We'll see similar sections of this monkey brain in the lab next week, and you can cut similar sections through the brain of a sheep. Silver staining, such as the Golgi stain, reveals more details of the shapes and projections of neurons, allowing them to be classified. This figure is an important one and you should study it carefully. It is surface gray matter , of the order of a millimeter deep. To the top is the outside of the brain, and to the bottom is a largely unstained region because this region contains few cells, but in fact contains vast numbers of axons in passage to and from the neocortex.
Axons are the cable-like processes of neurons that carry impulses from one region to another.
In contrast, brain gray matter contains local circuits of interacting neurons. Within the cortex there is a layered arrangement, at first difficult for you to make out. Neocortex has six layers, and just how prominent each layer is varies according to the cortical area or function. The innermost layer, layer 6, is prominent in the figure just near the '3b' label, and again in the region labeled '2'. Layer 5 is prominent in primary motor cortex because it contains some relatively large neuronal somata.