 This is going to be demonstration of the deep compartment of the posterior compartment of the leg. So, in order to demonstrate the deep compartment, we have lifted up the gastrocnemius here, and we have lifted up the sodium here, and we have got it at the attachment of the tendocalcaneus. This is the deep part of the posterior compartment. The deep part of the posterior compartment is separated from the superficial part by a septum, a fascia which we have removed, and that is known as the transverse intramuscular septum, which extends from the posterior intramuscular septum, which is attached to the posterior margin of the fibula, and then it goes medially and gets attached to the fascia, deep fascia, and we can see that here. So, this is the deep aspect of the posterior compartment. So, let us take a look at the muscles here. Most medially, we have this muscle here. This is the flexor digitorum longus. Just after that, we have the next muscle, this one. This is the tibialis posterior, and further laterally, we have the third muscle here. This is the flexor halosus longus. So, in the back of the leg, the relationship is DTH. Let us trace them further down. As we trace them further down, we notice that the tibialis posterior, the big tendon, it goes under the flexor digitorum longus, and therefore, in the posterior aspect of the ankle, the relationship becomes TDH. T stands for tibialis posterior, this big strong tendon that we see, which is a very powerful plantar flexor. Then we have the flexor digitorum longus, and then finally, we have the third tendon, which I have lifted up here. This is the flexor halosus longus. So, this is what you see in the tarsal tunnel. The next thing which I wanted to point out to you was the neurovascular structure. I have picked up this structure here. This is the tibial nerve. The tibial nerve emerges from the pubrical fossa where my finger is going in under the tendons arch of the soleus, and it continues down, and it supplies all the muscles in the posterior compartment. The next structure that we see here is this. This is the posterior tibial vein. The posterior tibial vein is also a division from the pubrical vein, and the pubrical vein is seen in the pubrical fossa here, which passes under the tendons arch of the soleus. And the next structure that we can see here is this. This is the posterior tibial artery. The posterior tibial artery also is a larger terminal division of the pubrical artery, which we can see here in the pubrical fossa. As it passes under the tendons arch of the soleus, it divides into a posterior tibial artery and an anterior tibial artery. The posterior tibial artery is accompanied by numerous small veins, and we have removed them here, and these are known as the vene comitantes. The posterior tibial artery gives off a branch which we can see here. This is the fibular artery. The fibular artery supplies nutrient artery to the fibular. It gives lateral malular branch and lateral calcaneal branch. The tibial artery gives off a circumflex fibular branch, and it continues down, and it supplies medial malular branch and medial calcaneal branch. This fibular nutrient artery, which is coming from the fibular artery, is clinically very useful. This allows us to use a segment of the fibular as a vascularized graft when we are using the fibular to graft a defect in the tibia on the other leg. So, this is one clinical importance of the vascular supply. Now, we will trace these neuromascular structures and the tendinous structures to this space here, where my finger is located. This space is referred to as the tarsal tunnel. This tarsal tunnel is a space which is bridged over by this flexor retiniculum, and we have got it, and part of it is visible here on this side, and a little bit of it is visible on the other side. This flexor retiniculum is a tough structure which extends from the calcaneus to the medial malulus, and we have split it open to show the tarsal tunnel. Passing through the tarsal tunnel, we have the tendinous structures and the neurovascular structures in this order, and there is a mnemonic for this. Anterior to posterior, we have the tibialis posterior. Then we have the next structure, the flexor digitorum longus. Then we have the blood vessels. Collectively, this is the posterior tibial artery and the venaecomitantes, which form the posterior tibial vein together. And we can clearly see that the posterior tibial artery is encircled by a series of veins on either side, which are the accompanying veins of the posterior tibial artery. The next structure that we see here is this one. This is the tibial nerve. The nerve and the artery, both of them, go to the sole of the foot and they divide into a medial planter and a lateral planter. And the next last structure that we can see here is this one. This is the flexor halosus longus tendon. So therefore, we have a mnemonic here. Away from anterior to posterior, we have tom, dick, bloody, nervous, harry. The tibialis posterior, flexor digitorum longus. Bloody refers to the posterior tibial artery and venae. Nervous refers to the tibial nerve. And harry refers to the tendon of the flexor halosus longus. All these tendons are enclosed in synovial sheath. And we can see remnants of the synovial sheath here. This is the synovial sheath of the flexor halosus longus. Here also, we notice something. The posterior tibial artery and vein are giving branches to the calcaneus. These are the medial calcaneal branches. And simultaneously, we can also see the tibial nerve is also giving branch to the calcaneus. These are the medial calcaneal branches. That brings me to an important clinical correlation here. This tibial nerve can get entrapped under this flexor retinaculum. And that condition is known as the Tarsal Tunnel Syndrome. In which condition, the patient will have weakness of the muscles of the sole of the foot as well as numbness tingling of the region distributed by the medial and the lateral plantar nerves. And additionally, the person will also have heel pain because of compression and irritation of the calcaneal branches of the tibial nerve. This is to be differentiated from another condition which happens in the foot. And that is known as the jogger's foot where the medial plantar nerve gets entrapped under the abductor halosus muscle. That also produces very similar manifestations. The difference being that there will be no heel pain. These veins, which I mentioned, the deep calf veins, which are very important in circulating pushing blood, venous blood up towards the heart. Because the blood inside the calf veins is under very low pressure, 0 to 2 millimeters of mercury. And they have to travel up against gravity to the heart. So therefore, they need external assistance. And in that situation, these muscles, the deep calf muscles and the triceps sure, when they are contracting and relaxing within the tight, artificial compartment, they act as what is known as a peripheral pump or a peripheral heart. And they squeeze the venous blood up. If due to any reason, either immobility or bed-ridden invalid, the calf muscles are not active, then stasis will occur in these veins and that will lead to deep vein thrombosis. That is the reason why, after surgery, the patient is mobilized within 24 hours. And at the same time, prophylactically, we have to give herparin, low dose herparin to prevent deep vein thrombosis. When the deep vein thrombosis is a very serious condition, apart from producing swelling of the calf, it can also produce pulmonary embolism. And that is for the same reason, when people are on long flights, people are advised to keep themselves well hydrated and they're supposed to walk up and down the aisle of the plane just to keep their calf muscles moving. And communicating with these deep calf veins are these perforating veins which perforate through the deep fascia. And we can see one perforator here, we can see another perforator here and there are several such perforators. When deep vein thrombosis, these perforators, which normally receive blood from superficial to deep, the flow is reversed and can lead to very close veins. So that is all for now about the deep muscles of the posterior compartment and the neurovascular structures. Thank you very much for watching. If you have any questions or comments, please put them in the comment section below. Dr. Sajja Sanyal signing off. Have a nice day.