 of the facial nerve. This structure which I have picked up here deep inside the parotid gland. This one, this is the facial nerve. The facial nerve emerges by passing through the stylo-mastered foremen which of course we cannot see here. It's a foremen between the mastoid process and the styloid process and then it winds around the neck of the mandible lateral to the neck of the mandible and before it enters the parotid gland it gives a branch which goes like this behind the ear and it supplies the occipitalis muscle that is referred to as the posterior auricular branch. Thereafter the facial nerve enters into the parotid gland and this is the portion that we can see here. Inside the parotid gland the facial nerve divides into multiple small branches and forms of plexus and that plexus is referred to as the pest anserinas and we can see some of the fibers of the plexus here. It runs in the facial venous plane of PT and this is the facial venous plane of PT. It's a surgical plane produced by the facial nerve and the retromandibular vein and this is the facial venous plane which separates the superficial part of the parotid gland from the deep part and it's also a plane for surgical resection of the superficial part of the parotid gland and then it comes out from the anterior border of the parotid gland and we can see one of the branches coming out here and once it comes out it forms two principal trunks, temporal facial and the cervical facial. The temporal facial trunk divides into two branches, a temporal branch, a zygomatic branch and the cervical facial branch divides into a buccal branch, a marginal mandibular branch and the cervical branch and we can see the cervical branch here. The cervical branch is the one which supplies the platysma muscle and this is the platysma muscle here. We cannot see the other branches but we can mention what of this supply. The temporal branch supplies the frontalis muscle. This is the frontalis muscle that we can see here and it also supplies the upper fibers of the orbicularis oculi. The zygomatic branch supplies the lower fibers of the orbicularis oculi which we can see here. The buccal branch is the one which has got the maximum supply. It supplies the major part of the muscles of facial expression in this region by means of multiple sub branches. Then we have this marginal mandibular branch which runs along the marginal mandible and that supplies the muscles of the lower lip at the chin namely the risorius, depressor labia inferioris, depressor angular inferioris, mentalis. Cervical branch I already mentioned supplies the platysma muscle. Most common cause of facial nerve injury is parotid surgery. As we can very well see because the parotid gland provides access to the facial nerve. Apart from that the facial nerve can be injured inside the facial canal which of course we cannot see here and the most common cause is non-specific inflammation or idiopathic though some say it is caused by herpes simplex infection. When the facial nerve is injured inside the facial canal inside the petriostemporal bone that condition is referred to as pels palsy. Please remember injury to the facial nerve in the parotid gland during parotid surgery is not pels palsy. Pels palsy is to define it is idiopathic facial palsy occurring inside the facial canal. When there is an injury to the facial nerve then all these muscles will be paralyzed, muscles of facial expression and one of the predominant manifestations will be drooping of the angle of the mouth and that is because the modulus which is a fibromuscular condensation here where eight muscles converge that drops down and that produces drooping of the angle of the mouth. Apart from that the person will not be able to make vertical wrinkles horizontal wrinkles of his forehead because the paralysis of the frontalis muscle the person will not be able to close his or her eyes because the paralysis of the orbicularis oculi there will be bell's phenomenon the person will not be able to move one part of the mouth so therefore when the person tries to show his or her teeth only one side will move the other side will not move so therefore the smile will be asymmetrical. This groove that we see around the side of the nose still angle of the mouth which is known as the nasolabial furrow which is normally present in everybody that nasolabial furrow will be flattened out. Patient will have dribbling of tears from the lower eyelid because of the drooping of the lower eyelid. Drooping of the lower eyelid is referred to as ectropion and overflow of tears is referred to as epiphoria. Additionally if the person tries to drink liquid liquid may dribble down from the angle of the mouth because of the drooping of the angle of the mouth. Person will not be able to blow out his or her cheek because of the paralysis of the buccinator and the person will not be able to make the skin of his neck taut because of the paralysis of the platysma muscle. The marginal mandibular branch which I mentioned just now which runs in along the lower border of the body of the mandible that is liable to be injury during submandibular gland surgery and this is the submandibular salivary gland that we have picked up here. So pre-ordered surgery, submandibular surgery are all places where either whole or part of the facial nerve can be injured. That is all for now. If you have any questions or comments please put them in the comment section below. Dr. Sanjay Sanyal signing out. Anderson is the camera person. Have a nice day.