CEREBELLUM, PONS, AND MEDULLA. 227 



power of controlling its equilibrium. In the dog a similar operation 

 is followed by a longer period of inability to control perfectly the 

 movements of locomotion, and it is probable that in man after such 

 an operation the power of locomotion would be acquired more slowly, 

 if at all. On the other hand, the violent effect upon such move- 

 ments caused by the removal of the cerebellum in the pigeon is less 

 evident in the dog, and, if we may judge from the incomplete data 

 of clinical neurology, very much less evident in man. In man the 

 motor control of the voluntary muscular system through the cere- 

 brum is more highly developed than in the lower animals. 



The most important objection to the view that the cerebellum 

 is an organ of co-ordination for the movements of equilibrium 

 and locomotion is that in the bird as well as in man the animal 

 eventually learns to carry out these movements after loss of the 

 cerebellum. This fact is clear proof that the cerebellum is not 

 the only mechanism through which such co-ordination is possible ; 

 but it is no valid objection to the view that normally this control 

 is effected through this organ. The sensory tracts on which this 

 co-ordination depends make connection with the thalamus or cere- 

 brum as well as the cerebellum, and when the latter arc is broken 

 the higher centers may be used to replace its functions in part 

 at least. The replacement is not complete, since even in man loss 

 of the cerebellum is followed by a permanent condition of slight 

 ataxia. Lewandowsky's* suggestion that normally in man the 

 finer, more conscious movements of the body are controlled directly 

 from the cerebrum, while the subconscious or dimly conscious 

 movements of locomotion and equilibrium are regulated through 

 the cerebellar centers seems to be in accord with the facts known. 



The Psychical Functions of the Cerebellum. In the cerebel- 

 lum, as in the other nerve centers below the cerebrum, we have to 

 consider the possibility of a psychical or conscious side to the activity 

 of the organ. It seems clear, however, that the degree of conscious- 

 ness, if any, exhibited by the cerebellum is of a much lower order 

 than that shown by the cerebrum. All observers agree that there 

 is no marked loss of sensations, but Luciani, Russell, and others 

 state their belief that in some indefinable way the mentality of 

 the animal is affected by removal of the cerebellum. Whatever 

 functions of this kind are present we can define only by the un- 

 satisfactory term of subconscious rather than unconscious. As far 

 as can be determined, this effect is felt mainly upon the muscular 

 sense and the sense of direction. 



Localization of Function in the Cerebellum. All observers 

 agree that so far as the influence of the cerebellum on the muscula- 



* Lewandowsky, " Archiv f. Physiologic," 1903, 129; see also Kohnstamm, 

 "Archiv f. d. gesammte Physiologic," 89, 240, 1902. 



