CEREBELLUM. 135 



pons Varolii. It is brought into connection with the medulla oblongata 

 and spinal cord, through the prolongation of the restiform bodies ; with 

 the cerebrum, by fibres passing upward beneath the corpora quadrigemina 

 and the optic thalami, and then forming part of the diverging cerebral 

 fibres. 



Structure. It is composed of both white and gray matter, the former 

 being internal, the latter external, and convoluted, for economy of space. 



The White matter consists of a central stem, the interior of which is a 

 dentated capsule of gray matter, the corpus denlatum. From the external 

 surface of the stem of white matter processes are given off, forming the 

 lamince, which are covered with gray matter. 



The Gray matter is convoluted and covers externally the laminated pro- 

 cesses; a vertical section through the gray matter reveals the following 

 structures : 



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

 ing rounded corpuscles, and branching fibres passing toward the external 

 surface. 



2. The cells of Purkinje, forming a layer of la-ge, nucleated, branched 

 nerve cells sending off processes to the external layer. 



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 cerebullum is not followed 

 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 movements 

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

 portions are removed, all power Q{ 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 evacua- 

 tions. 



Forced Movements. Division of one crus cerebelli causes the animal 



