 We are demonstrating the right side of the cadaver and the camera person is also on the right side. The strap muscles of the neck are divided into two broad groups, supra-hyoid and infra-hyoid. This is the hyoid bone. This is the body of the hyoid and on either side is the greater corner of the hyoid where my fingers are located. So therefore these muscles are the supra-hyoid and the ones below are the infra-hyoid muscles. So let's take the supra-hyoid muscles first. This muscle that I have picked up here, this is the posterior belly of digastric. This muscle which I have lifted up, this is the anterior belly of digastric. Same thing on this side, we can see this is the anterior belly of digastric. The posterior belly of digastric is more posteriorly on the left side. The posterior belly of digastric takes attachment from the mastoid process and then it comes here and there is an intermediate tendon which is attached by means of a facial sling to the hyoid bone and then the anterior belly gets attached to the inner surface of the mandible. This angulation is achieved by this facial sling which is derived from the pre-tracheal fascia which is a part of the deep cervical fascia. There is another muscle which is closely related to the posterior belly of digastric and that is this muscle. This is the style of hyoid which is just under that. It arises from the styloid process which is deep where the instrument is located and then it comes here and as it comes closer to the posterior belly it splits and we can see one layer outside and one layer inside and it gets attached to the hyoid bone. So the splitting allows the intermediate tendon of the digastric to pass through. The next muscle in the suprahyoid compartment is once we reflect this and under this we can see this muscle here. We can see these muscle fibers and we can see it here also. Similarly on this side also once we reflect this we can see these horizontal muscle fibers. This is the mylohyoid. The mylohyoid muscle actually forms the floor of the mouth and the fibers they take attachment from the mylohyoid line on the inner surface of the body of the mandible. This is the mandible and the fibers then converge medially and they get attached to a midline fibrous raffae known as the mylohyoid raffae. And then deep to the mylohyoid which we have not removed is the geniohyoid which also takes attachment from a small tubercle on the inner surface of the mandible near the symphysis mentai known as the genio tubercle and gets attached to the hyoid bone hence the name geniohyoid. So these are the suprahyoid group of strap muscles. Now let's come to the infrahyoid strap muscles. This is the inferior belly of the omohyoid we can see here. This is the only infrahyoid strap muscle which is not in the anterior cervical region. It is in the lateral cervical region. And here also there is an intermediate tendon which was damaged when they did an embalming of the cadaver through the carotid artery here. And after the intermediate tendon we have this segment here. This is the superior belly of the omohyoid. So here also we can see a change in angulation. And this change in angulation is because of a facial sling which part of which we have retained here which attaches the intermediate tendon to the clavicle. This facial sling also is derived from the pre tracheal layer of deep cervical fascia. The superior belly gets attached to the hyoid bone. That's why it's called omohyoid. The next one that we can see here is this muscle that we have gifted up on the right side and the corresponding muscle on the left side. This is the sternohyoid. Because it takes attachment from the inner surface of the manupreum sterni. Upper attachment is to the hyoid bone. And deep to the sternohyoid once we reflect the sternohyoid on this side and the reflect the sternohyoid on this side we can see yet one more muscle here and one muscle above. The deeper muscle the lower one is the sternohyoid. It also takes attachment from the inner surface of the manupreum sterni and it spreads out and gets attached to an oblique line on the thyroid cartilage. That's the sternohyoid. Again starting from the oblique line of the thyroid cartilage there's a muscle which goes up like this. We can see it here and we can see it partly on this side also. That is ending at the hyoid bone. This is the thyrohyoid. So again we have four intrahyoid strap muscles. Now let's come to the actions and the uses of these muscles. The intrahyoid strap muscles because they are located below the hyoid bone their function is to depress the hyoid bone or stabilize and fix the hyoid bone so that the suprahyoid muscles can act better. So that brings me to the action of the suprahyoid muscles. When the intrahyoid muscles have fixed the hyoid bone or depressed it then the suprahyoid muscles act to depress the mandible. So therefore they can act as accessory muscles of mastication. And in this action they are assisted by the datisma which also does the same thing it depresses the mandible. The other action of the suprahyoid muscle is when the hyoid bone is not fixed by the intrahyoid muscles it elevates the hyoid bone and that comes to play during the second phase or the oropharyngeal phase of deglutation. When the hyoid bone is elevated and the pharynx becomes short and wide to receive the bolus of food. So these are the two actions of the suprahyoid group of muscles. Now let's come to the nerve supply. The nerve supply is quite varied. Most of these strap muscles are supplied by one set of nerves which are referred to as the anus cervicalis. Anus cervicalis is actually derived from the motor component of the cervical plexus. This is the cervical plexus but this is the sensory component. There are secondary loops which run anteriorly. There is one from the loop of C1, C2 which runs along with the hypoglossal nerve and there is another separate route coming from C2 and C3 which unites with the loop from the hypoglossal and they form what is known as the anus cervicalis. Upper limb of the anus cervicalis is also referred to as the descending hypoglossi and the lower limb which comes out from C2 and C3 is also referred to as descending cervicalis. So this whole loop of anus cervicalis was not very clearly visible in this category and little bit of that is visible here. They supply the following muscles. The superior limb of anus cervicalis which comes with the hypoglossal nerve that supplies the geniohyoid which is deep to the mylohyoid and the thyrohyoid which extends from the thyroid cartilage to the hyoid bone. So these two. The rest of the infrahyoid strap muscles omohyoid, sternohyoid, sternothyroid they are all supplied by the rest of the anus cervicalis. That brings me to the nerve supply of the suprahyoid strap muscles. The posterior belly of the digastric and the stylohyoid muscle they are supplied by branches of the fascia nerve. The anterior belly of the digastric and the mylohyoid are supplied by the branches of the mandibular nerve which is C5B3. Coming to clinical and functional aspects about these strap muscles. All these strap muscles they were enclosed in a layer of cervical lymph fascia which is referred to as pre-tracheal fascia. The pre-tracheal fascia has got two subcomponents. One portion of the pre-tracheal fascia covered the visceral organs and specifically the thyroid and the parathyroid that is referred to as the visceral part of pre-tracheal fascia. While there is another component of the pre-tracheal fascia little bit of which we have retained here that is referred to as the muscular component of the pre-tracheal fascia and we can see on this side this white portion here. This muscular component of the pre-tracheal fascia which completely encircles all these strap muscles and they also form the facial slings of the digastric and the facial sling of the omohiod, which attaches these muscles respectively to the hyoid bone and to the clavicle. Because these muscles are attached to the inner surface of the manabrium, if there is any infection in relation to the muscular component of the pre-tracheal fascia, the infection cannot travel to the chest and to the media center. However, if there is any infection in relation to or anterior to the visceral component of the pre-tracheal fascia, then the infection can travel where my finger is gone in and it can go into the anterior and to the superior mediasthenum. The same pre-tracheal fascia posteriorly it goes up and it becomes known as the buccofaryngeal fascia, which is the fascia of the pharynx and any infection behind that can also travel via the retro pharyngeal space into the posterior mediasthenum. That is one clinical functional aspect about the facial sheet of these muscles. The nerve supply, especially the ancestral vicaris which I mentioned, the nerve supply to these muscles they all come from below and then they supply the muscles. So therefore, if it is any time necessary to cut these muscles, like for example during thyroid surgery, we should not cut these muscles low down, we should cut them as high as possible and reflate them down because cutting them low down will jeopardize the nerve supply to the rest of the muscle. So that is another clinical functional aspect about these strap muscles. And the third important point about these strap muscles is that these strap muscles, they all form boundaries of various triangles. Anatomical triangles have been created for the ease of understanding of the various structures. Thank you very much for watching. 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.