492 THE NERVOUS SYSTEM. 



lamellae or along them. These dendrons are invested at their 

 attachment to the cell, and to some extent along their branchings, 

 by basketworks formed by the terminal arborizations of certain 

 fibers of the medullary center. The body of the cell of Purkinje 

 is further invested by a feltwork of fibrils formed by the arboriza- 

 tion of axis-cylinder processes of the same nerve-cells in the outer 

 layer of the gray matter. Each cell has therefore a double invest- 

 ment of this nature, one covering the dendrons, the other the body 

 of the cell. Ramifying among the granule-layer are peculiar 

 fibers derived from the white center, and characterized by having 

 pencils of fine short branches at intervals like tufts of moss. 

 These are termed by Cajal the moss-fibers; they end partly in the 

 granule-layer, partly in the molecular layer." 



Functions of the Cerebellum. If the surface of the cerebellum 

 is irritated, no muscular movements are produced, nor is there any 

 evidence of sensation ; if, however, the irritation is applied near 

 the medulla or inferior peduncles, both pain and muscular contrac- 

 tion result. If the cerebellum is removed wholly or partially, 

 sensation is not diminished in the part of the body below, nor is 

 there any impairment of the power of producing muscular move- 

 ments, nor of the special senses, nor of the intelligence ; but there 

 is a marked want of harmony in the muscular movements a lack 

 of co-ordination. Attention has already been called to the fact 

 that even the simplest movements that are made require the 

 harmonious action of different muscles, and when these move- 

 ments are more complex, they require different sets of muscles. 

 If these movements do not occur at just the right time and are 

 not produced in the right manner, the result is disorder instead 

 of harmony ; or, as it is expressed, there is a want of co-ordina- 

 tion, or a condition of inco-ordination or cerebellar ataxy. This 

 is the effect of removing the cerebellum. Thus, if the cerebellum 

 of a pigeon is removed, and an attempt is then made by it to 

 fly, it is unsuccessful, for this act requires the consentaneous action 

 of both wings, which action is absent. In walking the bird reels 

 like a person intoxicated, and cannot go to the spot for which it 

 apparently set out. It should be borne in mind that there is no 

 paralysis either of motion or of sensation in this condition, but 

 the voluntary movements which originate in the cerebrum, and 

 which are in the normal condition co-ordinated by the cerebellum, 

 pass to the muscles without this regulating influence, and the 

 result is a series of disordered movements. 



Especially marked is this inco-ordination in connection with 

 the maintenance of the equilibrium of the body and locomotion. 

 Indeed, some authorities are inclined to limit the functions of 

 the cerebellum to this, and to regard it as not being the con- 

 trolling organ of co-ordination in general, quoting experiments 

 upon animals in which, after the first effects of its removal had 

 passed away, there was a return of the co-ordinating power, 



