 Good day everybody. Dr. Sanjay Sanyal, Professor, Department Chair. Welcome to our section of the phase. This time I'm going to demonstrate a few of the muscles of facial expression. But before I start demonstrating the muscles, I need to tell you a few general things about these muscles. First of all, these muscles are all derived from the second bronchial arch, or the second pharyngeal arch, and therefore they are all supplied by branches of the facial nerve. And the facial nerve supplies them through five principal branches, which are as per the distributionation by my fingers. Temporal, zygomatic, buccal, marginal mandibular, and cervical. The second point about these muscles of facial expression is that even though the textbooks show them in vivid clarity, in real life they are not so clear. They are very thin, they are almost like fibers. And more importantly, these muscles, because they have to keep the facial skin mobile, one end of the muscle is attached to the bone, the other end of the muscle is attached to the skin. And therefore, while dissecting them, it is quite possible that we may have to remove some of the fibers. And not only that, the facial artery and the facial vein sometimes they run deep to some muscles, and sometimes they run superficial to muscles which we shall see. So therefore, we cannot see all the muscles in as clarity as we can see them in the pictures. Having mentioned these points, let's start off with whatever muscles we have been able to dissect out here. The first muscle that we can see here, this is a part of the frontalis muscle. The frontalis muscle takes origin from the gallia aponeurotica, and that is shown here, or the epicranial aponeurosis. And it gets inserted, as you can see here, on the skin of the forehead. And the function of this is when it contracts it produces horizontal wrinkles of the forehead. Now, this function of the frontalis is facilitated by another opposing muscle and that is the occipitalis muscle. The occipitalis muscle takes attachment from the superior nuclear line and it gets inserted onto the gallia aponeurotica. And when this occipitalis muscle contracts, it tenses the gallia aponeurotica and therefore, it increases the functionality of the frontalis muscle. Because the frontalis muscle is the opposite, it takes origin from the gallia and gets inserted onto the skin. Incidentally, whenever there is any injury of the scalp, this layer that we see here, this is the layer number 4 of the loose aerial tissue layer of the scalp, which separates the gallia aponeurotica from the periosteum. Blood can track on this loose aerial tissue layer and it tracks under the frontalis muscle and it then spreads under the skin of this upper eyelid and the lower eyelid, around the auricularis oculi producing what is known as the black eye or the racoon eye. Now, let's come to the next muscle that we can see here. For that, I have lifted up the skin on the nasal side of the face and we can see this muscle here. This is the proceder's muscle. One side is attached to the under surface of the skin, other side gets attached to the bone and it moves from lateral to medial. And this is the one which produces the disdainful appearance. Now, let's take a look at the fibres which are just deep to the proceder's and that is these fibres here. We can see some of these fibres here. These are the fibres of the auricularis oculi and we can see some of the fibres of the auricularis oculi in this also. These are the fibres of the auricularis oculi. The auricularis oculi has got three parts. One portion is the orbital part which is the more peripheral part and that is the one which is responsible for closing the eyelids tightly. Then we have a few fibres which are closed over the eyelids and they are the ones which are responsible for gentle closure of the eyelids. And finally, there are a few small fibres which are located right on the nasal side of the eye which are in contact with the lacrimal sac and they are responsible for facilitating drainage of the tears. Next muscle that we can see here, actually it's a group of muscles, we can see some of these fibres here. These are the fibres of the levator labiae superioris alec nasi and we can see some of the fibres are going down and some of the fibres are coming from the nose. They are the ones which elevate one side of the nose when the person is making a sneering expression. Next, we have some other muscle fibres and incidentally when I am dissecting this out, you would have noticed that the facial artery is running partly under the muscles and partly superficial to the muscles. These are the fibres of the zygomaticus major, the lateral fibres, and the zygomaticus minor are the medial fibres. Zygomaticus major, when it acts on one side, it produces a sneering appearance and when it acts bilaterally, it produces a smiling appearance. Deep to the zygomaticus major and zygomaticus minor, we have the levator anguli oris and the levator labiae superioris. The levator anguli oris produces a grin or a grimace expression. This is the buccanator muscle which takes origin from the alveolar process of the maxilla medial and from the terico medibular raffae and inserts with the fibres of the orbicularis oris. This is also known as the trumpeter's muscle which the trumpeter uses to blow out his cheek. It also acts as an accessory muscle of mastication. Importantly, we notice that the buccanator muscle is pierced by this structure here. This is the perotid or the stensin duct which pierces the buccanator and it opens on opposite the crown of the upper second molar tube. I would like to draw your attention to this cavity here. This cavity was filled with a big pad of fat and that is known as the buccal pad of fat. This buccal pad of fat actually has got multiple extensions. One extension goes above the zygomatic arch to the temporal region and the bulk of it fills up this region. This buccal pad of fat is the one which gives the rounded appearance of the cheek especially in babies or in fat people. This buccal pad of fat is supposedly useful for suckling in children. When a person undergoes starvation or when the person is bedridden and malarished, then the sunken cheeks appearance is produced by loss of this buccal pad of fat. And finally, cosmetic surgeons use this buccal pad of fat for various cosmetic and reconstructive beautification surgery. That is about the buccal pad of fat which is located here superficial to the buccanator but deep to the other facial muscles. Let us continue with what other muscles that we can see here. We can see some of the fibres of the orbicularis oris here, the circular fibres which completely encircle the upper and the lower lip. In this correction, I would like to draw your attention to yet another structure which is located just about 1 cm lateral to the angle of the mouth and that is here where my finger is located. There is a fibromuscular condensation here that is known as the modulus of the face. The modulus of the face is like the hub of a wheel. Three muscles from the top, three muscles from below, one muscle from lateral side and one muscle from medial side. All of them meet at the fibromuscular condensation that is the modulus. The three from the top are the zygomaticus major, the levator angulari oris and the levator labisuperioris. The muscle from the side is the buccanator, the muscle from the medial side is the orbicularis oris and the three muscles from below are the depressor angulari oris. Some of those fibres we can see them here. The risorius which we can see some of the fibres here and the depressor labi inferioris. So these are the three muscles from below. All these eight muscles meet at the modulus and in facial palsy when the injury to the facial nerve. One of the common findings is flattening of the nasal labial furrow that is this furrow here as well as drooping of the angle of the mouth. And that is because of this fibromuscular condensation, the modulus dropping down because it is no longer supported by these muscles. And finally as I mentioned already these are some of the fibres of the risorius. These are some of the fibres of the platysma and these are some of the fibres of the mentalis muscle. The platysma is also a muscle of the face but it is located more in the neck. It is a subcutaneous muscle and that is located here. And just to complete the story though it is not a muscle of facial expression we can see this strong muscle here on the lateral surface of the ramus of the mandible. This is the masseter muscle which is a very important muscle of mastication. So these are the muscles which are related to the muscles of facial expression and which are all supplied by branches of the facial nerve. When a person has got injury to the facial nerve which travels through the parotid gland then there can be paralysis of the muscles of facial expression. And which can produce a whole host of manifestations some of which I already mentioned. One important manifestation apart from drooping of the angle of the mouth is inability to close the upper eyelid. And therefore when the person tries to close his upper eyelid the eyeball moves up and that is known as Bell's Phenomenon. Thank you very much for watching. Ladies and gentlemen if you have any questions or comments please put them in the comment section below. Have a nice day. Dr. Sanjay Sanyal signing out. Don't forget to like and subscribe.