. Carnegie Institution of Washington publication. THE DEVELOPMENT OF CERTAIN FEATURES OF THE CEREBELLUM. 369 in the former than in the latter. An average field in the vermis shows 36 cells, in the flocculus 22, and in the hemisphere 45. In the infant 16 days old the Purkinje cells in these three structures have maintained their relative number and size, being largest and least numerous in the flocculus, smallest and most numerous in the hemispheres, and in the vermis occupy- ing an intermediate position as to size and number be- tween the two extremes. An average field in the flocculus shows 1
. Carnegie Institution of Washington publication. THE DEVELOPMENT OF CERTAIN FEATURES OF THE CEREBELLUM. 369 in the former than in the latter. An average field in the vermis shows 36 cells, in the flocculus 22, and in the hemisphere 45. In the infant 16 days old the Purkinje cells in these three structures have maintained their relative number and size, being largest and least numerous in the flocculus, smallest and most numerous in the hemispheres, and in the vermis occupy- ing an intermediate position as to size and number be- tween the two extremes. An average field in the flocculus shows cells (Zeiss Oc. 4, Obj. A. A.), in the vermis 27, and in the hemispheres 34. Upon the theory that the ac- tual number of Purkinje cells in the cortex of a child of 16 days is the same as in a fetus of 7 months, we may regard the decrease in the num- ber per field as inversely proportional to the increase in the growth of the cortex. In table A each number is the average of 20 different fields (Zeiss Oc. 4, Obj. A. A.). A study of this table shows that although at 3 months the number of cells per field is still greatest in the hemispheres, and greater in the vermis than in the flocculus, the ratio is approaching 1:1. TABLE FIG. 3.—A contour drawing of the cerebellar hemisphere; a and b indicate the position of the cell groups a and 6. The same difference noted between cell group a, deeply placed, and cell group b, superficially placed in the flocculus (fig. 2), are noted in this hemisphere also. Age. Number of cells per field. Flocculus. Vermis. Hemisphere. °2 18 15 36 27 20 45 34 21 16 16 days 35 years If we may regard the number of cells per field as an index of the relative growth of these different parts of the cerebellum, we are led to the conclusion that the cortex of the cerebellar hemisphere increases 100 per cent during the first 3 months of postnatal life, while the vermis undergoes an increase of 80 per cent, and the flocculus an i
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