 This is a demonstration of the muscles of the back. Before I start, first things first, take a look at the skin of the back. The skin of the back is very thick, and the subcutaneous tissue is firmly adhering to the skin. And under then, there's a thick layer of fat. The skin of the back is quite different from the skin in other regions. After we have reflected the skin, we see the muscles of the back, and we shall classify the muscles of the back into two broad groups. The extrinsic back muscles and the intrinsic back muscles. The extrinsic back muscles are not the true back muscles, and that's the one which we can see here first. Take a look at this muscle that we see in front of us. This is one muscle on one side. There will be a similar muscle on the other side, and this muscle is the trapezius muscle. The trapezius muscle is one of the extrinsic back muscles. It does not act on the back. It acts on the pectoral girdle. It is called the trapezius, because when both the sides are combined together, they'll form a trapezium. That's why it's called trapezius. The next muscle that we can see here is this big muscle. This is the latsomus dorsi. This is also extrinsic back muscle. It is not a true back muscle. This also acts on the upper lip. Now let's cut the trapezius and reflect it up, and we have cut it here, and we are reflecting the trapezius up. Once we reflect the trapezius up like this, we see yet another layer of muscles under the trapezius. This muscle that we see here, this is the rhomboids major. Just about that we have another muscle. This is the rhomboids minor. And further up we have the third muscle. This is the libator scapulae. These three are also the extrinsic back muscles. They are not true back muscles. They act on the pectoral girdle. Now we shall reflect the rhomboids major, and we have cut it, and we are reflecting the rhomboids major, and we are retracting the rhomboids minor to show you yet one more muscle underneath. And that is this muscle here. This is the cirrhosis posterior superior. This is also an extrinsic back muscle. This does not act on the pectoral girdle, but it is an accessory muscle of respiration. This is the cirrhosis posterior superior. Now we shall do the same thing with the latsomus dorsi. We have cut it here, and latsomus dorsi also takes partial origin from the outer layer of the thoracolumbar fascia. So we have split the thoracolumbar fascia here, and we have cut the latsomus dorsi here, and we are reflecting it. And once we reflect it, we see yet one more muscle under the latsomus dorsi. And we can see that the direction of fibers are opposite to that the cirrhosis posterior superior. Cirrhosis posterior superior fibers were running like this. These fibers are running like this. This is the cirrhosis posterior inferior. This is also an accessory muscle of respiration. So all these muscles are the extrinsic back muscles. They are not the true muscles of the back. Now we will reflect this. As I mentioned earlier, we have already split the posterior layer of the thoracolumbar fascia, all along its length, right from here up. After we have split the outermost layer of the thoracolumbar fascia, as you can see here, now we have exposed the true or the intrinsic back muscles. The intrinsic back muscles are so-called, are called intrinsic back muscles because of a few special features which they possess. Number one, they are all supplied by the dorsal ramia of spinal nerves. Number two, they are located between the outer layer of the thoracolumbar fascia and the middle layer of the thoracolumbar fascia. And the third point is they act specifically on the vertebral column, and that's why they're... In this particular case, the muscles that we see in front of us, this is the intermediate layer of the intrinsic back muscles. And they are also called the erector spinae muscle or the sacrospinalis muscle. This has been classified into three subgroups, going from lateral to medial. Let's pick up the first subgroup, which I have lifted up here. This is the iliocostalis. And we can see it is starting from a thick, strong tendon at the back, and this is the tendon which we can feel on our back, on either side of the vertebral column, in any normal person. This starts from the ilium, and partly from the sacrum, and goes all the way up, and it gets attached by means of multiple slips to the ribs. Therefore, this is called iliocostalis. And depending on the region, it can be called iliocostalis lumborum, iliocostalis thoracis, iliocostalis services. Going next medially, we have the next muscle, and that is this one which I have lifted up here. This is the longest muscle. This also has a common origin as the iliocostalis, from the ilium and the sacrum, and it goes straight up all the way. Of course, it does have a few slips attaching to the ribs, but most of the muscle goes straight up, and I have lifted that muscle up here. And it goes continues up, and it gets ends at the occipital bone in the region of the buccal line. So, this is the longismus. This also, depending on the region, is divided into longismus thoracis and capitis. Going further medially, we have the third subgroup, and we can see those muscles here. This is the spinalis muscle. Spinalis muscle is relatively small, and it is situated right next to the vertebral column. And this also, depending on the location, can be either spinalis thoracis or spinalis services. So, this is the intermediate group. There is a group deep to this, which is collectively called the transversal spinalis, but that is clinically not so important. The importance lies in these three groups of this subgroup of muscles, namely the iliocostalis, longismus, and spinalis. They are the type one. Red muscle, posterior muscle, anti-gravity muscle. They are fatigue resistance, they are slow twitch, and they are the ones which are responsible for us maintaining our erect postures. There is yet one more group of muscle, which is very small, and which is called the superficial group of intrinsic back muscle, and that can be seen if we look very closely here. Now I'm focusing on the superficial group of intrinsic back muscles. There are two very small muscles which are located superficial to the erector spine, and they are collectively called the spleenus services and spleenus capitis. Spleenus means in Greek bandage. So it's a thin, flat muscle, almost like a bandage, and the muscle that we see here, which is located just under the cilidus posterior superior. This is the spleenus services. Spleenus services, and further higher up, will be the spleenus capitis. So this is the superficial group of intrinsic back muscles. So these are the three groups of muscles which are located in the back, which are the intrinsic back muscles. 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.