CEREBELLUM, PONS, AND MEDULLA. 243 



which the normal co-ordination of the muscles is effected. The 

 fact that in birds as well as in higher forms the animal eventually 

 learns to co-ordinate such movements after the loss of the cerebel- 

 lum does not invalidate this conclusion. In the first place, the 

 recovery in such cases is not entirely complete, since some ataxia 

 is still manifested in vigorous or hurried movements, and the 

 amount of restoration of normal activity which is obtained may 

 be referred to a possible adaptation or training in the cerebral 

 portion of the mechanism. The relative parts taken by the 

 cerebellum and the cerebrum in such movements vary probably in 

 different animals and in different movements in the same animal. 

 Removal of the cerebrum from a pigeon leaves an animal with 

 almost perfect power of controlling its equilibrium. In the dog a 

 similar operation is followed by a longer period of inability to con- 

 trol 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 movements caused by the removal of the cerebel- 

 lum 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 cerebrum is more highly developed 

 than in the lower animals. 



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 apparent loss of sensations after removal of the cerebellum, 

 but Luciani, Russell, and others state their belief that in some 

 indefinable way the mentality of the animal is affected by such 

 operations. Whatever functions of this kind are present we can 

 define only by the unsatisfactory 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 position and of direction. 



Localization of Function in the Cerebellum. All observers 

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

 ture of the body is concerned, it is homolateral, that is, each 

 half of the cerebellum is connected with its own half of the 

 body. The connection with the motor areas of the brain is the 

 reverse, the right half of the cerebrum being in relation with the 

 left half of the cerebellum. These relations are, in the main, 

 borne out by the anatomical course of the motor and sensory 

 paths described above. There arises, however, the question 



