THE DEVELOPMENT OF CERTAIN FEATURES OF THE CEREBELLUM. 



375 



TABLE F. Thickness of cortical and medul- 

 lary portions of the cerebellum. 



In each of the series in which measurements are recorded sections were selected 

 at a level just below the place in which the corpus restiforme passes over into the 

 cerebellum. Measurements were made in each 

 section along the line ab, figure 5, passing from 

 the base of the floccular peduncle to meet the sur- 

 face of the cerebellar cortex at right angles. 



In the sixth and seventh months, though 

 medullation is very slight, the medullary and cor- 

 tical zones are very clearly defined in well-stained 

 sections. The ratio of cortical to medullary field 

 in these series is 3.5 : 4.5. By birth the ratio of 

 1 : 1 has been established between cortical and 

 medullary zones, and this is maintained up to and in the adult. It will be observed 

 that the first two years represent a growth of 100 per cent in thickness of cortical 

 and medullary zones, and that one-third of this growth takes place in the first 3 

 months. 



Though the molecular layer increases in thickness only 1 or 2 per cent after the 

 second year, there is an increase of 15 per cent in the thickness of the cortical zone 

 from the second year to the adult stage. 



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