 Dr. Sanjay Sanyal, Professor, Department Chair. So this is going to be a demonstration of the posterior arm with a quick overview of the posterior pectoral muscles. This is the prone cadaver. I'm narrating from the left side, the camera person is on the left side. The muscles that you can see in front of us, this is the trapezius. This is the latsomus dorsi. When I reflect the trapezius, we can see the rhombus major, rhombus minor and the libator scapulae. And under the trapezius, we can also see the supraspinatus muscle here where my finger is located. This is the infraspinatus. This is the TV's major. This is the TV's minor. This is the deltoid muscle. And this is the triceps. Let me mention a few quick words about the triceps. The triceps has got three heads. This is the long head. It takes origin from the intraglena tubercula, the scapula. This is the lateral head of the triceps. It takes origin from the posterior aspect of the humerus above the radial or the spiral groove. And when I reflect this, this is the medial head of the triceps which takes origin from the posterior aspect of the humerus below the spiral groove. The long head of the triceps does not have much of an extensor action of the elbow. It acts on the shoulder joint. It's a weak adductor of the shoulder joint. It, however, acts as a shunt muscle. It resists inferior dislocation of the shoulder. The workhorse extensor is the medial head which works in all positions as an extensor of the elbow. While the lateral head is a power extensor when it is used against resistance. Now let's take a look at the triangles and the spaces that are visible in the posterior aspect. This space where my instrument is located, this is the quadrangular space. And we can see that the structures are coming out from the quadrangular space. So let's take a quick look at the boundaries of the quadrangular space. The quadrangular space is bounded superiorly by the teres minor, inferiorly by the teres major. It is bounded medially by the long head of the triceps and it's bounded laterally by the surgical neck of the humerus. Situated just above the quadrangular space is the head of the humerus. Now let's take a look at the content which I picked up. This is the axillary arm. It comes out through the quadrangular space and it is accompanied by blood vessels. We can see that is the posterior circumflex humeral artery in the vein which are branches from the axillary artery. The axillary nerve passes here and it supplies the deltoid from its deep aspect and we can see before it supplies the deltoid it is also giving a branch to the teres minor. The axillary nerve as it passes from here it can be injured in inferior dislocation of the shoulder joint or even in fracture of the surgical neck of humerus. This is an x-ray of the arm to show the fracture of the surgical neck of humerus that the author attended to. This is likely to injure the axillary nerve. In which case there will be paralysis of the deltoid. This fullness of the shoulder will be lost. The chromium process will become prominent and additionally there will be a patch of venesthesia on the upper lateral arm because this axillary nerve after it supplies the deltoid it pierces through the deltoid and supplies the skin in this region. So these will be the manifestations of injury to the axillary nerve in the quadrangular space. The point to remember is during axillary dissection for metastatic lymph nodes the axillary nerve because it is located so high up it is usually not injured in axillary dissection. The next space that we see here is this one here. This is referred to as the triangular space. So let's take a look at the boundary of the triangular space superiorly that is bounded by the T-dice minor. Inferiorly it's bounded by the T-dice major and laterally it is bounded by the long head of the triceps. When I separate them we can see a blood vessel passing through the triangular space. This is the circumflex scapular artery. The circumflex scapular artery is one of the branches of the subscapular artery the other branch being the dracodorsal artery. It passes between the origin of the T-dice major and the T-dice minor through the triangular space and it participates in the scapular anastomosis. The scapular anastomosis is basically anastomosis between the branches of the first part of the subclavian artery and the third part of the axillary artery. This artery, anastomosis with the branches of the first part of the subclavian artery namely the dorsal scapular artery and the supra scapular. The dorsal scapular they participate in communications with the posterior intercostal arteries and therefore in coactation of aorta they produce the condition known as dancing scapula where pulsations are felt in this region. If there is an occlusion of the axillary artery above the subscapular artery this scapular anastomosis can provide collateral circulation and by the same argument if we need to surgically ligate the axillary artery we can do so above the origin of the subscapular artery. So this is about the triangular space. Now let's take a look at the next space. This is the triangular interval. The triangular interval is bounded medially by the long head of the triceps laterally by the lateral head of the triceps and superiorly it is bounded by the t-rease major. Through the triangular interval we can see these neurovascular structures coming. This is the radial nerve and accompanying that we can see this one here. This is the profunda brachii artery and the profunda brachii vein. We are visible through the triangular interval and then they go behind the humerus in a groove which is referred to as the spiral or the radial groove which is located between the lateral head of the triceps and the medial head of the triceps and then it goes to the back of the arm. This radial nerve can be injured in fracture of the mid-shaft of the humerus or in abnormal hypertrophy or abnormal attachments of these muscles can also compress the radial nerve. If the radial nerve is injured in fracture of the mid-shaft of the humerus I would like to point out to you something very unique here. If I reflect the triceps this way we notice that the radial nerve is giving a branch before it enters the radial groove it gives a branch to the long head and it also gives a branch to the medial head and we can see that here. So therefore the long and the middle head gets branches before the radial nerve enters the radial groove. So in the radial groove only the lateral head receives branches. So therefore if the radial nerve is injured in the radial groove only the lateral head will be paralyzed and of course the extensors of the arm will also be paralyzed but that's a different issue. Profounder Brecaille Archery which I said accompanies the radial nerve through the radial and spiral groove. As it goes behind it participates in the elbow anastomosis. Therefore the elbow anastomosis receives four arteries from the top and it receives four arteries from below. So therefore this Profounder Brecaille Archery also provides an important collateral circulation to the arm in occlusion of the Brecaille Archery below the Profounder Brecaille. Or if it is required to surgically like at the Brecaille Archery we can do so below the origin of the Profounder Brecaille Archery. So this is also an important clinical correlation pertaining to the Profounder Brecaille Archery in the radial groove. While we are on this topic I would like to draw your attention to the fact that we can see that the Profounder Brecaille Archery is also giving a branch which is going up and it is anastomosing with the structures that is the posterior circumflex humoral archery which we had mentioned coming through the quadrangular space. So therefore to summarize we saw the quadrangular space the axial nerve. We saw the triangular space with the circumflex scapular archery. We saw the triangular interval with the radial nerve and the Profounder Brecaille Archery. Just to complete the story let me mention one more structure though it is not in this relation it is somewhere else because this is a prone cadaver we can see this nerve here which I have lifted up. This is the ulnar nerve and this is the other side. The ulnar nerve as it comes down it pierces through the medial intermuscular septum and comes from the posterior aspect. So therefore this is the right place to see it and we have split the medial intermuscular septum to show the ulnar nerve. The ulnar nerve then goes behind the medial epicondyle and this is the medial epicondyle and here it enters a tunnel which is known as the cubital tunnel. This cubital tunnel is formed by an aponeurotic expansion from this muscle which is the flexor carpi ulnaris which gives an aponeurotic expansion which merges with the anti-brachal fissure. It gets attached to the subcutaneous part of the ulnar and it bridges from the medial epicondyle to the olegran process. That cubital tunnel gives passage to the ulnar nerve. So therefore this ulnar nerve can be injured in fracture of the medial epicondyle or it can get compressed in this cubital tunnel producing what is known as cubital tunnel syndrome. And we can also see that this ulnar nerve is accompanied by the ulnar collateral vessels especially the superior ulnar collateral vessels that runs behind. So therefore these are the structures that we can see in this particular dissection with the appropriate clinical correlations. Thank you very much for watching. Dr. Sanjay Sanyal signing out. Mr. Kendall Kumberbatch is the camera person. If you have any questions or comments please put them in the comment section below. Have a nice day.