368 



THE DEVELOPMENT OF CERTAIN FEATURES OF THE CEREBELLUM. 



The cells have reached their greatest development in the flocculus. Those of 

 the vermis are more uniformly developed than in any other portion of the cere- 

 bellum, though the stage of their development is not so advanced as it is in the depth 



molecular 

 layer. 



outer 

 nuclear layer. 



FIG 



1. Drawing of the cerebellar 

 cortex in which each cell is 

 repreeented in the field diawn. 

 The most prominent feature of 

 figure 1 is the transitory outer 

 nuclear layer, which occupies a 

 most superficial position in the 

 molecular layer. It disap- 

 pears at different periods in 

 different animals, correspond- 

 ing to the age at which mye- 

 linization in the cerebellum 

 becomes pronounced and loco- 

 motion acquired. This outer 

 nuclear layer is probably ab- 

 sorbed by the inner nuclear 

 layer. 



of the floccular fissures. It should be mentioned that in a fetus of 6 months the 

 Purkinje cells in the depth of a fissure show a development markedly beyond that 

 of cells more superficially placed. This difference is illustrated in figure 2, a drawing 

 of the contour of the flocculus; a and b indicate the positions in which the corre- 

 sponding groups of cells are 

 found. The cells in the depth 

 of the fissure (a) show a denser 

 protoplasm, a more definite 

 contour, and better developed 

 protoplasmic processes and 



nucleus than the more super- ^J\^ ^ ^ ^> 



ficially placed cells (6). The 

 protoplasm of cells b, having 

 no definite boundaries, merges 

 into the surrounding proto- 

 plasmic mass. It is less dense, hence the cells appear larger than cells o. This 

 same difference is shown in figure 3 for the hemisphere. In the contour drawing a 

 and b indicate the positions of the cell-groups o and 6. A comparison of the two 

 figures shows how far the Purkinje cells of the flocculus are in advance of those of 

 the hemisphere. 



In the seventh, as in the sixth month of prenatal life, the Purkinje cells of the 

 vermis show a development in advance of those of the hemisphere. Likewise in 

 the new-born the cells of the flocculus are by far the largest, while the cells of the 

 vermis are larger than those of the hemisphere. In both vermis and flocculus the 

 protoplasmic processes are well developed. The Purkinje cells are more numerous 



b.. 



FIG. 2. A contour drawing of the flocculus. In this drawing a and b indicate 

 the positions in which the cell groups a and b are found. The cells in 

 the depth of the fissure a show a denser cell protoplasm, more definite 

 contour, and better developed protoplasmic processes and nucleus, than 

 the cells of 6, more superficially placed. 



