182 HUMAN PHYSIOLOGY. 



The gray matter is convoluted and covers externally the laminated processes; 

 a vertical section through the gray matter reveals the following structures: 



1. A delicate connective-tissue layer, just beneath the pia mater, containing 

 rounded corpuscles, and with branching fibers passing toward the external 

 surface. 



2. The cells of Purkinje, forming a layer of large, nucleated, branched nerve- 

 cells sending off processes to the external layer. 



3. A granular layer of small but numerous corpuscles. 



4. A nerve-fiber layer, formed by a portion of the white matter. 



Properties and Functions. Irritation of the cerebellum is not followed 

 by any evidences either of pain or convulsive movements; it is, therefore, 

 insensible and inexcitable. 



Coordination of Movements. Removal of the superficial portions of the 

 cerebellum in pigeons produces feebleness and want of harmony in the muscular 

 movements; as successive slices are removed, the movements become more 

 irregular, and the pigeon becomes restless; when the last portions are removed, 

 all powers of flying, -walking, standing, etc., is entirely gone, and the equili- 

 brium can not be maintained, the power of coordinating muscular movements 

 being wholly lost. The same results have been obtained by operating on all 

 classes of animals. 



The following symptoms were noticed by Wagner, after removing the 

 whole or a large part of the cerebellum: 



1. A tendency on the part of the animal to throw itself on one side, and to 

 extend the legs as far as possible. 



2. Torsion of the head on the neck. 



3. Trembling of the muscles of the body, which was general. 



4. Vomiting and occasional liquid evacuations. 



Forced Movements. Division of one crus cerebelli causes the animal to 

 fall on one side and roll rapidly on its longitudinal axis. According to Schiff, 

 if the peduncle be divided from behind, the animal falls on the same side as 

 the injury; if the section be made in front, the animal turns to the opposite 

 side. 



Disease of the cerebellum partially corroborates the result of experiments; 

 in many cases symptoms of unsteadiness of gait, from a want of coordination 

 have been noticed. 



Comparative anatomy reveals a remarkable correspondence between the 

 development of the cerebellum and the increase in complexity of muscular 

 actions. It attains a much greater development, relatively to the rest of the 

 brain, in those animals whose movements are very complex and varied in 

 character, such as the kangaroo, shark, and swallow. 



