In terms of developmental history, a distinction must be made between the substantia grisea centralis (central gray, cave gray) and the substantia grisea corticalis et intermedia (peripheral gray).
The peripheral gray has separated from the cavity system of the ventricles and the central gray found there. The peripheral gray is further subdivided into the cortical and the intermediate gray. It represents a peculiarity of the brain and is the seat of summary functions. No peripheral gray is found in the spinal cord. The intermediate grey of the brain (substantia grisea intermedia), which is to be distinguished from the substance of the same name in the spinal cord, forms the basal diencephalic nuclei (basal ganglia), nucleus hypothalamicus, substantia nigra, nucleus ruber, bridge nuclei, cerebellar nuclei, nucleus olivaris, etc., surrounded by white matter.
The cortical gray (substantia grisea corticalis) is characterized by layered structure or lamination. Here we can assume an organizing principle which, during the increase of the ganglion cell mass occurring in the course of development, does not allow the thickness of the cell masses to increase, but rather their areal expansion (surface enlargement). The excessive increase in surface expansion is counteracted by folding. This is how the outer formations of peculiarly winding gyri of the brain (substantia grisea corticalis), which are typical of the brain, are formed. But also in the intermediate gray, the folded cross-sectional images of nuclei such as the nucleus dentatus, or the nucleus olivaris are characteristic of this organizational principle. This planar spread of gray matter is found in the cerebrum and cerebellum, but also in the region of the superior tetrahedra. The advantage resulting from this principle is the better accessibility of the circuitry and therefore also of the retrieval, roughly comparable to the handiness of a chip card.
The central gray is considered within the brain as a nervous tissue connected to the ventricular system. The ventricular system has connection to the central canal in the area of the spinal cord. The entire cavity system arises from the clearing of the embryonic neural tube. The gray matter surrounding the central canal of the spinal cord is also called substantia grisea intermedia, see above. It has received this name because it connects the formations of the anterior horn and posterior horn, which are located on both sides of the spinal cord and also consist of gray matter, but it is not to be understood as substantia grisea intermedia in the sense of the developmental classification. Within the brain, the central gray is primarily the seat of the cranial nerve nuclei. The central cavernous gray represents the supreme center and the superior coordinating center for all vegetative functions. Such functions are heat and circulation regulation, digestion, excretion, sexual functions, etc.
