CHAPTER XI. 



THE FUNCTIONS OF THE CEREBELLUM, THE PONS, 

 AND THE MEDULLA. 



Before attempting to give a summary of the views held in 

 regard to the functions of the cerebellum it will be helpful to re- 

 call briefly some points in its structure which have a direct bear- 

 ing upon its physiological relations and activities. 



Anatomical Structure and Relations of the Cerebellum. — 

 The finer histology of the cerebellar cortex is represented in Fig. 

 103. Three layers may be distinguished. The external molecular 

 layer {A), the middle granular laj^er (B), and the internal meduUary 

 layer consisting of the white matter or meduUated nerve fibers, 

 afferent and efferent (C). Between the molecular and granular 

 layers lie the large and characteristic Purkinje cells (a). The 

 dendrites of these cells branch profusely in the molecular layer; 

 their axons pass into the medullary layer. From the standpoint 

 of the neuron doctrine these cells, so far as the cerebellum is con- 

 cerned, are efferent- They form, indeed, the sole efferent system 

 of the cerebellar cortex.. The afferent fibers of the cerebellum end 

 in both the granular and the molecular layers. Those that termi- 

 nate in the granular layer — designated by Cajal as moss fibers, 

 have at their terminations and points of branching curious clumps 

 of small processes ; they probably connect with the dendrites of the 

 nerve cells in this layer. Those that pass deeper into the molec- 

 ular layer come into connection with the dendrites of the Purkinje 

 cells, around which, indeed, they seem to twine, so that Cajal desig- 

 nated them as climbing fibers. The granular layer (B) contains 

 numerous granules (g) or small nerve cells. These cells are spherical, 

 and have a relatively large nucleus and a small amount of cyto- 

 plasm. Their dendrites are few and short; their axons nm into 

 the molecular layer, divide in T, and the two branches then run 

 parallel to the surface and doubtless make connections with the den- 

 drites of the Purkinje cells as well as with the cells of the moleculai 

 layer. A few larger nerve cells of Golgi's second type (/) are found 

 also in the granular layer. In the molecular layer are found two 

 types of cells: the larger basket cells (b) whose axons terminate in a 

 group of small branches that inclose the body of the Purkinje cells, 

 and a number of smaller cells (e), situated more superficially, 

 whose axons pass longitudinally in the molecular layer and termi- 



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