122 HUMAN PHYSIOLOGY. 



3. A granular layer of small, but numerous corpuscles. 



4. Nerve fibre layer, formed by a portion of the white matter. 



Properties and Functions. Irritation of the cerebellum is not fol- 

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

 therefore, insensible and inexcitable. 



Co-ordination 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 move- 

 ments become more irregular, and the pigeon becomes restless ; when 

 the last portions are removed, all power of flying, -walking, standing, etc., 

 is entirely gone, and the equilibrium cannot be maintained, the power of 

 coordinating muscular movements being entirely gone. 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. I. 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 occasionally 

 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 experi- 

 ments ; 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 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 char- 

 acter, such as the kangaroo, shark and swallow. 



The cerebellum may possibly exert some influence over the sexual func- 

 tion, but physiological and pathological facts are opposed to the idea of 

 its being the seat of the sexual instinct. It appears to be simply a centre 

 for the coordination and equilibration of muscular movements. 



