ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 691 



PHYSIOLOGY OF THE CEREBELLUM AND MESENCEPHALON. 



Cerebellum. Mechanical irritation applied to the cortical sub- 

 stance of the cerebellum does not cause the animal to cry out nor are 

 contractions of his members provoked. Even a prick or a wound that 

 is not very deep in the cerebellar cortex does not cause any noticeable 

 or constant disturbances, particularly in movements. More often the 

 only movements are those of the ocular globes. 



However, a deep lesion of the cerebellum a large compression, 

 tumor, haemorrhage, the removal of all or a large portion of the 

 cerebellum determines a peculiar ataxia which shows the loss of 

 equilibration. The animal, desiring to move, shows great uncertainty, 

 irregularity, and want of coordination of movement. Often when it 

 wishes to take some steps, it falls backward, slipping with the feet 

 foremost. 



Fig. 278. Effects of Removal of Cerebellum. (DALTON.) 



The experiment succeeds best in birds. After removal of the 

 irebellum they can no longer keep their balance. This is known as 

 rebellar tottering. Sometimes after several efforts they succeed in 

 jmaining upon their feet for a little while, but they soon fall and 

 Iways in a particular manner. They slip either with the feet spread 

 r ide apart laterally, so as to touch the ground with the breast, or else, 

 ipping with the legs extended forward, they support themselves with 

 wings behind. The head is folded with more or less twisting upon 

 ie back. When these animals continue to live for some time with 

 ich a lesion they end by presenting characteristic obstructions with 

 ie feet, especially in the disposal of the toes. 



A man with deep lesions of the cerebellum has very noticeably 

 >rdered movements in walking and standing erect. He cannot bal- 

 ice himself well. While walking he appears like one who is drunk. 



