 So this is a demonstration of the triceps muscle, the radial nerve, and a few other related structures. This is a prone cadaver, we are standing on the left side of the cadaver and the camera person is also on the left side towards the headed. So this is the triceps muscle that we see in front of us. The triceps arguably is the largest muscle in the arm, it's on the extensor aspect of the arm. The triceps has got three heads. So let's take a look at the heads and the origin insertions. This head that we see here, starting from here and going down, this is the long head of the triceps. The long head of the triceps takes origin from the intraglinal tubercle of the scapula where my finger is located and it descends down. This head that we see here, this is the lateral head of the triceps. The lateral head of the triceps takes origin from the posterior surface of the humerus above the radial groove or the spinal groove, which I shall show you just now. And if you were to look further medially, this is the medial head of the triceps. The medial head of the triceps also takes origin from the posterior surface of the humerus below the radial groove. And these three heads then unite to form the bulk of the triceps muscle and lower down we can see on the posterior aspect of the arm this thick tendinous aponeurotic structure. This is the insertion, the tendon of insertion of the triceps muscle. The bulk of this is contributed by the medial head of the triceps. And then the triceps tendon descends down and gets inserted onto the olegranon process of the ulna. So this is the origin and the insertion of the triceps. At the point of insertion on the olegranon process, there can be a bursa. The bursa is between the tendon of insertion and the olegranon process to reduce the friction. That is known as the deep, subtenduous bursa of the olegranon. There can also be a bursa on the surface of the olegranon process where my finger is located. That is known as the subcutaneous olegranon bursa and it can get inflamed from repeated friction and that condition or bursa test is known as student's elbow or minor's elbow. What are the functions and the actions of each belly of the triceps? The workhorse extensor of the elbow is the medial head. It is a regular day-to-day extensor of the elbow that is the medial head and it is the medial head which contributes to the bulk of this aponeurotic tendinous insertion of the triceps. The lateral head of the triceps comes into play only when there is forceful extension of the elbow. The long head of the triceps has got very weak extension action of the elbow because it takes oxygen from the intra-glynoid tubercle of the scapula. It acts on the shoulder joint. It is a weak adductor of the shoulder joint of the arm. It acts as a shunt muscle. A shunt muscle by definition is a muscle which resists inferior dislocation of the shoulder especially when carrying heavy weight. So the long head of the triceps along with other muscles acts as a shunt muscle. So that is another function of the long head of the triceps. Assisting the triceps in extension is a weak extensor which is not visible here and that is known as the anconious muscle which is located deep and that also gets inserted onto the olegranon process. So that is also a weak extensor of the arm along with the triceps. I am going to separate the long head of the triceps and the lateral head of the triceps and I have separated them. And in so doing we have created a space here. This space that we see here, this is the triangular interval. Triangular interval is bounded by medially by the long head of the triceps, laterally by the lateral head of the triceps and the humerus and superially it is bounded by this muscle. This is the T-rease measure. So this is the triangular interval and that brings me to the contents of the triangular interval which are very important here and we have dissected them out meticulously. This structure that I have picked up here, this is the radial nerve and you can see it is giving multiple branches to the triceps and the other content of the triangular interval is this. This is the profunda brachae artery and the profunda brachae vein. So these are the contents of the triangular interval. Let me turn this to show you from the other side. We can see from here, we can see the radial nerve here and we can see the profunda brachae vein and the profunda brachae artery. These are the same structures that we saw through the triangular interval here. They enter the triangular interval and after that they run obliquely on the posterior aspect of the humerus and this is the radial groove or the spiral groove and once we lift it up, we can see much more clearly. So in order to demonstrate the radial groove or the spiral groove, we had to split the triceps muscle and we can see the cottages of the triceps here. So that brings me again to the origin of the lateral and the medial head. Of the radial groove or the spiral groove, the origin is this is the lateral head and below the spiral groove, this is the medial head of the triceps. The radial nerve, the textbook description is that before it enters the spiral groove or the radial groove, it gives the branches to the long head and the medial head and we can see that it is giving branches to the long head, the medial head and in the spiral groove it gives branches to the lateral head of the triceps that also we can see here. This brings me to a very important clinical correlation in fracture of the shaft of the humerus either in the triangular interval or in the spiral groove. The radial nerve can be injured, the radial nerve and in which case it will produce paralysis of the lateral head of the triceps because the long head of the triceps and the medial of the triceps have already received the nerve supply. However, because of the injury to the radial nerve, there will be wrist drop because of the paralysis of the extensor muscles of the forearm. Let's trace the radial nerve further down, we can see that after the radial nerve has given off all the branches to the various bellies of the triceps, the main medial nerve continues down where my instrument has disappeared and here it goes in the cubital fossa anterior surface of the lateral epicondi and thereafter it goes to the forearm. Now let's take a look at the profunda brachae. Now I have picked up the profunda brachae vein and the profunda brachae artery. They also run through the triangular interval with the radial nerve and they run in the spiral groove. However, after that they have a different course. The profunda brachae goes to the posterior aspect of the humerus and it finishes by means of two terminal branches, the middle and the radial collateral artery and vein respectively which participates in the elbow elastomosis. Now let's come to a few important relationships of the long head of the triceps. The long head of the triceps forms boundary of three spaces and triangles. So this is the long head of the triceps. We can see this space here where my instrument, my finger is located and the instrument is gone. This is the quadrangular space. I have already mentioned the boundaries of the spaces in another section. So here I will just relate that this is the long head of the triceps and passing through the quadrangular space we have this important structure here. This is the axillary nerve and the posterior circumflexed humeral vessels. So the long head of the triceps forms one of the boundaries of the quadrangular space. This same long head of the triceps also forms a boundary of this space where my hand is tracing. This is the triangular space and this triangular space is also on the lateral side bounded by the long head of the triceps and the content of this triangular space is this artery which I picked up here. This is the circumflexed scapular artery which is the branch of the sub scapular artery, the branch of the axillary artery. The long head of the triceps as I mentioned a little while back also forms a boundary of the triangular interval and this is the triangular interval. So therefore the long head of the triceps forms boundaries of three triangles and spaces. The triceps muscle is located on the posterior compartment as we mentioned. It is separated from the anterior compartment by a facial structure which is the lateral intermuscular septum and we have retained a little bit of the lateral intermuscular septum here and we can see that here. Running just posterior to the lateral intermuscular septum we see this nerve here. This is not a nerve of the triceps but it runs in the posterior compartment and this is the ulnar nerve and we can see the ulnar nerve is running here in accompaniment with this vessel. This is the superior ulnar collateral artery and vein and then it runs and continues down and goes behind the medial epicondyle. Now let's go to a few clinical correlations pertaining to the triceps. Paralysis of the triceps I have only mentioned in injury of the radial nerve where there is injury to the radial nerve in the spinal groove. The lateral head is the one which is usually involved. When there is a fracture of the olecranine process like for example when a person falls on his elbow because of the attachment of the triceps to the olecranine process the proximal fragment gets pulled upwards and there is always a separation between the fragments. Now this is a very difficult fracture to treat conservatively and therefore the only way to unite a fracture of the olecranine is by open reduction and screw insertion. Tapping the triceps tendon just above the olecranine process is a means of eliciting the triceps reflex. It tests the integrity of C6-7.