 Let's start from the first layer that we see here. You can see this white structure here This is the outermost layer of the thoracolumbar fascia And I told you the thoracolumbar fascia is a tough fascia Which closes the intrinsic back muscles So the intrinsic back muscles are enclosed in the outer layer and The middle layer so we have split open the outer layer Just to show you the thoracolumbar fascia, but we are going to come back to the thoracolumbar fascia a little later Let me just point out to you the muscles which we are visible right now. Just get out You can see this triangular shape muscle here. This is half a triangle If we were to open up that side also, we will see another half of a triangle So the two together constitutes a muscle like a trapezius That's why this muscle is called the trapezius The trapezius has got three sets of fibers a descending set of fiber a horizontal set of fiber and ascending set of fibers and you can see that I sure fibers But we shall talk more about the trapezius when we come to the upper level because it's a muscle acting on the pectin And it's a unique muscle in the sense that it is not supplied by the brachial plexus also trapezius is supplied by Cradle num number 11 that is accessor So now let me I have already split open the trapezius at its attachment to the spinous processes here Let me just reflect the trapezius So this is the one of the large muscles of the extrinsic group of back muscles, which I said is the not the true muscles Okay, so now I have reflected the trapezius now Let's come to the next big muscle which is also not the true back muscle and that is this one which has been split here This is the latzimus dorsi It is really a big and a very powerful muscle and it is going all the way and it gets attached to the arm But we have cut it here The unique thing about this latzimus dorsi is that it's got an extensive origin It takes origin from the iliac Christian and takes quite a big of bit of origin from the outermost layer of the Thoracolumbar fascia and you can see it is actually taking origin from the thoracolumbar fascia You can see it here and then it continues So what we are going to talk again about the latzimus dorsi when we come to the pectoral girdle upper limb again Now that I've reflected the trapezius and I've shown you the latzimus dorsi Which are the two extrinsic back muscles which I told you were not the true then let's come to the next We can see a muscle here This muscle that you see this is the levator scapulae This muscle that you see next This is the rhomboids minor and the next muscle that you see this one is the rhomboids major So levator scapulae rhomboids minor rhomboids major They are all inserted on to the medial border of the scapulae here. This is the scapulae And again, we will see the these three muscles. They are also extrinsic back muscles, but they're the intermediate group and they Do not act on the back. They are part of the pectoral girdle muscles Now I'm going to reflect the rhomboids major rhomboids minor Incidentally, I have exposed the neurovascular bundle which runs deep to the attachment of the Levator scapulae and the rhomboids minor But we shall talk more about the neurovascular structures when we come to these respective muscles later on We see yet one more layer of muscle and I'm lifting it up now here What is this muscle any cases? This is the serratus posterior superior This was also an extrinsic back muscle, not the true back muscle And this I told you is an accessory muscle of respiration and the serratus posterior superior and you can see the fibers are running like this They are supplied by the intercostal nerves and they are accessory muscles of respiration and this is that muscle here I'm lifting it up here and all of you can see much more clearly here This is located deep to the rhomboids So I have to reflect the rhomboids to show you this So your question is where is the serratus posterior inferior? The serratus posterior inferior is located deep to the latsomus dorsi And for that you have cut it here and we can see a muscle underneath this muscle here I have cut the latsomus dorsi from here also so that we can see this muscle that is running down like this These are some of the fibers These are the fibers of the serratus posterior inferior This is also an accessory muscle of respiration There's also an extrinsic back muscle It is not a true back muscle and it is also supplies supplied by the intercostal nerves So to summarize quickly we have seen the Trapezius we have seen the latsomus dorsi We have seen the elevator scapulae rhomboids minor rhomboids major and then we have seen the Intermediate group of extrinsic back muscles namely the serratus posterior superior and the serratus posterior inferior now let's come to the True back muscles or the deep or the intrinsic back muscles and our definition was that they are acting directly on the back They are enclosed by the two layers of thoracolumbar fascia One was the Outermost layer and that is the middle layer and they are supplied by the dorsal drama So now let's come back again to our thoracolumbar fascia We have split open the outer layer of the thoracolumbar fascia and you can see how thick and strong it is This is the outer layer of the thoracolumbar fascia So I'm going to I'll need somebody here to reflect for me those of you who are wearing gloves can do that for me and As I told you attaching taking origin from the outermost layer of the thoracolumbar fascia was the Latissimus dorsi and you can see taking origin from there So we will reflect the other part of it also So with that I have reflected the Latissimus dorsi now we are seeing the This tough strong muscle which I made all of you feel and what name did we give it? We call it erector spinae or the sacrospinalis muscle the true intrinsic back muscles the most strong Muscles the posture muscle which helps to maintain your erect posture This muscle which I'm lifting up What is this? This is the erector spinae part of it and what was the lateral most muscle of the erector spinae group? Elio costalis it is taking origin from the Iliac bone here and It as it goes up it giving slips of fibers, which you can see are getting attached to the ribs here That's why it's called illiocostalis and Depending on where it is attached it is called illiocostalis lumborum illiocostalis thoracis But we will not bother about the individual subcomponents of them So this is the lateral most group and this is the one which is giving you the bulk of your erected spinae Going further medially. What was the next group? The next group was this muscle here The longest must which goes all the way up to the To the occipital bone. That's why we called it the longest must that was the next middle one so after the illiocostalis we have the Longest must and I have gained split open this Facial structure to show you that Longest must so the medial most is the Not the medial most the second and then finally the smallest of this group the medial most group was the Spinalis which is right next to the spinous processes to see that I Have split open these Eponeurotic tendinous structures and we can see the small muscle fibers here. We can see this muscle fibers here these are the Spinalis muscle and you can see can you hold it here for me? These are the spinalis muscle fibers So illiocostalis Longest must Spinalis These are the true posture muscles Airtid spine and if we remove this we will see the next group That is the transversals finalists Why are they called transversals finalists because they are located in the angle between the Transverse process and the spinous process and we had seen that they are also divided into three groups the semi-spinalists Multi-fitters and rotators, but they are not so clinically important as this group So we have shown you the intermediate group of the intrinsic back muscles and not shown you but I told you about the deep group of Intrinsic back muscles, but one small group still remains the superficial group of intrinsic back muscles. Remember bandage Spineus capitis and spinaeus services and you saw how they were distributed Let's come to the spinaeus group here This muscle that you see here This is the spinaeus The spinaeus services is the lower one and the upper fibers are the spinaeus capitis So if you were to take this side and you will take the side they will be like this and they will be oriented like this So this is the superficial group of the intrinsic back muscles the spinaeus capitis and the spinaeus services And once we reflect the spinaeus capitis and the spinaeus services We can see the next group which I have already described to you and we can see the fibers of the longism is going up We can see the fibers of the long distance going up and my finger is going in that is where it gets attached to the oxidable So we have seen the three layers. We have seen this previous capitis in the services We have seen this erector spinae group and we have mentioned about the transfer source finalists So these are the muscles of the intrinsic group and the extrinsic group that I wanted to show you That's all for now. Thank you very much for watching. Ladies and gentlemen if you have any questions or comments Please put them in the comment section below. Dr. Sanjay Sanyal signing out