260 NORMAL HISTOLOGY. 



The large stellate cells of the granular layer lie near its external 

 margin, whence they send their dendrites into a large area of the 

 molecular layer, while their neurites are distributed in the granular 

 layer, where they must come into relations with the dendrites of the 

 small stellate cells (Fig. 241,/). 



The distribution of the cells and their processes in the cerebellum 

 indicates a very complex interchange of nervous impulses and an 

 extraordinary coordination in the action of the various neurons. 



This complication is still further increased by the presence of 

 centripetal neurites, which enter the cerebellum through the white 

 matter and are distributed in the gray matter. These are of two 

 sorts : first, neurites which penetrate the granular layer and are 

 distributed among the proximal dendrites of the cells of Purkinje 

 (Fig. 241, n) ; second, neurites, called " moss " fibres, which are dis- 

 tributed among the cells of the granular layer. The teleneurites of 

 these fibres have a mossy appearance, whence the name (Fig. 241, h). 

 The origin of these centripetal neurites is not known, but it is sur- 

 mised that the " moss " fibres may enter the cerebellum through the 

 direct cerebellar tracts of the cord. 



III. THE CEREBRUM. 



The gray matter of the cerebral cortex has been divided into four 

 layers : first, an external molecular layer ; second, the layer of 

 small pyramidal cells ; third, the layer of large pyramidal cells ; 

 and, fourth, an internal layer of irregular or stellate cells. Of 

 these layers, the second and third are not clearly distinguishable 

 from each other (Fig. 243). 



The molecular layer contains three sorts of nerve-cells, two of 

 which are closely related to each other, differing onlv in the form 

 of the cell-bodies, which are small in both varieties (Fig. 244, A y 

 B, and C) ; while the cell-bodies of the third variety are large and 

 polygonal (Fig. 244, D). The small cells (A, B, C, Fig. 244) pos- 

 sess two or three tapering processes, which at first resemble proto- 

 plasmic processes, but soon assume the characters of neurites or axis- 

 cylinders. These neurons, then, resemble the type depicted in Fig. 

 232, III. Their neurites run parallel to the surface of the convo- 

 lution in which they are situated, sending off numerous perpen- 

 dicular collaterals, and finally end in teleneurites within the molec- 

 ular layer. The collateral and terminal teleneurites are probably 

 in relations with the dendrites of the pyramidal cells of the under- 



