 to here. This is the midbrain section. If you follow closely, the portion which is posterior to the aqueduct of sylvia, this region is known as the tectal area and the portion anteriorly is known as the tegmentum of the midbrain. If you follow the tectal area, this area is known as the quadregeminal plate. It has got two swelling, one superiorly, one inferiorly. The superior swelling is the superior colliculus. The inferior swelling is the inferior colliculus. The superior swelling is concerned with visual reflexes, like visual body reflex. The inferior swelling is concerned with oratory localization, with oratory processing. Like they say, then there's a thunderstorm going on. You see a lightning first and then you hear the thunder. You see the lightning first and then you hear the thunder. That's what they say. This whole thing is to continue with the story of the pineal tumor, which I was talking about a little earlier. This is the location of the pineal gland. Once the pineal gland to the tumor enlarges, after it compresses the posterior commissure, it can even compress on the superior colliculus in all the structures in this region and then it can give rise to a condition known as perinode syndrome where there is paralysis of convergence and paralysis of upward gaze, because the upward gaze center is situated in this part of the mid-brain and that upward gaze center is known as the rostral interstitial nucleus of MLF. Let's not digress too much. Come back here. The aqueduct of sylvius leads into the fourth ventricle. What are the boundaries of the fourth ventricle? The fourth ventricle is bounded by the pons in its upper half, medulla in its lower half anteriorly. Posteriorly, it is bounded by a tent-shaped roof consisting of an upper half and a lower half. The upper half of the tent-shaped roof is known as the superior medullary velum, which is a thin sheet of gray and white matter. And the inferior half of the tent-shaped roof is formed is called the inferior medullary velum, which does not contain any neural tissue. It contains only pyramid and ependymia, that's all. So this is the boundary of the fourth ventricle. This is the floor of the fourth ventricle, which is also known as the rhomboid fossa. We can see only one half of it because this is a sagittal section. And as I told you a little while back, upper half of the floor is formed by the pons, the lower half of the floor is formed by the posterior surface of the medulla. If you look closely, this front leg structure which you see here, this is the coroid plexus of the fourth ventricle. The coroid plexus of the fourth ventricle is situated only in the inferior medullary velum. The superior medullary velum does not contain any coroid plexus. So this is the coroid plexus. And what is also seen here is this opening where my probe is situated right now. This is the location. This is the location of the foramen of magindai. What is the foramen of magindai? It is the midline foramen through which the fourth ventricle communicates with the cerebellum medullary system, subarachnoid system. This is the foramen of magindai. Laterally will be situated the foramen of lushka. The foramen of lushka will be situated further laterally. That is also known as the pontometallary cistern or the fontan angle cistern. Okay. So these are the structures which constitute the components of the ventricular system. Now I'll say a few words about all the other structures which are visible in this particular dissection. Let's start from below. As I mentioned in the beginning, this whole thing is the brainstem. This portion from here to here is the midbrain. This is the tegmentum of the midbrain. Sorry, one more time it blurred out. Sorry? Do it one more time it blurred. Okay. This portion from here to here is the midbrain. The portion anterior is called the tegmentum of the midbrain. The posterior is called the tectum. The tegmentum of the midbrain, if you see closely, this area here, this is known as the decastation of the pyramids. What does it do? It gives rise to the crisscrossing fibers from all the deep nuclei of the cerebellum. Deep nuclei of the cerebellum. The vestigial, interposed, and dentate nucleus. All those which go towards the red nucleus and the thalamus, they all decasate in the decastation of the superior cerebellar pyramid. I've already described the tectum, the superior and the inferior colic in this. Let's come to the lower part. This section from here to here is the pons. The anterior portion of the pons is known as the basilar part of the pons. If you look closely, you will find that the basilar part of pons has got the descending corticospinal tract, the corticobulbar tract, and it also contains the corticopont tank fibers. These are all situated in the basilar part of pons. This is the site of central pontine myelinolysis. The portion posteriorly is known as the tegmentum of the pons, which is continuous with the tegmentum of the midbrain. This is the tegmentum of the midbrain. This is the site of hemorrhage, which we had described as duress hemorrhage when there's a tentorial conic. Incidentally, if you follow this up, you'll find that the tegmentum of the midbrain becomes continuous with the hypothalamus and the thalamus. Or to put it the other way around, the thalamus and the hypothalamus becomes continuous inferiorly with the tegmentum of the midbrain, which is continuous with the tegmentum of the pons. And finally, this is the medulla. Most of the medulla has been cut here, but if we're able to trace these fibers down, then this portion would have been the pyramids of the medulla, which contains the corticospinal tracts. So these are the structures in the midbrain, brainstem. This portion that we see here, this is the vermice of the cerebellum, the cut section of the vermice of the cerebellum. And if you take a good look at this, you'll find that this has got a central core of white matter with multiple fronts of gray matter. This is known as the arbor vitae for the tree of life. This is referred to as the arbor, this cut appearance is called the arbor vitae of the tree of life, consisting of a central core of white matter with a surrounding rim of gray matter. It has got several components. We shall not describe them. They are not important for us at this stage. Let us continue. This thin membrane that we see here, this is the septum pellucidum. What is the septum pellucidum? It is composed, it's a thin double layer membrane. It is composed of epindima on either side and a thin double layer of epindima with a slit like space in between. This septum pellucidum stretches between the phornix here. This is the phornix and the body and the genu of corpus callosum. This septum pellucidum separates one lateral ventricle from the other lateral ventricle and as you have already mentioned, this is the interventricular foramenum monarum. So this is the structure here. This is our corpus callosum. This is the rostrum of the corpus callosum. This thin inferior most limit, the rostrum continues up as the genu of the corpus callosum. Then it continues as the body of the corpus callosum. This is the cut section. The corpus callosum is much extensive and it continues and ends in the large enlarged posterior portion which is known as the spleenium of the corpus callosum. Take a good hard look at this structure here. This space to be more precise. This triangular space that we see here. This is known as the cistern of the great cerebral vein of galleon or the cerebellum medullary cistern. This is known as the great cistern of the great cerebral vein of galleon. This is bounded anteriorly by the tectum of the midbrain. Superiorly it is bounded by the spleenium of the corpus callosum and inferiorly it is bounded by the cerebellum. This cistern contains the great cerebral vein. The great cerebral vein of galleon runs under this. This sulcus which is situated around the corpus callosum. This is known as the callosal sulcus and that separates it from the medial surface of the cerebral hemisphere of the cortex which we had already described.