COURSE OF THE FIBRES IX THE CEREEELLOI. 361 



layers. The most external portion of tins layer contains a 

 few small nerve-cells and fine filaments of connective tissue ; 

 and the rest of the layer contains a great number of large 

 cells, rounded or ovoid, with two or three, and sometimes, 

 though rarely, four prolongations. 1 The mode of connection 

 between the nerve-cells and the fibres has already been de- 

 scribed under the head of the general structure of the nervous 

 system. 2 



Course of the Fibres in the Cerebellum. Most anatomical 

 writers give a very simple description of the course of the 

 nerve-fibres in the cerebellum. From the gray substance 

 of the convolutions and their prolongations, the fibres con- 

 verge to form finally the three crura, or peduncles on each 

 side. The superior peduncles pass forward and upward to 

 the crura cerebri and the optic thalami. These connect the 

 cerebellum with the cerebrum. Beneath the tubercular quad- 

 rigemina, some of these fibres decussate with the corre- 

 sponding fibres upon the opposite side ; so that certain of 

 the fibres of the superior peduncles pass to the corresponding 

 side of the cerebrum, and others pass to the cerebral hemi- 

 sphere of the opposite side. 



The middle peduncles arise from the lateral hemispheres 

 of the cerebellum, pass to the pons Yarolii, where they de- 

 cussate, connecting together the two sides of the cerebellum. 



The inferior peduncles pass to the medulla oblongata, 

 and are continuous with the restiform bodies, which, in turn, 

 are continuations chiefly of the posterior columns of the 

 spinal cord. 



According to Luys, the fibres from the cortical substance 

 of the cerebellum all pass to the corpora dentata and there 

 terminate, being connected with the cells. From the cor- 

 pora dentata, new fibres arise, which go to form the cerebel- 

 lar peduncles. Luys does not admit the existence of com- 



1 KOLLIKEI^ Elements tfhistologie humaine, Paris, 1868, p. 387, et seq. 

 9 See page 50. 



