 look at an axial section through the brain. When we take an axial section through the brain we see first a thin rim of gray matter which is referred to as the cortex the cerebral cortex but let us focus on this white matter here. This is referred to as the subcautical white matter which becomes confluent with the central white matter and which merges with the periventricular white matter. This whole thing is composed of nerve fibers which are malenated and that's why it's referred to as the white matter. For the ease of understanding this white matter has been divided into three broad groups the so-called commissural fibers the projection fibers and association fibers. Let's take a look at how these fibers are disposed. This is a very special type of investigation which is referred to as diffusion tensor imaging with white matter tractography. It's a very sophisticated investigation which gives a three-dimensional representation of the white matter inside the brain. So this is a coronal view of the brain and you can see that this is one hemisphere here this is another hemisphere this is the longitudinal fissure this is a commissural fiber here. These colors have been coded by the computer this band of fibers that are running down here on either side this is an example of a projection fiber and these fibers that you see here these are some association fibers. This is a pictorial representation of the corpus callosum seen from the top above we can see this whole thing is the corpus callosum which absolutely descends down like this and separates the cordate nucleus medially and the thalamus medially from the lentiform nucleus laterally. There these are the white matter subcortical white matter I'm separating them now and you can see the descending fibers of the internal nerves. Here we can see another part of the projection fibers which are referred to as the posterior thalamic radiation and here we can see the inferior longitudinal fasciculus. Corpus callosum here. So corpus callosum is situated medially projection fibers are just lateral to that and the association fibers are the lateral most which connect individual parts of the brain. So this