 continuation of the dissection of the posterior chest wall. This time is going to be more of the clinical functional aspects. So let's focus on these joints that we see here. These are the known as the costopransfer's joints. This is where the tubercle of the rib articulates with the transverse processes and that's what constitutes the costopransfer's articulation. And what you cannot see here are the costo-vertibular articulation where head of the rib articulates with the vertebral body because that is deep inside. So let's focus on the costopransfer's articulations. We have two different types of movements taking place at the costopransfer's articulations. The upper ribs from rib one to rib eight, they undergo what is known as the pump handle movement. They rotate on the costopransfer's articulation around an axis which goes through the head and the neck of the rib like this and they rotate. And this movement is called the pump handle movement and this increases the anterior posterior diameter of the chest. The lower ribs eight, ninth and tenth, they undergo what is known as the bucket handle movement. They do not rotate, they slide on the costopransfer's articulation and they produce what is known as the bucket handle movement and that increases the transverse diameter of the chest wall. So these are the two different types of movements which take place at the costopransfer's articulations. Now let you mention these muscles that we can see here. These are the external intercostal muscles and we can see the rational fibers are like this. External intercostal muscles are responsible for elevation of the ribs. In this place we have split the external intercostal to show the internal intercostal. And we can see if you look very carefully the rational fibers are exactly at right angles to the external intercostal. The internal intercostal, the inter-ocious part is responsible for depression of the ribs. It is an interconded part of the internal intercostal which is visible anteriorly but it is not visible posteriorly so we shall not talk about that. Now let's focus on the functions of these accessory muscles of respiration. This muscle that I picked up here, this is the serratus posterior superior. And below we have this muscle here, this is the serratus posterior inferior. The serratus posterior superior is responsible for elevation of the ribs and the serratus posterior inferior is responsible for depression of the ribs. Apart from that both these muscles have got proprioceptive function. So these are accessory muscles of respiration. Accessory muscles of respiration by definition are those which come into play only during forced respiration. Another accessory muscle of respiration that we see are these muscles here. These are the libatoris costorum. They come from the crassus process of the vertebra above and they get attached to the rib below and we can see one here we can see another one we can see. These are the libatoris costorum. They are responsible for elevation of the ribs. The libatoris costorum is unique in so far that it is an accessory muscle of respiration. At the same time it is also an intrinsic muscle of the back. So therefore it is supplied by the dorsal ramai of the spinal nerve and we can see a dorsal ramai of the spinal nerve here. I've lifted up one here. This dorsal ramai of spinal nerve emerges through a triangular space bounded by the libatoris costorum by the inter-transverse ligament which stretches from one transverse process to the next and the lateral costotransverse ligament. This is another dorsal ramai coming between the same triangular space and this is the third dorsal ramai. So these dorsal ramai are the ones which supply the deep muscles of the back and it also supplies the libatoris costorum. In contrast these two accessory muscles, serratus posterior superior and serratus posterior inferior, they are supplied by the intercostal nerves which I shall show you shortly. There's another muscle which I wanted to show you which is strictly speaking not part of the posterior chest wall but it also has a role to play. This muscle that we see here, this is the quadratus lumborum. The quadratus lumborum takes origin from the iliac crest and it goes up and gives multiple slips to the lumbar vertebrae transverse processes and it gets attached to the twelfth rib and the twelfth rib is here. By virtue of its attachment to the twelfth rib it also places an accessory muscle of respiration apart from acting on the lumbar vertebrae. It fixes the twelfth rib to allow the diaphragm to move the chest wall during inspiration. It also assists the chest during forced expiration. Therefore this is also an accessory muscle of respiration. The next thing which I wanted to show you is the intercostal neurobascular structure and for that we have split open the external intercostal and the internal intercostal because the neurobascular structure is run between the internal intercostal and the innermost intercostal. The innermost intercostal actually is a composite muscle. It's composed of muscles in relation to the costal angle which are known as the subcostal muscles that and they continue as the innermost intercostal. So we can see the neurobascular structures running here and I have picked it up here. This is the intercostal nerve and this is the posterior intercostal artery and vein and we know the relationship going from above downwards is vein artery nerve. The vein and artery are together and this is the nerve. We can see them more clearly on the posterior view and as they go anteriorly they become smaller and thinner therefore we cannot see them and they typically run in this place where my finger is tracing and that is known as the costal groove. So these intercostal nerves are the ones which supply the all the intercostal muscles. The lower six intercostal nerves also supply the diaphragm. Now let's come to some clinical aspects. When we have fracture of the ribs the weakest part of the rib to fracture is what is known as the posterior lateral bend that is where the rib bend makes a bend from the posterior to the anterior. That is the weakest part of the rib and when there is a compression injury of the chest like for example in the steering wheel the posterior lateral bend is the place which is likely to fracture by indirect compression or it can also fracture at the site of direct trauma but fourth and the ninth ribs are the ones which are most likely to fracture. The first rib is rarely fractured and if it does fracture it usually fractures at the site where the subclavian artery is crossing. When there is a rib fracture apart from possible injury to the lung hemothorax, pneumothorax, antilectasis etc we also have to keep in mind injury to the intercostal vessels which can produce profuse bleeding and in my clinical practice I have seen profuse bleeding coming from here and it can also be potentially life-threatening in which case we may have to do thoracotomy and ligate the bleeding point. That is all for now regarding the clinical functional aspects of the posterior chest wall. 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. Have a nice day.