve will not be damaged. However, the operation should be terminated when it reaches the anterior border of the occlusal muscle. If the operation damages the mandibular margin branch, it will cause paralysis of the lower lip muscles and crookedness of the corners of the mouth. The facial nerve is composed of two nerves, which exit the brain at the lower edge of the cerebral bridge. In the temporal bone, the facial nerve resides in the curved facial nerve canal, which begins at the base of the internal auditory canal and opens at the foramen magnum. The facial nerve trunk is the section of the facial nerve that exits the foramen magnum to the facial nerve bifurcation. In adults, the facial nerve trunk exits the foramen caudalis and travels outward and slightly downward, tending to be slightly posterior to the caudal process in relation to the caudal process, i.e., above the posterior superior ventral border of the bicipital muscle. In adults, the facial nerve trunk corresponds to the height of the center of the anterior border of the mastoid process; in children, because the mastoid process is not fully developed, the facial nerve trunk is not located at the midpoint of the anterior border of the mastoid process, but mostly at the height of the mastoid tip. When the facial nerve trunk is exposed at the root of the mastoid process, it is usually in a deeper position. In adults, the vertical distance between the facial nerve trunk and the skin ranges from 1.8-4.1 cm, with most being around 2-3 cm. The posterior auricular artery is closely related to the facial nerve trunk, and the posterior auricular artery is mostly located superficially and slightly inferior to the facial nerve trunk. The postauricular artery is similar in thickness to the facial nerve trunk and should be carefully distinguished when dissecting the facial nerve trunk, which is about 2-2.5 cm in diameter. After the facial nerve trunk exits the mammary foramen, it immediately enters the parotid gland from the deep posterior border of the parotid gland and travels 1-1.5 cm within the parotid gland to divide into two general branches, namely the superior temporal-facial branch and the inferior maxillofacial branch. The temporofacial branch and the inferior maxillofacial branch. The temporofacial branch is 1-2 times thicker than the maxillofacial branch. The vertical distance between the bifurcation point of the trunk and the skin surface is about 1.2-2.3 cm, and the vertical distance between the bifurcation point and the horizontal line drawn from the tip of the mandibular angle is 1.9-5.0 cm, mostly between 2.1-3.5 cm; the distance from the posterior edge of the mandibular branch is 0.5-1.7 cm, mostly between 0.1-1.5 cm. The distance from the posterior edge of the mandibular branch is 0.5-1.7 cm, mostly 0.5-1.0 cm. 2. Relationship between facial nerve and parotid gland From the clinical point of view, the facial nerve passes through the parotid gland and divides the parotid gland into two lobes, i.e. the superficial lobe is located on the superficial side of the facial nerve and the deep lobe is located on the deep side of the facial nerve. Since the superficial lobe is thicker and the deep lobe is thinner, the facial nerve is located in the deep part of the parotid gland. In a normal parotid gland, the facial nerve has a nerve membrane outside, so it does not adhere to the parotid gland and can be easily separated; however, when there are pathological changes, adhesions may occur. 3. Branches of the facial nerve After the facial nerve leaves the stem mammary foramen, it branches out into the postauricular branch, which is first located between the parotid gland and the anterior border of the sternocleidomastoid muscle, and then between the mastoid and the external auditory canal. This branch innervates the posterior auricular muscle and the supratrochlear muscle, and when the facial nerve trunk reaches the stem, it branches to innervate the posterior belly of the bicipital muscle and the lingual muscle of the stem. After dividing into two general branches in the parotid gland, the facial nerve is divided into temporal, zygomatic, buccal, mandibular rim and cervical branches by the two general branches. The facial nerve is mostly divided into bifurcation, called bifurcation type, but sometimes it is not bifurcated, but divided into trifurcation, quadifurcation and pentfurcation type in order. Since the bifurcation of the trunk varies, the branches are not exactly the same for each individual. The branches of the facial nerve are first located in the parotid gland and then leave the parotid gland to appear under the marginal cover of the parotid gland. Although the facial nerve is divided into five branches, each branch actually has not only one but two or more branches. If the facial nerve is counted at the point of emergence from the parotid margin, the temporal branch is 1-2; the zygomatic branch is 1-4; the buccal branch is 2-6; and the mandibular margin branch is 1-4. Therefore, 11-12 branches can be found at the parotid margin in general. Not only does the facial nerve have many branches, but after it is divided into two main branches, the branches anastomose with each other until they enter the muscle. Thus, the facial nerve forms an irregular network distribution. Since the branches of the facial nerve anastomose with each other, there is a certain compensatory effect after a certain injury. The facial nerve is divided into 5 branches, which actually go to 5 parts, and its travel path and innervated muscles are as follows: (1) Temporal branch: there are 1 or 2 branches, which are divided from the general temporofacial branch, emerge from the upper edge of the parotid gland, travel upward, before the temporomandibular joint obliquely upward, and distribute in the frontalis muscle, orbicularis oculi, preauricular muscle and supraspinatus muscle. There may be traffic branches between it and the zygomaticotemporal branch of the maxillary nerve, the auriculotemporal nerve, the supraorbital nerve, the lacrimal nerve, and the eyelid branch of the maxillary nerve. (2) Zygomatic branch: It is divided from the general temporal facial branch and emerges from the anterior-superior border of the parotid gland, sloping upward. It usually has 1-4 branches when it leaves the anterior border of the parotid gland. The zygomatic branch is divided into two parts: the upper part crosses the zygomatic arch to innervate the upper part of the frontalis and orbicularis oculi, and the lower part supplies the lower part of the orbicularis oculi and the infraorbital muscles. It is believed that: there are 2-4 larger branches across the midpoint of the zygomatic arch, which dominate the frontalis muscle and the upper part of the orbicularis oris muscle; immediately below the zygomatic arch, the branch that crosses the zygomatic bone toward the canthus is smaller, less important, and there is no harm in cutting it off; the largest branch, which bends along the zygomatic bone obliquely forward and moves forward 1cm below the bone edge, dominates the muscles of the eyelid and upper lip, and has great significance in surgery. (3) Buccal branch: There are 2-6 branches of the buccal branch, which are divided from the temporal and cervical facets of the common trunk. They emerge from the anterior border of the parotid gland and travel above and below the parotid duct, with anastomotic branches between them, which can be located on the deep or superficial side of the parotid duct. The superficial branches of the buccal branch run between the skin and the superficial expression muscles, and the deep branches run on the deep surface of the zygomaticus muscle and the square muscle of the upper lip. The buccal branch innervates the buccal muscle, the orbicularis oris muscle, and the inferior portion of the superior labial square and zygomaticus muscles. The buccal branch has an anastomosing branch with the buccal nerve of the mandibular nerve. In addition, the buccal branch intertwines with the zygomatic branch of the facial nerve and the branch of the mandibular rim, the buccal nerve of the trigeminal nerve, and the terminal branch of the maxillary nerve to form the infraorbital plexus. (4) Mandibular marginal branch: The mandibular marginal branch emerges from the lower anterior border of the parotid gland, 98% of the mandibular marginal branch crosses over the surface of the posterior facial vein and 2% penetrates the deep surface of the vein, the mandibular marginal branch is immediately adjacent to the surface of the vein, therefore, the posterior facial vein is a marker to find the mandibular marginal branch. When the mandibular rim branch continues anteriorly, it mostly passes in the anterior facial vein. Most of the mandibular rim branches travel above the mandibular rim, and only 12.4%-19% have one or more mandibular rim branches bypassing the lower mandibular rim, with their lowest point no more than 1 cm from the lower mandibular rim. It also passes immediately before or after the artery. The mandibular rim branch innervates the descending labial muscles, i.e., the lower lip square and deltoid muscles, and enters the muscle from the deep lateral surface of the muscle. The mandibular rim branch can communicate with the buccal nerve of the mandibular nerve, the buccal branch of the facial nerve, and the cervical branch. (5) Cervical branch: The cervical branch emerges from the inferior border of the parotid gland and innervates the broad cervical muscle. When the cervical branch travels under the inferior border of the mandible and innervates the broad cervical muscle forward, it can be considered as the mandibular border branch. 4, the function of the facial nerve The facial nerve has three kinds of fibers, namely motor fibers, secretory fibers and gustatory fibers. 5.Facial nerve and facial and cervical incision Since the facial nerve is distributed in a reticular pattern, there is no obvious dysfunction if a particular one is injured due to compensatory effect, but the zygomatic and buccal branches should not be completely cut off. Cutting the temporal branch and the mandibular margin branch can restore its function after 3-6 months, and those who cannot recover account for a minority. (1) Depth of the incision: The depth of the facial and cervical incision has a close relationship with whether the facial nerve is damaged or not. On the surface of the parotid gland, if the surgical operation is limited to the parotid fascia, the facial nerve will never be damaged, and even if it enters the superficial layer of the parotid gland, the facial nerve will not be easily damaged, because the facial nerve is located in the deep part of the parotid parenchyma. The temporal, zygomatic or buccal branches, when they leave the parotid gland, travel on the deep surface of the superficial subcutaneous fascia, on the surface of the occlusal fascia, and sometimes even through the tunnel formed by the occlusal fascia, where it is not difficult to separate the subcutaneous fat and identify the white and bright branches of the facial nerve. As the nerve approaches the muscle it innervates, it enters the muscle from the deep lateral surface of the muscle. In the case of the orbicularis oris muscle, for example, when the incision is made in the superficial part of the muscle, there is little effect of damage to the nerve because the nerve fibers enter the orbicularis oris muscle from the deeper part of the muscle. (2) Choice of facial incision: When choosing the facial incision, attention should be paid not only to the scar deformity after surgery, but also to avoid damaging the main branches of the facial nerve, and making an incision at the mandibular joint, there is no main branch except for the main trunk of the facial nerve; above the zygomatic arch, a transverse incision is made along the upper edge of the zygomatic arch, and there is no obvious functional disorder after surgery, and even the front end of this transverse incision is extended upward along the lateral edge of the zygomatic bone to the zygomatic frontal suture There is no obvious dysfunction even if the front end of this transverse incision is extended upward along the lateral border of the zygomatic bone to the zygomatic-frontal suture or its rear end is extended upward to the height of the superior border of the ears. A transverse incision can be made below the parotid duct, but it is not aesthetically pleasing. A transverse incision 1.5 cm below the inferior mandibular margin will not damage the mandibular margin branch that runs below the inferior mandibular margin because it is not more than 1 cm away from the inferior mandibular margin. However, there are three possible reasons for this type of incision to have a skewed lower lip after surgery: one is the result of excessive pulling and compression during surgery; the second is because the attachment (point) of the descending labial muscle is stripped up during surgery, so the muscle temporarily loses its role; another reason is that although the incision is correct, when the fascial layer of the deep side of the broad cervical muscle is not cut, that is, when the lower edge of the mandible is exposed in a hurry, it may be damaged in the process of separation The mandibular rim branch may be damaged due to insufficient depth during separation. Because the superficial fascia of the neck has a thin layer on the deep side of the broad cervical muscle, and the mandibular border branch of the facial nerve is located within this layer, the tissue should be separated upward along the deep fascia surface instead of close to the broad cervical muscle when turning up the tissue office to avoid damaging the mandibular border branch.