THE DEVELOPMENT OF CERTAIN FEATURES OF THE CEREBELLUM. 



371 



of mesial sections of a series of cerebella this writer shows that the superficial folding 

 proceeds most intensively during the second .half of the prenatal period and the 

 first 3 months of postnatal life. In order to secure more accurate results and a 

 numerical expression of the relation, he measured the periphery of a mesial section 

 in a series of cerebella of different ages, by means of a cyclometer on contour draw- 

 ings of about 7 magnifications. These measurements show that the period of most 

 rapid growth is from the fifth month of intrauterine to the fourth month of post- 

 natal life. 



TABLE C. 



The average thickness, recorded in table C, represents an average of 20 different 

 measurements in each of the specimens enumerated. Measurements were made 

 with the ocular micrometer and reduced to microns. Care was taken to select 

 places for measurement where the cortex was vertically cut. It will be noted, from 

 an examination of this table, that although before birth the molecular layer of the 

 flocculus shows a greater thickness than that of the hemispheres or the vermis, 

 from birth on the greatest thickness of this layer is found uniformly in the vermis. 

 In certain instances, as the 16-day-old child, the thickness of the molecular layer of 

 the vermis and of the flocculus is so nearly the same that the difference is negligible. 



TABLE D. Percentage of growth of molecular layer. 



As with the Purkinje cells, so with the development of the molecular layer, 

 the period of greatest general growth is between birth and the third month of 

 postnatal life. Table D, based upon the preceding, gives the growth in percentages 

 for different periods. It is apparent that the period of most rapid growth in thick- 

 ness of the molecular layer of the vermis is from the sixth month of intrauterine 

 life to birth; while for the flocculus and hemispheres it is from birth to the third 

 month, though for this period the percentage increase in the thickness of the molec- 

 ular layer of the vermis is nearly as great as that of the flocculus. It is evident, 

 therefore, that the period of most rapid growth of the layer as a whole is from the 



