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Cortical Gray Matter

layer, stratum, cells, fibers, processes, deep and cell-bodies

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CORTICAL GRAY MATTER The cerebellar cortex is inexcitable (Horsley and Clarke). It originates no fibers that pass out of the cerebellum, only cortico-nuclear fibers; but, with very few exceptions, it receives all fibers that enter the cerebellum. The cerebellar cortex is a great receptive organ which correlates afferent impulses. The impulse-complex, produced by such correlations, passes through the cortico-nuclear fibers to the cerebellar nuclei, and leaves the cerebellum through the nucleo-fugal, or cerebello-tegmental fibers; ultimately it arrives in motor nuclei and regulates their discharges so as to secure coordinated movement (Brain, Vols. 28, 29, 31, etc.).

The cortex of the cerebellum (substantia cortitalis cerebelli) is made up of two thick layers visible to the naked eye, viz., (1) a superficial layer, and (2) a deep, granular layer. At the junc tion of these two layers is a single row of large pitcher-shaped cell-bodies, which are characteristic of the cerebellar cortex and are almost visible to the unaided eye. They are the bodies of Purkinje's cells, and are considered in the deep part of the first macroscopic layer, where they form the stratum gangliosum. Under the microscope three layers are easily seen, viz., (I) the gray layer (stratum cinereum); (2) the ganglion cell layer (stratum gangliosum); and (3) the granular layer (stratum granulosum).

1. Superficial Layer (Figs. io8 and 1o9).—Thickest on the lamina and thinnest beneath the sulci, this layer contains small and large stellate cell-bodies with their processes, which constitute the stratum cinereum proper; and the large Purkinje cell-bodies with their dendrites and recurrent collaterals, to gether with many corticipetal fibers. The Purkinje cells form the stratum gangliosum.

Cells.—The bodies of Purkinje's cells (Figs. io8 and 109) are located near the deep surface of the superficial layer in the stratum gangliosum. They measure from ioopt to 135A in their longest axis, 6oµ in diameter. Each has one axone which, after piercing the deep layer, becomes a fiber of the medullary body. It medullates very close to the cell-body and gives off, in the deep layer, several recurrent collaterals, which form contact rela tions with other cells in both layers. From the outer end of

each cell-body antler-like processes, the dendrites, are given off; they ramify toward the surface in a wide plane at right angles to the free border of the gyrus. The edge of the plane only is seen in a longitudinal section of the gyrus and the arborization is very narrow and tall. The stellate cell-bodies, an outer and inner layer, together form the stratum cinereum. They measure io-2o,“ and increase in size toward the Purkinje cells. They have rich dendritic processes and one axis-cylinder each. Their processes ramify throughout the stratum cinereum and stratum gangliosum. The inner layer of the stratum cinereum contains the larger cells; they are called the "basket cells." Their axis cylinder processes run parallel with the surface and at right angles to the border of the gyrus; they give off vertical branches, which descend to Purkinje's corpuscles and inclose them in a basket work of filaments. In the outer layer of the stratum cinereum the stellate cell-bodies are smaller than in the inner layer. They branch freely and terminate in end-tufts in contact with other stellate cells.

The fibers of the superficial layer (Figs. 108 and 109) have three sources: (a) The processes of neurones within the layer, which include the dendrites and axones of the stellate cells and the dendritic planes and recurrent collaterals of Purkinje's cells. (b) The processes of cell-bodies in the deep layer, whose T branched axones pierce the dendritic planes of Purkinje in the first layer; and, the processes of the large granules whose den drites ramify toward the surface. (c) The fibers of the medul lary projection rise or end largely in the cellular layer. The axones of Purkinje's neurones compose all of the corticifugal fibers. They end in the cerebellar nuclei of the cat, dog and monkey (Clark and Horsley) also, in the rabbit (Van Ge huchten) and probably have these endings in the human brain.

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