CEREBELLUM. 121 



internal capsule is followed by a loss of sensation on the opposite side of 

 the body, and a loss of the senses of smell and vision on the same side 

 (Charcot). The precise function of the corpora striata is unknown, but 

 they are in some way connected with motion. 



The Optic thalami receives the fibres of the tegmentum, the posterior 

 portion of the crura cerebri. They are insensible and inexcitable to direct 

 irritation. Removal of one optic thalamus, or destruction of its substance 

 by disease or hemorrhage, is followed by a loss of sensibility of the oppo- 

 site side of the body, but there is no loss of motion ; their precise function 

 is also unknown, but in some way connected with sensation. In both cases 

 their action is crossed. 



CEREBELLUM. 



The Cerebellum is situated in the inferior fossoe of the occipital bone, 

 beneath the posterior lobes of the cerebrum. It attains its maximum 

 weight, which is about 5 ozs., between the twenty-fifth and fortieth years ; 

 the proportion between the cerebellum and cerebrum being I to 8|-. 



It is composed of two lateral hemispheres and a central elongated lobe, 

 the vermiform process ; the two hemispheres are connected with each 

 other by the fibres of the middle peduncle forming the superficial portion 

 of the 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 quadri- 

 gemina and the optic thalami, and then forming part of the diverging cere- 

 bral 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 dentatum. From the external 

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

 lamina , 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 tlie pia mater, contain- 

 ing rounded corpuscles, and branching fibres 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. 



I 



