324 THE NERVOUS SYSTEM 



3. Fibres from the nucleus dentatus to Deiters' nucleus, 

 from which arises the vestibulospinal tract of the same 

 side. 



Removal of the Cerebellum. — When one half of the 

 cerebellum is removed and sufficient time has elapsed to 

 allow the efiects of irritation to pass away, the following 

 condition occurs :— 



1. Shght weakness on the same side {asthenia). 



2. Loss of muscular tone on the same side (atonia). 



3. Tremors on performing voluntary movements on the 

 same side (astasia). 



The animal is at first unable to walk, and hes down 

 curled towards the side of the lesion, with the eyes directed 

 to the opposite side. After several months it learns to 

 stand, first by buttressing itself up against a wall. Later, 

 it gains the power of walking in a modified way (drunken 

 gait), the legs being abducted so as to overcome the 

 tendency to fall over on the affected side. The recovery 

 is due to the re-education of the motor area of the cerebrum, 

 for when this is subsequently removed on the side opposite 

 to the cerebellar lesion, the animal reverts permanently to 

 its former condition. 



When the cerebellum is completely removed the con- 

 dition is in reahty intensified, though owing to the sym- 

 metrical nature of the disorder it may be apparently less 

 severe. 



Cerebellar Lesions in Man. — In unilateral lesions the 

 same symptoms are produced as after removal in animals^ 

 asthenia, atonia and astasia. Disturbance of equihbrium 

 is shown in the gait, which is reefing, as that of a drunken 

 man. Movements are slow, executed inaccurately, with 

 a tendency to over-action. In walking, for instance, the 

 feet are raised unnecessarily high (hen-gait). Speech is 

 often affected, becoming slurred. On looking to one side, 

 particularly to the side of the lesion, the eyes, owing to 

 the muscular weakness, do not remain steady but tend to 



