Layers four and six (4 & 6) of the LGN also connect to the opposite eye, but to the P cells (color and edges) of the optic nerve. By contrast, layers two, three and five (2, 3, & 5) of the LGN connect to the M cells and P (parvocellular) cells of the optic nerve for the same side of the brain as its respective LGN.
A gyrus (gyri pl) is a rounded ridge, as on the surfaces of the cerebral hemispheres. A sulcus is a groove in the surface between gyri.
The human cerebral cortex is very deeply wrinkled, so it has a lot of grey matter, which has the large majority of all the neurons in the CNS. In Figure 5-2d, sulci (singular = sulcus) are shown by the curving lines on the cerebral hemispheres. The ridges between the sulci are the gyri (singular = gyrus).