CHAPTER XI. 



THE FUNCTIONS OF THE CEREBELLUM, THE PONS, 

 AND THE MEDULLA. 



The functions of the cerebellum are, in some respects, less satis- 

 factorily known than those of any other part of the central nervous 

 system. Many theories have been held. Most of these views 

 have been attempts to assign to the organ a single function of a 

 definite character, but latterly the insufficiency of the theories 

 proposed has led observers to attribute to the cerebellum general 

 properties the nature of which can not be expressed satisfactorily 

 in a single phrase. Before attempting to give a summary of exist- 

 ing views it will be helpful to recall briefly the important facts re- 

 garding its structure and relations, so far as they are known and can 

 be used to explain its functional value. 



Anatomical Structure and Relations of the Cerebellum. 

 The finer histology of the cerebellar cortex is represented in Fig. 98. 

 Three layers may be distinguished. The external molecular 

 layer (A), the middle granular layer (B), and the internal medullary 

 layer consisting of the white matter or medullated 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 run into 

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



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