 So let's trace the first terminal branch of the posterior cord, and that is this one here, which I have lifted up. This is axillary nerve. Axillary nerve goes naturally. It goes through the quadrangular space. And we can see that it is accompanied by these vascular structures here. This is the posterior circumflexed humeral artery and the posterior circumflexed humeral vein coming from the axillary artery. So this axillary nerve points around the surgical neck of the humerus. It goes through the quadrangular space. So what is the boundary of the quadrangular space? Inferiorly, it is bounded by the T.D.'s minor, the head of the humerus, and it's bounded by the subscapularis. Inferiorly, it is bounded by the T.D.'s major. Laterally, it is bounded by the surgical neck of humerus. And medially, it is bounded by the long head of the triceps. Quadrangular space is the one which gives passage to this axillary nerve, the posterior circumflexed humeral artery, and the posterior circumflexed humeral vein, and we can see that here. Here, the axillary nerve can be injured in two different ways. If there is a fracture of the surgical neck of humerus, then the axillary nerve can be injured. And if there is an inferior dislocation of the shoulder joint, then also the axillary nerve can be injured. This is an x-ray of the right shoulder to fracture the surgical neck of humerus in a patient. Injured to the axillary nerve will produce the maximum disability in terms of paralysis of the deltoid muscle. The deltoid is supplied from the inner aspect by the axillary nerve here. We can see that here. And that will lead to inability to abduct the shoulder above 15 degrees. It will also lead to paralysis of the T.D.'s minor, but that is not of much clinical significance. And additionally, there will be a loss of sensation in the upper lateral aspect of the arm, because the axillary nerve also supplies the arm. So that is about the axillary nerve which is arising from the posterior cord of the brachial plexus, the first terminal branch, and we can see that here. Now we are going to demonstrate the radial nerve which is the second larger terminal branch of the posterior cord of the brachial plexus in the same cadabra. This is the radial nerve. This is the largest branch of the posterior cord, and it goes behind, and we can see it is disappearing again somewhere here. This is the radial nerve, and we can see it is accompanied by these vascular structures. These are the profunda brachiae artery in the profunda brachiae vein, which come from respectively from the brachial artery and the venae comitantes of the brachial vein. Actually, we can see them from behind more clearly, and that region is referred to as the triangular interval. They do not pass through the triangular interval, but they pass in relation to the triangular interval. That's why it is called interval. This triangular interval is bounded superiorly by the T.D.'s major, laterally by the lateral head of the triceps, and it's bounded medially by the long head of the triceps. After that, it goes behind the humerus in a groove called the spiral groove or the radial groove. The spiral groove or the radial groove is the groove between the lateral head and the medial head of the triceps, and the triceps is located where my finger is pointing here. Before it enters the radial groove, it gives a branch, and we can see that branch here. It gives a branch to the long head, and it gives a branch to the medial head of the triceps. And in the radial groove, it gives a branch to the lateral head of the triceps. Here also the radial nerve can be endured the fracture the shaft of the humerus and in such a case The long and the medial head will be spared because they the branches already come off But the lateral head will be paralyzed But that will not produce any significant disability in terms of extension of the elbow because the lateral head is used only for powerful Extension the workhorse extensor of the elbow is the medial head, which will be spared now We have come in the cubital fossil And we can see this is the radial nerve which I picked up here. That means the radial nerve went through the spinal groove like this It went behind this arm and it came in front of the lateral epicondyle and here I can feel the lateral epicondyle with my finger and it is located in front of the lateral epicondyle in the cubital Fossa undercover of this muscle here. This is the brachioradialis So therefore this is the lateral most content of the cubital Fossa and this is the cubital fossil the other contents of the cubital Fossa are the medial nerve the brachial artery Tendon of the biceps and the lateral most is the radial nerve the radial nerve here is likely to be injured in Dislocation of the proximal radial nerve joint, which is not very uncommon in children Especially if we try to lift them up by holding the hand It can also be injured in adults when there is a Montegy a fracture where there is Unlar fracture and proximal radial nerve joint dislocation This is an x-ray to show Montegy a fracture dislocation This is another x-ray of Montegy a fracture dislocation fracture of the upper end of the Allah and proximal radial nerve joint dislocation So that is when the radial nerve can be injured here if the radial nerve is injured here Then it will lead to wrist drop. Let us see how the radial nerve is distributed here in front of the lateral epicondyle Undercover of the brachioradialis the radial nerve divides into a superficial division and a deep division Let's take a look at the superficial division. This is the superficial division. I've lifted it up here This is a cutaneous branch of the radial nerve and you can see this runs undercover of the brachioradialis here And it goes all the way undercover of the brachioradialis. It does not supply any structure And the other part of the superficial branch we can see it here It comes out from undercover and it runs on the surface of the anatomical snuff box on the roof of the anatomical snuff box And then it supplies the skin on the major part of the dorsum of the head So this is the cutaneous distribution of the superficial branch of the radial nerve Now let's take a look at the deep branch. The rest of the radial nerve is the deep branch Immediately we can see it is giving some branches to the muscles on the extensor aspect It supplies the extensor carpyradialis longus extensor carpyradialis brevis and extensor carpyrallaris And thereafter it pierces through the supinator muscle which forms the floor of the cubital fossa And thereafter it becomes known as posterior interosseous nerve And as the posterior interosseous nerve the radial nerve supplies all the muscles on the extensor aspect of the arm Injury to the radial nerve will produce a very serious disability and that is called wrist drop As shown by my hand here. Person will be unable to dorsiflexus wrist And it is such a serious disability that there are many instruments which have been created One of them being the nest instrument which is used to stimulate the extensor muscles in order to produce wrist elevation This is a picture of the functional electrical stimulation which is used to stimulate paralyzed hand muscles And it is showing the stimulation of the extensor muscle of the hand So this is the full course in distribution of the radial nerve with its clinical significance Thank you very much for watching Dr. Sanjay Sanyal. Sunny out. Please like and subscribe If you have any questions or comments, please put them in the comment section below. Have a nice day