 Good day, everybody. This is Dr. Sanjay Asaniya, Professor, Department Chair. This is going to be a demonstration of the lateral cervical region. It's also called the posterior triangle of the neck. This is a supine cadaver. We are showing the right side. We are narrating from the right side. So first, let's take a look at the boundaries of the lateral cervical region. This is the posterior boundary. It is formed by the disening fibers of the trapezius. The disening fibers, as you know, they take origin from the medial part of the superior nuclei and the fibers, they descend down. And we can see the fibers coming down here. And they get inserted onto the chromium process and the clavicle here. This is the posterior boundary. Coming to the anterior boundary, we have this muscle here. This is the sternocleidomastoid, which takes origin by means of two heads. The sternal head takes origin from the mammogram sterni and the clavicular head, which has been removed here because it was destroyed during the process of embalming, takes origin from the clavicle and the two, then go up like this. And they get inserted onto the mastoid process and to the lateral half of the superior nuclei. So this is the medial anterior boundary of the lateral cervical region. The base of the lateral cervical region is this portion here, the middle one third of the clavicle. So this is the whole lateral cervical region, also called the posterior triangle of the neck. The apex of the triangle is where the trapezius meets with the insertion of the sternocleidomastoid. Coming to the roof, the roof was bridged over by one of the layers of deep fascia of the neck. The deep cervical fascia, that is called the investing layer of the deep cervical fascia. The investing layer of deep cervical fascia, it splits to enclose the trapezius. Then it bridges over like this and then again it splits to enclose the sternocleidomastoid. So therefore the roof was formed by the investing layer of deep cervical fascia. Coming to the floor, the floor was covered by yet another layer of deep cervical fascia and that is called the pre-vertebral layer of deep cervical fascia. It was covering these muscles. Once we removed it, what are the muscles that we see in the floor? First of all we see this muscle here. This is the splenius capitis. The next muscle that we see here is this one. This is the levator scapulae. The third muscle that we see is this one. This is the scaliness posterior. The fourth muscle that we see is this one here. This is the scaliness medius. And finally we see a little bit of another muscle here. This is the scaliness anterior. So these are the muscles which form the floor of the lateral cervical region. That brings me to one important point in the floor itself. Now if you look closely, between the scaliness medius muscle and the scaliness anterior muscle, there is a triangular space here. This triangular space is called the scalene triangle because the scaliness medius and the scaliness anterior, both of them get inserted onto the surface of the first rib, which is behind the clavicle. So therefore there is a small triangular space and that is called the scalene triangle. This scalene triangle is clinically very important because passing through the scalene triangle are these structures. Number one, we can see these are the trunks of the brachial plexus. These can get entrapped in the scalene triangle producing what is known as scalene syndrome. Also passing through the scalene triangle is this artery here. I'm going to trace the artery from the axilla. This is the axillary artery. Once the axillary artery crosses the first rib, it becomes known as the subclavian artery. This is the third part of the subclavian artery which is also passing through the scalene triangle. This can also get entrapped in the scalene triangle as part of the scalene syndrome which is a part of a bigger syndrome called the costoclavicular syndrome. So all these things are happening in the floor of the lateral cervical region. Now let's take a look at the contents of the lateral cervical region. First of all, if you look, I have lifted up this bundle of nerves here. These bundle of nerves is actually the cervical plexus. Most specifically the cutaneous branches of the cervical plexus. We have purposely not separated them out because I want to show an important clinical correlation here. You notice that most of these nerves are coming out from here behind the posterior border of the sternocleomastoid. Here we have got four nerves. Great auricular, lesser occipital, transverse cervical and supraclavicular. So all these, they come out approximately in this region of the posterior border of the sternocleomastoid. And this region is referred to as the nerve point of the neck. Means that if we give a nerve block here, we will anesthetize a huge portion of the neck and the front of the chest in this region here. That's why this is called the nerve point of the neck. One way of determining the nerve point of the neck, I've already told you, it is the posterior border of the sternocleomastoid, the midpoint. Another way of determining the nerve point is if you feel the mastoid process here and if you drop a vertical line to the middle of the cervical, the midpoint of that line is also approximately the nerve point of the neck. Okay. The next structure that we see is this nerve here. This is the spinal accessory nerve, CN11. The CN11, it comes from the neck. And we can see the proximal part of the CN11 here. It comes out through the jugular ferramen. It crosses in front of the internal jugular vein. Then it goes under the sternocleomastoid. It supplies the sternocleomastoid and then it emerges from behind to the sternocleomastoid. And then it runs on the surface of the levator scapulae muscle. And then it disappears under the trapezius muscle and it supplies the trapezius muscle. So therefore this is the CN11. CN11 is the nerve supply of both these muscles, sternocleomastoid and trapezius. That's why when we have troticolus, spasmodic troticolus, we have spasm of both sternocleomastoid and trapezius. This CN11 has communications from C2-3 of the cervical plexus, which are proprioceptive to this trapezius. This CN11, it can get injured in surgery of the lateral cervical region, like for example removing cervical lymph nodes, secondary deposits. It can also injure in stab injury or conch shot injury, in which case there will be paralysis of the trapezius muscle. So this is the spinal accessory nerve. That's the next content. Now let's take a look at this structure here. This is the inferior belly of the omohiad muscle. This takes origin from the supirebord of the scapula and it goes across like this. And it is attached by means of patient's sling to the clavicle ear, which we have removed and then it goes under the sternocleomastoid and the supirebelly goes in the anterior triangle of the neck. This inferior belly of the omohiad divides the lateral cervical region into two parts and we can see one part here and another part above. The lower portion is called the subclavian triangle. It's also called the omoclavicular triangle because one border is formed by the omohiad or the other border is formed by the clavicle. This also called the subclavian triangle because the third part of the subclavian artery is located here. And this larger portion of the lateral cervical region is called the occipital triangle because at the apex of this lateral cervical region will pass the occipital artery, which is a branch of the external carotid artery and will supply the scapula. The next structure which I will draw your attention to, it is not very clearly demonstrated in this particular cadaver is this one here. This is the remnant of the external jugular vein. In this particular cadaver the external jugular vein was very small as you can see here. It is formed by the union of the posterior particular vein and the posterior division of the retromannabular vein. This is the parotid gland. But in this cadaver all those classical anatomical description does not apply. So this is the remnant of the external jugular vein. This runs on the surface of the sternocleidomastoid and then it pierces the investing layer of the deep cervical fascia and then it opens into the subclavian vein. So this is another content of the lateral cervical region. The next structure which I will draw your attention to is this nerve here. This is the phrenic nerve. The phrenic nerve is also a branch of the cervical plexus. But unlike the other branches, this is a mixed nerve. C345. This runs on the surface of the scalyneus anterior muscle and this is the scalyneus anterior muscle as I told you earlier. And it runs like this. It goes behind the subclavian vein. This is the axillary vein which comes continuous as the subclavian vein. It runs behind the subclavian vein and then it enters into the thorax. It supplies the fibrospericardium and it goes and supplies the diaphragm. So this is the phrenic nerve. This phrenic nerve may sometimes have an axillary phrenic nerve which comes from the nerve to the subclavius. This is the subclavius muscle. And that axillary phrenic nerve goes in front of the subclavian vein and it can entrap the subclavian vein between the main phrenic nerve and the axillary phrenic nerve. But that is not a very common problem. So that's another structure which I wanted to draw your attention to. So these are the points which I wanted to show you in the lateral cervical region. The boundaries, the roof, the floor, the clinical correlations and the contents of the lateral cervical region. Thank you very much for watching. Dr. Sanjay Sanyal signing off. Mr. Ken Dahlkambar batch is the camera person. If you have any questions or comments, please put them in the comment section below. Have a nice day. Please like and subscribe.