564 THE NERVOUS SYSTEM 



The granular layer contains a large number of very small granule-like 

 cells that Golgi was the first to show are really nerve cells. They are only 

 about 5 fji in diameter, and they have a number of short dendrites which end 

 in clubbed extremities. They give off a very slender axis-cylinder process 

 or axone which runs up into the superficial part of the molecular layer and 

 there divides in a T-shaped fashion, the fibers run parallel to the surface of the 

 convolution and pass in between the branches of the cells of Purkinje. 



The white substance of the cerebellum consists of nerve fibers, which are of 

 three kinds: i, Descending fibers, that are made up of the axis-cylinders 

 of the cells of Purkinje, carrying impulses down from the cerebellar cortex. 

 2, Ascending fibers, which pass into the granular layer, and there end in a 

 number of very short, finely divided brushes of fibers presenting a mossy ap- 

 pearance, so that these are known as the mossy fibers. These connect with the 

 granular cells of this layer. 3, Ascending fibers, which pass up through the 

 granular into the molecular layer and there break up into a fine network which 

 interlaces with the dendritic branches of the cells of Purkinje. 



Paths through the Cerebellar Cortex. It will be seen that the ar- 

 rangements for the transmission and diffusion of nerve impulses and for the co- 

 operation of different cells are extremely complicated and delicate. It is not 

 possible to indicate absolutely by any schema the course of fibers and the 

 course of impulses through the cerebellum, but approximately it is some- 

 what like that in the accompanying figure 396. 



Impulses pass up along the ascending fibers to the granular cells by way of 

 the direct cerebellar, the fibers of the gracile and of the cuneatus, from the 

 restiform body, etc. These cells, being stimulated, send the impulses by their 

 axis -cylinders to the molecular layer, and through their T-shaped divisions to 

 the dendrites cf the cells of Purkinje. Thence an impulse is sent out by the 

 axis-cylinder process of this cell. Other ascending impulses are brought up 

 by those fibers which pass directly to the molecular layer and send their ter- 

 minals winding around among the dendrites of the cells of Purkinje. Proba- 

 bly impulses pass up also through the ascending fibers which affect the 

 basket cells, and, through them and their basket-like terminals, the cells of 

 Purkinje. Purkinje cells send cerebellar motor fibers to the nucleus dentatus 

 cerebelli and through the superior peduncles to the nuclei of the oculo-motor 

 nerves, and to the ventro-lateral descending tract of the cord, to end about 

 the anterior-horn cells. 



Functions of the Cerebellum. With the exception of its middle 

 lobe, the cerebellum is itself insensible to irritation and may be all cut away 

 without eliciting signs of pain (Longet). Its removal or disorganization by 

 disease is also generally unaccompanied by loss or disorder of sensibility; 

 animals from which it is removed can smell, see, hear, and feel pain, to all 

 appearances, as perfectly as before (Flourens; Magendie). It cannot, there- 

 fore, be regarded as a principal organ of sensation. Yet if any of its crura 



