The decision-tree algorithm below compiles a systematic and detailed list of morphological criteria that can facilitate and standardize identification of cells in Nissl-stained brain sections examined under the microscope. We describe specific cytological features of neurons, glial and endothelial cell types in the cerebral cortex of the macaque monkey and the human. We used the Nissl staining technique because it labels all cells in the brain in distinct ways. There are two major cell types that form the nervous system: supporting cells and conducting cells. The supporting cells of the peripheral nervous system consist of Schwann cells, fibroblasts, and satellite cells, while the supporting cells in the CNS consist of the glia; the lining cells of the ventricles, the ependymal; the meningeal coverings of the brain; the circulating blood cells; and the endothelial lining cells of the blood vessels. The conducting cells, or neurons, form the circuitry within the brain and spinal cord, and their axons can be as short as a few microns or as long as 1 m.