THE CEREBELLUM 605 



3. THE CEREBELLUM 



The cerebellum is connected by means of its peduncles on the one hand 

 with the spinal cord and on the other with the higher parts of the brain. 

 Impulses to and from the cerebellum are conveyed over pathways contained 

 in these peduncles. 



Many nerve cells are found both in the gray cortex of the cerebellum and 

 in the gray nuclei located in its interior. The various nuclei are connected 

 by means of association fibers with the cerebellar cortex, and the different 

 subdivisions of the latter are connected with each other in numerous ways 

 by means of other association fibers. 



In animals deprived of the cerebellum, and also in men suffering from 

 extensive destruction of this organ, various characteristic symptoms are ob- 

 served. But among them we do not find either motor or sensory paralysis 

 of any kind. Hence we may conclude, what is borne out also by anatomical 

 connections, that the cerebellum is not in the direct line of connection between 

 the higher parts of the brain and the medulla or the spinal cord, but that it 

 constitutes a system in itself branching off to one side, which both acts upon 

 and is acted upon by the other parts of the central nervous system. 



Removal of the cerebellum does not of itself endanger life; it is therefore 

 not an indispensable organ, although it does exert a profound influence over 

 certain functions of the body. 



According to Steiner, artificial stimulation of the cerebellum in fish has no 

 effect. By mechanical stimulation with a fine needle Nothnagel observed in the 

 rabbit that the head was turned to the opposite side and the vertebral column 

 was curved so as to become concave toward the opposite side. Electrical stimu- 

 lation between the left hemisphere and the vermis of a dog moving freely about 

 the laboratory produced, in experiments by Lewandowsky, forced flexion toward 

 the same side, so that the vertebral column became bent convexly to the right; 

 ultimately the animal fell over to the right or went off in circular movements 

 in the same direction. On the other hand the tonic contraction of the skeletal 

 muscles is inhibited by stimulation of the surface of the cerebellum (Sherring- 

 ton). But from such observations as these we can only conclude that the cere- 

 bellum is in some way related to the bodily movements. For more exact infor- 

 mation as to what that relation is, we must direct our attention to the study of 

 the symptoms attending lesions of the cerebellum. 



In certain fishes where the cerebellum is highly developed, it can be 

 removed without producing any apparent disturbance either to the bodily 

 movements or to equilibrium; the animals merely wabble slightly sidewise 

 while swimming. The cleaner cut the operation, the less marked are these 

 wabblings, and within a day or so they practically disappear. Likewise after 

 unilateral ablation of the cerebellum there is no disturbance in locomotion 

 (Steiner). 



In frogs, where the cerebellum is very slightly developed, the posture of 

 the body and the leaping movements after extirpation are not to be distin- 

 guished from those of the normal animal. When the animal is placed in 

 water, it swims and behaves otherwise quite normally. But when it leaps 

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