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NEUROLOGY 





Finally, in the gray substance of the cerebellar cortex there are fibers which 

 come from the white center and penetrate the cortex. The cell-origin of these 

 fibers is unknown, though it is believed that it is probably in the gray substance 

 of the medulla spinalis. Some of these fibers end in the nuclear layer by dividing 

 into numerous branches, on which are to be seen peculiar moss-like appendages; 

 hence they have been termed by Ramon y Cajal the moss fibers; they form an 

 arborescence around the cells of the nuclear layer and are said to come from fibers 

 in the inferior peduncle. Other fibers, the clinging or tendril fibers, derived from the 

 medullary center can be traced into the molecular layer, where their branches 

 cling around the dendrites of Purkinje's cells. They are said to come from fibers 

 of the middle peduncle. 



(2) The independent centers of gray substance in the cerebellum are four in 

 number on either side : one is of large size, and is known as the nucleus dentatus ; 

 the other three, much smaller, are situated near the middle of the cerebellum, and 

 are known as the nucleus emboliformis, nucleus globosus, and nucleus fastigii. 



Nucleus dentatu^ Superior peduncle 



Corpora quadrigemina 



Inferior olivary nucleus 

 Fia. 707. Sagittal section through right cerebellar hemisphere. The right olive has also been cut sagitally. 



The nucleus dentatus (Fig. 707) is situated a little to the medial side of the center 

 of the stem of the white substance of the hemisphere. It consists of an irregularly 

 folded lamina, of a grayish-yellow color, containing w r hite fibers, and presenting 

 on its antero-medial aspect an opening, the hilus, from which most of the fibers of 

 the superior peduncle emerge (page 792). 



The nucleus emboliformis lies immediately to the medial side of the nucleus 

 dentatus, and partly covering its hilus. The nucleus globosus is an elongated 

 mass, directed antero-posteriorly, and placed medial to preceding. The nucleus 

 fastigii is somewhat larger than the other two, and is situated close to the middle 

 line at the anterior end of the superior vermis, and immediately over the roof 

 of the fourth ventricle, from which it is separated by a thin layer of white substance. 



The cerebellum is concerned with the coordination of movements necessary in equilibration, 

 locomotion and prehension. In it terminate pathways conducting impulses of mugcle sense, 

 tendon sense, joint sense and equilibratory disturbances. With the exception of the ventral 

 spinocerebellar fasciculus these impulses enter through the inferior peduncle. The reflex arc is 

 completed by fibers in the superior peduncle which pass to the red nucleus and the thalamus and 

 thence by additional neurons (rubrospinal tract) to the motor centers. The exact functions of its 

 different parts are still quite uncertain, owing to the contradictory nature of the evidence furnished 

 by (1) ablation experiments upon animals, and (2) clinical observations in man of the effects 

 produced by abscesses or tumors affecting different portions of the organ. 



