NUCLEI OF THE CEREBELLUM 



809 



laminse are subdivided into from two to four secondary laminae of varying size. 

 Such subdivision is especially marked in the vermis. Here each lamina comprises 

 a lobule and is, therefore, separated by a fissure, and each lobule is usually sub- 

 divided with the exception of the nodule, the folium, and the lingula. In sagittal 

 sections, or sections transverse to the general direction of the sulci, this arrange- 

 ment of the laminae gives a foliate appearance, which, especially in sagittal sec- 

 tions of the vermis, is termed the arbor vitae (see fig. 634). 



^The cerebellar cortex consists of three layers and contains four general types of cell-bodies 

 of. neurones, all of which possess features peculiar to the cerebellum. 



The outermost or molecular layer contains small stellate cells, "basket cells," with rel- 

 atively long dendrites. These serve to associate the diiTerent portions of a given fohum. 

 The axones of the largest of them give off branches which form pericellular baskets about the 

 bodies of the cells of Purkinje, each axone contributing to several baskets. The layer of Pur- 

 kinje cells, or the middle layer, is quite thin. The bodies of the cells of Purkinje are arranged 

 in a single layer, and their elaborate systems of dendrites extend throughout and largely compose 

 the molecular layer. The dendrites of these, the most essential cells of the cortex, are displayed 

 in the form of arborescent fans (see fig. 604), arranged parallel with each other and transverse 



Fig. 636. — Diagram of the Inferior Surface of the Cerebellum after the Removal 

 OF the Medulla Oblongata, Pons, and Mesencephalon. 

 The tonsil of the right side is omitted in order to display the connection of the pyramid 

 with the biventral lobe, the furrowed band of the uvula, and more fuUy the posterior medullary 

 velum. The anterior notch is less evident than in the actual specimen. 



Superior cerebellar peduncle 

 Posterior medullary velum 

 Middle cerebellar peduncle 

 (brachium of pons) 



Flocculus 



Uvula 



Biventral lobe 



Anterior slender '__ 



lobule I \ \ 



Posterior ' ^ ^ 

 slender 

 lobule 

 Inferior semilu- 

 nar lobe 



Tonsil 



Tuber vermis 



Pyramid 

 Posterior cerebellar notch 



to the long axis of the folium containing them. Their axones are given off from the base of the 

 cell-body and acquire their medullary sheaths quite close to the cell-body, and, after giving off 

 several collaterals in the inner layer, pass into the general white substance and thence to other 

 laminse or lobes. Certain of them go to structures outside the cerebellum. The inner layer 

 is the granular layer. It contains numerous small nerve-cells or "granule-cells" which pos- 

 sess from two to five radiating dendrites, unbranched except at their termination, which occurs 

 suddenly in the form of three to six claw-Hke twigs. Their axones are given off either from the 

 cell-body direct or more often from the base of one of the dendrites, and pass outward into 

 the molecular layer, where they bifurcate and course in both directions parallel to the long axis 

 of the folium, to become associated with the dendrites of the ceUs of Purkinje. In the layer 

 of the cells of Purkinje there is situated at intervals a neurone of the Golgi type II (see fig. 

 604). The short, elaborately branched axone of this neurone is distributed among the cells 

 of the granular layer. Axones conveying impulses to the cerebellar cortex terminate in the 

 granular layer as 'moss fibres,' or directly upon the cells of Purkinje as 'climbing fibres,' and 

 probably upon the cells of the Golgi type II. 



Thus the neurones which receive impulses coming to the cortex are the cells of Purkinje, 

 probably the Golgi cells of type II, and the granule-cells; those which distribute these impulses 

 to other neurones of the folium are the Golgi cells of type II, the granule-cells, and the basket- 

 cells (association neurones), and the collaterals of the cells of Purkinje. Impulses are conveyed 

 from the cortex of a folium to that of other folia, lamina, lobules or lobes, or to the nuclei of 

 the cerebellum, or to structures outside the cerebellum by the axones of the cells of Purkinje. 



The nuclei of the cerebellum (fig. 637) are in its central core of white substance. 

 They are four in number, and all are paired, those of each pair being situated 

 opposite each other on either side of the mid-line. 



