520 THE NEKVOUS SYSTEM 



The molecular layer consists chiefly of the processes of cells 

 which are found in the deeper layers ; it possesses but few cells of 

 its own. Such nerve cells as it may possess, though all of small 

 size, fall under two types, the one whose processes spread out 

 lateralward and interlace with the dendrites of Purkinje's cells, 

 and the other whose processes pass transversely through the cere- 

 bellar convolutions and give off collaterals which dip inward to 

 form end baskets around the bodies of the Purkinje cells. The 

 neuraxes of these latter cells, in the tangential portion of their 

 course, form a stratum of fibres which occupies the deeper third 

 of the molecular layer and overlies the outer poles of the Purkinje 

 cells. 



Glia cells also occur in the molecular layer, many of them dis- 

 tributing their processes in planes perpendicular to the surface of 

 the convolutions. These glia fibres penetrate the entire depth of 

 the molecular layer, and on the surface of the convolutions beneath 

 the pia mater form a superficial " basal membrane.' 99 



The greater part of the molecular layer is composed of fibres 

 which, however, are not only derived from the intrinsic cells of 

 this layer, but also include processes from Purkinje's cells and 

 from the granule cells of the nuclear layer, together with certain 

 fibres which enter from the white matter of the medulla and 

 terminate in a network about the chief dendrites of Purkinje's 

 cells. 



According to the classification of Nissl, nearly all the nerve 

 cells of the cerebellar cortex, with the exception of Purkinje's 

 cells, are of the cytochrome variety ; their nucleus stains deeply, 

 and corresponds in size to that of a leucocyte ; mere traces of cyto- 

 plasm are present. Nevertheless, a few cells of the granular layer 

 possess a much larger nucleus, one which equals in size that of the 

 average nerve cell ; they are therefore of the karyochrome type of 

 Mssl. 



Purkinje's cells come under the arkyo-stichochrome or arkyo- 

 chrome variety (Mssl *), their large granules of stainable substance 

 being arranged in the form of an indistinct network whose meshes 

 are more or less parallel to the nuclear membrane and to the 

 surface of the cell. These coarse granules are continued out- 

 ward into the dendrites; they also frequently form a "nuclear 

 cap " for that pole of the nucleus which adjoins the stem of the 

 dendrite. 



* Allg. Zeitschr. f. Psychiat., 1898. 



