 of the back. Oh, by the way, my name is Dr. Sanjay Sanyal. I'm the professor and department chair of the anatomical sciences. And my camera persons are Jenae, Saha, and Zelika. And I'm surrounded by all the MD1 anatomy students, and they're reading from year to year, and they're wrinkling their noses because of the formalism smell. Okay. So let's start off. What do you see here? We have the section out the left side of the back of the cadaver. The muscles of the back are divided into two broad groups, as you know already. The first group is the extrinsic muscles, which are not the true muscles of the back. So let's take a quick look at the extrinsic muscle. Straight away, we can see this muscle here, this triangular shaped muscle, this one. This is the trapezius muscle. It is not a true muscle of the back, that's why we call it the extrinsic muscle. And the reason why it's called trapezius is because when you connect both the sides together, then they form like a trapezius. That's why it is called the trapezius. Here, we are seeing only one side of it. This is one extrinsic muscle. I'm going to reflect this a little later. The next extrinsic muscle that you see here is this muscle here that you see here. And this is the latissimus dorsi. This is the other extrinsic muscle. Both these muscles are technically situated on the back, but they are not concerned with movements of the back. They are muscles which control the pectoral girdle, and therefore they are all supplied by other nerves, other dorsograms, the spinal nerves, and we shall deal with them in more detail when we come to the back. Now what we shall do, we shall reflect. We have cut the medial attachment of the trapezius only, and I'm reflecting the trapezius up. So I've left side trapezius up, and when we do that, what do we see? Let's take a good look. Under the trapezius, we see these muscles here. The uppermost muscle is the levator scapulae. That is also a muscle which controls the pectoral girdle. This is the levator muscle, the levator scapulae. Then we have this one here. This is the rhomboids minor, and then we have this muscle here, which is the rhomboids major. Just to bring up the speed, what you see here, this is the medial border of the scapulae. And so therefore the levator scapulae, the rhomboids minor, the rhomboids major are all attached to the medial border of the scapulae. And if you dig your finger deep inside, my finger is going and getting attached to the inferior border of the scapulae. Okay, so these three muscles that we mentioned just now, they are also extrinsic muscles of the back, situated under the trapezius. They are referred to as the extrinsic intermediate muscles. They are also not concerned with movements of the back, they are concerned with movements of the pectoral girdle. So leave it scapulae. And under these, the rhomboids, rhomboids minor and rhomboids major, we see a few small muscle slip, which has been partially mashed out here. And that is the serratus posterior superior, the serratus posterior superior. The serratus posterior superior is also not a muscle, true muscle of the back. It is a proprioceptive muscle which is concerned with respiration and it is supplied with the posterior intercostal nerves and we shall talk about them when we come to the thoracic region. Before I reflect back this specimen, I would like you to notice something which I shall mention any way later on. See this small vessel here. This is a dorsal scapular artery and a dorsal scapular vein which runs on the inner surface of the trapezius and that is an important supply of the trapezius. So this is one extrinsic muscle of the back. Okay, now let me keep this reflected away. Let me show you the next extrinsic muscle of the back. We see this big strong muscle here, which has been partially illustrated here but we shall put it back in its place. This muscle that you see here, this is the latsimus dorsi. The latsimus dorsi, this is the latsimus dorsi. As we all know, the latsimus dorsi takes partial origin from the posterior layer of the thoracolumbar fascia and that is what you see here but I'm going to show it in more detail just a little later. It also got numerous other attachments but that is not the concern at this moment and this latsimus dorsi is the next big muscle which is also a muscle extrinsic muscle of the back. Okay, and under the latsimus dorsi which I have not dissected now because I'm keeping it for the upper limb dissection will be the cirrhosis posterior, the counterpart of the cirrhosis posterior superior will be the cirrhosis posterior inferior which will be located under the latsimus dorsi. Okay, so these are the extrinsic muscles of the back. Now let's come to the muscles of the back proper or the so-called intrinsic back muscles or the IBM. Let's bring you up to speed. What do you see here? This is the posterior layer of the thoracolumbar fascia. The true muscles of the back are situated between the posterior layer of the thoracolumbar fascia which you can see here and the middle layer of the thoracolumbar fascia which obviously you cannot see. So therefore in order to see the back muscles we have to slit open the posterior layer of the thoracolumbar fascia which I had mentioned gives partial origin to the latsimus dorsi. So let's, I've already slit open the posterior layer and let me just reflect it. So I have cut open and I'm reflecting the posterior layer of the thoracolumbar fascia. This is one leaf, this is another leaf. This is one leaf and this is another leaf. And this, so this is another leaf. So I have completely reflected the posterior layer of the thoracolumbar fascia on this side and the posterior layer of the thoracolumbar fascia on this side. And now let's see what we notice. What do you see here? This bulk of the muscle here and which you can all see in your own body. If you stand with a mirror holding against your back and a mirror standing in front of a mirror and hold a mirror against your back you see a thick richer muscle on either side of the vertebral column. This by the way is the vertebral column. And this is called the erector spinae muscle also referred to as the sacro spinalis muscle. This is the first layer of the back muscles. That is what we are seeing here. After we have reflected out, yes, good. Please hold one layer. And once we have reflected the posterior of the thoracolumbar fascia, we can see three muscles which together constitute the erector spinae. The first one is this which I'm holding up. This is attached below to the iliac bone and above it is attached to the ribs. Therefore this is the iliocostalis. The muscle which is just medial to the iliocostalis is the longasmus. And finally the muscle way up in the top and medial is the spinalis. So the iliocostalis, longasmus, spinalis. These three together constitute the intermediate group of back muscles. Why did I call this intermediate? Because there is a superficial group of the true back muscles which are very small and which are located way up on the top which is respectively referred to as the spleenus capitis and the spleenus services. But they are very small and they are located under this. So therefore we cannot see them. That's why I'm not showing them. I'm showing you the most important. Let's say a few quick words about the sacrosfinalis or the erector spinae muscle. These are the most powerful. These are red muscles. These are posterior muscles. They are constantly under tonic contraction and they are the ones which are responsible for us maintaining an erect posture. They maintain their tone by means of the vestibular spinal tract which I have not told you but you learn about it in neuroscience and they also get their tonic contraction. They also get supply from the lateral reticulose spinal tract which are all responsible for extensor muscle tone. The reason why is because a human being during their erect posture, the center of gravity passes in such a way that the bulk of the body is anterior to the line of center of gravity. So therefore there is a tendency for the human body to fall forward. In order to prevent us from doing so, these posterior back muscles, especially the erector spinae muscle which is always in a state of tonic contraction, it helps us to maintain an erect posture and ensures that the center of gravity stands right between our two feet. So these are the posterior, the back muscles and this is the posterior layer of the thoracolumbar fascia and this is what I wanted to show you. What is not visible and which is really not so important anatomically, which is not so important clinically is that if we were to reflect out these intermediate layer of back muscles, the strong, the erector spinae muscle, we would see a group of very small muscles which are the deep intrinsic back muscles which are collectively referred to as the transversal spinalis muscles, but that is clinically not so important and therefore we are not showing that. So that's all for now for the dissection of the back, the muscles of the back. Let me put back the muscles in the normal place and let me restore the anatomy as it was in earlier stage. Thank you very much, ladies and gentlemen for watching. Dr. Sanjay Sanyam standing out. If you have any questions or comments, please put them in the comment section below. Thank you, Jini. Thank you, Zeria. And thank you, Saheha. Have a nice day.