CONDUCTION PATHS OF THE METENCEPHALON.
Before considering the individual fibre-tracts connecting the cerebellum and the pons with other parts of the brain and the spinal cord, the structure of the cerebellar cortex must be more closely examined.
The cerebellar cortex presents the following layers : i. The molecular outermost stratum ; 2. The layer of Purkinje middle stratum ; 3. The granule innermost stratum.
The Purkinje cells send their richly branched protoplasmic processes or dendrites into the molecular layer, while the axones of the cells pass through the granule layer to the white substance of the cerebellum.
Within the molecular layer, in addition to small cortical cells with short axones, are found the The latter are distinguished by their axones, which run sagittally and parallel to the surface and give off numerous collaterals that pass inward and surround- the cell-bodies of the Purkinje cells with basket-like ramifications (Fig. 143).
Within the granule layer, the small are the chief elements. They are small spherical cells with from three to five short dendrites. Their axones pass into the molec ular layer, where they divide into two branches, that run parallel to the surface and in corre spondence with the direction of the cerebellar convolutions or folia. These axones
extend, therefore, in the frontal plane and not, as do those of the basket-cells, in the sagittal plane. During their course, the branches give off collaterals which pass to the Purkinje cells. In addition to the granule-cells, Golgi II type cells occur, whose dendrites often extend far into the molecular layer and whose axones resolve into branchings of unusual richness.
enter the cortex from the subjacent white substance. Of these, the "climbing fibres" pass to the molecular layer and there end among the dendrites of the Purkinje-cells, while the "moss fibres" terminate chiefly within the granule layer. Im pulses, conveyed by these fibres which enter the cerebellum, are transferred to the different varieties of cortical cells. In this connection, it is worthy of special note, that by means of the basket-cells impulses are conveyed in the sagittal direction and by means of the granule-cells in the frontal direction and transferred to numerous Purkinje cells.