 Good day everybody, this is a continuation from previous dissection that is part one where we shall open the Dural sac Now what I'm going to do, I'm going to open the Dural sac and I'm going to open it in several places Let's start first with the lumbar cistern which I mentioned to you just to bring you up to speed the lumbar cistern Is that portion of the Dural sac which extends from L2 to S2 the place where we do the lumbar puncture So I'm going to lift this up And I'm going to make a snip here and I'm going to open it So basically what I'm cutting is I'm cutting open the Dura and the arachnoid and I'm opening the lumbar cistern If this had been a living specimen CSF should have cushed out from here, but this is not a living specimen. So therefore it is dry So I'm opening the lumbar cistern and When I open it fully you will see that it is filled with not the spinal cord, but guess what The corda equina. What is the meaning of the word corda equina? The corda equina refers to the corda means tail, equina means horse The corda equina refers to the tail of a horse and you can see this looks like the tail of a horse, doesn't it? Well, we have to use your imagination So this is the corda equina Somewhere here, maybe this one perhaps Is the phylum terminate, but then that's very difficult because it's a very thin structure So this is the lumbar cistern which has been opened up and you can see the corda equina and at each final level The spinal respective spinal nerve emerges through the corda equina So this is the region of the lumbar cistern and the most common site of doing a lumbar puncture For CSF tap as you know very well is between the l3 and l4 Spinal process that's the most common site because that is the place where we can be sure that there is no spinal cord And we are not likely to injure We do not injure the nerve of the corda equina because when the needle goes in the nerve spread out separate away And we get the CSF tap. Now what I'm doing is I'm extending the dural incision further higher up I'm going through the thoracic part of the spinal cord I'm cutting the spinal the dural sac I'm going higher up And here we can see The spinal cord You notice this filamentous structures These are known as the arachnoid trabeculae. They are A constituent part of the Subarachnoid space. In fact, that is how the word arachnoid has come into Existence the term arachnoid means comes from the word arachnus, which means like the legs of a spider so this is We can see the spinal cord here Just to bring you up to speed you can see the spinal cord is ending Here This is the region of the corda equina. Can you see this pointed structure here? This is the corda equina. Sorry. Sorry. So correctly. This is the conus medullaris This is the conus medullaris and the corda equina starts from there So this is the exact location of the conus medullaris and as I told you earlier The conus medullaris is at the lower border of l1 vertebra. So it's between l1 and l2 And we can see it very clearly here. Let's continue with our opening of the spinal of the dural sac And as I told you in the beginning, can you see one spinal now emerging? It is piercing the dural sac and as it pierces the dural sac it takes a sheath of dura with it And then it as it emerges through the interval for oven the dural sac gets adherent to the periosteum and then the spinal nerve continues The same thing applies to all the levels Let's continue further We have to be a little gentle here because I don't want to damage any structures unnecessarily more than that is required Let's proceed further in certain places This space is very limited and therefore We have to be a little careful Okay, because here The spinal canal is very narrow. Therefore, we shall not district any further without damaging. Let me go here now straight To the region of the foremen magnum I'm going to use the knife for this purpose as I told you earlier This is the medulla And this is the this medullary Sorry, correct me. This is the cerebellar hemispheres. This is the posterior cranial fossa The squamous occiput has been cut The foremen magnum has been opened And in between the two cerebellar hemispheres, you can see the cerebellar verbis The medulla is deep inside and you can see a little bit of that. So what I'm going to do is I'm going to put my finger And I'm going to cut this open because this is a very tough fibro structure and I'm going to cut it open There it's going through This is the cranial part of the dura the true dura or the meningeal layer of the dura which you can see here this one The periosteal or the endosteal layer of the dura is not the true dura Now I have cut through the cranial dura Now I'm cutting The spinal dura and my finger is just slicing through it. It is a kind of blunt dissection that I'm making here and there Now we can see something very clearly We can see the medulla here The posterior surface of the medulla The posterior surface of the medulla Contains two elevations which are actually the dorsal column composed of the face-equalus cuneatus Laterally and the face-equalus gracilis immediately on either side You learn more about this when you come to Neuroscience Let me slice open a little bit here So that we can see a little better there Now let me go further down as I told you the dura and the arachnoid Are almost inseparable at the dura arachnoid interface so now This is where The medulla becomes continuous with the spinal cord and we are seeing the posterior surface of the spinal cord There are many landmarks of the posterior surface of the spinal cord But this is too small a specimen too narrow a view to demonstrate all the landmarks on the posterior surface But to give you a quick overview there is a posterior median sulcus Right in the midline Then there's a posterior intermediate sulcus one on either side of the midline and there's a posterior lateral sulcus from where the posterior Spinal nerve root emerges So now we can see the cervical spinal cord We can see the cervical spinal cord As you can see the medulla is slightly wider and it narrows down into the spinal cord from here The thoracic spinal cord starts This is the region of the cervical spinal cord From here the thoracic spinal cord starts and the spinal thoracic spinal cord ends here thoracic spinal nerves and at the lower border of l1 Is the corda equina Let me just try to Complete the dissection of the spinal cord so that we can completely open the whole thing out The dura when you're cutting it it is like a leathery structure It's tough and leathery If you look closely You see some denticulate ligaments which are strands of piometer which connect the spinal cord to the inner surface of the dura we can see the rootlets of the Posterior spinal nerve And this is one spinal segment one spinal segment is defined as That segment of the spinal cord which gives attachment to the rootlets of one spinal nerve So we have posterior rootlets which form the posterior root of the spinal nerve and anteriorly We'll have the ventral rootlets which will form the ventral or the anterior root of the spinal nerve And the two of them as you know will unite to form the spinal nerve and there will be a ganglion on the dorsal root So these are the posterior spinal nerve rootlets Okay, this much for this dissection as we can see them here And before I conclude The boys and girls have done a wonderful job of opening the sacral canal also This is the region of the sacral canal where The sacral spinal nerves go through and they immerse through the dorsal sacral foramen There's supposed to be four foramen on the dorsal aspect and four foramen on the ventral aspect from where the sacral spinal nerves emerge So that's all for the dissection as you can see them here Thank you very much for watching ladies and gentlemen If you have any questions or comments put them in the comment section below Thank you Doug. Thank you selvi. Dr. Sanjay Sanyal signing out. Have a nice day